Pressure-induced structural modifications of rare-earth hafnate pyrochlore

NASA Astrophysics Data System (ADS)

Turner, Katlyn M.; Rittman, Dylan R.; Heymach, Rachel A.; Tracy, Cameron L.; Turner, Madison L.; Fuentes, Antonio F.; Mao, Wendy L.; Ewing, Rodney C.

2017-06-01

Complex oxides with the pyrochlore (A2B2O7) and defect-fluorite ((A,B)4O7) structure-types undergo structural transformations under high-pressure. Rare-earth hafnates (A2Hf2O7) form the pyrochlore structure for A  =  La-Tb and the defect-fluorite structure for A  =  Dy-Lu. High-pressure transformations in A2Hf2O7 pyrochlore (A  =  Sm, Eu, Gd) and defect-fluorite (A  =  Dy, Y, Yb) were investigated up to ~50 GPa and characterized by in situ Raman spectroscopy and synchrotron x-ray diffraction (XRD). Raman spectra at ambient pressure revealed that all compositions, including the defect-fluorites, have some pyrochlore-type short-range order. In situ high-pressure synchrotron XRD showed that all of the rare earth hafnates investigated undergo a pressure-induced phase transition to a cotunnite-like (orthorhombic) structure that begins between 18 and 25 GPa. The phase transition to the cotunnite-like structure is not complete at 50 GPa, and upon release of pressure, the hafnates transform to defect-fluorite with an amorphous component. For all compositions, in situ Raman spectroscopy showed that disordering occurs gradually with increasing pressure. Pyrochlore-structured hafnates retain their short-range order to a higher pressure (30 GPa vs.  <10 GPa) than defect-fluorite-structured hafnates. Rare earth hafnates quenched from 50 GPa show Raman spectra consistent with weberite-type structures, as also reported for irradiated rare-earth stannates. The second-order Birch-Murnaghan equation of state fit gives a bulk modulus of ~250 GPa for hafnates with the pyrochlore structure, and ~400 GPa for hafnates with the defect-fluorite structure. Dy2Hf2O7 is intermediate in its response, with some pyrochlore-type ordering, based on Raman spectroscopy and the equation of state, with a bulk modulus of ~300 GPa. As predicted based on the similar ionic radius of Zr4+ and Hf4+, rare-earth hafnates show similar behavior to that reported for rare earth zirconates at high pressure.

Pressure-induced structural modifications of rare-earth hafnate pyrochlore.

PubMed

Turner, Katlyn M; Rittman, Dylan R; Heymach, Rachel A; Tracy, Cameron L; Turner, Madison L; Fuentes, Antonio F; Mao, Wendy L; Ewing, Rodney C

2017-06-28

Complex oxides with the pyrochlore (A 2 B 2 O 7 ) and defect-fluorite ((A,B) 4 O 7 ) structure-types undergo structural transformations under high-pressure. Rare-earth hafnates (A 2 Hf 2 O 7 ) form the pyrochlore structure for A  =  La-Tb and the defect-fluorite structure for A  =  Dy-Lu. High-pressure transformations in A 2 Hf 2 O 7 pyrochlore (A  =  Sm, Eu, Gd) and defect-fluorite (A  =  Dy, Y, Yb) were investigated up to ~50 GPa and characterized by in situ Raman spectroscopy and synchrotron x-ray diffraction (XRD). Raman spectra at ambient pressure revealed that all compositions, including the defect-fluorites, have some pyrochlore-type short-range order. In situ high-pressure synchrotron XRD showed that all of the rare earth hafnates investigated undergo a pressure-induced phase transition to a cotunnite-like (orthorhombic) structure that begins between 18 and 25 GPa. The phase transition to the cotunnite-like structure is not complete at 50 GPa, and upon release of pressure, the hafnates transform to defect-fluorite with an amorphous component. For all compositions, in situ Raman spectroscopy showed that disordering occurs gradually with increasing pressure. Pyrochlore-structured hafnates retain their short-range order to a higher pressure (30 GPa vs.  <10 GPa) than defect-fluorite-structured hafnates. Rare earth hafnates quenched from 50 GPa show Raman spectra consistent with weberite-type structures, as also reported for irradiated rare-earth stannates. The second-order Birch-Murnaghan equation of state fit gives a bulk modulus of ~250 GPa for hafnates with the pyrochlore structure, and ~400 GPa for hafnates with the defect-fluorite structure. Dy 2 Hf 2 O 7 is intermediate in its response, with some pyrochlore-type ordering, based on Raman spectroscopy and the equation of state, with a bulk modulus of ~300 GPa. As predicted based on the similar ionic radius of Zr 4+ and Hf 4+ , rare-earth hafnates show similar behavior to that reported for rare earth zirconates at high pressure.

Transformation of multiwall carbon nanotubes to onions with layers cross-linked by sp3 bonds under high pressure and shear deformation

NASA Astrophysics Data System (ADS)

Pankov, A. M.; Bredikhina, A. S.; Kulnitskiy, B. A.; Perezhogin, I. A.; Skryleva, E. A.; Parkhomenko, Yu. N.; Popov, M. Yu.; Blank, V. D.

2017-08-01

A pressure-induced phase transition of multiwall carbon nanotubes (MWNT) to a new structure at room temperature is studied using a shear diamond anvil cell, X-ray photoelectron spectra (XPS), transmission electron microscope (TEM) and Raman procedures. We observe a cardinal pressure-induced change in the nanoparticles shape from multi-shell tubes to multi-shell spheres. MWNT transforms to onions with layers cross-linked by sp3 bonds under the 45-65 GPa compressive stress combined with shear deformation at room temperature. TEM and XPS results show that about 40% of the carbon atoms in the new phase are sp3-bounded.

Pressure-induced transformations of nitrogen implanted into silicon

NASA Astrophysics Data System (ADS)

Akhmetov, V. D.; Misiuk, A.; Barcz, A.; Richter, H.

2006-03-01

Czochralski (CZ) Si samples implanted with nitrogen, with doses 1017 ion/cm2 and 1018 ion/cm2, at 140 keV, were studied by means of Fourier transform infrared spectroscopy after annealing at 1130 °C/5 h under different hydrostatic pressures, from 1 bar to 10.7 kbar. It has been found for each pressure applied, that the increased nitrogen dose leads to transformation of the broadband spectra to the fine structure ones, corresponding to crystalline silicon nitride. The spectral position of observed sharp peaks in the investigated pressure region is red shifted in comparison to that for the peaks of crystalline silicon oxynitride found recently by other investigators in nitrogen-containing poly-Si as well as in a residual melt of nitrogen-doped CZ-Si. The application of the pressure during annealing results in further red shift of the nitrogen-related bands. The observed decrease of frequency of vibrational bands is explained in terms of the pressure induced lowered incorporation of oxygen into growing oxynitride phase. Secondary ion mass spectrometry data reveal the decrease of oxygen content in implanted layer with increasing pressure during annealing.

High-pressure phase transitions, amorphization, and crystallization behaviors in Bi2Se3.

PubMed

Zhao, Jinggeng; Liu, Haozhe; Ehm, Lars; Dong, Dawei; Chen, Zhiqiang; Gu, Genda

2013-03-27

The phase transition, amorphization, and crystallization behaviors of the topological insulator bismuth selenide (Bi2Se3) were discovered by performing in situ high-pressure angle-dispersive x-ray diffraction experiments during an increasing, decreasing, and recycling pressure process. In the compression process, Bi2Se3 transforms from the original rhombohedral structure (phase I(A)) to a monoclinic structure (phase II) at about 10.4 GPa, and further to a body-centered tetragonal structure (phase III) at about 24.5 GPa. When releasing pressure to ambient conditions after the complete transformation from phase II to III, Bi2Se3 becomes an amorphous solid (AM). In the relaxation process from this amorphous state, Bi2Se3 starts crystallizing into an orthorhombic structure (phase I(B)) about five hours after releasing the pressure to ambient. A review of the pressure-induced phase transition behaviors of A2B3-type materials composed from the V and VI group elements is presented.

Nanoindentation hardness and atomic force microscope imaging studies of pressure-quenched zirconium metal

NASA Astrophysics Data System (ADS)

Catledge, Shane A.; Spencer, Philemon T.; Vohra, Yogesh K.

2000-11-01

We have carried out mechanical property measurements on zirconium metal compressed in a diamond anvil cell to 19 GPa at room temperature with subsequent quenching to room pressure. The irreversible transformation from the ambient hexagonal-close-packed phase to the simple hexagonal ω phase (AlB2 structure) is confirmed by synchrotron energy dispersive x-ray diffraction followed by nanoindentation of the pressure-quenched sample. We document an 80% increase in hardness as a consequence of the pressure-induced transformation to the ω phase at room temperature. This is a large increase for a metallic phase transformation and can be attributed to the presence of sp2-hybrid bonds forming graphite-like nets in the (0001) plane of the AlB2 structure. Atomic force microscopy of the indents shows that a plastic deformation of 2 μm in depth was achieved with a force of 200 mN.

Pressure-induced reversible amorphization and an amorphous–amorphous transition in Ge2Sb2Te5 phase-change memory material

PubMed Central

Sun, Zhimei; Zhou, Jian; Pan, Yuanchun; Song, Zhitang; Mao, Ho-Kwang; Ahuja, Rajeev

2011-01-01

Ge2Sb2Te5 (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCl structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18 GPa and the system become completely random at approximately 22 GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te–Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST. PMID:21670255

Pressure-induced reversible amorphization and an amorphous-amorphous transition in Ge₂Sb₂Te₅ phase-change memory material.

PubMed

Sun, Zhimei; Zhou, Jian; Pan, Yuanchun; Song, Zhitang; Mao, Ho-Kwang; Ahuja, Rajeev

2011-06-28

Ge(2)Sb(2)Te(5) (GST) is a technologically very important phase-change material that is used in digital versatile disks-random access memory and is currently studied for the use in phase-change random access memory devices. This type of data storage is achieved by the fast reversible phase transition between amorphous and crystalline GST upon heat pulse. Here we report pressure-induced reversible crystalline-amorphous and polymorphic amorphous transitions in NaCl structured GST by ab initio molecular dynamics calculations. We have showed that the onset amorphization of GST starts at approximately 18 GPa and the system become completely random at approximately 22 GPa. This amorphous state has a cubic framework (c-amorphous) of sixfold coordinations. With further increasing pressure, the c-amorphous transforms to a high-density amorphous structure with trigonal framework (t-amorphous) and an average coordination number of eight. The pressure-induced amorphization is investigated to be due to large displacements of Te atoms for which weak Te-Te bonds exist or vacancies are nearby. Upon decompressing to ambient conditions, the original cubic crystalline structure is restored for c-amorphous, whereas t-amorphous transforms to another amorphous phase that is similar to the melt-quenched amorphous GST.

The Pressure-Induced Polymorphic Transformations in Fluconazole.

PubMed

Gorkovenko, Ekaterina A; Kichanov, Sergey E; Kozlenko, Denis P; Belushkin, Alexandr V; Wąsicki, Jan; Nawrocik, Wojciech; Mielcarek, Jadwiga; Dubrovinsky, Leonid S; Lathe, Christian; Savenko, Boris N

2015-12-01

The structural properties and Raman spectra of fluconazole have been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 2.5 and 5.5 GPa, respectively. At a pressure of 0.8 GPa, a polymorphic phase transition from the initial form I to a new triclinic form VIII has been observed. At higher pressure of P = 3.2 GPa, possible transformation into another new polymorphic form IX has been detected. The unit cell parameters and volumes, and vibration modes as functions of pressure have been obtained for the different forms of fluconazole. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Phase transformations and equation of state of praseodymium metal to 103 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesnut, Gary N.; Vohra, Yogesh K.

2000-08-01

Pressure-induced structural phase transformations in a trivalent rare-earth metal praseodymium (Pr) were studied at room temperature in a diamond anvil cell to 103 GPa by energy dispersive x-ray diffraction using a synchrotron source. Our x-ray diffraction studies document the following crystal structure sequence: dhcp{yields}fcc{yields}distorted fcc(hR24 type){yields}monoclinic(C2/m){yields}{alpha}-uranium with increasing pressure. We measure a 16.7% volume collapse at the transition to the {alpha}-uranium phase at 20 GPa. The high-pressure {alpha}-uranium phase in Pr was found to be stable to the highest pressure of 103 GPa, which corresponds to a volume compression V/V{sub 0}=0.407. (c) 2000 The American Physical Society.

X-ray diffraction and spectroscopy study of nano-Eu 2O 3 structural transformation under high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Zhenhai; Wang, Qinglin; Ma, Yanzhang

Nanoscale materials exhibit properties that are quite distinct from those of bulk materials because of their size restricted nature. Here, we investigated the high-pressure structural stability of cubic (C-type) nano-Eu2O3 using in situ synchrotron X-ray diffraction (XRD), Raman and luminescence spectroscopy, and impedance spectra techniques. Our high-pressure XRD experimental results revealed a pressure-induced structural phase transition in nano-Eu2O3 from the C-type phase (space group: Ia-3) to a hexagonal phase (A-type, space group: P-3m1). Our reported transition pressure (9.3 GPa) in nano-Eu2O3 is higher than that of the corresponding bulk-Eu2O3 (5.0 GPa), which is contrary to the preceding reported experimental result.more » After pressure release, the A-type phase of Eu2O3 transforms into a new monoclinic phase (B-type, space group: C2/m). Compared with bulk-Eu2O3, C-type and A-type nano-Eu2O3 exhibits a larger bulk modulus. Our Raman and luminescence findings and XRD data provide consistent evidence of a pressure-induced structural phase transition in nano-Eu2O3. To our knowledge, we have performed the first high-pressure impedance spectra investigation on nano-Eu2O3 to examine the effect of the structural phase transition on its transport properties. We propose that the resistance inflection exhibited at ~12 GPa results from the phase boundary between the C-type and A-type phases. Besides, we summarized and discussed the structural evolution process by the phase diagram of lanthanide sesquioxides (Ln2O3) under high pressure.« less

Transition of dislocation glide to shear transformation in shocked tantalum

DOE PAGES

Hsiung, Luke L.; Campbell, Geoffrey H.

2017-02-28

A TEM study of pure tantalum and tantalum-tungsten alloys explosively shocked at a peak pressure of 30 GPa (strain rate: ~1 x 10 4 sec -1) is presented. While no ω (hexagonal) phase was found in shock-recovered pure Ta and Ta-5W that contain mainly a low-energy cellular dislocation structure, shock-induced ω phase was found to form in Ta-10W that contains evenly distributed dislocations with a stored dislocation density higher than 1 x 10 12 cm -2. The TEM results clearly reveal that shock-induced α (bcc) → ω (hexagonal) shear transformation occurs when dynamic recovery reactions which lead the formation low-energymore » cellular dislocation structure become largely suppressed in Ta-10W shocked under dynamic (i.e., high strain-rate and high-pressure) conditions. A novel dislocation-based mechanism is proposed to rationalize the transition of dislocation glide to twinning and/or shear transformation in shock-deformed tantalum. Lastly, twinning and/or shear transformation take place as an alternative deformation mechanism to accommodate high-strain-rate straining when the shear stress required for dislocation multiplication exceeds the threshold shear stresses for twinning and/or shear transformation.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reimanis, Ivar; Cioabanu, Cristian

The study of materials with unusual properties offers new insight into structure-property relations as well as promise for the design of novel composites. In this spirit, the PIs seek to (1) understand fundamental mechanical phenomena in ceramics that exhibit pressure-induced phase transitions, negative coefficient of thermal expansion (CTE), and negative compressibility, and (2) explore the effect of these phenomena on the mechanical behavior of composites designed with such ceramics. The broad and long-term goal is to learn how to utilize these unusual behaviors to obtain desired mechanical responses. While the results are expected to be widely applicable to many ceramics,more » most of the present focus is on silicates, as they exhibit remarkable diversity in structure and properties. Eucryptite, a lithium aluminum silicate (LiAlSiO 4), is specifically targeted because it exhibits a pressure-induced phase transition at a sufficiently low pressure to be accessible during conventional materials processing. Thus, composites with eucryptite may be designed to exhibit a novel type of transformation toughening. The PIs have performed a combination of activities that encompass synthesis and processing to control structures, atomistic modeling to predict and understand structures, and characterization to study mechanical behavior. Several materials behavior discoveries were made. It was discovered that small amounts of Zn (as small as 0.1 percent by mol) reverse the sign of the coefficient of thermal expansion of beta-eucryptite from negative to slightly positive. The presence of Zn also significantly mitigates microcracking that occurs during thermal cycling of eucryptite. It is hypothesized that Zn disrupts the Li ordering in beta-eucryptite, thereby altering the thermal expansion behavior. A nanoindentation technique developed to characterize incipient plasticity was applied to examine the initial stages of the pressure induced phase transformation from beta to epsilon-eucryptite and show that the transformation nucleation is related to the motion of the tetrahedral units making up the structure. It was revealed that the conduction of Li ions through the structure is also dictated by the tetrahedral unit arrangement and how their positions change with temperature. The critical pressure to obtain the high pressure phase of eucryptite was shown to depend on the grain size. The structure of the high pressure phase was determined with a combination of atomistic modeling and in situ x-ray diffraction experiments.« less

Pressure-induced amorphization and reactivity of solid dimethyl acetylene probed by in situ FTIR and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Guan, Jiwen; Daljeet, Roshan; Kieran, Arielle; Song, Yang

2018-06-01

Conjugated polymers are prominent semiconductors that have unique electric conductivity and photoluminescence. Synthesis of conjugated polymers under high pressure is extremely appealing because it does not require a catalyst or solvent used in conventional chemical methods. Transformation of acetylene and many of its derivatives to conjugated polymers using high pressure has been successfully achieved, but not with dimethyl acetylene (DMA). In this work, we present a high-pressure study on solid DMA using a diamond anvil cell up to 24.4 GPa at room temperature characterized by in situ Fourier transform infrared and Raman spectroscopy. Our results show that solid DMA exists in a phase II crystal structure and is stable up to 12 GPa. Above this pressure, amorphization was initiated and the process was completed at 24.4 GPa. The expected polymeric transformation was not evident upon compression, but only observed upon decompression from a threshold compression pressure (e.g. 14.4 GPa). In situ florescence measurements suggest excimer formation via crystal defects, which induces the chemical reactions. The vibrational spectral analysis suggests the products contain the amorphous poly(DMA) and possibly additional amorphous hydrogenated carbon material.

Pressure-induced amorphization and reactivity of solid dimethyl acetylene probed by in situ FTIR and Raman spectroscopy.

PubMed

Guan, Jiwen; Daljeet, Roshan; Kieran, Arielle; Song, Yang

2018-06-06

Conjugated polymers are prominent semiconductors that have unique electric conductivity and photoluminescence. Synthesis of conjugated polymers under high pressure is extremely appealing because it does not require a catalyst or solvent used in conventional chemical methods. Transformation of acetylene and many of its derivatives to conjugated polymers using high pressure has been successfully achieved, but not with dimethyl acetylene (DMA). In this work, we present a high-pressure study on solid DMA using a diamond anvil cell up to 24.4 GPa at room temperature characterized by in situ Fourier transform infrared and Raman spectroscopy. Our results show that solid DMA exists in a phase II crystal structure and is stable up to 12 GPa. Above this pressure, amorphization was initiated and the process was completed at 24.4 GPa. The expected polymeric transformation was not evident upon compression, but only observed upon decompression from a threshold compression pressure (e.g. 14.4 GPa). In situ florescence measurements suggest excimer formation via crystal defects, which induces the chemical reactions. The vibrational spectral analysis suggests the products contain the amorphous poly(DMA) and possibly additional amorphous hydrogenated carbon material.

Pressure-induced transformations in computer simulations of glassy water.

PubMed

Chiu, Janet; Starr, Francis W; Giovambattista, Nicolas

2013-11-14

Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a "P-T phase diagram" for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water.

Pressure-induced transformations in computer simulations of glassy water

NASA Astrophysics Data System (ADS)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2013-11-01

Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a "P-T phase diagram" for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water.

Simulation studies of GST phase change alloys

NASA Astrophysics Data System (ADS)

Martyna, Glenn

2008-03-01

In order to help drive post-Moore's Law technology development, switching processes involving novel materials, in particular, GeSbTe (GST) alloys are being investigated for use in memory and eFuse applications. An anneal/quench thermal process crystallizes/amorphosizes a GST alloy which then has a low/high resistance and thereby forms a readable/writeable bit; for example, a ``one'' might be the low resistance, conducting crystalline state and a ``zero'' might be the high resistance, glassy state. There are many open questions about the precise nature of the structural transitions and the coupling to electronic structure changes. Computational and experimental studies of the effect of pressure on the GST materials were initiated in order to probe the physics behind the thermal switching process. A new pathway to reversible phase change involving pressure-induced structural metal insulator transitions was discovered. In a binary GS system, a room-temperature, direct, pressure-induced transformation from the high resistance amorphous phase to the low resistance crystalline phase was observed experimentally while the reverse process under tensile load was demonstrated via ab initio MD simulations performed on IBM's Blue Gene/L enabled by massively parallel software. Pressure induced transformations of the ternary material GST-225 (Ge2Sb2Te5) were, also, examined In the talk, the behavior of the two systems will be compared and insight into the nature of the phase change given.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Efthimiopoulos, I.; Tsurkan, V.; Loidl, A.

We have conducted high-pressure measurements on the CuCr2O4 and CuCr2Se4 spinels to unravel the structural systematics of these materials under compression. Our studies have revealed diverse structural behavior in these two compounds. In particular, CuCr2O4 retains its ambient-pressure I41/amd structure up to 50 GPa. Close inspection of the lattice and interatomic parameters reveals a compressibility change near 23 GPa, which is accompanied by an expansion of the apical Cr–O bond distances. We speculate that an outer Cr3+ 3d orbital reorientation might be at play in this system, manifesting as the change in compressibility at that pressure point. On the othermore » hand, CuCr2Se4 undergoes a structural transformation from the starting Fd3¯m phase toward a monoclinic structure initiated at ~8 GPa and completed at ~20 GPa. This high-pressure behavior resembles that of ZnCr2Se4, and it appears that, unlike similar chalcogenide Cr spinels, steric effects take a leading role in this pressure-induced Fd3¯m → monoclinic transition. Close comparison of our results with the reported literature yields significant insights behind the pressure-induced structural systematics of this important family of materials, thus both allowing for the careful manipulation of the structural/physical properties of these systems by strain and promoting our understanding of similar pressure-induced effects in relevant systems.« less

Pressure-induced kinetics of the α to ω transition in zirconium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobsen, M. K.; Velisavljevic, N., E-mail: nenad@lanl.gov; Sinogeikin, S. V.

Diamond anvil cells (DAC) coupled with x-ray diffraction (XRD) measurements are one of the primary techniques for investigating structural stability of materials at high pressure-temperature (P-T) conditions. DAC-XRD has been predominantly used to resolve structural information at set P-T conditions and, consequently, provides P-T phase diagram information on a broad range of materials. With advances in large scale synchrotron x-ray facilities and corresponding x-ray diagnostic capabilities, it is now becoming possible to perform sub-second time resolved measurements on micron sized DAC samples. As a result, there is an opportunity to gain valuable information about the kinetics of structural phase transformationsmore » and extend our understanding of material behavior at high P-T conditions. Using DAC-XRD time resolved measurements, we have investigated the kinetics of the α to ω transformation in zirconium. We observe a clear time and pressure dependence in the martensitic α-ω transition as a function of pressure-jump, i.e., drive pressure. The resulting data are fit using available kinetics models, which can provide further insight into transformation mechanism that influence transformation kinetics. Our results help shed light on the discrepancies observed in previous measurements of the α-ω transition pressure in zirconium.« less

Pressure-induced kinetics of the α to ω transition in zirconium

DOE PAGES

Jacobsen, M. K.; Velisavljevic, N.; Sinogeikin, S. V.

2015-07-13

Diamond anvil cells (DAC) coupled with x-ray diffraction (XRD) measurements are one of the primary techniques for investigating structural stability of materials at high pressure-temperature (P-T) conditions. DAC-XRD has been predominantly used to resolve structural information at set P-T conditions and, consequently, provides P-T phase diagram information on a broad range of materials. With advances in large scale synchrotron x-ray facilities and corresponding x-ray diagnostic capabilities, it is now becoming possible to perform sub-second time resolved measurements on micron sized DAC samples. As a result, there is an opportunity to gain valuable information about the kinetics of structural phase transformationsmore » and extend our understanding of material behavior at high P-T conditions. Using DAC-XRD time resolved measurements, we have investigated the kinetics of the α to ω transformation in zirconium. We observe a clear time and pressure dependence in the martensitic α-ω transition as a function of pressure-jump, i.e., drive pressure. The resulting data are fit using available kinetics models, which can provide further insight into transformation mechanism that influence transformation kinetics. Our results help shed light on the discrepancies observed in previous measurements of the α-ω transition pressure in zirconium.« less

Pressure-induced phase transitions of β-type pyrochlore CsTaWO 6

DOE PAGES

Zhang, F. X.; Tracy, C. L.; Shamblin, J.; ...

2016-09-30

The β-type pyrochlore CsTaWO 6 was studied by synchrotron X-ray diffraction (XRD) and Raman scattering methods up to pressures of 43 GPa using a diamond anvil cell (DAC). With increasing pressure, the cubic pyrochlore in space group of Fd-3¯m with combining macron]m transforms to an orthorhombic structure (space group: Pnma) at 5.9 GPa and then to a monoclinic structure (space group: P2 1/c) at ~18 GPa. The structural evolution in CsTaWO 6 is a continuous process and experimental results suggest that the initial cubic phase has a tetragonal distortion at ambient conditions. Both XRD and Raman measurements indicate that themore » pressure-induced phase transitions in CsTaWO 6 are reversible. Lastly, these results may provide a structural explanation of previous experimental resistivity measurement results for the isostructural superconductor K(Cs)Os 2O 6 at high pressure conditions.« less

Pressure-induced phase transitions of β-type pyrochlore CsTaWO 6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, F. X.; Tracy, C. L.; Shamblin, J.

The β-type pyrochlore CsTaWO 6 was studied by synchrotron X-ray diffraction (XRD) and Raman scattering methods up to pressures of 43 GPa using a diamond anvil cell (DAC). With increasing pressure, the cubic pyrochlore in space group of Fd-3¯m with combining macron]m transforms to an orthorhombic structure (space group: Pnma) at 5.9 GPa and then to a monoclinic structure (space group: P2 1/c) at ~18 GPa. The structural evolution in CsTaWO 6 is a continuous process and experimental results suggest that the initial cubic phase has a tetragonal distortion at ambient conditions. Both XRD and Raman measurements indicate that themore » pressure-induced phase transitions in CsTaWO 6 are reversible. Lastly, these results may provide a structural explanation of previous experimental resistivity measurement results for the isostructural superconductor K(Cs)Os 2O 6 at high pressure conditions.« less

High-Pressure-Induced Comminution and Recrystallization of CH3 NH3 PbBr3 Nanocrystals as Large Thin Nanoplates.

PubMed

Yin, Tingting; Fang, Yanan; Chong, Wee Kiang; Ming, Koh Teck; Jiang, Shaojie; Li, Xianglin; Kuo, Jer-Lai; Fang, Jiye; Sum, Tze Chien; White, Timothy J; Yan, Jiaxu; Shen, Ze Xiang

2018-01-01

High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic-inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic-orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane. Beyond bulk perovskites, in which pressure-induced modifications on crystal structures and functional properties will disappear after pressure release, the pressure-formed variants, i.e., large (≈100 nm) and thin (<10 nm) perovskite nanoplates, are retained and these exhibit simultaneous photoluminescence emission enhancing (a 15-fold enhancement in the photoluminescence) and carrier lifetime shortening (from ≈18.3 ± 0.8 to ≈7.6 ± 0.5 ns) after releasing of pressure from 11 GPa. This pressure-induced comminution of hybrid perovskite NCs and a subsequent amorphization-recrystallization treatment offer the possibilities of engineering the advanced hybrid perovskites with specific properties. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Anomalous expansion of Nb nanowires in a NiTi matrix under high pressure

DOE PAGES

Yu, Cun; Ren, Yang; Cui, Lishan; ...

2016-10-17

Under high pressure, materials usually shrink during compression as described by an equation of state. Here, we present the anomalous volume expansion behavior of a one-dimensional Nb nanowire embedded in a NiTi transforming matrix, while the matrix undergoes a pressure-induced martensitic transformation. The Nb volume expansion depends on the NiTi transition pressure range from the matrix, which is controlled by the shear strain induced by different pressure transmitting media. The transformation-induced interfacial stresses between Nb and NiTi may play a major role in this anomaly. In conclusion, our discovery sheds new light on the nano-interfacial effect on mechanical anomalies inmore » heterogeneous systems during a pressure-induced phase transition.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Cun; Ren, Yang; Cui, Lishan

Under high pressure, materials usually shrink during compression as described by an equation of state. Here, we present the anomalous volume expansion behavior of a one-dimensional Nb nanowire embedded in a NiTi transforming matrix, while the matrix undergoes a pressure-induced martensitic transformation. The Nb volume expansion depends on the NiTi transition pressure range from the matrix, which is controlled by the shear strain induced by different pressure transmitting media. The transformation-induced interfacial stresses between Nb and NiTi may play a major role in this anomaly. In conclusion, our discovery sheds new light on the nano-interfacial effect on mechanical anomalies inmore » heterogeneous systems during a pressure-induced phase transition.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulvestad, A.; Welland, M. J.; Cha, W.

Crystallographic imperfections can significantly alter material properties and responses to external stimuli, including solute induced phase transformations and crystal growth and dissolution . Despite recent progress in imaging defects using both electron and x-ray techniques, in situ three-dimensional imaging studies of defect dynamics, necessary to understand and engineer nanoscale processes, remains challenging. Here, we report in situ three-dimensional imaging of defect dynamics during the hydriding phase transformation of individual palladium nanocrystals by Bragg Coherent Diffractive Imaging (BCDI) . During constant pressure experiments, we observed that the phase transformation begins after the nucleation of dislocations in large (300 nm) particles. Themore » 3D dislocation network shows that dislocations are close to the phase boundary. The 3D phase morphology resolved by BCDI suggests that the hydrogen-rich phase is more similar to a spherical cap on the hydrogen-poor phase than the core-shell model commonly assumed. We substantiate this conclusion using 3D phase field modeling and demonstrate how phase morphology affects the critical size for dislocation nucleation. We determine the size dependence of the transformation pressure for large (150-300 nm) palladium nanocrystals using variable pressure experiments. Our results reveal a pathway for solute induced structural phase transformations in nanocrystals and demonstrate BCDI as a novel method for understanding dislocation dynamics in phase transforming systems at the nanoscale.« less

High pressure phase transformations revisited

NASA Astrophysics Data System (ADS)

Levitas, Valery I.

2018-04-01

High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The main reason for the above mentioned discrepancy is the lack of understanding that there is a fundamental difference between pressure-induced transformations under hydrostatic conditions, stress-induced transformations under nonhydrostatic conditions below yield, and strain-induced transformations during plastic flow. Each of these types of transformations has different mechanisms and requires a completely different thermodynamic and kinetic description and experimental characterization. In comparison with other fields the following challenges are indicated for high pressure phase transformation: (a) initial and evolving microstructure is not included in characterization of transformations; (b) continuum theory is poorly developed; (c) heterogeneous stress and strain fields in experiments are not determined, which leads to confusing material transformational properties with a system behavior. Some ways to advance the field of high pressure phase transformations are suggested. The key points are: (a) to take into account plastic deformations and microstructure evolution during transformations; (b) to formulate phase transformation criteria and kinetic equations in terms of stress and plastic strain tensors (instead of pressure alone); (c) to develop multiscale continuum theories, and (d) to couple experimental, theoretical, and computational studies of the behavior of a tested sample to extract information about fields of stress and strain tensors and concentration of high pressure phase, transformation criteria and kinetics. The ideal characterization should contain complete information which is required for simulation of the same experiments.

High pressure phase transformations revisited.

PubMed

Levitas, Valery I

2018-04-25

High pressure phase transformations play an important role in the search for new materials and material synthesis, as well as in geophysics. However, they are poorly characterized, and phase transformation pressure and pressure hysteresis vary drastically in experiments of different researchers, with different pressure transmitting media, and with different material suppliers. Here we review the current state, challenges in studying phase transformations under high pressure, and the possible ways in overcoming the challenges. This field is critically compared with fields of phase transformations under normal pressure in steels and shape memory alloys, as well as plastic deformation of materials. The main reason for the above mentioned discrepancy is the lack of understanding that there is a fundamental difference between pressure-induced transformations under hydrostatic conditions, stress-induced transformations under nonhydrostatic conditions below yield, and strain-induced transformations during plastic flow. Each of these types of transformations has different mechanisms and requires a completely different thermodynamic and kinetic description and experimental characterization. In comparison with other fields the following challenges are indicated for high pressure phase transformation: (a) initial and evolving microstructure is not included in characterization of transformations; (b) continuum theory is poorly developed; (c) heterogeneous stress and strain fields in experiments are not determined, which leads to confusing material transformational properties with a system behavior. Some ways to advance the field of high pressure phase transformations are suggested. The key points are: (a) to take into account plastic deformations and microstructure evolution during transformations; (b) to formulate phase transformation criteria and kinetic equations in terms of stress and plastic strain tensors (instead of pressure alone); (c) to develop multiscale continuum theories, and (d) to couple experimental, theoretical, and computational studies of the behavior of a tested sample to extract information about fields of stress and strain tensors and concentration of high pressure phase, transformation criteria and kinetics. The ideal characterization should contain complete information which is required for simulation of the same experiments.

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI{sub 4}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, H.; Tse, J. S., E-mail: john.tse@usask.ca; Hu, M. Y.

2015-10-28

The pressure-induced amorphization and subsequent recrystallization of SnI{sub 4} have been investigated using first principles molecular dynamics calculations together with high-pressure {sup 119}Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI{sub 4} under ambient conditions. Although high pressure structures of SnI{sub 4} were thought to be determined by randommore » packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.« less

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of Snl 4

DOE PAGES

Liu, Hanyu; Tse, John S.; Hu, Michael Y.; ...

2015-10-27

The pressure-induced amorphization and subsequent recrystallization of SnI 4 have been investigated using first principles molecular dynamics calculations together with high-pressure 119Sn nuclear resonant inelastic x-ray scattering measurements. Above ~8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ~64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI 4 under ambient conditions. Although high pressure structures of SnI 4 were thought to be determined by random packingmore » of equal-sized spheres, we detected electron charge transfer in each phase. As a result, this charge transfer results in a crystal structure packing determined by larger than expected iodine atoms. (C) 2015 AIP Publishing LLC.« less

Mechanisms for pressure-induced crystal-crystal transition, amorphization, and devitrification of SnI4.

PubMed

Liu, H; Tse, J S; Hu, M Y; Bi, W; Zhao, J; Alp, E E; Pasternak, M; Taylor, R D; Lashley, J C

2015-10-28

The pressure-induced amorphization and subsequent recrystallization of SnI4 have been investigated using first principles molecular dynamics calculations together with high-pressure (119)Sn nuclear resonant inelastic x-ray scattering measurements. Above ∼8 GPa, we observe a transformation from an ambient crystalline phase to an intermediate crystal structure and a subsequent recrystallization into a cubic phase at ∼64 GPa. The crystalline-to-amorphous transition was identified on the basis of elastic compatibility criteria. The measured tin vibrational density of states shows large amplitude librations of SnI4 under ambient conditions. Although high pressure structures of SnI4 were thought to be determined by random packing of equal-sized spheres, we detected electron charge transfer in each phase. This charge transfer results in a crystal structure packing determined by larger than expected iodine atoms.

Static high pressure studies on Nd and Sc

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akella, J.; Xu, J.; Smith, G.S.

1985-06-24

We have investigated the crystal structural transformations in neodymium and scandium up to 4.0 GPa pressure and at room temperature, in a diamond-anvil high pressure apparatus. Nd has a double hexagonal-close packed (dhcp) structure at ambient pressure and temperature. Then it transforms to a face-centered cubic (fcc) structure at 3.8 GPa, which further transforms to a triple hexagonal-close packed structure (thcp) at about 18.0 GPa. In scandium we observed only one transformation from the hexagonal-close packed (hcp) structure at room temperature to a tetragonal structure. This transformation occurs between 19.0 and 23.2 GPa pressure.

Low pressure-induced secondary structure transitions of regenerated silk fibroin in its wet film studied by time-resolved infrared spectroscopy.

PubMed

He, Zhipeng; Liu, Zhao; Zhou, Xiaofeng; Huang, He

2018-06-01

The secondary structure transitions of regenerated silk fibroin (RSF) under different external perturbations have been studied extensively, except for pressure. In this work, time-resolved infrared spectroscopy with the attenuated total reflectance (ATR) accessory was employed to follow the secondary structure transitions of RSF in its wet film under low pressure. It has been found that pressure alone is favorable only to the formation of β-sheet structure. Under constant pressure there is an optimum amount of D 2 O in the wet film (D 2 O : film = 2:1) so as to provide the optimal condition for the reorganization of the secondary structure and to have the largest formation of β-sheet structure. Under constant amount of D 2 O and constant pressure, the secondary structure transitions of RSF in its wet film can be divided into three stages along with time. In the first stage, random coil, α-helix, and β-turn were quickly transformed into β-sheet. In the second stage, random coil and β-turn were relatively slowly transformed into β-sheet and α-helix, and the content of α-helix was recovered to the value prior to the application of pressure. In the third and final stage, no measurable changes can be found for each secondary structure. This study may be helpful to understand the secondary structure changes of silk fibroin in silkworm's glands under hydrostatic pressure. © 2018 Wiley Periodicals, Inc.

Ion-beam-induced magnetic and structural phase transformation of Ni-stabilized face-centered-cubic Fe films on Cu(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gloss, Jonas; Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology, Technická 2, 616 69 Brno; Shah Zaman, Sameena

2013-12-23

Metastable face-centered cubic (fcc) Fe/Cu(100) thin films are good candidates for ion-beam magnetic patterning due to their magnetic transformation upon ion-beam irradiation. However, pure fcc Fe films undergo spontaneous transformation when their thickness exceeds 10 ML. This limit can be extended to approximately 22 ML by deposition of Fe at increased CO background pressures. We show that much thicker films can be grown by alloying with Ni for stabilizing the fcc γ phase. The amount of Ni necessary to stabilize nonmagnetic, transformable fcc Fe films in dependence on the residual background pressure during the deposition is determined and a phasemore » diagram revealing the transformable region is presented.« less

Stability limits and transformation pathways of α-quartz under high pressure

NASA Astrophysics Data System (ADS)

Hu, Q. Y.; Shu, J.-F.; Yang, W. G.; Park, C.; Chen, M. W.; Fujita, T.; Mao, H.-K.; Sheng, H. W.

2017-03-01

Ubiquitous on Earth, α-quartz plays an important role in modern science and technology. However, despite extensive research in the past, the mechanism of the polymorphic transitions of α-quartz at high pressures remains poorly understood. Here, combining in situ single-crystal x-ray diffraction experiment and advanced ab initio modeling, we report two stability limits and competing transition pathways of α-quartz under high pressure. Under near-equilibrium compression conditions at room temperature, α-quartz transits to a new P 2 /c silica phase via a structural intermediate. If the thermally activated transition is kinetically suppressed, the ultimate stability of α-quartz is controlled by its phonon instability and α-quartz collapses into a different crystalline phase. Our studies reveal that pressure-induced solid-state transformation of α-quartz undergoes a succession of structural stability limits, due to thermodynamic and mechanical catastrophes, and exhibits a hierarchy of transition pathways contingent upon kinetic conditions.

Pressure induced para-antiferromagnetic switching in BiFeO3-PbTiO3 as determined using in-situ neutron diffraction

NASA Astrophysics Data System (ADS)

Comyn, Tim P.; Stevenson, Tim; Al-Jawad, Maisoon; Marshall, William G.; Smith, Ronald I.; Herrero-Albillos, Julia; Cywinski, Robert; Bell, Andrew J.

2013-05-01

BiFeO3-PbTiO3 exhibits both ferroelectric and antiferromagnetic order, depending on the composition. Moderate hydrostatic pressures have been used at room temperature to transform the crystallographic phase from P4mm to R3c for the compositions 0.7BiFeO3-0.3PbTiO3 and 0.65BiFeO3-0.35PbTiO3, as determined using in-situ neutron diffraction. Using Rietveld refinements, the resultant data showed that, for both compositions, a transformation from para- to G-type antiferromagnetic order accompanied the structural transition. The transformation occurred over the range 0.4-0.77 and 0.67-0.88 GPa for 0.7BiFeO3-0.3PbTiO3 and 0.65BiFeO3-0.35PbTiO3, respectively; at intermediate pressures, a mixture of P4mm and R3c phases were evident. These pressures are far lower than required to induce a phase transition in either the BiFeO3 or PbTiO3 end members. The driving force for this pressure induced first order phase transition is a significant difference in volume between the two phases, P4mm > R3c of 4%-5%, at ambient pressure. Upon removal of the pressure, 0.65BiFeO3-0.35PbTiO3 returned to the paramagnetic tetragonal state, whereas in 0.7BiFeO3-0.3PbTiO3 antiferromagnetic ordering persisted, and the structural phase remained rhombohedral. Using conventional laboratory x-ray diffraction with a hot-stage, the phase readily reverted back to a tetragonal phase, at temperatures between 100 and 310 °C for 0.7BiFeO3-0.3PbTiO3, far lower than the ferroelectric Curie point for this composition of 632 °C. To our knowledge, the reported pressure induced para- to antiferromagnetic transition is unique in the literature.

Theoretical analysis of the structural phase transformation in the ZnO under high pressure

NASA Astrophysics Data System (ADS)

Verma, Saligram; Jain, Arvind; Nagarch, R. K.; Shah, S.; Kaurav, Netram

2018-05-01

We report a phenomenological model based calculation of pressure-induced structural phase transition and elastic properties of ZnO compound. Gibb's free energy is obtained as a function of pressure by applying an effective inter ionic interaction potential, which includes the long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach. From the present study, we predict a structural phase transition from ZnS structure (B3) to NaCl structure (B1) at 8.5 GPa. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data. The variations of elastic constants with pressure follow a systematic trend identical to that observed in others compounds of ZnS type structure family.

Three-dimensional imaging of dislocation dynamics during the hydriding phase transformation

DOE PAGES

Ulvestad, A.; Welland, M. J.; Cha, W.; ...

2017-01-16

Crystallographic imperfections can significantly alter material properties and responses to external stimuli, including solute induced phase transformations and crystal growth and dissolution . Despite recent progress in imaging defects using both electron and x-ray techniques, in situ three-dimensional imaging studies of defect dynamics, necessary to understand and engineer nanoscale processes, remains challenging. Here, we report in situ three-dimensional imaging of defect dynamics during the hydriding phase transformation of individual palladium nanocrystals by Bragg Coherent Diffractive Imaging (BCDI) . During constant pressure experiments, we observed that the phase transformation begins after the nucleation of dislocations in large (300 nm) particles. Themore » 3D dislocation network shows that dislocations are close to the phase boundary. The 3D phase morphology resolved by BCDI suggests that the hydrogen-rich phase is more similar to a spherical cap on the hydrogen-poor phase than the core-shell model commonly assumed. We substantiate this conclusion using 3D phase field modeling and demonstrate how phase morphology affects the critical size for dislocation nucleation. We determine the size dependence of the transformation pressure for large (150-300 nm) palladium nanocrystals using variable pressure experiments. Our results reveal a pathway for solute induced structural phase transformations in nanocrystals and demonstrate BCDI as a novel method for understanding dislocation dynamics in phase transforming systems at the nanoscale.« less

Instability induced by orthopyroxene phase transformation and implications for deep earthquakes below 300 km depth

NASA Astrophysics Data System (ADS)

Shi, F.; Wang, Y.; Zhang, J.; Yu, T.; Zhu, L.

2017-12-01

Global earthquake occurrence rate falls exponentially from the surface to 300 km depth, and then peaks again near 500 km depth. Unassisted frictional sliding will not function at depth below the brittle-ductile transition depth (10-15 km) because increasing pressure trends to inhibit frictional sliding and increasing temperature promotes ductile flow. Two main hypotheses have been proposed and demonstrated in the laboratory for the generation of earthquakes at depth, including dehydration embrittlement (e.g., Rayleigh and Paterson, 1965) for intermediate-depth (70-300 km) earthquakes, metastable olivine phase transformation induced anticrack faulting (e.g., Green and Burnley, 1989) for deep-focus (410-660 km) earthquakes. However, the possibility of earthquake generation by pyroxene phase transformation, another important constituent mineral in the upper mantle and transition zone has never been explored in the laboratory. Here we report axial deformation experiments on hypersthene [(Mg,Fe)SiO3], which has the same structure as enstatite, with the phase transformation to high-pressure monoclinic phase (same structure as the high-pressure clinoenstatite) occurring at lower pressures, in a deformation-DIA (D-DIA) apparatus interfaced with an acoustic emission (AE) monitoring system. Our results show that hypersthene deformed within its stability field (<2GPa and 1000 oC) behaves in a ductile manner without any AE activity. In contrast, numerous AE events were observed during the deformation of metastable hyposthene in its high pressure monoclinic phase field (>5GPa, 1000-1300 oC). This finding provides an additional viable mechanism for earthquakes at depths >300km and moonquakes at 700 - 1200 km depths. Reference: Barcheck, C. Grace, et al. EPSL,349 (2012): 153-160;van Keken, Peter E., et al.JGR,116.B1 (2011);Green II, H. W., and P. C. Burnley. Nature 341.6244 (1989): 733-737.

Synthesis, characterization and thermodynamic study of carbon dioxide adsorption on akaganéite

DOE PAGES

Roque-Malherbe, R.; Lugo, F.; Rivera-Maldonado, C.; ...

2015-04-01

A mixture of akaganeite nanoparticles and sodium salts was synthesized and modi fied, first by washing, and then by Li exchange. The structural characterization of the produced materials was performed with: powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectrometry, Mossbauer spectros- € copy and magnetization measurements. Additionally low pressure nitrogen and high pressure carbon dioxide adsorption experiments were performed. The sum of the characterization information made possible to conclude that the produced akaganeite phases crystallized in a structure exhibiting the symmetry of the I2/m space group, where the measured equivalentmore » spherical diameter of the akaganeite crystallites yielded 9 nm, as well, the tested phases exhibited a standard behaviour under heating and displayed a superparamagnetic behaviour. Finally the high pressure carbon dioxide adsorption experiments demonstrated a pressure-responsive framework opening event due to a structural transformation of the adsorbent framework induced by the guest molecules. This fact opens new applications for akaganeite as a high pressure adsorbent.« less

Pressure induced Ag 2Te polymorphs in conjunction with topological non trivial to metal transition

DOE PAGES

Zhu, J.; Oganov, A. R.; Feng, W. X.; ...

2016-08-01

Silver telluride (Ag 2Te) is well known as superionic conductor and topologica insulator with polymorphs. Pressure induced three phase transitions in Ag 2Te hav been reported in previous. Here, we experimentally identified high pressure phas above 13 GPa of Ag 2Te by using high pressure synchrotron x ray diffraction metho in combination with evolutionary crystal structure prediction, showing it crystallize into a monoclinic structure of space group C2/m with lattice parameters a = 6.081Å b = 5.744Å, c = 6.797 Å, β = 105.53°. The electronic properties measurements of Ag 2Te reveal that the topologically non-trivial semiconducting phase I andmore » semimetalli phase II previously predicated by theory transformed into bulk metals fo high pressure phases in consistent with the first principles calculations« less

Melting in feldspar-bearing systems to high pressures and the structures of aluminosilicate liquids

NASA Astrophysics Data System (ADS)

Boettcher, Art; Guo, Qiti; Bohlen, Steve; Hanson, Brooks

1984-04-01

To test the possibility that aluminosilicate liquids exhibit pressure-induced transformations, particularly involving changes in the coordination of aluminum, we determined melting relationships for the feldspar-bearing systems NaAlSi3O8-SiO2, KAlSi3O8-SiO2, and CaAl2Si2O8-SiO2 from 1 atm to 25 kbar. Albite and anorthite behave similarly in that they, and presumably liquids of these compositions, transform at high pressures to jadeite, kyanite, corundum, and other structures with aluminum in six-fold coordination, releasing SiO2 component. This results in a large increase in the activity of SiO2 component in the liquid (alqz), which is manifested by a significant decrease in the melting-point depression of albite and of anorthite by the addition of quartz at pressures above ˜15 kbar. In contrast, sanidine does not transform to denser phases at pressures below at least 100 kbar, but it melts incongruently to leucite + SiO2-rich liquid up to ˜ 15 kbar. This produces a relatively large alqz and a small freezing-point depression by quartz below this pressure; the opposite holds above ˜15 kbar. These results support the concept that significant structural changes, including coordination changes in aluminum, occur in magmas in the upper mantle.

Pressure Induced Phase Transformations of Silica Polymorphs and Glasses

NASA Astrophysics Data System (ADS)

Cagin, Tahir; Demiralp, Ersan; Goddard, William A., III

1998-03-01

Silica, SiO_2, is one of the most widely studied substance, and it has some complex and unusual properties. We have used a recently developed 2-body interaction force field (E. Demiralp, T. Cagin, W.A. Goddard, III, unpublished.) to study the structural phase transformations in silica under various pressure loading conditions. The specific transformations we studied are α-quartz to stishovite, coesite to stishovite and fused glass to stishovite-like dense, a dominantly six-coordinated glassy phase. Molecular dynamics simulations are performed under the constant loading rates ranging from 0.1 GPa/ps to 2.0 GPa/ps, pressures upto 100 GPa and at temperatures 300, 500, 700 and 900 K. We observe the crystal to crystal transformations to occur reconstructively, whereas it occurs in a smooth and displacive manner from glass to a stishovite-like phase confirming earlier conjectures. (E.M. Stolper and T.J. Ahrens, Geophys. Res. Let.) 14, 1231 (1987). To elucidate the shock loading experiments, we studied the dependence of transition pressure on the loading rate and the temperature. To assess the hysterisis effect we also studied the unloading behavior of each transformation.

Structural properties of pressure-induced structural phase transition of Si-doped GaAs by angular-dispersive X-ray diffraction

NASA Astrophysics Data System (ADS)

Lin, Kung-Liang; Lin, Chih-Ming; Lin, Yu-Sheng; Jian, Sheng-Rui; Liao, Yen-Fa; Chuang, Yu-Chun; Wang, Chuan-Sheng; Juang, Jenh-Yih

2016-02-01

Pressure-induced phase transitions in n-type silicon-doped gallium arsenide (GaAs:Si ) at ambient temperature were investigated by using angular-dispersive X-ray diffraction (ADXRD) under high pressure up to around 18.6 (1) GPa, with a 4:1 (in volume ratio) methanol-ethanol mixture as the pressure-transmitting medium. In situ ADXRD measurements revealed that n-type GaAs:Si starts to transform from zinc- blende structure to an orthorhombic structure [GaAs-II phase], space group Pmm2, at 16.4 (1) GPa. In contrast to previous studies of pure GaAs under pressure, our results show no evidence of structural transition to Fmmm or Cmcm phase. The fitting of volume compression data to the third-order Birch-Murnaghan equation of state yielded that the zero-pressure isothermal bulk moduli and the first-pressure derivatives were 75 (3) GPa and 6.4 (9) for the B3 phase, respectively. After decompressing to the ambient pressure, the GaAs:Si appears to revert to the B3 phase completely. By fitting to the empirical relations, the Knoop microhardness numbers are between H PK = 6.21 and H A = 5.85, respectively, which are substantially smaller than the values of 7-7.5 for pure GaAs reported previously. A discontinuous drop in the pressure-dependent lattice parameter, N- N distances, and V/ V 0 was observed at a pressure of 11.5 (1) GPa, which was tentatively attributed to the pressure-induced dislocation activities in the crystal grown by vertical gradient freeze method.

First-principles predictions of structural, mechanical and electronic properties of βTiNb under high pressure

NASA Astrophysics Data System (ADS)

Wang, Z. P.; Fang, Q. H.; Li, J.; Liu, B.

2018-04-01

Structural, mechanical and electronic properties of βTiNb alloy under high pressure have been investigated based on the density functional theory (DFT). The dependences of dimensionless volume ratio, elastic constants, bulk modulus, Young's modulus, shear modulus, ductile/brittle, anisotropy and Poisson's ratio on applied pressure are all calculated successfully. The results reveal that βTiNb alloy is mechanically stable under pressure below 23.45 GPa, and the pressure-induced phase transformation could occur beyond this critical value. Meanwhile, the applied pressure can effectively promote the mechanical properties of βTiNb alloy, including the resistances to volume change, elastic deformation and shear deformation, as well as the material ductility and metallicity. Furthermore, the calculated electronic structures testify that βTiNb alloy performs the metallicity and the higher pressure reduces the structural stability of unit cell.

Heating- and pressure-induced transformations in amorphous and hexagonal ice: A computer simulation study using the TIP4P/2005 model

NASA Astrophysics Data System (ADS)

Engstler, Justin; Giovambattista, Nicolas

2017-08-01

We characterize the phase behavior of glassy water by performing extensive out-of-equilibrium molecular dynamics simulations using the TIP4P/2005 water model. Specifically, we study (i) the pressure-induced transformations between low-density (LDA) and high-density amorphous ice (HDA), (ii) the pressure-induced amorphization (PIA) of hexagonal ice (Ih), (iii) the heating-induced LDA-to-HDA transformation at high pressures, (iv) the heating-induced HDA-to-LDA transformation at low and negative pressures, (v) the glass transition temperatures of LDA and HDA as a function of pressure, and (vi) the limit of stability of LDA upon isobaric heating and isothermal decompression (at negative pressures). These transformations are studied systematically, over a wide range of temperatures and pressures, allowing us to construct a P-T phase diagram for glassy TIP4P/2005 water. Our results are in qualitative agreement with experimental observations and with the P-T phase diagram obtained for glassy ST2 water that exhibits a liquid-liquid phase transition and critical point. We also discuss the mechanism for PIA of ice Ih and show that this is a two-step process where first, the hydrogen-bond network (HBN) is distorted and then the HBN abruptly collapses. Remarkably, the collapse of the HB in ice Ih occurs when the average molecular orientations order, a measure of the tetrahedrality of the HBN, is of the same order as in LDA, suggesting a common mechanism for the LDA-to-HDA and Ih-to-HDA transformations.

Heating- and pressure-induced transformations in amorphous and hexagonal ice: A computer simulation study using the TIP4P/2005 model.

PubMed

Engstler, Justin; Giovambattista, Nicolas

2017-08-21

We characterize the phase behavior of glassy water by performing extensive out-of-equilibrium molecular dynamics simulations using the TIP4P/2005 water model. Specifically, we study (i) the pressure-induced transformations between low-density (LDA) and high-density amorphous ice (HDA), (ii) the pressure-induced amorphization (PIA) of hexagonal ice (I h ), (iii) the heating-induced LDA-to-HDA transformation at high pressures, (iv) the heating-induced HDA-to-LDA transformation at low and negative pressures, (v) the glass transition temperatures of LDA and HDA as a function of pressure, and (vi) the limit of stability of LDA upon isobaric heating and isothermal decompression (at negative pressures). These transformations are studied systematically, over a wide range of temperatures and pressures, allowing us to construct a P-T phase diagram for glassy TIP4P/2005 water. Our results are in qualitative agreement with experimental observations and with the P-T phase diagram obtained for glassy ST2 water that exhibits a liquid-liquid phase transition and critical point. We also discuss the mechanism for PIA of ice I h and show that this is a two-step process where first, the hydrogen-bond network (HBN) is distorted and then the HBN abruptly collapses. Remarkably, the collapse of the HB in ice I h occurs when the average molecular orientations order, a measure of the tetrahedrality of the HBN, is of the same order as in LDA, suggesting a common mechanism for the LDA-to-HDA and I h -to-HDA transformations.

Density driven structural transformations in amorphous semiconductor clathrates

DOE PAGES

Tulk, Christopher A.; dos Santos, Antonio M.; Neuefeind, Joerg C.; ...

2015-01-16

The pressure induced crystalline collapse at 14.7 GPa and polyamorphic structures of the semiconductor clathrate Sr8Ga16Ge30 are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicate that this feature is associated with gradual cage collapse and breakdown of the tetrahedral structure with themore » consequent systematic lengthening of the nearest-neighbor framework bonds. This suggests an overall local coordination change to an even higher density amorphous form. Upon recovery from high pressure, the sample remains amorphous, and while there is some indication of the guest-host cage reforming, it doesn't seem that the tetrahedral coordination is recovered. As such, the compresion-decompression process in this systems gives rise to three distict amorphous forms.« less

Experimental studies of transplutonium metals and compounds under pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peterson, J.R.; Haire, R.G.; Benedict, U.

1986-01-01

The structural behavior of the first four transplutonium metals and two Bk-Cf alloys as a function of pressure has been studied in diamond anvil cells via x-ray diffraction. The sequence of structures exhibited as pressure is increased is dhcp ..-->.. ccp ..-->.. orthorhombic. In addition a distorted ccp phase is observed in Am, Bk/sub 0.40/Cf/sub 0.60/, and Cf between the ccp and orthorhombic phases. Diamond anvil cells have also been used to contain AmI/sub 3/, CfBr/sub 3/, and CfCl/sub 3/ under pressure for investigation by absorption spectrophotometry. Both AmI/sub 3/ and CfBr/sub 3/ exhibit pressure-induced, irreversible phase transformations to themore » PuBr/sub 3/-type orthorhombic structure, a more dense form of these compounds. Thus the driving force for these transformations is more efficient crystal packing. Both hexagonal (to 22 GPa) and orthorhombic (to 35 GPa) CfCl/sub 3/ exhibit only reversible spectral changes with pressure. This probably reflects their nearly identical RTP unit cell volumes. In both cases the spectra obtained are consistent with a continuous alteration of the RTP structure with pressure; physical compression seems to make a given f-f transition easier. Additional data are being sought to elucidate more completely the behavior of CfCl/sub 3/ under pressure. 23 refs., 4 figs.« less

Pressure-induced transformations in amorphous silicon: A computational study

NASA Astrophysics Data System (ADS)

Garcez, K. M. S.; Antonelli, A.

2014-02-01

We study the transformations between amorphous phases of Si through molecular simulations using the environment dependent interatomic potential (EDIP) for Si. Our results show that upon pressure, the material undergoes a transformation from the low density amorphous (LDA) Si to the high density amorphous (HDA) Si. This transformation can be reversed by decompressing the material. This process, however, exhibits clear hysteresis, suggesting that the transformation LDA ↔ HDA is first-order like. The HDA phase is predominantly five-fold coordinated, whereas the LDA phase is the normal tetrahedrally bonded amorphous Si. The HDA phase at 400 K and 20 GPa was submitted to an isobaric annealing up to 800 K, resulting in a denser amorphous phase, which is structurally distinct from the HDA phase. Our results also show that the atomic volume and structure of this new amorphous phase are identical to those of the glass obtained by an isobaric quenching of the liquid in equilibrium at 2000 K and 20 GPa down to 400 K. The similarities between our results and those for amorphous ices suggest that this new phase is the very high density amorphous Si.

Pressure-induced effects and phase relations in Mg2NiH4

NASA Astrophysics Data System (ADS)

Gavra, Z.; Kimmel, G.; Gefen, Y.; Mintz, Moshe H.

1985-05-01

The low-temperature (<210 °C) crystallographic structure, electrical conductivity, and thermal stability of Mg2NiH4 powders compacted under isostatic pressures of up to 10 kbar were studied. A comparison is made with the corresponding properties of the noncompressed material. It has been concluded that under stress-free hydriding conditions performed below 210 °C, a two-phase hydride mixture is formed. Each of the hydride particles consists of an inner core composed of an hydrogen-deficient monoclinic phase coated by a layer of a stoichiometric orthorhombic phase. The monoclinic phase has a metalliclike electrical conductivity while the orthorhombic phase is insulating. High compaction pressures cause the transformation of the orthorhombic structure into the monoclinic one, thereby resulting in a pressure-induced insulator-to-conductor transition. Reduced decomposition temperatures are obtained for the compressed hydrides. This reduction is attributed to kinetic factors rather than to a reduced thermodynamic stability.

Reversible switching between pressure-induced amorphization and thermal-driven recrystallization in VO2(B) nanosheets.

PubMed

Wang, Yonggang; Zhu, Jinlong; Yang, Wenge; Wen, Ting; Pravica, Michael; Liu, Zhenxian; Hou, Mingqiang; Fei, Yingwei; Kang, Lei; Lin, Zheshuai; Jin, Changqing; Zhao, Yusheng

2016-07-18

Pressure-induced amorphization (PIA) and thermal-driven recrystallization have been observed in many crystalline materials. However, controllable switching between PIA and a metastable phase has not been described yet, due to the challenge to establish feasible switching methods to control the pressure and temperature precisely. Here, we demonstrate a reversible switching between PIA and thermally-driven recrystallization of VO2(B) nanosheets. Comprehensive in situ experiments are performed to establish the precise conditions of the reversible phase transformations, which are normally hindered but occur with stimuli beyond the energy barrier. Spectral evidence and theoretical calculations reveal the pressure-structure relationship and the role of flexible VOx polyhedra in the structural switching process. Anomalous resistivity evolution and the participation of spin in the reversible phase transition are observed for the first time. Our findings have significant implications for the design of phase switching devices and the exploration of hidden amorphous materials.

Pyroxenes and olivines: Structural implications of shock-wave data for high pressure phases

NASA Technical Reports Server (NTRS)

Jeanloz, R.; Ahrens, T. J.

1975-01-01

The nature of the shock-induced, high-pressure phases of olivine and pyroxene rocks is examined in the light of data for the densities of a new class of perovskite-related silicate structures. Also examined are some new Hugoniot and release adiabat data for bronzite. Reexamining available shock data for magnesian pyroxenes and olivines leads to the conclusion that they define a mixed phase (or disequilibrium) region to about the 100 GPa range, related to the kinetics of phase transformation in these silicates. By recognizing this point, certain discrepancies in previous interpretations of shock data can be explained. A set of theoretical Hugonoits for pyroxene and olivine stoichiometry, perovskite-bearing assemblages was constructed based on their properties deduced from high-pressure work, showing that the shock data is compatible with transformations to perovskites in the 45-7GPa region. Finally, the shock data indicate very similar properties for olivine and pyroxene at high pressures making them both equally likely candidates for the lower mantle.

Structure and elasticity of serpentine at high-pressure

NASA Astrophysics Data System (ADS)

Mookherjee, Mainak; Stixrude, Lars

2009-03-01

Serpentines occur in the subduction zone settings, both along the slab and within the mantle wedge, they are candidates for transporting water in to the deep earth. Their presence is manifested by serpentine mud volcanoes, high electrical conductivities, magnetic and seismic anomalies. Using theoretical methods, we predict a pressure induced structural transformations in serpentine. The transformations are related to the behavior of the silicate framework and misfit between octahedral and tetrahedral layers. As the structure is compressed, the octahedral layer and tetrahedral layers are compressed at different rates. At 7 GPa, the misfit between the layers vanishes. This causes non-linear pressure dependence of tetrahedral rotational angle. This is also manifested by the onset of anomalous pressure dependence of the elastic constants c11, c33, c12, c13. Beyond 7 GPa, the misfit between the layers grows again reaching extremum at 22 GPa. This is also manifested by discontinuity in average Si-O bond length, volume of tetrahedron and re-orientation of hydroxyl vector. The symmetry of the crystal-structure however, remains unaffected. Evidence of pressure-induced hydrogen bonding is absent in serpentine, as evident from reduction of O-H bond length upon compression. Results of compression for the low-pressure regime ( P < 7 GPa) is well represented by a fourth order Birch-Murnaghan finite strain expression with K0 = 79 GPa, K0' = 12 and K0″ = - 2, where K is the bulk modulus, prime indicates pressure derivatives, and O refers to zero pressure. Our best estimates of K0, K0' and the Grüneisen parameter, γ at 300 K and zero pressure based on our results are: 61 GPa, 17, and 0.77, respectively. At low pressures, serpentine structure is anisotropic with c11 ~ 2.4 × c33. The pressure derivative of elastic constants ( ∂cij/ ∂P) are such, that around 22 GPa c11~ c33. An elastic instability ( c66 < 0) at somewhat higher pressures (> 50 GPa) is also noted. The elastic constant tensor reveals large acoustic anisotropy (41% in VP) and seismic wave velocities that are significantly higher than those inferred from experiments on serpentinites.

Kinetic effects on the morphology and stability of the pressure-induced extended-solid of carbon monoxide

NASA Astrophysics Data System (ADS)

Dang, Nhan C.; Ciezak-Jenkins, Jennifer A.

2018-04-01

In this work, the dependence of the morphology and stability of the extended solid of carbon monoxide (CO) is correlated to the rate of transformation from the molecular CO to extended solid of CO using optical imaging, photoluminescence, Raman spectroscopy, and X-ray diffraction. The analyses show the rate and pressure of the transformation to be strongly controlled by catalytic effects, both chemical and optical. In a larger volume per reaction area, the transformation was found to require either a longer time at an elevated pressure or a higher pressure compared to a sample synthesized in a smaller volume per reaction area, leading to the conclusion that the transformation rate is slower for a sample in a larger volume per reaction area. A faster rate of transformation was also noted when the reaction area of a CO sample was catalyzed with H2SO4. Through variation of the volume per reaction area, pressure or the addition of catalysts, it was possible to control the rate of the phase transition and therefore the morphology. In general, the extended solid of CO synthesized with a faster rate showed a more ordered structure and increased metastability relative to the material formed with a slower compression rate.

The Investigation on Strain Strengthening Induced Martensitic Phase Transformation of Austenitic Stainless Steel: A Fundamental Research for the Quality Evaluation of Strain Strengthened Pressure Vessel

NASA Astrophysics Data System (ADS)

Li, Bo; Cai Ren, Fa; Tang, Xiao Ying

2018-03-01

The manufacture of pressure vessels with austenitic stainless steel strain strengthening technology has become an important technical means for the light weight of cryogenic pressure vessels. In the process of increasing the strength of austenitic stainless steel, strain can induce the martensitic phase transformation in austenite phase. There is a quantitative relationship between the transformation quantity of martensitic phase and the basic mechanical properties. Then, the martensitic phase variables can be obtained by means of detection, and the mechanical properties and safety performance are evaluated and calculated. Based on this, the quantitative relationship between strain hardening and deformation induced martensite phase content is studied in this paper, and the mechanism of deformation induced martensitic transformation of austenitic stainless steel is detailed.

Electronic Subband Reconfiguration in a d0-Perovskite Induced by Strain-Driven Structural Transformations

NASA Astrophysics Data System (ADS)

Laukhin, V.; Copie, O.; Rozenberg, M. J.; Weht, R.; Bouzehouane, K.; Reyren, N.; Jacquet, E.; Bibes, M.; Barthélémy, A.; Herranz, G.

2012-11-01

It is well known that transport in lightly n-doped SrTiO3 involves light and heavy electron bands. We have found that upon application of moderate quasi-isotropic pressures, the relative positions of these subbands are changed by a few meV and, eventually, a band inversion occurs at ˜1kbar. Such effects are, however, suppressed in the closely related KTaO3 perovskite. We show that the extremely subtle electronic reconfiguration in SrTiO3 is triggered by strain-induced structural transformations that are accompanied by remarkable mobility enhancements up to about Δμ/μ≈300%. Our results provide a microscopic rationale for the recently discovered transport enhancement under strain and underscore the role of the internal structural degrees of freedom in the modulation of the perovskite electronic properties.

Reversible pressure-induced crystal-amorphous structural transformation in ice Ih

NASA Astrophysics Data System (ADS)

English, Niall J.; Tse, John S.

2014-08-01

Molecular dynamics (MD) simulation of depressurised high-density amorphous ice (HDA) at 80 K and at negative pressures has been performed. Over several attempts, HDA recrystallised to a form close to hexagonal ice Ih, albeit with some defects. The results support the hypothesis that compression of ice-Ih to HDA is a reversible first-order phase transition, with a large hysteresis. Therefore, it would appear that LDA is not truly amorphous. The elastic energy estimated from the area of the hysteresis loop is ca. 4.5 kJ/mol, in some way consistent with experimentally-determined accumulated successive heats of transformations from recovered HDA → ice Ih.

Pressure-induced densification in GeO{sub 2} glass: A transmission x-ray microscopy study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Yu, E-mail: lyforest@stanford.edu; Zeng, Qiaoshi; Yang, Wenge

2013-12-23

Nanoscale transmission x-ray microscopy measurements have been performed to determine the effect of pressure (P) on the volume (V) change in GeO{sub 2} glass up to 38.5 GPa. The P-V data show a continuous increase upon compression, indicating that the density-driven structural transformation is a gradual process. Over the pressure range studied, a transition is observed at approximately 10–13 GPa, where the material displays distinct compression behaviors. The pressure-induced densification that involves the coordination number change has been discussed. Using this newly developed high-pressure imaging technique with tens of nanometer resolution, we have provided a direct and unequivocal way for measuring densitymore » of amorphous materials to much higher pressures with accuracy rivaling x-ray diffraction of crystalline solids.« less

Formation of superconducting platinum hydride under pressure: an ab initio approach

NASA Astrophysics Data System (ADS)

Kim, Duck Young; Scheicher, Ralph; Pickard, Chris; Needs, Richard; Ahuja, Rajeev

2012-02-01

Noble metals such as Pt, Au, or Re are commonly used for electrodes and gaskets in diamond anvil cells for high-pressure research because they are expected to rarely undergo structural transformation and possess simple equation of states. Specifically Pt has been used widely for high-pressure experiments and has been considered to resist hydride formation under pressure. Pressure-induced reactions of metals with hydrogen are in fact quite likely because hydrogen atoms can occupy interstitial positions in the metal lattice, which can lead to unexpected effects in experiments. In our study, PRL 107 117002 (2011), we investigated crystal structures using ab initio random structure searching (AIRSS) and predicted the formation of platinum mono-hydride above 22 GPa and superconductivity Tc was estimated to be 10 -- 25 K above around 80 GPa. Furthermore, we showed that the formation of fcc noble metal hydrides under pressure is common and examined the possibility of superconductivity in these materials.

Pressure-induced transformations of multiferroic relaxor PbFe0.5Nb0.5O3

NASA Astrophysics Data System (ADS)

Basu, Abhisek; Ahart, Muhtar; Holtgrewe, Nicholas; Lin, Chuanlong; Hemley, Russell J.

2018-02-01

The effects of hydrostatic pressure at ambient temperature on the structural and dielectric properties of PbFe0.5Nb0.5O3 (PFN) were investigated using second harmonic generation (SHG) and powder x-ray diffraction measurements to 31 GPa. The results demonstrate that PFN undergoes a pressure-induced structural transition from the R3m ferroelectric to the R 3 ¯ m paraelectric phase. SHG measurements showed a continuous decrease in the signal with pressure and complete disappearance at 7.1 GPa. Effective nonlinear optical coefficients were determined from the SHG data, and their pressure behavior was used to infer the nature of the transition. The loss of the SHG signal is accompanied by drastic changes in line widths of Bragg reflections, but no discontinuous change in volume was observed. The pressure-volume data were fit to various equations of state, and a bulk modulus K0 = 136 (±2) GPa, bulk modulus pressure derivative K0' = 4.0 (±0.2), and initial volume V0 = 64.5 (±0.1) Å3 were obtained.

Effect of high pressure on the photochemical reaction center from Rhodobacter sphaeroides R26.1.

PubMed Central

Gall, A; Ellervee, A; Bellissent-Funel, M C; Robert, B; Freiberg, A

2001-01-01

High-pressure studies on the photochemical reaction center from the photosynthetic bacterium Rhodobacter sphaeroides, strain R26.1, shows that, up to 0.6 GPa, this carotenoid-less membrane protein does not loose its three-dimensional structure at room temperature. However, as evidenced by Fourier-transform preresonance Raman and electronic absorption spectra, between the atmospheric pressure and 0.2 GPa, the structure of the bacterial reaction center experiences a number of local reorganizations in the binding site of the primary electron donor. Above that value, the apparent compressibility of this membrane protein is inhomogeneous, being most noticeable in proximity to the bacteriopheophytin molecules. In this elevated pressure range, no more structural reorganization of the primary electron donor binding site can be observed. However, its electronic structure becomes dramatically perturbed, and the oscillator strength of its Q(y) electronic transition drops by nearly one order of magnitude. This effect is likely due to very small, pressure-induced changes in its dimeric structure. PMID:11222309

Phase transformation of GaAs at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Ono, Shigeaki; Kikegawa, Takumi

2018-02-01

The high-pressure behavior of gallium arsenide, GaAs, has been investigated using an in-situ X-ray powder diffraction technique in a diamond anvil cell combined with a resistance heating method, at pressures and temperatures up to 25 GPa and 1000 K respectively. The pressure-induced phase transition from a zincblende to an orthorhombic (Cmcm) structure was observed. This transition occurred at 17.3 GPa and at room temperature, where a negative temperature dependence for this transition was confirmed. The transition boundary was determined to be P (GPa) = 18.0 - 0.0025 × T (K).

Reversible switching between pressure-induced amorphization and thermal-driven recrystallization in VO2(B) nanosheets

PubMed Central

Wang, Yonggang; Zhu, Jinlong; Yang, Wenge; Wen, Ting; Pravica, Michael; Liu, Zhenxian; Hou, Mingqiang; Fei, Yingwei; Kang, Lei; Lin, Zheshuai; Jin, Changqing; Zhao, Yusheng

2016-01-01

Pressure-induced amorphization (PIA) and thermal-driven recrystallization have been observed in many crystalline materials. However, controllable switching between PIA and a metastable phase has not been described yet, due to the challenge to establish feasible switching methods to control the pressure and temperature precisely. Here, we demonstrate a reversible switching between PIA and thermally-driven recrystallization of VO2(B) nanosheets. Comprehensive in situ experiments are performed to establish the precise conditions of the reversible phase transformations, which are normally hindered but occur with stimuli beyond the energy barrier. Spectral evidence and theoretical calculations reveal the pressure–structure relationship and the role of flexible VOx polyhedra in the structural switching process. Anomalous resistivity evolution and the participation of spin in the reversible phase transition are observed for the first time. Our findings have significant implications for the design of phase switching devices and the exploration of hidden amorphous materials. PMID:27426219

Evidence for photo-induced monoclinic metallic VO{sub 2} under high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsieh, Wen-Pin, E-mail: wphsieh@stanford.edu; Mao, Wendy L.; Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305

2014-01-13

We combine ultrafast pump-probe spectroscopy with a diamond-anvil cell to decouple the insulator-metal electronic transition from the lattice symmetry changing structural transition in the archetypal strongly correlated material vanadium dioxide. Coherent phonon spectroscopy enables tracking of the photo-excited phonon vibrational frequencies of the low temperature, monoclinic (M{sub 1})-insulating phase that transforms into the metallic, tetragonal rutile structured phase at high temperature or via non-thermal photo-excitations. We find that in contrast with ambient pressure experiments where strong photo-excitation promptly induces the electronic transition along with changes in the lattice symmetry, at high pressure, the coherent phonons of the monoclinic (M{sub 1})more » phase are still clearly observed upon the photo-driven phase transition to a metallic state. These results demonstrate the possibility of synthesizing and studying transient phases under extreme conditions.« less

Microbial production of metabolites and associated enzymatic reactions under high pressure.

PubMed

Dong, Yongsheng; Jiang, Hua

2016-11-01

High environmental pressure exerts an external stress on the survival of microorganisms that are commonly found under normal pressure. In response, many growth traits alter, including cell morphology and physiology, cellular structure, metabolism, physical and chemical properties, the reproductive process, and defense mechanisms. The high-pressure technology (HP) has been industrially utilized in pressurized sterilization, synthesis of stress-induced products, and microbial/enzymatic transformation of chemicals. This article reviews current research on pressure-induced production of metabolites in normal-pressure microbes and their enzymatic reactions. Factors that affect the production of such metabolites are summarized, as well as the effect of pressure on the performance of microbial fermentation and the yield of flavoring compounds, different categories of induced enzymatic reactions and their characteristics in the supercritical carbon dioxide fluid, effects on enzyme activity, and the selection of desirable bacterial strains. Technological challenges are discussed, and future research directions are proposed. Information presented here will benefit the research, development, and application of the HP technology to improve microbial fermentation and enzymatic production of biologically active substances, thereby help to meet their increasing demand from the ever-expanding market.

Simulations of nanocrystals under pressure: combining electronic enthalpy and linear-scaling density-functional theory.

PubMed

Corsini, Niccolò R C; Greco, Andrea; Hine, Nicholas D M; Molteni, Carla; Haynes, Peter D

2013-08-28

We present an implementation in a linear-scaling density-functional theory code of an electronic enthalpy method, which has been found to be natural and efficient for the ab initio calculation of finite systems under hydrostatic pressure. Based on a definition of the system volume as that enclosed within an electronic density isosurface [M. Cococcioni, F. Mauri, G. Ceder, and N. Marzari, Phys. Rev. Lett. 94, 145501 (2005)], it supports both geometry optimizations and molecular dynamics simulations. We introduce an approach for calibrating the parameters defining the volume in the context of geometry optimizations and discuss their significance. Results in good agreement with simulations using explicit solvents are obtained, validating our approach. Size-dependent pressure-induced structural transformations and variations in the energy gap of hydrogenated silicon nanocrystals are investigated, including one comparable in size to recent experiments. A detailed analysis of the polyamorphic transformations reveals three types of amorphous structures and their persistence on depressurization is assessed.

Simulations of nanocrystals under pressure: Combining electronic enthalpy and linear-scaling density-functional theory

NASA Astrophysics Data System (ADS)

Corsini, Niccolò R. C.; Greco, Andrea; Hine, Nicholas D. M.; Molteni, Carla; Haynes, Peter D.

2013-08-01

We present an implementation in a linear-scaling density-functional theory code of an electronic enthalpy method, which has been found to be natural and efficient for the ab initio calculation of finite systems under hydrostatic pressure. Based on a definition of the system volume as that enclosed within an electronic density isosurface [M. Cococcioni, F. Mauri, G. Ceder, and N. Marzari, Phys. Rev. Lett. 94, 145501 (2005)], 10.1103/PhysRevLett.94.145501, it supports both geometry optimizations and molecular dynamics simulations. We introduce an approach for calibrating the parameters defining the volume in the context of geometry optimizations and discuss their significance. Results in good agreement with simulations using explicit solvents are obtained, validating our approach. Size-dependent pressure-induced structural transformations and variations in the energy gap of hydrogenated silicon nanocrystals are investigated, including one comparable in size to recent experiments. A detailed analysis of the polyamorphic transformations reveals three types of amorphous structures and their persistence on depressurization is assessed.

Pressure induced phase transitions in ceramic compounds containing tetragonal zirconia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sparks, R.G.; Pfeiffer, G.; Paesler, M.A.

Stabilized tetragonal zirconia compounds exhibit a transformation toughening process in which stress applied to the material induces a crystallographic phase transition. The phase transition is accompanied by a volume expansion in the stressed region thereby dissipating stress and increasing the fracture strength of the material. The hydrostatic component of the stress required to induce the phase transition can be investigated by the use of a high pressure technique in combination with Micro-Raman spectroscopy. The intensity of Raman lines characteristic for the crystallographic phases can be used to calculate the amount of material that has undergone the transition as a functionmore » of pressure. It was found that pressures on the order of 2-5 kBar were sufficient to produce an almost complete transition from the original tetragonal to the less dense monoclinic phase; while a further increase in pressure caused a gradual reversal of the transition back to the original tetragonal structure.« less

Synthesis, Structure, and Pressure-Induced Polymerization of Li3Fe(CN)6 Accompanied with Enhanced Conductivity.

PubMed

Li, Kuo; Zheng, Haiyan; Hattori, Takanori; Sano-Furukawa, Asami; Tulk, Christopher A; Molaison, Jamie; Feygenson, Mikhail; Ivanov, Ilia N; Yang, Wenge; Mao, Ho-Kwang

2015-12-07

Pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal-carbon network composite, thus providing a new route to synthesize inorganic/organic conductors with tunable composition and properties. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li3Fe(CN)6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutron diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. The conductivity of the polymer is above 10(-3) S · cm(-1), which reaches the range of conductive polymers. This investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.

A new phase transformation path from nanodiamond to new-diamond via an intermediate carbon onion

NASA Astrophysics Data System (ADS)

Xiao, J.; Li, J. L.; Liu, P.; Yang, G. W.

2014-11-01

The investigation of carbon allotropes such as graphite, diamond, fullerenes, nanotubes and carbon onions and mechanisms that underlie their mutual phase transformation is a long-standing problem of great fundamental importance. New diamond (n-diamond) is a novel metastable phase of carbon with a face-centered cubic structure; it is called ``new diamond'' because many reflections in its electron diffraction pattern are similar to those of diamond. However, producing n-diamond from raw carbon materials has so far been challenging due to n-diamond's higher formation energy than that of diamond. Here, we, for the first time, demonstrate a new phase transformation path from nanodiamond to n-diamond via an intermediate carbon onion in the unique process of laser ablation in water, and establish that water plays a crucial role in the formation of n-diamond. When a laser irradiates colloidal suspensions of nanodiamonds at ambient pressure and room temperature, nanodiamonds are first transformed into carbon onions serving as an intermediate phase, and sequentially carbon onions are transformed into n-diamonds driven by the laser-induced high temperature and high pressure from the carbon onion as a nanoscaled temperature and pressure cell upon the process of laser irradiation in a liquid. This phase transformation not only provides new insight into the physical mechanism involved, but also offers one suitable opportunity for breaking controllable pathways between n-diamond and carbon allotropes such as diamond and carbon onions.The investigation of carbon allotropes such as graphite, diamond, fullerenes, nanotubes and carbon onions and mechanisms that underlie their mutual phase transformation is a long-standing problem of great fundamental importance. New diamond (n-diamond) is a novel metastable phase of carbon with a face-centered cubic structure; it is called ``new diamond'' because many reflections in its electron diffraction pattern are similar to those of diamond. However, producing n-diamond from raw carbon materials has so far been challenging due to n-diamond's higher formation energy than that of diamond. Here, we, for the first time, demonstrate a new phase transformation path from nanodiamond to n-diamond via an intermediate carbon onion in the unique process of laser ablation in water, and establish that water plays a crucial role in the formation of n-diamond. When a laser irradiates colloidal suspensions of nanodiamonds at ambient pressure and room temperature, nanodiamonds are first transformed into carbon onions serving as an intermediate phase, and sequentially carbon onions are transformed into n-diamonds driven by the laser-induced high temperature and high pressure from the carbon onion as a nanoscaled temperature and pressure cell upon the process of laser irradiation in a liquid. This phase transformation not only provides new insight into the physical mechanism involved, but also offers one suitable opportunity for breaking controllable pathways between n-diamond and carbon allotropes such as diamond and carbon onions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05246c

Structure of Oxide Glass and Melts at High-Pressure: A View from Inelastic X-ray Scattering and 2D Solid-State NMR

NASA Astrophysics Data System (ADS)

Lee, S.; Mysen, B. O.; Fei, Y.; Cody, G. D.; Mao, H.; Eng, P.

2006-12-01

Full understanding of the atomic arrangement of oxides glasses and melts both at ambient and high-pressure has long been one of the fundamental and yet difficult problems in earth sciences, condensed matter physics as well as glass sciences. The structures of archetypal oxide glasses (e.g. SiO2 and B2O3) as well as complex silicate glasses (ternary and quaternary aluminosilicate glasses) at high pressure are essential to elucidate origins of anomalous macroscopic properties of melts and global geophysical processes in the Earth's interior. Recent progress in inelastic x-ray scattering (IXS) with high brilliance 3rd generation synchrotron x-rays combined with DAC techniques allows us to explore pressure-induced changes in the bonding nature of archetypal amorphous oxide, illustrating a new opportunity to study amorphous oxides with IXS (Lee SK et al. Nature Materials 2005, 4, p851). 2 dimensional solid-state NMR have offered much improved resolution over conventional 1D NMR, unveiling previously unknown structural details of amorphous silicates at high pressure (Lee SK. Geochim. Cosmochim. Acta 2005, 69, p3695; J. Phys. Chem. B. 2006, 110, p16408) Here, we report the synchrotron inelastic x-ray scattering results (oxygen and boron K-edge) for divers oxide glasses at pressure up to 40 GPa, revealing the nature of pressure-induced bonding changes and the structure. Direct in-situ measurements provide evidence for a continuous transformation with multiple densification mechanisms. 2D solid-state NMR spectra for silicate and germinate glasses shows detailed information about extent of disorder among framework units at high pressure. The chemical ordering among framework units leads to the formation of ^{[5,6]}Si-O-^{[4]}Si in silicates and ^{[5,6]}Al-O-^{[4]}Si in aluminosilicates. Whereas the densification mechanism can be dependent on the chemical composition and the fraction of non-bridging oxygen, the pressure dependence of both simple and complex multi-component silicate glasses showed similar characteristics: low pressure regime was marked with topological variation without coordination transformation and inter-mediate pressure region (about 5-10 GPa) was characterized by the largest (d(^{[4]}B or ^{[5,6]}Si)/dP) value. Finally high-pressure regime (above 10 GPa) was characterized by a larger energy penalty for coordination transformation than in intermediate pressure regime. These results provide improved prospect for the bonding nature of amorphous materials at high pressure using synchrotron inelastic x-ray scattering and 2D NMR and aid in understanding the microscopic origins of the properties of melts and geological processes in the Earth's interior.

Pressure-induced amorphization of YVO₄:Eu³⁺ nanoboxes.

PubMed

Ruiz-Fuertes, J; Gomis, O; León-Luis, S F; Schrodt, N; Manjón, F J; Ray, S; Santamaría-Pérez, D; Sans, J A; Ortiz, H M; Errandonea, D; Ferrer-Roca, C; Segura, A; Martínez-García, D; Lavín, V; Rodríguez-Mendoza, U R; Muñoz, A

2016-01-15

A structural transformation from the zircon-type structure to an amorphous phase has been found in YVO4:Eu(3+) nanoboxes at high pressures above 12.7 GPa by means of x-ray diffraction measurements. However, the pair distribution function of the high-pressure phase shows that the local structure of the amorphous phase is similar to the scheelite-type YVO4. These results are confirmed both by Raman spectroscopy and Eu(3+) photoluminescence which detect the phase transition to a scheelite-type structure at 10.1 and 9.1 GPa, respectively. The irreversibility of the phase transition is observed with the three techniques after a maximum pressure in the upstroke of around 20 GPa. The existence of two (5)D0-->(7)F0 photoluminescence peaks confirms the existence of two local environments for Eu(3+), at least for the low-pressure phase. One environment is the expected for substituting Y(3+) and the other is likely a disordered environment possibly found at the surface of the nanoboxes.

Creation and formation mechanism of new carbon phases constructed by amorphous carbon

NASA Astrophysics Data System (ADS)

Yao, Mingguang; Cui, Wen; Liu, Bingbing

Our recent effort is focusing on the creation of new hard/superhard carbon phases constructed by disordered carbons or amorphous carbon clusters under high pressure. We showed that the pressure-induced amorphous hard carbon clusters from collapsed fullerenes can be used as building blocks (BBs) for constructing novel carbon structures. This new strategy has been verified by compressing a series of intercalated fullerides, pre-designed by selecting various dopants with special features. We demonstrate that the boundaries of the amorphous BBs are mediated by intercalated dopants and several new superhard materials have been prepared. We also found that the dopant-mediated BBs can be arranged in either ordered or disordered structures, both of which can be hard enough to indent the diamond anvils. The hardening mechanisms of the new phases have also been discussed. For the glassy carbon (GC) constructructed by disordered fullerene-like nanosized fragments, we also found that these disordered fragments can bond and the compressed GC transformed into a transparent superhard phase. Such pressure-induced transformation has been discovered to be driven by a novel mechanism (unpublished). By understanding the mechanisms we can clarify the controversial results on glassy carbon reported recently. The authors would like to thank the financial support from the National Natural Science Foundation of China (No. 11474121, 51320105007).

AB-stacked square-like bilayer ice in graphene nanocapillaries.

PubMed

Zhu, YinBo; Wang, FengChao; Bai, Jaeil; Zeng, Xiao Cheng; Wu, HengAn

2016-08-10

Water, when constrained between two graphene sheets and under ultrahigh pressure, can manifest dramatic differences from its bulk counterparts such as the van der Waals pressure induced water-to-ice transformation, known as the metastability limit of two-dimensional (2D) liquid. Here, we present result of a new crystalline structure of bilayer ice with the AB-stacking order, observed from molecular dynamics simulations of constrained water. This AB-stacked bilayer ice (BL-ABI) is transformed from the puckered monolayer square-like ice (pMSI) under higher lateral pressure in the graphene nanocapillary at ambient temperature. BL-ABI is a proton-ordered ice with square-like pattern. The transition from pMSI to BL-ABI is through crystal-to-amorphous-to-crystal pathway with notable hysteresis-loop in the potential energy during the compression/decompression process, reflecting the compression/tensile limit of the 2D monolayer/bilayer ice. In a superheating process, the BL-ABI transforms into the AB-stacked bilayer amorphous ice with the square-like pattern.

Multiple pathways in pressure-induced phase transition of coesite

NASA Astrophysics Data System (ADS)

Liu, Wei; Wu, Xuebang; Liang, Yunfeng; Liu, Changsong; Miranda, Caetano R.; Scandolo, Sandro

2017-12-01

High-pressure single-crystal X-ray diffraction method with precise control of hydrostatic conditions, typically with helium or neon as the pressure-transmitting medium, has significantly changed our view on what happens with low-density silica phases under pressure. Coesite is a prototype material for pressure-induced amorphization. However, it was found to transform into a high-pressure octahedral (HPO) phase, or coesite-II and coesite-III. Given that the pressure is believed to be hydrostatic in two recent experiments, the different transformation pathways are striking. Based on molecular dynamic simulations with an ab initio parameterized potential, we reproduced all of the above experiments in three transformation pathways, including the one leading to an HPO phase. This octahedral phase has an oxygen hcp sublattice featuring 2 × 2 zigzag octahedral edge-sharing chains, however with some broken points (i.e., point defects). It transforms into α-PbO2 phase when it is relaxed under further compression. We show that the HPO phase forms through a continuous rearrangement of the oxygen sublattice toward hcp arrangement. The high-pressure amorphous phases can be described by an fcc and hcp sublattice mixture.

Ultrahigh-pressure polyamorphism in GeO2 glass with coordination number >6

NASA Astrophysics Data System (ADS)

Kono, Yoshio; Kenney-Benson, Curtis; Ikuta, Daijo; Shibazaki, Yuki; Wang, Yanbin; Shen, Guoyin

2016-03-01

Knowledge of pressure-induced structural changes in glasses is important in various scientific fields as well as in engineering and industry. However, polyamorphism in glasses under high pressure remains poorly understood because of experimental challenges. Here we report new experimental findings of ultrahigh-pressure polyamorphism in GeO2 glass, investigated using a newly developed double-stage large-volume cell. The Ge-O coordination number (CN) is found to remain constant at ∼6 between 22.6 and 37.9 GPa. At higher pressures, CN begins to increase rapidly and reaches 7.4 at 91.7 GPa. This transformation begins when the oxygen-packing fraction in GeO2 glass is close to the maximal dense-packing state (the Kepler conjecture = ∼0.74), which provides new insights into structural changes in network-forming glasses and liquids with CN higher than 6 at ultrahigh-pressure conditions.

Pressure-induced phase transition and fracture in α-MoO3 nanoribbons

NASA Astrophysics Data System (ADS)

Silveira, Jose V.; Vieira, Luciana L.; Aguiar, Acrisio L.; Freire, Paulo T. C.; Mendes Filho, Josue; Alves, Oswaldo L.; Souza Filho, Antonio G.

2018-03-01

MoO3 nanoribbons were studied under different pressure conditions ranging from 0 to 21 GPa at room temperature. The effect of the applied pressure on the spectroscopic and morphologic properties of the MoO3 nanoribbons was investigated by means of Raman spectroscopy and scanning electron microscopy techniques. The pressure dependent Raman spectra of the MoO3 nanoribbons indicate that a structural phase transition occurs at 5 GPa from the orthorhombic α-MoO3 phase (Pbnm) to the monoclinic MoO3-II phase (P21/m), which remains stable up to 21 GPa. Such phase transformation occurs at considerably lower pressure than the critical pressure for α-MoO3 microcrystals (12 GPa). We suggested that the applanate morphology combined with the presence of crystalline defects in the sample play an important role in the phase transition of the MoO3 nanoribbons. Frequencies and linewidths of the Raman bands as a function of pressure also suggest a pressure-induced morphological change and the decreasing of the nanocrystal size. The observed spectroscopic changes are supported by electron microscopy images, which clearly show a pressure-induced morphologic change in MoO3 nanoribbons.

Guest-Induced Switchable Breathing Behavior in a Flexible Metal-Organic Framework with Pronounced Negative Gas Pressure.

PubMed

Shi, Yi-Xiang; Li, Wu-Xiang; Zhang, Wen-Hua; Lang, Jian-Ping

2018-06-29

Flexible metal-organic frameworks (MOFs) have attracted great interest for their dynamically structural transformability in response to external stimuli. Herein, we report a switchable "breathing" or "gate-opening" behavior associated with the phase transformation between a narrow pore (np) and a large pore (lp) in a flexible pillared-layered MOF, denoted as MOF-1 as, which is also confirmed by SCXRD and PXRD. The desolvated phase (MOF-1 des) features a unique stepwise adsorption isotherm for N 2 coupled with a pronounced negative gas adsorption pressure. For comparison, however, no appreciable CO 2 adsorption and gate-opening phenomenon with stepwise sorption can be observed. Furthermore, the polar micropore walls decorated with thiophene groups in MOF-1 des reveals the selective sorption of toluene over benzene and p-xylene associated with self-structural adjustment in spite of the markedly similar physicochemical properties of these vapor molecules.

Pressure-induced silica quartz amorphization studied by iterative stochastic surface walking reaction sampling.

PubMed

Zhang, Xiao-Jie; Shang, Cheng; Liu, Zhi-Pan

2017-02-08

The crystal to amorphous transformation is a common phenomenon in Nature and has important impacts on material properties. Our current knowledge on such complex solid transformation processes is, however, limited because of their slow kinetics and the lack of long-range ordering in amorphous structures. To reveal the kinetics in the amorphization of solids, this work, by developing iterative reaction sampling based on the stochastic surface walking global optimization method, investigates the well-known crystal to amorphous transformation of silica (SiO 2 ) under external pressures, the mechanism of which has long been debated for its non-equilibrium, pressure-sensitive kinetics and complex product components. Here we report for the first time the global potential energy surface (PES) and the lowest energy pathways for α-quartz amorphization from first principles. We show that the pressurization at 15 GPa, the reaction condition, can lift the quartz phase energetically close to the amorphous zone, which thermodynamically initializes the amorphization. More importantly, the large flexibility of Si cation coordination (including four, five and six coordination) results in many kinetically competing routes to more stable dense forms, including the known MI, stishovite, newly-identified MII and TI phases. All these pathways have high barriers due to the local Si-O bond breaking and are mediated by amorphous structures with five-fold Si. This causes simultaneous crystal-to-crystal and crystal-to-amorphous transitions. The high barrier and the reconstructive nature of the phase transition are the key kinetics origin for silica amorphization under pressures.

Synthesis, Structure, and Pressure-Induced Polymerization of Li 3 Fe(CN) 6 Accompanied with Enhanced Conductivity

DOE PAGES

Li, Kuo; Zheng, Haiyan; Hattori, Takanori; ...

2015-11-17

By providing a new route to synthesize inorganic/organic conductors with tunable composition and properties, pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal–carbon network composite. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li 3Fe(CN) 6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutronmore » diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. Moreover, the conductivity of the polymer is above 10 –3 S·cm –1, which reaches the range of conductive polymers. Our investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.« less

Phase transformations in nanograin materials under high pressure and plastic shear: nanoscale mechanisms.

PubMed

Levitas, Valery I; Javanbakht, Mahdi

2014-01-07

There are two main challenges in the discovery of new high pressure phases (HPPs) and transforming this discovery into technologies: finding conditions to synthesize new HPPs and finding ways to reduce the phase transformation (PT) pressure to an economically reasonable level. Based on the results of pressure-shear experiments in the rotational diamond anvil cell (RDAC), superposition of plastic shear on high pressure is a promising way to resolve these problems. However, physical mechanisms behind these phenomena are not yet understood. Here, we elucidate generic mechanisms of coupled nucleation and evolution of dislocation and HPP structures in the nanograin material under pressure and shear utilizing the developed advanced phase field approach (PFA). Dislocations are generated at the grain boundaries and are densely piled up near them, creating a strong concentrator of the stress tensor. Averaged shear stress is essentially larger in the nanograin material due to grain boundary strengthening. This leads to the increase in the local thermodynamic driving force for PT, which allows one to significantly reduce the applied pressure. For all cases, the applied pressure is 3-20 times lower than the PT pressure and 2-12.5 times smaller than the phase equilibrium pressure. Interaction between nuclei leads sometimes to their coalescence and growth of the HPP away from stress concentrators. Plasticity plays a dual role: in addition to creating stress concentrators, it may relax stresses at other concentrators, thus competing with PT. Some ways to optimize the loading parameters have been found that lead to methods for controlling PT. Since such a local stress tensor with high shear stress component cannot be created without plastic deformations, this may lead to new transformation paths and phases, which are hidden during pressure induced PTs.

Reversible switching between pressure-induced amorphization and thermal-driven recrystallization in VO2(B) nanosheets

DOE PAGES

Wang, Yonggang; Zhu, Jinlong; Yang, Wenge; ...

2016-07-18

Pressure-induced amorphization (PIA) and thermal-driven recrystallization have been observed in many crystalline materials. However, controllable switching between PIA and a metastable phase has not been described yet, due to the challenge to establish feasible switching methods to control the pressure and temperature precisely. Here, we demonstrate a reversible switching between PIA and thermally-driven recrystallization of VO 2(B) nanosheets. Comprehensive in situ experiments are performed to establish the precise conditions of the reversible phase transformations, which are normally hindered but occur with stimuli beyond the energy barrier. Spectral evidence and theoretical calculations reveal the pressure–structure relationship and the role of flexiblemore » VO x polyhedra in the structural switching process. Anomalous resistivity evolution and the participation of spin in the reversible phase transition are observed for the first time. Our findings have significant implications for the design of phase switching devices and the exploration of hidden amorphous materials.« less

Pressure-induced magnetic collapse and metallization of TlF e1.6S e2

NASA Astrophysics Data System (ADS)

Naumov, P. G.; Filsinger, K.; Shylin, S. I.; Barkalov, O. I.; Ksenofontov, V.; Qi, Y.; Palasyuk, T.; Schnelle, W.; Medvedev, S. A.; Greenblatt, M.; Felser, C.

2017-08-01

The crystal structure, magnetic ordering, and electrical resistivity of TlF e1.6S e2 were studied at high pressures. Below ˜7 GPa , TlF e1.6S e2 is an antiferromagnetically ordered semiconductor with a ThC r2S i2 -type structure. The insulator-to-metal transformation observed at a pressure of ˜7 GPa is accompanied by a loss of magnetic ordering and an isostructural phase transition. In the pressure range ˜7.5 -11 GPa a remarkable downturn in resistivity, which resembles a superconducting transition, is observed below 15 K. We discuss this feature as the possible onset of superconductivity originating from a phase separation in a small fraction of the sample in the vicinity of the magnetic transition.

Magneto-structural transformations via a solid-state nudged elastic band method: Application to iron under pressure

DOE PAGES

Zarkevich, N. A.; Johnson, D. D.

2015-08-14

We extend the solid-state nudged elastic band method to handle a non-conserved order parameter, in particular, magnetization, that couples to volume and leads to many observed effects in magnetic systems. We apply this formalism to the well-studied magneto-volume collapse during the pressure-induced transformation in iron—from ferromagnetic body-centered cubic (bcc) austenite to hexagonal close-packed (hcp) martensite. We also find a bcc-hcp equilibrium coexistence pressure of 8.4 GPa, with the transition-state enthalpy of 156 meV/Fe at this pressure. A discontinuity in magnetization and coherent stress occurs at the transition state, which has a form of a cusp on the potential-energy surface (yetmore » all the atomic and cell degrees of freedom are continuous); the calculated pressure jump of 25 GPa is related to the observed 25 GPa spread in measured coexistence pressures arising from martensitic and coherency stresses in samples. Furthermore, our results agree with experiments, but necessarily differ from those arising from drag and restricted parametrization methods having improperly constrained or uncontrolled degrees of freedom.« less

Multiple pathways in pressure-induced phase transition of coesite

PubMed Central

Liu, Wei; Wu, Xuebang; Liu, Changsong; Miranda, Caetano R.; Scandolo, Sandro

2017-01-01

High-pressure single-crystal X-ray diffraction method with precise control of hydrostatic conditions, typically with helium or neon as the pressure-transmitting medium, has significantly changed our view on what happens with low-density silica phases under pressure. Coesite is a prototype material for pressure-induced amorphization. However, it was found to transform into a high-pressure octahedral (HPO) phase, or coesite-II and coesite-III. Given that the pressure is believed to be hydrostatic in two recent experiments, the different transformation pathways are striking. Based on molecular dynamic simulations with an ab initio parameterized potential, we reproduced all of the above experiments in three transformation pathways, including the one leading to an HPO phase. This octahedral phase has an oxygen hcp sublattice featuring 2 × 2 zigzag octahedral edge-sharing chains, however with some broken points (i.e., point defects). It transforms into α-PbO2 phase when it is relaxed under further compression. We show that the HPO phase forms through a continuous rearrangement of the oxygen sublattice toward hcp arrangement. The high-pressure amorphous phases can be described by an fcc and hcp sublattice mixture. PMID:29162690

Alpha – omega and omega – alpha phase transformations in zirconium under hydrostatic pressure: A 3D mesoscale study

DOE PAGES

Yeddu, Hemantha Kumar; Zong, Hongxiang; Lookman, Turab

2015-09-28

Here, a three dimensional (3D) elastoplastic phase-field model is developed for modeling the hydrostatic pressure-induced alpha – omega phase transformation and the reverse phase transformation, i.e. omega – alpha, in zirconium (Zr). Plastic deformation and strain hardening of the material are also considered in the model. The microstructure evolution during both phase transformations is studied. The transformation start pressures at different temperatures are predicted and are plotted as a phase diagram. The effect of phase transformations on the mechanical properties of the material is also studied. The input data corresponding to pure Zr are acquired from experimental studies as wellmore » as by using the CALPHAD method. Our simulations show that three different omega variants form as laths. On release of pressure, reverse phase transformation initiates at lath boundaries. We observe that both phase transformations are martensitic in nature and also occur at the same pressure, i.e. little hysteresis. The transformation start pressures and the kinetics of the transformation predicted by our model are in good agreement with experimental results.« less

Alpha – omega and omega – alpha phase transformations in zirconium under hydrostatic pressure: A 3D mesoscale study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeddu, Hemantha Kumar; Zong, Hongxiang; Lookman, Turab

Here, a three dimensional (3D) elastoplastic phase-field model is developed for modeling the hydrostatic pressure-induced alpha – omega phase transformation and the reverse phase transformation, i.e. omega – alpha, in zirconium (Zr). Plastic deformation and strain hardening of the material are also considered in the model. The microstructure evolution during both phase transformations is studied. The transformation start pressures at different temperatures are predicted and are plotted as a phase diagram. The effect of phase transformations on the mechanical properties of the material is also studied. The input data corresponding to pure Zr are acquired from experimental studies as wellmore » as by using the CALPHAD method. Our simulations show that three different omega variants form as laths. On release of pressure, reverse phase transformation initiates at lath boundaries. We observe that both phase transformations are martensitic in nature and also occur at the same pressure, i.e. little hysteresis. The transformation start pressures and the kinetics of the transformation predicted by our model are in good agreement with experimental results.« less

Pressure-induced phase transformation, reversible amorphization, and anomalous visible light response in organolead bromide perovskite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yonggang; Lu, Xujie; Yang, Wenge

Hydrostatic pressure, as an alternative of chemical pressure to tune the crystal structure and physical properties, is a significant technique for novel function material design and fundamental research. In this article, we report the phase stability and visible light response of the organolead bromide perovskite, CH 3NH 3PbBr 3 (MAPbBr 3), under hydrostatic pressure up to 34 GPa at room temperature: Two phase transformations below 2 GPa (from Pm3¯m to Im3¯, then to Pnma) and a reversible amorphization starting from about 2 GPa were observed, which could be attributed to the tilting of PbBr 6 octahedra and destroying of long-rangemore » ordering of MA cations, respectively. The visible light response of MAPbBr 3 to pressure was studied by in situ photoluminescence, electric resistance, photocurrent measurements and first-principle simulations. The anomalous band gap evolution during compression with red-shift followed by blue-shift is explained by the competition between compression effect and pressure-induced amorphization. Along with the amorphization process accomplished around 25 GPa, the resistance increased by 5 orders of magnitude while the system still maintains its semiconductor characteristics and considerable response to the visible light irradiation. Lastly, our results not only show that hydrostatic pressure may provide an applicable tool for the organohalide perovskites based photovoltaic device functioning as switcher or controller, but also shed light on the exploration of more amorphous organometal composites as potential light absorber.« less

Pressure-Induced Phase Transformation, Reversible Amorphization, and Anomalous Visible Light Response in Organolead Bromide Perovskite.

PubMed

Wang, Yonggang; Lü, Xujie; Yang, Wenge; Wen, Ting; Yang, Liuxiang; Ren, Xiangting; Wang, Lin; Lin, Zheshuai; Zhao, Yusheng

2015-09-02

Hydrostatic pressure, as an alternative of chemical pressure to tune the crystal structure and physical properties, is a significant technique for novel function material design and fundamental research. In this article, we report the phase stability and visible light response of the organolead bromide perovskite, CH3NH3PbBr3 (MAPbBr3), under hydrostatic pressure up to 34 GPa at room temperature. Two phase transformations below 2 GPa (from Pm3̅m to Im3̅, then to Pnma) and a reversible amorphization starting from about 2 GPa were observed, which could be attributed to the tilting of PbBr6 octahedra and destroying of long-range ordering of MA cations, respectively. The visible light response of MAPbBr3 to pressure was studied by in situ photoluminescence, electric resistance, photocurrent measurements and first-principle simulations. The anomalous band gap evolution during compression with red-shift followed by blue-shift is explained by the competition between compression effect and pressure-induced amorphization. Along with the amorphization process accomplished around 25 GPa, the resistance increased by 5 orders of magnitude while the system still maintains its semiconductor characteristics and considerable response to the visible light irradiation. Our results not only show that hydrostatic pressure may provide an applicable tool for the organohalide perovskites based photovoltaic device functioning as switcher or controller, but also shed light on the exploration of more amorphous organometal composites as potential light absorber.

Pressure-induced phase transformation, reversible amorphization, and anomalous visible light response in organolead bromide perovskite

DOE PAGES

Wang, Yonggang; Lu, Xujie; Yang, Wenge; ...

2015-08-18

Hydrostatic pressure, as an alternative of chemical pressure to tune the crystal structure and physical properties, is a significant technique for novel function material design and fundamental research. In this article, we report the phase stability and visible light response of the organolead bromide perovskite, CH 3NH 3PbBr 3 (MAPbBr 3), under hydrostatic pressure up to 34 GPa at room temperature: Two phase transformations below 2 GPa (from Pm3¯m to Im3¯, then to Pnma) and a reversible amorphization starting from about 2 GPa were observed, which could be attributed to the tilting of PbBr 6 octahedra and destroying of long-rangemore » ordering of MA cations, respectively. The visible light response of MAPbBr 3 to pressure was studied by in situ photoluminescence, electric resistance, photocurrent measurements and first-principle simulations. The anomalous band gap evolution during compression with red-shift followed by blue-shift is explained by the competition between compression effect and pressure-induced amorphization. Along with the amorphization process accomplished around 25 GPa, the resistance increased by 5 orders of magnitude while the system still maintains its semiconductor characteristics and considerable response to the visible light irradiation. Lastly, our results not only show that hydrostatic pressure may provide an applicable tool for the organohalide perovskites based photovoltaic device functioning as switcher or controller, but also shed light on the exploration of more amorphous organometal composites as potential light absorber.« less

Ion specific 2D to 3D structural modification of Langmuir monolayer at lower surface pressure

NASA Astrophysics Data System (ADS)

Das, Kaushik; Kundu, Sarathi

2017-05-01

2D to 3D structural transformation of stearic acid Langmuir monolayer in presence of Ca2+ and Zn2+ ions at lower surface pressure (≈25 mN/m) has been studied at lower (pH ≈ 6.8) and higher (pH ≈ 9.5) subphase pH. Generally, 2D to 3D structural transformation of monolayer occurs at higher surface pressure (>50 mN/m) after collapse point which can be identified from surface pressure (π) vs. specific molecular area (A) isotherms. In presence of Ca2+ ions and for both lower and higher subphase pH, stearic acid monolayer remains as 2D monolayer at that lower surface pressure as confirmed from the Atomic Force Microscopy (AFM) studies on the films deposited at π ≈ 25mN/m. However, in presence of Zn2+ at higher subphase pH, stearic acid monolayer shows 2D to 3D structural transformation where less covered bilayer-like structure forms on top of the monolayer as obtained from the AFM studies. Fourier transform infrared (FTIR) spectroscopy results reveal that formation of relatively more amount of bidentate bridging coordination of metal carboxylate headgroup may be the key reason of such 2D to 3D structural transformation for Zn2+.

Structure and mechanical properties of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation by high-pressure torsion

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2015-04-01

The structural and phase transformations have been studied in aging commercial aluminum-lithium alloy Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg in the as-delivered state and after severe plastic deformation by torsion for 1, 5 and 10 revolutions under a high pressure of 4 GPa. Deformation-induced nanofragmentation and dynamic recrystallization have been found to occur in the alloy. The degree of recrystallization increases with deformation. Nanofragmentation and recrystallization processes are accompanied by the deformation-induced decomposition of solid solution and changes in both the nucleation mechanism of precipitation and the phase composition of the alloy. The influence of a nanostructured nanophase state of the alloy on its mechanical properties (microhardness, plasticity, elastic modulus, and stiffness) is discussed.

Simple-to-Complex Transformation in Liquid Rubidium.

PubMed

Gorelli, Federico A; De Panfilis, Simone; Bryk, Taras; Ulivi, Lorenzo; Garbarino, Gaston; Parisiades, Paraskevas; Santoro, Mario

2018-05-18

We investigated the atomic structure of liquid Rb along an isothermal path at 573 K, up to 23 GPa, by X-ray diffraction measurements. By raising the pressure, we observed a liquid-liquid transformation from a simple metallic liquid to a complex one. The transition occurs at 7.5 ± 1 GPa which is slightly above the first maximum of the T-P melting line. This transformation is traced back to the density-induced hybridization of highest electronic orbitals leading to the accumulation of valence electrons between Rb atoms and to the formation of interstitial atomic shells, a behavior that Rb shares with Cs and is likely to be common to all alkali metals.

Experimental evidence for a phase transition in magnesium oxide at exoplanet pressures

DOE PAGES

Coppari, F.; Smith, R. F.; Eggert, J. H.; ...

2013-09-22

Here, magnesium oxide, an important component of the Earth’s mantle, has been extensively studied in the pressure and temperature range found within the Earth. However,much less is known about its behavior under conditions appropriate for newly-discovered super-Earth planets, where pressures can exceed 1000 GPa (10 Mbar). It is widely believed that MgO will follow the rocksalt (B1) to cesium chloride (B2) transformation pathway commonly found for many alkali halides, alkaline earth oxides and various other ionic compounds. Static compression experiments have determined the structure of MgO to 250 GPa but have been unable to reach pressures necessary to induce themore » predicted transformation, resulting in large uncertainties regarding its properties under conditions relevant to super-Earths and other large planets. Here we report new dynamic x-ray diffraction measurements of ramp-compressed MgO to 900 GPa.We report evidence for the B2 phase beginning near 600 GPa, remaining stable on further compression to 900 GPa, the highest pressure diffraction data ever collected.« less

Boron monosulfide: Equation of state and pressure-induced phase transition

NASA Astrophysics Data System (ADS)

Cherednichenko, K. A.; Kruglov, I. A.; Oganov, A. R.; Le Godec, Y.; Mezouar, M.; Solozhenko, V. L.

2018-04-01

Quasi-hydrostatic compression of rhombohedral boron monosulfide (r-BS) has been studied up to 50 GPa at room temperature using diamond-anvil cells and angle-dispersive synchrotron X-ray diffraction. A fit of the experimental P-V data to the Vinet equation of state yields the bulk modulus B0 of 42.2(1.4) GPa and its first pressure derivative B0' of 7.6(2) that are in excellent agreement with our ab initio calculations. Formation of a new high-pressure phase of boron monosulfide (hp-BS) has been observed above 35 GPa. According to ab initio evolutionary crystal structure predictions combined with Rietveld refinement of high-pressure X-ray diffraction data, the structure of hp-BS has trigonal symmetry and belongs to the space group P-3m1. As it follows from the electron density of state calculations, the phase transformation is accompanied by an insulator-metal transition.

Coordination of Fe, Ga and Ge in high pressure glasses by Moessbauer, Raman and X-ray absorption spectroscopy, and geological implications

NASA Technical Reports Server (NTRS)

Fleet, M. E.; Henderson, G. S.; Herzberg, C. T.; Crozier, E. D.; Osborne, M. D.; Scarfe, C. M.

1984-01-01

For some time, it has been recognized that the structure of silicate liquids has a great bearing on such magma properties as viscosity, diffusivity, and thermal expansion and on the extrapolation of thermodynamic quantities outside of the experimentally measurable range. In this connection it is vital to know if pressure imposes changes in melt structure similar to the pressure-induced reconstructive transformations in crystals. In the present study on 1 bar and high pressure glasses, an investigation is conducted regarding the coordination of Fe(3+) in Fe silicate glasses by Moessbauer spectroscopy. Raman spectroscopy is employed to explore the coordinations of Ge(4+) in GeO2 glasses and of Ga(3+) in NaGa silicate glasses, while the coordination of Ga(3+) in NaGaSiO4 glasses is studied with the aid of methods of X-ray absorption spectroscopy.

Coordination of Fe, Ga and Ge in high pressure glasses by Moessbauer, Raman and X-ray absorption spectroscopy, and geological implications

NASA Astrophysics Data System (ADS)

Fleet, M. E.; Herzberg, C. T.; Henderson, G. S.; Crozier, E. D.; Osborne, M. D.; Scarfe, C. M.

1984-07-01

For some time, it has been recognized that the structure of silicate liquids has a great bearing on such magma properties as viscosity, diffusivity, and thermal expansion and on the extrapolation of thermodynamic quantities outside of the experimentally measurable range. In this connection it is vital to know if pressure imposes changes in melt structure similar to the pressure-induced reconstructive transformations in crystals. In the present study on 1 bar and high pressure glasses, an investigation is conducted regarding the coordination of Fe(3+) in Fe silicate glasses by Moessbauer spectroscopy. Raman spectroscopy is employed to explore the coordinations of Ge(4+) in GeO2 glasses and of Ga(3+) in NaGa silicate glasses, while the coordination of Ga(3+) in NaGaSiO4 glasses is studied with the aid of methods of X-ray absorption spectroscopy.

Pressure evolution of electrical transport in the 3D topological insulator (Bi,Sb) 2 (Se,Te) 3

DOE PAGES

Jeffries, J. R.; Butch, N. P.; Vohra, Y. K.; ...

2015-03-18

The group V-VI compounds|like Bi 2Se 3, Sb 2Te 3, or Bi 2Te 3|have been widely studied in recent years for their bulk topological properties. The high-Z members of this series form with the same crystal structure, and are therefore amenable to isostructural substitution studies. It is possible to tune the Bi-Sb and Te-Se ratios such that the material exhibits insulating behavior, thus providing an excellent platform for understanding how a topological insulator evolves with applied pressure. We report our observations of the pressure-dependent electrical transport and crystal structure of a pseudobinary (Bi,Sb) 2(Te,Se) 3 compound. Similar to some ofmore » its sister compounds, the (Bi,Sb) 2(Te,Se) 3 pseudobinary compound undergoes multiple, pressure-induced phase transformations that result in metallization, the onset of a close-packed crystal structure, and the development of distinct superconducting phases.« less

In situ structural analysis of calcium aluminosilicate glasses under high pressure.

PubMed

Muniz, R F; de Ligny, D; Martinet, C; Sandrini, M; Medina, A N; Rohling, J H; Baesso, M L; Lima, S M; Andrade, L H C; Guyot, Y

2016-08-10

In situ micro-Raman spectroscopy was used to investigate the structural evolution of OH(-)-free calcium aluminosilicate glasses, under high pressure and at room temperature. Evaluation was made of the role of the SiO2 concentration in percalcic join systems, for Al/(Al  +  Si) in the approximate range from 0.9 to 0.2. Under high pressure, the intensity of the main band related to the bending mode of bridging oxygen ([Formula: see text][T-O-T], where T  =  Si or Al) decreased gradually, suggesting that the bonds were severely altered or even destroyed. In Si-rich glasses, compression induced a transformation of Q (n) species to Q (n-1). In the case of Al-rich glass, the Al in the smallest Q (n) units evolved from tetrahedral to higher-coordinated Al (([5])Al and ([6])Al). Permanent structural changes were observed in samples recovered from the highest pressure of around 15 GPa and, particularly for Si-rich samples, the recovered structure showed an increase of three-membered rings in the Si/Al tetrahedral network.

Hydrostatic pressure effects on the structural and electronicproperties of carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Capaz,Rodrigo B.; Spataru, Catalin D.; Tangney, Paul

2004-03-15

We study the structural and electronic properties ofisolated single-wall carbon nanotubes (SWNTs) under hydrostatic pressureusing a combination of theoretical techniques: continuum elasticitymodels, classical molecular dynamics simulations, tight-bindingelectronic structure methods, and first-principles total energycalculations within the density-functional and pseudopotentialframeworks. For pressures below a certain critica pressure Pc, the SWNTs'structure remains cylindrical and the Kohn-Sham energy gaps ofsemiconducting SWNTs have either positive or negative pressurecoefficients depending on the value of (n,m) with a distinct "family" (ofthe same n-m) behavior. The diameter and chirality dependence of thepressure coefficients can be described by a simple analytical expression.At Pc, molecular-dynamics simulations predict that isolated SWNTsmore » undergoa pressure-induced symmetry-breaking transformation from a cylindricalshape to a collapsed geometry. This transition is described by a simpleelastic model as arising from the competition between the bond-bendingand PV terms in the enthalpy. The good agreement between calculated andexperimental values of Pc provides a strong support to the "collapse"interpretation of the experimental transitions in bundles.« less

Pressure-induced structural transformations and polymerization in ThC2

PubMed Central

Guo, Yongliang; Yu, Cun; Lin, Jun; Wang, Changying; Ren, Cuilan; Sun, Baoxing; Huai, Ping; Xie, Ruobing; Ke, Xuezhi; Zhu, Zhiyuan; Xu, Hongjie

2017-01-01

Thorium-carbon systems have been thought as promising nuclear fuel for Generation IV reactors which require high-burnup and safe nuclear fuel. Existing knowledge on thorium carbides under extreme condition remains insufficient and some is controversial due to limited studies. Here we systematically predict all stable structures of thorium dicarbide (ThC2) under the pressure ranging from ambient to 300 GPa by merging ab initio total energy calculations and unbiased structure searching method, which are in sequence of C2/c, C2/m, Cmmm, Immm and P6/mmm phases. Among these phases, the C2/m is successfully observed for the first time via in situ synchrotron XRD measurements, which exhibits an excellent structural correspondence to our theoretical predictions. The transition sequence and the critical pressures are predicted. The calculated results also reveal the polymerization behaviors of the carbon atoms and the corresponding characteristic C-C bonding under various pressures. Our work provides key information on the fundamental material behavior and insights into the underlying mechanisms that lay the foundation for further exploration and application of ThC2. PMID:28383571

Pressure-induced structural transformations and polymerization in ThC2

NASA Astrophysics Data System (ADS)

Guo, Yongliang; Yu, Cun; Lin, Jun; Wang, Changying; Ren, Cuilan; Sun, Baoxing; Huai, Ping; Xie, Ruobing; Ke, Xuezhi; Zhu, Zhiyuan; Xu, Hongjie

2017-04-01

Thorium-carbon systems have been thought as promising nuclear fuel for Generation IV reactors which require high-burnup and safe nuclear fuel. Existing knowledge on thorium carbides under extreme condition remains insufficient and some is controversial due to limited studies. Here we systematically predict all stable structures of thorium dicarbide (ThC2) under the pressure ranging from ambient to 300 GPa by merging ab initio total energy calculations and unbiased structure searching method, which are in sequence of C2/c, C2/m, Cmmm, Immm and P6/mmm phases. Among these phases, the C2/m is successfully observed for the first time via in situ synchrotron XRD measurements, which exhibits an excellent structural correspondence to our theoretical predictions. The transition sequence and the critical pressures are predicted. The calculated results also reveal the polymerization behaviors of the carbon atoms and the corresponding characteristic C-C bonding under various pressures. Our work provides key information on the fundamental material behavior and insights into the underlying mechanisms that lay the foundation for further exploration and application of ThC2.

Pressure-induced structural transformations and polymerization in ThC2.

PubMed

Guo, Yongliang; Yu, Cun; Lin, Jun; Wang, Changying; Ren, Cuilan; Sun, Baoxing; Huai, Ping; Xie, Ruobing; Ke, Xuezhi; Zhu, Zhiyuan; Xu, Hongjie

2017-04-06

Thorium-carbon systems have been thought as promising nuclear fuel for Generation IV reactors which require high-burnup and safe nuclear fuel. Existing knowledge on thorium carbides under extreme condition remains insufficient and some is controversial due to limited studies. Here we systematically predict all stable structures of thorium dicarbide (ThC 2 ) under the pressure ranging from ambient to 300 GPa by merging ab initio total energy calculations and unbiased structure searching method, which are in sequence of C2/c, C2/m, Cmmm, Immm and P6/mmm phases. Among these phases, the C2/m is successfully observed for the first time via in situ synchrotron XRD measurements, which exhibits an excellent structural correspondence to our theoretical predictions. The transition sequence and the critical pressures are predicted. The calculated results also reveal the polymerization behaviors of the carbon atoms and the corresponding characteristic C-C bonding under various pressures. Our work provides key information on the fundamental material behavior and insights into the underlying mechanisms that lay the foundation for further exploration and application of ThC 2 .

bcc-to-hcp transformation pathways for iron versus hydrostatic pressure: Coupled shuffle and shear modes

NASA Astrophysics Data System (ADS)

Liu, J. B.; Johnson, D. D.

2009-04-01

Using density-functional theory, we calculate the potential-energy surface (PES), minimum-energy pathway (MEP), and transition state (TS) versus hydrostatic pressure σhyd for the reconstructive transformation in Fe from body-centered cubic (bcc) to hexagonal closed-packed (hcp). At fixed σhyd , the PES is described by coupled shear (γ) and shuffle (η) modes and is determined from structurally minimized hcp-bcc energy differences at a set of (η,γ) . We fit the PES using symmetry-adapted polynomials, permitting the MEP to be found analytically. The MEP is continuous and fully explains the transformation and its associated magnetization and volume discontinuity at TS. We show that σhyd (while not able to induce shear) dramatically alters the MEP to drive reconstruction by a shuffle-only mode at ≤30GPa , as observed. Finally, we relate our polynomial-based results to Landau and nudge-elastic-band approaches and show they yield incorrect MEP in general.

Shear-Induced Isostructural Phase Transition and Metallization of Layered Tungsten Disulfide under Nonhydrostatic Compression

DOE PAGES

Duwal, Sakun; Yoo, Choong-Shik

2016-02-16

Pressure-induced structural and electronic transformations of tungsten disulfide (WS 2) have been studied to 60 GPa, in both hydrostatic and non-hydrostatic conditions, using four-probe electrical resistance measurements, micro-Raman spectroscopy and synchrotron x-ray diffraction. Our results show the evidence for an isostructural phase transition from hexagonal 2H c phase to hexagonal 2H a phase, which accompanies the metallization at ~37 GPa. This isostructural transition occurs displacively over a large pressure range between 15 and 45 GPa and is driven by the presence of strong shear stress developed in the layer structure of WS 2 under non-hydrostatic compression. Interestingly, this transition ismore » absent in hydrostatic conditions using He pressure medium, underscoring its strong dependence on the state of stress. We also attribute the absence to the incorporation of He atoms between the layers, mitigating the development of shear stress. We also conjecture a possibility of magnetic ordering in WS 2 that may occur at low temperature near the metallization.« less

Effect of impurity on high pressure behavior of nano indium titanate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chitnis, Abhishek, E-mail: abhishekchitnis87@gmail.com; Garg, Nandini; Mishra, A. K.

2015-06-24

Angle dispersive x-ray diffraction studies were carried out on a mixture of nano particles of indium titanate, indium oxide, and disordered TiO{sub 2} upto pressures of ∼ 45 GPa. Our studies show that indium titanate undergoes a partial decomposition to its constituent high pressure oxides. However, concomitantly a very small fraction of indium titanate transforms to a denser phase at ∼ 27.5 GPa. This transformation to new phase was found to be irreversible. At this pressure even cubic In{sub 2}O{sub 3} transformed to the In{sub 2}O{sub 3} (II) (iso-structural to Rh{sub 2}O{sub 3} (II)) phase, without any signature of themore » intermediate corundum phase. The high pressure In{sub 2}O{sub 3} (II) phase transforms to the corundum structure on release of pressure. These studies indicate that the presence of a large fraction of seed impurities could have facilitated the decomposition of indium titanate into its constituent oxides at the cost of its incomplete transformation to the high pressure denser phase.« less

Mechanical Anisotropy and Pressure Induced Structural Changes in Piroxicam Crystals Probed by In Situ Indentation and Raman Spectroscopy

NASA Astrophysics Data System (ADS)

Manimunda, Praveena; Hintsala, Eric; Asif, Syed; Mishra, Manish Kumar

2017-01-01

The ability to correlate mechanical and chemical characterization techniques in real time is both lacking and powerful tool for gaining insights into material behavior. This is demonstrated through use of a novel nanoindentation device equipped with Raman spectroscopy to explore the deformation-induced structural changes in piroxicam crystals. Mechanical anisotropy was observed in two major faces ( 0bar{1}1 ) and (011), which are correlated to changes in the interlayer interaction from in situ Raman spectra recorded during indentation. The results of this study demonstrate the considerable potential of an in situ Raman nanoindentation instrument for studying a variety of topics, including stress-induced phase transformation mechanisms, mechanochemistry, and solid state reactivity under mechanical forces that occur in molecular and pharmaceutical solids.

Nature of metastable amorphous-to-crystalline reversible phase transformations in GaSb

NASA Astrophysics Data System (ADS)

Kalkan, B.; Edwards, T. G.; Raoux, S.; Sen, S.

2013-08-01

The structural, thermodynamic, and kinetic aspects of the transformations between the metastable amorphous and crystalline phases of GaSb are investigated as a function of pressure at ambient temperature using synchrotron x-ray diffraction experiments in a diamond anvil cell. The results are consistent with the hypothesis that the pressure induced crystallization of amorphous GaSb into the β-Sn crystal structure near ˜5 GPa is possibly a manifestation of an underlying polyamorphic phase transition between a semiconducting, low density and a metallic, high density amorphous (LDA and HDA, respectively) phases. In this scenario, the large differences in the thermal crystallization kinetics between amorphous GaSb deposited in thin film form by sputtering and that prepared by laser melt quenching may be related to the relative location of the glass transition temperature of the latter in the pressure-temperature (P-T) space with respect to the location of the critical point that terminate the LDA ↔ HDA transition. The amorphous → β-Sn phase transition is found to be hysteretically reversible as the β-Sn phase undergoes decompressive amorphization near ˜2 GPa due to the lattice instabilities that give rise to density fluctuations in the crystal upon decompression.

High pressure synthesis of amorphous TiO2 nanotubes

NASA Astrophysics Data System (ADS)

Li, Quanjun; Liu, Ran; Wang, Tianyi; Xu, Ke; Dong, Qing; Liu, Bo; Liu, Jing; Liu, Bingbing

2015-09-01

Amorphous TiO2 nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO2 nanotubes. The structural phase transitions of anatase TiO2 nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD) method. The starting anatase structure is stable up to ˜20GPa, and transforms into a high-density amorphous (HDA) form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO2 nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO2 phase was revealed by high-resolution transmission electron microscopy (HRTEM) study. In addition, the bulk modulus (B0 = 158 GPa) of the anatase TiO2 nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa). We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO2 nanotubes.

Pressure, temperature, and electric field dependence of phase transformations in niobium modified 95/5 lead zirconate titanate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Wen D.; Carlos Valadez, J.; Gallagher, John A.

2015-06-28

Ceramic niobium modified 95/5 lead zirconate-lead titanate (PZT) undergoes a pressure induced ferroelectric to antiferroelectric phase transformation accompanied by an elimination of polarization and a volume reduction. Electric field and temperature drive the reverse transformation from the antiferroelectric to ferroelectric phase. The phase transformation was monitored under pressure, temperature, and electric field loading. Pressures and temperatures were varied in discrete steps from 0 MPa to 500 MPa and 25 °C to 125 °C, respectively. Cyclic bipolar electric fields were applied with peak amplitudes of up to 6 MV m{sup −1} at each pressure and temperature combination. The resulting electric displacement–electric field hysteresis loops weremore » open “D” shaped at low pressure, characteristic of soft ferroelectric PZT. Just below the phase transformation pressure, the hysteresis loops took on an “S” shape, which split into a double hysteresis loop just above the phase transformation pressure. Far above the phase transformation pressure, when the applied electric field is insufficient to drive an antiferroelectric to ferroelectric phase transformation, the hysteresis loops collapse to linear dielectric behavior. Phase stability maps were generated from the experimental data at each of the temperature steps and used to form a three dimensional pressure–temperature–electric field phase diagram.« less

Pressure effect on the Raman and photoluminescence spectra of Eu3+-doped Na2Ti6O13 nanorods

NASA Astrophysics Data System (ADS)

Zeng, Q. G.; Yang, G. T.; Chen, F.; Luo, J. Y.; Zhang, Z. M.; Leung, C. W.; Ding, Z. J.; Sheng, Y. Q.

2013-12-01

Eu3+-doped Na2Ti6O13 (Na2Ti6O13:Eu) nanorods with diameters of 30 nm and lengths 400 nm were synthesized by hydrothermal and heat treatment methods. Raman spectra at ambient conditions indicated a pure monoclinic phase (space group C2/m) of the nanorods. The relations between structural and optical properties of Na2Ti6O13:Eu nanorods under high pressures were obtained by photoluminescence and Raman spectra. Two structural transition points at 1.39 and 15.48 GPa were observed when the samples were pressurized. The first transition point was attributed to the crystalline structural distortion. The later transition point was the result of pressure-induced amorphization, and the high-density amorphous (HDA) phase formed after 15.48 GPa was structurally related to the monoclinic baddeleyite structured TiO2 (P21/c). However, the site symmetry of the local environment around the Eu3+ ions in Na2Ti6O13 increased with the rising pressure. These above results indicate the occurrence of short-range order for the local asymmetry around the Eu3+ ions and long-range disorder for the crystalline structure of Na2Ti6O13:Eu nanorods by applying pressure. After releasing the pressure from 22.74 GPa, the HDA phase is transformed to low-density amorphous form, which is attributed to be structurally related to the α-PbO2-type TiO2.

The transformation of nitrogen during pressurized entrained-flow pyrolysis of Chlorella vulgaris.

PubMed

Maliutina, Kristina; Tahmasebi, Arash; Yu, Jianglong

2018-08-01

The transformation of nitrogen in microalgae during entrained-flow pyrolysis of Chlorella vulgaris was systematically investigated at the temperatures of 600-900 °C and pressures of 0.1-4.0 MPa. It was found that pressure had a profound impact on the transformation of nitrogen during pyrolysis. The nitrogen retention in bio-char and its content in bio-oil reached a maximum value at 1.0 MPa. The highest conversion of nitrogen (50.25 wt%) into bio-oil was achieved at 1.0 MPa and 800 °C, which was about 7 wt% higher than that at atmospheric pressure. Higher pressures promoted the formation of pyrrolic-N (N-5) and quaternary-N (N-Q) compounds in bio-oil at the expense of nitrile-N and pyridinic-N (N-6) compounds. The X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results on bio-chars clearly evidenced the transformation of N-5 structures into N-6 and N-Q structures at elevated pressures. The nitrogen transformation pathways during pyrolysis of microalgae were proposed and discussed. Copyright © 2018 Elsevier Ltd. All rights reserved.

Theoretical calculations of high-pressure phases of NiF2: An ab initio constant-pressure study

NASA Astrophysics Data System (ADS)

Kürkçü, Cihan; Merdan, Ziya; Öztürk, Hülya

2016-12-01

We have studied the structural properties of the antiferromagnetic NiF2 tetragonal structure with P42/ mnm symmetry using density functional theory (DFT) under rapid hydrostatic pressure up to 400 GPa. For the exchange correlation energy we used the local density approximation (LDA) of Ceperley and Alder (CA). Two phase transformations are successfully observed through the simulations. The structures of XF2-type compounds crystallize in rutile-type structure. NiF2 undergoes phase transformations from the tetragonal rutile-type structure with space group P42/ mnm to orthorhombic CaCl2-type structure with space group Pnnm and from this orthorhombic phase to monoclinic structure with space group C2/ m at 152 GPa and 360 GPa, respectively. These phase changes are also studied by total energy and enthalpy calculations. According to these calculations, we perdict these phase transformations at about 1.85 and 30 GPa.

The Transformation of Enterovirus Replication Structures: a Three-Dimensional Study of Single- and Double-Membrane Compartments

PubMed Central

Limpens, Ronald W. A. L.; van der Schaar, Hilde M.; Kumar, Darshan; Koster, Abraham J.; Snijder, Eric J.; van Kuppeveld, Frank J. M.; Bárcena, Montserrat

2011-01-01

ABSTRACT All positive-strand RNA viruses induce membrane structures in their host cells which are thought to serve as suitable microenvironments for viral RNA synthesis. The structures induced by enteroviruses, which are members of the family Picornaviridae, have so far been described as either single- or double-membrane vesicles (DMVs). Aside from the number of delimiting membranes, their exact architecture has also remained elusive due to the limitations of conventional electron microscopy. In this study, we used electron tomography (ET) to solve the three-dimensional (3-D) ultrastructure of these compartments. At different time points postinfection, coxsackievirus B3-infected cells were high-pressure frozen and freeze-substituted for ET analysis. The tomograms showed that during the exponential phase of viral RNA synthesis, closed smooth single-membrane tubules constituted the predominant virus-induced membrane structure, with a minor proportion of DMVs that were either closed or connected to the cytosol in a vase-like configuration. As infection progressed, the DMV number steadily increased, while the tubular single-membrane structures gradually disappeared. Late in infection, complex multilamellar structures, previously unreported, became apparent in the cytoplasm. Serial tomography disclosed that their basic unit is a DMV, which is enwrapped by one or multiple cisternae. ET also revealed striking intermediate structures that strongly support the conversion of single-membrane tubules into double-membrane and multilamellar structures by a process of membrane apposition, enwrapping, and fusion. Collectively, our work unravels the sequential appearance of distinct enterovirus-induced replication structures, elucidates their detailed 3-D architecture, and provides the basis for a model for their transformation during the course of infection. PMID:21972238

Thermal and structural alternations in CuAlMnNi shape memory alloy by the effect of different pressure applications

NASA Astrophysics Data System (ADS)

Canbay, Canan Aksu; Polat, Tercan

2017-09-01

In this work the effects of the applied pressure on the characteristic transformation temperatures, the high temperature order-disorder phase transitions, the variation in diffraction peaks and the surface morphology of the CuAlMnNi shape memory alloy was investigated. The evolution of the transformation temperatures was studied by differential scanning calorimetry (DSC) with different heating and cooling rates. The differential thermal analysis measurements were performed to obtain the ordered-disordered phase transformations from room temperature to 900 °C. The characteristic transformation temperatures and the thermodynamic parameters were highly sensitive to variations in the applied pressure and also the applied pressure affected the thermodynamic parameters. The activation energy of the sample according to applied pressure values calculated by Kissinger method. The structural changes of the samples were studied by X-ray diffraction (XRD) measurements and by optical microscope observations at room temperature.

Dense Carbon Monoxide to 160 GPa: Stepwise Polymerization to Two-Dimensional Layered Solid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryu, Young-Jay; Kim, Minseob; Lim, Jinhyuk

Carbon monoxide (CO) is the first molecular system found to transform into a nonmolecular “polymeric” solid above 5.5 GPa, yet been studied beyond 10 GPa. Here, we show a series of pressure-induced phase transformations in CO to 160 GPa: from a molecular solid to a highly colored, low-density polymeric phase I to translucent, high-density phase II to transparent, layered phase III. The properties of these phases are consistent with those expected from recently predicted 1D P2 1/m, 3D I2 12 12 1, and 2D Cmcm structures, respectively. Thus, the present results advocate a stepwise polymerization of CO triple bonds tomore » ultimately a 2D singly bonded layer structure with an enhanced ionic character.« less

Pressure-induced Ge coordination change in SiO2-GeO2 glasses

NASA Astrophysics Data System (ADS)

Majérus, O.; Cormier, L.; Itié, J.-P.; Calas, G.

2003-04-01

Among the parameters controlling igneous processes in Earth, the density and transport properties of silicate melts are playing a major role. These properties are strongly dependent upon pressure, in a way that can significantly differ from the crystalline phases. The study of the pressure-induced structural changes can give a further understanding of the peculiar microscopic origins of these properties in molten phases. As in silicate minerals, the coordination change IVSi towards VISi is expected to be the major transformation occurring in melts at mantle conditions, yielding amorphous phases with properties distinct to those corresponding to a tetrahedral framework. This change is predicted by molecular dynamics simulations, but experimental evidences are scarce because of difficult technical constraints. The binary SiO_2-GeO_2 system allows a further insight into the compression mechanism of a tetrahedral framework glass structure. The Ge coordination change and its composition dependence can be assessed by using XAS spectroscopy at Ge K-edge with a diamond anvil cell. In this study, we report an in situ investigation carried out on well characterized glasses of the SiO_2-GeO_2 system. Experiments were preformed on the D11 beamline which is a unique dispersive experimental setup developed at the Laboratoire pour l’Utilisation du Rayonnement Magnétique (LURE, Orsay, France). Pressures up to 25 GPa have been obtained. With increasing SiO_2 content, both Ge-O distances extracted from EXAFS data and XANES features indicate the regular increase of the pressure threshold for the Ge coordination change (from 4 in pure GeO_2 to 12 Gpa in 80 mol% SiO_2-bearing glass), which corresponds to the end of the elastic compression regime, and the achievement of the transformation on a broader pressure range as predicted in pure SiO_2. These data are compared to results on slightly depolymerised glasses of Na_2O-GeO_2 composition, where a greater variety of compression mechanisms takes place.

Atomic structure and pressure-induced phase transformations in a phase-change alloy

NASA Astrophysics Data System (ADS)

Xu, Ming

Phase-change materials exist in at least two phases under the ambient condition. One is the amorphous state and another is crystalline phase. These two phases have vastly different physical properties, such as electrical conductivity, optical reflectivity, mass density, thermal conductivity, etc. The distinct physical properties and the fast transformation between amorphous and crystalline phases render these materials the ability to store information. For example, the DVD and the Blue-ray discs take advantage of the optical reflectivity contrast, and the newly developed solid-state memories make use of the large conductivity difference. In addition, both the amorphous and crystalline phases in phase-change memories (PCMs) are very stable at room temperature, and they are easy to be scaled up in the production of devices with large storage density. All these features make phase-change materials the ideal candidates for the next-generation memories. Despite of the fast development of these new memory materials in industry, many fundamental physics problems underlying these interesting materials are still not fully resolved. This thesis is aiming at solving some of the key issues in phase-change materials. Most of phase-change materials are composed of Ge-Sb-Te constituents. Among all these Ge-Sb-Te based materials, Ge2Sb2Te5 (GST) has the best performance and has been frequently studied as a prototypical phase-change material. The first and foremost issue is the structure of the two functioning phases. In this thesis, we investigate the unique atomic structure and bonding nature of amorphous GST (a-GST) and crystalline GST ( c-GST), using ab initio tools and X-ray diffraction (XRD) methods. Their local structures and bonding scenarios are then analyzed using electronic structure calculations. In order to gain insight into the fast phase transformation mechanism, we also carried out a series of high-pressure experiments on GST. Several new polymorphs and their transformations have been revealed under high pressure via in situ XRD and in situ electrical resistivity measurements. The mechanisms of the structural and property changes have been uncovered via ab initio molecular dynamics simulations.

First principles electronic and thermal properties of some AlRE intermetallics

NASA Astrophysics Data System (ADS)

Srivastava, Vipul; Sanyal, Sankar P.; Rajagopalan, M.

2008-10-01

A study on structural and electronic properties of non-magnetic cubic B 2-type AlRE (RE=Sc, Y, La, Ce, Pr and Lu) intermetallics has been done theoretically. The self-consistent tight binding linear muffin tin orbital method is used to describe the electronic properties of these intermetallics at ambient and at high pressure. These compounds show metallic behavior under ambient conditions. The variation of density of states under compression indicates some possibility of structural phase transformation in AlLa, AlCe and AlPr. Thermal properties like Debye temperature and Grüneisen constant are calculated at T=0 K and at ambient pressure within the Debye-Grüneisen model and compared with the others’ theoretical results. Our results are in good agreement. We have also performed a pressure-induced variation of Debye temperature and have found a decrease in Debye temperature around 40 kbar in AlRE (RE=La, Ce, Pr) intermetallics.

Experimental shock deformation in zircon: a transmission electron microscopic study

NASA Astrophysics Data System (ADS)

Leroux, H.; Reimold, W. U.; Koeberl, C.; Hornemann, U.; Doukhan, J.-C.

1999-06-01

In recent years, apparently shock-induced and, thus, impact-characteristic microdeformations, in the form of planar microdeformation features and so-called strawberry (granular) texture, have been observed in zircons in rocks from confirmed impact structures and from the K/ T boundary. The nature of the planar microdeformations in this mineral is, however, still unknown, and critical information is needed regarding the shock pressure range in which these deformation effects are produced. We experimentally shock deformed two series of thin zircon (ZrSiO 4) target plates, cut perpendicular to the c-axis, at shock pressures of 20, 40, and 60 GPa. The recovered samples were characterized by optical and scanning electron microscopy. In addition, one sample series was studied by transmission electron microscopy (TEM). Microdeformation effects observed at 20 GPa include pervasive micro-cleavage and dislocation patterns. Plastic deformation is indicated by a high density of straight dislocations in glide configuration. The dominant glide systems are <100>{010}. Micro-cleavages, induced by shear stresses during the compression stage, occur mostly in the {100} planes. The large density of dislocations at crack tips shows that plastic deformation was initiated by the micro-cracking processs. At 40 GPa, the sample was partly transformed from the zircon (z) to a scheelite (CaWO 4)-type (s) structure. Planar deformation features (PDFs) containing an amorphous phase of zircon composition are present in the not yet transformed zircon relics. The phase with scheelite structure, initiated in the {100} planes of zircon, consists of thin (0.1 to several μm) bands that crosscut the zircon matrix. The phase transformation is displacive (martensitic) and can be related by {100} z // {112} s and [001] z // <110> s. The scheelite structure phase is densely twinned, with twins in the (112) plane. The 60-GPa sample consists completely of the scheelite structure phase. Crosscutting and displacing relationships between twins and PDFs demonstrate that PDFs are formed in the zircon structure, i.e., before the phase transformation to the scheelite structure occurred, most likely at the shock front. Crystallographic orientations of optically visible planar features in zircon, in comparison with orientations of planar defects at the TEM scale, suggest that the optically visible features are more likely planar microfractures than PDFs.

Nanoscale heterogeneity as remnant hexagonal-type local structures in shocked Cu-Pb and Zr

NASA Astrophysics Data System (ADS)

Tayal, Akhil; Conradson, Steven D.; Batuk, Olga N.; Fensin, Saryu; Cerreta, Ellen; Gray, George T.; Saxena, Avadh

2017-09-01

Extended X-ray absorption fine structure spectroscopy was used to determine the local structure in: (1) Zr that had undergone quasistatic elongation; (2) Zr that had undergone plastic deformation by shock at pressures above and below the ω-phase transformation; and (3) shocked Cu that contained a few percent of insoluble Pb. Below the transition pressure, Zr samples showed only general disorder as increases in the widths of the Zr-Zr pair distributions. Above this pressure, Zr that was a mixture of the original hcp and the high pressure ω-phase when measured by diffraction showed two sets of peaks in its distribution corresponding to these two phases. Some of the ones from the ω-phase were at distances substantially different from those calculated from the diffraction pattern, although they are still consistent with small domains exhibiting stacking faults associated with hexagonal-type structural components exhibiting variability in the [0001] basal plane spacing. A similar result, new pairs at just over 3 and 4 Å consistent with hexagonal-type stacking faults in addition to the original fcc structure, is found in shocked Cu despite the absence of a second diffraction pattern and peak pressures being far below those expected to induce an fcc to hcp transition. This result, therefore, demonstrates that the correlation between high strain rates and reduced stacking fault energy continues down to the length scale of atom pairs. These findings are significant as: (1) a microscopic description of the behavior of systems far from equilibrium; (2) a demonstration of the importance of strain rate at short length scales; and (3) a bridge between the abruptness of macroscopic pressure-induced phase transitions and the continuity of martensitic ones over their fluctuation region in terms of the inverse relationship between the length scale of the martensitic texture, manifested here as ordered lattice distortions and the lower pressure at which such texture first appears relative to the bulk transition pressure.

Pressure-induced transformations in glassy water: A computer simulation study using the TIP4P/2005 model

NASA Astrophysics Data System (ADS)

Wong, Jessina; Jahn, David A.; Giovambattista, Nicolas

2015-08-01

We study the pressure-induced transformations between low-density amorphous (LDA) and high-density amorphous (HDA) ice by performing out-of-equilibrium molecular dynamics (MD) simulations. We employ the TIP4P/2005 water model and show that this model reproduces qualitatively the LDA-HDA transformations observed experimentally. Specifically, the TIP4P/2005 model reproduces remarkably well the (i) structure (OO, OH, and HH radial distribution functions) and (ii) densities of LDA and HDA at P = 0.1 MPa and T = 80 K, as well as (iii) the qualitative behavior of ρ(P) during compression-induced LDA-to-HDA and decompression-induced HDA-to-LDA transformations. At the rates explored, the HDA-to-LDA transformation is less pronounced than in experiments. By studying the LDA-HDA transformations for a broad range of compression/decompression temperatures, we construct a "P-T phase diagram" for glassy water that is consistent with experiments and remarkably similar to that reported previously for ST2 water. This phase diagram is not inconsistent with the possibility of TIP4P/2005 water exhibiting a liquid-liquid phase transition at low temperatures. A comparison with previous MD simulation studies of SPC/E and ST2 water as well as experiments indicates that, overall, the TIP4P/2005 model performs better than the SPC/E and ST2 models. The effects of cooling and compression rates as well as aging on our MD simulations results are also discussed. The MD results are qualitatively robust under variations of cooling/compression rates (accessible in simulations) and are not affected by aging the hyperquenched glass for at least 1 μs. A byproduct of this work is the calculation of TIP4P/2005 water's diffusion coefficient D(T) at P = 0.1 MPa. It is found that, for T ≥ 210 K, D(T) ≈ (T - TMCT)-γ as predicted by mode coupling theory and in agreement with experiments. For TIP4P/2005 water, TMCT = 209 K and γ = 2.14, very close to the corresponding experimental values TMCT = 221 K and γ = 2.2.

Pressure-induced transformations in glassy water: A computer simulation study using the TIP4P/2005 model.

PubMed

Wong, Jessina; Jahn, David A; Giovambattista, Nicolas

2015-08-21

We study the pressure-induced transformations between low-density amorphous (LDA) and high-density amorphous (HDA) ice by performing out-of-equilibrium molecular dynamics (MD) simulations. We employ the TIP4P/2005 water model and show that this model reproduces qualitatively the LDA-HDA transformations observed experimentally. Specifically, the TIP4P/2005 model reproduces remarkably well the (i) structure (OO, OH, and HH radial distribution functions) and (ii) densities of LDA and HDA at P = 0.1 MPa and T = 80 K, as well as (iii) the qualitative behavior of ρ(P) during compression-induced LDA-to-HDA and decompression-induced HDA-to-LDA transformations. At the rates explored, the HDA-to-LDA transformation is less pronounced than in experiments. By studying the LDA-HDA transformations for a broad range of compression/decompression temperatures, we construct a "P-T phase diagram" for glassy water that is consistent with experiments and remarkably similar to that reported previously for ST2 water. This phase diagram is not inconsistent with the possibility of TIP4P/2005 water exhibiting a liquid-liquid phase transition at low temperatures. A comparison with previous MD simulation studies of SPC/E and ST2 water as well as experiments indicates that, overall, the TIP4P/2005 model performs better than the SPC/E and ST2 models. The effects of cooling and compression rates as well as aging on our MD simulations results are also discussed. The MD results are qualitatively robust under variations of cooling/compression rates (accessible in simulations) and are not affected by aging the hyperquenched glass for at least 1 μs. A byproduct of this work is the calculation of TIP4P/2005 water's diffusion coefficient D(T) at P = 0.1 MPa. It is found that, for T ≥ 210 K, D(T) ≈ (T - T(MCT))(-γ) as predicted by mode coupling theory and in agreement with experiments. For TIP4P/2005 water, T(MCT) = 209 K and γ = 2.14, very close to the corresponding experimental values T(MCT) = 221 K and γ = 2.2.

Anisotropy of the ferromagnetic L10 phase in the Mn-Al-C alloys induced by high-pressure spark plasma sintering

NASA Astrophysics Data System (ADS)

Tyrman, Muriel; Ahmim, Smail; Pasko, Alexandre; Etgens, Victor; Mazaleyrat, Frédéric; Quetel-Weben, Simon; Perrière, Loïc; Guillot, Ivan

2018-05-01

The metastable τ-phase of MnAl equi-atomic compound belongs to a family of ferromagnetic alloys with L10 crystal structure. Stabilization of the phase by adding 2 at. % using manganese carbide (Mn23C6) enhances the magnetization in relation with the increase in lattice volume. It is thus a promising candidate for rare-earth-free permanent magnets. Coercivity of Mn-Al-C alloys being still weak, there is an interest to see to which extend sintering/transformation of the ɛ-phase by Spark Plasma Sintering (SPS) can increase the coercivity and the anisotropy. The structural and the magnetic properties were studied for samples sintered at 550 °C under uniaxial pressure of 100, 200, 300 and 400 MPa. Coercivity, remanence and anistotropy appears with the sintering pressure. The high pressure applied while sintering produces preferential orientation of the flake-shaped grains which influences the remanence.

Quantum simulation of thermally-driven phase transition and oxygen K-edge x-ray absorption of high-pressure ice

PubMed Central

Kang, Dongdong; Dai, Jiayu; Sun, Huayang; Hou, Yong; Yuan, Jianmin

2013-01-01

The structure and phase transition of high-pressure ice are of long-standing interest and challenge, and there is still a huge gap between theoretical and experimental understanding. The quantum nature of protons such as delocalization, quantum tunneling and zero-point motion is crucial to the comprehension of the properties of high-pressure ice. Here we investigated the temperature-induced phase transition and oxygen K-edge x-ray absorption spectra of ice VII, VIII and X using ab initio path-integral molecular dynamics simulations. The tremendous difference between experiments and the previous theoretical predictions is closed for the phase diagram of ice below 300 K at pressures up to 110 GPa. Proton tunneling assists the proton-ordered ice VIII to transform into proton-disordered ice VII where only thermal activated proton-transfer cannot occur. The oxygen K edge with its shift is sensitive to the order-disorder transition, and therefore can be applied to diagnose the dynamics of ice structures. PMID:24253589

Visible light response, electrical transport, and amorphization in compressed organolead iodine perovskites.

PubMed

Ou, Tianji; Yan, Jiejuan; Xiao, Chuanhai; Shen, Wenshu; Liu, Cailong; Liu, Xizhe; Han, Yonghao; Ma, Yanzhang; Gao, Chunxiao

2016-06-02

Recent scientific advances on organic-inorganic hybrid perovskites are mainly focused on the improvement of power conversion efficiency. So far, how compression tunes their electronic and structural properties remains less understood. By combining in situ photocurrent, impedance spectroscopy, and X-ray diffraction (XRD) measurements, we have studied the electrical transport and structural properties of compressed CH3NH3PbI3 (MAPbI3) nanorods. The visible light response of MAPbI3 remains robust below 3 GPa while it is suppressed when it becomes amorphous. Pressure-induced electrical transport properties of MAPbI3 including resistance, relaxation frequency, and relative permittivity have been investigated under pressure up to 8.5 GPa by in situ impedance spectroscopy measurements. These results indicate that the discontinuous changes of these physical parameters occur around the structural phase transition pressure. The XRD studies of MAPbI3 under high pressure up to 20.9 GPa show that a phase transformation below 0.7 GPa, could be attributed to the tilting and distortion of PbI6 octahedra. And pressure-induced amorphization is reversible at a low density amorphous state but irreversible at a relatively higher density state. Furthermore, the MAPbI3 nanorods crush into nanopieces around 0.9 GPa which helps us to explain why the mixed phase of tetragonal and orthorhombic was observed at 0.5 GPa. The pressure modulated changes of electrical transport and visible light response properties open up a new approach for exploring CH3NH3PbI3-based photo-electronic applications.

Onset of ice VII phase during ps laser pulse propagation through liquid water

NASA Astrophysics Data System (ADS)

Kumar, V. Rakesh; Kiran, P. Prem

2017-01-01

Water dominantly present in liquid state on earth gets transformed to crystalline polymorphs under different dynamic loading conditions. Out of different crystalline phases discovered till date, ice VII is observed to be stable over wide pressure (2-63 GPa) and temperature (>273 K) ranges. The formation of ice VII crystalline structure has been vastly reported during high pressure static compression using diamond anvil cell and propagation of high energy (>50 mJ/pulse) nanosecond laser pulse induced dynamic high pressures through liquid water. We present the onset of ice VII phase at low threshold of 2 mJ/pulse during 30 ps (532 nm, 10 Hz) laser pulse induced shock propagating through liquid water. Role of input pulse energy on the evolution of Stoke's and anti-Stoke's Raman shift of the dominant A1g mode of ice VII, filamentation, free-electrons, plasma shielding is presented. The H-bond network rearrangement, electron ion energy transfer time coinciding with the excitation pulse duration supported by the filamentation and plasma shielding of the ps laser pulses reduced the threshold of ice VII structure formation. Filamentation and the plasma shielding have shown the localized creation and sustenance of ice VII structure in liquid water over 3 mm length and 50 μm area of cross-section.

Unraveling the nature of electric field- and stress- induced structural transformations in soft PZT by a new powder poling technique.

PubMed

Kalyani, Ajay Kumar; V, Lalitha K; James, Ajit R; Fitch, Andy; Ranjan, Rajeev

2015-02-25

A 'powder-poling' technique was developed to study electric field induced structural transformations in ferroelectrics exhibiting a morphotropic phase boundary (MPB). The technique was employed on soft PZT exhibiting a large longitudinal piezoelectric response (d(33) ∼ 650 pC N(-1)). It was found that electric poling brings about a considerable degree of irreversible tetragonal to monoclinic transformation. The same transformation was achieved after subjecting the specimen to mechanical stress, which suggests an equivalence of stress and electric field with regard to the structural mechanism in MPB compositions. The electric field induced structural transformation was also found to be accompanied by a decrease in the spatial coherence of polarization.

Pressure-induced phase transitions and correlation between structure and superconductivity in iron-based superconductor Ce(O(0.84)F(0.16))FeAs.

PubMed

Zhao, Jinggeng; Liu, Haozhe; Ehm, Lars; Dong, Dawei; Chen, Zhiqiang; Liu, Qingqing; Hu, Wanzheng; Wang, Nanlin; Jin, Changqing

2013-07-15

High-pressure angle-dispersive X-ray diffraction experiments on iron-based superconductor Ce(O(0.84)F(0.16))FeAs were performed up to 54.9 GPa at room temperature. A tetragonal to tetragonal isostructural phase transition starts at about 13.9 GPa, and a new high-pressure phase has been found above 33.8 GPa. At pressures above 19.9 GPa, Ce(O(0.84)F(0.16))FeAs completely transforms to a high-pressure tetragonal phase, which remains in the same tetragonal structure with a larger a-axis and smaller c-axis than those of the low-pressure tetragonal phase. The structure analysis shows a discontinuity in the pressure dependences of the Fe-As and Ce-(O, F) bond distances, as well as the As-Fe-As and Ce-(O, F)-Ce bond angles in the transition region, which correlates with the change in T(c) of this compound upon compression. The isostructural phase transition in Ce(O(0.84)F(0.16))FeAs leads to a drastic drop in the superconducting transition temperature T(c) and restricts the superconductivity at low temperature. For the 1111-type iron-based superconductors, the structure evolution and following superconductivity changes under compression are related to the radius of lanthanide cations in the charge reservoir layer.

First-principle study of pressure-induced phase transitions and electronic properties of electride Y2C

NASA Astrophysics Data System (ADS)

Feng, Caihui; Shan, Jingfeng; Xu, Aoshu; Xu, Yang; Zhang, Meiguang; Lin, Tingting

2017-10-01

Trigonal yttrium hypocarbide (Y2C), crystallizing in a layered hR3 structure, is an intriguing quasi-two-dimensional electride metal with potential application for the next generation of electronics. By using an efficient structure search method in combination with first-principles calculations, we have extensively explored the phase transitions and electronic properties of Y2C in a wide pressure range of 0-200 GPa. Three structural transformations were predicted, as hR3 → oP12 → tI12 → mC12. Calculated pressures of phase transition are 20, 118, and 126 GPa, respectively. The high-pressure oP12 phase exhibits a three-dimensional extended C-Y network built up from face- and edge-sharing CY8 hendecahedrons, whereas both the tI12 and mC12 phases are featured by the presence of C2 units. No anionic electrons confined to interstitial spaces have been found in the three predicted high-pressure phases, indicating that they are not electrides. Moreover, Y2C is dynamically stable and also energetically stable relative to the decomposition into its elemental solids.

High pressure–low temperature phase diagram of barium: Simplicity versus complexity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Desgreniers, Serge; Tse, John S., E-mail: John.Tse@usask.ca; State Key Laboratory of Superhard Materials, Jilin University, 130012 Changchun

2015-11-30

Barium holds a distinctive position among all elements studied upon densification. Indeed, it was the first example shown to violate the long-standing notion that high compression of simple metals should preserve or yield close-packed structures. From modest pressure conditions at room temperature, barium transforms at higher pressures from its simple structures to the extraordinarily complex atomic arrangements of the incommensurate and self-hosting Ba-IV phases. By a detailed mapping of the pressure/temperature structures of barium, we demonstrate the existence of another crystalline arrangement of barium, Ba-VI, at low temperature and high pressure. The simple structure of Ba-VI is unlike that ofmore » complex Ba-IV, the phase encountered in a similar pressure range at room temperature. First-principles calculations predict Ba-VI to be stable at high pressure and superconductive. The results illustrate the complexity of the low temperature-high pressure phase diagram of barium and the significant effect of temperature on structural phase transformations.« less

Causal Correlation Functions and Fourier Transforms: Application in Calculating Pressure Induced Shifts

NASA Technical Reports Server (NTRS)

Ma, Q.; Tipping, R. H.; Lavrentieva, N. N.

2012-01-01

By adopting a concept from signal processing, instead of starting from the correlation functions which are even, one considers the causal correlation functions whose Fourier transforms become complex. Their real and imaginary parts multiplied by 2 are the Fourier transforms of the original correlations and the subsequent Hilbert transforms, respectively. Thus, by taking this step one can complete the two previously needed transforms. However, to obviate performing the Cauchy principal integrations required in the Hilbert transforms is the greatest advantage. Meanwhile, because the causal correlations are well-bounded within the time domain and band limited in the frequency domain, one can replace their Fourier transforms by the discrete Fourier transforms and the latter can be carried out with the FFT algorithm. This replacement is justified by sampling theory because the Fourier transforms can be derived from the discrete Fourier transforms with the Nyquis rate without any distortions. We apply this method in calculating pressure induced shifts of H2O lines and obtain more reliable values. By comparing the calculated shifts with those in HITRAN 2008 and by screening both of them with the pair identity and the smooth variation rules, one can conclude many of shift values in HITRAN are not correct.

Analytical one-dimensional model for laser-induced ultrasound in planar optically absorbing layer.

PubMed

Svanström, Erika; Linder, Tomas; Löfqvist, Torbjörn

2014-03-01

Ultrasound generated by means of laser-based photoacoustic principles are in common use today and applications can be found both in biomedical diagnostics, non-destructive testing and materials characterisation. For certain measurement applications it could be beneficial to shape the generated ultrasound regarding spectral properties and temporal profile. To address this, we studied the generation and propagation of laser-induced ultrasound in a planar, layered structure. We derived an analytical expression for the induced pressure wave, including different physical and optical properties of each layer. A Laplace transform approach was employed in analytically solving the resulting set of photoacoustic wave equations. The results correspond to simulations and were compared to experimental results. To enable the comparison between recorded voltage from the experiments and the calculated pressure we employed a system identification procedure based on physical properties of the ultrasonic transducer to convert the calculated acoustic pressure to voltages. We found reasonable agreement between experimentally obtained voltages and the voltages determined from the calculated acoustic pressure, for the samples studied. The system identification procedure was found to be unstable, however, possibly from violations of material isotropy assumptions by film adhesives and coatings in the experiment. The presented analytical model can serve as a basis when addressing the inverse problem of shaping an acoustic pulse from absorption of a laser pulse in a planar layered structure of elastic materials. Copyright © 2013 Elsevier B.V. All rights reserved.

Hydrogen-induced morphotropic phase transformation of single-crystalline vanadium dioxide nanobeams.

PubMed

Hong, Woong-Ki; Park, Jong Bae; Yoon, Jongwon; Kim, Bong-Joong; Sohn, Jung Inn; Lee, Young Boo; Bae, Tae-Sung; Chang, Sung-Jin; Huh, Yun Suk; Son, Byoungchul; Stach, Eric A; Lee, Takhee; Welland, Mark E

2013-04-10

We report a morphotropic phase transformation in vanadium dioxide (VO2) nanobeams annealed in a high-pressure hydrogen gas, which leads to the stabilization of metallic phases. Structural analyses show that the annealed VO2 nanobeams are hexagonal-close-packed structures with roughened surfaces at room temperature, unlike as-grown VO2 nanobeams with the monoclinic structure and with clean surfaces. Quantitative chemical examination reveals that the hydrogen significantly reduces oxygen in the nanobeams with characteristic nonlinear reduction kinetics which depend on the annealing time. Surprisingly, the work function and the electrical resistance of the reduced nanobeams follow a similar trend to the compositional variation due mainly to the oxygen-deficiency-related defects formed at the roughened surfaces. The electronic transport characteristics indicate that the reduced nanobeams are metallic over a large range of temperatures (room temperature to 383 K). Our results demonstrate the interplay between oxygen deficiency and structural/electronic phase transitions, with implications for engineering electronic properties in vanadium oxide systems.

New structure of high-pressure body-centered orthorhombic Fe 2 SiO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamanaka, Takamitsu; Kyono, Atsushi; Nakamoto, Yuki

2015-08-01

A structural change in Fe2SiO4 spinel (ringwoodite) has been found by synchrotron powder diffraction study and the structure of a new high-pressure phase was determined by Monte-Carlo simulation method and Rietveld profile fitting of X-ray diffraction data up to 64 GPa at ambient temperature. A transition from the cubic spinel structure to a body centered orthorhombic phase (I-Fe2SiO4) with space group Imma and Z = 4 was observed at approximately 34 GPa. The structure of I-Fe2SiO4 has two crystallographically independent FeO6 octahedra. Iron resides in two different sites of sixfold coordination: Fe1 and Fe2, which are arranged in layers parallelmore » to (101) and (011) and are very similar to the layers of FeO6 octahedra in the spinel structure. Silicon is located in the sixfold coordination in I-Fe2SiO4. The transformation to the new high-pressure phase is reversible under decompression at ambient temperature. A martensitic transformation of each slab of the spinel structure with translation vector Embedded Image generates the I-Fe2SiO4 structure. Laser heating of I-Fe2SiO4 at 1500 K results in a decomposition of the material to rhombohedral FeO and SiO2 stishovite. FeKβ X-ray emission measurements at high pressure up to 65 GPa show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17 GPa in the spinel phase. The IS electron spin state is gradually enhanced with pressure. The Fe2+ ion at the octahedral site changes the ion radius under compression at the low spin, which results in the changes of the lattice parameter and the deformation of the octahedra of the spinel structure. The compression curve of the lattice parameter of the spinel is discontinuous at ~20 GPa. The spin transition induces an isostructural change.« less

Pressure-induced amorphization in orthorhombic Ta{sub 2}O{sub 5}: An intrinsic character of crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Quanjun; Zhang, Huafang; Cheng, Benyuan

2014-05-21

The phase transition of orthorhombic Ta{sub 2}O{sub 5} was investigated by in situ synchrotron X-ray diffraction and Raman spectroscopy. The orthorhombic phase transforms into an amorphous form completely at 24.7 GPa. A bulk modulus B{sub 0} = 139 (9) GPa for the orthorhombic Ta{sub 2}O{sub 5} is derived from the P-V data. We suggest that the pressure-induced amorphization (PIA) in Ta{sub 2}O{sub 5} can be attributed to the unstability of the a axis under high pressure leads to the connections of polyhedral breaking down and even triggers disorder of the whole crystal frame. These results demonstrate that the PIA is an intrinsic charactermore » of Ta{sub 2}O{sub 5} which depends on its orthorhombic crystal structure rather than nanosize effects. This study provides a new kind of bulk material for investigating PIA in metal oxides.« less

In-situ x-ray diffraction of a shock-induced phase transition in fluorite, CaF2

NASA Astrophysics Data System (ADS)

Glam, Benny; June Tracy, Sally; Turneaure, Stefan; Duffy, Thomas

2017-06-01

The difluorides are an important class of ionic compounds that show extensive polymorphism under both static and dynamic loading. In this study, the shock-induced phase transitions in CaF2 were investigated by in situ x-ray diffraction measurements in plate impact experiments carried out with the two-stage gas gun at the Dynamic Compression Sector of Argonne National Laboratory. Single-crystal samples in (100) and (111) orientations were shock loaded to pressures between 32 GPa to 70 GPa. The particle velocities at the interface between the sample and a LiF window were measured by VISAR and PDV. Synchrotron x-ray diffraction data were recorded at 153.4 ns intervals using a four-frame detector. The measured diffraction patterns show a high degree of sample texturing at all pressures. We observe evidence for a transition to a high-pressure phase followed by reverse transformation at late times during release. This study provides the first direct constraints on the high-pressure lattice structure of fluorite under shock compression.

Effect of the fcc-hcp martensitic transition on the equation of state of solid krypton up to 140 GPa

NASA Astrophysics Data System (ADS)

Rosa, A. D.; Garbarino, G.; Briggs, R.; Svitlyk, V.; Morard, G.; Bouhifd, M. A.; Jacobs, J.; Irifune, T.; Mathon, O.; Pascarelli, S.

2018-03-01

Solid krypton (Kr) undergoes a pressure-induced martensitic phase transition from a face-centered cubic (fcc) to a hexagonal close-packed (hcp) structure. These two phases coexist in a very wide pressure domain inducing important modifications of the bulk properties of the resulting mixed phase system. Here, we report a detailed in situ x-ray diffraction and absorption study of the influence of the fcc-hcp phase transition on the compression behavior of solid krypton in an extended pressure domain up to 140 GPa. The onset of the hcp-fcc transformation was observed in this study at around 2.7 GPa and the coexistence of these two phases up to 140 GPa, the maximum investigated pressure. The appearance of the hcp phase is also evidenced by the pressure-induced broadening and splitting of the first peak in the XANES spectra. We demonstrate that the transition is driven by a continuous nucleation and intergrowth of nanometric hcp stacking faults that evolve in the fcc phase. These hcp stacking faults are unaffected by high-temperature annealing, suggesting that plastic deformation is not at their origin. The apparent small Gibbs free-energy differences between the two structures that decrease upon compression may explain the nucleation of hcp stacking faults and the large coexistence domain of fcc and hcp krypton. We observe a clear anomaly in the equation of state of the fcc solid at ˜20 GPa when the proportion of the hcp form reaches ˜20 % . We demonstrate that this anomaly is related to the difference in stiffness between the fcc and hcp phases and propose two distinct equation of states for the low and high-pressure regimes.

Crystal grain growth at the α -uranium phase transformation in praseodymium

NASA Astrophysics Data System (ADS)

Cunningham, Nicholas C.; Velisavljevic, Nenad; Vohra, Yogesh K.

2005-01-01

Structural phase transformations under pressure are examined in praseodymium metal for the range 0-40GPa at ambient temperature. Pressure was generated with a diamond-anvil cell, and data were collected using high-resolution synchrotron x-ray diffraction and the image plate technique. The structural sequence double hexagonal close packed (dhcp)→face centered cubic (fcc)→distorted-fcc (d-fcc)→ α -uranium (α-U) is observed with increasing pressure. Rietveld refinement of all crystallographic phases provided confirmation of the hR24 structure for the d-fcc phase while the previously reported monoclinic phase between the d-fcc and the α-U phase was not confirmed. We observe dramatic crystal grain growth during the volume collapse concurrent with the symmetry-lowering transition to the α-U structure. No preferred orientation axis is observed, and the formation process for these large grains is expected to be via a nucleation and growth mechanism. An analogous effect in rare earth metal cerium suggests that the grain growth during transformation to the α-U structure is a common occurrence in f -electron metals at high pressures.

Large-Scale Structure and Hyperuniformity of Amorphous Ices

NASA Astrophysics Data System (ADS)

Martelli, Fausto; Torquato, Salvatore; Giovambattista, Nicolas; Car, Roberto

2017-09-01

We investigate the large-scale structure of amorphous ices and transitions between their different forms by quantifying their large-scale density fluctuations. Specifically, we simulate the isothermal compression of low-density amorphous ice (LDA) and hexagonal ice to produce high-density amorphous ice (HDA). Both HDA and LDA are nearly hyperuniform; i.e., they are characterized by an anomalous suppression of large-scale density fluctuations. By contrast, in correspondence with the nonequilibrium phase transitions to HDA, the presence of structural heterogeneities strongly suppresses the hyperuniformity and the system becomes hyposurficial (devoid of "surface-area fluctuations"). Our investigation challenges the largely accepted "frozen-liquid" picture, which views glasses as structurally arrested liquids. Beyond implications for water, our findings enrich our understanding of pressure-induced structural transformations in glasses.

Mechanisms of the Wurtzite to Rocksalt Transformation in CdSe Nanocrystals

NASA Astrophysics Data System (ADS)

Grünwald, Michael; Rabani, Eran; Dellago, Christoph

2006-06-01

We study the pressure-driven phase transition from the four-coordinate wurtzite to the six-coordinate rocksalt structure in CdSe nanocrystals with molecular dynamics computer simulations. With an ideal gas as the pressure medium, we apply hydrostatic pressure to spherical and faceted nanocrystals ranging in diameter from 25 to 62 Å. In spherical crystals, the main mechanism of the transformation involves the sliding of (100) planes, but depending on the specific surface structure we also observe a second mechanism proceeding through the flattening of (100) planes. In faceted crystals, the transition proceeds via a five-coordinated hexagonal structure, which is stabilized at intermediate pressures due to dominant surface energetics.

Experimental and Theoretical Investigations on d and f Electron Systems under High Pressure

NASA Astrophysics Data System (ADS)

Gupta, Satish C.; Joshi, K. D.; Banerjee, S.

2008-07-01

The pressure-induced electron transfer from sp to d band in transition elements, and spd to f band in the light actinides significantly influences the stability of crystal structures in these metals. Although α → ω → β phase transition with increasing pressure in group IV transition elements is well documented, the β → ω transition under pressure has not been reported until recently. Our experimental study on the β-stabilized Zr-20Nb alloy reveals that it transforms to ω phase on shock compression, whereas this transition is not seen in a hydrostatic pressure condition. The platelike morphology of ω formed under shock compression is in contrast to the fine particle morphology seen in this system under thermal treatment, which clearly indicates that the mechanism of the β → ω transformation under shock treatment involves a large shear component. In this article, we have analyzed why the ω → β transition pressures in Ti, Zr, and Hf do not follow the trend implied by the principle of corresponding states. Our analysis shows that the ω → β transition depends on how the increased d population caused by the sp → d transfer of electron is distributed among various d substates. In Th, we have analyzed the role of 5f electrons in determining the mechanical stability of fcc and bct structures under hydrostatic compressions. Our analysis shows that the fcc to bct transition in this metal, which has been reported by high-pressure experiments, occurs because of softening of the tetragonal shear modulus C' = ( C 11 - C 12)/2 under compression. From the total energy calculated as a function of specific volume, we have determined the 0 K isotherm, which is then used to deduce the shock Hugoniot. The theoretical Hugoniot compares well with the experimental data.

Pressure effects on the structure, kinetic, and thermodynamic properties of heat-induced aggregation of protein studied by FT-IR spectroscopy

NASA Astrophysics Data System (ADS)

Taniguchi, Y.; Okuno, A.; Kato, M.

2010-03-01

Pressure can retrain the heat-induced aggregation and dissociate the heat-induced aggregates. We observed the aggregation-preventing pressure effect and the aggregates-dissociating pressure effect to characterize the heat-induced aggregation of equine serum albumin (ESA) by FT-IR spectroscopy. The results suggest the α-helical structure collapses at the beginning of heat-induced aggregation through the swollen structure, and then the rearrangement of structure to the intermolecular β-sheet takes place through partially unfolded structure. We determined the activation volume for the heat-induced aggregation (ΔV# = +93 ml/mol) and the partial molar volume difference between native state and heat-induced aggregates (ΔV=+32 ml/mol). This positive partial molar volume difference suggests that the heat-induced aggregates have larger internal voids than the native structure. Moreover, the positive volume change implies that the formation of the intermolecular β-sheet is unfavorable under high pressure.

Diffraction studies of the high pressure phases of GaAs and GaP

NASA Technical Reports Server (NTRS)

Baublitz, M., Jr.; Ruoff, A. L.

1982-01-01

High pressure structural phase transitions of GaAs and GaP have been studied by energy dispersive X-ray diffraction with the radiation from the Cornell High Energy Synchrotron Source. GaAs began to transform at 172 + or - 7 kbar to an orthorhombic structure possibly belonging to space group Fmmm. GaP transformed to a tetragonal beta-Sn type phase at 215 + or - 8 kbar. Although pressure transmitting media were used to minimize shear stresses in the specimens, the high pressure diffraction results were interpreted as showing evidence for planar defects in the specimens.

High-pressure polymorphism of acetylsalicylic acid (aspirin): Raman spectroscopy

NASA Astrophysics Data System (ADS)

Crowell, Ethan L.; Dreger, Zbigniew A.; Gupta, Yogendra M.

2015-02-01

Micro-Raman spectroscopy was used to elucidate the high-pressure polymorphic behavior of acetylsalicylic acid (ASA), an important pharmaceutical compound known as aspirin. Using a diamond anvil cell (DAC), single crystals of the two polymorphic phases of aspirin existing at ambient conditions (ASA-I and ASA-II) were compressed to 10 GPa. We found that ASA-I does not transform to ASA-II, but instead transforms to a new phase (ASA-III) above ∼2 GPa. It is demonstrated that this transformation primarily introduces structural changes in the bonding and arrangement of the acetyl groups and is reversible upon the release of pressure. In contrast, a less dense ASA-II shows no transition in the pressure range studied, though it appears to exhibit a disordered structure above 7 GPa. Our results suggest that ASA-III is the most stable polymorph of aspirin at high pressures.

Phase transformation in tantalum under extreme laser deformation

DOE PAGES

Lu, C. -H.; Hahn, E. N.; Remington, B. A.; ...

2015-10-19

The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centeredmore » cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. In conclusion, molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear).« less

Phase Transformation in Tantalum under Extreme Laser Deformation

PubMed Central

Lu, C.-H.; Hahn, E. N.; Remington, B. A.; Maddox, B. R.; Bringa, E. M.; Meyers, M. A.

2015-01-01

The structural and mechanical response of metals is intimately connected to phase transformations. For instance, the product of a phase transformation (martensite) is responsible for the extraordinary range of strength and toughness of steel, making it a versatile and important structural material. Although abundant in metals and alloys, the discovery of new phase transformations is not currently a common event and often requires a mix of experimentation, predictive computations, and luck. High-energy pulsed lasers enable the exploration of extreme pressures and temperatures, where such discoveries may lie. The formation of a hexagonal (omega) phase was observed in recovered monocrystalline body-centered cubic tantalum of four crystallographic orientations subjected to an extreme regime of pressure, temperature, and strain-rate. This was accomplished using high-energy pulsed lasers. The omega phase and twinning were identified by transmission electron microscopy at 70 GPa (determined by a corresponding VISAR experiment). It is proposed that the shear stresses generated by the uniaxial strain state of shock compression play an essential role in the transformation. Molecular dynamics simulations show the transformation of small nodules from body-centered cubic to a hexagonal close-packed structure under the same stress state (pressure and shear). PMID:26478106

An interatomic pair potential for cadmium selenide

NASA Astrophysics Data System (ADS)

Rabani, Eran

2002-01-01

We have developed a set of interatomic pair potentials for cadmium selenide based on a form similar to the Born-Mayer model. We show that this simple form of the pair potential, which has been used to describe the properties of alkali halides in the sixfold-coordinate structure, provides a realistic description of the properties of cadmium selenide in all three crystal structures: wurtzite, zinc blende, and rocksalt. Using the new pair potential we have studied the pressure-induced phase transition from the fourfold-coordinate wurtzite structure to the sixfold-coordinate rocksalt structure. The pressure transformation and the equation of state are in good agreement with experimental observations. Using the dispersion term in our pair potential we have also calculated the Hamaker constant for cadmium selenide within the framework of the original microscopic approach due to Hamaker. The results indicate that for ionic materials many-body terms that are included in the Lifshitz theory are well captured by the simple pair potential.

Shock-induced microstructural response of mono- and nanocrystalline SiC ceramics

NASA Astrophysics Data System (ADS)

Branicio, Paulo S.; Zhang, Jingyun; Rino, José P.; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya

2018-04-01

The dynamic behavior of mono- and nanocrystalline SiC ceramics under plane shock loading is revealed using molecular-dynamics simulations. The generation of shock-induced elastic compression, plastic deformation, and structural phase transformation is characterized at different crystallographic directions as well as on a 5-nm grain size nanostructure at 10 K and 300 K. Shock profiles are calculated in a wide range of particle velocities 0.1-6.0 km/s. The predicted Hugoniot agree well with experimental data. Results indicate the generation of elastic waves for particle velocities below 0.8-1.9 km/s, depending on the crystallographic direction. In the intermediate range of particle velocities between 2 and 5 km/s, the shock wave splits into an elastic precursor and a zinc blende-to-rock salt structural transformation wave, which is triggered by shock pressure over the ˜90 GPa threshold value. A plastic wave, with a strong deformation twinning component, is generated ahead of the transformation wave for shocks in the velocity range between 1.5 and 3 km/s. For particle velocities greater than 5-6 km/s, a single overdriven transformation wave is generated. Surprisingly, shocks on the nanocrystalline sample reveal the absence of wave splitting, and elastic, plastic, and transformation wave components are seamlessly connected as the shock strength is continuously increased. The calculated strengths 15.2, 31.4, and 30.9 GPa for ⟨001⟩, ⟨111⟩, and ⟨110⟩ directions and 12.3 GPa for the nanocrystalline sample at the Hugoniot elastic limit are in excellent agreement with experimental data.

New perspectives on potential hydrogen storage materials using high pressure.

PubMed

Song, Yang

2013-09-21

In addressing the global demand for clean and renewable energy, hydrogen stands out as the most suitable candidate for many fuel applications that require practical and efficient storage of hydrogen. Supplementary to the traditional hydrogen storage methods and materials, the high-pressure technique has emerged as a novel and unique approach to developing new potential hydrogen storage materials. Static compression of materials may result in significant changes in the structures, properties and performance that are important for hydrogen storage applications, and often lead to the formation of unprecedented phases or complexes that have profound implications for hydrogen storage. In this perspective article, 22 types of representative potential hydrogen storage materials that belong to four major classes--simple hydride, complex hydride, chemical hydride and hydrogen containing materials--were reviewed. In particular, their structures, stabilities, and pressure-induced transformations, which were reported in recent experimental works together with supporting theoretical studies, were provided. The important contextual aspects pertinent to hydrogen storage associated with novel structures and transitions were discussed. Finally, the summary of the recent advances reviewed and the insight into the future research in this direction were given.

Phase transition and chemical decomposition of hydrogen peroxide and its water mixtures under high pressures.

PubMed

Chen, Jing-Yin; Kim, Minseob; Yoo, Choong-Shik; Dattelbaum, Dana M; Sheffield, Stephen

2010-06-07

We have studied the pressure-induced phase transition and chemical decomposition of hydrogen peroxide and its mixtures with water to 50 GPa, using confocal micro-Raman and synchrotron x-ray diffractions. The x-ray results indicate that pure hydrogen peroxide crystallizes into a tetragonal structure (P4(1)2(1)2), the same structure previously found in 82.7% H(2)O(2) at high pressures and in pure H(2)O(2) at low temperatures. The tetragonal phase (H(2)O(2)-I) is stable to 15 GPa, above which transforms into an orthorhombic structure (H(2)O(2)-II) over a relatively large pressure range between 13 and 18 GPa. Inferring from the splitting of the nu(s)(O-O) stretching mode, the phase I-to-II transition pressure decreases in diluted H(2)O(2) to around 7 GPa for the 41.7% H(2)O(2) and 3 GPa for the 9.5%. Above 18 GPa H(2)O(2)-II gradually decomposes to a mixture of H(2)O and O(2), which completes at around 40 GPa for pure and 45 GPa for the 9.5% H(2)O(2). Upon pressure unloading, H(2)O(2) also decomposes to H(2)O and O(2) mixtures across the melts, occurring at 2.5 GPa for pure and 1.5 GPa for the 9.5% mixture. At H(2)O(2) concentrations below 20%, decomposed mixtures form oxygen hydrate clathrates at around 0.8 GPa--just after H(2)O melts. The compression data of pure H(2)O(2) and the stability data of the mixtures seem to indicate that the high-pressure decomposition is likely due to the pressure-induced densification, whereas the low-pressure decomposition is related to the heterogeneous nucleation process associated with H(2)O(2) melting.

Structural evolution of nanoscale metallic glasses during high-pressure torsion: A molecular dynamics analysis

NASA Astrophysics Data System (ADS)

Feng, S. D.; Jiao, W.; Jing, Q.; Qi, L.; Pan, S. P.; Li, G.; Ma, M. Z.; Wang, W. H.; Liu, R. P.

2016-11-01

Structural evolution in nanoscale Cu50Zr50 metallic glasses during high-pressure torsion is investigated using molecular dynamics simulations. Results show that the strong cooperation of shear transformations can be realized by high-pressure torsion in nanoscale Cu50Zr50 metallic glasses at room temperature. It is further shown that high-pressure torsion could prompt atoms to possess lower five-fold symmetries and higher potential energies, making them more likely to participate in shear transformations. Meanwhile, a higher torsion period leads to a greater degree of forced cooperative flow. And the pronounced forced cooperative flow at room temperature under high-pressure torsion permits the study of the shear transformation, its activation and characteristics, and its relationship to the deformations behaviors. This research not only provides an important platform for probing the atomic-level understanding of the fundamental mechanisms of high-pressure torsion in metallic glasses, but also leads to higher stresses and homogeneous flow near lower temperatures which is impossible previously.

P-T phase diagram and structural transformations of molten P2O5 under pressure

NASA Astrophysics Data System (ADS)

Brazhkin, V. V.; Katayama, Y.; Lyapin, A. G.; Saitoh, H.

2014-03-01

The P2O5 compound is an archetypical glass-forming oxide with a record high hygroscopicity, which makes its study extremely difficult. We present the in situ x-ray diffraction study of the pressure-temperature phase diagram of P2O5 and, particularly, of the liquid P2O5 structure under high pressure up to 10 GPa. Additionally, quenching from the melt has been used to extend the melting curve up to 15 GPa. We found that structural transformation in the liquid P2O5 under pressure is unique and includes three stages: first, the disappearance of the intermediate range order of the melt together with a slow increase in the average first-coordination number (P-O and O-P neighbors) up to 4 GPa; second, the "normal" compression almost without structural modification at higher pressures up to 8-9 GPa; and, finally, the abrupt change of the short-range order structure of the liquid with the jumplike increase at 9-10 GPa. The last stage correlates with the melting curve maximum (≈1250 °C) at ≈10 GPa and can be interpreted as a transformation to the liquid phase with entirely fivefold-coordinated phosphorus and twofold-coordinated oxygen atoms.

Guest-Induced Two-Way Structural Transformation in a Layered Metal-Organic Framework Thin Film.

PubMed

Haraguchi, Tomoyuki; Otsubo, Kazuya; Sakata, Osami; Fujiwara, Akihiko; Kitagawa, Hiroshi

2016-12-28

Fabrication of thin films made of metal-organic frameworks (MOFs) has been intensively pursued for practical applications that use the structural response of MOFs. However, to date, only physisorption-induced structural response has been studied in these films. Chemisorption can be expected to provide a remarkable structural response because of the formation of bonds between guest molecules and reactive metal sites in host MOFs. Here, we report that chemisorption-induced two-way structural transformation in a nanometer-sized MOF thin film. We prepared a two-dimensional layered-type MOF Fe[Pt(CN) 4 ] thin film using a step-by-step approach. Although the as-synthesized film showed poor crystallinity, the dehydrated form of this thin film had a highly oriented crystalline nature (Film-D) as confirmed by synchrotron X-ray diffraction (XRD). Surprisingly, under water and pyridine vapors, Film-D showed chemisorption-induced dynamic structural transformations to Fe(L) 2 [Pt(CN) 4 ] thin films [L = H 2 O (Film-H), pyridine (Film-P)], where water and pyridine coordinated to the open Fe 2+ site. Dynamic structural transformations were also confirmed by in situ XRD, sorption measurement, and infrared reflection absorption spectroscopy. This is the first report of chemisorption-induced dynamic structural response in a MOF thin film, and it provides useful insights, which would lead to future practical applications of MOFs utilizing chemisorption-induced structural responses.

Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles.

PubMed

Corsini, Niccolo R C; Zhang, Yuanpeng; Little, William R; Karatutlu, Ali; Ersoy, Osman; Haynes, Peter D; Molteni, Carla; Hine, Nicholas D M; Hernandez, Ignacio; Gonzalez, Jesus; Rodriguez, Fernando; Brazhkin, Vadim V; Sapelkin, Andrei

2015-11-11

Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge.

Structural phase transitions in Bi2Se3 under high pressure

PubMed Central

Yu, Zhenhai; Wang, Lin; Hu, Qingyang; Zhao, Jinggeng; Yan, Shuai; Yang, Ke; Sinogeikin, Stanislav; Gu, Genda; Mao, Ho-kwang

2015-01-01

Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi2Se3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi2Se3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculations favor the viewpoint that the I4/mmm phase Bi2Se3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi2Se3 from this work (two independent runs) are still Raman active up to ~35 GPa. It is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi2Se3 may explain why Bi2Se3 shows different structural behavior than isocompounds Bi2Te3 and Sb2Te3. PMID:26522818

Structural phase transitions in Bi 2Se 3 under high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Zhenhai; Gu, Genda; Wang, Lin

2015-11-02

Raman spectroscopy and angle dispersive X-ray diffraction (XRD) experiments of bismuth selenide (Bi 2Se 3) have been carried out to pressures of 35.6 and 81.2 GPa, respectively, to explore its pressure-induced phase transformation. The experiments indicate that a progressive structural evolution occurs from an ambient rhombohedra phase (Space group (SG): R-3m) to monoclinic phase (SG: C2/m) and eventually to a high pressure body-centered tetragonal phase (SG: I4/mmm). Evidenced by our XRD data up to 81.2 GPa, the Bi 2Se 3 crystallizes into body-centered tetragonal structures rather than the recently reported disordered body-centered cubic (BCC) phase. Furthermore, first principles theoretical calculationsmore » favor the viewpoint that the I4/mmm phase Bi 2Se 3 can be stabilized under high pressure (>30 GPa). Remarkably, the Raman spectra of Bi 2Se 3 from this work (two independent runs) are still Raman active up to ~35 GPa. Furthermore, it is worthy to note that the disordered BCC phase at 27.8 GPa is not observed here. The remarkable difference in atomic radii of Bi and Se in Bi 2Se 3 may explain why Bi 2Se 3 shows different structural behavior than isocompounds Bi 2Te 3 and Sb 2Te 3.« less

Theoretical analysis of the structural phase transformation from B3 to B1 in BeO under high pressure

NASA Astrophysics Data System (ADS)

Jain, Arvind; Verma, Saligram; Nagarch, R. K.; Shah, S.; Kaurav, Netram

2018-05-01

We have performed the phase transformation and elastic properties of BeO at high pressure by formulating effective interionic interaction potential. The elastic constants, including the long-range Coulomb and van der Waals (vdW) interactions and the short-range repulsive interaction of up to second-neighbor ions within the Hafemeister and Flygare approach, are derived. Assuming that both the ions are polarizable, we employed the Slater-Kirkwood variational method to estimate the vdW coefficients, a structural phase transition (Pt) from ZnS structure (B3) to NaCl structure (B1) at 108 GPa has been predicted for BeO. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the theoretical data. The variations of elastic constants with pressure follow a systematic trend identical to that observed in others compounds of ZnS type structure family.

New transformations between crystalline and amorphous ice

NASA Technical Reports Server (NTRS)

Hemley, R. J.; Chen, L. C.; Mao, H. K.

1989-01-01

High-pressure optical and spectroscopic techniques were used to obtain directly the ice I(h) - hda-ice transformation in a diamond-anvil cell, and the stability of the amorphous form is examined as functions of pressure and temperature. It is demonstrated that hda-ice transforms abruptly at 4 GPa and 77 K to a crystalline phase close in structure to orientationally disordered ice-VII and to a more highly ordered, ice-VIII-like structure at higher temperatures. This is the first time that an amorphous solid is observed to convert to a crystalline solid at low temperatures by compression alone. Phase transitions of this type may be relevant on icy planetary satellites, and there may also be implications for the high-pressure behavior of silica.

A 2 TiO 5 (A = Dy, Gd, Er, Yb) at High Pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Sulgiye; Rittman, Dylan R.; Tracy, Cameron L.

The structural evolution of lanthanide A2TiO5 (A = Dy, Gd, Yb, and Er) at high pressure is investigated using synchrotron X-ray diffraction. The effects of A-site cation size and of the initial structure are systematically examined by varying the composition of the isostructural lanthanide titanates, and the structure of dysprosium titanate polymorphs (orthorhombic, hexagonal and cubic), respectively. All samples undergo irreversible high pressure phase transformations, but with different onset pressures depending on the initial structure. While individual phase exhibits different phase transformation histories, all samples commonly experience a sluggish transformation to a defect cotunnite-like (Pnma) phase for a certain pressuremore » range. Orthorhombic Dy2TiO5 and Gd2TiO5 form P21am at pressures below 9 GPa and Pnma above 13 GPa. Pyrochlore-type Dy2TiO5 and Er2TiO5 as well as defect-fluorite-type Yb2TiO5 form Pnma at ~ 21 GPa, followed by Im-3m. Hexagonal Dy2TiO5 forms Pnma directly, although a small amount of remnants of hexagonal Dy2TiO5 is observed even at the highest pressure (~ 55 GPa) reached, indicating a kinetic limitations in the hexagonal Dy2TiO5 phase transformations at high pressure. Decompression of these materials leads to different metastable phases. Most interestingly, a high pressure cubic X-type phase (Im-3m) is confirmed using highresolution transmission electron microscopy on recovered pyrochlore-type Er2TiO5. The kinetic constraints on this metastable phase yield a mixture of both the X-type phase and amorphous domains upon pressure release. This is the first observation of an X-type phase for an A2BO5 composition at high pressure.« less

Contribution of High-Pressure-Induced Protein Modifications to the Microenvironment and Functional Properties of Rabbit Meat Sausages.

PubMed

Xue, Siwen; Yu, Xiaobo; Yang, Huijuan; Xu, Xinglian; Ma, Hanjun; Zhou, Guanghong

2017-06-01

Rabbit meat batters were subjected to high pressure (HP, 100 to 300 MPa for 3, 9, or 15 min) to elucidate their effects on proteins structures, the microenvironment, and the resulting functionalities of the subsequently heated products. To determine these effects, we investigated structural and microenvironmental changes using Raman spectroscopy and also expressible moisture content, textural characteristics, and dynamic rheological properties of batters during heating (20 to 80 °C). Untreated samples served as controls. Analysis of specific Raman spectral regions demonstrated that applications of HP to rabbit meat batters tended to induce the transformation of the all-gauche S-S conformation to gauche-gauche-trans in the batter system. HP treatment higher than 100 MPa for 9 min promoted secondary structural rearrangements, and molecular polarity enhancement in the proteins prior to cooking. Also, increases of O-H stretching intensities of rabbit meat sausages were obtained by HP treatment, denoting the strengthening of water-holding capacity. These HP-induced alterations resulted in improved texture and, perhaps, improved juiciness of rabbit meat sausages (P < 0.05), however they had relatively poorer rheological properties than the controls. Nevertheless, HP treatment, especially 200 MPa for 9 or 15 min, was an effective technique for improving the functionalities of gel-type products through modification of meat proteins. © 2017 Institute of Food Technologists®.

Transforming growth factor-β inhibits myocardial PPARγ expression in pressure overload-induced cardiac fibrosis and remodeling in mice

PubMed Central

Gong, Kaizheng; Chen, Yiu-Fai; Li, Peng; Lucas, Jason A.; Hage, Fadi G.; Yang, Qinglin; Nozell, Susan E.; Oparil, Suzanne; Xing, Dongqi

2012-01-01

Objectives Pharmacological activation of peroxisome proliferator-activated receptor gamma (PPARγ) has been shown to attenuate pressure overload-induced cardiac fibrosis, suggesting that PPARγ has an antifibrotic effect. This study tested the hypothesis that there is a functional interaction between transforming growth factor-β (TGF-β) signaling and endogenous PPARγ expression in cardiac fibroblasts and pressure overloaded heart. Methods and results We observed that, in response to pressure overload induced by transverse aortic constriction, left-ventricular PPARγ protein levels were decreased in wild-type mice, but increased in mice with an inducible overexpression of dominant negative mutation of the human TGF-β type II receptor (DnTGFβRII), in which TGF-β signaling is blocked. In isolated mouse cardiac fibroblasts, we demonstrated that TGF-β1 treatment decreased steady state PPARγ mRNA (−34%) and protein (−52%) levels, as well as PPARγ transcriptional activity (−53%). Chromatin immunoprecipitation analysis showed that TGF-β1 treatment increased binding of Smad2/3, Smad4 and histone deacetylase 1, and decreased binding of acetylated histone 3 to the PPARγ promoter in cardiac fibroblasts. Both pharmacological activation and overexpression of PPARγ significantly inhibited TGF-β1-induced extracellular matrix molecule expression in isolated cardiac fibroblasts, whereas treatment with the PPARγ agonist rosiglitazone inhibited, and treatment with the PPARγ antagonist T0070907 exacerbated chronic pressure overload-induced cardiac fibrosis and remodeling in wild-type mice in vivo. Conclusion These data provide strong evidence that TGF-β1 directly suppresses PPARγ expression in cardiac fibroblasts via a transcriptional mechanism and suggest that the down-regulation of endogenous PPARγ expression by TGF-β may be involved in pressure overload-induced cardiac fibrosis. PMID:21836474

Structure evolution upon chemical and physical pressure in (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiittanen, T.; Karppinen, M., E-mail: maarit.karppinen@aalto.fi

Here we demonstrate the gradual structural transformation from the monoclinic I2/m to tetragonal I4/m, cubic Fm-3m and hexagonal P6{sub 3}/mmc structure upon the isovalent larger-for-smaller A-site cation substitution in the B-site ordered double-perovskite system (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6}. This is the same transformation sequence previously observed up to Fm-3m upon heating the parent Sr{sub 2}FeSbO{sub 6} phase to high temperatures. High-pressure treatment, on the other hand, transforms the hexagonal P6{sub 3}/mmc structure of the other end member Ba{sub 2}FeSbO{sub 6} back to the cubic Fm-3m structure. Hence we may conclude that chemical pressure, physical pressure and decreasing temperature allmore » work towards the same direction in the (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6} system. Also shown is that with increasing Ba-for-Sr substitution level, i.e. with decreasing chemical pressure effect, the degree-of-order among the B-site cations, Fe and Sb, decreases. - Graphical abstract: In the (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6} double-perovskite system the gradual structural transformation from the monoclinic I2/m to tetragonal I4/m, cubic Fm-3m and hexagonal P6{sub 3}/mmc structure is seen upon the isovalent larger-for-smaller A-site cation substitution. High-pressure treatment under 4 GPa extends stability of the cubic Fm-3m structure within a wider substitution range of x. - Highlights: • Gradual structural transitions upon A-cation substitution in (Sr{sub 1−x}Ba{sub x}){sub 2}FeSbO{sub 6.} • With increasing x structure changes from I2/m to I4/m, Fm-3m and P6{sub 3}/mmc. • Degree of B-site order decreases with increasing x and A-site cation radius. • High-pressure treatment extends cubic Fm-3m phase stability for wider x range. • High-pressure treatment affects bond lengths mostly around the A-cation.« less

Enhanced structural stability and photo responsiveness of CH 3NH 3SnI 3 perovskite via pressure-induced amorphization and recrystallization

DOE PAGES

Lu, Xujie; Wang, Yonggang; Stoumpos, Constantinos C.; ...

2016-10-01

An organic–inorganic halide CH 3NH 3SnI 3 perovskite with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. In conclusion, the mechanism underlying the enhanced properties is shown to be associated with the pressure-induced structural modification.

Crystallographic and magnetic structure of HAVAR under high-pressure using diamond anvil cell (DAC)

NASA Astrophysics Data System (ADS)

Halevy, Itzhak; Haroush, Shlomo; Eisen, Yosef; Silberman, Ido; Moreno, Dany; Hen, Amir; Winterrose, Mike L.; Ghose, Sanjit; Chen, Zhiqiang

2010-04-01

Annealed (H1) and cold-rolled (H2) HAVAR has been studied using high-pressure synchrotron X-ray diffraction. A structural phase transformation was discovered at ˜13 GPa at ambient temperature, transforming from m - 3 m (S.G. 225) to P 63/m m c (S.G. 194) symmetry. The transition was not reversible on pressure release. The low-pressure cubic phase was found to be more compressible than the high-pressure hexagonal phase. Conventional Mössbauer and NFS shows that the HAVAR is not magnetic at room temperature and no splitting is observed. The SQUID indicates a huge difference in the temperature dependence of the magnetic susceptibility between the cold Rolled HAVAR compared to the annealed HAVAR.

Molecular dynamics simulation of shock-wave loading of copper and titanium

NASA Astrophysics Data System (ADS)

Bolesta, A. V.; Fomin, V. M.

2017-10-01

At extreme pressures and temperatures common materials form new dense phases with compacted atomic arrangements. By classical molecular dynamics simulation we observe that FCC copper undergo phase transformation to BCC structure. The transition occurs under shock wave loading at the pressures above 80 GPa and corresponding temperatures above 2000 K. We calculate phase diagram, show that at these pressures and low temperature FCC phase of copper is still stable and discuss the thermodynamic reason for phase transformation at high temperature shock wave regime. Titanium forms new hexagonal phase at high pressure as well. We calculate the structure of shock wave in titanium and observe that shock front splits in three parts: elastic, plastic and phase transformation. The possibility of using a phase transition behind a shock wave with further unloading for designing nanocrystalline materials with a reduced grain size is also shown.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Kuo; Zheng, Haiyan; Hattori, Takanori

By providing a new route to synthesize inorganic/organic conductors with tunable composition and properties, pressure-induced polymerization of charged triple-bond monomers like acetylide and cyanide could lead to formation of a conductive metal–carbon network composite. The industry application of this promising synthetic method is mainly limited by the reaction pressure needed, which is often too high to be reached for gram amounts of sample. Here we successfully synthesized highly conductive Li 3Fe(CN) 6 at maximum pressure around 5 GPa and used in situ diagnostic tools to follow the structural and functional transformations of the sample, including in situ X-ray and neutronmore » diffraction and Raman and impedance spectroscopy, along with the neutron pair distribution function measurement on the recovered sample. The cyanide anions start to react around 1 GPa and bond to each other irreversibly at around 5 GPa, which are the lowest reaction pressures in all known metal cyanides and within the technologically achievable pressure range for industrial production. Moreover, the conductivity of the polymer is above 10 –3 S·cm –1, which reaches the range of conductive polymers. Our investigation suggests that the pressure-induced polymerization route is practicable for synthesizing some types of functional conductive materials for industrial use, and further research like doping and heating can hence be motivated to synthesize novel materials under lower pressure and with better performances.« less

Size-dependent pressure-induced amorphization: a thermodynamic panorama.

PubMed

Machon, Denis; Mélinon, Patrice

2015-01-14

Below a critical particle size, some pressurized compounds (e.g. TiO2, Y2O3, PbTe) undergo a crystal-to-amorphous transformation instead of a polymorphic transition. This effect reflects the greater propensity of nanomaterials for amorphization. In this work, a panorama of thermodynamic interpretations is given: first, a descriptive analysis based on the energy landscape concept gives a general comprehension of the balance between thermodynamics and kinetics to obtain an amorphous state. Then, a formal approach based on Gibbs energy to describe the thermodynamics and phase transitions in nanoparticles gives a basic explanation of size-dependent pressure-induced amorphization. The features of this transformation (amorphization occurs at pressures lower than the polymorphic transition pressure!) and the nanostructuration can be explained in an elaborated model based on the Ginzburg-Landau theory of phase transition and on percolation theory. It is shown that the crossover between polymorphic transition and amorphization is highly dependent on the defect density and interfacial energy, i.e., on the synthesis process. Their behavior at high pressure is a quality control test for the nanoparticles.

Adiabatic Shear - An Annotated Bibliography

DTIC Science & Technology

1974-07-01

A. Deformation Hardening/Softening B. Cryogenic Deformation C. Ductaity D. Plasticity !•-. Fracture F, Structure and Phase Transformation ...Structural changes and phase transformations are also noted. The Hiidden release of elastic stored energy, the high hydrostatic pressure, and the...crackintr increased with increasing pellet velocity. Slip without transformation was oliservcd in both the aluminum alloy and stainless steel plates

Kinetically Controlled Two-Step Amorphization and Amorphous-Amorphous Transition in Ice.

PubMed

Lin, Chuanlong; Yong, Xue; Tse, John S; Smith, Jesse S; Sinogeikin, Stanislav V; Kenney-Benson, Curtis; Shen, Guoyin

2017-09-29

We report the results of in situ structural characterization of the amorphization of crystalline ice Ih under compression and the relaxation of high-density amorphous (HDA) ice under decompression at temperatures between 96 and 160 K by synchrotron x-ray diffraction. The results show that ice Ih transforms to an intermediate crystalline phase at 100 K prior to complete amorphization, which is supported by molecular dynamics calculations. The phase transition pathways show clear temperature dependence: direct amorphization without an intermediate phase is observed at 133 K, while at 145 K a direct Ih-to-IX transformation is observed; decompression of HDA shows a transition to low-density amorphous ice at 96 K and ∼1  Pa, to ice Ic at 135 K and to ice IX at 145 K. These observations show that the amorphization of compressed ice Ih and the recrystallization of decompressed HDA are strongly dependent on temperature and controlled by kinetic barriers. Pressure-induced amorphous ice is an intermediate state in the phase transition from the connected H-bond water network in low pressure ices to the independent and interpenetrating H-bond network of high-pressure ices.

Kinetically Controlled Two-Step Amorphization and Amorphous-Amorphous Transition in Ice

NASA Astrophysics Data System (ADS)

Lin, Chuanlong; Yong, Xue; Tse, John S.; Smith, Jesse S.; Sinogeikin, Stanislav V.; Kenney-Benson, Curtis; Shen, Guoyin

2017-09-01

We report the results of in situ structural characterization of the amorphization of crystalline ice Ih under compression and the relaxation of high-density amorphous (HDA) ice under decompression at temperatures between 96 and 160 K by synchrotron x-ray diffraction. The results show that ice Ih transforms to an intermediate crystalline phase at 100 K prior to complete amorphization, which is supported by molecular dynamics calculations. The phase transition pathways show clear temperature dependence: direct amorphization without an intermediate phase is observed at 133 K, while at 145 K a direct Ih-to-IX transformation is observed; decompression of HDA shows a transition to low-density amorphous ice at 96 K and ˜1 Pa , to ice Ic at 135 K and to ice IX at 145 K. These observations show that the amorphization of compressed ice Ih and the recrystallization of decompressed HDA are strongly dependent on temperature and controlled by kinetic barriers. Pressure-induced amorphous ice is an intermediate state in the phase transition from the connected H-bond water network in low pressure ices to the independent and interpenetrating H-bond network of high-pressure ices.

Kinetically Controlled Two-Step Amorphization and Amorphous-Amorphous Transition in Ice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Chuanlong; Yong, Xue; Tse, John S.

We report the results of in situ structural characterization of the amorphization of crystalline ice Ih under compression and the relaxation of high-density amorphous (HDA) ice under decompression at temperatures between 96 and 160 K by synchrotron x-ray diffraction. The results show that ice Ih transforms to an intermediate crystalline phase at 100 K prior to complete amorphization, which is supported by molecular dynamics calculations. The phase transition pathways show clear temperature dependence: direct amorphization without an intermediate phase is observed at 133 K, while at 145 K a direct Ih-to-IX transformation is observed; decompression of HDA shows a transitionmore » to low-density amorphous ice at 96 K and ~ 1 Pa , to ice Ic at 135 K and to ice IX at 145 K. These observations show that the amorphization of compressed ice Ih and the recrystallization of decompressed HDA are strongly dependent on temperature and controlled by kinetic barriers. Pressure-induced amorphous ice is an intermediate state in the phase transition from the connected H-bond water network in low pressure ices to the independent and interpenetrating H-bond network of high-pressure ices.« less

Structural phase transitions in GaAs to 108 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weir, S.T.; Vohra, Y.K.; Vanderborgh, C.A.

1989-01-15

The III-V compound GaAs was studied using energy-dispersive x-ray diffraction with a synchro- tron source up to a pressure of 108 GPa. When the pressure was increased to 16.6 GPa, the GaAs sample transformed from the zinc-blende structure to an orthorhombic structure (GaAs(II)), space group Pmm2, consisting of a primitive orthorhombic lattice with a basis of (0,0,0) and (0,(1/2,..cap alpha..), where ..cap alpha.. = 0.35. Upon a further increase of pressure to 24 +- 1 GPa, GaAs(II) transformed to another orthorhombic structure (GaAs(III)), space group Imm2, consisting of a body-centered orthorhombic lattice with a basis of (0,0,0) and (0, (1/2,..delta..),more » where ..delta.. is 0.425 at 28.1 GPa. With increasing pressure, ..delta.. approached (1/2 and the GaAs(III) structure gradually assumed the symmetry of the simple hexagonal structure. The transition to the simple hexagonal structure (GaAs(IV)) was completed in the vicinity of 60--80 GPa. The structure remains simple hexagonal up to at least 108 GPa, the highest pressure reached in this study.« less

Modeling normal shock velocity curvature relations for heterogeneous explosives

NASA Astrophysics Data System (ADS)

Yoo, Choong-Shik; Tomasino, Dane; Smith, Jesse; Kim, Minseob

2017-01-01

Many simple molecules such as N2 and CO2 have the potential to form extended "polymeric" solids under extreme conditions, which can store a large sum of chemical energy in its three-dimensional network structures made of strong covalent bonds. Diatomic nitrogen is particularly of interest because of the uniquely large energy difference between the single (160 kJ/mol) and triple (950 kJ/mol) bonds. As such, the transformation of singly bonded polymeric nitrogen back to triply bonded diatomic nitrogen molecules can release large energy ( 33 kJ/cm3 - three times that of HMX) without any negative environmental impact. Therefore, the goal of the present study has been to investigate the transformation of nitrogen and nitrogen-rich compounds to new singly bonded nitrogen-rich solids at high pressures and temperatures, using heated diamond anvil cells, Raman spectroscopy, and third-generation synchrotron x-ray diffraction. Recently, we have found a new form of singly bonded layered polymeric nitrogen (LP-N), synthesized in the stability pressure-temperature field higher than that of cg-N. This new phase is characterized by a 2D layered structure similar to the predicted Pba2 and two colossal Raman bands, arising from two groups of highly polarized nitrogen atoms. This result also provides a new constraint for the nitrogen phase diagram, highlighting an unusual symmetry lowering 3D cg- to 2D LP-N transition and thereby the enhanced electrostatic contribution to the stabilization of this densely packed LP-N. In this paper, we will review this finding of LP-N, update the phase diagram of nitrogen, and offer a chemistry view of pressure-induced transformations in dense molecular solids.

Swift heavy ion induced modifications in optical and electrical properties of cadmium selenide thin films

NASA Astrophysics Data System (ADS)

Choudhary, Ritika; Chauhan, Rishi Pal

2017-07-01

The modification in various properties of thin films using high energetic ion beam is an exciting area of basic and applied research in semiconductors. In the present investigations, cadmium selenide (CdSe) thin films were deposited on ITO substrate using electrodeposition technique. To study the swift heavy ion (SHI) induced effects, the deposited thin films were irradiated with 120 MeV heavy Ag9+ ions using pelletron accelerator facility at IUAC, New Delhi, India. Structural phase transformation in CdSe thin film from metastable cubic phase to stable hexagonal phase was observed after irradiation leading to decrease in the band gap from 2.47 eV to 2.12 eV. The phase transformation was analyzed through X-ray diffraction patterns. During SHI irradiation, Generation of high temperature and pressure by thermal spike along the trajectory of incident ions in the thin films might be responsible for modification in the properties of thin films.[Figure not available: see fulltext.

Suppression of superconductivity and structural phase transitions under pressure in tetragonal FeS

DOE PAGES

Lai, Xiaofang; Liu, Ying; Lu, Xujie; ...

2016-08-08

Pressure is a powerful tool to study iron-based superconductors. Here, we report systematic high-pressure transport and structural characterizations of the newly discovered superconductor FeS. It is found that superconductor FeS (tetragonal) partly transforms to a hexagonal structure at 0.4 GPa, and then completely transforms to an orthorhombic phase at 7.4 GPa and finally to a monoclinic phase above 9.0 GPa. The superconducting transition temperature of tetragonal FeS was gradually depressed by pressure, different from the case in tetragonal FeSe. With pressure increasing, the S-Fe-S angles only slightly change but the anion height deviates farther from 1.38 Å. This change ofmore » anion height, together with the structural instability under pressure, should be closely related to the suppression of superconductivity. We also observed an anomalous metal-semiconductor transition at 6.0 GPa and an unusual increased resistance with further compression above 9.6 GPa. The former can be ascribed to the tetragonal-orthorhombic structural phase transition, and the latter to the electronic structure changes of the high-pressure monoclinic phase. Lastly, a phase diagram of tetragonal FeS as functions of pressure and temperature was mapped out for the first time, which will shed new light on understanding of the structure and physics of the superconducting FeS.« less

Phase Stability and Transformations in Vanadium Oxide Nanocrystals

NASA Astrophysics Data System (ADS)

Bergerud, Amy Jo

Vanadium oxides are both fascinating and complex, due in part to the many compounds and phases that can be stabilized as well as the phase transformations which occur between them. The metal to insulator transitions (MITs) that take place in vanadium oxides are particularly interesting for both fundamental and applied study as they can be induced by a variety of stimuli ( i.e., temperature, pressure, doping) and utilized in many applications (i.e., smart windows, sensors, phase change memory). Nanocrystals also tend to demonstrate interesting phase behavior, due in part to the enhanced influence of surface energy on material thermodynamics. Vanadium oxide nanocrystals are thus expected to demonstrate very interesting properties in regard to phase stability and phase transformations, although synthesizing vanadium oxides in nanocrystal form remains a challenge. Vanadium sesquioxide (V2O3) is an example of a material that undergoes a MIT. For decades, the low temperature monoclinic phase and high temperature corundum phase were the only known crystal structures of V2O3. However, in 2011, a new metastable polymorph of V2O3 was reported with a cubic, bixbyite crystal structure. In Chapter 2, a colloidal route to bixbyite V2O 3 nanocrystals is presented. In addition to being one of the first reported observations of the bixbyite phase in V2O3, it is also one of the first successful colloidal syntheses of any of the vanadium oxides. The nanocrystals possess a flower-like morphology, the size and shape of which are dependent on synthesis time and temperature, respectively. An aminolysis reaction mechanism is determined from Fourier transform infrared spectroscopy data and the bixbyite crystal structure is confirmed by Rietveld refinement of X-ray diffraction (XRD) data. Phase stability is assessed in both air and inert environments, confirming the metastable nature of the material. Upon heating in an inert atmosphere above 700°C, the nanocrystals irreversibly transform to the bulk stable corundum phase of V2O3 with concurrent particle coarsening. This, in combination with the enhanced stability of the nanocrystals over bulk, suggests that the bixbyite phase may be stabilized due to surface energy effects, a well-known phenomenon in nanocrystal research. In Chapter 3, the reversible incorporation of oxygen in bixbyite V 2O3 is reported, which can be controlled by varying temperature and oxygen partial pressure. Based on XRD and thermogravimetric analysis, it is found that oxygen occupies interstitial sites in the bixbyite lattice. Two oxygen atoms per unit cell can be incorporated rapidly and with minimal changes to the structure while the addition of three or more oxygen atoms destabilizes the structure, resulting in a phase change that can be reversed upon oxygen removal. Density functional theory (DFT) supports the reversible occupation of interstitial sites in bixbyite by oxygen and the 1.1 eV barrier to oxygen diffusion predicted by DFT matches the activation energy of the oxidation process derived from observations by in situ XRD. The observed rapid oxidation kinetics are thus facilitated by short diffusion paths through the bixbyite nanocrystals. Due to the exceptionally low temperatures of oxidation and reduction, this material, made from earth-abundant atoms, is proposed for use in oxygen storage applications, where oxygen is reversibly stored and released. Further oxidation of bixbyite V2O3 under controlled oxygen partial pressure can lead to the formation of nanocrystalline vanadium dioxide (VO2), a material that is studied for its MIT that occurs at 68 C in the bulk. This transformation is accompanied by a change in crystal structure, from monoclinic to rutile phase, and a change in optical properties, from infrared transparent to infrared blocking. Because of this, VO2 is promising for thermochromic smart window applications, where optical properties vary with temperature. Recently, alternative stimuli have been utilized to trigger MITs in VO2, including electrochemical gating. Rather than inducing the expected monoclinic to rutile phase transition as originally proposed, electrochemical gating of the insulating phase was recently shown to induce oxygen vacancy formation in VO2, thereby inducing metallization, while the characteristic V-V dimerization of the monoclinic phase was retained. In Chapter 4, the preparation and electrochemical reduction of VO2 nanocrystal films is presented. The nanocrystalline morphology allows for the study of transformations under conditions that enhance the gating effect by creating a large VO2-electrolyte interfacial area and by reducing the path length for diffusion. The resulting transitions are observed optically, from insulator to metal to insulator and back, with in situ visible-near infrared spectroelectrochemistry and correlated with structural changes monitored by Raman and X-ray absorption spectroscopies. The never-before-seen transition to an insulating phase under progressive electrochemical reduction is attributed to an oxygen defect induced phase transition to a new phase. This is likely enabled by the nanocrystalline nature of the sample, which may enhance the kinetics of oxygen diffusion, support a higher degree of lattice expansion-induced strain, or simply alter the thermodynamics of the system.

Enhanced Structural Stability and Photo Responsiveness of CH3 NH3 SnI3 Perovskite via Pressure-Induced Amorphization and Recrystallization.

PubMed

Lü, Xujie; Wang, Yonggang; Stoumpos, Constantinos C; Hu, Qingyang; Guo, Xiaofeng; Chen, Haijie; Yang, Liuxiang; Smith, Jesse S; Yang, Wenge; Zhao, Yusheng; Xu, Hongwu; Kanatzidis, Mercouri G; Jia, Quanxi

2016-10-01

An organic-inorganic halide CH 3 NH 3 SnI 3 perovskite with significantly improved structural stability is obtained via pressure-induced amorphization and recrystallization. In situ high-pressure resistance measurements reveal an increased electrical conductivity by 300% in the pressure-treated perovskite. Photocurrent measurements also reveal a substantial enhancement in visible-light responsiveness. The mechanism underlying the enhanced properties is shown to be associated with the pressure-induced structural modification. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Changes in the myosin secondary structure and shrimp surimi gel strength induced by dense phase carbon dioxide.

PubMed

Guo, Minghui; Liu, Shucheng; Ismail, Marliya; Farid, Mohammed M; Ji, Hongwu; Mao, Weijie; Gao, Jing; Li, Chengyong

2017-07-15

Dense phase carbon dioxide (DPCD) could induce protein conformation changes. Myosin and shrimp surimi from Litopenaeus vannamei were treated with DPCD at 5-25MPa and 40-60°C for 20min. Myosin secondary structure was investigated by circular dichroism and shrimp surimi gel strength was determined using textural analysis to develop correlations between them. DPCD had a greater effect on secondary structure and gel strength than heating. With increasing pressure and temperature, the α-helix content of DPCD-treated myosin decreased, while the β-sheet, β-turn and random coil contents increased, and the shrimp surimi gel strength increased. The α-helix content was negatively correlated with gel strength, while the β-sheet, β-turn and random coil contents were positively correlated with gel strength. Therefore, when DPCD induced myosin to form a gel, the α-helix of myosin was unfolded and gradually converted to a β-sheet. Such transformations led to protein-protein interactions and cross-linking, which formed a three-dimensional network to enhance the gel strength. Copyright © 2017 Elsevier Ltd. All rights reserved.

High pressure phase-transformation induced texture evolution and strengthening in zirconium metal: Experiment and modeling

DOE PAGES

Yu, Xiaohui; Zhang, Ruifeng; Weldon, David; ...

2015-07-28

We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can bemore » attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation.« less

Probing the electronic and local structural changes across the pressure-induced insulator-to-metal transition in VO2

NASA Astrophysics Data System (ADS)

Marini, C.; Bendele, M.; Joseph, B.; Kantor, I.; Mitrano, M.; Mathon, O.; Baldini, M.; Malavasi, L.; Pascarelli, S.; Postorino, P.

2014-11-01

Local and electronic structures of vanadium in \\text{VO}2 are studied across the high-pressure insulator-to-metal (IMT) transition using V K-edge x-ray absorption spectroscopy. Unlike the temperature-induced IMT, pressure-induced metallization leads to only subtle changes in the V K-edge prepeak structure, indicating a different mechanism involving smaller electronic spectral weight transfer close to the chemical potential. Intriguingly, upon application of the hydrostatic pressure, the electronic structure begins to show substantial changes well before the occurrence of the IMT and the associated structural transition to an anisotropic compression of the monoclinic metallic phase.

Hydraulic pressure inducing renal tubular epithelial-myofibroblast transdifferentiation in vitro.

PubMed

Li, Fei-yan; Xie, Xi-sheng; Fan, Jun-ming; Li, Zi; Wu, Jiang; Zheng, Rong

2009-09-01

The effects of hydraulic pressure on renal tubular epithelial-myofibroblast transdifferentiation (TEMT) were investigated. We applied hydraulic pressure (50 cm H2O) to normal rat kidney tubular epithelial cells (NRK52E) for different durations. Furthermore, different pressure magnitudes were applied to cells. The morphology, cytoskeleton, and expression of myofibroblastic marker protein and transforming growth factor-beta1 (TGF-beta1) of NRK52E cells were examined. Disorganized actin filaments and formation of curling clusters in actin were seen in the cytoplasm of pressurized cells. We verified that de novo expression of alpha-smooth muscle actin induced by pressure, which indicated TEMT, was dependent on both the magnitude and duration of pressure. TGF-beta1 expression was significantly upregulated under certain conditions, which implies that the induction of TEMT by hydraulic pressure is related with TGF-beta1. We illustrate for the first time that hydraulic pressure can induce TEMT in a pressure magnitude- and duration-dependent manner, and that this TEMT is accompanied by TGF-beta1 secretion.

Negative-pressure-induced enhancement in a freestanding ferroelectric

NASA Astrophysics Data System (ADS)

Wang, Jin; Wylie-van Eerd, Ben; Sluka, Tomas; Sandu, Cosmin; Cantoni, Marco; Wei, Xian-Kui; Kvasov, Alexander; McGilly, Leo John; Gemeiner, Pascale; Dkhil, Brahim; Tagantsev, Alexander; Trodahl, Joe; Setter, Nava

2015-10-01

Ferroelectrics are widespread in technology, being used in electronics and communications, medical diagnostics and industrial automation. However, extension of their operational temperature range and useful properties is desired. Recent developments have exploited ultrathin epitaxial films on lattice-mismatched substrates, imposing tensile or compressive biaxial strain, to enhance ferroelectric properties. Much larger hydrostatic compression can be achieved by diamond anvil cells, but hydrostatic tensile stress is regarded as unachievable. Theory and ab initio treatments predict enhanced properties for perovskite ferroelectrics under hydrostatic tensile stress. Here we report negative-pressure-driven enhancement of the tetragonality, Curie temperature and spontaneous polarization in freestanding PbTiO3 nanowires, driven by stress that develops during transformation of the material from a lower-density crystal structure to the perovskite phase. This study suggests a simple route to obtain negative pressure in other materials, potentially extending their exploitable properties beyond their present levels.

Pressure-magnetic field induced phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rama Rao, N. V., E-mail: nvrrao@dmrl.drdo.in; Manivel Raja, M.; Pandian, S.

2014-12-14

The effect of hydrostatic pressure and magnetic field on the magnetic properties and phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy was investigated. Pressure (P)-magnetic field (H)-temperature (T) phase diagram has been constructed from experimental results. In the P–T contour of the phase diagram, the slope of the austenite-martensite phase boundary line appears positive (dT/dP > 0), while it appears negative (dT/dH < 0) in the H–T contour. The results revealed that pressure and magnetic field have opposite effect on phase stabilization. The combined effect of pressure and magnetic field on martensitic transition has led to two important findings: (i) pressure dependent shiftmore » of austenite start temperature (A{sub s}) is higher when larger field is applied, and (ii) field dependent shift of A{sub s} is lowered when a higher pressure is applied. The pressure and magnetic field dependent shift observed in the martensitic transformation has been explained on the basis of thermodynamic calculations. Curie temperature of the phases was found to increase with pressure at a rate of 0.6 K/kbar.« less

Shock metamorphism of Elephant Moraine A79001: Implications for olivine-ringwoodite transformation and the complex thermal history of heavily shocked Martian meteorites

NASA Astrophysics Data System (ADS)

Walton, Erin L.

2013-04-01

Lithology A of Martian meteorite Elephant Moraine (EET) A79001 contains fragments entrained within a 100 μm-thick shear-induced shock vein. These fragments, the shock vein matrix and walls of olivine along the vein, as well as shock deformation and transformation in rock-forming minerals in the bulk rock, were investigated using scanning electron microscopy, the electron microprobe and Raman spectroscopy. The presence of ringwoodite, the spinel-structured high-pressure (Mg,Fe)2SiO4 polymorph, has been confirmed in EETA79001 for the first time. Ringwoodite occurs within and around the shock vein, exhibiting granular and lamellar textures. In both textures ringwoodite consists of ˜500 nm size distinct grains. Ringwoodite lamellae are 115 nm to 1.3 μm wide. Planar fractures in olivine provided sites for heterogeneous nucleation of ringwoodite. Analyses performed on the largest grains (⩾1 μm) show that ringwoodite is consistently higher in iron (Fa27.4-32.4) relative to surrounding olivine (Fa25.1-267.7), implying that there was Fe-Mg exchange during their transformation, and therefore their growth was diffusion-controlled. In the shock environment, diffusion takes place dynamically, i.e., with concurrent deformation and grain size reduction. This results in enhanced diffusion rates (⩾10-8 m2/s) over nm - μm distances. Shock deformation in host rock minerals including strong mosaicism, pervasive fracturing, polysynthetic twinning (pyroxene only), extensive shock melting, local transformation of olivine to ringwoodite, and complete transformation of plagioclase to maskelynite in the bulk rock, indicate that EETA79001 was strongly shocked. The short shock duration (0.01 s) combined with a complex thermal history, resulted in crystallization of the 100 μm thick shock vein in EETA79001 during the pressure release, and partial back-transformation of ringwoodite to olivine. Based on the pressure stabilities of clinopyroxene + ringwoodite, crystallization at the shock vein margin began at ˜18 GPa. Olivine and clinopyroxene crystallized at <14 GPa closer to the shock vein center. These represent a minimum limit to the shock pressure loading experienced by EETA79001.

Pressure-Induced Phase Transitions in the Cd-Yb Periodic Approximant to a Quasicrystal

NASA Astrophysics Data System (ADS)

Watanuki, Tetsu; Machida, Akihiko; Ikeda, Tomohiro; Aoki, Katsutoshi; Kaneko, Hiroshi; Shobu, Takahisa; Sato, Taku J.; Tsai, An Pang

2006-03-01

The phase study of a Cd-Yb 1/1 approximant crystal over a wide pressure and temperature range is crucial for the comparison study between periodic and quasiperiodic crystals. The Cd4 tetrahedra, the most inner part of the atomic clusters, exhibited various structural ordering in the orientation sensitive to pressure and temperature. Five ordered phases appeared in a P-T span up to 5.2 GPa and down to 10 K. The propagation direction of ordering alternated from [110] to ⟨111⟩ at about 1.0 GPa and again to [110] at 3.5 4.3 GPa. The primarily ordered phases that appeared by cooling to 210 250 K between 1.0 5.2 GPa further transformed to finely ordered ones at 120 155 K. Besides the original short-range type interaction, a long-range type interaction was likely developed under pressure to lead to the primary ordering of Cd4 tetrahedra. Coexistence of these interactions is responsible for the complicated phase behavior.

Magnetic properties of solid oxygen under pressure (Review Article)

NASA Astrophysics Data System (ADS)

Freiman, Yu. A.

2015-11-01

Solid oxygen is a unique crystal combining properties of a simple molecular solid and a magnet. Unlike ordinary magnets, the exchange interaction in solid oxygen acts on a background of weak Van der Waals forces, providing a significant part of the total lattice energy. Therefore, the magnetic and lattice properties of solid oxygen are very closely related. This manifests itself in a very rich phase diagram and numerous anomalies of thermal, magnetic and optical properties. Low-temperature low-pressure α-O2 is a two-sublattice collinear Neel antiferromagnet. At a pressure of ˜6 GPa, α-O2 is transformed into δ-O2, in which three different magnetic structures are realized upon increasing temperature. At ˜8 GPa δ-O2 is transformed into ɛ-O2. In this transition, O2 molecules combine into four-molecule clusters (O2)4. This transformation is accompanied by a magnetic collapse. This review describes the evolution of the magnetic structure with increasing pressure, and analyzes the causes behind this behavior.

Shock-induced deformation of Shergottites: Shock-pressures and perturbations of magmatic ages on Mars

NASA Astrophysics Data System (ADS)

El Goresy, Ahmed; Gillet, Ph.; Miyahara, M.; Ohtani, E.; Ozawa, S.; Beck, P.; Montagnac, G.

2013-01-01

Shergottites and Chassignites practiced major deformation effects whose nature, magnitude and relevance were controversially evaluated and disputatively debated. Our studies of many shocked shergottites present, contrary to numerous previous reports, ample evidence for pervasive shock-induced melting amounting of at least 23 vol.% of the shergottite consisting of maskelynite and pyrrhotite, partial melting of pyroxene, titanomagnetite, ilmenite and finding of several high-pressure polymorphs and pressure-induced dissociation reactions. Our results cast considerable doubt on using the refractive index (RI) or cathodoluminescence (CL) spectra of maskelynite, in estimating the magnitudes of peak-shock pressure in both shergottites and ordinary chondrites. RI of maskelynite was set after quenching of the feldspar liquid before decompression to maskelynite glass followed by glass relaxation after decompression at the closure temperature of relaxation. The RI procedure widely practiced in the past 38 years revealed unrealistic very high-pressure estimates discrepant with the high-pressure mineral inventory in shocked shergottites and ordinary chondrites and with results obtained by robust laboratory static experiments. Shergottites contain the silica high-pressure polymorphs: the scrutinyite-structured polymorph seifertite, a monoclinic ultra dense polymorph of silica with ZrO2-structure, stishovite, a dense liquidus assemblage consisting of stishovite + Na-hexa-aluminosilicate (Na-CAS) and both K-lingunite and Ca-lingunite. Applying individual high-pressure silica polymorphs alone like stishovite, to estimate the equilibrium shock pressure, is inadequate due to the considerable shift of their nominal upper pressure bounds intrinsically induced by spatially variable absorptions of minor oxides like Al2O3, Na2O, FeO, MgO and TiO2. This practice revealed variable pressure estimates even within the same shergottite subjected to the same peak-shock pressure. Occurrence of Na-CAS + stishovite, lack of the NaAlSiO4 Ca-ferrite structured polymorph or jadeite indicates that the peak-shock pressures barely exceeded 22 GPa. We present convincing and ample evidence refuting the claim that the shock-induced high-pressure inventory in shergottites and ordinary chondrites are disequilibrium assemblages resulted from local pressure spikes in excess of 80 GPa and during the decompression stage. Such scenario calls for a series of incomplete and quenched retrograde reactions starting with the crystallization of Mg-silicate perovskite + magnesiowüstite, if the claimed peak-shock pressure was in excess of 80 GPa. This would be followed by replacement of this pair by majorite-pyropess + magnesiowüstite or akimotoite + magnesiowüstite below 23 GPa and 2000 °C, polycrystalline ringwoodite above 16 GPa, respectively and finally replacement by polycrystalline olivine below 16 GPa. Such incomplete retrograde reactions were never encountered in any shergottite, chassignite or shocked ordinary chondrite so far. Olivine-ringwoodite phase transformation in the L6 Y-791384 commences with the coherent mechanism producing ringwoodite lamellae with their (1 1 1) planes parallel to the (1 0 0) of olivine followed by the incoherent mechanism due to build up of strain in the parental olivine. This is in accord with the olivine-ringwoodite settings produced in static laboratory experiments in a multi-anvil device. Olivine-ringwoodite phase transitions were also encountered in comparable settings in the shergottite NWA 1068. Application of experimentally obtained kinetic parameters of the olivine-ringwoodite phase transitions reveals possible duration of the natural dynamic events up to few seconds thus unambiguously refuting the claimed disequilibrium decompression mechanism. The shock-induced pervasive melting of labradorite, pyrrhotite, titanomagnetite, ilmenite and partial melting of clinopyroxene strongly suggests shock-induced partial to complete resetting of the Ar-Ar, Rb-Sr, Sm-Nd, Re-Os, U-Pb and Lu-Hf radiometric systems. This also casts considerable doubt on the radiometric ages shorter than 575 Ma reported in the past 38 years to allegedly be the igneous crystallization ages. These short ages probably resulted from partial or total shock-induced age resetting.

Exploration of phase transition in ThS under pressure: An ab-initio investigation

NASA Astrophysics Data System (ADS)

Sahoo, B. D.; Mukherjee, D.; Joshi, K. D.; Kaushik, T. C.

2018-04-01

The ab-initio total energy calculations have been performed in thorium sulphide (ThS) to explore its high pressure phase stability. Our calculations predict a phase transformation from ambient rocksalt type structure (B1 phase) to a rhombohedral structure (R-3m phase) at ˜ 15 GPa and subsequently R-3m phase transforms to CsCl type structure (B2 phase) at ˜ 45 GPa. The first phase transition has been identified as second order type; whereas, the second transition is of first order type with volume discontinuity of 6.5%. The predicted high pressure R-3m phase is analogous to the experimentally observed hexagonal (distorted fcc) phase (Benedict et al., J. Less-Common Met., 1984) above 20 GPa. Further, using these calculations we have derived the equation of state which has been utilized to determine various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus at ambient conditions.

Research on a new fiber-optic axial pressure sensor of transformer winding based on fiber Bragg grating

NASA Astrophysics Data System (ADS)

Liu, Yuan; Li, Lianqing; Zhao, Lin; Wang, Jiqiang; Liu, Tongyu

2017-12-01

Based on the principle of the fiber Bragg grating, a new type of fiber-optic pressure sensor for axial force measurement of transformer winding is designed, which is designed with the structure of bending plate beam, the optimization of the packaging process, and material of the sensor. Through the calibration experiment to calibrate the sensor, the field test results of the Taikai transformer factory show that the sensitivity of the sensor is 0.133 pm/kPa and the repeatability error is 2.7% FS. The data of the fiber-optic pressure sensor in different positions maintain consistent and repeatable, which can meet the requirement of the real-time monitoring of the axial force of transformer winding.

Study of bulk Hafnium oxide (HfO2) under compression

NASA Astrophysics Data System (ADS)

Pathak, Santanu; Mandal, Guruprasad; Das, Parnika

2018-04-01

Hafnium oxide (HfO2) is a technologically important material. This material has K-value of 25 and band gap 5.8 eV. A k value of 25-30 is preferred for a gate dielectric [1]. As it shows good insulating and capacitive properties, HfO2 is being considered as a replacement to SiO2 in microelectronic devices as gate dielectrics. On the other hand because of toughening mechanism due to phase transformation induced by stress field observed in these oxides, HFO2 has been a material of investigations in various configurations for a very long time. However the controversies about phase transition of HfO2 under pressure still exists. High quality synchrotron radiation has been used to study the structural phase transition of HfO2 under pressure.

Pressure induced phase transformations in NaZr{sub 2}(PO{sub 4}){sub 3} studied by X-ray diffraction and Raman spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamali, K.; Ravindran, T.R., E-mail: trr@igcar.gov.in; Chandra Shekar, N.V.

2015-01-15

Raman spectroscopic and x-ray diffraction measurements on NaZr{sub 2}(PO{sub 4}){sub 3} were carried out up to 30 GPa at close intervals of pressure, revealing two structural phase transformations around 5 and 6.6 GPa. The second phase at 5.4 GPa is indexed to R3 space group similar to that of RbTi{sub 2}(PO{sub 4}){sub 3}. Bulk modulus decreases abruptly from 53 GPa (B′=4) to 36 GPa (B′=4) in the second phase above 5 GPa. The structure of the phase III at 8.2 GPa is indexed as orthorhombic similar to the case of high temperature phase of monoclinic LiZr{sub 2}(PO{sub 4}){sub 3}. Bulkmore » modulus of this phase III is found to be 65 GPa (B′=4), which is higher than that of the ambient phase. In high pressure Raman studies, modes corresponding to 72 and 112 cm{sup −1} soften in the ambient phase whereas around 5 GPa, the ones at 60, 105, 125 and 190 cm{sup −1} soften with pressure contributing negatively to overall thermal expansion. - Graphical abstract: High pressure study of NaZr{sub 2}(PO{sub 4}){sub 3} shows a reversible phase transition from R-3c to R3 structure at 5 GPa accompanied by an increase in compressibility signaling a polyhedral tilt transition. - Highlights: • NaZr{sub 2}(PO{sub 4}){sub 3} undergoes two reversible phase transitions at 5 and 6.7 GPa. • The transition at 5 is from rhombohedral R-3c to R3 structure. • Bulk modulus of NaZr{sub 2}(PO{sub 4}){sub 3} is lower than that for the isostructural RbTi{sub 2}(PO{sub 4}){sub 3.} • Compressibility increases with substitution of a smaller cation (Na). • Zr-translational and PO{sub 4} librational modes contribute to phase transition.« less

High pressure study of acetophenone azine

NASA Astrophysics Data System (ADS)

Tang, X. D.; Ding, Z. J.; Zhang, Z. M.

2009-02-01

High pressure Raman spectra of acetophenone azine (APA) have been measured up to 17.7 GPa with a diamond anvil cell. Two crystalline-to-crystalline phase transformations are found at pressures about 3.6 and 5.8 GPa. A disappearance of external modes and the C-H vibration at pressures higher than 8.7 GPa suggests that the sample undergoes a phase transition to amorphous or orientationally disordered (plastic) state, and the amorphization was completed at about 12.1 GPa. The disordered state is unstable and, then, a polymerization transformation reaction occurs with a further pressure increase. After the pressure has been released, the polymerization state can remain at the ambient condition, indicating that the virgin crystalline state is not recovered. The results show that the phenomenon underlying the pressure induced phase transition of APA may involve profound changes in the coordination environments of the symmetric aromatic azine.

High-pressure structural behavior of hydrogarnet, katoite Ca3Al2(O4H4)3

NASA Astrophysics Data System (ADS)

Kyono, A.; Kato, M.; Sano-Furukawa, A.; Machida, S. I.; Hattori, T.

2016-12-01

High-pressure structural behavior of hydrogarnet, katoite Ca3Al2(O4H4)3, was investigated using single-crystal synchrotron x-ray diffraction, Raman spectroscopic, and neutron diffraction analyses. The high-pressure single-crystal synchrotron x-ray diffraction was performed at BL10A, Photon Factory, KEK, Japan. With compression, the a lattice parameter decreased continuously from 12.565 (1) Å to 12.226 (3) Å up to 7.1 GPa. A fit to the Birch-Murnaghan equation of state (EoS) based on the P-V data gives K0 = 56.0 (6) GPa, K' = 4.3 (1), and V0 = 1984.2 (5) Å3, which were consistent with the previous study by Lager et al. (2002). Weak reflections forbidden by the systematic absence of hk0 with k, l = 2n were observed at 5.5 GPa and their intensities became stronger as increasing pressure. The pattern change of systematic absence implies phase transformation from space group Ia-3d to its non-centrosymmetric space group I-43d. High-pressure Raman spectroscopic study was performed up to 8.3 GPa at room temperature. The pressure dependence of lattice modes showed a positive pressure shifts, whereas that of OH stretching vibration mode was changed negative above 5.1 GPa. The change indicates that the strength of hydrogen bonding turns to increase above 5.1 GPa. High-pressure and high-temperature neutron diffraction study was performed with six-axis large volume press, ATSUHIME, at BL11 (PLANET), J-PARC, Japan. At a pressure of approximately 8 GPa, the a lattice parameter increased with temperature, but neither thermal decomposition nor dehydroxylation process occurred up to 1123 K. The crystal structure of katoite was determined by Rietveld method using neutron diffraction data with the space group I-43d. The volume of dodecahedral site containing Ca cations and that of octahedral site occupied by Al cations remained almost constant with temperature, but two crystallographically inequivalent tetrahedral sites which were caused by phase transformation behaved differently from each other. The volume of T2 site was continuously increased, but that of T1 site was constantly decreased, resulting from anisotropic expansion of the dodecahedral site. Consequently, these anisotropic modifications of coordination polyhedra seem to induce the thermal decomposition of katoite at 1123 K and 8 GPa.

High-pressure phase transitions of Fe 3-xTi xO 4 solid solution up to 60 GPa correlated with electronic spin transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamanaka, Takamitsu; Kyono, Atsushi; Nakamoto, Yuki

2013-06-12

The structural phase transition of the titanomagnetite (Fe 3–xTi xO 4) solid solution under pressures up to 60 GPa has been clarified by single-crystal and powder diffraction studies using synchrotron radiation and a diamond-anvil cell. Present Rietveld structure refinements of the solid solution prove that the prefered cation distribution is based on the crystal field preference rather than the magnetic spin ordering in the solid solution. The Ti-rich phases in 0.734 ≤ x ≤1.0 undergo a phase transformation from the cubic spinel of Fd3m to the tetragonal spinel structure of I4 1/amd with c/a < 1.0. The transition is drivenmore » by a Jahn-Teller effect of IVFe 2+ (3d 6) on the tetrahedral site. The c/a < 1 ratio is induced by lifting of the degeneracy of the e orbitals by raising the d x2-y2 orbital below the energy of the d z2 orbital. The distortion characterized by c/a < 1 is more pronounced with increasing Ti content in the Fe 3–xTi xO 4 solid solutions and with increasing pressure. An X-ray emission experiment of Fe 2TiO 4 at high pressures confirms the spin transition of FeKβ from high spin to intermediate spin (IS) state. The high spin (HS)-to-low spin (LS) transition starts at 14 GPa and the IS state gradually increases with compression. The VIFe 2+ in the octahedral site is more prone for the HS-to-LS transition, compared with Fe 2+ in the fourfold- or eightfold-coordinated site. The transition to the orthorhombic post-spinel structure with space group Cmcm has been confirmed in the whole compositional range of Fe 3–xTi xO 4. The transition pressure decreases from 25 GPa (x = 0.0) to 15 GPa (x = 1.0) with increasing Ti content. There are two cation sites in the orthorhombic phase: M1 and M2 sites of eightfold and sixfold coordination, respectively. Fe 2+ and Ti 4+ are disordered on the M2 site. This structural change is accelerated at higher pressures due to the spin transition of Fe 2+ in the octahedral site. This is because the ionic radius of VIFe 2+ becomes 20% shortened by the spin transition. At 53 GPa, the structure transforms to another high-pressure polymorph with Pmma symmetry with the ordered structure of Ti and Fe atoms in the octahedral site. This structure change results from the order-disorder transition.« less

High pressure and temperature induced structural and elastic properties of lutetium chalcogenides

NASA Astrophysics Data System (ADS)

Shriya, S.; Kinge, R.; Khenata, R.; Varshney, Dinesh

2018-04-01

The high-pressure structural phase transition and pressure as well temperature induced elastic properties of rock salt to CsCl structures in semiconducting LuX (X = S, Se, and Te) chalcogenides compound have been performed using effective interionic interaction potential with emphasis on charge transfer interactions and covalent contribution. Estimated values of phase transition pressure and the volume discontinuity in pressure-volume phase diagram indicate the structural phase transition from ZnS to NaCl structure. From the investigations of elastic constants the pressure (temperature) dependent volume collapse/expansion, melting temperature TM, Hardness (HV), and young modulus (E) the LuX lattice infers mechanical stiffening, and thermal softening.

Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal Halide Perovskite-Based Methylammonium Lead Chloride.

PubMed

Wang, Lingrui; Wang, Kai; Xiao, Guanjun; Zeng, Qiaoshi; Zou, Bo

2016-12-15

Organometal halide perovskites are promising materials for optoelectronic devices. Further development of these devices requires a deep understanding of their fundamental structure-property relationships. The effect of pressure on the structural evolution and band gap shifts of methylammonium lead chloride (MAPbCl 3 ) was investigated systematically. Synchrotron X-ray diffraction and Raman experiments provided structural information on the shrinkage, tilting distortion, and amorphization of the primitive cubic unit cell. In situ high pressure optical absorption and photoluminescence spectra manifested that the band gap of MAPbCl 3 could be fine-tuned to the ultraviolet region by pressure. The optical changes are correlated with pressure-induced structural evolution of MAPbCl 3 , as evidenced by band gap shifts. Comparisons between Pb-hybrid perovskites and inorganic octahedra provided insights on the effects of halogens on pressure-induced transition sequences of these compounds. Our results improve the understanding of the structural and optical properties of organometal halide perovskites.

High-pressure behavior of A 2 B 2 O 7 pyrochlore (A=Eu, Dy; B=Ti, Zr)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rittman, Dylan R.; Turner, Katlyn M.; Park, Sulgiye

2017-01-24

In situ high-pressure X-ray diffraction and Raman spectroscopy were used to determine the influence of composition on the high-pressure behavior of A 2B 2O 7 pyrochlore (A = Eu, Dy; B = Ti, Zr) up to ~50 GPa. Based on X-ray diffraction results, all compositions transformed to the high-pressure cotunnite structure. The B-site cation species had a larger effect on the transition pressure than the A-site cation species, with the onset of the phase transformation occurring at ~41 GPa for B = Ti and ~16 GPa B = Zr. But, the A-site cation affected the kinetics of the phase transformation,more » with the transformation for compositions with the smaller ionic radii, i.e., A = Dy, proceeding faster than those with a larger ionic radii, i.e., A = Eu. Our results were consistent with previous work in which the radius-ratio of the A- and B-site cations determined the energetics of disordering, and compositions with more similarly sized A- and B-site cations had a lower defect formation energy. Raman spectra revealed differences in the degree of short-range order of the different compositions. Due to the large phase fraction of cotunnite at high pressure for B = Zr compositions, Raman modes for cotunnite could be observed, with more modes recorded for A = Eu than A = Dy. These additional modes are attributed to increased short-to-medium range ordering in the initially pyrochlore structured Eu 2Zr 2O 7 as compared with the initially defect-fluorite structured Dy 2Zr 2O 7.« less

High-pressure behavior of A 2 B 2 O 7 pyrochlore (A=Eu, Dy; B=Ti, Zr)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rittman, Dylan R.; Turner, Katlyn M.; Park, Sulgiye

2017-01-28

In situ high-pressure X-ray diffraction and Raman spectroscopy were used to determine the influence of composition on the high-pressure behavior of A 2B 2O 7 pyrochlore (A=Eu, Dy; B=Ti, Zr) up to ~50GPa. Based on X-ray diffraction results, all compositions transformed to the high-pressure cotunnite structure. The B-site cation species had a larger effect on the transition pressure than the A-site cation species, with the onset of the phase transformation occurring at ~41 GPa for B=Ti and ~16 GPa B=Zr. However, the A-site cation affected the kinetics of the phase transformation, with the transformation for compositions with the smaller ionicmore » radii, i.e., A=Dy, proceeding faster than those with a larger ionic radii, i.e., A=Eu. These results were consistent with previous work in which the radius-ratio of the A- and B-site cations determined the energetics of disordering, and compositions with more similarly sized A- and B-site cations had a lower defect formation energy. Raman spectra revealed differences in the degree of short-range order of the different compositions. Due to the large phase fraction of cotunnite at high pressure for B=Zr compositions, Raman modes for cotunnite could be observed, with more modes recorded for A=Eu than A=Dy. These additional modes are attributed to increased short-to-medium range ordering in the initially pyrochlore structured Eu 2Zr 2O 7 as compared with the initially defect-fluorite structured Dy 2Zr 2O 7.« less

Estimation of Time Dependent Properties from Surface Pressure in Open Cavities

DTIC Science & Technology

2008-02-01

static pressure of the cavity. The stagnation and static pressures are measured separately with Druck Model DPI 145 pressure transducers (with a quoted...interacting with the ZNMF actuator jets, the 2D shape of the vortical structures transform to a 3D shape with spanwise vortical structures. These...Therefore, the pressure gradient in the d direction is dd ° 3d Substituting Equation (5.3) into Equation (5.5) results in ^l = PJk(e^-Re^)/c^ (5.6

Highly porous micro-roughened structures developed on aluminum surface using the jet of rotating arc discharges at atmospheric pressure

NASA Astrophysics Data System (ADS)

Asadollahi, Siavash; Farzaneh, Masoud; Stafford, Luc

2018-02-01

Aluminum 6061 samples were exposed to the jet of an atmospheric pressure rotating arc discharge operated in either nitrogen or air. After multiple passes of treatment with an air-based plasma jet at very short source-to-substrate distances, scanning electron microscopy combined with x-ray photoelectron spectroscopy revealed a highly porous micro-roughened alumina-based structure on the surface of aluminum. Based on optical emission spectroscopy and high-speed optical imaging of the jet interacting with aluminum samples, it was found that the process is mainly driven by the energy transfer from the plasma source to the surface through transient plasma-transferred arcs. The occurrence of multiple arc discharges over very short time scales can induce rapid phase transformations of aluminum with characteristics similar to the ones usually observed during laser ablation of materials with femto- to nanosecond laser pulses or during the formation of cathode spots on the surface of metals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Varga, Tamas

Despite the fact that all chemical bonds expand on heating, a small class of materials shrinks when heated. These, so called negative thermal expansion (NTE) materials, are a unique class of materials with some exotic properties. The present chapter offers insight into the structural aspects of pressure- (or temperature-) induced phase transformations, and the energetics of those changes in these fascinating materials, in particular NTE compound cubic ZrW2O8, orthorhombic Sc2W3O12 and Sc2Mo3O12, as well as other members of the 'scandium tungstate family'. In subsequent sections, (i) combined in situ high-pressure synchrotron XRD and XAS studies of NTE material ZrW2O8; (ii)more » an in situ high-pressure synchrotron XRD study of Sc2W3O12, Sc2Mo3O12, and Al2W3O12; and (iii) thermochemical studies of the above materials are presented and discussed. In all of these studies, chemical bonds change, sometimes break and new ones form. Correlations between structure, chemistry, and energetics are revealed. It is also shown that (iv) NTE materials are good candidates as precursors to make novel solid state materials, such as the conducting Sc0.67WO4, using high-pressure, high-temperature synthesis, through modification of bonding and electronic structure, and thus provide vast opportunities for scientific exploration.« less

Pressure-induced phase transitions in the CdC r2S e4 spinel

NASA Astrophysics Data System (ADS)

Efthimiopoulos, I.; Liu, Z. T. Y.; Kucway, M.; Khare, S. V.; Sarin, P.; Tsurkan, V.; Loidl, A.; Wang, Y.

2016-11-01

We have conducted high-pressure x-ray diffraction and Raman spectroscopic studies on the CdC r2S e4 spinel at room temperature up to 42 GPa. We have resolved three structural transitions up to 42 GPa, i.e., the starting F d 3 ¯m phase transforms at ˜11 GPa into a tetragonal I 41/a m d structure, an orthorhombic distortion was observed at ˜15 GPa , whereas structural disorder initiates beyond 25 GPa. Our ab initio density functional theory studies successfully reproduced the observed crystalline-to-crystalline structural transitions. In addition, our calculations propose an antiferromagnetic ordering as a potential magnetic ground state for the high-pressure tetragonal and orthorhombic modifications, compared with the starting ferromagnetic phase. Furthermore, the computational results indicate that all phases remain insulating in their stability pressure range, with a direct-to-indirect band gap transition for the F d 3 ¯m phase taking place at 5 GPa. We attempted also to offer an explanation behind the peculiar first-order character of the F d 3 ¯m (cubic ) →I 41/a m d (tetragonal) transition observed for several relevant Cr spinels, i.e., the sizeable volume change at the transition point, which is not expected from space group symmetry considerations. We detected a clear correlation between the cubic-tetragonal transition pressures and the next-nearest-neighbor magnetic exchange interactions for the Cr-bearing sulfide and selenide members, a strong indication that the cubic-tetragonal transitions in these systems are principally governed by magnetic effects.

Deviatoric stress-induced phase transitions in diamantane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Fan; Lin, Yu; Dahl, Jeremy E. P.

2014-10-21

The high-pressure behavior of diamantane was investigated using angle-dispersive synchrotron x-ray diffraction (XRD) and Raman spectroscopy in diamond anvil cells. Our experiments revealed that the structural transitions in diamantane were extremely sensitive to deviatoric stress. Under non-hydrostatic conditions, diamantane underwent a cubic (space group Pa3) to a monoclinic phase transition at below 0.15 GPa, the lowest pressure we were able to measure. Upon further compression to 3.5 GPa, this monoclinic phase transformed into another high-pressure monoclinic phase which persisted to 32 GPa, the highest pressure studied in our experiments. However, under more hydrostatic conditions using silicone oil as a pressuremore » medium, the transition pressure to the first high-pressure monoclinic phase was elevated to 7–10 GPa, which coincided with the hydrostatic limit of silicone oil. In another experiment using helium as a pressure medium, no phase transitions were observed to the highest pressure we reached (13 GPa). In addition, large hysteresis and sluggish transition kinetics were observed upon decompression. Over the pressure range where phase transitions were confirmed by XRD, only continuous changes in the Raman spectra were observed. This suggests that these phase transitions are associated with unit cell distortions and modifications in molecular packing rather than the formation of new carbon-carbon bonds under pressure.« less

Polymorphism in Strontium Tungstate SrWO4 under Quasi-Hydrostatic Compression.

PubMed

Santamaria-Perez, David; Errandonea, Daniel; Rodriguez-Hernandez, Placida; Muñoz, Alfonso; Lacomba-Perales, Raul; Polian, Alain; Meng, Yue

2016-10-03

The structural and vibrational properties of SrWO 4 have been studied experimentally up to 27 and 46 GPa, respectively, by angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy measurements as well as using ab initio calculations. The existence of four polymorphs upon quasi-hydrostatic compression is reported. The three phase transitions were found at 11.5, 19.0, and 39.5 GPa. The ambient-pressure SrWO 4 tetragonal scheelite-type structure (S.G. I4 1 /a) undergoes a transition to a monoclinic fergusonite-type structure (S.G. I2/a) at 11.5 GPa with a 1.5% volume decrease. Subsequently, at 19.0 GPa, another structural transformation takes place. Our calculations indicate two possible post-fergusonite phases, one monoclinic and the other orthorhombic. In the diffraction experiments, we observed the theoretically predicted monoclinic LaTaO 4 -type phase coexisting with the fergusonite-type phase up to 27 GPa. The coexistence of the two phases and the large volume collapse at the transition confirm a kinetic hindrance typical of first-order phase transitions. Significant changes in Raman spectra suggest a third pressure-induced transition at 39.5 GPa. The conclusions extracted from the experiments are complemented and supported by ab initio calculations. Our data provides insight into the structural mechanism of the first transition, with the formation of two additional W-O contacts. The fergusonite-type phase can be therefore considered as a structural bridge between the scheelite structure, composed of [WO 4 ] tetrahedra, and the new higher pressure phases, which contain [WO 6 ] octahedra. All the observed phases are compatible with the high-pressure structural systematics predicted for ABO 4 compounds using crystal-chemistry arguments such as the diagram proposed by Bastide.

Exploration of stable compounds, crystal structures, and superconductivity in the Be-H system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Shuyin, E-mail: yushuyin2014@gmail.com; Zeng, Qingfeng; Zhang, Litong

2014-10-15

Using first-principles variable-composition evolutionary methodology, we explored the high-pressure structures of beryllium hydrides between 0 and 400 GPa. We found that BeH{sub 2} remains the only stable compound in this pressure range. The pressure-induced transformations are predicted as Ibam→P3{sup -}m1→R3{sup -}m→Cmcm→P4/nmm, which occur at 24, 139, 204 and 349 GPa, respectively. P3{sup -}m1 and R3{sup -}m structures are layered polytypes based on close packings of H atoms with Be atoms filling all octahedral voids in alternating layers. Cmcm and P4/nmm contain two-dimensional triangular networks with each layer forming a kinked slab in the ab-plane. P3{sup -}m1 and R3{sup -}m aremore » semiconductors while Cmcm and P4/nmm are metallic. We have explored superconductivity of both metal phases, and found large electron-phonon coupling parameters of λ = 0.63 for Cmcm with a T{sub c} of 32.1-44.1 K at 250 GPa and λ = 0.65 for P4/nmm with a T{sub c} of 46.1-62.4 K at 400 GPa. The dependence of T{sub c} on pressure indicates that T{sub c} initially increases to a maximum of 45.1 K for Cmcm at 275 GPa and 97.0 K for P4/nmm at 365 GPa, and then decreases with increasing pressure for both phases.« less

Predicting kinetics of polymorphic transformations from structure mapping and coordination analysis

NASA Astrophysics Data System (ADS)

Stevanović, Vladan; Trottier, Ryan; Musgrave, Charles; Therrien, Félix; Holder, Aaron; Graf, Peter

2018-03-01

To extend materials design and discovery into the space of metastable polymorphs, rapid and reliable assessment of transformation kinetics to lower energy structures is essential. Herein we focus on diffusionless polymorphic transformations and investigate routes to assess their kinetics using solely crystallographic arguments. As part of this investigation we developed a general algorithm to map crystal structures onto each other, and ascertain the low-energy (fast-kinetics) transformation pathways between them. Pathways with minimal dissociation of chemical bonds, along which the number of bonds (in ionic systems the first-shell coordination) does not decrease below that in the end structures, are shown to always be the fast-kinetics pathways. These findings enable the rapid assessment of the kinetics of polymorphic transformation and the identification of long-lived metastable structures. The utility is demonstrated on a number of transformations including those between high-pressure SnO2 phases, which lack a detailed atomic-level understanding.

Real-Time Examination of Atomistic Mechanisms during Shock-Induced Structural Transformation in Silicon

DOE PAGES

Turneaure, Stefan J.; Sinclair, N.; Gupta, Y. M.

2016-07-20

Experimental determination of atomistic mechanisms linking crystal structures during a compression driven solid-solid phase transformation is a long standing and challenging scientific objective. Also, when using new capabilities at the Dynamic Compression Sector at the Advanced Photon Source, the structure of shocked Si at 19 GPa was identified as simple hexagonal and the lattice orientations between ambient cubic diamond and simple hexagonal structures were related. Furthermore, this approach is general and provides a powerful new method for examining atomistic mechanisms during stress-induced structural changes.

Air-broadened Lorentz halfwidths and pressure-induced line shifts in the nu(4) band of C-13H4

NASA Technical Reports Server (NTRS)

Devi, V. Malathy; Benner, D. Chris; Rinsland, Curtis P.; Smith, Mary Ann H.

1988-01-01

Air-broadened halfwidths and pressure-induced line shifts in the nu(4) fundamental of C-13H4 were determined from spectra recorded at room temperature and at 0.01/cm resolution using a Fourier transform spectrometer. Halfwidths and pressure shifts were determined for over 180 transitions belonging to J-double prime values of less than or = to 16. Comparisons of air-broadened halfwidths and pressure-induced line shifts made for identical transitions in the nu(4) bands of C-12H4 and C-13H4 have shown that C-13H4 air-broadened halfwidths are about 5 percent smaller than the corresponding C-12H4 halfwidths, and the pressure shifts for C-13H4 lines are about 5-15 percent larger than those for C-12H4.

Relaxation dynamics and transformation kinetics of deeply supercooled water: Temperature, pressure, doping, and proton/deuteron isotope effects.

PubMed

Lemke, Sonja; Handle, Philip H; Plaga, Lucie J; Stern, Josef N; Seidl, Markus; Fuentes-Landete, Violeta; Amann-Winkel, Katrin; Köster, Karsten W; Gainaru, Catalin; Loerting, Thomas; Böhmer, Roland

2017-07-21

Above its glass transition, the equilibrated high-density amorphous ice (HDA) transforms to the low-density pendant (LDA). The temperature dependence of the transformation is monitored at ambient pressure using dielectric spectroscopy and at elevated pressures using dilatometry. It is found that near the glass transition temperature of deuterated samples, the transformation kinetics is 300 times slower than the structural relaxation, while for protonated samples, the time scale separation is at least 30 000 and insensitive to doping. The kinetics of the HDA to LDA transformation lacks a proton/deuteron isotope effect, revealing that this process is dominated by the restructuring of the oxygen network. The x-ray diffraction experiments performed on samples at intermediate transition stages reflect a linear combination of the LDA and HDA patterns implying a macroscopic phase separation, instead of a local intermixing of the two amorphous states.

Relaxation dynamics and transformation kinetics of deeply supercooled water: Temperature, pressure, doping, and proton/deuteron isotope effects

NASA Astrophysics Data System (ADS)

Lemke, Sonja; Handle, Philip H.; Plaga, Lucie J.; Stern, Josef N.; Seidl, Markus; Fuentes-Landete, Violeta; Amann-Winkel, Katrin; Köster, Karsten W.; Gainaru, Catalin; Loerting, Thomas; Böhmer, Roland

2017-07-01

Above its glass transition, the equilibrated high-density amorphous ice (HDA) transforms to the low-density pendant (LDA). The temperature dependence of the transformation is monitored at ambient pressure using dielectric spectroscopy and at elevated pressures using dilatometry. It is found that near the glass transition temperature of deuterated samples, the transformation kinetics is 300 times slower than the structural relaxation, while for protonated samples, the time scale separation is at least 30 000 and insensitive to doping. The kinetics of the HDA to LDA transformation lacks a proton/deuteron isotope effect, revealing that this process is dominated by the restructuring of the oxygen network. The x-ray diffraction experiments performed on samples at intermediate transition stages reflect a linear combination of the LDA and HDA patterns implying a macroscopic phase separation, instead of a local intermixing of the two amorphous states.

Effects of a high-pressure treatment on the wheat alpha-amylase inhibitor and its relationship to elimination of allergenicity

NASA Astrophysics Data System (ADS)

Yamamoto, S.; Takanohashi, K.; Hara, T.; Odani, S.; Suzuki, A.; Nishiumi, T.

2010-03-01

In this study, the effects of high-pressure treatment on structure and allergeincity of alpha amylase inhibitor (a-AI) were investigated. The pressure-induced structural changes of α-AI were estimated by fluorescence spectra and by fourth derivative UV-spectroscopy for probed tyrosine residues and by circular dichroism (CD) spectroscopy. The changes in the tertiary structure detected by fluorescence spectra and by fourth derivative UV-spectroscopy under high pressure were indicated at over 300 MPa. Measurements of CD spectroscopy suggested that the effects of a high-pressure treatment on changes in the secondary structure of α-AI were little. From our results, pressure-induced changes of the α-AI structure were not apparent. On the other hands, the IgE-specific binding activities of pressurized α-AI to sera from allergic patients against wheat, which is estimated by observations of dot-blotting, were decreased by high-pressure treatment. It is known that the pressure-induced elimination of allergenicity is related to the tertiary structural changes of allergen molecules. This study are suspected that the epitopes of α-AI do not contain tyrosine residues, and thus the decrease of IgE-specific binding activities is probably caused by the tertiary structural changes of these parts of α-AI.

High-Pressure Behavior of Difluorides: The Case of SrF2

NASA Astrophysics Data System (ADS)

Swadba, K. E.; Stan, C. V.; Dutta, R.; Prakapenka, V.; Duffy, T. S.

2016-12-01

The high-pressure behavior of compounds in the AX2 family has attracted much attention due to their extensive polymorphism, highly coordinated structures, and diverse transformation pathways. The canonical transformation sequence for alkaline earth difluorides is from the fluorite-type structure (8 coordinated) to cotunnite (9 coordinated) to Ni2In (11 coordinated). Lead Fluoride, on the other hand, undergoes an unusual isosymmetric transition from cotunnite to a Co2Si-type structure (10 coordinated) at high pressures, during which it exhibits highly anisotropic lattice parameter trends (Haines et al, 1998; Stan et al 2016). Sr has a similar ionic radius as Pb, and is thus a good candidate for further exploring the compressional anisotropy in alkaline earth fluorides. In this study, we report a detailed examination of the compressional behavior of SrF2 to identify whether an intermediate phase occurs in this system prior to transformation to the Ni2In structure. Raman spectroscopy and x-ray diffraction experiments, performed at Princeton University and the Advanced Photon Source GSECARS beamline, respectively, were carried out on SrF2 up to 63 GPa using a diamond anvil cell. From Raman spectroscopy, we observed evidence for a high-pressure phase transition between 38.9 and 51.0 GPa. The x-ray diffraction data in this region show evidence for highly anisotropic compression, most notably a strong negative compressibility in the b direction, in the pressure region from 45.2 to 51.6 GPa. Comparison of our data with lattice parameter systematics for AX2 phases indicates that our results are consistent with the formation of the Co2Si phase in this region, along with a sluggish transformation to the Ni2In-type structure. Our findings contribute to a broader understanding of AX2 compounds and their phase transition pathways.

Experimental evidence of new tetragonal polymorphs of silicon formed through ultrafast laser-induced confined microexplosion

DOE PAGES

Rapp, L.; Haberl, B.; Pickard, C. J.; ...

2015-06-29

Ordinary materials can transform into novel phases with new crystal structures at extraordinary high pressure and temperature applied under both equilibrium and non-equilibrium conditions 1-6. The recently developed method of ultra-short laser-induced confined microexplosions 7-9 extends the range of possible new phases by initiating a highly non-equilibrium plasma state deep inside a bulk material 7-12. Ultra-high quenching rates can help to overcome kinetic barriers to the formation of new metastable phases, while the surrounding pristine crystal confines the affected material and preserves it for further study 10-12. Here we demonstrate that ultra-rapid pressure release from a completely disordered plasma statemore » in silicon produces several new metastable end phases quenched to ambient conditions. Their structure is determined from comparison to an ab initio random structure search which revealed six new energetically competitive potential phases, four tetragonal and two monoclinic ones. We show the presence of bt8 and st12, which have been predicted theoretically previously 13-15, but have not been observed in nature or in laboratory experiments. Additionally, the presence of the as yet unidentified silicon phase, Si-VIII and two of our other predicted tetragonal phases are highly likely within laser-affected zones. These findings pave the way for new materials with novel and exotic properties.« less

Pressure-induced phase transitions of exposed curved surface nano-TiO{sub 2} with high photocatalytic activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Yanwei, E-mail: yanwei.huang@hpstar.ac.cn, E-mail: wangling@hpstar.ac.cn; College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018; Chen, Fengjiao

We report a unique phase transition in compressed exposed curved surface nano-TiO{sub 2} with high photocatalytic activity using in situ synchrotron X-ray diffraction and Raman Spectroscopy. High-pressure studies indicate that the anatase phase starts to transform into baddeleyite phase upon compression at 19.4 GPa, and completely transforms into the baddeleyite phase above 24.6 GPa. Upon decompression, the baddeleyite phase was maintained until the pressure was released to 6.4 GPa and then transformed into the α-PbO{sub 2} phase at 2.7 GPa. Together with the results of high-resolution transmission electron microscopy and the pressure-volume relationship, this phase transition's characteristics during the compression-decompression cycle demonstrate that themore » truncated biconic morphology possessed excellent stability. This study may provide an insight to the mechanisms of stability for high photocatalytic activity of nano-TiO{sub 2}.« less

High pressure synthesis of a hexagonal close-packed phase of the high-entropy alloy CrMnFeCoNi

NASA Astrophysics Data System (ADS)

Tracy, Cameron L.; Park, Sulgiye; Rittman, Dylan R.; Zinkle, Steven J.; Bei, Hongbin; Lang, Maik; Ewing, Rodney C.; Mao, Wendy L.

2017-05-01

High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed to suppression of the local magnetic moments, destabilizing the initial fcc structure. Similar to fcc-to-hcp transformations in Al and the noble gases, the transformation is sluggish, occurring over a range of >40 GPa. However, the behaviour of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures. This demonstrates a means of tuning the structures and properties of high-entropy alloys in a manner not achievable by conventional processing techniques.

Increased likelihood of induced seismicity in highly overpressured shale formations

NASA Astrophysics Data System (ADS)

Eaton, David W.; Schultz, Ryan

2018-05-01

Fluid-injection processes such as disposal of saltwater or hydraulic fracturing can induce earthquakes by increasing pore pressure and/or shear stress on faults. Natural processes, including transformation of organic material (kerogen) into hydrocarbon and cracking to produce gas, can similarly cause fluid overpressure. Here we document two examples from the Western Canada Sedimentary Basin where earthquakes induced by hydraulic fracturing are strongly clustered within areas characterized by pore-pressure gradient in excess of 15 kPa/m. Despite extensive hydraulic-fracturing activity associated with resource development, induced earthquakes are virtually absent in the Montney and Duvernay Formations elsewhere. Statistical analysis suggests a negligible probability that this spatial correlation developed by chance. This implies that, in addition to known factors such as anthropogenic pore-pressure increase and proximity to critically stressed faults, high in-situ overpressure of shale formations may also represent a controlling factor for inducing earthquakes by hydraulic fracturing. On a geological timescale, natural pore-pressure generation may lead to fault-slip episodes that regulate magnitude of formation-overpressure.

X-ray-diffraction study of californium metal to 16 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peterson, J.R.; Benedict, U.; Dufour, C.

1983-01-01

The first series of measurements to determine the structural behavior of californium (Cf) metal under pressure has been carried out. The initial dhcp structure transformed sluggishly with increasing pressure to a fcc structure. A bulk modulus of 50(5) GPa was derived for dhcp Cf metal from the relative volume (V/V/sub 0/) data to 10 GPa.

Petalite under pressure: Elastic behavior and phase stability

DOE PAGES

Ross, Nancy L.; Zhao, Jing; Slebodnick, Carla; ...

2015-04-01

The lithium aluminosilicate mineral petalite (LiAlSi 4O 10) has been studied using high-pressure single-crystal X-ray diffraction (HP-XRD) up to 5 GPa. Petalite undergoes two pressure-induced first-order phase transitions, never reported in the literature, at ca. 1.5 and 2.5 GPa. The first of these transforms the low-pressure α-phase of petalite (P2/c) to an intermediate β-phase that then fully converts to the high-pressure β-phase at ca. 2.5 GPa. The α→β transition is isomorphic and is associated with a commensurate modulation that triples the unit cell volume. Analysis of the HP-XRD data show that although the fundamental features of the petalite structure aremore » retained through this transition, there are subtle alterations in the internal structure of the silicate double-layers in the β-phase relative to the α-phase. Measurement of the unit cell parameters of petalite as a function of pressure, and fitting of the data with 3rd order Birch-Murnaghan equations of state, has provided revised elastic constants for petalite. The bulk moduli of the α and β-phases are 49(1) and 35(3) GPa, respectively. These values indicate that the compressibility of the- phase of petalite lies between the alkali feldpsars and alkali feldspathoids, whereas the β-phase has a compressibility more comparable with layered silicates. Structure analysis has shown that the compression of the -phase is facilitated by the rigid body movement of the Si 2O 7 units from which the silicate double-layers are constructed.« less

Kinetics and mechanism of the pressure-induced lamellar order/disorder transition in phosphatidylethanolamine: a time-resolved X-ray diffraction study.

PubMed

Mencke, A P; Caffrey, M

1991-03-05

By using synchrotron radiation, a movie was made of the X-ray scattering pattern from a biological liquid crystal undergoing a phase transition induced by a pressure jump. The system studied includes the fully hydrated phospholipid dihexadecylphosphatidylethanolamine in the lamellar gel (L beta') phase at a temperature of 68 degrees C and a pressure of 9.7 MPa (1400 psig). Following the rapid release of pressure to atmospheric the L beta' phase transforms slowly into the lamellar liquid crystal (L alpha) phase. The pressure perturbation is applied with the intention of producing a sudden phase disequilibrium followed by monitoring the system as it relaxes to its new equilibrium condition. Remarkably, the proportion of sample in the L alpha phase grows linearly with time, taking 37 s to totally consume the L beta' phase. The time dependencies of radius, peak intensity, and width of the powder diffraction ring of the low-angle (001) lamellar reflections were obtained from the movie by image processing. The concept of an "effective pressure" is introduced to account for the temperature variations that accompany the phase transition and to establish that the observed large transit time is indeed intrinsic to the sample and not due to heat exchange with the environment. The reverse transformation, L alpha to L beta', induced by a sudden jump from atmospheric pressure to 9.7 MPa, is complete in less than 13 s. These measurements represent a new approach for studying the kinetics of lipid phase transitions and for gaining insights into the mechanism of the lamellar order/disorder transition.

Structure and bulk modulus of Ln-doped UO2 (Ln = La, Nd) at high pressure

NASA Astrophysics Data System (ADS)

Rittman, Dylan R.; Park, Sulgiye; Tracy, Cameron L.; Zhang, Lei; Palomares, Raul I.; Lang, Maik; Navrotsky, Alexandra; Mao, Wendy L.; Ewing, Rodney C.

2017-07-01

The structure of lanthanide-doped uranium dioxide, LnxU1-xO2-0.5x+y (Ln = La, Nd), was investigated at pressures up to ∼50-55 GPa. Samples were synthesized with different lanthanides at different concentrations (x ∼ 0.2 and 0.5), and all were slightly hyperstoichiometric (y ∼ 0.25-0.4). In situ high-pressure synchrotron X-ray diffraction was used to investigate their high-pressure phase behavior and determine their bulk moduli. All samples underwent a fluorite-to-cotunnite phase transformation with increasing pressure. The pressure of the phase transformation increased with increasing hyperstoichiometry, which is consistent with results from previous computational simulations. Bulk moduli are inversely proportional to both the ionic radius of the lanthanide and its concentration, as quantified using a weighted cationic radius ratio. This trend was found to be consistent with the behavior of other elastic properties measured for Ln-doped UO2, such as Young's modulus.

Structure and bulk modulus of Ln-doped UO 2 (Ln = La, Nd) at high pressure

DOE PAGES

Rittman, Dylan R.; Park, Sulgiye; Tracy, Cameron L.; ...

2017-04-10

The structure of lanthanide-doped uranium dioxide, Ln xU 1-xO 2-0.5x+y (Ln = La, Nd), was investigated at pressures up to ~50–55 GPa. Samples were synthesized with different lanthanides at different concentrations (x ~ 0.2 and 0.5), and all were slightly hyperstoichiometric (y ~ 0.25–0.4). In situ high-pressure synchrotron X-ray diffraction was used to investigate their high-pressure phase behavior and determine their bulk moduli. All samples underwent a fluorite-to-cotunnite phase transformation with increasing pressure. The pressure of the phase transformation increased with increasing hyperstoichiometry, which is consistent with results from previous computational simulations. Bulk moduli are inversely proportional to both themore » ionic radius of the lanthanide and its concentration, as quantified using a weighted cationic radius ratio. As a result, this trend was found to be consistent with the behavior of other elastic properties measured for Ln-doped UO 2, such as Young's modulus.« less

Coexistence pressure for a martensitic transformation from theory and experiment: Revisiting the bcc-hcp transition of iron under pressure

DOE PAGES

Zarkevich, N. A.; Johnson, D. D.

2015-05-12

We revisit results from decades of pressure experiments on the bcc ↔ hcp transformations in iron, which are sensitive to non-hydrostatic conditions and sample size. We emphasize the role of martensitic stress in the observed pressure hysteresis and address the large spread in values for onset pressures of the nucleating phase. From electronic-structure calculations, we find a bcc ↔ hcp equilibrium coexistence pressure of 8.4 GPa. Accounting for non-hydrostatic martensitic stress and a stress-dependent transition barrier, we suggest a pressure inequality for better comparison to experiment and observed hysteresis. We construct the equation of state for bcc and hcp phasesmore » under hydrostatic pressure, and compare to experiments and previous calculations.« less

Pressure-induced phase transition in GaN nanocrystals

NASA Astrophysics Data System (ADS)

Cui, Q.; Pan, Y.; Zhang, W.; Wang, X.; Zhang, J.; Cui, T.; Xie, Y.; Liu, J.; Zou, G.

2002-11-01

High-pressure in situ energy-dispersive x-ray diffraction experiments on GaN nanocrystals with 50 nm diameter have been carried out using a synchrotron x-ray source and a diamond-anvil cell up to about 79 GPa at room temperature. A pressure-induced first-order structural phase transition from the wurtzite-type structure to the rock-salt-type structure starts at about 48.8 GPa. The rock-salt-type phase persists to the highest pressure in our experimental range.

Structural complexity of simple Fe 2O 3 at high pressures and temperatures

DOE PAGES

Bykova, Elena; Dubrovinsky, L.; Dubrovinskaia, N.; ...

2016-02-11

Although chemically very simple, Fe 2O 3 is known to undergo a series of enigmatic structural, electronic and magnetic transformations at high pressures and high temperatures. So far, these transformations have neither been correctly described nor understood because of the lack of structural data. Here we report a systematic investigation of the behaviour of Fe 2O 3 at pressures over 100 GPa and temperatures above 2,500 K employing single crystal X-ray diffraction and synchrotron Mössbauer source spectroscopy. Crystal chemical analysis of structures presented here and known Fe(II, III) oxides shows their fundamental relationships and that they can be described bymore » the homologous series nFeO·mFe 2O 3. Decomposition of Fe 2O 3 and Fe 3O 4 observed at pressures above 60 GPa and temperatures of 2,000 K leads to crystallization of unusual Fe 5O 7 and Fe 25O 32 phases with release of oxygen. Lastly, our findings suggest that mixed-valence iron oxides may play a significant role in oxygen cycling between earth reservoirs.« less

Structural alterations in rat liver proteins due to streptozotocin-induced diabetes and the recovery effect of selenium: Fourier transform infrared microspectroscopy and neural network study

NASA Astrophysics Data System (ADS)

Bozkurt, Ozlem; Haman Bayari, Sevgi; Severcan, Mete; Krafft, Christoph; Popp, Jürgen; Severcan, Feride

2012-07-01

The relation between protein structural alterations and tissue dysfunction is a major concern as protein fibrillation and/or aggregation due to structural alterations has been reported in many disease states. In the current study, Fourier transform infrared microspectroscopic imaging has been used to investigate diabetes-induced changes on protein secondary structure and macromolecular content in streptozotocin-induced diabetic rat liver. Protein secondary structural alterations were predicted using neural network approach utilizing the amide I region. Moreover, the role of selenium in the recovery of diabetes-induced alterations on macromolecular content and protein secondary structure was also studied. The results revealed that diabetes induced a decrease in lipid to protein and glycogen to protein ratios in diabetic livers. Significant alterations in protein secondary structure were observed with a decrease in α-helical and an increase in β-sheet content. Both doses of selenium restored diabetes-induced changes in lipid to protein and glycogen to protein ratios. However, low-dose selenium supplementation was not sufficient to recover the effects of diabetes on protein secondary structure, while a higher dose of selenium fully restored diabetes-induced alterations in protein structure.

Structural phase transitions of (Bi 1$-$xSb x ) 2(Te 1$-$y Se y) 3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Jinggeng; Yu, Zhenhai; Hu, Qingyang

Recently, A 2B 3-type tetradymites have developed into a hot topic in physical and material research fields, where the A and B atoms represent V and VI group elements, respectively. In this study, in situ angle-dispersive X-ray diffraction measurements were performed on Bi 2Te 2Se, BiSbTeSe 2, and Sb 2Te 2Se tetradymites under high pressure. Bi 2Te 2Se transforms from a layered rhombohedral structure (phase I) into 7-fold monoclinic (phase II) and body-centered tetragonal (phase IV) structures at about 8.0 and 14.3 GPa, respectively, without an 8-fold monoclinic structure (phase III) similar to that in Bi 2Te 3. Thus, themore » compression behavior of Bi 2Te 2Se is the same as that of Bi 2Se 3, which could also be obtained from first-principles calculations and in situ high-pressure electrical resistance measurements. Under high pressure, BiSbTeSe 2 and Sb 2Te 2Se undergo similar structural phase transitions to Bi 2Te 2Se, which indicates that the compression process of tellurides can be modulated by doping Se in Te sites. According to these high-pressure investigations of A 2B 3-type tetradymites, the decrease of the B-site atomic radius shrinks the stable pressure range of phase III and expands that of phase II, whereas the decrease of the A-site atomic radius induces a different effect, i.e. expanding the stable pressure range of phase III and shrinking that of phase II. Lastly, the influence of the atomic radius on the compression process of tetradymites is closely related to the chemical composition and the atom arrangement in the quintuple layer.« less

Structural phase transitions of (Bi 1$-$xSb x ) 2(Te 1$-$y Se y) 3 compounds under high pressure and the influence of the atomic radius on the compression processes of tetradymites

DOE PAGES

Zhao, Jinggeng; Yu, Zhenhai; Hu, Qingyang; ...

2016-12-14

Recently, A 2B 3-type tetradymites have developed into a hot topic in physical and material research fields, where the A and B atoms represent V and VI group elements, respectively. In this study, in situ angle-dispersive X-ray diffraction measurements were performed on Bi 2Te 2Se, BiSbTeSe 2, and Sb 2Te 2Se tetradymites under high pressure. Bi 2Te 2Se transforms from a layered rhombohedral structure (phase I) into 7-fold monoclinic (phase II) and body-centered tetragonal (phase IV) structures at about 8.0 and 14.3 GPa, respectively, without an 8-fold monoclinic structure (phase III) similar to that in Bi 2Te 3. Thus, themore » compression behavior of Bi 2Te 2Se is the same as that of Bi 2Se 3, which could also be obtained from first-principles calculations and in situ high-pressure electrical resistance measurements. Under high pressure, BiSbTeSe 2 and Sb 2Te 2Se undergo similar structural phase transitions to Bi 2Te 2Se, which indicates that the compression process of tellurides can be modulated by doping Se in Te sites. According to these high-pressure investigations of A 2B 3-type tetradymites, the decrease of the B-site atomic radius shrinks the stable pressure range of phase III and expands that of phase II, whereas the decrease of the A-site atomic radius induces a different effect, i.e. expanding the stable pressure range of phase III and shrinking that of phase II. Lastly, the influence of the atomic radius on the compression process of tetradymites is closely related to the chemical composition and the atom arrangement in the quintuple layer.« less

Rhenium doping induced structural transformation in mono-layered MoS2 with improved catalytic activity for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Shi, Wenwu; Wang, Zhiguo; Qing Fu, Yong

2017-10-01

This paper reports a new design methodology to improve catalytic activities of catalysts based on 2D transition metal dichalcogenides through elemental doping which induces structural transformations. Effects of rhenium (Re) doping on structural stability/phase transformation and catalytic activity of mono-layered trigonal prismatic (2H) MoS2 were investigated using density functional theory as one example. Results show that 2H-Mo1-x Re x S2 transforms into 1T‧-Mo1-x Re x S2MoS2 as the value of x is larger than 0.4, and the transfer of the electron from Re to Mo is identified as the main reason for this structural transformation. The 1T‧-Mo1-x Re x S2 shows a good catalytic activity for the hydrogen evolution reaction when 0.75  ⩽  x  ⩽  0.94.

Phase transition induced strain in ZnO under high pressure

DOE PAGES

Yan, Xiaozhi; Dong, Haini; Li, Yanchun; ...

2016-05-13

Under high pressure, the phase transition mechanism and mechanical property of material are supposed to be largely associated with the transformation induced elastic strain. However, the experimental evidences for such strain are scanty. The elastic and plastic properties of ZnO, a leading material for applications in chemical sensor, catalyst, and optical thin coatings, were determined using in situ high pressure synchrotron axial and radial x-ray diffraction. The abnormal elastic behaviors of selected lattice planes of ZnO during phase transition revealed the existence of internal elastic strain, which arise from the lattice misfit between wurtzite and rocksalt phase. Furthermore, the strengthmore » decrease of ZnO during phase transition under non-hydrostatic pressure was observed and could be attributed to such internal elastic strain, unveiling the relationship between pressure induced internal strain and mechanical property of material. Ultimately, these findings are of fundamental importance to understanding the mechanism of phase transition and the properties of materials under pressure.« less

Bonding Transition in SiO2 Glass at High Pressures: Applications to SiO2 Liquid in Earth's Interior

NASA Astrophysics Data System (ADS)

Yoo, C.; Lin, J.; Fukui, H.; Prendergast, D.; Okuchi, T.; Cai, Y.; Hiraoka, N.; Trave, A.; Eng, P.; Hu, M. Y.; Chow, P.

2006-12-01

SiO2 and MgSiO3 liquids are two major components in the magma deep inside the Earth. Knowledge of their electronic bonding characters at high pressures is essential to understanding the complex properties of the materials in the melts. The nature of pressure-induced bonding change in amorphous SiO2 has been an intriguing and long-standing problem that remains to be further understood. For example, previous infrared and X-ray diffraction studies suggested that a continuous transformation from the four- to six-fold coordinated silicon occurred in amorphous SiO2 at high pressures, whereas separate optical Raman studies attributed to a pressure-induced shift in the local ring statistics and a breakdown in the intermediate-range order. Here we have studied the oxygen near K-edge spectra of SiO2 glass to 51 GPa obtained using X-ray Raman scattering in a diamond-anvil cell, which directly probes the electronic bonding character of the sample. Our results provide conclusive evidence for a pressure-induced electronic bonding transition in SiO2 glass at high pressures. Although a progressive decrease in the mean Si-O-Si angle in the SiO4 tetrahedra is believed to be responsible for the irreversible densification in SiO2 glass at high pressures, our observed transition is reversible upon decompression. A similar transformation is also expected to occur in silicate glasses and melts, which will most definitely alter their physical, mechanical and transport properties in the magma chamber deep in the Earth's interior. This work was performed under the auspices of the U.S. DOE by UC/LLNL under Contract W-7405-Eng-48.

Shock-induced Plasticity and Brittle Cracks in Aluminum Nitride

NASA Astrophysics Data System (ADS)

Branicio, Paulo; Kalia, Rajiv

2005-03-01

Two hundred and nine million atom molecular-dynamics simulation of hypervelocity projectile impact in aluminum nitride reveals strong interplay between shock-induced structural phase transformation, plastic deformation and brittle cracks. The shock wave splits into an elastic precursor and a wurtzite-to-rocksalt structural transformation wave. When the elastic wave reflected from the boundary of the sample interacts with the transformation wave front, nanocavities are generated along the penetration path of the projectile and dislocations in adjacent regions. The nanocavities coalesce to form mode I brittle cracks while dislocations generate kink bands that give rise to mode II cracks. These simulations provide a microscopic view of defects associated with simultaneous tensile and shear cracking at the structural phase transformation boundary due to shock impact in high-strength ceramics.

Martensitic Transformation in a β-Type Mg-Sc Alloy

NASA Astrophysics Data System (ADS)

Ogawa, Yukiko; Ando, Daisuke; Sutou, Yuji; Somekawa, Hidetoshi; Koike, Junichi

2018-03-01

Recently, we found that a Mg-Sc alloy with a bcc (β) phase exhibits superelasticity and a shape memory effect at low temperature. In this work, we examined the stress-induced and thermally induced martensitic transformation of the β-type Mg-Sc alloy and investigated the crystal structure of the thermally induced martensite phase based on in situ X-ray diffraction (XRD) measurements. The lattice constants of the martensite phase were calculated to be a = 0.3285 nm, b = 0.5544 nm, and c = 0.5223 nm when we assumed that the martensite phase has an orthorhombic structure (Cmcm). Based on the lattice correspondence between a bcc and an orthorhombic structures such as that in the case of β-Ti shape memory alloys, we estimated the transformation strain of the β Mg-Sc alloy. As a result, the transformation strains along the 001, 011, and 111 directions in the β phase were calculated to be + 5.7, + 8.8, and + 3.3%, respectively.

Pressure induced elastic softening in framework aluminosilicate- albite (NaAlSi 3O 8)

DOE PAGES

Mookherjee, Mainak; Mainprice, David; Maheshwari, Ketan; ...

2016-10-13

Albite (NaAlSi 3O 8) is an aluminosilicate mineral. Its crystal structure consists of 3-D framework of Al and Si tetrahedral units. We have used Density Functional Theory to investigate the high-pressure behavior of the crystal structure and how it affects the elasticity of albite. Our results indicate elastic softening between 6–8 GPa. This is observed in all the individual elastic stiffness components. Our analysis indicates that the softening is due to the response of the three-dimensional tetrahedral framework, in particular by the pressure dependent changes in the tetrahedral tilts. At pressure <6 GPa, the PAW-GGA can be described by amore » Birch-Murnaghan equation of state with V GGA 0 = 687.4Å 3, K GGA 0 = 51.7 GPa, and G GGA 0 = 4.7. The shear modulus and its pressure derivative are K ⊕GGA 0 = 33.7 GPa, and G ⊕GGA 0 = 2.9. At 1 bar, the azimuthal compressional and shear wave anisotropy AV GGA P = 42.8%, and AV GGA S = 50.1%. We also investigate the densification of albite to a mixture of jadeite and quartz. The transformation is likely to cause a discontinuity in density, compressional, and shear wave velocity across the crust and mantle. Furthermore, this could partially account for the Mohorovicic discontinuity in thickened continental crustal regions.« less

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films.

PubMed

Cao, Shi-Gu; Li, Yunsong; Wu, Hong-Hui; Wang, Jie; Huang, Baoling; Zhang, Tong-Yi

2017-08-09

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO 3 ) with a special thermomechanical treatment (TMT), where BaTiO 3 nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.

UV-induced reaction kinetics of dilinoleoylphosphatidylethanolamine monolayers.

PubMed Central

Viitala, T; Peltonen, J

1999-01-01

The UV-induced reactivity of dilinoleoylphosphatidylethanolamine (DLiPE) Langmuir and Langmuir-Blodgett films has been studied by in situ measurements of the changes in the mean molecular area, UV-vis and Fourier transform infrared spectroscopy, and atomic force microscopy (AFM). Optimum orientation and packing density of the DLiPE molecules in the monolayer were achieved by adding uranyl acetate to the subphase. A first-order reaction kinetic model was successfully fitted to the experimental reaction kinetics data obtained at a surface pressure of 30 mN/m. Topographical studies of LB films by AFM were performed on bilayer structures as a function of subphase composition and UV irradiation time. The orientational effect of the uranyl ions on the monolayer molecules was observed as an enhanced homogeneity of the freshly prepared monomeric LB films. However, the long-term stability of these films proved to be bad; clear reorganization and loss of a true monolayer structure were evidenced by the AFM images. This instability was inhibited for the UV-irradiated films, indicating that the UV irradiation gave rise to a cross-linked structure. PMID:10233096

Influence of Ar-ion implantation on the structural and mechanical properties of zirconia as studied by Raman spectroscopy and nanoindentation techniques

NASA Astrophysics Data System (ADS)

Kurpaska, L.; Jasinski, J.; Wyszkowska, E.; Nowakowska-Langier, K.; Sitarz, M.

2018-04-01

In this study, structural and nanomechanical properties of zirconia polymorphs induced by ion irradiation were investigated by means of Raman spectroscopy and nanoindentation techniques. The zirconia layer have been produced by high temperature oxidation of pure zirconium at 600 °C for 5 h at normal atmospheric pressure. In order to distinguish between the internal and external parts of zirconia, the spherical metallographic sections have been prepared. The samples were irradiated at room temperature with 150 keV Ar+ ions at fluences ranging from 1 × 1015 to 1 × 1017 ions/cm2. The main objective of this study was to distinguish and confirm different structural and mechanical properties between the interface layer and fully developed scale in the internal/external part of the oxide. Conducted studies suggest that increasing ion fluence impacts Raman bands positions (especially characteristic for tetragonal phase) and increases the nanohardness and Young's modulus of individual phases. This phenomenon has been examined from the point of view of stress-induced hardening effect and classical monoclinic → tetragonal (m → t) martensitic phase transformation.

Volume and structural relaxation in compressed sodium borate glass.

PubMed

Svenson, Mouritz N; Youngman, Randall E; Yue, Yuanzheng; Rzoska, Sylwester J; Bockowski, Michal; Jensen, Lars R; Smedskjaer, Morten M

2016-11-21

The structure and properties of glass can be modified through compression near the glass transition temperature (T g ), and such modified structure and properties can be maintained at ambient temperature and pressure. However, once the compressed glass undergoes annealing near T g at ambient pressure, the modified structure and properties will relax. The challenging question is how the property relaxation is correlated with both the local and the medium-range structural relaxation. In this paper, we answer this question by studying the volume (density) and structural relaxation of a sodium borate glass that has first been pressure-quenched from its T g at 1 GPa, and then annealed at ambient pressure under different temperature-time conditions. Using 11 B MAS NMR and Raman spectroscopy, we find that the pressure-induced densification of the glass is accompanied by a conversion of six-membered rings into non-ring trigonal boron (B III ) units, i.e. a structural change in medium-range order, and an increase in the fraction of tetrahedral boron (B IV ), i.e. a structural change in short-range order. These pressure-induced structural conversions are reversible during ambient pressure annealing near T g , but exhibit a dependence on the annealing temperature, e.g. the ring/non-ring B III ratio stabilizes at different values depending on the applied annealing temperature. We find that conversions between structural units cannot account for the pressure-induced densification, and instead we suggest the packing of structural units as the main densification mechanism.

Irradiation-induced phenomena in carbon nanomaterials

NASA Astrophysics Data System (ADS)

Krasheninnikov, Arkady

2008-03-01

The irradiation of solids with energetic particles such as electrons or ions is associated with disorder, normally an undesirable phenomenon. However, recent experiments [for an overview, see A.V Krasheninnikov, F. Banhart, Nature Materials, 6 (2007) 723] on bombardment of carbon nanostructures with energetic particles demonstrate that irradiation can have beneficial effects and that electron or ion beams may serve as tools to change the morphology and tailor mechanical, electronic and even magnetic properties of nanostructured carbon systems. We systematically study irradiation effects in carbon nanotubes and other forms of nano-structured carbon experimentally and theoretically by employing various atomistic models ranging from empirical potentials to time-dependent density functional theory. In my presentation, I will briefly review the recent progress in our understanding of ion-irradiation-induced phenomena in nano-structured carbon and present our recent theoretical [A.V Krasheninnikov, et al., Phys. Rev. Lett., 99 (2007) 016104, A. Tolvanen et al, Appl. Phys. Lett. 91 (2007) 173109.] and experimental [O. Lehtinen et al., to be published] results. I dwell on the ``beneficial'' role of defects and impurities in nanotubes and related systems. Finally, I will present the results of simulations of irradiation-induced pressure build-up inside nanotubes encapsulated with metals [L. Sun, et al., Science 312 (2006) 1199]. Electron irradiation of such composite systems in the transmission electron microscope gives rise to contraction of nanotube shells and thus to high pressure. The irradiation-stimulated pressure can be as high as 40 GPa, which makes it possible to study phase transformations at the nanoscale with high spatial resolution. I will also address the mechanisms of plastic deformation of small metal particles inside carbon shells at high temperatures, which may be important for understanding catalytic growth of carbon nanotubes.

Observation of a New High-Pressure Solid Phase in Dynamically Compressed Aluminum

NASA Astrophysics Data System (ADS)

Polsin, D. N.

2017-10-01

Aluminum is ideal for testing theoretical first-principles calculations because of the relative simplicity of its atomic structure. Density functional theory (DFT) calculations predict that Al transforms from an ambient-pressure, face-centered-cubic (fcc) crystal to the hexagonal close-packed (hcp) and body-centered-cubic (bcc) structures as it is compressed. Laser-driven experiments performed at the University of Rochester's Laboratory for Laser Energetics and the National Ignition Facility (NIF) ramp compressed Al samples to pressures up to 540 GPa without melting. Nanosecond in-situ x-ray diffraction was used to directly measure the crystal structure at pressures where the solid-solid phase transformations of Al are predicted to occur. Laser velocimetry provided the pressure in the Al. Our results show clear evidence of the fcc-hcp and hpc-bcc transformations at 216 +/- 9 GPa and 321 +/- 12 GPa, respectively. This is the first experimental in-situ observation of the bcc phase in compressed Al and a confirmation of the fcc-hcp transition previously observed under static compression at 217 GPa. The observations indicate these solid-solid phase transitions occur on the order of tens of nanoseconds time scales. In the fcc-hcp transition we find the original texture of the sample is preserved; however, the hcp-bcc transition diminishes that texture producing a structure that is more polycrystalline. The importance of this dynamic is discussed. The NIF results are the first demonstration of x-ray diffraction measurements at two different pressures in a single laser shot. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Transformation with TT8 and HB12 RNAi Constructs in Model Forage (Medicago sativa, Alfalfa) Affects Carbohydrate Structure and Metabolic Characteristics in Ruminant Livestock Systems.

PubMed

Li, Xinxin; Zhang, Yonggen; Hannoufa, Abdelali; Yu, Peiqiang

2015-11-04

Lignin, a phenylpropanoid polymer present in secondary cell walls, has a negative impact on feed digestibility. TT8 and HB12 genes were shown to have low expression levels in low-lignin tissues of alfalfa, but to date, there has been no study on the effect of down-regulation of these two genes in alfalfa on nutrient chemical profiles and availability in ruminant livestock systems. The objectives of this study were to investigate the effect of transformation of alfalfa with TT8 and HB12 RNAi constructs on carbohydrate (CHO) structure and CHO nutritive value in ruminant livestock systems. The results showed that transformation with TT8 and HB12 RNAi constructs reduced rumen, rapidly degraded CHO fractions (RDCA4, P = 0.06; RDCB1, P < 0.01) and totally degraded CHO fraction (TRDCHO, P = 0.08). Both HB12 and TT8 populations had significantly higher in vitro digestibility of neutral detergent fiber (NDF) at 30 h of incubation (ivNDF30) compared to the control (P < 0.01). The TT8 populations had highest ivDM30 and ivNDF240. Transformation of alfalfa with TT8 and HB12 RNAi constructs induced molecular structure changes. Different CHO functional groups had different sensitivities and different responses to the transformation. The CHO molecular structure changes induced by the transformation were associated with predicted CHO availability. Compared with HB12 RNAi, transformation with TT8 RNAi could improve forage quality by increasing the availability of both NDF and DM. Further study is needed on the relationship between the transformation-induced structure changes at a molecular level and nutrient utilization in ruminant livestock systems when lignification is much higher.

Predicting the thermal/structural performance of the atmospheric trace molecules spectroscopy /ATMOS/ Fourier transform spectrometer

NASA Technical Reports Server (NTRS)

Miller, J. M.

1980-01-01

ATMOS is a Fourier transform spectrometer to measure atmospheric trace molecules over a spectral range of 2-16 microns. Assessment of the system performance of ATMOS includes evaluations of optical system errors induced by thermal and structural effects. In order to assess the optical system errors induced from thermal and structural effects, error budgets are assembled during system engineering tasks and line of sight and wavefront deformations predictions (using operational thermal and vibration environments and computer models) are subsequently compared to the error budgets. This paper discusses the thermal/structural error budgets, modelling and analysis methods used to predict thermal/structural induced errors and the comparisons that show that predictions are within the error budgets.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Haiyan; Li, Kuo; Cody, George D.

Acetonitrile (CH 3CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. In this study, it is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH 3 to CN along the CH···N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed spmore » 2 and sp 3 bonded carbon. Lastly, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst.« less

Influence of Pressure on Physical Property of Ammonia Borane and its Re-hydrogenation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jiuhua

The project systematically studied the high pressure behavior of ammonia borane and its derivative lithium amidoborane. Phase transitions in these materials are investigated in the pressure range up to 20 GPa and temperature range from 80 K to 400K. A number of new phase transitions are discovered in this pressure and temperature range including a second order transformation at 5 GPa and a first order transformation at 12 GPa at room temperature, and four new transitions at high pressure and low temperatures. The Clapeyron slopes for both pressure-induce tetragonal (I4mm) phase to orthorhombic (Cmc21) phase and temperature-induce tetragonal (I4mm) phasemore » to orthorhombic (Pmn21) phase are determined to be positive, indicating these phase transitions are exothermic. This result demonstrates that the high pressure orthorhombic phase of ammonia borane has lower enthalpy than that of tetragonal phase at ambient conditions. If we assume decomposition from the orthorhombic phase yields the same products as that from the tetragonal phase, the decomposition of the orthorhombic phase will be less exothermic. Therefore rehydrogenation from the decomposed product into the orthorhombic phase at high pressure may become easier. The project also studied the influences of nanoconfinement on the phase transitions. Comparative study using Raman spectroscopy indicates that the temperature induced I4mm to Pmn21 transition is suppressed from 217 K to 195 K when the sample is confined in SBA15 (7-9 nm pore size). When the pore size is reduced from 7-9 nm to 3-4 nm, this transition is totally suppressed in the temperature down to 80 K. A similar influence of the nanoconfiement on pressure induced phase transitions is also observed using Raman spectroscopy. The phase boundary between the I4mm phase and high pressure Cmc21 phase at ambient temperature shifts from 0.9 GPa to 0.5 GPa; and that between the Cmc21 phase and higher pressure P21 phase shifts from 10.2 GPa to 9.7 GPa.« less

Pressure-Induced Structural Phase Transition in CeNi: X-ray and Neutron Scattering Studies and First-Principles Calculations

DOE PAGES

Mirmelstein, A.; Podlesnyak, Andrey A.; dos Santos, Antonio M.; ...

2015-08-03

The pressure-induced structural phase transition in the intermediate-valence compound CeNi has been investigated by x-ray and neutron powder diffraction techniques. It is shown that the structure of the pressure-induced CeNi phase (phases) can be described in terms of the Pnma space group. Equations of state for CeNi on both sides of the phase transition are derived and an approximate P-T phase diagram is suggested for P<8 GPa and T<300 K. The observed Cmcm→Pnma structural transition is then analyzed using density functional theory calculations, which successfully reproduce the ground state volume, the phase transition pressure, and the volume collapse associated withmore » the phase transition.« less

Shock temperatures in silica glass - Implications for modes of shock-induced deformation, phase transformation, and melting with pressure

NASA Technical Reports Server (NTRS)

Schmitt, Douglas R.; Ahrens, Thomas J.

1989-01-01

Observations of shock-induced radiative thermal emissions are used to determine the gray body temperatures and emittances of silica glass under shock compression between 10 and 30 GPa. The results suggest that fused quartz deforms heterogeneously in this shock pressure range. It is shown that the 10-16 GPa range coincides with the permanent densification region, while the 16-30 GPa range coincides with the inferred mixed phase region along the silica glass Hugoniot. Low emittances in the mixed phase region are thought to represent the melting temperature of the high-pressure phase, stishovite. Also, consideration is given to the effects of pressure on melting relations for the system SiO2-Mg2SiO4.

Uranyl peroxide nanoclusters at high-pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turner, Katlyn M.; Szymanowski, Jennifer E. S.; Zhang, Fuxiang

Here, U 60 ([UO 2(O 2)(OH)] 60 60– in water) is a uranyl peroxide nanocluster with a fullerene topology and O h symmetry. U 60 clusters can exist in crystalline solids or in liquids; however, little is known of their behavior at high pressures. We compressed the U 60-bearing material: Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 ( Fm3¯; a = 37.884 Å) in a diamond anvil cell to determine its response to increasing pressure. Three length scales and corresponding structural features contribute to the compression response: uranyl peroxide bonds (<0.5 nm), isolated single nanoclusters (2.5 nm), andmore » the long-range periodicity of nanoclusters within the solid (>3.7 nm). Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 transformed to a tetragonal structure below 2 GPa and irreversibly amorphized between 9.6 and 13 GPa. The bulk modulus of the tetragonal U 60-bearing material was 25 ± 2 GPa. The pressure-induced amorphous phase contained intact U 60 clusters, which were preserved beyond the loss of long-range periodicity. The persistence of U 60 clusters at high pressure may have been enhanced by the interaction between U 60 nanoclusters and the alcohol pressure medium. Once formed, U 60 nanoclusters persist regardless of their associated long-range ordering—in crystals, amorphous solids, or solutions.« less

Uranyl peroxide nanoclusters at high-pressure

DOE PAGES

Turner, Katlyn M.; Szymanowski, Jennifer E. S.; Zhang, Fuxiang; ...

2017-08-14

Here, U 60 ([UO 2(O 2)(OH)] 60 60– in water) is a uranyl peroxide nanocluster with a fullerene topology and O h symmetry. U 60 clusters can exist in crystalline solids or in liquids; however, little is known of their behavior at high pressures. We compressed the U 60-bearing material: Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 ( Fm3¯; a = 37.884 Å) in a diamond anvil cell to determine its response to increasing pressure. Three length scales and corresponding structural features contribute to the compression response: uranyl peroxide bonds (<0.5 nm), isolated single nanoclusters (2.5 nm), andmore » the long-range periodicity of nanoclusters within the solid (>3.7 nm). Li 68K 12(OH) 20[UO 2(O 2)(OH)] 60(H 2O) 310 transformed to a tetragonal structure below 2 GPa and irreversibly amorphized between 9.6 and 13 GPa. The bulk modulus of the tetragonal U 60-bearing material was 25 ± 2 GPa. The pressure-induced amorphous phase contained intact U 60 clusters, which were preserved beyond the loss of long-range periodicity. The persistence of U 60 clusters at high pressure may have been enhanced by the interaction between U 60 nanoclusters and the alcohol pressure medium. Once formed, U 60 nanoclusters persist regardless of their associated long-range ordering—in crystals, amorphous solids, or solutions.« less

High pressure structural behavior of YGa2: A combined experimental and theoretical study

NASA Astrophysics Data System (ADS)

Sekar, M.; Shekar, N. V. Chandra; Babu, R.; Sahu, P. Ch.; Sinha, A. K.; Upadhyay, Anuj; Singh, M. N.; Babu, K. Ramesh; Appalakondaiah, S.; Vaitheeswaran, G.; Kanchana, V.

2015-03-01

High pressure structural stability studies were carried out on YGa2 (AlB2 type structure at NTP, space group P6/mmm) up to a pressure of 35 GPa using both laboratory based rotating anode and synchrotron X-ray sources. An isostructural transition with reduced c/a ratio, was observed at 6 GPa and above 17.5 GPa, the compound transformed to orthorhombic structure. Bulk modulus B0 for the parent and high pressure phases were estimated using Birch-Murnaghan and modified Birch-Murnaghan equation of state. Electronic structure calculations based on projector augmented wave method confirms the experimentally observed two high pressure structural transitions. The calculations also reveal that the 'Ga' networks remains as two dimensional in the high pressure isostructural phase, whereas the orthorhombic phase involves three dimensional networks of 'Ga' atoms interconnected by strong covalent bonds.

In situ 3D-X-ray diffraction tracking of individual grains of olivine during high-pressure/ high-temperature phase transitions

NASA Astrophysics Data System (ADS)

Rosa, A. D.; Merkel, S.; Ghosh, S.; Hilairet, N.; Perrillat, J.; Mezouar, N.; Vaughan, G.

2013-12-01

The series of phase transitions between olivine, wadsleyite and ringwoodite play an essential role for large scale dynamical processes in the Earth mantle. Detailed knowledge of the microscopic mechanism at the origin of these high-pressure and high-temperature phase transformations is useful to connect global seismic observations and geodynamics. Indeed, the textures of these phases can be induced either during mantle flow or during the phase transformations and they greatly affect the characteristics of seismic wave propagation. Here, we present a new design of diamond anvil cell experiments to collect three-dimensional diffraction images and track individual grains inside a polycristalline sample at high pressure and high temperature. The instrumentation includes a new resistively heated diamond anvil cell developed at beamline ID27 of the ESRF which provided stable and homogenous temperature condition over more than 24 hours. In our experiments, the pressure is first increased up to 12 GPa at a constant temperature of T = 800 K. The temperature is then further increased to 1300 K to reach the stability field of the high-pressure polymorph. Upon further compression the transformation of olivine to its high-pressure polymorph is successfully monitored. At each pressure-temperature step and while the sample is transforming the crystallographic parameters, the orientations and positions of grains within the sample are tracked in situ using three-dimensional X-ray diffraction. This will provide important information on the micromechanical properties of olivine including orientation statistics, orientation relations between parent and daughter phases, and transformation textures at different stages of the phase transition. This in turn will help in interpreting the geophysical observations. Details of the experimental and analytical approach used in this study will be given.

Effect of high pressure homogenization on the structure and the interfacial and emulsifying properties of β-lactoglobulin.

PubMed

Ali, Ali; Le Potier, Isabelle; Huang, Nicolas; Rosilio, Véronique; Cheron, Monique; Faivre, Vincent; Turbica, Isabelle; Agnely, Florence; Mekhloufi, Ghozlene

2018-02-15

The effect of high pressure homogenization (HPH) on the structure of β-lactoglobulin (β-lg) was studied by combining spectroscopic, chromatographic, and electrophoretic methods. The consequences of the resulting structure modifications on oil/water (O/W) interfacial properties were also assessed. Moderated HPH treatment (100 MPa/4 cycles) showed no significant modification of protein structure and interfacial properties. However, a harsher HPH treatment (300 MPa/5 cycles) induced structural transformation, mainly from β-sheets to random coils, wide loss in lipocalin core, and protein aggregation via intermolecular disulfide bridges. HPH-modified β-lg displayed higher surface hydrophobicity leading to a faster adsorption rate at the interface and an earlier formation of an elastic interfacial film at C β-lg  = 0.1 wt%. However, no modification of the interfacial properties was observed at C β-lg  = 1 wt%. At this protein concentration, the prior denaturation of β-lg by HPH did not modify the droplet size of nanoemulsions prepared with these β-lg solutions as the aqueous phases. A slightly increased creaming rate was however observed. The effects of HPH and heat denaturations appeared qualitatively similar, but with differences in their extent. Copyright © 2017 Elsevier B.V. All rights reserved.

Temperature- and pressure-dependent structural transformation of methane hydrates in salt environments

NASA Astrophysics Data System (ADS)

Shin, Donghoon; Cha, Minjun; Yang, Youjeong; Choi, Seunghyun; Woo, Yesol; Lee, Jong-Won; Ahn, Docheon; Im, Junhyuck; Lee, Yongjae; Han, Oc Hee; Yoon, Ji-Ho

2017-03-01

Understanding the stability of volatile species and their compounds under various surface and subsurface conditions is of great importance in gaining insights into the formation and evolution of planetary and satellite bodies. We report the experimental results of the temperature- and pressure-dependent structural transformation of methane hydrates in salt environments using in situ synchrotron X-ray powder diffraction, solid-state nuclear magnetic resonance, and Raman spectroscopy. We find that under pressurized and concentrated brine solutions methane hydrate forms a mixture of type I clathrate hydrate, ice, and hydrated salts. Under a low-pressure condition, however, the methane hydrates are decomposed through a rapid sublimation of water molecules from the surface of hydrate crystals, while NaCl · 2H2O undergoes a phase transition into a crystal growth of NaCl via the migration of salt ions. In ambient pressure conditions, the methane hydrate is fully decomposed in brine solutions at temperatures above 252 K, the eutectic point of NaCl · 2H2O.

High Pressure Phase Transformations in Heavy Rare Earth Metals and Connections to Actinide Crystal Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vohra, Yogesh K.; Sangala, Bagvanth Reddy; Stemshorn, Andrew K.

2008-07-01

High-pressure studies have been performed on heavy rare earth metals Terbium (Tb) to 155 GPa and Holmium (Ho) to 134 GPa in a diamond anvil cell at room temperature. The following crystal structure sequence was observed in both metals hcp {yields} Sm-type {yields} dhcp {yields} distorted fcc (hR-24) {yields} monoclinic (C2/m) with increasing pressure. The last transformation to a low symmetry monoclinic phase is accompanied by a volume collapse of 5 % for Tb at 51 GPa and a volume collapse of 3 % for Ho at 103 GPa. This volume collapse under high pressure is reminiscent of f-shell delocalizationmore » in light rare earth metal Cerium (Ce), Praseodymium (Pr), and heavy actinide metals Americium (Am) and Curium (Cm). The orthorhombic Pnma phase that has been reported in Am and Cm after f-shell delocalization is not observed in heavy rare earth metals under high pressures. (authors)« less

Discovery of Ahrensite γ-Fe2SiO4 and Tissintite (Ca,Na,[])AlSi2O6, Two New Shock-induced Minerals from the Tissint Martian Meteorite: a Nanomineralogy Investigation

NASA Astrophysics Data System (ADS)

Ma, C.; Tschauner, O. D.; Liu, Y.; Sinogeikin, S. V.; Zhuravlev, K. K.; Prakapenka, V.; Dera, P. K.; Taylor, L. A.

2013-12-01

The recent Martian meteorite fall, Tissint, is a fresh olivine-phyric shergottite, with strong shock features. During our nano-mineralogy investigation of the Tissint meteorite with a combined analytical scanning electron microscope and synchrotron diffraction approach, two new shock-induced minerals have been discovered; these provide new insights into understanding shock conditions and impact processes on Mars. Ahrensite (IMA 2013-028), the Fe-analogue (γ-Fe2SiO4) of ringwoodite, is a new high-pressure mineral identified in Tissint. Both ahrensite and ringwoodite occur in Tissint as fine-grained polycrystalline aggregates in the rims of olivines around some shock-melt pockets. The morphology and texture of these silicate-spinels suggest formation by a solid-state transformation from Fe-rich olivine. Associated with the ahrensite and ringwoodite, inside melt pockets, often resides a thin layer of vitrified silicate-perovskite and magnesio-wüstite or wüstite. Such transitions represent a unique pressure and temperature gradient. Tissintite (IMA 2013-027), (Ca,Na,[])AlSi2O6 with the C2/c clinopyroxene structure, is a new jadeite-like mineral in Tissint. It appears as fine-grained aggregates within plagioclase glass, inside many shock-melt pockets. Both ahrensite and tissintite are high-pressure minerals formed by shock during the impact event(s) on Mars that excavated and ejected the rock off Mars. We will discuss the path of structure analysis for both new-mineral cases. Such novel methodology be utilized for many cases of mineralogical phase identification or structure analysis; this demonstrates how nano-mineralogy can be addressed and how it may play a unique role in meteorite and Mars rock research, in general.

Pressure induced structural, electronic topological, and semiconductor to metal transition in AgBiSe2

NASA Astrophysics Data System (ADS)

Rajaji, V.; Malavi, Pallavi S.; Yamijala, Sharma S. R. K. C.; Sorb, Y. A.; Dutta, Utpal; Guin, Satya N.; Joseph, B.; Pati, Swapan K.; Karmakar, S.; Biswas, Kanishka; Narayana, Chandrabhas

2016-10-01

We report the effect of strong spin orbit coupling inducing electronic topological and semiconductor to metal transitions on the thermoelectric material AgBiSe2 at high pressures. The synchrotron X-ray diffraction and the Raman scattering measurement provide evidence for a pressure induced structural transition from hexagonal (α-AgBiSe2) to rhombohedral (β-AgBiSe2) at a relatively very low pressure of around 0.7 GPa. The sudden drop in the electrical resistivity and clear anomalous changes in the Raman line width of the A1g and Eg(1) modes around 2.8 GPa was observed suggesting a pressure induced electronic topological transition. On further increasing the pressure, anomalous pressure dependence of phonon (A1g and Eg(1)) frequencies and line widths along with the observed temperature dependent electrical resistivity show a pressure induced semiconductor to metal transition above 7.0 GPa in β-AgBiSe2. First principles theoretical calculations reveal that the metallic character of β-AgBiSe2 is induced mainly due to redistributions of the density of states (p orbitals of Bi and Se) near to the Fermi level. Based on its pressure induced multiple electronic transitions, we propose that AgBiSe2 is a potential candidate for the good thermoelectric performance and pressure switches at high pressure.

Theoretical study of the partial molar volume change associated with the pressure-induced structural transition of ubiquitin

PubMed Central

Imai, Takashi; Ohyama, Shusaku; Kovalenko, Andriy; Hirata, Fumio

2007-01-01

The partial molar volume (PMV) change associated with the pressure-induced structural transition of ubiquitin is analyzed by the three-dimensional reference interaction site model (3D-RISM) theory of molecular solvation. The theory predicts that the PMV decreases upon the structural transition, which is consistent with the experimental observation. The volume decomposition analysis demonstrates that the PMV reduction is primarily caused by the decrease in the volume of structural voids in the protein, which is partially canceled by the volume expansion due to the hydration effects. It is found from further analysis that the PMV reduction is ascribed substantially to the penetration of water molecules into a specific part of the protein. Based on the thermodynamic relation, this result implies that the water penetration causes the pressure-induced structural transition. It supports the water penetration model of pressure denaturation of proteins proposed earlier. PMID:17660257

Theoretical study of the partial molar volume change associated with the pressure-induced structural transition of ubiquitin.

PubMed

Imai, Takashi; Ohyama, Shusaku; Kovalenko, Andriy; Hirata, Fumio

2007-09-01

The partial molar volume (PMV) change associated with the pressure-induced structural transition of ubiquitin is analyzed by the three-dimensional reference interaction site model (3D-RISM) theory of molecular solvation. The theory predicts that the PMV decreases upon the structural transition, which is consistent with the experimental observation. The volume decomposition analysis demonstrates that the PMV reduction is primarily caused by the decrease in the volume of structural voids in the protein, which is partially canceled by the volume expansion due to the hydration effects. It is found from further analysis that the PMV reduction is ascribed substantially to the penetration of water molecules into a specific part of the protein. Based on the thermodynamic relation, this result implies that the water penetration causes the pressure-induced structural transition. It supports the water penetration model of pressure denaturation of proteins proposed earlier.

Pressure-induced stable BeN4 as a high-energy density material

NASA Astrophysics Data System (ADS)

Zhang, Shoutao; Zhao, Ziyuan; Liu, Lulu; Yang, Guochun

2017-10-01

Polynitrogens are the ideal rocket fuels or propellants. Due to strong triple N≡N bond in N2, the direct polymerization of nitrogen is rather difficult (i.e. extreme high temperature and high pressure). However, the use of nitrides as precursors or the reaction of N2 with other elements has been proved to be an effective way to obtain polynitrogens. Here, with assistance of the advanced first-principles swarm-intelligence structure searches, we found that P 1 bar -BeN4, containing infinite zigzag-like polymeric nitrogen chains, can be synthesized by compressing the mixture of Be3N2 and N2 at 25.4 GPa, which is greatly lower than 110 GPa for synthesizing cubic gauche nitrogen and other polynitrogen compounds (e.g. bulk CNO at 52 GPa and SN4 at 49 GPa). Its structural stability can be attributed to the coexistence of ionic Be-N and covalent N-N bonds. Intriguingly, this phase has high kinetic stability and remains metastable at ambient pressure. The exceptional properties, including high energy density (3.60 kJ g-1), high nitrogen content (86.1%), high dynamical stability, and low polymerization pressure, make P 1 bar -structured BeN4 a promising high energy material. Infinite nitrogen chains in P 1 bar -BeN4 transform to N10 rings network in P21/c phase at 115.1 GPa. P 1 bar -BeN4 is metallic, while P21/c-BeN4 is an insulator.

Protective effects of intercalated disk protein afadin on chronic pressure overload-induced myocardial damage

PubMed Central

Zankov, Dimitar P.; Shimizu, Akio; Tanaka-Okamoto, Miki; Miyoshi, Jun; Ogita, Hisakazu

2017-01-01

Adhesive intercellular connections at cardiomyocyte intercalated disks (IDs) support contractile force and maintain structural integrity of the heart muscle. Disturbances of the proteins at IDs deteriorate cardiac function and morphology. An adaptor protein afadin, one of the components of adherens junctions, is expressed ubiquitously including IDs. At present, the precise role of afadin in cardiac physiology or disease is unknown. To explore this, we generated conditional knockout (cKO) mice with cardiomyocyte-targeted deletion of afadin. Afadin cKO mice were born according to the expected Mendelian ratio and have no detectable changes in cardiac phenotype. On the other hand, chronic pressure overload induced by transverse aortic constriction (TAC) caused systolic dysfunction, enhanced fibrogenesis and apoptosis in afadin cKO mice. Afadin deletion increased macrophage infiltration and monocyte chemoattractant protein-1 expression, and suppressed transforming growth factor (TGF) β receptor signaling early after TAC procedure. Afadin also associated with TGFβ receptor I at IDs. Pharmacological antagonist of TGFβ receptor I (SB431542) augmented mononuclear infiltration and fibrosis in the hearts of TAC-operated control mice. In conclusion, afadin is a critical molecule for cardiac protection against chronic pressure overload. The beneficial effects are likely to be a result from modulation of TGFβ receptor signaling pathways by afadin. PMID:28045017

Potential energy landscape of the apparent first-order phase transition between low-density and high-density amorphous ice.

PubMed

Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W; Poole, Peter H

2016-12-14

The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.

Potential energy landscape of the apparent first-order phase transition between low-density and high-density amorphous ice

NASA Astrophysics Data System (ADS)

Giovambattista, Nicolas; Sciortino, Francesco; Starr, Francis W.; Poole, Peter H.

2016-12-01

The potential energy landscape (PEL) formalism is a valuable approach within statistical mechanics to describe supercooled liquids and glasses. Here we use the PEL formalism and computer simulations to study the pressure-induced transformations between low-density amorphous ice (LDA) and high-density amorphous ice (HDA) at different temperatures. We employ the ST2 water model for which the LDA-HDA transformations are remarkably sharp, similar to what is observed in experiments, and reminiscent of a first-order phase transition. Our results are consistent with the view that LDA and HDA configurations are associated with two distinct regions (megabasins) of the PEL that are separated by a potential energy barrier. At higher temperature, we find that low-density liquid (LDL) configurations are located in the same megabasin as LDA, and that high-density liquid (HDL) configurations are located in the same megabasin as HDA. We show that the pressure-induced LDL-HDL and LDA-HDA transformations occur along paths that interconnect these two megabasins, but that the path followed by the liquid is different from the path followed by the amorphous solid. At higher pressure, we also study the liquid-to-ice-VII first-order phase transition, and find that the behavior of the PEL properties across this transition is qualitatively similar to the changes found during the LDA-HDA transformation. This similarity supports the interpretation that the LDA-HDA transformation is a first-order phase transition between out-of-equilibrium states. Finally, we compare the PEL properties explored during the LDA-HDA transformations in ST2 water with those reported previously for SPC/E water, for which the LDA-HDA transformations are rather smooth. This comparison illuminates the previous work showing that, at accessible computer times scales, a liquid-liquid phase transition occurs in the case of ST2 water, but not for SPC/E water.

Shock-induced fine-grained recrystallization of olivine - Evidence against subsolidus reduction of Fe/2+/

NASA Technical Reports Server (NTRS)

Ahrens, T. J.; Tsay, F.-D.; Live, D. H.

1976-01-01

Electron spin resonance (ESR) studies have been carried out on three single grains of terrestrial olivine (Fo90) shock loaded along the 010 line to peak pressures of 280, 330, and 440 kbar. The results indicate that neither metallic Fe similar to that observed in returned lunar soils nor paramagnetic Fe(3+) caused by oxidation of Fe(2+) has been produced in these shock experiments. Trace amounts of Mn (2+) have been detected in both shocked and unshocked olivine. The ESR signals of Mn(2+) show spectral features which are found to correlate with the degree of shock-induced recrystallization observed petrographically. The increasing mass fraction of recrystallized olivine correlates with increasing shock pressures. This phenomenon is modelled assuming it results from the progressive effect of the shock-induced transformation of the olivine to a yet unknown high-pressure phase and its subsequent reversion to the low-pressure olivine phase. The mass fraction of recrystallized material is predicted to be nearly linear with shock pressure.

Effect of grain boundaries on shock-induced phase transformation in iron bicrystals

NASA Astrophysics Data System (ADS)

Zhang, Xueyang; Wang, Kun; Zhu, Wenjun; Chen, Jun; Cai, Mengqiu; Xiao, Shifang; Deng, Huiqiu; Hu, Wangyu

2018-01-01

Non-equilibrium molecular-dynamic simulations with a modified analytic embedded-atom model potential have been performed to investigate the effect of three kinds of grain boundaries (GBs) on the martensitic transformation in iron bicrystals with three different GBs under shock loadings. Our results show that the phase transition was influenced by the GBs. All three GBs provide a nucleation site for the α → ɛ transformation in samples shock-loaded with up = 0.5 km/s, and in particular, the elastic wave can induce the phase transformation at Σ3 ⟨110⟩ twist GB, which indicates that the phase transformation can occur at Σ3 ⟨110⟩ twist GB with a much lower pressure. The effect of GBs on the stress assisted transformation (SAT) mechanisms is discussed. All variants nucleating at the vicinity of these GBs meet the maximum strain work (MSW) criterion. Moreover, all of the variants with the MSW nucleate at Σ5 ⟨001⟩ twist GB and Σ3 ⟨110⟩ tilt GB, but only part of them nucleate at Σ3 ⟨110⟩ twist GB. This is because the coincident planes between both sides of the GB would affect the slip process, which is the second stage of the martensitic transformation and influences the selection of variant. We also find that the martensitic transformation at the front end of the bicrystals would give rise to stress attenuation in samples shock-loaded with up = 0.6 km/s, which makes the GBs seem to be unfavorable to the martensitic transformation. Our findings have the potential to affect the interface engineering and material design under high pressure conditions.

Humidity-dependent compression-induced glass transition of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA).

PubMed

Kim, Hyun Chang; Lee, Hoyoung; Jung, Hyunjung; Choi, Yun Hwa; Meron, Mati; Lin, Binhua; Bang, Joona; Won, You-Yeon

2015-07-28

Constant rate compression isotherms of the air-water interfacial Langmuir films of poly(D,L-lactic acid-ran-glycolic acid) (PLGA) show a distinct feature of an exponential increase in surface pressure in the high surface polymer concentration regime. We have previously demonstrated that this abrupt increase in surface pressure is linked to the glass transition of the polymer film, but the detailed mechanism of this process is not fully understood. In order to obtain a molecular-level understanding of this behavior, we performed extensive characterizations of the surface mechanical, structural and rheological properties of Langmuir PLGA films at the air-water interface, using combined experimental techniques including the Langmuir film balance, X-ray reflectivity and double-wall-ring interfacial rheometry methods. We observed that the mechanical and structural responses of the Langmuir PLGA films are significantly dependent on the rate of film compression; the glass transition was induced in the PLGA film only at fast compression rates. Surprisingly, we found that this deformation rate dependence is also dependent on the humidity of the environment. With water acting as a plasticizer for the PLGA material, the diffusion of water molecules through the PLGA film seems to be the key factor in the determination of the glass transformation properties and thus the mechanical response of the PLGA film against lateral compression. Based on our combined results, we hypothesize the following mechanism for the compression-induced glass transformation of the Langmuir PLGA film; (1) initially, a humidified/non-glassy PLGA film is formed in the full surface-coverage region (where the surface pressure shows a plateau) during compression; (2) further compression leads to the collapse of the PLGA chains and the formation of new surfaces on the air side of the film, and this newly formed top layer of the PLGA film is transiently glassy in character because the water evaporation rate in the top surface region is momentarily faster than the humidification rate (due to the initial roughness of the newly formed surface); (3) after some time, the top layer itself becomes humidified through diffusion of water from the subphase, and thus it becomes non-glassy, leading to the relaxation of the applied compressive stress.

Influence of sample preparation on the transformation of low-density to high-density amorphous ice: An explanation based on the potential energy landscape

NASA Astrophysics Data System (ADS)

Giovambattista, Nicolas; Starr, Francis W.; Poole, Peter H.

2017-07-01

Experiments and computer simulations of the transformations of amorphous ices display different behaviors depending on sample preparation methods and on the rates of change of temperature and pressure to which samples are subjected. In addition to these factors, simulation results also depend strongly on the chosen water model. Using computer simulations of the ST2 water model, we study how the sharpness of the compression-induced transition from low-density amorphous ice (LDA) to high-density amorphous ice (HDA) is influenced by the preparation of LDA. By studying LDA samples prepared using widely different procedures, we find that the sharpness of the LDA-to-HDA transformation is correlated with the depth of the initial LDA sample in the potential energy landscape (PEL), as characterized by the inherent structure energy. Our results show that the complex phenomenology of the amorphous ices reported in experiments and computer simulations can be understood and predicted in a unified way from knowledge of the PEL of the system.

High-pressure polymorphism of Pb F 2 to 75 GPa

DOE PAGES

Stan, Camelia V.; Dutta, Rajkrishna; White, Claire E.; ...

2016-07-06

Lead fluoride, PbF 2, was investigated experimentally in the laser-heated diamond anvil cell by x-ray diffraction to pressures of 75 GPa at room temperature and to 64.5 GPa and 2430 K, as well as through first-principles density functional theory calculations up to 70 GPa. During room temperature compression, no discontinuous changes in the x-ray diffraction pattern or volume were observed, but the lattice parameters displayed highly anomalous trends between 10-22 GPa with enhanced compressibility along the a direction and reduced or even negative compressibility along b and c. Theoretical calculations of valence electron densities at 22 GPa showed that α-PbFmore » 2 underwent a pressure-induced isosymmetric phase transition to a postcotunnite Co 2Si structure and also revealed the detailed atomic rearrangements associated with the development of an extra Pb-F bond in the high-pressure phase. Our x-ray results and theoretical calculations are consistent with an isosymmetric phase transition smoothly occurring over 10-22 GPa rather than abruptly as previously suggested. The characteristic values for the cell constants a/c and (a+c)/b, which are used to distinguish among cotunnite-, Co 2Si-, and Ni 2In-type phases, require modification based on our results. An equation of state fit yields a bulk modulus, K 0, of 72(3) GPa for the cotunnite-type, and an ambient-pressure volume, V 0, of 182(2)Å 3, and K 0=81(4)GPa for the Co 2Si-type phase when fixing the pressure derivative of the bulk modulus, K 0'=4. Upon heating above 1200 K at pressures at or above 25.9 GPa, PbF 2 partially transformed to the hexagonal Ni 2In-type phase but wholly or partially reverted back to Co 2Si-type phase upon temperature quench. From 43-65 GPa, nearly complete transformation to the Ni 2In-type PbF 2 was observed at high temperature, but the material partially transformed back to the orthorhombic phase upon temperature quench. Our results show that high-pressure behavior of PbF 2 is distinct from that of the alkaline earth fluorides with similar ionic radii. These results also have relevance to understanding the behavior of lanthanide and actinide dioxides, which have been predicted theoretically to exhibit similar isosymmetric transitions at Mbar pressures.« less

High-pressure polymorphism of Pb F2 to 75 GPa

NASA Astrophysics Data System (ADS)

Stan, Camelia V.; Dutta, Rajkrishna; White, Claire E.; Prakapenka, Vitali; Duffy, Thomas S.

2016-07-01

Lead fluoride, Pb F2 , was investigated experimentally in the laser-heated diamond anvil cell by x-ray diffraction to pressures of 75 GPa at room temperature and to 64.5 GPa and 2430 K, as well as through first-principles density functional theory calculations up to 70 GPa. During room temperature compression, no discontinuous changes in the x-ray diffraction pattern or volume were observed, but the lattice parameters displayed highly anomalous trends between 10-22 GPa with enhanced compressibility along the a direction and reduced or even negative compressibility along b and c . Theoretical calculations of valence electron densities at 22 GPa showed that α -Pb F2 underwent a pressure-induced isosymmetric phase transition to a postcotunnite C o2Si structure and also revealed the detailed atomic rearrangements associated with the development of an extra Pb-F bond in the high-pressure phase. Our x-ray results and theoretical calculations are consistent with an isosymmetric phase transition smoothly occurring over 10-22 GPa rather than abruptly as previously suggested. The characteristic values for the cell constants a /c and (a +c )/b , which are used to distinguish among cotunnite-, C o2Si -, and N i2In -type phases, require modification based on our results. An equation of state fit yields a bulk modulus, K0, of 72(3) GPa for the cotunnite-type, and an ambient-pressure volume, V0, of 182 (2 ) Å3 , and K0=81 (4 ) GPa for the C o2Si -type phase when fixing the pressure derivative of the bulk modulus, K0 '=4 . Upon heating above 1200 K at pressures at or above 25.9 GPa, Pb F2 partially transformed to the hexagonal N i2In -type phase but wholly or partially reverted back to C o2Si -type phase upon temperature quench. From 43-65 GPa, nearly complete transformation to the N i2In -type Pb F2 was observed at high temperature, but the material partially transformed back to the orthorhombic phase upon temperature quench. Our results show that high-pressure behavior of Pb F2 is distinct from that of the alkaline earth fluorides with similar ionic radii. Our results also have relevance to understanding the behavior of lanthanide and actinide dioxides, which have been predicted theoretically to exhibit similar isosymmetric transitions at Mbar pressures.

Tuning and synthesis of metallic nanostructures by mechanical compression

DOEpatents

Fan, Hongyou; Li, Binsong

2015-11-17

The present invention provides a pressure-induced phase transformation process to engineer metal nanoparticle architectures and to fabricate new nanostructured materials. The reversible changes of the nanoparticle unit cell dimension under pressure allow precise control over interparticle separation in 2D or 3D nanoparticle assemblies, offering unique robustness for interrogation of both quantum and classic coupling interactions. Irreversible changes above a threshold pressure of about 8 GPa enables new nanostructures, such as nanorods, nanowires, or nanosheets.

High-pressure-induced structural changes, amorphization and molecule penetration in MFI microporous materials: a review.

PubMed

Vezzalini, Giovanna; Arletti, Rossella; Quartieri, Simona

2014-06-01

This is a comparative study on the high-pressure behavior of microporous materials with an MFI framework type (i.e. natural mutinaite, ZSM-5 and the all-silica phase silicalite-1), based on in-situ experiments in which penetrating and non-penetrating pressure-transmitting media were used. Different pressure-induced phenomena and deformation mechanisms (e.g. pressure-induced over-hydration, pressure-induced amorphization) are discussed. The influence of framework and extra-framework composition and of the presence of silanol defects on the response to the high pressure of MFI-type zeolites is discussed.

Raman studies of nanocomposites catalysts: temperature and pressure effects of CeAl, CeMn and NiAl oxides

NASA Astrophysics Data System (ADS)

da Silva, Antonio N.; Neto, Antonio B. S.; Oliveira, Alcemira C.; Junior, Manoel C.; Junior, Jose A. L.; Freire, Paulo T. C.; Filho, Josué M.; Oliveira, Alcineia C.; Lang, Rossano

2018-06-01

High temperature and pressure effects on the physicochemical properties of binary oxides catalysts were investigated. The nanocomposites catalysts comprising of CeAl, CeMn and NiAl were characterized through various physicochemical techniques. A study of the temperature and pressure induced phenomena monitored by Raman spectroscopy was proposed and discussed. Spectral modifications of the Raman modes belonging to the CeMn suggest structural changes in the solid due to the MnO2 phase oxidation with increasing temperature. The thermal expansion and lattice anharmonicity effects were observed on CeMn due to lack of stability of the lattice vacancies. The CeAl and NiAl composites presented crystallographic stability at low temperatures however, undertake a phase transformation of NiO/Al2O3 into NiAl2O4, mostly without any deformation in its structure with increasing the temperature. It was also inferred that the binary oxides are more stables in comparison with monoxides. Detailed pressure-dependent Raman measurements of the T2g phonon mode of CeMn and NiAl revealed that the pressure contributes to modify bonds length and reduces the particles sizes of the solids. On the contrary, high pressure on CeAl sample improved the stability with addition of Al2O3 in the CeO2 lattice. The results then suggest a good stability of CeAl and NiAl composite catalysts at high pressure and low temperature and show how to prospect of tuning the catalysis for surface reactions entirely through in situ spectroscopic investigations means.

Toward pressure-induced multiferroicity in PrMn2O5

NASA Astrophysics Data System (ADS)

Peng, W.; Balédent, V.; Chattopadhyay, S.; Lepetit, M.-B.; Yahia, G.; Colin, C. V.; Gooch, M. J.; Pasquier, C. R.; Auban-Senzier, P.; Greenblatt, M.; Foury-Leylekian, P.

2017-08-01

The series of multiferroics R Mn2O5 is extensively studied for its quasicollinear spin arrangement, which results in an electrical polarization according to the exchange-striction model. Variations of the interatomic distances modified by the external pressure can strongly influence the multiferroic properties. Understanding this influence is of great importance, especially for the future realization of multiferroic devices. As PrMn2O5 is paraelectric at ambient pressure, it is the most suitable candidate to search for pressure induced multiferroicity. In this paper, we report the emergence of a new pressure induced magnetic phase in PrMn2O5 determined by powder neutron diffraction under pressure. This new magnetic phase presenting at relatively low pressure becomes completely exclusive at 8 GPa. The determination of its magnetic structure has thus been possible for the first time. More importantly, the magnetic structure stabilized under pressure should induce a strong spontaneous electric polarization due to the nearly perfect collinearity of the Mn3 + and Mn4 + spins.

Resilience of biochemical activity in protein domains in the face of structural divergence.

PubMed

Zhang, Dapeng; Iyer, Lakshminarayan M; Burroughs, A Maxwell; Aravind, L

2014-06-01

Recent studies point to the prevalence of the evolutionary phenomenon of drastic structural transformation of protein domains while continuing to preserve their basic biochemical function. These transformations span a wide spectrum, including simple domains incorporated into larger structural scaffolds, changes in the structural core, major active site shifts, topological rewiring and extensive structural transmogrifications. Proteins from biological conflict systems, such as toxin-antitoxin, restriction-modification, CRISPR/Cas, polymorphic toxin and secondary metabolism systems commonly display such transformations. These include endoDNases, metal-independent RNases, deaminases, ADP ribosyltransferases, immunity proteins, kinases and E1-like enzymes. In eukaryotes such transformations are seen in domains involved in chromatin-related peptide recognition and protein/DNA-modification. Intense selective pressures from 'arms-race'-like situations in conflict and macromolecular modification systems could favor drastic structural divergence while preserving function. Published by Elsevier Ltd.

Dynamic permeability in fault damage zones induced by repeated coseismic fracturing events

NASA Astrophysics Data System (ADS)

Aben, F. M.; Doan, M. L.; Mitchell, T. M.

2017-12-01

Off-fault fracture damage in upper crustal fault zones change the fault zone properties and affect various co- and interseismic processes. One of these properties is the permeability of the fault damage zone rocks, which is generally higher than the surrounding host rock. This allows large-scale fluid flow through the fault zone that affects fault healing and promotes mineral transformation processes. Moreover, it might play an important role in thermal fluid pressurization during an earthquake rupture. The damage zone permeability is dynamic due to coseismic damaging. It is crucial for earthquake mechanics and for longer-term processes to understand how the dynamic permeability structure of a fault looks like and how it evolves with repeated earthquakes. To better detail coseismically induced permeability, we have performed uniaxial split Hopkinson pressure bar experiments on quartz-monzonite rock samples. Two sample sets were created and analyzed: single-loaded samples subjected to varying loading intensities - with damage varying from apparently intact to pulverized - and samples loaded at a constant intensity but with a varying number of repeated loadings. The first set resembles a dynamic permeability structure created by a single large earthquake. The second set resembles a permeability structure created by several earthquakes. After, the permeability and acoustic velocities were measured as a function of confining pressure. The permeability in both datasets shows a large and non-linear increase over several orders of magnitude (from 10-20 up to 10-14 m2) with an increasing amount of fracture damage. This, combined with microstructural analyses of the varying degrees of damage, suggests a percolation threshold. The percolation threshold does not coincide with the pulverization threshold. With increasing confining pressure, the permeability might drop up to two orders of magnitude, which supports the possibility of large coseismic fluid pulses over relatively large distances along a fault. Also, a relatively small threshold could potentially increase permeability in a large volume of rock, given that previous earthquakes already damaged these rocks.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tracy, Cameron L.; Park, Sulgiye; Rittman, Dylan R.

High-entropy alloys, near-equiatomic solid solutions of five or more elements, represent a new strategy for the design of materials with properties superior to those of conventional alloys. However, their phase space remains constrained, with transition metal high-entropy alloys exhibiting only face- or body-centered cubic structures. Here, we report the high-pressure synthesis of a hexagonal close-packed phase of the prototypical high-entropy alloy CrMnFeCoNi. This martensitic transformation begins at 14 GPa and is attributed to suppression of the local magnetic moments, destabilizing the initial fcc structure. Similar to fcc-to-hcp transformations in Al and the noble gases, the transformation is sluggish, occurring overmore » a range of >40 GPa. However, the behaviour of CrMnFeCoNi is unique in that the hcp phase is retained following decompression to ambient pressure, yielding metastable fcc-hcp mixtures. This demonstrates a means of tuning the structures and properties of high-entropy alloys in a manner not achievable by conventional processing techniques.« less

Challenges in Modelling of Lightning-Induced Delamination; Effect of Temperature-Dependent Interfacial Properties

NASA Technical Reports Server (NTRS)

Naghipour, P.; Pineda, E. J.; Arnold, S.

2014-01-01

Lightning is a major cause of damage in laminated composite aerospace structures during flight. Due to the dielectric nature of Carbon fiber reinforced polymers (CFRPs), the high energy induced by lightning strike transforms into extreme, localized surface temperature accompanied with a high-pressure shockwave resulting in extensive damage. It is crucial to develop a numerical tool capable of predicting the damage induced from a lightning strike to supplement extremely expensive lightning experiments. Delamination is one of the most significant failure modes resulting from a lightning strike. It can be extended well beyond the visible damage zone, and requires sophisticated techniques and equipment to detect. A popular technique used to model delamination is the cohesive zone approach. Since the loading induced from a lightning strike event is assumed to consist of extreme localized heating, the cohesive zone formulation should additionally account for temperature effects. However, the sensitivity to this dependency remains unknown. Therefore, the major focus point of this work is to investigate the importance of this dependency via defining various temperature dependency profiles for the cohesive zone properties, and analyzing the corresponding delamination area. Thus, a detailed numerical model consisting of multidirectional composite plies with temperature-dependent cohesive elements in between is subjected to lightning (excessive amount of heat and pressure) and delamination/damage expansion is studied under specified conditions.

Pressure-induced ferroelectric to paraelectric transition in LiTaO 3 and (Li,Mg)TaO 3

DOE PAGES

Yamanaka, Takamitsu; Nakamoto, Yuki; Takei, Fumihiko; ...

2016-02-16

X-ray powder diffraction and Raman scattering of LiTaO 3 (LT) and (Li,Mg)TaO 3 (LMT) have been measured under pressure up to 46 GPa. Above 30 GPa, the ferroelectric rhombohedral phase (R3c, Z – 6) of LiTaO 3 transforms to a paraelectric orthorhombic phase (Pnma with Z – 4) with a large hysteresis. Rietveld profile fitting analysis shows that the Li-O bond is compressed and approaches that of Ta-O with pressure. The cation distribution analysis of the orthorhombic perovskite structure shows that Li and Ta are located in the octahedral 8-fold coordination sites. Difference Fourier |F obs(hkl)| - |F cal(hkl)| mapsmore » of LiTaO 3 and (Li,Mg)TaO 3 indicate polarization in the c axis direction and a more distinct electron density distribution around the Ta position for (Li,Mg)TaO 3 compared to LiTaO 3. The observed effective charges indicate that for (Li,Mg)TaO 3 without vacancies Ta 5+ becomes less ionized as a function of Mg substitution. Considering both site occupancy and effective charge analysis, Ta 5+ is reduced to Ta 4.13+. Mg 2+ and O 2- change to Mg 1.643+ and O 1.732 -, respectively. The space- and time-averaged structures of the dynamical vibration of atoms can be elucidated from the electron density analysis by difference Fourier and temperature factors T(hkl) in the structure refinement. The refinement of the temperature factor is consistent with the cation distribution assuming full stoichiometry. The residual electron density induced from the excess electron in (Li,Mg)TaO 3 indicates more electrons around the Ta site, as confirmed by the effective charge analysis. Raman spectra of LiTaO 3 and (Li,Mg)TaO 3 show notable changes over the measured pressure range. Raman peaks centered at 250 cm –1 and 350 cm –1 at ambient pressure merge above 8 GPa, which we associate with the diminishing of difference in distances between Li-O and Ta-O bonds with pressure in both materials. Finally, Raman spectra show significant changes at 28 GPa and 33 GPa for LT and LMT, respectively, due to the structural transition from R3c to Pnma consistent with the x-ray diffraction results.« less

Equation of state and pressure induced amorphization of beta-boron from X-ray measurements up to 100 GPa.

PubMed

Sanz, Delia Nieto; Loubeyre, Paul; Mezouar, Mohamed

2002-12-09

The equation of state of boron has been measured up to 100 GPa by single-crystal x-ray diffraction with helium as the pressure transmitting medium. Rhombohedral beta-boron is the stable structure up to 100 GPa under hydrostatic conditions. Nonhydrostatic stress stabilizes a different rhombohedral structure. At about 100 GPa a pressure-induced amorphization is observed. The amorphous phase can be quenched to ambient pressure. An explanation is proposed based on the different stability under pressure between intraicosahedra and intericosahedra bonds.

Phase Transformations and Metallization of Magnesium Oxide at High Pressure and Temperature

NASA Astrophysics Data System (ADS)

McWilliams, R. Stewart; Spaulding, Dylan K.; Eggert, Jon H.; Celliers, Peter M.; Hicks, Damien G.; Smith, Raymond F.; Collins, Gilbert W.; Jeanloz, Raymond

2012-12-01

Magnesium oxide (MgO) is representative of the rocky materials comprising the mantles of terrestrial planets, such that its properties at high temperatures and pressures reflect the nature of planetary interiors. Shock-compression experiments on MgO to pressures of 1.4 terapascals (TPa) reveal a sequence of two phase transformations: from B1 (sodium chloride) to B2 (cesium chloride) crystal structures above 0.36 TPa, and from electrically insulating solid to metallic liquid above 0.60 TPa. The transitions exhibit large latent heats that are likely to affect the structure and evolution of super-Earths. Together with data on other oxide liquids, we conclude that magmas deep inside terrestrial planets can be electrically conductive, enabling magnetic field-producing dynamo action within oxide-rich regions and blurring the distinction between planetary mantles and cores.

Metastable high-pressure transformations of orthoferrosilite Fs82

NASA Astrophysics Data System (ADS)

Dera, Przemyslaw; Finkelstein, Gregory J.; Duffy, Thomas S.; Downs, Robert T.; Meng, Yue; Prakapenka, Vitali; Tkachev, Sergey

2013-08-01

High-pressure single-crystal X-ray diffraction experiments with natural ferrosilite Fs82 (Fe2+0.82Mg0.16Al0.01Ca0.01)(Si0.99Al0.01)O3 orthopyroxene (opx) reveal that at ambient temperature the sample does not transform to the clinopyroxene (cpx) structure, as reported earlier for a synthetic Fs100 end-member (Hugh-Jones et al., 1996), but instead undergoes a series of two polymorphic transitions, first above 10.1(1) GPa, to the monoclinic P21/c phase β-opx (distinctly different from both P21/c and C2/c cpx), also observed in natural enstatite (Zhang et al., 2012), and then, above 12.3(1) GPa to a high-pressure orthorhombic Pbca phase γ-opx, predicted for MgSiO3 by atomistic simulations (Jahn, 2008). The structures of phases α, β and γ have been determined from the single-crystal data at pressures of 2.3(1), 11.1(1), and 14.6(1) GPa, respectively. The two new high-pressure transitions, very similar in their character to the P21/c-C2/c transformation of cpx, make opx approximately as dense as cpx above 12.3(1) GPa and significantly change the elastic anisotropy of the crystal, with the [1 0 0] direction becoming almost twice as stiff as in the ambient α-opx phase. Both transformations involve mainly tetrahedral rotation, are reversible and are not expected to leave microstructural evidence that could be used as a geobarometric proxy. The high Fe2+ content in Fs82 shifts the α-β transition to slightly lower pressure, compared to MgSiO3, and has a very dramatic effect on reducing the (meta) stability range of the β-phase.

Phase transitions in MgSiO3 post-perovskite in super-Earth mantles

NASA Astrophysics Data System (ADS)

Umemoto, Koichiro; Wentzcovitch, Renata M.; Wu, Shunqing; Ji, Min; Wang, Cai-Zhuang; Ho, Kai-Ming

2017-11-01

The highest pressure form of the major Earth-forming mantle silicate is MgSiO3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-Earths-type exoplanets, arguably the most interesting for their similarities with Earth. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO2 and MgO as the ultimate aggregation form at ∼3 TPa. However, none of these studies have addressed the problem of mantle composition, particularly major element abundances usually expressed in terms of three main variables, the Mg/Si and Fe/Si ratios and the Mg#, as in the Earth. Here we show that the critical compositional parameter, the Mg/Si ratio, whose value in the Earth's mantle is still debated, is a vital ingredient for modeling phase transitions and internal structure of super-Earth mantles. Specifically, we have identified new sequences of phase transformations, including new recombination reactions that depend decisively on this ratio. This is a new level of complexity that has not been previously addressed, but proves essential for modeling the nature and number of internal layers in these rocky mantles.

The structure of CO 2 hydrate between 0.7 and 1.0 GPa

DOE PAGES

Tulk, Chris A.; Machida, Shinichi; Klug, Dennis D.; ...

2014-11-05

A deuterated sample of CO 2 structure I (sI) clathrate hydrate (CO 2 ∙ 8.3 D 2O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO 2 hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai, et al. (J. Phys. Chem. 133, 124511 (2010)) and O. Bollengier et al. (Geochim. Cosmochim. AC. 119, 322 (2013)), but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO 2 molecules filling the watermore » channels. This CO 2+water system has also been investigated using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts an MH-III ‘like’ filled ice structure with considerable disorder of the orientations of the CO 2molecule. Furthermore, the disorder appears be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al. our neutron diffraction data shows that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, and recrystallization to sI hydrate occurs upon subsequent heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO 2 hydrate transforms directly from the sI form to the filled ice structure.« less

The structure of CO 2 hydrate between 0.7 and 1.0 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tulk, C. A.; Machida, S.; Klug, D. D.

A deuterated sample of CO2 structure I (sI) clathrate hydrate (CO2·8.3 D2O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO2 hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai et al. [J. Phys. Chem. 133, 124511 (2010)] and Bollengier et al. [Geochim. Cosmochim. Acta 119, 322 (2013)], but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO2 molecules filling the water channels. This CO2+water system has also been investigatedmore » using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts a MH-III “like” filled ice structure with considerable disorder of the orientations of the CO2 molecule. Furthermore, the disorder appears to be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al., our neutron diffraction data show that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, and recrystallization to sI hydrate occurs upon subsequent heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO2 hydrate transforms directly from the sI form to the filled ice structure.« less

The structure of CO{sub 2} hydrate between 0.7 and 1.0 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tulk, C. A.; Molaison, J. J.; Machida, S.

A deuterated sample of CO{sub 2} structure I (sI) clathrate hydrate (CO{sub 2}·8.3 D{sub 2}O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO{sub 2} hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai et al. [J. Phys. Chem. 133, 124511 (2010)] and Bollengier et al. [Geochim. Cosmochim. Acta 119, 322 (2013)], but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO{sub 2} molecules filling the water channels. This CO{submore » 2}+water system has also been investigated using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts a MH-III “like” filled ice structure with considerable disorder of the orientations of the CO{sub 2} molecule. Furthermore, the disorder appears to be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al., our neutron diffraction data show that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, and recrystallization to sI hydrate occurs upon subsequent heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO{sub 2} hydrate transforms directly from the sI form to the filled ice structure.« less

The structure of CO 2 hydrate between 0.7 and 1.0 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tulk, Chris A.; Machida, Shinichi; Klug, Dennis D.

A deuterated sample of CO 2 structure I (sI) clathrate hydrate (CO 2 ∙ 8.3 D 2O) has been formed and neutron diffraction experiments up to 1.0 GPa at 240 K were performed. The sI CO 2 hydrate transformed at 0.7 GPa into the high pressure phase that had been observed previously by Hirai, et al. (J. Phys. Chem. 133, 124511 (2010)) and O. Bollengier et al. (Geochim. Cosmochim. AC. 119, 322 (2013)), but which had not been structurally identified. The current neutron diffraction data were successfully fitted to a filled ice structure with CO 2 molecules filling the watermore » channels. This CO 2+water system has also been investigated using classical molecular dynamics and density functional ab initio methods to provide additional characterization of the high pressure structure. Both models indicate the water network adapts an MH-III ‘like’ filled ice structure with considerable disorder of the orientations of the CO 2molecule. Furthermore, the disorder appears be a direct result of the level of proton disorder in the water network. In contrast to the conclusions of Bollengier et al. our neutron diffraction data shows that the filled ice phase can be recovered to ambient pressure (0.1 MPa) at 96 K, and recrystallization to sI hydrate occurs upon subsequent heating to 150 K, possibly by first forming low density amorphous ice. Unlike other clathrate hydrate systems, which transform from the sI or sII structure to the hexagonal structure (sH) then to the filled ice structure, CO 2 hydrate transforms directly from the sI form to the filled ice structure.« less

Group-III elements under high pressure.

NASA Astrophysics Data System (ADS)

Simak, S. I.; Haussermann, U.; Ahuja, R.; Johansson, B.

2000-03-01

At ambient conditions the Group-III elements Ga and In attain unusual open ground-state crystal structures. Recent experiments have discovered that Ga under high pressure transforms into the face-centered (fcc) cubic close-packed structure, while such a transition for In has so far not been observed. We offer a simple explanation for such different behavior based on results from first principles calculations. We predict a so far undiscovered transition of In to the fcc structure at extreme pressures and show that the structure determining mechanism originates from the degree of s-p mixing of the valence orbitals. A unified bonding picture for the Group-III elements is discussed.

Thermal evolution of the metastable r8 and bc8 polymorphs of silicon

DOE PAGES

Haberl, Bianca; Guthrie, Malcolm; Sinogeikin, Stanislav V.; ...

2015-01-28

The kinetics of two metastable polymorphs of silicon under thermal annealing was investigated. These phases with body-centered cubic bc8 and rhombohedral r8 structures can be formed upon pressure release from metallic silicon.We study these metastable polymorphs were formed by two different methods, via point loading and in a diamond anvil cell (DAC). Upon thermal annealing different transition pathways were detected. In the point loading case, the previously reported Si-XIII formed and was confirmed as a new phase with an as-yet-unidentified structure. In the DAC case, bc8-Si transformed to the hexagonal-diamond structure at elevated pressure, consistent with previous studies at ambientmore » pressure. In contrast, r8-Si transformed directly to diamond-cubic Si at a temperature of 255⁰C. In conclusion, these data were used to construct diagrams of the metastability regimes of the polymorphs formed in a DAC and may prove useful for potential technological applications of these metastable polymorphs.« less

Thermal evolution of the metastable r8 and bc8 polymorphs of silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haberl, Bianca; Guthrie, Malcolm; Sinogeikin, Stanislav V.

The kinetics of two metastable polymorphs of silicon under thermal annealing was investigated. These phases with body-centered cubic bc8 and rhombohedral r8 structures can be formed upon pressure release from metallic silicon.We study these metastable polymorphs were formed by two different methods, via point loading and in a diamond anvil cell (DAC). Upon thermal annealing different transition pathways were detected. In the point loading case, the previously reported Si-XIII formed and was confirmed as a new phase with an as-yet-unidentified structure. In the DAC case, bc8-Si transformed to the hexagonal-diamond structure at elevated pressure, consistent with previous studies at ambientmore » pressure. In contrast, r8-Si transformed directly to diamond-cubic Si at a temperature of 255⁰C. In conclusion, these data were used to construct diagrams of the metastability regimes of the polymorphs formed in a DAC and may prove useful for potential technological applications of these metastable polymorphs.« less

Crystal structure of simple metals at high pressures

NASA Astrophysics Data System (ADS)

Degtyareva, Olga

2010-09-01

The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14-17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a behaviour normally expected under pressure. Group 1 and 2 metallic elements, however, show a reverse trend towards structures with low packing density due to intricate changes in their electronic structure. Complex crystal structures such as host-guest and incommensurately modulated structures found in these elements are given special attention in this review in an attempt to determine their role in the observed phase-transition sequences.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stan, Camelia V.; Dutta, Rajkrishna; White, Claire E.

Lead fluoride, PbF 2, was investigated experimentally in the laser-heated diamond anvil cell by x-ray diffraction to pressures of 75 GPa at room temperature and to 64.5 GPa and 2430 K, as well as through first-principles density functional theory calculations up to 70 GPa. During room temperature compression, no discontinuous changes in the x-ray diffraction pattern or volume were observed, but the lattice parameters displayed highly anomalous trends between 10-22 GPa with enhanced compressibility along the a direction and reduced or even negative compressibility along b and c. Theoretical calculations of valence electron densities at 22 GPa showed that α-PbFmore » 2 underwent a pressure-induced isosymmetric phase transition to a postcotunnite Co 2Si structure and also revealed the detailed atomic rearrangements associated with the development of an extra Pb-F bond in the high-pressure phase. Our x-ray results and theoretical calculations are consistent with an isosymmetric phase transition smoothly occurring over 10-22 GPa rather than abruptly as previously suggested. The characteristic values for the cell constants a/c and (a+c)/b, which are used to distinguish among cotunnite-, Co 2Si-, and Ni 2In-type phases, require modification based on our results. An equation of state fit yields a bulk modulus, K 0, of 72(3) GPa for the cotunnite-type, and an ambient-pressure volume, V 0, of 182(2)Å 3, and K 0=81(4)GPa for the Co 2Si-type phase when fixing the pressure derivative of the bulk modulus, K 0'=4. Upon heating above 1200 K at pressures at or above 25.9 GPa, PbF 2 partially transformed to the hexagonal Ni 2In-type phase but wholly or partially reverted back to Co 2Si-type phase upon temperature quench. From 43-65 GPa, nearly complete transformation to the Ni 2In-type PbF 2 was observed at high temperature, but the material partially transformed back to the orthorhombic phase upon temperature quench. Our results show that high-pressure behavior of PbF 2 is distinct from that of the alkaline earth fluorides with similar ionic radii. These results also have relevance to understanding the behavior of lanthanide and actinide dioxides, which have been predicted theoretically to exhibit similar isosymmetric transitions at Mbar pressures.« less

Pressure induced structural phase transition from NaCl-type (B1) to CsCl-type (B2) structure in sodium chloride

NASA Astrophysics Data System (ADS)

Jain, Aayushi; Dixit, R. C.

2018-05-01

Pressure induced structural phase transition of NaCl-type (B1) to CsCl-type (B2) structure in Sodium Chloride NaCl are presented. An effective interionic interaction potential (EIOP) with long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge is reported here. The reckon value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are compatible as compared with reported data. The variations of elastic constants and their combinations with pressure follow ordered behavior. The present approach has also succeeded in predicting the Born and relative stability criteria.

High-pressure deformation of calcite marble and its transformation to aragonite under non-hydrostatic conditions

USGS Publications Warehouse

Hacker, B.R.; Kirby, S.H.

1993-01-01

We conducted deformation experiments on Carrara marble in the aragonite and calcite stability fields to observe the synkinematic transformation of calcite to aragonite, and to identify any relationships between transformation and deformation or sample strength. Deformation-induced microstructures in calcite crystals varied most significantly with temperature, ranging from limited slip and twinning at 400??C, limited recrystallization at 500??C, widespread recrystallization at 600 and 700??C, to grain growth at 800-900??C. Variations in confining pressure from 0.3 to 2.0 GPa have no apparent effect on calcite deformation microstructures. Aragonite grew in 10-6-10-7 s-1strain rate tests conducted for 18-524 h at confining pressures of 1.7-2.0 GPa and temperatures of 500-600??C. As in our previously reported hydrostatic experiments on this same transformation, the aragonite nucleated on calcite grain boundaries. The extent of transformation varied from a few percent conversion near pistons at 400??C, 2.0 GPa and 10-4 s-1 strain rate in a 0.8 h long experiment, to 98% transformation in a 21-day test at a strain rate of 10-7 s-7, a temperature of 600??C and a pressure of 2.0 GPa. At 500??C, porphyroblastic 100-200 ??m aragonite crystals grew at a rate faster than 8 ?? 10-1m s-1. At 600??C, the growth of aragonite neoblasts was slower, ???6 ?? 10-1 m s -1, and formed 'glove-and-finger' cellularprecipitation-like textures identical to those observed in hydrostatic experiments. The transformation to aragonite is not accompanied by a shear instability or anisotropic aragonite growth, consistent with its relatively small volume change and latent heat in comparison with compounds that do display those features. ?? 1993.

Control of shock-wave boundary-layer interactions by bleed in supersonic mixed compression inlets

NASA Technical Reports Server (NTRS)

Fukuda, M. K.; Reshotko, E.; Hingst, W. R.

1975-01-01

An experimental investigation has been conducted to determine the effect of bleed region geometry and bleed rate on shock wave-boundary layer interactions in an axisymmetric, mixed-compression inlet at a Mach number of 2.5. The full realizable reduction in transformed form factor is obtained by bleeding off about half the incident boundary layer mass flow. Bleeding upstream or downstream of the shock-induced pressure rise is preferable to bleeding across the shock-induced pressure rise. Slanted holes are more effective than normal holes. Two different bleed hole sizes were tested without detectable difference in performance.

Pressure-Induced Phase Transitions of n-Tridecane

NASA Astrophysics Data System (ADS)

Yamashita, Motoi

Pressure-induced phase transition behavior of n-tridecane from the ordered phase through the rotator phase into the liquid phase has been investigated by using Fourier transform infrared spectroscopy at 25 °C. The transition between the ordered and rotator phases has been observed in the pressure range of 270-220 MPa and the transition between the rotator and liquid phases has been observed in the pressure range of 171-112 MPa, within the experimental error of ±50 MPa. The populations of the -gtg- + -gtg'-, -gg- and gt- defects determined from the methylene wagging mode are smaller in the rotator phase than in the liquid phase and are smaller under higher pressure in both of the rotator and liquid phases. A relationship has been found between the conformation and the intensity of the 890 cm-1 band, which has been assigned as the methyl rocking mode and has been considered as insensitive to conformation.

A shear localization mechanism for lubricity of amorphous carbon materials

PubMed Central

Ma, Tian-Bao; Wang, Lin-Feng; Hu, Yuan-Zhong; Li, Xin; Wang, Hui

2014-01-01

Amorphous carbon is one of the most lubricious materials known, but the mechanism is not well understood. It is counterintuitive that such a strong covalent solid could exhibit exceptional lubricity. A prevailing view is that lubricity of amorphous carbon results from chemical passivation of dangling bonds on surfaces. Here we show instead that lubricity arises from shear induced strain localization, which, instead of homogeneous deformation, dominates the shearing process. Shear localization is characterized by covalent bond reorientation, phase transformation and structural ordering preferentially in a localized region, namely tribolayer, resulting in shear weakening. We further demonstrate an anomalous pressure induced transition from stick-slip friction to continuous sliding with ultralow friction, due to gradual clustering and layering of graphitic sheets in the tribolayer. The proposed shear localization mechanism sheds light on the mechanism of superlubricity, and would enrich our understanding of lubrication mechanism of a wide variety of amorphous materials. PMID:24412998

Mild pressure induces rapid accumulation of neutral lipid (triacylglycerol) in Chlorella spp.

PubMed

Praveenkumar, Ramasamy; Kim, Bohwa; Lee, Jiye; Vijayan, Durairaj; Lee, Kyubock; Nam, Bora; Jeon, Sang Goo; Kim, Dong-Myung; Oh, You-Kwan

2016-11-01

Effective enhancement of neutral lipid (especially triacylglycerol, TAG) content in microalgae is an important issue for commercialization of microalgal biorefineries. Pressure is a key physical factor affecting the morphological, physiological, and biochemical behaviors of organisms. In this paper, we report a new stress-based method for induction of TAG accumulation in microalgae (specifically, Chlorella sp. KR-1 and Ch. sp. AG20150) by very-short-duration application of mild pressure. Pressure treatments of 10-15bar for 2h resulted in a considerable, ∼55% improvement of the 10-100g/Lcells' TAG contents compared with the untreated control. The post-pressure-treatment increase of cytoplasmic TAG granules was further confirmed by transmission electron microscopy (TEM). Notwithstanding the increased TAG content, the total lipid content was not changed by pressurization, implying that pressure stress possibly induces rapid remodeling/transformation of algal lipids rather than de novo biosynthesis of TAG. Copyright © 2016 Elsevier Ltd. All rights reserved.

Pressure-induced enhancement in the thermoelectric properties of monolayer and bilayer SnSe2

NASA Astrophysics Data System (ADS)

Zou, Daifeng; Yu, Chuanbin; Li, Yuhao; Ou, Yun; Gao, Yongyi

2018-03-01

The electronic structures of monolayer and bilayer SnSe2 under pressure were investigated by using first-principles calculations including van der Waals interactions. For monolayer SnSe2, the variation of electronic structure under pressure is controlled by pressure-dependent lattice parameters. For bilayer SnSe2, the changes in electronic structure under pressure are dominated by intralayer and interlayer atomic interactions. The n-type thermoelectric properties of monolayer and bilayer SnSe2 under pressure were calculated on the basis of the semi-classical Boltzmann transport theory. It was found that the electrical conductivity of monolayer and bilayer SnSe2 can be enhanced under pressure, and such dependence can be attributed to the pressure-induced changes of the Se-Sn antibonding states in conduction band. Finally, the doping dependence of power factors of n-type monolayer and bilayer SnSe2 at three different pressures were estimated, and the results unveiled that thermoelectric performance of n-type monolayer and bilayer SnSe2 can be improved by applying external pressure. This study benefits to understand the nature of the transport properties for monolayer and bilayer SnSe2 under pressure, and it offers valuable insight for designing high-performance thermoelectric few-layered SnSe2 through strain engineering induced by external pressure.

Pressure-induced enhancement in the thermoelectric properties of monolayer and bilayer SnSe2.

PubMed

Zou, Daifeng; Yu, Chuanbin; Li, Yuhao; Ou, Yun; Gao, Yongyi

2018-03-01

The electronic structures of monolayer and bilayer SnSe 2 under pressure were investigated by using first-principles calculations including van der Waals interactions. For monolayer SnSe 2 , the variation of electronic structure under pressure is controlled by pressure-dependent lattice parameters. For bilayer SnSe 2 , the changes in electronic structure under pressure are dominated by intralayer and interlayer atomic interactions. The n -type thermoelectric properties of monolayer and bilayer SnSe 2 under pressure were calculated on the basis of the semi-classical Boltzmann transport theory. It was found that the electrical conductivity of monolayer and bilayer SnSe 2 can be enhanced under pressure, and such dependence can be attributed to the pressure-induced changes of the Se-Sn antibonding states in conduction band. Finally, the doping dependence of power factors of n -type monolayer and bilayer SnSe 2 at three different pressures were estimated, and the results unveiled that thermoelectric performance of n -type monolayer and bilayer SnSe 2 can be improved by applying external pressure. This study benefits to understand the nature of the transport properties for monolayer and bilayer SnSe 2 under pressure, and it offers valuable insight for designing high-performance thermoelectric few-layered SnSe 2 through strain engineering induced by external pressure.

Solvent-induced controllable synthesis, single-crystal to single-crystal transformation and encapsulation of Alq3 for modulated luminescence in (4,8)-connected metal-organic frameworks.

PubMed

Lan, Ya-Qian; Jiang, Hai-Long; Li, Shun-Li; Xu, Qiang

2012-07-16

In this work, for the first time, we have systematically demonstrated that solvent plays crucial roles in both controllable synthesis of metal-organic frameworks (MOFs) and their structural transformation process. With solvent as the only variable, five new MOFs with different structures have been constructed, in which one MOF undergoes solvent-induced single-crystal to single-crystal (SCSC) transformation that involves not only solvent exchange but also the cleavage and formation of coordination bonds. Particularly, a significant crystallographic change has been realized through an unprecedented three-step SCSC transformation process. Furthermore, we have demonstrated that the obtained MOF could be an excellent host for chromophores such as Alq3 for modulated luminescent properties.

Theoretical prediction of the structural properties of uranium chalcogenides under high pressure

NASA Astrophysics Data System (ADS)

Kapoor, Shilpa; Yaduvanshi, Namrata; Singh, Sadhna

2018-05-01

Uranium chalcogenides crystallize in rock salt structure at normal condition and transform to Cesium Chloride structure at high pressure. We have investigated the transition pressure and volume drop of USe and UTe using three body potential model (TBIP). Present model includes long range Columbic, three body interaction forces and short range overlap forces operative up to next nearest neighbors. We have reported the phase transition pressure, relative volume collapses, the thermo physical properties such as molecular force constant (f), infrared absorption frequency (v0), Debye temperature (θD) and Gruneisen parameter (γ) of present chalcogenides and found that our results in general good agreement with experimental and other theoretical data.

High Pressure X-Ray Diffraction Studies of Bi2-xSbxTe3 (x = 0,1,2)

NASA Astrophysics Data System (ADS)

Jacobsen, M. K.; Kumar, R. S.; Cornelius, A. L.; Sinogeiken, S. V.; Nico, M. F.

2007-12-01

Recently, pressure tuning of the thermoelectric figure of merit has been reported for several materials Bi2Te3 based thermoelectric materials [2],[10],[12]. In order to investigate the bulk properties of Bi2Te3, Sb2Te3, and their solid solution in detail, we have performed structural studies up to 20 GPa. Our diffraction results show that all three compounds transform from the ambient pressure structure to a high pressure phase between 7 and 10 GPa. In addition, these diffraction results have been converted to Vinet and Holzapfel equations of state to test the claim of electronic topological transitions in these structures [3].

Pressure-induced Lifshitz and structural transitions in NbAs and TaAs: experiments and theory

NASA Astrophysics Data System (ADS)

Nath Gupta, Satyendra; Singh, Anjali; Pal, Koushik; Muthu, D. V. S.; Shekhar, C.; Elghazali, Moaz A.; Naumov, Pavel G.; Medvedev, Sergey A.; Felser, C.; Waghmare, U. V.; Sood, A. K.

2018-05-01

High pressure Raman, resistivity and synchrotron x-ray diffraction studies on Weyl semimetals NbAs and TaAs have been carried out along with density functional theoretical (DFT) analysis to explain pressure induced structural and electronic topological phase transitions. The frequencies of first order Raman modes harden with increasing pressure, exhibiting a slope change at GPa for NbAs and GPa for TaAs. The resistivities of NbAs and TaAs exhibit a minimum at pressures close to these transition pressures and also a change in the bulk modulus is observed. Our first-principles calculations reveal that the transition is associated with an electronic Lifshitz transition at for NbAs while it is a structural phase transition from body centered tetragonal to hexagonal phase at for TaAs. Further, our DFT calculations show a structural phase transition at 24 GPa from body centered tetragonal phase to hexagonal phase.

Apex shift of a circular biconcave vesicle induced by osmotic pressure

NASA Astrophysics Data System (ADS)

Liu, Quan-Hui; Yan, Jie; Zhong-Can, Ou-Yang

1999-09-01

The contribution of a small osmotic pressure into the exact circular biconcave solution (H. Naito, M. Okuda, Ou-Yang Zhong-Can, Phys. Rev. E 48 (1993) 2304; 54 (1996) 2816) of the spontaneous curvature model of Helfrich leads to a definite and new theoretical consequence, the radius of the apex of the biconcave shape can shift toward to or apart from the center depending on the increase or decrease of the osmotic pressure. This result is in agreement with the following observed phenomena: The first stage of the discocyte-echinocyte and the discocyte-spherocyte transformation induced by exposing the cells to high concentrations of certain chemical agents; and the ring-shaped torocyte formation due to the iron deficiency or thalassemia.

Electron-density critical points analysis and catastrophe theory to forecast structure instability in periodic solids.

PubMed

Merli, Marcello; Pavese, Alessandro

2018-03-01

The critical points analysis of electron density, i.e. ρ(x), from ab initio calculations is used in combination with the catastrophe theory to show a correlation between ρ(x) topology and the appearance of instability that may lead to transformations of crystal structures, as a function of pressure/temperature. In particular, this study focuses on the evolution of coalescing non-degenerate critical points, i.e. such that ∇ρ(x c ) = 0 and λ 1 , λ 2 , λ 3 ≠ 0 [λ being the eigenvalues of the Hessian of ρ(x) at x c ], towards degenerate critical points, i.e. ∇ρ(x c ) = 0 and at least one λ equal to zero. The catastrophe theory formalism provides a mathematical tool to model ρ(x) in the neighbourhood of x c and allows one to rationalize the occurrence of instability in terms of electron-density topology and Gibbs energy. The phase/state transitions that TiO 2 (rutile structure), MgO (periclase structure) and Al 2 O 3 (corundum structure) undergo because of pressure and/or temperature are here discussed. An agreement of 3-5% is observed between the theoretical model and experimental pressure/temperature of transformation.

Polymerization of Acetonitrile via a Hydrogen Transfer Reaction from CH3 to CN under Extreme Conditions.

PubMed

Zheng, Haiyan; Li, Kuo; Cody, George D; Tulk, Christopher A; Dong, Xiao; Gao, Guoying; Molaison, Jamie J; Liu, Zhenxian; Feygenson, Mikhail; Yang, Wenge; Ivanov, Ilia N; Basile, Leonardo; Idrobo, Juan-Carlos; Guthrie, Malcolm; Mao, Ho-Kwang

2016-09-19

Acetonitrile (CH3 CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. It is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH3 to CN along the CH⋅⋅⋅N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed sp(2) and sp(3) bonded carbon. Finally, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polymerization of Acetonitrile via a Hydrogen Transfer Reaction from CH 3 to CN under Extreme Conditions

DOE PAGES

Zheng, Haiyan; Li, Kuo; Cody, George D.; ...

2016-08-25

Acetonitrile (CH 3CN) is the simplest and one of the most stable nitriles. Reactions usually occur on the C≡N triple bond, while the C-H bond is very inert and can only be activated by a very strong base or a metal catalyst. In this study, it is demonstrated that C-H bonds can be activated by the cyano group under high pressure, but at room temperature. The hydrogen atom transfers from the CH 3 to CN along the CH···N hydrogen bond, which produces an amino group and initiates polymerization to form a dimer, 1D chain, and 2D nanoribbon with mixed spmore » 2 and sp 3 bonded carbon. Lastly, it transforms into a graphitic polymer by eliminating ammonia. This study shows that applying pressure can induce a distinctive reaction which is guided by the structure of the molecular crystal. It highlights the fact that very inert C-H can be activated by high pressure, even at room temperature and without a catalyst.« less

Nb-H system at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Liu, Guangtao; Besedin, Stanislav; Irodova, Alla; Liu, Hanyu; Gao, Guoying; Eremets, Mikhail; Wang, Xin; Ma, Yanming

2017-03-01

We studied the Nb-H system over extended pressure and temperature ranges to establish the highest level of hydrogen abundance we could achieve from the resulting alloy. We probed the Nb-H system with laser heating and x-ray diffraction complemented by numerical density functional theory-based simulations. New quenched double hexagonal close-packed (hcp) Nb H2.5 appears under 46 GPa, and above 56 GPa cubic Nb H3 is formed as theoretically predicted. Nb atoms are arranged in close-packed lattices which are martensitically transformed in the sequence: face-centered cubic (fcc) → hcp → double hcp (dhcp) → distorted body-centered cubic (bcc) as pressure increases. The appearance of fcc Nb H2.5 -3 and dhcp Nb H2.5 cannot be understood in terms of enthalpic stability, but can be rationalized when finite temperatures are taken into account. The structural and compressional behavior of Nb Hx >2 is similar to that of NbH. Nevertheless, a direct H-H interaction emerges with hydrogen concentration increases, which manifests itself via a reduction in the lattice expansion induced by hydrogen dissolution.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

NASA Astrophysics Data System (ADS)

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone; Dotti, Massimo; Moustakas, Leonidas A.

2017-02-01

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N-body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f gas, in the disk of the progenitor dwarf. Our numerical experiments incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs (f gas ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless (f gas = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f gas ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N -body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f {sub gas}, in the disk of the progenitor dwarf. Our numerical experimentsmore » incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs ( f {sub gas} ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless ( f {sub gas} = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f {sub gas} ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.« less

Temperatures of shock-induced shear instabilities and their relationship to fusion curves. [emission from glass

NASA Technical Reports Server (NTRS)

Schmitt, D. R.; Ahrens, T. J.

1983-01-01

New emission spectra for MgO and CaAl2Si2O8 (glass) are observed from 430 to 820 nm. Taken with previous data, it is suggested that transparent solids display three regimes of light emission upon shock compression to successively higher pressures: (1) characteristic radiation such as observed in MgO and previously in other minerals, (2) heterogeneous hot spot (greybody) radiation observed in CaAl2Si2O8 and previously in all transparent solids undergoing shock-induced phase transformations, and (3) blackbody emission observed in the high pressure phase regime in NaCl, SiO2, CaO, CaAl2Si2O8, and Mg2SiO4. The onset of the second regime may delineate the onset of shock-induced polymorphism whereas the onset of the third regime delineates the Hugoniot pressure required to achieve local thermal equilibrium in the shocked solid. It is also proposed that the hot spot temperatures and corresponding shock pressures determined in the second regime delineate points on the fusion curves of the high pressure phase.

Lattice dynamics, elasticity and magnetic abnormality in ordered crystalline alloys Fe3Pt at high pressures

NASA Astrophysics Data System (ADS)

Cheng, Tai-min; Yu, Guo-Liang; Su, Yong; Ge, Chong-Yuan; Zhang, Xin-Xin; Zhu, Lin; Li, Lin

2018-05-01

The ordered crystalline Invar alloy Fe3Pt is in a special magnetic critical state, under which the lattice dynamic stability of the system is extremely sensitive to external pressures. We studied the pressure dependence of enthalpy and magnetism of Fe3Pt in different crystalline alloys by using the first-principles projector augmented-wave method based on the density functional theory. Results show that the P4/mbm structure is the ground state structure and is more stable relative to other structures at pressures below 18.54 GPa. The total magnetic moments of L12, I4/mmm and DO22 structures decrease rapidly with pressure and oscillate near the ferromagnetic collapse critical pressure. At the pressure of 43 GPa, the ferrimagnetic property in DO22 structure becomes apparently strengthened and its volume increases rapidly. The lattice dynamics calculation for L12 structures at high pressures shows that the spontaneous magnetization of the system in ferromagnetic states induces the softening of the transverse acoustic phonon TA1 (M), and there exists a strong spontaneous volume magnetostriction at pressures below 26.95 GPa. Especially, the lattice dynamics stability is sensitive to pressure, in the pressure range between the ferromagnetic collapse critical pressure (41.9 GPa) and the magnetism completely disappearing pressure (57.25 GPa), and near the pressure of phase transition from L12 to P4/mbm structure (27.27 GPa). Moreover, the instability of magnetic structure leads to a prominent elastic modulus oscillation, and the spin polarizability of electrons near the Fermi level is very sensitive to pressures in that the pressure range. The pressure induces the stability of the phonon spectra of the system at pressures above 57.25 GPa.

New structure of high-pressure body-centered orthorhombic Fe 2SiO 4

DOE PAGES

Yamanaka, Takamitsu; Kyono, Atsushi; Nakamoto, Yuki; ...

2015-08-01

Here, a structural change in Fe 2SiO 4 spinel and the structure of a new high pressure phase are determined by Rietveld 26 profile fitting of x-ray diffraction data up to 64 GPa at ambient temperature. The compression curve of the spinel is discontinuous at approximately 20 GPa. Fe Kβ x-ray emission measurements at high pressure show that the transition from a high spin (HS) to an intermediate spin (IS) state begins at 17 GPa in the spinel phase. The IS electronic state is gradually enhanced with pressure, which results in an isostructural phase transition. A transition from the cubic spinel structure to a body centered orthorhombic phase (I-Fe 2SiO 4) with space group Imma and Z=4 was observed at approximately 34 GPa. The structure of I-Fe 2SiO 4 has two crystallographically distinct FeO 6 octahedra, which are arranged in layers parallel to (101) and (011) and are very similar to the layers of FeO 6 octahedra that constitute the spinel structure. Silicon also exists in six-fold coordination in I-Fe 2SiO 4. The transformation to the new high-pressure phase is reversible under decompression at ambient temperature. A Martensitic transformation of each slab of the spinel structure with translation vector [more » $$\\vec{1/8}$$ $$\\vec{1/8}$$ $$\\vec{1/8}$$] generates the I-Fe 2SiO 4 structure. Laser heating of I-Fe 2SiO 4 at 1500 K results in a decomposition of the material to rhombohedral FeO and SiO 2 stishovite.« less

Phase diagram calculations and high pressure Raman spectroscopy studies of organic "plastic crystal" thermal energy storage materials

NASA Astrophysics Data System (ADS)

Chellappa, Raja S.

This dissertation presents the phase diagram calculations and high pressure Raman spectroscopy studies on organic "plastic crystal" thermal storage materials. The organic "plastic crystals" that were studied include pentaerythritol [PE:C(CH 2OH)4], neopentylglycol [NPG:(CH3)2C(CH 2OH)2], tris(hydroxymethyl)-aminomethane [TRIS:(NH2 )C(CH2OH)3], and 2-amino-2-methyl-1,3-propanediol [AMPL: (NH2)(CH3)C(CH2OH)2]. Thermodynamic optimization of the experimental data of AMPL-NPG and PE-AMPL binary system was performed and the calculated phase diagrams are presented. A preliminary calculated phase diagram of the TRIS-NPG binary system is also presented. A thorough reevaluation of the existing calorimetric and x-ray diffraction data of the PE-AMPL binary system is also presented. This analysis resulted in the correct interpretation of the phase boundaries and a revised phase diagram has been drawn. The results of high pressure Raman spectroscopy experiments on neopentylglycol and pentaerythritol presented. The phase transformation pressures were determined by analyzing the frequency shifts as a function of pressure as well as the changes in the internal modes of vibration for these compounds. A simplified assignment of the vibrational modes for NPG at ambient pressure is presented. The results indicate experiments were carried out using Diamond Anvil Cell (DAC) and the pressure induced transformations were studied by Raman spectroscopy. In NPG, a phase transition occurs at ˜3.6 GPa from Phase I (Monoclinic) to Phase II (unknown structure). In PE, the proposed phase transformation pressures are ˜4.8 GPa (Phase I to Phase II), ˜6.9 GPa (Phase II to Phase III), ˜9.5 GPa (Phase III to Phase IV), and ˜15 GPa (Phase IV to Amorphous). The results of a critical assessment of the vapor pressure data of solid metal carbonyls. The vapor pressure data of Chromium Carbonyl (Cr(CO)6), Tungsten Carbonyl (W(CO)6 ), Osmium Carbonyl (Os3(CO)12), Molybdenum Carbonyl (MO(CO)6). Rhenium Carbonyl (Re2(CO)10), and Manganese Carbonyl (Mn(CO)5) were assessed using the "Oonk Methodology". The sublimation properties using the assessed data (Delta subGo,DeltasubH o and Deltasub Cop,m ) of these compounds have been evaluated and a discussion on the mutual consistency of various data sets for each compound over a wide range of temperature is also presented.

Pressure dependence of excited-state charge-carrier dynamics in organolead tribromide perovskites

NASA Astrophysics Data System (ADS)

Liu, X. C.; Han, J. H.; Zhao, H. F.; Yan, H. C.; Shi, Y.; Jin, M. X.; Liu, C. L.; Ding, D. J.

2018-05-01

Excited-state charge-carrier dynamics governs the performance of organometal trihalide perovskites (OTPs) and is strongly influenced by the crystal structure. Characterizing the excited-state charge-carrier dynamics in OTPs under high pressure is imperative for providing crucial insights into structure-property relations. Here, we conduct in situ high-pressure femtosecond transient absorption spectroscopy experiments to study the excited-state carrier dynamics of CH3NH3PbBr3 (MAPbBr3) under hydrostatic pressure. The results indicate that compression is an effective approach to modulate the carrier dynamics of MAPbBr3. Across each pressure-induced phase, carrier relaxation, phonon scattering, and Auger recombination present different pressure-dependent properties under compression. Responsiveness is attributed to the pressure-induced variation in the lattice structure, which also changes the electronic band structure. Specifically, simultaneous prolongation of carrier relaxation and Auger recombination is achieved in the ambient phase, which is very valuable for excess energy harvesting. Our discussion provides clues for optimizing the photovoltaic performance of OTPs.

Study of the hydrostatic pressure dependence of the Raman spectrum of W/WS2 fullerene-like nanosphere with core shell structure

NASA Astrophysics Data System (ADS)

Yu, S. D.; Chang, L. X.; Yang, H. B.; Liu, B. B.; Hou, Y. Y.; Wang, L.; Yao, M. G.; Cui, T.; Zou, G. T.

2007-10-01

The structural behavior of a W/WS2 fullerene-like nanosphere with a core-shell structure has been studied in the hydrostatic pressure range from atmospheric pressure to 18 GPa by Raman spectroscopy using a methanol-ethanol-water mixture (16:3:1) as the pressure transmitting medium (PTM). We found that it is interesting that the intensity ratio of the LA+TA mode and the A1g mode changes with increasing pressure. We attribute this change to the shape transformation of an inorganic fullerene-like IF-W/WS2 nanosphere under high hydrostatic pressure. By comparing the Raman spectra of an IF-W/WS2 nanosphere released from high pressure with that of the original one, we found that the change in morphology is reversible. This indicates that the spherical shape of the IF-W/WS2 has excellent behavior in resisting compression.

Pressure-induced structural transition of mature HIV-1 protease from a combined NMR/MD simulation approach.

PubMed

Roche, Julien; Louis, John M; Bax, Ad; Best, Robert B

2015-12-01

We investigate the pressure-induced structural changes in the mature human immunodeficiency virus type 1 protease dimer, using residual dipolar coupling (RDC) measurements in a weakly oriented solution. (1)DNH RDCs were measured under high-pressure conditions for an inhibitor-free PR and an inhibitor-bound complex, as well as for an inhibitor-free multidrug resistant protease bearing 20 mutations (PR20). While PR20 and the inhibitor-bound PR were little affected by pressure, inhibitor-free PR showed significant differences in the RDCs measured at 600 bar compared with 1 bar. The structural basis of such changes was investigated by MD simulations using the experimental RDC restraints, revealing substantial conformational perturbations, specifically a partial opening of the flaps and the penetration of water molecules into the hydrophobic core of the subunits at high pressure. This study highlights the exquisite sensitivity of RDCs to pressure-induced conformational changes and illustrates how RDCs combined with MD simulations can be used to determine the structural properties of metastable intermediate states on the folding energy landscape. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Equation of state and phase transformations study of Nd at ultra-high pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akella, J.; Smith, G.S.; Weir, S.

1991-10-01

Neodymium was investigated to 96.0 GPa pressure in a diamond-anvil ell at room temperature. The observed structural sequence as a function of pressure is dhcp-fcc- six layered'' structure. In the diffraction pattern hexagonal doublets; notably 102, 006 and 100, 108; appear as single reflection when the c/a ratio is 4.899. However, when cc/a approaches 4.7, the splitting is clear. So far in this study, no monoclinic phase or tetragonal phase were observed. 1 fig., 18 refs.

High-pressure behavior of methylammonium lead iodide (MAPbI3) hybrid perovskite

NASA Astrophysics Data System (ADS)

Capitani, Francesco; Marini, Carlo; Caramazza, Simone; Postorino, Paolo; Garbarino, Gaston; Hanfland, Michael; Pisanu, Ambra; Quadrelli, Paolo; Malavasi, Lorenzo

2016-05-01

In this paper we provide an accurate high-pressure structural and optical study of the MAPbI3 hybrid perovskite. Structural data show the presence of a phase transition toward an orthorhombic structure around 0.3 GPa followed by full amorphization of the system above 3 GPa. After releasing the pressure, the system keeps the high-pressure orthorhombic phase. The occurrence of these structural transitions is further confirmed by pressure induced variations of the photoluminescence signal at high pressure. These variations clearly indicate that the bandgap value and the electronic structure of MAPI change across the phase transition.

Pressure-induced amorphization of charge ordered spinel AlV{sub 2}O{sub 4} at low temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malavi, Pallavi S., E-mail: malavips@barc.gov.in; Karmakar, S., E-mail: malavips@barc.gov.in; Sharma, S. M.

2014-04-24

Structural properties of charge ordered spinel AlV{sub 2}O{sub 4} have been investigated under high pressure at low temperature (80K) by synchrotron based x-ray diffraction measurements. It is observed that upon increasing pressure the structure becomes progressively disordered due to the distortion of the AlO{sub 4} tetrahedral unit and undergoes amorphization above ∼12 GPa. While releasing pressure, the rhombohedral phase is only partially recovered at a much lower pressure (below 5 GPa). Within the stability of the rhombohedral phase, the distortion in the vanadium heptamer increases monotonically with pressure, suggesting enhanced charge ordering. This result is in sharp contrast with themore » recent observation of pressure-induced frustration in the charge ordered state leading to structural transition to the cubic phase at room temperature [JPCM 25, 292201, 2013].« less

First-principles study of high-pressure structural phase transitions of magnesium

NASA Astrophysics Data System (ADS)

Liu, Qiuxiang; Fan, Changzeng; Zhang, Ruijun

2009-06-01

The structural phase transitions for the hcp, bcc, dhcp, and fcc of magnesium at hydrostatic pressures larger than about 200 GPa at zero temperature are studied by first-principles total energy calculations. The plane-wave basis pseudopotential method has been adopted, in which the generalized gradient approximation implanted in the CASTEP code is employed. By comparing the enthalpy differences of the hcp structure with other three structures under different pressures, it can be seen that when the pressure becomes higher than about 65, 130, and 190 GPa, the bcc, dhcp, and fcc structures become more stable relative to the hcp structure, respectively. Due to the lowest enthalpy value of the bcc structure above 65 GPa, it can be deduced that magnesium may transform to the bcc structure from the ground state hcp structure around 65 GPa, but no further phase transitions occur without additionally applying high temperature. In addition, the equation of state of magnesium is calculated, indicating that bcc structure is the softest phase.

Genomic variation and DNA repair associated with soybean transgenesis: a comparison to cultivars and mutagenized plants.

PubMed

Anderson, Justin E; Michno, Jean-Michel; Kono, Thomas J Y; Stec, Adrian O; Campbell, Benjamin W; Curtin, Shaun J; Stupar, Robert M

2016-05-12

The safety of mutagenized and genetically transformed plants remains a subject of scrutiny. Data gathered and communicated on the phenotypic and molecular variation induced by gene transfer technologies will provide a scientific-based means to rationally address such concerns. In this study, genomic structural variation (e.g. large deletions and duplications) and single nucleotide polymorphism rates were assessed among a sample of soybean cultivars, fast neutron-derived mutants, and five genetically transformed plants developed through Agrobacterium based transformation methods. On average, the number of genes affected by structural variations in transgenic plants was one order of magnitude less than that of fast neutron mutants and two orders of magnitude less than the rates observed between cultivars. Structural variants in transgenic plants, while rare, occurred adjacent to the transgenes, and at unlinked loci on different chromosomes. DNA repair junctions at both transgenic and unlinked sites were consistent with sequence microhomology across breakpoints. The single nucleotide substitution rates were modest in both fast neutron and transformed plants, exhibiting fewer than 100 substitutions genome-wide, while inter-cultivar comparisons identified over one-million single nucleotide polymorphisms. Overall, these patterns provide a fresh perspective on the genomic variation associated with high-energy induced mutagenesis and genetically transformed plants. The genetic transformation process infrequently results in novel genetic variation and these rare events are analogous to genetic variants occurring spontaneously, already present in the existing germplasm, or induced through other types of mutagenesis. It remains unclear how broadly these results can be applied to other crops or transformation methods.

Element-resolved magnetism across the temperature- and pressure-induced spin reorientation in MnBi

DOE PAGES

Choi, Yongseong; Jiang, Xiujuan; Bi, Wenli; ...

2016-11-01

Rare-earth free permanent magnet MnBi (NiAs-type crystal structure) displays strong magnetic anisotropy above its 90 K spin reorientation transition (SRT). X-ray magnetic circular dichroism (XMCD) shows induced magnetism in Bi 5d band, which is strongly coupled to the magnetism of Mn. A clear increase in Bi orbital-to-spin moment ratio is observed above the SRT. Hydrostatic pressure mimics the e*ect of temperature on the SRT, and the pressure effect also leads to anisotropic lattice contraction, which is known to be induced by cooling. These results reveal that temperature and pressure can similarly induce the coupled structural and magnetic responses, suggesting themore » importance of the anisotropic lattice change and Mn-Bi hybridization to the magnetic anisotropy change across the SRT.« less

Pressure-induced multiband superconductivity in pyrite PtB i2 with perfect electron-hole compensation

NASA Astrophysics Data System (ADS)

Chen, Xuliang; Shao, Dexi; Gu, Chuanchuan; Zhou, Yonghui; An, Chao; Zhou, Ying; Zhu, Xiangde; Chen, Tong; Tian, Mingliang; Sun, Jian; Yang, Zhaorong

2018-05-01

We report on the discovery of pressure-induced superconductivity in the compensated semimetal pyrite PtB i2 , which exhibits extreme magnetoresistance (XMR) and nontrivial band structure at ambient pressure. The appearance of superconductivity, first observed at PC˜13 GPa with an onset critical temperature TC of ˜2.2 K , is accompanied by a pronounced enhancement of the density of electrons and holes based on Hall-effect measurements. Upon further compression, TC remains almost unchanged up to 50.0 GPa; remarkably, the perfect electron-hole compensation still holds, while the carrier mobility greatly reduces. No evident trace of structural phase transitions is detected through synchrotron x-ray diffraction over the measured pressure range of 1.5-51.2 GPa. These results highlight a multiband characteristic of the observed superconductivity, making pyrite PtB i2 unique among the compensated XMR materials where the pressure-induced superconductivity usually links to structural transitions and carrier imbalance.

Exploiting pattern transformation to tune phononic band gaps in a two-dimensional granular crystal.

PubMed

Göncü, F; Luding, S; Bertoldi, K

2012-06-01

The band structure of a two-dimensional granular crystal composed of silicone rubber and polytetrafluoroethylene (PTFE) cylinders is investigated numerically. This system was previously shown to undergo a pattern transformation with uniaxial compression by Göncü et al. [Soft Matter 7, 2321 (2011)]. The dispersion relations of the crystal are computed at different levels of deformation to demonstrate the tunability of the band structure, which is strongly affected by the pattern transformation that induces new band gaps. Replacement of PTFE particles with rubber ones reveals that the change of the band structure is essentially governed by pattern transformation rather than particles' mechanical properties.

Friction and the development of hard alloy surface microstructures during wear

NASA Astrophysics Data System (ADS)

Gnyusov, S. F.; Tarassov, S. Yu.

1997-12-01

Investigations of wear in sliding friction of WC-Hadfield steel hard alloy against cast tool steel have been carried out in a broad range of velocities and pressure values. Structural and phase composition variations have been revealed. Friction-affected zone was found to be 450 µm in depth. Structural γ → α, γ → transformation regions are located within 100 μm of the surface. These transformations contributed to the total solid solution deformation hardening.

Measurement of Body-Centered-Cubic Aluminum at 475 GPa [Observation of Body-Centered-Cubic Aluminum at 475 GPa

DOE PAGES

Polsin, D. N.; Fratanduono, D. E.; Rygg, J. R.; ...

2017-10-27

Nanosecond in situ x-ray diffraction and simultaneous velocimetry measurements were used to determine the crystal structure and pressure, respectively, of ramp compressed aluminum at stress states between 111 and 475 GPa. The solid-solid Al phase transformations, fcc-hcp and hcp-bcc, are observed at 216 ± 9 GPa and 321 ± 12 GPa, respectively, with the bcc phase persisting to 475 GPa. Here, this is the first in situ observation of the high-pressure bcc phase of Al. High-pressure texture of the hcp and bcc phases suggests close-packed or nearly close-packed lattice planes remain parallel through both transformations.

Measurement of Body-Centered-Cubic Aluminum at 475 GPa [Observation of Body-Centered-Cubic Aluminum at 475 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polsin, D. N.; Fratanduono, D. E.; Rygg, J. R.

Nanosecond in situ x-ray diffraction and simultaneous velocimetry measurements were used to determine the crystal structure and pressure, respectively, of ramp compressed aluminum at stress states between 111 and 475 GPa. The solid-solid Al phase transformations, fcc-hcp and hcp-bcc, are observed at 216 ± 9 GPa and 321 ± 12 GPa, respectively, with the bcc phase persisting to 475 GPa. Here, this is the first in situ observation of the high-pressure bcc phase of Al. High-pressure texture of the hcp and bcc phases suggests close-packed or nearly close-packed lattice planes remain parallel through both transformations.

Comparing Sliding-Wear Characteristics of the Electro-Pressure Sintered and Wrought Cobalt

NASA Astrophysics Data System (ADS)

Lee, J. E.; Kim, Y. S.; Kim, T. W.

Dry sliding wear tests of hot-pressure sintered and wrought cobalt were carried out to compare their wear characteristics. Cobalt powders with average size of 1.5µm were electro-pressure sintered to make sintered-cobalt disk wear specimens. A vacuum-induction melted cobalt ingot was hot-rolled at 800°C to a plate, from which wrought-cobalt disk specimens were machined. The specimens were heat treated at various temperatures to vary grain size and phase fraction. Wear tests of the cobalt specimens were carried out using a pin-on-disk wear tester against a glass (83% SiO2) bead at 100N with the constant sliding speed and distance of 0.36m/s and 600m, respectively. Worn surfaces, their cross sections, and wear debris were examined by an SEM. The wear of the cobalt was found to be strongly influenced by the strain-induced phase transformation of ɛ-Co (hcp) to α-Co (fcc). The sintered cobalt had smaller uniform grain size and showed higher wear rate than the wrought cobalt. The higher wear rate of the sintered cobalt was explained by the more active deformation-induced phase transformation than in the wrought cobalt with larger irregular grains.

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water.

PubMed

Chiu, Janet; Starr, Francis W; Giovambattista, Nicolas

2014-03-21

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water

NASA Astrophysics Data System (ADS)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2014-03-01

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Phase transitions in orthopyroxene (En 90) to 49GPa from single-crystal X-ray diffraction

DOE PAGES

Finkelstein, Gregory J.; Dera, Przemyslaw K.; Duffy, Thomas S.

2014-10-29

Synchrotron-based high-pressure single-crystal X-ray diffraction experiments were conducted on ~Mg 0.9Fe 0.1SiO 3 (En 90) orthopyroxene crystals at room temperature to a maximum pressure of 48.5 GPa. The sample was compressed in a diamond anvil cell with a neon pressure medium and a gold pressure calibrant. In addition to the previously described orthopyroxene to β-opx transition (designated HPCEN2 in previous studies), we observe two further phase transitions at 29.9 GPa and 40.3 GPa. However, we do not observe the γ-opx phase recently described in an Fe-rich orthopyroxene composition. The structures of both of the new phases were solved in spacemore » group Pca21. While their Mg-O layers remain pyroxene-like, their Si-O layers transform in a stepwise fashion to akimotoite-like sheets, with sites in 4-, 5-, or 6-fold coordination, depending on the specific structure and layer. Due to the increased Si-O coordination number, we designate the new structures α- and β-post-orthopyroxene (α-popx and β-popx). α-popx has one Si-O layer that is entirely tetrahedral, and one layer that contains both tetrahedra and 5-coordinated Si in distorted square pyramids. β-popx retains the mixed 4- and 5-coordinated Si layer found in α-popx, while the other Si layer adopts fully octahedral coordination. The α- and β-popx structures show a progressive transformation towards the arrangement of Si layers found in akimotoite, a potentially important phase in the earth’s transition zone. Metastable transformations in pyroxenes are of interest for understanding possible metastability in geological environments such as subducting slabs and meteorite impacts« less

Phase transitions in orthopyroxene (En 90) to 49GPa from single-crystal X-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finkelstein, Gregory J.; Dera, Przemyslaw K.; Duffy, Thomas S.

Synchrotron-based high-pressure single-crystal X-ray diffraction experiments were conducted on ~Mg 0.9Fe 0.1SiO 3 (En 90) orthopyroxene crystals at room temperature to a maximum pressure of 48.5 GPa. The sample was compressed in a diamond anvil cell with a neon pressure medium and a gold pressure calibrant. In addition to the previously described orthopyroxene to β-opx transition (designated HPCEN2 in previous studies), we observe two further phase transitions at 29.9 GPa and 40.3 GPa. However, we do not observe the γ-opx phase recently described in an Fe-rich orthopyroxene composition. The structures of both of the new phases were solved in spacemore » group Pca21. While their Mg-O layers remain pyroxene-like, their Si-O layers transform in a stepwise fashion to akimotoite-like sheets, with sites in 4-, 5-, or 6-fold coordination, depending on the specific structure and layer. Due to the increased Si-O coordination number, we designate the new structures α- and β-post-orthopyroxene (α-popx and β-popx). α-popx has one Si-O layer that is entirely tetrahedral, and one layer that contains both tetrahedra and 5-coordinated Si in distorted square pyramids. β-popx retains the mixed 4- and 5-coordinated Si layer found in α-popx, while the other Si layer adopts fully octahedral coordination. The α- and β-popx structures show a progressive transformation towards the arrangement of Si layers found in akimotoite, a potentially important phase in the earth’s transition zone. Metastable transformations in pyroxenes are of interest for understanding possible metastability in geological environments such as subducting slabs and meteorite impacts« less

High pressure study of Pu(0.92)Am(0.08) binary alloy.

PubMed

Klosek, V; Griveau, J C; Faure, P; Genestier, C; Baclet, N; Wastin, F

2008-07-09

The phase transitions (by means of x-ray diffraction) and electrical resistivity of a Pu(0.92)Am(0.08) binary alloy were determined under pressure (up to 2 GPa). The evolution of atomic volume with pressure gives detailed information concerning the degree of localization of 5f electronic states and their delocalization process. A quasi-linear V = f(P) dependence reflects subtle modifications of the electronic structure when P increases. The electrical resistivity measurements reveal the very high stability of the δ phase for pressures less than 0.7 GPa, since no martensitic-like transformation occurs at low temperature. Remarkable electronic behaviours have also been observed. Finally, resistivity curves have shown the temperature dependence of the phase transformations together with unexpected kinetic effects.

Mechanically Induced Graphite-Nanodiamonds-Phase Transformations During High-Energy Ball Milling

NASA Astrophysics Data System (ADS)

El-Eskandarany, M. Sherif

2017-05-01

Due to their unusual mechanical, chemical, physical, optical, and biological properties, nearly spherical-like nanodiamonds have received much attention as desirable advanced nanomaterials for use in a wide spectrum of applications. Although, nanodiamonds can be successfully synthesized by several approaches, applications of high temperature and/or high pressure may restrict the real applications of such strategic nanomaterials. Distinct from the current preparation approaches used for nanodiamonds preparation, here we show a new process for preparing ultrafine nanodiamonds (3-5 nm) embedded in a homogeneous amorphous-carbon matrix. Our process started from high-energy ball milling of commercial graphite powders at ambient temperature under normal atmospheric helium gas pressure. The results have demonstrated graphite-single wall carbon nanotubes-amorphous-carbon-nanodiamonds phase transformations carried out through three subsequent stages of ball milling. Based on XRD and RAMAN analyses, the percentage of nanodiamond phase + C60 (crystalline phase) produced by ball milling was approximately 81%, while the amorphous phase amount was 19%. The pressure generated on the powder together the with temperature increase upon the ball-powder-ball collision is responsible for the phase transformations occurring in graphite powders.

Crystal structure of simple metals at high pressures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Degtyareva, Olga

2010-10-22

The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14-17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a behaviour normally expected under pressure. Group 1 and 2 metallic elements, however, show a reverse trend towards structures with low packing density due to intricate changes in their electronic structure. Complex crystal structures such as host-guest and incommensurately modulated structuresmore » found in these elements are given special attention in this review in an attempt to determine their role in the observed phase-transition sequences.« less

Surface deformation in volcanic rift zones

USGS Publications Warehouse

Pollard, D.D.; Delaney, P.T.; Duffield, W.A.; Endo, E.T.; Okamura, A.T.

1983-01-01

The principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes, some of which feed fissure eruptions. Elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression. Concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift. If eruption occurs the characteristic ridge-trough-ridge displacement profile changes to a single ridge, centered at the fissure, and the erupted lava alters the local topography. A well-developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events. To investigate this process we compute the elastic displacements and stresses in a homogeneous, two-dimensional half-space driven by a pressurized crack that may breach the surface. A derivative graphical method permits one to estimate the three geometric parameters of the dike (height, inclination, and depth-to-center) and the mechanical parameter (driving pressure/rock stiffness) from a smoothly varying displacement profile. Direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation, notably normal faulting, creates discontinuities in the profile. Geological structures (open cracks, normal faults, buckles, and thrust faults) form because of stresses induced by dike emplacement and fissure eruption. Theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation. ?? 1983.

Weak ferromagnetism in a high-pressure phase of FeTiO3 with polar lattice distortion

NASA Astrophysics Data System (ADS)

Varga, Tamas; Mitchell, John; Fennie, Craig; Streiffer, Stephen; Hong, Seungbum; Park, Moonkyu; Gopalan, Venkatraman; Kumar, Amit; Vlahos, Eftihia; Sanehira, Takeshi; Wang, Yanbin

2009-03-01

Today's challenge in multiferroics is to identify materials in which polarization and magnetization -- normally considered contraindicated properties - are strongly coupled. Recent density functional theory calculations have predicted that the family of compounds MTiO3 (M = Mn, Fe, Ni) are promising candidates where a polar lattice distortion can induce weak ferromagnetism. The crucial insight is that while the equilibrium one-atmosphere structure of these is ilmenite, they must be transformed to a closely related LiNbO3-type structure. We have prepared the corresponding FeTiO3 phase at 18 GPa and 1200 ^oC. It shows a sharp antiferromagnetic (AF) transition at 111.5 K. FeTiO3 also displays ferroelectric domains, and weak ferromagnetism coincident with the AF transition. Possible coupling between its polarization and weak ferromagnetism is discussed based on results of piezoelectric force microscopy (PFM), second harmonic generation (SHG), dielectric, and polarization measurements.

Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses.

PubMed

Dmowski, W; Gierlotka, S; Wang, Z; Yokoyama, Y; Palosz, B; Egami, T

2017-07-26

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids, but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.

In situ observation of quasimelting of diamond and reversible graphite-diamond phase transformations.

PubMed

Huang, J Y

2007-08-01

Because of technique difficulties in achieving the extreme high-pressure and high-temperature (HPHT) simultaneously, direct observation of the structures of carbon at extreme HPHT conditions has not been possible. Banhart and Ajayan discovered remarkably that carbon onions can act as nanoscopic pressure cells to generate high pressures. By heating carbon onions to approximately 700 degrees C and under electron beam irradiation, the graphite-to-diamond transformation was observed in situ by transmission electron microscopy (TEM). However, the highest achievable temperature in a TEM heating holder is less than 1000 degrees C. Here we report that, by using carbon nanotubes as heaters and carbon onions as high-pressure cells, temperatures higher than 2000 degrees C and pressures higher than 40 GPa were achieved simultaneously in carbon onions. At such HPHT conditions and facilitated by electron beam irradiation, the diamond formed in the carbon onion cores frequently changed its shape, size, orientation, and internal structure and moved like a fluid, implying that it was in a quasimelting state. The fluctuation between the solid phase of diamond and the fluid/amorphous phase of diamond-like carbon, and the changes of the shape, size, and orientation of the solid diamond, were attributed to the dynamic crystallization of diamond crystal from the quasimolten state and the dynamic graphite-diamond phase transformations. Our discovery offers unprecedented opportunities to studying the nanostructures of carbon at extreme conditions in situ and at an atomic scale.

Modifications of structural and physical properties induced by swift heavy ions in Gd2Ti2O7 and Y2Ti2O7 pyrochlores

NASA Astrophysics Data System (ADS)

Sellami, N.; Sattonnay, G.; Grygiel, C.; Monnet, I.; Debelle, A.; Legros, C.; Menut, D.; Miro, S.; Simon, P.; Bechade, J. L.; Thomé, L.

2015-12-01

The structural transformations induced by ionization processes in Gd2Ti2O7 and Y2Ti2O7 pyrochlores irradiated with swift heavy ions have been studied using XRD and Raman experiments. Results show that irradiation induces amorphization and that the phase transformation build-up can be accounted for in the framework of a model involving a single-impact mechanism. The radiation induced amorphization build-up is faster in Gd2Ti2O7 than in Y2Ti2O7. Moreover, a decrease of the thermal conductivity (measured by the laser flash method) is induced by irradiation both in Gd2Ti2O7 and Y2Ti2O7.

Structural and environmental dependence of superlow friction in ion vapour-deposited a-C : H : Si films for solid lubrication application

NASA Astrophysics Data System (ADS)

Chen, Xinchun; Kato, Takahisa; Kawaguchi, Masahiro; Nosaka, Masataka; Choi, Junho

2013-06-01

Understanding the tribochemical interaction of water molecules in humid environment with carbonaceous film surfaces, especially hydrophilic surface, is fundamental for applications in tribology and solid lubrication. This paper highlights some experimental evidence to elucidate the structural and environmental dependence of ultralow or even superlow friction in ion vapour-deposited a-C : H : Si films. The results indicate that both surface density of silicon hydroxyl group (Si-OH) and humidity level (RH) determine the frictional performance of a-C : H : Si films. Ultralow friction coefficient μ (˜0.01-0.055) is feasible in a wide range of RH. The dissociative formation of hydrophilic Si-OH surface and the following nanostructure of interfacial water molecules under contact pressure are the origin of ultralow friction for a-C : H : Si films in humid environment. The correlation between contact pressure and friction coefficient derived from Hertzian contact model is not valid in the present case. Under this nanoscale boundary lubrication, the friction coefficient tends to increase as the contact pressure increases. There even exists a contact pressure threshold for the transition from ultralow to superlow friction (μ ˜ 0.007). In comparison, when tribotested in dry N2, the observed superlow friction (μ ˜ 0.004) in the absence of water is correlated with the formation of a low shear strength tribolayer by wear-induced phase transformation.

Pressure-induced Lifshitz and structural transitions in NbAs and TaAs: experiments and theory.

PubMed

Gupta, Satyendra Nath; Singh, Anjali; Pal, Koushik; Muthu, D V S; Shekhar, C; Elghazali, Moaz A; Naumov, Pavel G; Medvedev, Sergey A; Felser, C; Waghmare, U V; Sood, A K

2018-05-10

High pressure Raman, resistivity and synchrotron x-ray diffraction studies on Weyl semimetals NbAs and TaAs have been carried out along with density functional theoretical (DFT) analysis to explain pressure induced structural and electronic topological phase transitions. The frequencies of first order Raman modes harden with increasing pressure, exhibiting a slope change at [Formula: see text] GPa for NbAs and [Formula: see text] GPa for TaAs. The resistivities of NbAs and TaAs exhibit a minimum at pressures close to these transition pressures and also a change in the bulk modulus is observed. Our first-principles calculations reveal that the transition is associated with an electronic Lifshitz transition at [Formula: see text] for NbAs while it is a structural phase transition from body centered tetragonal to hexagonal phase at [Formula: see text] for TaAs. Further, our DFT calculations show a structural phase transition at 24 GPa from body centered tetragonal phase to hexagonal phase.

Multiple Fermi pockets revealed by Shubnikov-de Haas oscillations in WTe2

NASA Astrophysics Data System (ADS)

Xiang, Fei-Xiang; Veldhorst, Menno; Dou, Shi-Xue; Wang, Xiao-Lin

2015-11-01

The recently discovered non-saturating and parabolic magnetoresistance and the pressure-induced superconductivity at low temperature in WTe2 imply its rich electronic structure and possible practical applications. Here we use magnetotransport measurements to investigate the electronic structure of WTe2 single crystals. A non-saturating and parabolic magnetoresistance is observed from low temperature to high temperature up to 200 K with magnetic fields up to 8 T. Shubnikov-de Haas (SdH) oscillations with beating patterns are observed, the fast Fourier transform of which reveals three oscillation frequencies, corresponding to three pairs of Fermi pockets with comparable effective masses, m* ∼ 0.31~me . By fitting the Hall resistivity, we infer that they can be attributed to one pair of electron pockets and two pairs of hole pockets, together with nearly perfect compensation of the electron-hole carrier concentration. These magnetotransport measurements reveal the complex electronic structure in WTe2, explaining the non-saturating magnetoresistance.

Temperature and field induced strain measurements in single crystal Gd 5Si 2Ge 2

DOE PAGES

McCall, S. K.; Nersessian, N.; Carman, G. P.; ...

2016-03-29

The first-order magneto-structural transformation that occurs in Gd 5Si 2Ge 2 near room temperature makes it a strong candidate for many energy harvesting applications. Understanding the single crystal properties is crucial for allowing simulations of device performance. In this study, magnetically and thermally induced transformation strains were measured in a single crystal of Gd 5Si 2.05Ge 1.95 as it transforms from a high-temperature monoclinic paramagnet to a lower-temperature orthorhombic ferromagnet. Thermally induced transformation strains of –8500 ppm, +960 ppm and +1800 ppm, and magnetically induced transformation strains of –8500 ppm, +900 ppm and +2300 ppm were measured along the a,more » b and c axes, respectively. Furthermore, using experimental data coupled with general thermodynamic considerations, a universal phase diagram was constructed showing the transition from the monoclinic to the orthorhombic phase as a function of temperature and magnetic field.« less

Influence of supercritical CO(2) pressurization on the phase behavior of mixed cholesteryl esters.

PubMed

Huang, Zhen; Feng, Mei; Su, Junfeng; Guo, Yuhua; Liu, Tie-Yan; Chiew, Yee C

2010-09-15

Evidences indicating the presence of phase transformations in the mixed cholesteryl benzoate (CBE) and cholesteryl butyrate (CBU) under the supercritical CO(2) pressurization, by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD), are presented in this work. These include (1) the DSC heating curve of pure CBU; (2) the DSC heating curves of CBU/CBE mixtures; (3) the XRD spectra of pure CBU; (4) the XRD spectra of CBU/CBE mixtures; (5) CBU and CBE are miscible in either solid phase or liquid phase over the whole composition range. As a result of the presence of these phase transformations induced by pressurization, it could be deduced that a solid solution of the CBU/CBE mixture might have formed at the interfaces under supercritical conditions, subsequently influencing their dissolving behaviors in supercritical CO(2). Copyright 2010 Elsevier B.V. All rights reserved.

Identification of pesticide transformation products in agricultural soils using liquid chromatography/quadrupole-time-of-flight mass spectrometry.

PubMed

Padilla-Sánchez, Juan A; Michael Thurman, E; Plaza-Bolaños, Patricia; Ferrer, Imma

2012-05-15

A study of pesticide transformation products (TPs) was carried out in soils of agricultural areas working under integrated pest management programs (IPMs). Bupirimate and cyromazine were the pesticides detected in soils after an initial pre-screening. The aim of this work was the identification of relevant TPs of these two pesticides. Soil samples were extracted by pressurized liquid extraction (PLE), using a mixture of ethyl acetate/methanol (3:1, v/v), and analyzed by ultra-high-pressure liquid chromatography coupled to hybrid quadrupole-time-of-flight mass spectrometry (UHPLC-QTOF-MS). For confirmation purposes, tandem mass spectrometry (MS(2) ) experiments were carried out using QTOF-MS, obtaining specific fragment structures of the pesticides and their degradates. Retention times and exact masses of the protonated molecules were used for the identification of the pesticides bupirimate (m/z 317.1642) and cyromazine (m/z 167.1040) and their respective TPs, namely ethirimol (m/z 210.1601) and melamine (m/z 127.0727). A novel strategy using pseudo-MS(3) experiments was developed to confirm the structure of bupirimate TP (ethirimol). This strategy consists of generating the particular TP in the ion source, via collision-induced fragmentation, and then performing MS/MS to the fragment ion formed in-source. Ethirimol and melamine were identified as degradation products of bupirimate and cyromazine, respectively. The study was applied to the analysis of 15 agricultural soil samples finding bupirimate and ethirimol in seven samples, cyromazine in one sample and melamine in four samples. Copyright © 2012 John Wiley & Sons, Ltd.

Anisotropic crystal structure distortion of the monoclinic polymorph of acetaminophen at high hydrostatic pressures.

PubMed

Boldyreva, E V; Shakhtshneider, T P; Vasilchenko, M A; Ahsbahs, H; Uchtmann, H

2000-04-01

The anisotropy of structural distortion of the monoclinic polymorph of acetaminophen induced by hydrostatic pressure up to 4.0 GPa was studied by single-crystal X-ray diffraction in a Merrill-Bassett diamond anvil cell (DAC). The space group (P2(1)/n) and the general structural pattern remained unchanged with pressure. Despite the overall decrease in the molar volume with pressure, the structure expanded in particular crystallographic directions. One of the linear cell parameters (c) passed through a minimum as the pressure increased. The intramolecular bond lengths changed only slightly with pressure, but the changes in the dihedral and torsion angles were very large. The compressibility of the intermolecular hydrogen bonds NH...O and OH...O was measured. NH...O bonds were shown to be slightly more compressible than OH...O bonds. The anisotropy of structural distortion was analysed in detail in relation to the pressure-induced changes in the molecular conformations, to the compression of the hydrogen-bond network, and to the changes in the orientation of molecules with respect to each other in the pleated sheets in the structure. Dirichlet domains were calculated in order to analyse the relative shifts of the centroids of the hydrogen-bonded cycles and of the centroids of the benzene rings with pressure.

Stress-state effects on the stress-induced martensitic transformation of carburized 4320 steels

NASA Astrophysics Data System (ADS)

Karaman, I.; Balzer, M.; Sehitoglu, Huseyin; Maier, H. J.

1998-02-01

The effect of different stress states on the stress-induced martensitic transformation of retained austenite was investigated in carburized 4320 steels with an initial retained austenite content of 15 pct. Experiments were conducted utilizing a specialized pressure rig and comparison between stress-strain behaviors of specimens with different austenitization and tempering histories was performed under these stress states. Experimental results indicated considerable asymmetry between tension and compression, with triaxial stress states resulting in the highest strength levels for the untempered material. Fine carbide precipitates due to low-temperature tempering increased the strength and ductility of the specimens and also changed the austenite-to-martensite transformation behavior. Numerical simulations of stress-strain behaviors under different stress states were obtained, with an existing micromechanical self-consistent framework utilizing the crystallographic theory of austenite/martensite transformation and the minimum complementary free-energy principle. The model was modified for carburized steels upon microstructural investigation and predicted the same trends in effective stress-effective strain behavior as observed experimentally.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manikandan, M.; Santhosh, M.; Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com

Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of actinide carbides AnC (An=U, Np) for three different crystal structures, namely NaCl, CsCl and ZnS. Among the considered structures, NaCl structure is found to be the most stable structure for these carbides at normal pressure. A pressure induced structural phase transition from NaCl to ZnS is observed. The electronic structure reveals that these carbides are metals. The calculated elastic constants indicate that these carbides are mechanically stable at normal pressure.

Transformation between divacancy defects induced by an energy pulse in graphene.

PubMed

Xia, Jun; Liu, XiaoYi; Zhou, Wei; Wang, FengChao; Wu, HengAn

2016-07-08

The mutual transformations among the four typical divacancy defects induced by a high-energy pulse were studied via molecular dynamics simulation. Our study revealed all six possible mutual transformations and found that defects transformed by absorbing energy to overcome the energy barrier with bonding, debonding, and bond rotations. The reversibility of defect transformations was also investigated by potential energy analysis. The energy difference was found to greatly influence the transformation reversibility. The direct transformation path was irreversible if the energy difference was too large. We also studied the correlation between the transformation probability and the input energy. It was found that the transformation probability had a local maxima at an optimal input energy. The introduction of defects and their structural evolutions are important for tailoring the exceptional properties and thereby performances of graphene-based devices, such as nanoporous membranes for the filtration and desalination of water.

Transformation of the Surface Structure of Marble under the Action of a Shock Wave

NASA Astrophysics Data System (ADS)

Shcherbakov, I. P.; Vettegren, V. I.; Bashkarev, A. Ya.; Mamalimov, R. I.

2018-01-01

The structure of marble fracture fragments formed after the destruction under the action of a shock wave have been analyzed by Raman, infrared, and luminescence spectroscopic techniques. It has been found that calcite I in the surface layer of fragments with thicknesses of about 2 μm is transformed into high-pressure phase calcite III. At the same time, concentrations of Mn2+, Eu3+, and other ions decrease to about onefourth of their initial values.

Static high-pressure structural studies on Dy to 119 GPa

NASA Astrophysics Data System (ADS)

Patterson, Reed; Saw, Cheng K.; Akella, Jagannadham

2004-05-01

Structural phase transitions in the rare-earth metal dysprosium have been studied in a diamond anvil cell to 119 GPa by x-ray diffraction. Four transformations following the sequence hcp→Sm-type→dhcp→hR24 (hexagonal)→bcm (monoclinic) are observed at 6, 15, 43, and 73 GPa, respectively. The hexagonal to monoclinic transformation is accompanied by a 6% reduction in volume, which is attributed to delocalization of the 4f electrons, similar to that seen in Ce, Pr, and Gd.

Molecular Dynamics Simulations of Shear Induced Transformations in Nitromethane

NASA Astrophysics Data System (ADS)

Larentzos, James; Steele, Brad

2017-06-01

Recent experiments demonstrate that NM undergoes explosive chemical initiation under compressive shear stress. The atomistic dynamics of the shear response of single-crystalline and bi-crystalline nitromethane (NM) are simulated using molecular dynamics simulations under high pressure conditions to aid in interpreting these experiments. The atomic interactions are described using a recently re-optimized ReaxFF-lg potential trained specifically for NM under pressure. The simulations demonstrate that the NM crystal transforms into a disordered state upon sufficient application of shear stress; its maximum value, shear angle, and atomic-scale dynamics being highly dependent on crystallographic orientation of the applied shear. Shear simulations in bi-crystalline NM show more complex behavior resulting in the appearance of the disordered state at the grain boundary.

Molecular Dynamics Simulations of Shear Induced Transformations in Nitromethane

NASA Astrophysics Data System (ADS)

Larentzos, James; Steele, Brad

Recent experiments demonstrate that NM undergoes explosive chemical initiation under compressive shear stress. The atomistic dynamics of the shear response of single-crystalline and bi-crystalline nitromethane (NM) are simulated using molecular dynamics simulations under high pressure conditions to aid in interpreting these experiments. The atomic interactions are described using a recently re-optimized ReaxFF-lg potential trained specifically for NM under pressure. The simulations demonstrate that the NM crystal transforms into a disordered state upon sufficient application of shear stress; its maximum value, shear angle, and atomic-scale dynamics being highly dependent on crystallographic orientation of the applied shear. Shear simulations in bi-crystalline NM show more complex behavior resulting in the appearance of the disordered state at the grain boundary.

Pressure-induced anomalies and structural instability in compressed β-Sb 2 O 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zou, Yongtao; Zhang, Wei; Li, Xuefei

2018-01-01

Here, we have discovered a new high-pressure phase of Sb 2 O 3 , and reported pressure-induced anomalies in orthorhombic β-Sb 2 O 3 (valentinite) by the combination of synchrotron in situ X-ray diffraction and first-principles theoretical calculations up to 40.5 GPa.

A case study of the fluid structure interaction of a Francis turbine

NASA Astrophysics Data System (ADS)

Müller, C.; Staubli, T.; Baumann, R.; Casartelli, E.

2014-03-01

The Francis turbine runners of the Grimsel 2 pump storage power plant showed repeatedly cracks during the last decade. It is assumed that these cracks were caused by flow induced forces acting on blades and eventual resonant runner vibrations lead to high stresses in the blade root areas. The eigenfrequencies of the runner were simulated in water using acoustic elements and compared to experimental data. Unsteady blades pressure distribution determined by a transient CFD simulation of the turbine were coupled to a FEM simulation. The FEM simulation enabled analyzing the stresses in the runner and the eigenmodes of the runner vibrations. For a part-load operating point, transient CFD simulations of the entire turbine, including the spiral case, the runner and the draft tube were carried out. The most significant loads on the turbine runner resulted from the centrifugal forces and the fluid forces. Such forces effect temporally invariant runner blades loads, in contrast rotor stator interaction or draft tube instabilities induce pressure fluctuations which cause the temporally variable forces. The blades pressure distribution resulting from the flow simulation was coupled by unidirectional-harmonic FEM simulation. The dominant transient blade pressure distribution of the CFD simulation were Fourier transformed, and the static and harmonic portion assigned to the blade surfaces in the FEM model. The evaluation of the FEM simulation showed that the simulated part load operating point do not cause critical stress peaks in the crack zones. The pressure amplitudes and frequencies are very small and interact only locally with the runner blades. As the frequencies are far below the modal frequencies of the turbine runner, resonant vibrations obviously are not excited.

Revealing nanoparticle assembly under high pressure.

NASA Astrophysics Data System (ADS)

Fan, Hongyou

Precise control of structural parameters through nanoscale engineering to improve optical and electronic properties of functional nanoparticles continuously remains an outstanding challenge. Previous work on nanoparticle assembly has been conducted largely at ambient pressure. Here I will present a new Stress-Induced Fabrication method in which we applied high pressure or stress to nanoparticle arrays to induce structural phase transition and to consolidate new nanomaterials with precisely controlled structures and tunable properties. By manipulating nanoparticle coupling through external pressure, a reversible change in their assemblies and properties can be achieved and demonstrated. In addition, over a certain threshold, the external pressure will force these nanoparticles into contact, thereby allowing the formation and consolidation of one- to three-dimensional nanostructures. Through stress induced nanoparticle assembly, materials engineering and synthesis become remarkably flexible without relying on traditional crystallization process where atoms/ions are locked in a specific crystal structure. Therefore, morphology or architecture can be readily tuned to produce desirable properties for practical applications. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Electronic and structural properties of Lu under pressure: Relation to structural phases of the rare-earth metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Min, B.I.; Oguchi, T.; Jansen, H.J.F.

1986-07-15

Ground-state electronic and structural properties of Lu under pressure are investigated with use of the self-consistent all-electron total-energy linear muffin-tin orbital band-structure method within a local-density-functional approximation. Pressure-induced structural transitions are found to occur in the following sequence: hcp--(Sm-type)--dhcp--fcc, which is the same as that observed in the crystal structures of the trivalent rare-earth metals with decreasing atomic number. This structural transition is correlated with the increase in the number of d-italic electrons under pressure.

Quasi-dynamic pressure and temperature initiated β<-->δ solid phase transitions in HMX

NASA Astrophysics Data System (ADS)

Zaug, Joseph M.; Farber, Daniel L.; Craig, Ian M.; Blosch, Laura L.; Shuh, David K.; Hansen, Donald W.; Aracne-Ruddle, Chantel M.

2000-04-01

The phase transformation of β-HMX (>0.5% RDX) to δ phase has been studied for over twenty years and more recently with an high-contrast optical second harmonic generation technique. Shock studies of the plastic binder composites of HMX have indicated that the transition is perhaps irreversible, a result that concurs with the static pressure results published by F. Goetz et al. [1] in 1978. However, the stability field favors the β polymorph over δ as pressure is increased (up to 5.4 GPa) along any thermodynamically reasonable isotherm. In this experiment, strict control of pressure and temperature is maintained while x-ray and optical diagnostics are applied to monitor the conformational dynamics of HMX. Unlike the temperature induced β→δ transition, the pressure induced is heterogeneous in nature. The 1 bar 25 °C δ→β transition is not immediate, occuring over tens of hours. Transition points and kinetics are path dependent and consequently this paper describes our work in progress.

Structural transition and amorphization in compressed α - Sb 2 O 3

DOE PAGES

Zhao, Zhao; Zeng, Qiaoshi; Zhang, Haijun; ...

2015-05-27

Sb₂O₃-based materials are of broad interest in materials science and industry. High-pressure study using diamond anvil cells shows promise in obtaining new crystal and electronic structures different from their pristine states. Here, we conducted in situ angle dispersive synchrotron x-ray-diffraction and Raman spectroscopy experiments on α-Sb₂O₃ up to 50 GPa with neon as the pressure transmitting medium. A first-order structural transition was observed in between 15 and 20 GPa, where the cubic phase I gradually transformed into a layered tetragonal phase II through structural distortion and symmetry breaking. To explain the dramatic changes in sample color and transparency, we performedmore » first-principles calculations to track the evolution of its density of states and electronic structure under pressure. At higher pressure, a sluggish amorphization was observed. Our results highlight the structural connections among the sesquioxides, where the lone electron pair plays an important role in determining the local structures.« less

Origin of negative thermal expansion in Zn2GeO4 revealed by high pressure study

NASA Astrophysics Data System (ADS)

Cheng, Xuerui; Yuan, Jie; Zhu, Xiang; Yang, Kun; Liu, Miao; Qi, Zeming

2018-03-01

Zn2GeO4, as an open-framework structure compound, exhibits negative thermal expansion (NTE) below room temperature. In this work, we investigated the structural stability and phonon modes employing the x-ray diffraction and Raman spectroscopy under high pressure up to 23.0 GPa within a diamond anvil cell, and we observed that a pressure-induced irreversible amorphization took place around 10.1 GPa. Bulk modulus, pressure coefficients, and Grüneisen parameters were measured for the initial rhombohedral structure. Several low-frequency rigid-unit modes are found to have negative Grüneisen parameter, which accounts for the primary part of NTE in Zn2GeO4. These results further confirm the hypothesis that the pressure-induced amorphization and the negative thermal expansion are correlated phenomena.

Effects of high pressure on microstructure evolution and crystallization mechanisms during solidification of nickel

NASA Astrophysics Data System (ADS)

Zhang, Hai-Tao; Mo, Yun-Fei; Liu, Rang-Su; Tian, Ze-An; Liu, Hai-Rong; Hou, Zhao-Yang; Zhou, Li-Li; Liang, Yong-Chao; Peng, Ping

2018-03-01

To deeply understand the effects of high pressure on microstructural evolutions and crystallization mechanisms of liquid metal Ni during solidification process, MD simulation studies have been performed under 7 pressures of 0 ˜ 30 GPa, at cooling rate of 1.0 × 1011 K s-1. Adopting several microstructural analyzing methods, especially the cluster-type index method (CTIM-2) to analyze the local microstructures in the system. It is found that the pressure has important influence on the formation and evolution of microstructures, especially of the main basic clusters in the system. All the simulation systems are directly solidified into crystal structures, and the 1421, 1422, 1441 and 1661 bond-types, as well the FCC (12 0 0 0 12 0), HCP (12 0 0 0 6 6) and BCC (14 6 0 8 0 0) clusters play a key role in the microstructure transitions from liquid to crystal structures. The crystallization temperature T c is enhanced almost linearly with the increase of pressure. Highly interesting, it is found for the first time that there is an important phase transformation point from FCC to BCC structures between 20 ˜ 22.5 GPa during the solidification processes from the same initial liquid system at the same cooling rate. And the effect of increasing pressure is similar to that of decreasing cooling rate for the phase transformation of microstructures during solidification process of liquid metal Ni system, though they have different concrete effecting mechanisms.

Ab Initio Study of Interfacial Structure Transformation of Amorphous Carbon Catalyzed by Ti, Cr, and W Transition Layers.

PubMed

Li, Xiaowei; Li, Lei; Zhang, Dong; Wang, Aiying

2017-11-29

Amorphous carbon (a-C) films composited with transition layers exhibit the desirable improvement of adhesion strength between films and substrate, but the further understanding on the interfacial structure transformation of a-C structure induced by transition layers is still lacked. In this paper, using ab initio calculations, we comparatively studied the interfacial structure between Ti, Cr, or W transition layers and a-C film from the atomic scale, and demonstrated that the addition of Ti, Cr, or W catalyzed the graphitic transformation of a-C structure at different levels, which provided the theoretical guidance for designing a multilayer nanocomposite film for renewed application.

Structural changes induced by high-pressure processing in micellar casein and milk protein concentrates.

PubMed

Cadesky, Lee; Walkling-Ribeiro, Markus; Kriner, Kyle T; Karwe, Mukund V; Moraru, Carmen I

2017-09-01

Reconstituted micellar casein concentrates and milk protein concentrates of 2.5 and 10% (wt/vol) protein concentration were subjected to high-pressure processing at pressures from 150 to 450 MPa, for 15 min, at ambient temperature. The structural changes induced in milk proteins by high-pressure processing were investigated using a range of physical, physicochemical, and chemical methods, including dynamic light scattering, rheology, mid-infrared spectroscopy, scanning electron microscopy, proteomics, and soluble mineral analyses. The experimental data clearly indicate pressure-induced changes of casein micelles, as well as denaturation of serum proteins. Calcium-binding α S1 - and α S2 -casein levels increased in the soluble phase after all pressure treatments. Pressurization up to 350 MPa also increased levels of soluble calcium and phosphorus, in all samples and concentrations, whereas treatment at 450 MPa reduced the levels of soluble Ca and P. Experimental data suggest dissociation of calcium phosphate and subsequent casein micelle destabilization as a result of pressure treatment. Treatment of 10% micellar casein concentrate and 10% milk protein concentrate samples at 450 MPa resulted in weak, physical gels, which featured aggregates of uniformly distributed, casein substructures of 15 to 20 nm in diameter. Serum proteins were significantly denatured by pressures above 250 MPa. These results provide information on pressure-induced changes in high-concentration protein systems, and may inform the development on new milk protein-based foods with novel textures and potentially high nutritional quality, of particular interest being the soft gel structures formed at high pressure levels. The Authors. Published by the Federation of Animal Science Societies and Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Explosion-Induced Implosions of Cylindrical Shell Structures

NASA Astrophysics Data System (ADS)

Ikeda, C. M.; Duncan, J. H.

2010-11-01

An experimental study of the explosion-induced implosion of cylindrical shell structures in a high-pressure water environment was performed. The shell structures are filled with air at atmospheric pressure and are placed in a large water-filled pressure vessel. The vessel is then pressurized to various levels P∞=αPc, where Pc is the natural implosion pressure of the model and α is a factor that ranges from 0.1 to 0.9. An explosive is then set off at various standoff distances, d, from the model center line, where d varies from R to 10R and R is the maximum radius of the explosion bubble. High-speed photography (27,000 fps) was used to observe the explosion and resulting shell structure implosion. High-frequency underwater blast sensors recorded dynamic pressure waves at 6 positions. The cylindrical models were made from aluminum (diameter D = 39.1 mm, wall thickness t = 0.89 mm, length L = 240 mm) and brass (D = 16.7 mm, t = 0.36 mm, L=152 mm) tubes. The pressure records are interpreted in light of the high-speed movies. It is found that the implosion is induced by two mechanisms: the shockwave generated by the explosion and the jet formed during the explosion-bubble collapse. Whether an implosion is caused by the shockwave or the jet depends on the maximum bubble diameter and the standoff distance.

Pressure variation of Rashba spin splitting toward topological transition in the polar semiconductor BiTeI

NASA Astrophysics Data System (ADS)

Ideue, T.; Checkelsky, J. G.; Bahramy, M. S.; Murakawa, H.; Kaneko, Y.; Nagaosa, N.; Tokura, Y.

2014-10-01

BiTeI is a polar semiconductor with gigantic Rashba spin-split bands in bulk. We have investigated the effect of pressure on the electronic structure of this material via magnetotransport. Periods of Shubunikov-de Haas (SdH) oscillations originating from the spin-split outer Fermi surface and inner Fermi surface show disparate responses to pressure, while the carrier number derived from the Hall effect is unchanged with pressure. The associated parameters which characterize the spin-split band structure are strongly dependent on pressure, reflecting the pressure-induced band deformation. We find the SdH oscillations and transport response are consistent with the theoretically proposed pressure-induced band deformation leading to a topological phase transition. Our analysis suggests the critical pressure for the quantum phase transition near Pc=3.5 GPa.

Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dmowski, W.; Gierlotka, S.; Wang, Z.

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids,more » but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.« less

High-pressure protein crystallography of hen egg-white lysozyme

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamada, Hiroyuki; Nagae, Takayuki; Watanabe, Nobuhisa, E-mail: nobuhisa@nagoya-u.jp

The crystal structure of hen egg-white lysozyme (HEWL) was analyzed under pressures of up to 950 MPa. The high pressure modified the conformation of the molecule and induced a novel phase transition in the tetragonal crystal of HEWL. Crystal structures of hen egg-white lysozyme (HEWL) determined under pressures ranging from ambient pressure to 950 MPa are presented. From 0.1 to 710 MPa, the molecular and internal cavity volumes are monotonically compressed. However, from 710 to 890 MPa the internal cavity volume remains almost constant. Moreover, as the pressure increases to 950 MPa, the tetragonal crystal of HEWL undergoes a phasemore » transition from P4{sub 3}2{sub 1}2 to P4{sub 3}. Under high pressure, the crystal structure of the enzyme undergoes several local and global changes accompanied by changes in hydration structure. For example, water molecules penetrate into an internal cavity neighbouring the active site and induce an alternate conformation of one of the catalytic residues, Glu35. These phenomena have not been detected by conventional X-ray crystal structure analysis and might play an important role in the catalytic activity of HEWL.« less

The effect of reservoir geometry, injection and production parameters and permeability structure on induced seismicity

NASA Astrophysics Data System (ADS)

Hosseini, S. M.; Goebel, T.; Aminzadeh, F.

2015-12-01

The recent increase in injection induced seismicity (IIS) in previously less seismically active regions highlighted a need for better mitigation strategies and physics-based models of induced seismicity. Previous models of pressure diffusion and fluid flow investigated the change in Coulomb stress as a result of induced pore-pressure perturbations (e.g. Zhang et al., 2013; Keranen et al., 2014; Hornbach et al., 2015; Segall and Lu, 2015). Here, we consider the additional effects of permeability structure, operational parameters and reservoir geometry. We numerically investigate the influence of net fluid injection volumes; linear, radial, and spherical reservoir geometry; as well as reservoir size. The latter can have a substantial effect on changes in Coulomb stress and subsequent induced seismicity. We report on results from two series of model runs, which explored pressure changes caused by wastewater disposal and water flooding. We observed that a typical water flooding operation that includes production wells and injectors has a lower probability of inducing seismicity. Our observations are in agreement with assessment by National Research Council report on induced seismicity (2012). We developed a third suite of models that investigate the effect of permeability structure on injection-induced seismicity. We examine two cases of wastewater disposal in proximity to active faults: 1) in Central Illinois Basin and 2) in central California. In both cases, we observed that the size of the reservoir, presence of faults, and permeability contrast relative to the host rock, strongly influences the pressure changes with distance and time. These pressure changes vary widely but can easily lead to fault instability and seismic activity at up to 10 km distance from the injection well. The results of this study may help to select safe injection sites and operational conditions in order to minimize injection induced seismicity hazard.

Shock-Induced Phase Transitions in the Martian Meteorite Tissint: Mechanisms and Constraints on Shock Pressure

NASA Astrophysics Data System (ADS)

Sharp, T. G.; Hu, J.; Walton, E. L.

2013-12-01

Martian meteorites are important samples for understanding the origin and age of the Martian crust. All of these samples have been shocked to some degree during their ejection from Mars or earlier. Tissint, a picritic shergottite, has many high-pressure phases that have been used to constrain shock conditions and suggest a deep crustal origin [1] and to argue for multiple impact events [2]. Here we investigate the products and mechanisms of various olivine transformation reactions. Olivine in and adjacent to shock-melt veins and pockets is transformed into high-pressure minerals. In the hottest parts of the sample, olivine dissociated into 50-nm crystals of magnesiowüstite intergrown with either a pyroxene-composition glass or with low-Ca clinopyroxene. In both cases, the olivine is inferred to have transformed to silicate perovskite + magnesiowüstite during shock with subsequent breakdown of the perovskite after pressure release. Olivine along the margins of shock veins transformed into ringwoodite. Polycrystalline ringwoodite formed at the olivine-melt interface wheras coherent ringwoodite lamellae formed farther from the melt. These ringwoodite lamellae have the same topotaxial relationship to olivine as seen in static high-pressure experiments [3] and shocked meteorites [4]: (100)Ol || {111}Rw and [011]Ol || <110>Rw. The various olivine reactions can be explained by a single shock to above 24 GPa where only the highest temperatures allowed the dissociation of olivine to silicate-perovskite plus magnesiowüstite. The silicate perovskite in the melt pocket transformed to pyroxene because the melt pocket remained very hot after pressure release. At lower temperatures, the kinetically easier polymorphic transformation of olivine to metastable ringwoodite occurred. At the lowest temperatures, this reaction was facilitated by nucleation of ringwoodite lamellae on stacking faults in olivine. The variation in assemblages that we see are consistent with a single shock and a relatively short shock pulse. References: [1] Baziotis1, I. P. et. al 2013 Nature Communications 4:1404, [2] El Goresey, A. et. al 2013 #1037. 44th LPSC. [3] Kerschhofer, L. et. al 1996 Science 274, 79-81. [4] Miyahara et. al, 2010 EPSL. 295, 321-327.

Influence of Temperature on Fatigue-Induced Martensitic Phase Transformation in a Metastable CrMnNi-Steel

NASA Astrophysics Data System (ADS)

Biermann, Horst; Glage, Alexander; Droste, Matthias

2016-01-01

Metastable austenitic steels can exhibit a fatigue-induced martensitic phase transformation during cyclic loading. It is generally agreed that a certain strain amplitude and a threshold of the cumulated plastic strain must be exceeded to trigger martensitic phase transformation under cyclic loading. With respect to monotonic loading, the martensitic phase transformation takes place up to a critical temperature—the so-called M d temperature. The goal of the present investigation is to determine an M d,c temperature which would be the highest temperature at which a fatigue-induced martensitic phase transformation can take place. For this purpose, fatigue tests controlled by the total strain were performed at different temperatures. The material investigated was a high-alloy metastable austenitic steel X3CrMnNi16.7.7 (16.3Cr-7.2Mn-6.6Ni-0.03C-0.09N-1.0Si) produced using the hot pressing technique. The temperatures were set in the range of 283 K (10 °C) ≤ T ≤ 473 K (200 °C). Depending on the temperature and strain amplitude, the onset of the martensitic phase transformation shifted to different values of the cumulated plastic strain, or was inhibited completely. Moreover, it is known that metastable austenitic CrMnNi steels with higher nickel contents can exhibit the deformation-induced twinning effect. Thus, at higher temperatures and strain amplitudes, a transition from the deformation-induced martensitic transformation to deformation-induced twinning takes place. The fatigue-induced martensitic phase transformation was monitored during cyclic loading using a ferrite sensor. The microstructure after the fatigue tests was examined using the back-scattered electrons, the electron channeling contrast imaging and the electron backscatter diffraction techniques to study the temperature-dependent dislocation structures and phase transformations.

High pressure transport and structural studies on Nb 3Ga superconductor

DOE PAGES

Mkrtcheyan, Vahe; Kumar, Ravhi; Baker, Jason; ...

2014-11-24

We investigated the crystal structure of A-15 superconductor Nb 3Ga with a critical temperature T c = 16.5 K by high pressure x-ray diffraction (HPXRD) using synchrotron x-rays and a diamond anvil cell under Ne pressure medium. Furthermore, the high pressure structural results indicate that Nb 3Ga is stable up to 41 GPa. The P-V plot shows an anomaly around 15 GPa even though there are no pressure induced structural transitions are observed. High pressure resistance measurements were performed up to 0.5 GPa to understand the variation of T c under pressure. Finally, our results show a positive pressure effectmore » on T c.« less

Atmospheric-Pressure Plasma Interaction with Soft Materials as Fundamental Processes in Plasma Medicine.

PubMed

Takenaka, Kosuke; Miyazaki, Atsushi; Uchida, Giichiro; Setsuhara, Yuichi

2015-03-01

Molecular-structure variation of organic materials irradiated with atmospheric pressure He plasma jet have been investigated. Optical emission spectrum in the atmospheric-pressure He plasma jet has been measured. The spectrum shows considerable emissions of He lines, and the emission of O and N radicals attributed to air. Variation in molecular structure of Polyethylene terephthalate (PET) film surface irradiated with the atmospheric-pressure He plasma jet has been observed via X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). These results via XPS and FT-IR indicate that the PET surface irradiated with the atmospheric-pressure He plasma jet was oxidized by chemical and/or physical effect due to irradiation of active species.

New structural phase obtained by exerting high pressure on (Br2)n@AFI composite material

NASA Astrophysics Data System (ADS)

Yao, Zhen; Lv, Jia-Yin; Liu, Bo; Liu, Bing-Bing; Yang, Bai

2018-06-01

In this paper, we present a theoretical study on the high-pressure behaviors of a (Br2)n@AlPO4-5 (AFI) peapod structure. The influence of the encapsulated Br2 molecule on the structural deformation of AFI crystal is analyzed using the volume-pressure function. The bonding process of the linearly arrayed Br2 molecule transferring to the bromine atomic chain is analyzed by the electron density distribution. A new high-pressure phase with P2 point group symmetry is obtained as the pressure increases to 34 GPa. In addition, electron density difference calculations are used to study the systematic charge transformation. Further analysis indicates that the encapsulated Br2 molecules can significantly modify the electronic structure of the AFI crystal. The band gap of the (Br2)n@AFI decreases with pressure and closes at 9 GPa. Moreover, the calculated bulk modulus and electronic properties indicate that the new structural phase is metallic with a high hardness, providing a new strategy for exploring novel nanomaterials.

Electrical and Structural Origin of Self-Healing Phenomena in Pentacene Thin Films.

PubMed

Kang, Evan S H; Zhang, Hongbin; Donner, Wolfgang; von Seggern, Heinz

2017-04-01

Self-healing induced by structural phase transformation is demonstrated using pentacene field-effect transistors. During the self-healing process, the electrical properties at the pentacene interfaces improve due to the phase transformation from monolayer phase to thin-film phase. Enhanced mobility is confirmed by first-principles calculations. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zinc-blende to rocksalt transition in SiC in a laser-heated diamond-anvil cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daviau, Kierstin; Lee, Kanani K. M.

2017-04-18

We explore the stability of the ambient pressure zinc-blende polymorph (B3) structure of silicon carbide (SiC) at high pressures and temperatures where it transforms to the rocksalt (B1) structure. We find that the transition occurs ~40 GPa lower than previously measured when heated to moderately high temperatures. A lower transition pressure is consistent with the transition pressures predicted in numerous ab initio computations. We find a large volume decrease across the transition of ~17%, with the volume drop increasing at higher formation pressures, suggesting this transition is volume driven yielding a nearly pressure-independent Clapeyron slope. Such a dramatic density increasemore » occurring at pressure is important to consider in applications where SiC is exposed to extreme conditions, such as in industrial applications or planetary interiors.« less

Pressure-Driven Spin Crossover Involving Polyhedral Transformation in Layered Perovskite Cobalt Oxyfluoride

PubMed Central

Tsujimoto, Yoshihiro; Nakano, Satoshi; Ishimatsu, Naoki; Mizumaki, Masaichiro; Kawamura, Naomi; Kawakami, Takateru; Matsushita, Yoshitaka; Yamaura, Kazunari

2016-01-01

We report a novel pressure-driven spin crossover in layered cobalt oxyfluoride Sr2CoO3F with a distorted CoO5 square pyramid loosely bound with a fluoride ion. Upon increasing pressure, the spin state of the Co(III) cation gradually changes from a high spin state (S = 2) to a low spin state (S = 0) accompanied by a anomalously large volume contraction (bulk modulus, 76.8(5) GPa). The spin state change occurs on the CoO5 pyramid in a wide pressure range, but the concomitant gradual shrinkage of the Co–F bond length with pressure gives rise to a polyhedral transformation to the CoO5F octahedron without a structural phase transition, leading to the full conversion to the LS state at 12 GPa. The present results provide new effective strategy to fine-tune electronic properties of mixed anion systems by controlling the covalency in metal-ligand bonds under pressure. PMID:27805031

Phase transformations in a Cu−Cr alloy induced by high pressure torsion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korneva, Anna, E-mail: a.korniewa@imim.pl; Straumal, Boris; Institut für Nanotechnologie, Karlsruher Institut für Technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen

2016-04-15

Phase transformations induced by high pressure torsion (HPT) at room temperature in two samples of the Cu-0.86 at.% Cr alloy, pre-annealed at 550 °C and 1000 °C, were studied in order to obtain two different initial states for the HPT procedure. Observation of microstructure of the samples before HPT revealed that the sample annealed at 550 °C contained two types of Cr precipitates in the Cu matrix: large particles (size about 500 nm) and small ones (size about 70 nm). The sample annealed at 1000 °C showed only a little fraction of Cr precipitates (size about 2 μm). The subsequentmore » HPT process resulted in the partial dissolution of Cr precipitates in the first sample and dissolution of Cr precipitates with simultaneous decomposition of the supersaturated solid solution in another. However, the resulting microstructure of the samples after HPT was very similar from the standpoint of grain size, phase composition, texture analysis and hardness measurements. - Highlights: • Cu−Cr alloy with two different initial states was deformed by HPT. • Phase transformations in the deformed materials were studied. • SEM, TEM and X-ray diffraction techniques were used for microstructure analysis. • HPT leads to formation the same microstructure independent of the initial state.« less

The role of modifier cation field strength, oxygen speciation and network cation interaction in pressure-induced structural changes of silicate melts and glasses: 27Al, and 11B MAS NMR studies

NASA Astrophysics Data System (ADS)

Bista, S.; Stebbins, J. F.

2017-12-01

In aluminosilicate melts and glasses, both non-bridging oxygen content (NBO) and modifier cation field strength (Mg>Ca>Na>K) are known to facilitate network cation (e.g. Al, B) coordination increase with pressure. However, the role of these two compositional parameters in pressure-induced structural changes is derived from data for a limited set of compositions, where effects of the interaction between these parameters is less understood. For example, the effects of NBO are largely based on studies of Na and K aluminosilicate glasses, but effects of geologically important, higher field strength modifier cations such as Mg2+ and Fe2+ could well be significantly different. In this study, we look at a wide compositional range of Na, Ca and Mg aluminosilicate glasses (quenched from high pressure melts near to the glass transition temperature) to understand the roles of NBO and modifier cation field strength that can extend our view of processes important for silicate melts common in nature. Our results show that the role of NBO in pressure-induced structural changes varies systematically with increasing field strength of the modifier cation. In Na aluminosilicate glasses recovered from 1.5 to 3 GPa, large increases in average aluminum coordination are observed in glasses with high NBO content, while no detectable increases are seen for low nominal NBO (jadeite). In contrast, Mg aluminosilicate glasses with both high and low NBO show similar, large increases in average aluminum coordination with increasing pressure. The behaviors of Ca aluminosilicates fall between those of Na and Mg-rich glasses. We have also looked at interactions between different network forming cations in pressure-induced structural changes in low NBO Ca-aluminoborosilicate glasses with varying B/Si. Both aluminum and boron increase dramatically in coordination in these compositions 1.5 to 3 GPa. Increases in both average aluminum coordination and densification are larger in compositions containing higher boron concentrations, suggesting an interaction between boron and aluminum network cations in pressure-induced structural changes.

Atomic Structure of Intrinsic and Electron-Irradiation-Induced Defects in MoTe2

PubMed Central

2018-01-01

Studying the atomic structure of intrinsic defects in two-dimensional transition-metal dichalcogenides is difficult since they damage quickly under the intense electron irradiation in transmission electron microscopy (TEM). However, this can also lead to insights into the creation of defects and their atom-scale dynamics. We first show that MoTe2 monolayers without protection indeed quickly degrade during scanning TEM (STEM) imaging, and discuss the observed atomic-level dynamics, including a transformation from the 1H phase into 1T′, 3-fold rotationally symmetric defects, and the migration of line defects between two 1H grains with a 60° misorientation. We then analyze the atomic structure of MoTe2 encapsulated between two graphene sheets to mitigate damage, finding the as-prepared material to contain an unexpectedly large concentration of defects. These include similar point defects (or quantum dots, QDs) as those created in the nonencapsulated material and two different types of line defects (or quantum wires, QWs) that can be transformed from one to the other under electron irradiation. Our density functional theory simulations indicate that the QDs and QWs embedded in MoTe2 introduce new midgap states into the semiconducting material and may thus be used to control its electronic and optical properties. Finally, the edge of the encapsulated material appears amorphous, possibly due to the pressure caused by the encapsulation. PMID:29503509

Pressure-induced quantum phase transition in the quantum antiferromagnet CsFeCl3

NASA Astrophysics Data System (ADS)

Hayashida, Shohei; Zaharko, Oksana; Kurita, Nobuyuki; Tanaka, Hidekazu; Hagihala, Masato; Soda, Minoru; Itoh, Shinichi; Uwatoko, Yoshiya; Masuda, Takatsugu

2018-04-01

We have studied the pressure-induced quantum phase transition in the singlet-ground-state antiferromagnet CsFeCl3. Neutron diffraction experiments under pressure evidence the magnetic long-range order at low temperatures. Magnetic structure analysis reveals a 120∘ structure with a propagation vector of kmag=(1 /3 ,1 /3 ,0 ) . The estimated critical exponent of the order parameter suggests that CsFeCl3 belongs to the universality class of U (1 ) ×Z2 symmetry which is expected to realize the chiral liquid state.

Links between clay transformation and earthquakes along the Costa Rican subduction margin

NASA Astrophysics Data System (ADS)

Lauer, Rachel M.; Saffer, Demian M.; Harris, Robert N.

2017-08-01

We investigate the depth distribution of smectite clay transformation and its along-strike variability at the Middle America Trench offshore Costa Rica. We take advantage of recent well-constrained thermal models that refine our understanding of the margin's thermal structure and which capture significant along-strike variability. Using these thermal models, together with sediment compositions defined by drilling, we compute the distribution of smectite transformation and associated fluid production. We show that the hypocenters of large (M > 6.9) well-located megathrust earthquakes lie consistently downdip of peak fluid production. We suggest that silica cementation associated with smectite transformation promotes lithification and slip-weakening behavior that, in combination with declining fluid pressures, facilitate the initiation of unstable slip. The earthquake ruptures extend updip into the region of peak reaction, possibly due to excess pore pressures that facilitate their propagation. These results are consistent with the hypothesis that smectite transformation contributes to the onset of stick-slip behavior and acts as an important control on earthquake nucleation and propagation.

The role of stoichiometric vacancy periodicity in pressure-induced amorphization of the Ga{sub 2}SeTe{sub 2} semiconductor alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdul-Jabbar, N. M.; Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; Kalkan, B.

2014-08-04

We observe that pressure-induced amorphization of Ga{sub 2}SeTe{sub 2} (a III-VI semiconductor) is directly influenced by the periodicity of its intrinsic defect structures. Specimens with periodic and semi-periodic two-dimensional vacancy structures become amorphous around 10–11 GPa in contrast to those with aperiodic structures, which amorphize around 7–8 GPa. The result is an instance of altering material phase-change properties via rearrangement of stoichiometric vacancies as opposed to adjusting their concentrations. Based on our experimental findings, we posit that periodic two-dimensional vacancy structures in Ga{sub 2}SeTe{sub 2} provide an energetically preferred crystal lattice that is less prone to collapse under applied pressure. This ismore » corroborated through first-principles electronic structure calculations, which demonstrate that the energy stability of III-VI structures under hydrostatic pressure is highly dependent on the configuration of intrinsic vacancies.« less

Phase transformations in the hematite-metal system during mechanical alloying

NASA Astrophysics Data System (ADS)

Kozlov, K. A.; Shabashov, V. A.; Litvinov, A. V.; Sagaradze, V. V.

2009-04-01

Mössbauer spectroscopy and X-ray diffraction are used to show that the phase transformations in hematite α-Fe2O3-metal ( M = Fe, Ni, Ti, Zr) powder mixtures induced by severe cold plastic deformation in ball mills occur via the formation of M-Fe-O solid solutions, redox reactions with the reduction of metallic iron, and the formation of secondary M x O y oxides and M x Fe y intermetallics. Mechanical activation in a ball mill is compared to that under high-pressure shear in Bridgman anvils. The transformations that take place in a ball mill are found to have several stages and to be accelerated.

Spatial and temporal dependencies of structure II to structure I methane hydrate transformation in porous media under moderate pressure and temperature conditions

NASA Astrophysics Data System (ADS)

Dong, T.; Lin, J. F.; Gu, J. T.; Polito, P. J.; O'Connell, J.; Flemings, P. B.

2017-12-01

We used Raman spectroscopy to monitor methane hydrates transforming from structure II to structure I at the pore scale as a function of space and time. It is well documented that structure I hydrate is the thermodynamically stable phase for pure methane hydrate (<100 MPa, < 20 °C), but due to kinetic limitation, initial methane hydrate formation produces a mixture of structure I and structure II hydrates. We observed that the structure transformation originated around the porous medium grains and over time slowly migrated into the pore space. We synthesized methane hydrates in spherical glass beads (210-297 µm in diameter) in a pressure cell with a sapphire window to integrate optical observations with Raman measurements. We injected CH4 vapor into the cell and supplied only deionized water thereafter to maintain a constant pressure of 14.6 MPa at 3.5 °C, with 14.5 °C subcooling. We used Raman spectroscopy to map the methane hydrates in pore spaces at 5-25 µm resolution, in order to monitor the occupancy ratio of CH4 in large cages to CH4 in small cages, by their Raman peak intensity ratio, i.e., I( 2905 cm-1)/I( 2915 cm-1). We identified 3 stages of hydrate formation at the pore scale: (1) after the initial hydrate formation, Raman mapping revealed that the occupancy ratio ranged from 0.5 to 3, indicating a mixture of structure I and II hydrates; (2) within 1 week, we observed that all structure I hydrates occurred on the glass bead surfaces and structure II hydrates occupied the pore spaces; (3) over the following 2 weeks, structure II hydrates gradually recrystallized into structure I hydrates from glass bead surfaces towards the pore space. These results imply that (1) due to kinetics, the formation of methane hydrate in porous media is more complex than previously thought, and (2) the bulk physical and chemical properties of laboratory-synthesized methane hydrates in porous media may drift over time, as methane hydrates recrystallize from a metastable phase (structure II) to the thermodynamically stable phase (structure I).

Extraterrestrial diamond inclusions reveal a Mars-sized planet

NASA Astrophysics Data System (ADS)

Nabiei, F.; Badro, J.; Dennenwaldt, T.; Oveisi, E.; Cantoni, M.; Hébert, C.; El Goresy, A.; Barrat, J. A.; Gillet, P.

2017-12-01

Ureilites are achondritic meteorites, distinct by their high carbon content. Carbon dominantly exists as graphite and diamond forming veins between olivine and pyroxene grains in the matrix. The presence of diamonds is, often, attributed to the shock-induced transformation from graphite. However, a recent study (Miyahara et al. 2016) on Almahata Sitta MS-170 mainly based on the large size of diamonds suggested their growth in the static high pressure conditions of planetary interior. We prepared five thin sections by the focused ion beam (FIB) from the diamonds in Almahatta Sitta MS-170 for transmission electron microscopy (TEM) analysis. Abundance of dislocations, stacking faults and {111} twinnings indicate significant deformation. Moreover, large numbers of inclusions are found in diamonds. Electron energy-loss spectroscopy (EELS) showed that when a twinning is intersected with an inclusion, it transforms to graphite. This together with other morphological and crystallographical characteristics of the graphite and diamond phases point to the shock-induced transformation of diamond to graphite. Energy dispersive X-ray (EDX) spectroscopy and electron diffraction were used to chemically and structurally characterize the diamond inclusions. Most of the inclusions are Fe-Ni-S-P type up to 60 nm in diameter, each consisting of three phases: kamacite (Fe, Ni), troilite (FeS) and Schreibersite ((Fe,Ni)3P). The inclusions always have euhedral shape indicating the existence of a parent phase that later broke down. Chemical analysis of complete inclusions (identified with electron tomography) agrees with the stoichiometric (Fe0.93,Ni0.07)3(S0.88,P0.12) phase that only forms above 21 GPa (Gu et al. 2016). The ureilite parent body (UPB) needs to be at least about Mars-sized to generate such a pressure at its core-mantle boundary. This is in the same size range estimated for the planetary embryos forming early in the Solar System. Moreover, although the UPB did not go through an extensive magma ocean period, it was partially differentiated through segregation of S-rich core (Warren et al. 2006). The existence of Mg-free chromite (Cr2FeO4) inclusions in diamond and the vein-like arrangement of Fe-S inclusions suggest that the diamonds are formed from Fe-S-C melt at the pressures exceeding 21 GPa inside the UPB.

High-pressure phases of Mg2Si from first principles

NASA Astrophysics Data System (ADS)

Huan, Tran Doan; Tuoc, Vu Ngoc; Le, Nam Ba; Minh, Nguyen Viet; Woods, Lilia M.

2016-03-01

First-principles calculations are presented to resolve the possible pressure-dependent phases of Mg2Si . Although previous reports show that Mg2Si is characterized by the cubic antifluorite F m 3 ¯m structure at low pressures, the situation at higher pressures is less clear with many contradicting results. Here we utilize several methods to examine the stability, electron, phonon, and transport properties of this material as a function of pressure and temperature. We find that Mg2Si is thermodynamically stable at low and high pressures. Between 6 and 24 GPa, Mg2Si can transform into Mg9Si5 , a defected compound, and vice versa, without energy cost. Perhaps this result is related to the aforementioned inconsistency in the structures reported for Mg2Si within this pressure range. Focusing solely on Mg2Si , we find a new monoclinic C 2 /m structure of Mg2Si , which is stable at high pressures within thermodynamical considerations. The calculated electrical conductivity and Seebeck coefficient taking into account results from the electronic structure calculations help us understand better how transport can be affected in this material by modulating pressure and temperature.

High-pressure structures of yttrium hydrides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Lu -Lu; Sun, Hui -Juan; Wang, C. Z.

2017-07-14

In this study, the crystal structures of YH 3 and YH 4 at high pressure (100–250 GPa) have been explored using a genetic algorithm combined with first-principles calculations. New structures of YH 3 with space group symmetries of P21/m and I4/mmm were predicted. The electronic structures and the phonon dispersion properties of various YH 3 and YH 4 structures at different temperatures and pressures were investigated. Among YH 3 phases, the P21/m structure of YH 3 was found to have a relatively high superconducting transformation temperature T c of 19 K at 120 GPa, which is reduced to 9 Kmore » at 200 GPa. Other YH 3 structures have much lower T cs. Compared with YH 3, the T c of the YH 4 compound is much higher, i.e. 94 K at 120 GPa and 55 K at 200 GPa.« less

The structure of MgO-SiO2 glasses at elevated pressure.

PubMed

Wilding, Martin; Guthrie, Malcolm; Kohara, Shinji; Bull, Craig L; Akola, Jaakko; Tucker, Matt G

2012-06-06

The magnesium silicate system is an important geophysical analogue and neutron diffraction data from glasses formed in this system may also provide an initial framework for understanding the structure-dependent properties of related liquids that are important during planetary formation. Neutron diffraction data collected in situ for a single composition (38 mol% SiO(2)) magnesium silicate glass sample shows local changes in structure as pressure is increased from ambient conditions to 8.6 GPa at ambient temperature. A method for obtaining the fully corrected, total structure factor, S(Q), has been developed that allows accurate structural characterization as this weakly scattering glass sample is compressed. The measured S(Q) data indicate changes in chemical ordering with pressure and the real-space transforms show an increase in Mg-O coordination number and a distortion of the local environment around magnesium ions. We have used reverse Monte Carlo methods to compare the high pressure and ambient pressure structures and also compare the high pressure form with a more silica-poor glass (Mg(2)SiO(4)) that represents the approach to a more dense, void-free and topologically ordered structure. The Mg-O coordination number increases with pressure and we also find that the degree of continuous connectivity of Si-O bonds increases via a collapse of interstices.

Polyamorphism in Yb-based metallic glass induced by pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Liangliang; Luo, Qiang; Li, Renfeng

2017-04-25

The Yb 62.5Zn 15Mg 17.5Cu 5 metallic glass is investigated using synchrotron x-ray total scattering method up to 38.4 GPa. The polyamorphic transformation from low density to high density with a transition region between 14.1 and 25.2 GPa is observed, accompanying with a volume collapse reflected by a discontinuousness of isothermal bulk modulus. This collapse is caused by that distortional icosahedron short range order precedes to perfect icosahedron, which might link to Yb 4f electron delocalization upon compression, and match the result of in situ electrical resistance measurement under high pressure conditions. Furthermore, this discovery in Yb-based metallic glass, combinedmore » with the previous reports on other metallic glass systems, demonstrates that pressure induced polyamorphism is the general behavior for typical lanthanide based metallic glasses.« less

The impact of splay faults on fluid flow, solute transport, and pore pressure distribution in subduction zones: A case study offshore the Nicoya Peninsula, Costa Rica

NASA Astrophysics Data System (ADS)

Lauer, Rachel M.; Saffer, Demian M.

2015-04-01

Observations of seafloor seeps on the continental slope of many subduction zones illustrate that splay faults represent a primary hydraulic connection to the plate boundary at depth, carry deeply sourced fluids to the seafloor, and are in some cases associated with mud volcanoes. However, the role of these structures in forearc hydrogeology remains poorly quantified. We use a 2-D numerical model that simulates coupled fluid flow and solute transport driven by fluid sources from tectonically driven compaction and smectite transformation to investigate the effects of permeable splay faults on solute transport and pore pressure distribution. We focus on the Nicoya margin of Costa Rica as a case study, where previous modeling and field studies constrain flow rates, thermal structure, and margin geology. In our simulations, splay faults accommodate up to 33% of the total dewatering flux, primarily along faults that outcrop within 25 km of the trench. The distribution and fate of dehydration-derived fluids is strongly dependent on thermal structure, which determines the locus of smectite transformation. In simulations of a cold end-member margin, smectite transformation initiates 30 km from the trench, and 64% of the dehydration-derived fluids are intercepted by splay faults and carried to the middle and upper slope, rather than exiting at the trench. For a warm end-member, smectite transformation initiates 7 km from the trench, and the associated fluids are primarily transmitted to the trench via the décollement (50%), and faults intercept only 21% of these fluids. For a wide range of splay fault permeabilities, simulated fluid pressures are near lithostatic where the faults intersect overlying slope sediments, providing a viable mechanism for the formation of mud volcanoes.

Effect of Time-Dependent Pinning Pressure on Abnormal Grain Growth: Phase Field Simulation

NASA Astrophysics Data System (ADS)

Kim, Jeong Min; Min, Guensik; Shim, Jae-Hyeok; Lee, Kyung Jong

2018-05-01

The effect of the time-dependent pinning pressure of precipitates on abnormal grain growth has been investigated by multiphase field simulation with a simple precipitation model. The application of constant pinning pressure is problematic because it always induces abnormal grain growth or no grain growth, which is not reasonable considering the real situation. To produce time-dependent pinning pressure, both precipitation kinetics and precipitate coarsening kinetics have been considered with two rates: slow and fast. The results show that abnormal grain growth is suppressed at the slow precipitation rate. At the slow precipitation rate, the overall grain growth caused by the low pinning pressure in the early stage indeed plays a role in preventing abnormal grain growth by reducing the mobility advantage of abnormal grains. In addition, the fast precipitate coarsening rate tends to more quickly transform abnormal grain growth into normal grain growth by inducing the active growth of grains adjacent to the abnormal grains in the early stage. Therefore, the present study demonstrates that the time dependence of the pinning pressure of precipitates is a critical factor that determines the grain growth mode.

Pressure induced polymerization of acetylide anions in CaC2 and 107 fold enhancement of electrical conductivity.

PubMed

Zheng, Haiyan; Wang, Lijuan; Li, Kuo; Yang, Youyou; Wang, Yajie; Wu, Jiajia; Dong, Xiao; Wang, Chun-Hai; Tulk, Christopher A; Molaison, Jamie J; Ivanov, Ilia N; Feygenson, Mikhail; Yang, Wenge; Guthrie, Malcolm; Zhao, Yusheng; Mao, Ho-Kwang; Jin, Changqing

2017-01-01

Transformation between different types of carbon-carbon bonding in carbides often results in a dramatic change of physical and chemical properties. Under external pressure, unsaturated carbon atoms form new covalent bonds regardless of the electrostatic repulsion. It was predicted that calcium acetylide (also known as calcium carbide, CaC 2 ) polymerizes to form calcium polyacetylide, calcium polyacenide and calcium graphenide under high pressure. In this work, the phase transitions of CaC 2 under external pressure were systematically investigated, and the amorphous phase was studied in detail for the first time. Polycarbide anions like C 6 6- are identified with gas chromatography-mass spectrometry and several other techniques, which evidences the pressure induced polymerization of the acetylide anions and suggests the existence of the polyacenide fragment. Additionally, the process of polymerization is accompanied with a 10 7 fold enhancement of the electrical conductivity. The polymerization of acetylide anions demonstrates that high pressure compression is a viable route to synthesize novel metal polycarbides and materials with extended carbon networks, while shedding light on the synthesis of more complicated metal organics.

Effect of Time-Dependent Pinning Pressure on Abnormal Grain Growth: Phase Field Simulation

NASA Astrophysics Data System (ADS)

Kim, Jeong Min; Min, Guensik; Shim, Jae-Hyeok; Lee, Kyung Jong

2018-03-01

The effect of the time-dependent pinning pressure of precipitates on abnormal grain growth has been investigated by multiphase field simulation with a simple precipitation model. The application of constant pinning pressure is problematic because it always induces abnormal grain growth or no grain growth, which is not reasonable considering the real situation. To produce time-dependent pinning pressure, both precipitation kinetics and precipitate coarsening kinetics have been considered with two rates: slow and fast. The results show that abnormal grain growth is suppressed at the slow precipitation rate. At the slow precipitation rate, the overall grain growth caused by the low pinning pressure in the early stage indeed plays a role in preventing abnormal grain growth by reducing the mobility advantage of abnormal grains. In addition, the fast precipitate coarsening rate tends to more quickly transform abnormal grain growth into normal grain growth by inducing the active growth of grains adjacent to the abnormal grains in the early stage. Therefore, the present study demonstrates that the time dependence of the pinning pressure of precipitates is a critical factor that determines the grain growth mode.

High-pressure-induced water penetration into 3-­isopropylmalate dehydrogenase

PubMed Central

Nagae, Takayuki; Kawamura, Takashi; Chavas, Leonard M. G.; Niwa, Ken; Hasegawa, Masashi; Kato, Chiaki; Watanabe, Nobuhisa

2012-01-01

Hydrostatic pressure induces structural changes in proteins, including denaturation, the mechanism of which has been attributed to water penetration into the protein interior. In this study, structures of 3-isopropylmalate dehydrogenase (IPMDH) from Shewanella oneidensis MR-1 were determined at about 2 Å resolution under pressures ranging from 0.1 to 650 MPa using a diamond anvil cell (DAC). Although most of the protein cavities are monotonically compressed as the pressure increases, the volume of one particular cavity at the dimer interface increases at pressures over 340 MPa. In parallel with this volume increase, water penetration into the cavity could be observed at pressures over 410 MPa. In addition, the generation of a new cleft on the molecular surface accompanied by water penetration could also be observed at pressures over 580 MPa. These water-penetration phenomena are considered to be initial steps in the pressure-denaturation process of IPMDH. PMID:22349232

Structural phase diagram for ultra-thin epitaxial Fe 3O 4 / MgO(0 01) films: thickness and oxygen pressure dependence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alraddadi, S.; Hines, W.; Yilmaz, T.

2016-02-19

A systematic investigation of the thickness and oxygen pressure dependence for the structural properties of ultra-thin epitaxial magnetite (Fe 3O 4) films has been carried out; for such films, the structural properties generally differ from those for the bulk when the thickness ≤10 nm. Iron oxide ultra-thin films with thicknesses varying from 3 nm to 20 nm were grown on MgO (001) substrates using molecular beam epitaxy under different oxygen pressures ranging from 1 × 10 -7 torr to 1 × 10 -5 torr. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED)more » and x-ray photoemission spectroscopy (XPS), respectively. Moreover, the quality of the epitaxial Fe 3O 4 ultra-thin films was judged by magnetic measurements of the Verwey transition, along with complementary XPS spectra. We observed that under the same growth conditions the stoichiometry of ultra-thin films under 10 nm transforms from the Fe 3O 4 phase to the FeO phase. In this work, a phase diagram based on thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤20 nm formed within a narrow range of oxygen pressure. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties for ultra-thin Fe 3O 4 films. Furthermore, these results are significant because they may indicate a general trend in the growth of other oxide films, which has not been previously observed or considered.« less

Universal elastic-hardening-driven mechanical instability in α-quartz and quartz homeotypes under pressure

PubMed Central

Dong, Juncai; Zhu, Hailiang; Chen, Dongliang

2015-01-01

As a fundamental property of pressure-induced amorphization (PIA) in ice and ice-like materials (notably α-quartz), the occurrence of mechanical instability can be related to violation of Born criteria for elasticity. The most outstanding elastic feature of α-quartz before PIA has been experimentally reported to be the linear softening of shear modulus C44, which was proposed to trigger the transition through Born criteria B3. However, by using density-functional theory, we surprisingly found that both C44 and C66 in α-quartz exhibit strong nonlinearity under compression and the Born criteria B3 vanishes dominated by stiffening of C14, instead of by decreasing of C44. Further studies of archetypal quartz homeotypes (GeO2 and AlPO4) repeatedly reproduced the same elastic-hardening-driven mechanical instability, suggesting a universal feature of this family of crystals and challenging the long-standing idea that negative pressure derivatives of individual elastic moduli can be interpreted as the precursor effect to an intrinsic structural instability preceding PIA. The implications of this elastic anomaly in relation to the dispersive softening of the lowest acoustic branch and the possible transformation mechanism were also discussed. PMID:26099720

Universal elastic-hardening-driven mechanical instability in α-quartz and quartz homeotypes under pressure.

PubMed

Dong, Juncai; Zhu, Hailiang; Chen, Dongliang

2015-06-23

As a fundamental property of pressure-induced amorphization (PIA) in ice and ice-like materials (notably α-quartz), the occurrence of mechanical instability can be related to violation of Born criteria for elasticity. The most outstanding elastic feature of α-quartz before PIA has been experimentally reported to be the linear softening of shear modulus C44, which was proposed to trigger the transition through Born criteria B3. However, by using density-functional theory, we surprisingly found that both C44 and C66 in α-quartz exhibit strong nonlinearity under compression and the Born criteria B3 vanishes dominated by stiffening of C14, instead of by decreasing of C44. Further studies of archetypal quartz homeotypes (GeO2 and AlPO4) repeatedly reproduced the same elastic-hardening-driven mechanical instability, suggesting a universal feature of this family of crystals and challenging the long-standing idea that negative pressure derivatives of individual elastic moduli can be interpreted as the precursor effect to an intrinsic structural instability preceding PIA. The implications of this elastic anomaly in relation to the dispersive softening of the lowest acoustic branch and the possible transformation mechanism were also discussed.

High- T c Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, J. P.; Ye, G. Z.; Shahi, P.

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (T c). However, high-T c superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in another high-T c phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-T c superconducting phase transforms into high-T c phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstratingmore » dominant hole carriers in striking contrast to other FeSe-derived high-T c systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviours, evidencing strongly enhanced interband spin fluctuations in the high-T c phase. These results in FeSe highlight similarities with high-T c phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.« less

High- T c Superconductivity in FeSe at High Pressure: Dominant Hole Carriers and Enhanced Spin Fluctuations

DOE PAGES

Sun, J. P.; Ye, G. Z.; Shahi, P.; ...

2017-04-07

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (T c). However, high-T c superconductivity without hole carriers has been suggested in FeSe single-layer films and intercalated iron-selenides, raising a fundamental question whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in another high-T c phase induced by pressure in bulk FeSe from magneto-transport measurements and first-principles calculations. With increasing pressure, the low-T c superconducting phase transforms into high-T c phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstratingmore » dominant hole carriers in striking contrast to other FeSe-derived high-T c systems. Moreover, the Hall coefficient is remarkably enlarged and the magnetoresistance exhibits anomalous scaling behaviours, evidencing strongly enhanced interband spin fluctuations in the high-T c phase. These results in FeSe highlight similarities with high-T c phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.« less

Pressure induced band inversion, electronic and structural phase transitions in InTe: A combined experimental and theoretical study

NASA Astrophysics Data System (ADS)

Rajaji, V.; Pal, Koushik; Sarma, Saurav Ch.; Joseph, B.; Peter, Sebastian C.; Waghmare, Umesh V.; Narayana, Chandrabhas

2018-04-01

We report high-pressure Raman scattering measurements on the tetragonal phase of InTe corroborated with the first-principles density functional theory and synchrotron x-ray diffraction measurements. Anomalous pressure-dependent linewidths of the A1 g and Eg phonon modes provide evidence of an isostructural electronic transition at ˜3.6 GPa . The first-principles theoretical analysis reveals that it is associated with a semiconductor-to-metal transition due to increased density of states near the Fermi level. Further, this pressure induced metallization acts as a precursor for structural phase transition to a face centered cubic phase (F m 3 ¯m ) at ˜6.0 GPa . Interestingly, theoretical results reveal a pressure induced band inversion at the Z and M points of the Brillouin zone corresponding to pressures ˜1.0 and ˜1.4 GPa , respectively. As the parity of bands undergoing inversions is the same, the topology of the electronic state remains unchanged, and hence InTe retains its trivial band topology (Z2=0 ) . The pressure dependent behavior of the A1 g and Eg modes can be understood based on the results from the synchrotron x-ray diffraction, which shows anisotropic compressibility of the lattice in the a and c directions. Our Raman measurements up to ˜19 GPa further confirms the pressure induced structural phase transition from a face-centered to primitive cubic (F m 3 ¯m to P m 3 ¯m ) at P ˜15 GPa .

Facile approach to the fabrication of a micropattern possessing nanoscale substructure.

PubMed

Ji, Qiang; Jiang, Xuesong; Yin, Jie

2007-12-04

On the basis of the combined technologies of photolithography and reaction-induced phase separation (RIPS), a facile approach has been successfully developed for the fabrication of a micropattern possessing nanoscale substructure on the thin film surface. This approach involves three steps. In the first step, a thin film was prepared by spin coating from a solution of a commercial random copolymer, polystyrene-r-poly(methyl methacrylate) (PS-r-PMMA) and a commercial crosslinker, trimethylolpropane triacrylate (TMPTA). In the second step, photolithograph was performed with the thin film using a 250 W high-pressure mercury lamp to produce the micropattern. Finally, the resulting micropattern was annealed at 200 degrees C for a certain time, and reaction-induced phase separation occurred. After soaking in chloroform for 4 h, nanoscale substructure was obtained. The whole processes were traced by atomic force microscopy (AFM), X-ray photoelectron spectrometry (XPS), and Fourier transform infrared (FTIR) spectroscopy, and the results supported the proposed structure.

Crew Launch Vehicle Mobile Launcher Solid Rocket Motor Plume Induced Environment

NASA Technical Reports Server (NTRS)

Vu, Bruce T.; Sulyma, Peter

2008-01-01

The plume-induced environment created by the Ares 1 first stage, five-segment reusable solid rocket motor (RSRMV) will impose high heating rates and impact pressures on Launch Complex 39. The extremes of these environments pose a potential threat to weaken or even cause structural components to fail if insufficiently designed. Therefore the ability to accurately predict these environments is critical to assist in specifying structural design requirements to insure overall structural integrity and flight safety. This paper presents the predicted thermal and pressure environments induced by the launch of the Crew Launch Vehicle (CLV) from Launch Complex (LC) 39. Once the environments are predicted, a follow-on thermal analysis is required to determine the surface temperature response and the degradation rate of the materials. An example of structures responding to the plume-induced environment will be provided.

Pressure-induced structural and semiconductor-semiconductor transitions in C o0.5M g0.5C r2O4

NASA Astrophysics Data System (ADS)

Rahman, S.; Saqib, Hajra; Zhang, Jinbo; Errandonea, D.; Menéndez, C.; Cazorla, C.; Samanta, Sudeshna; Li, Xiaodong; Lu, Junling; Wang, Lin

2018-05-01

The effect of pressure on the structural, vibrational, and electronic properties of Mg-doped Cr bearing spinel C o0.5M g0.5C r2O4 was studied up to 55 GPa at room-temperature using x-ray diffraction, Raman spectroscopy, electrical transport measurements, and ab initio calculations. We found that the ambient-pressure phase is cubic (spinel-type, F d 3 ¯m ) and underwent a pressure-induced structural transition to a tetragonal phase (space group I 4 ¯m 2 ) above 28 GPa. The ab initio calculation confirmed this first-order phase transition. The resistivity of the sample decreased at low pressures with the existence of a low-pressure (LP) phase and started to increase with the emergence of a high-pressure (HP) phase. The temperature dependent resistivity experiments at different pressures illustrated the wide band gap semiconducting nature of both the LP and HP phases with different activation energies, suggesting a semiconductor-semiconductor transition at HP. No evidence of chemical decomposition or a semiconductor-metal transition was observed in our studies.

Structural changes induced by lattice-electron interactions: SiO2 stishovite and FeTiO3 ilmenite.

PubMed

Yamanaka, Takamitsu

2005-09-01

The bright source and highly collimated beam of synchrotron radiation offers many advantages for single-crystal structure analysis under non-ambient conditions. The structure changes induced by the lattice-electron interaction under high pressure have been investigated using a diamond anvil pressure cell. The pressure dependence of electron density distributions around atoms is elucidated by a single-crystal diffraction study using deformation electron density analysis and the maximum entropy method. In order to understand the bonding electrons under pressure, diffraction intensity measurements of FeTiO3 ilmenite and gamma-SiO2 stishovite single crystals at high pressures were made using synchrotron radiation. Both diffraction studies describe the electron density distribution including bonding electrons and provide the effective charge of the cations. In both cases the valence electrons are more localized around the cations with increasing pressure. This is consistent with molecular orbital calculations, proving that the bonding electron density becomes smaller with pressure. The thermal displacement parameters of both samples are reduced with increasing pressure.

Visible Light Induced Organic Transformations Using Metal-Organic-Frameworks (MOFs).

PubMed

Deng, Xiaoyu; Li, Zhaohui; García, Hermenegildo

2017-08-22

With the aim of developing renewable energy based processes, researchers are paying increasing interest to light induced organic transformations. Metal-organic frameworks (MOFs), a class of micro-/mesoporous hybrid materials, are recently emerging as a new type of photoactive materials for organic syntheses due to their unique structural characteristics. In this Review, we summarized the recent applications of MOFs as photocatalysts for light induced organic transformations, including (1) oxidation of alcohols, amines, alkene, alkanes and sulfides; (2) hydroxylation of aromatic compounds like benzene; (3) activation of the C-H bonds to construct new C-C or C-X bonds; (4) atom-transfer radical polymerization (ATRP). This Review starts with general background information of using MOFs in photocatalysis, followed by a description of light induced organic transformations promoted by photoactive inorganic nodes and photocatalytic active ligands in MOFs, respectively. Thereafter, the use of MOFs as multifunctional catalysts for light induced organic transformations via an efficient merge of the metal/ligand/guest based catalysis where the photocatalytic activity of MOFs plays a key role are discussed. Finally, the limitations, challenges and the future perspective of the application of MOFs for light induced organic transformations were addressed. The objective of this Review is to serve as a starting point for other researchers to get into this largely unexplored field. It is also our goal to stimulate intensive research in this field for rational designing of MOF materials to overcome their current limitations in photocatalysis, which can lead to more creative visible-light-induced organic transformations. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ion irradiation induced structural modifications and increase in elastic modulus of silica based thin films

PubMed Central

Shojaee, S. A.; Qi, Y.; Wang, Y. Q.; Mehner, A.; Lucca, D. A.

2017-01-01

Ion irradiation is an alternative to heat treatment for transforming organic-inorganic thin films to a ceramic state. One major shortcoming in previous studies of ion-irradiated films is the assumption that constituent phases in ion-irradiated and heat-treated films are identical and that the ion irradiation effect is limited to changes in composition. In this study, we investigate the effects of ion irradiation on both the composition and structure of constituent phases and use the results to explain the measured elastic modulus of the films. The results indicated that the microstructure of the irradiated films consisted of carbon clusters within a silica matrix. It was found that carbon was present in a non-graphitic sp2-bonded configuration. It was also observed that ion irradiation caused a decrease in the Si-O-Si bond angle of silica, similar to the effects of applied pressure. A phase transformation from tetrahedrally bonded to octahedrally bonded silica was also observed. The results indicated the incorporation of carbon within the silica network. A combination of the decrease in Si-O-Si bond angle and an increase in the carbon incorporation within the silica network was found to be responsible for the increase in the elastic modulus of the films. PMID:28071696

Ion irradiation induced structural modifications and increase in elastic modulus of silica based thin films

DOE PAGES

Shojaee, S. A.; Qi, Y.; Wang, Y. Q.; ...

2017-01-10

Ion irradiation is an alternative to heat treatment for transforming organic-inorganic thin films to a ceramic state. One major shortcoming in previous studies of ion-irradiated films is the assumption that constituent phases in ion-irradiated and heat-treated films are identical and that the ion irradiation effect is limited to changes in composition. Here, we investigate the effects of ion irradiation on both the composition and structure of constituent phases and use the results to explain the measured elastic modulus of the films. Our results indicated that the microstructure of the irradiated films consisted of carbon clusters within a silica matrix. Itmore » was found that carbon was present in a non-graphitic sp 2-bonded configuration. It was also observed that ion irradiation caused a decrease in the Si-O-Si bond angle of silica, similar to the effects of applied pressure. A phase transformation from tetrahedrally bonded to octahedrally bonded silica was also observed. The results indicated the incorporation of carbon within the silica network. Finally, a combination of the decrease in Si-O-Si bond angle and an increase in the carbon incorporation within the silica network was found to be responsible for the increase in the elastic modulus of the films.« less

Coverage induced structural transformations of tetracene on Ag(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takasugi, Kazushiro; Yokoyama, Takashi, E-mail: tyoko@yokohama-cu.ac.jp

2016-03-14

Self-assembly of tetracene on an anisotropic surface of Ag(110) has been investigated using scanning tunneling microscopy and low-energy electron diffraction. We observe multistage structural transformations of the self-assembled tetracene on Ag(110) as a function of molecular coverages, which are accompanied by the changes in molecular orientations. They are analyzed by a balance between multiple molecule-molecule and anisotropic substrate-molecule interactions.

Conformational changes in human Hsp70 induced by high hydrostatic pressure produce oligomers with ATPase activity but without chaperone activity.

PubMed

Araujo, Thaís L S; Borges, Julio Cesar; Ramos, Carlos H; Meyer-Fernandes, José Roberto; Oliveira Júnior, Reinaldo S; Pascutti, Pedro G; Foguel, Debora; Palhano, Fernando L

2014-05-13

We investigated the folding of the 70 kDa human cytosolic inducible protein (Hsp70) in vitro using high hydrostatic pressure as a denaturing agent. We followed the structural changes in Hsp70 induced by high hydrostatic pressure using tryptophan fluorescence, molecular dynamics, circular dichroism, high-performance liquid chromatography gel filtration, dynamic light scattering, ATPase activity, and chaperone activity. Although monomeric, Hsp70 is very sensitive to hydrostatic pressure; after pressure had been removed, the protein did not return to its native sate but instead formed oligomeric species that lost chaperone activity but retained ATPase activity.

Ringwoodite rim around olivine core in shock-induced melt veins of Antarctic chondrite : Mechanisms of transformation and Fe-Mg diffusion

NASA Astrophysics Data System (ADS)

Xie, Z.; Li, X.; Sharp, T. G.; de Carli, P. S.

2009-12-01

Introduction: High-pressure minerals, produced by shock metamorphism, are common in and around melt veins in highly shocked chondrites. The shock duration can be constrained by using transformation kinetics, such as the crystallization rate of the melt-vein matrix[1-2], or growth rate of the high-pressure minerals [3-4], or using elements diffusion rate between two minerals [5]. Using transformation kinetics to constrain shock duration de-pend on the details of the transformation mechanism. For example, growth of topotaxial ringwoodite in olivine with coherent interfaces is slower than growth of inclusions with incoherent interfaces [4-5]. Similarly, diffusion-controlled growth, where rates are determined by long-range diffusion, is generally much slower than interface-controlled growth, which is only dependent on diffusion across the interface [6-8]. The occurrences of the high-pressure mineral rims were recently reported in shock-induced melt veins in several heavily shocked (S6) chondrites, ALH78003, Peace River and GRV052049 [9-11]. Here we report EMAP and Raman results of the ringwoodite rims around olivine cores in shock veins of the Antarctic chondrites GRV 022321, and to elucidate the mechanisms of transformation and Mg-Fe diffusion of the olivine to ringwoodite. Results: GRV022321 has a network of black veins which enclose abundant host-rock fragments. The enclosed fragments have sizes ranging from 5 µm to 30 µm, with a brighter rim up to several µm wide and a dark core in reflected light and BSE image. The Raman data reveal that the rim mineral is ringwoodite signature, and the core minerals are dominated by olivine and mixed minor ringwoodite. EMAP data confirm that the ringwoodite in rim is richer in faylite (Fa) than the olivine core. The Fa values range from 50 to 10 with the outer rim having highest Fa value, and the inside darker area with a lower value. Discussion: The occurrence of the rounded shape grains with smooth edges embedded in the fine matrix in shock-induced melt veins suggest that they are enclosed host-rock fragments and that the ringwoodite in the rim was transformed by solid-state transformation from previous olivine. The variable extent of transformation is likely a result of temperature variations during shock, with the hottest outer olivine forming the ringwoodite rim. The outer hotter ringwoodite attract more Fe than inside cooler olivine, and Mg-Fe diffusion occurs in rapid transformation at high pressure and temperature over up to 10 µm distance. The sample is unique because we can test and double check different shock duration constraints in future work. References: [1] Langenhorst and Poirier (2000) EPSL 184, 37-55. [2] Xie, Z. et al. (2006) GCA, 70. 504-515. [3] Ohtani et al. (2004) EPSL 227(3-4), 505-515. [4] Xie and Sharp (2007), EPLS, 433-445. [5] Beck, et al. (2005) Nature 435, 1071-1074. [6] Kerschhofer et al. (1996) Science 274 (5284), 79-81. [7] Kerschhofer et al. (2000) PEPI 121, 59-76. [8] Sharp and DeCarli (2006) MESS II, 653-677. [9] Ohtani et al. (2006), Shock Waves, 16:45-52. [10] Miyahara et al. (2008) Proceedings. of NAS 105,8542-8547. [11] Feng et al. (2007), MAPS 42, A45.

Thin-Film Transformation of NH4 PbI3 to CH3 NH3 PbI3 Perovskite: A Methylamine-Induced Conversion-Healing Process.

PubMed

Zong, Yingxia; Zhou, Yuanyuan; Ju, Minggang; Garces, Hector F; Krause, Amanda R; Ji, Fuxiang; Cui, Guanglei; Zeng, Xiao Cheng; Padture, Nitin P; Pang, Shuping

2016-11-14

Methylamine-induced thin-film transformation at room-temperature is discovered, where a porous, rough, polycrystalline NH 4 PbI 3 non-perovskite thin film converts stepwise into a dense, ultrasmooth, textured CH 3 NH 3 PbI 3 perovskite thin film. Owing to the beneficial phase/structural development of the thin film, its photovoltaic properties undergo dramatic enhancement during this NH 4 PbI 3 -to-CH 3 NH 3 PbI 3 transformation process. The chemical origins of this transformation are studied at various length scales. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Static High Pressure Structural studies on Dy to 119 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patterson, J R; Saw, C K; Akella, J

2003-11-12

Structural phase transitions in the rare-earth metal Dysprosium have been studied in a Diamond Anvil Cell (DAC) to 119 GPa by x-ray diffraction. Four transformations following the sequence hcp {yields} Sm-type {yields} dhcp {yields} hR24 (hexagonal) {yields} bcm (monoclinic) are observed at 6, 15, 43, and 73 GPa respectively. The hexagonal to monoclinic transformation is accompanied by a 6% reduction in volume, which is attributed to delocalization of the 4f electrons, similar to that seen in Ce, Pr, and Gd.

Structural transformation of Si-rich SiNx film on Si via swift heavy ions irradiation

NASA Astrophysics Data System (ADS)

Murzalinov, D.; Akilbekov, A.; Dauletbekova, A.; Vlasukova, L.; Makhavikov, M.; Zdorovets, M.

2018-03-01

The effects of 200 MeV-Xe+ irradiation with fluencies of (109–1014) cm‑2 on the phase-structural transformation of Si-rich SiNx film deposited on Si substrate by low-pressure chemical vapor deposition have been reported. It has been shown from Raman scattering data that the swift heavy ions irradiation results in the dissolution of amorphous Si nanoclusters in nitride matrix. It has been shown, too, that the swift heavy ion irradiation leads to quenching a visual photoluminescence from nitride films.

High pressure-high temperature phase diagram of an energetic crystal: Dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50)

DOE PAGES

Dreger, Z. A.; Breshike, C. J.; Gupta, Y. M.

2017-05-08

Raman spectroscopy was used to examine the high pressure-high temperature structural and chemical stability of an insensitive, high-performance energetic crystal – dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50). The phase diagram was determined over 8 GPa and (293-760) K. Under isobaric heating, the melting/decomposition of TKX-50 is preceded by a transformation to two consecutive high-temperature intermediates; a lower-temperature intermediate – diammonium 5,5’-bistetrazole-1,1'-diolate, and a higher-temperature intermediate – dihydroxylammonium 5,5'-bistetrazolate and/or diammonium 5,5'-bistetrazolate. Pressure strongly increases the transition temperatures for these transformations and subsequent decomposition. As a result, significant increase in the chemical stability of TKX-50 and intermediates with pressure was attributed to a suppressionmore » of hydrogen-transfer.« less

Investigations into the Membrane Interactions of m-Calpain Domain V

PubMed Central

Dennison, Sarah R.; Dante, Silvia; Hauß, Thomas; Brandenburg, Klaus; Harris, Frederick; Phoenix, David A.

2005-01-01

m-Calpain is a calcium-dependent heterodimeric protease implicated in a number of pathological conditions. The activation of m-calpain appears to be modulated by membrane interaction, which has been predicted to involve oblique-orientated α-helix formation by a GTAMRILGGVI segment located in domain V of the protein's small subunit. Here, we have investigated this prediction. Fourier transform infrared conformational analysis showed that VP1, a peptide homolog of this segment, exhibited α-helicity of ∼45% in the presence of dimyristoylphosphatidylcholine/dimyristoylphosphatidylserine (DMPS) vesicles. The level of helicity was unaffected over a 1- to 8-mM concentration range and did not alter when the anionic lipid composition of these vesicles was varied between 1% and 10% DMPS. Similar levels of α-helicity were observed in trifluoroethanol and the peptide appeared to adopt α-helical structure at an air/water interface with a molecular area of 164 Å2 at the monolayer collapse pressure. VP1 was found to penetrate dimyristoylphosphatidylcholine/DMPS monolayers, and at an initial surface pressure of 30 mN m−1, the peptide induced surface pressure changes in these monolayers that correlated strongly with their anionic lipid content (maximal at 4 mN m−1 in the presence of 10% DMPS). Neutron diffraction studies showed VP1 to be localized at the hydrophobic core of model palmitoyloleylphosphatidylcholine/palmitoyloleylphosphatidylserine (10:1 molar ratio) bilayer structures and, in combination, these results are consistent with the oblique membrane penetration predicted for the peptide. It would also appear that although not needed for structural stabilization anionic lipid was required for membrane penetration. PMID:15653743

Modeling of wave-coherent pressures in the turbulent boundary layer above water waves

NASA Technical Reports Server (NTRS)

Papadimitrakis, Yiannis ALEX.

1988-01-01

The behavior of air pressure fluctuations induced by progressive water waves generated mechanically in a laboratory tank was simulated by solving a modified Orr-Sommerfeld equation in a transformed Eulerian wave-following frame of reference. Solution is obtained by modeling the mean and wave-coherent turbulent Reynolds stresses, the behavior of which in the turbulent boundary layer above the waves was simulated using a turbulent kinetic energy-dissipation model, properly modified to account for free-surface proximity and favorable pressure gradient effects. The distribution of both the wave-coherent turbulent Reynolds stress and pressure amplitudes and their corresponding phase lags was found to agree reasonably well with available laboratory data.

Phase transition studies of germanium to 1. 25 Mbar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vohra, Y.K.; Brister, K.E.; Desgreniers, S.

1986-05-05

New phase transitions in Ge were observed by energy-dispersive x-ray diffraction techniques for pressures up to 125 GPa (1.25 Mbar) as follows: the ..beta..-Sn structure to the simple hexagonal (sh) phase at 75 +- 3 GPa and to the double hexagonal close-packed structure (dhcp) at 102 +- 5 GPa. These are the highest pressures for which a crystalline structure change has been directly observed in any material by x-ray diffraction. Total-energy pseudopotential calculations predict 84 +- 10 GPa for the ..beta..-Sn to sh phase transition and 105 +- 21 GPa for sh to hcp (not dhcp) transition. The role ofmore » 3d core electrons in increasing the transformation pressures in Ge, as compared to Si, is emphasized.« less

High-pressure phase of brucite stable at Earth's mantle transition zone and lower mantle conditions.

PubMed

Hermann, Andreas; Mookherjee, Mainak

2016-12-06

We investigate the high-pressure phase diagram of the hydrous mineral brucite, Mg(OH) 2 , using structure search algorithms and ab initio simulations. We predict a high-pressure phase stable at pressure and temperature conditions found in cold subducting slabs in Earth's mantle transition zone and lower mantle. This prediction implies that brucite can play a much more important role in water transport and storage in Earth's interior than hitherto thought. The predicted high-pressure phase, stable in calculations between 20 and 35 GPa and up to 800 K, features MgO 6 octahedral units arranged in the anatase-TiO 2 structure. Our findings suggest that brucite will transform from a layered to a compact 3D network structure before eventual decomposition into periclase and ice. We show that the high-pressure phase has unique spectroscopic fingerprints that should allow for straightforward detection in experiments. The phase also has distinct elastic properties that might make its direct detection in the deep Earth possible with geophysical methods.

Pressure induced structural phase transition in metal nitrides: An effective interionic potential calculations

NASA Astrophysics Data System (ADS)

Soni, Shubhangi; Choudhary, K. K.; Kaurav, Netram

2018-05-01

Structural and elastic properties of transition metal nitrides, XN (X = Co, Fe and Cu), are investigated through an effective inter-ionic potential method. The B3(ZnS) type ambient crystal structure of these compounds undergoes to B1(NaCl) type structure with pressure. Structural phase transition pressure in CoN, FeN and CuN was 35, 55 and 35 GPa, respectively, predicated by computing Gibbs' free energy (G) as a function of pressure and has good agreement with available theoretical results. The elastic properties were also estimated as a function of pressure. It is found that the elastic constants increased linearly with increasing pressure due to stronger hybridization, bonding and covalent properties of constituent elements of a compound.

Structural phase transition of gold under uniaxial, tensile, and triaxial stresses: An ab initio study

NASA Astrophysics Data System (ADS)

Durandurdu, Murat

2007-07-01

The behavior of gold crystal under uniaxial, tensile, and three different triaxial stresses is studied using an ab initio constant pressure technique within a generalized gradient approximation. Gold undergoes a phase transformation from the face-centered-cubic structure (fcc) to a body-centered-tetragonal (bct) structure having the space group of I4/mmm with the application of uniaxial stress, while it transforms to a face-centered-tetragonal (fct) phase within I4/mmm symmetry under uniaxial tensile loading. Further uniaxial compression of the bct phase results in a symmetry change from I4/mmm to P1 at high stresses and ultimately structural failure around 200.0GPa . For the case of triaxial stresses, gold also converts into a bct state. The critical stress for the fcc-to-bct transformation increases as the ratio of the triaxial stress increases. Both fct and bct phases are elastically unstable.

Aeroelastic-Acoustics Simulation of Flight Systems

NASA Technical Reports Server (NTRS)

Gupta, kajal K.; Choi, S.; Ibrahim, A.

2009-01-01

This paper describes the details of a numerical finite element (FE) based analysis procedure and a resulting code for the simulation of the acoustics phenomenon arising from aeroelastic interactions. Both CFD and structural simulations are based on FE discretization employing unstructured grids. The sound pressure level (SPL) on structural surfaces is calculated from the root mean square (RMS) of the unsteady pressure and the acoustic wave frequencies are computed from a fast Fourier transform (FFT) of the unsteady pressure distribution as a function of time. The resulting tool proves to be unique as it is designed to analyze complex practical problems, involving large scale computations, in a routine fashion.

Crystallographic phases in heavy rare earth metals under megabar pressures

NASA Astrophysics Data System (ADS)

Samudrala, G. K.; Vohra, Y. K.

2012-07-01

Experiments aimed at understanding the crystallographic phases of heavy rare earth metals were carried out in a diamond anvil cell at the Advanced Photon Source, Argonne National Laboratory. Heavy rare earth metals dysprosium (Dy), holmium (Ho), erbium (Er) and thulium (Tm) were compressed to multi-megabar pressures. The rare earth crystal sequence hcp→Sm-type→dhcp→distorted-fcc (dfcc) is observed in all four elements. Upon further compression, a structural transformation to a monoclinic C2/m phase has been observed. We summarize the results from these experiments and present Rietveld structural refinements on high pressure phases for the specific case of dysprosium.

Atmospheric-pressure plasma activation and surface characterization on polyethylene membrane separator

NASA Astrophysics Data System (ADS)

Tseng, Yu-Chien; Li, Hsiao-Ling; Huang, Chun

2017-01-01

The surface hydrophilic activation of a polyethylene membrane separator was achieved using an atmospheric-pressure plasma jet. The surface of the atmospheric-pressure-plasma-treated membrane separator was found to be highly hydrophilic realized by adjusting the plasma power input. The variations in membrane separator chemical structure were confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Chemical analysis showed newly formed carbonyl-containing groups and high surface concentrations of oxygen-containing species on the atmospheric-pressure-plasma-treated polymeric separator surface. It also showed that surface hydrophilicity primarily increased from the polar component after atmospheric-pressure plasma treatment. The surface and pore structures of the polyethylene membrane separator were examined by scanning electron microscopy, revealing a slight alteration in the pore structure. As a result of the incorporation of polar functionalities by atmospheric-pressure plasma activation, the electrolyte uptake and electrochemical impedance of the atmospheric-pressure-plasma-treated membrane separator improved. The investigational results show that the separator surface can be controlled by atmospheric-pressure plasma surface treatment to tailor the hydrophilicity and enhance the electrochemical performance of lithium ion batteries.

High-pressure crystal structures of an insensitive energetic crystal: 1,1-diamino-2,2-dinitroethene

DOE PAGES

Dreger, Zbigniew A.; Stash, Adam I.; Yu, Zhi -Gang; ...

2015-12-03

Understanding the insensitivity/stability of insensitive high explosive crystals requires detailed structural information at high pressures and high temperatures of interest. Synchrotron single crystal x-ray diffraction experiments were used to determine the high-pressure structures of 1,1-diamino-2,2-dinitroethene (FOX-7), a prototypical insensitive high explosive. The phase transition around 4.5 GPa was investigated and the structures were determined at 4.27 GPa (α’-phase) and 5.9 GPa (ε-phase). The α’-phase (monoclinic, P2 1/ n), structurally indistinguishable from the ambient α-phase, transforms to the new ε-phase (triclinic, P1). The most notable features of the ε-phase, compared to the α’-phase, are: formation of planar layers and flattening ofmore » molecules. Density functional theory (DFT-D2) calculations complemented the experimental results. Furthermore, the results presented here are important for understanding the molecular and crystalline attributes governing the high-pressure insensitivity/stability of insensitive high explosive crystals.« less

High-pressure crystal structures of an insensitive energetic crystal: 1,1-diamino-2,2-dinitroethene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dreger, Zbigniew A.; Stash, Adam I.; Yu, Zhi -Gang

Understanding the insensitivity/stability of insensitive high explosive crystals requires detailed structural information at high pressures and high temperatures of interest. Synchrotron single crystal x-ray diffraction experiments were used to determine the high-pressure structures of 1,1-diamino-2,2-dinitroethene (FOX-7), a prototypical insensitive high explosive. The phase transition around 4.5 GPa was investigated and the structures were determined at 4.27 GPa (α’-phase) and 5.9 GPa (ε-phase). The α’-phase (monoclinic, P2 1/ n), structurally indistinguishable from the ambient α-phase, transforms to the new ε-phase (triclinic, P1). The most notable features of the ε-phase, compared to the α’-phase, are: formation of planar layers and flattening ofmore » molecules. Density functional theory (DFT-D2) calculations complemented the experimental results. Furthermore, the results presented here are important for understanding the molecular and crystalline attributes governing the high-pressure insensitivity/stability of insensitive high explosive crystals.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glascoe, E A; Zaug, J M; Burnham, A K

The effect of pressure on the thermal decomposition rate of the energetic material HMX was studied. HMX was precompressed in a diamond anvil cell (DAC) and heated at various rates. The parent species population was monitored as a function of time and temperature using Fourier transform infrared (FTIR) spectroscopy. Decomposition rates were determined by fitting the fraction reacted to the extended-Prout-Tompkins nucleation-growth model and the Friedman isoconversional method. The results of these experiments and analysis indicate that pressure accelerates the decomposition at low to moderate pressures (i.e. between ambient pressure and 1 GPa) and decelerates the decomposition at higher pressures.more » The decomposition acceleration is attributed to pressure enhanced autocatalysis whereas the deceleration at high pressures is attributed pressure inhibiting bond homolysis step(s), which would result in an increase in volume. These results indicate that both {beta} and {delta} phase HMX are sensitive to pressure in the thermally induced decomposition kinetics.« less

Bubbles are responsive materials interesting for nonequilibrium physics

NASA Astrophysics Data System (ADS)

Andreeva, Daria; Granick, Steve

Understanding of nature and conditions of non-equilibrium transformations of bubbles, droplets, polysomes and vesicles in a gradient filed is a breath-taking question that dissipative systems raise. We ask: how to establish a dynamic control of useful characteristics, for example dynamic control of morphology and composition modulation in soft matter. A possible answer is to develop a new generation of dynamic impactors that can trigger spatiotemporal oscillations of structures and functions. We aim to apply acoustic filed for development of temperature and pressure oscillations at a microscale area. We demonstrate amazing dynamic behavior of gas-filled bubbles in pressure gradient field using a unique technique combining optical imaging, high intensity ultrasound and high speed camera. We find that pressure oscillations trigger continuous phase transformations that are considered to be impossible in physical systems.

Models of WO x films growth during pulsed laser deposition at elevated pressures of reactive gas

NASA Astrophysics Data System (ADS)

Gnedovets, A. G.; Fominski, V. Y.; Nevolin, V. N.; Romanov, R. I.; Fominski, D. V.; Soloviev, A. A.

2017-12-01

The films of tungsten oxides were prepared by pulsed laser ablation of W target in a reactive gas atmosphere (air of laboratory humidity). Optical analysis and ion signal measurements for the laser plume allowed to recognise a threshold gas pressure that suppresses the deposition of non-scattered atomic flux from the plume. When the pressure exceeds about 40 Pa, the films grow due to the deposition of species that could be formed in collisions of W atoms with reactive molecules (e.g., O2). Kinetic Monte Carlo method was used for modelling film growth. Comparison of the model structures with the experimentally prepared films has shown that the growth mechanism of ballistic deposition at a pressure of 40 Pa could be changed on the diffusion limited aggregation at a pressure of ~100 Pa. Thus, a cauliflower structure of the film transformed to a web-like structure. For good correlation of experimental and model structures of WO x , a dimension of structural elements in the model should coincide with W-O cluster size.

Electron Density Distribution Changes of Magnesiowüstite With Pressure

NASA Astrophysics Data System (ADS)

Diamond, M. R.; Popov, D.; Shen, G.; Jeanloz, R.

2017-12-01

Magnesiowüstite is one of the dominant minerals in the earth's lower mantle; its density and elasticity, substantially altered by its spin crossover, have direct consequence to interpreting deep-earth geophysical data. High-resolution single-crystal x-ray diffraction data can portray the 3-dimensional distribution of electron density through the Fourier transform of measured form factors. Here we present experimentally measured changes in electron density distribution of single-crystal (Mg.85,Fe.15)O as it goes through its iron(II) high-spin to low-spin electronic transition between about 40 and 60 GPa [Lin and Tsuchiya, 2008], in a diamond-anvil cell. As (Mg,Fe)O undergoes a pressure induced spin crossover (from high spin at low pressure to low spin at high pressure) due to overlap of its eg orbitals, the t2g orbitals become more pronounced to due a higher population of electrons, while the eg orbitals diminish. The spin splitting energy becomes increasingly unfavorable compared to the spin orbital pairing energy. By looking at the population of electrons at different directions in real space, we directly observe these changes in orbital occupation leading up to and during the spin crossover. Since high-Mg magnesiowüstite has a high symmetry structure at these pressure conditions, detecting relative changes in electron density distribution (comparing subsequent pressure steps) is feasible by collecting high resolution data offered by high-energy X rays and wide opening-angle diamond-anvil cells.

Initial stages of ion beam-induced phase transformations in Gd2O3 and Lu2O3

NASA Astrophysics Data System (ADS)

Chen, Chien-Hung; Tracy, Cameron L.; Wang, Chenxu; Lang, Maik; Ewing, Rodney C.

2018-02-01

The atomic-scale evolution of lanthanide sesquioxides Gd2O3 and Lu2O3 irradiated with 1 MeV Kr ions at room temperature and 120 K, up to fluences of 1 × 1016 ions/cm2 (˜20 dpa), has been characterized by in situ transmission electron microscopy. At room temperature, both oxides exhibited high radiation tolerance. Irradiation did not cause any observable structural change in either material, likely due to the mobility of irradiation-induced point defects, causing efficient defect annihilation. For Gd2O3, having the larger cation ionic radius of the two materials, an irradiation-induced stacking fault structure appeared at low fluences in the low temperature irradiation. As compared with the cubic-to-monoclinic phase transformations known to result from higher energy (˜GeV) ion irradiation, Kr ions of lower energies (˜MeV) yield much lower rates of damage accumulation and thus less extensive structural modification. At a fluence of 2.5 × 1015 ions/cm2, only the initial stages of the cubic-to-monoclinic (C to B) phase transformation process, consisting of the formation and aggregation of defects, have been observed.

Hugoniot equation of state and dynamic strength of boron carbide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grady, Dennis E.

Boron carbide ceramics have been particularly problematic in attempts to develop adequate constitutive model descriptions for purposes of analysis of dynamic response in the shock and impact environment. Dynamic strength properties of boron carbide ceramic differ uniquely from comparable ceramics. Furthermore, boron carbide is suspected, but not definitely shown, to undergoing polymorphic phase transformation under shock compression. In the present paper, shock-wave compression measurements conducted over the past 40 years are assessed for the purpose of achieving improved understanding of the dynamic equation of state and strength of boron carbide. In particular, attention is focused on the often ignored Losmore » Alamos National Laboratory (LANL) Hugoniot measurements performed on porous sintered boron carbide ceramic. The LANL data are shown to exhibit two compression anomalies on the shock Hugoniot within the range of 20–60 GPa that may relate to crystallographic structure transitions. More recent molecular dynamics simulations on the compressibility of the boron carbide crystal lattice reveal compression transitions that bear similarities to the LANL Hugoniot results. The same Hugoniot data are complemented with dynamic isentropic compression data for boron carbide extracted from Hugoniot measurements on boron carbide and copper granular mixtures. Other Hugoniot measurements, however, performed on near-full-density boron carbide ceramic differ markedly from the LANL Hugoniot data. These later data exhibit markedly less compressibility and tend not to show comparable anomalies in compressibility. Alternative Hugoniot anomalies, however, are exhibited by the near-full-density data. Experimental uncertainty, Hugoniot strength, and phase transformation physics are all possible explanations for the observed discrepancies. It is reasoned that experimental uncertainty and Hugoniot strength are not likely explanations for the observed differences. The notable mechanistic difference in the processes of shock compression between the LANL data and that of the other studies is the markedly larger inelastic deformation and dissipation experienced in the shock event brought about by compaction of the substantially larger porosity LANL test ceramics. High-pressure diamond anvil cell experiments reveal extensive amorphization, reasoned to be a reversion product of a higher-pressure crystallographic phase, which is a consequence of application of both high pressure and shear deformation to the boron carbide crystal structure. A dependence of shock-induced high-pressure phase transformation in boron carbide on the extent of shear deformation experienced in the shock process offers a plausible explanation for the differences observed in the LANL Hugoniot data on porous ceramic and that of other shock data on near-full-density boron carbide.« less

A (1)H-NMR study on the effect of high pressures on beta-lactoglobulin.

PubMed

Belloque, J; López-Fandiño, R; Smith, G M

2000-09-01

1H NMR was used to study the effect of high pressure on changes in the structure of beta-lactoglobulin (beta-Lg), particularly the strongly bonded regions, the "core". beta-Lg was exposed to pressures ranging from 100 to 400 MPa at neutral pH. After depressurization and acidification to pH 2.0, (1)H NMR spectra were taken. Pressure-induced unfolding was studied by deuterium exchange. Refolding was also evaluated. Our results showed that the core was unaltered at 100 MPa but increased its conformational flexibility at >/=200 MPa. Even though the core was highly flexible at 400 MPa, its structure was found to be identical to the native structure after equilibration back to atmospheric pressure. It is suggested that pressure-induced aggregates are formed by beta-Lg molecules maintaining most of their structure, and the intermolecular -SS- bonds, formed by -SH/-SS- exchange reaction, are likely to involve C(66)-C(160) rather than C(106)-C(119). In addition, the beta-Lg variants A and B could be distinguished in a (1)H NMR spectrum from a solution made with the AB mixed variant, by the differences in chemical shifts of M(107) and C(106); structural implications are discussed. Under pressure, the core of beta-Lg A seemed to unfold faster than that of beta-LgB. The structural recovery of the core was full for both variants.

Differential Stability of Dimeric and Monomeric Cytochrome c Oxidase Exposed to Elevated Hydrostatic Pressure†

PubMed Central

Staničová, Jana; Sedlák, Erik; Musatov, Andrej; Robinson, Neal C.

2007-01-01

Detergent-solubilized dimeric and monomeric cytochrome c oxidase (CcO) have significantly different quaternary stability when exposed to 2−3 kbar of hydrostatic pressure. Dimeric, dodecyl maltoside-solubilized cytochrome c oxidase is very resistant to elevated hydrostatic pressure with almost no perturbation of its quaternary structure or functional activity after release of pressure. In contrast to the stability of dimeric CcO, 3 kbar of hydrostatic pressure triggers multiple structural and functional alterations within monomeric cytochrome c oxidase. The perturbations are either irreversible or slowly reversible since they persist after the release of high pressure. Therefore, standard biochemical analytical procedures could be used to quantify the pressure-induced changes after the release of hydrostatic pressure. The electron transport activity of monomeric cytochrome c oxidase decreases by as much as 60% after exposure to 3 kbar of hydrostatic pressure. The irreversible loss of activity occurs in a time- and pressure-dependent manner. Coincident with the activity loss is a sequential dissociation of four subunits as detected by sedimentation velocity, high-performance ion-exchange chromatography, and reversed-phase and SDS–PAGE subunit analysis. Subunits VIa and VIb are the first to dissociate followed by subunits III and VIIa. Removal of subunits VIa and VIb prior to pressurization makes the resulting 11-subunit form of CcO even more sensitive to elevated hydrostatic pressure than monomeric CcO containing all 13 subunits. However, dimeric CcO, in which the association of VIa and VIb is stabilized, is not susceptible to pressure-induced inactivation. We conclude that dissociation of subunit III and/or VIIa must be responsible for pressure-induced inactivation of CcO since VIa and VIb can be removed from monomeric CcO without significant activity loss. These results are the first to clearly demonstrate an important structural role for the dimeric form of cytochrome c oxidase, i.e., stabilization of its quaternary structure. PMID:17530783

In situ X-Ray Diffraction of Shock-Compressed Fused Silica

NASA Astrophysics Data System (ADS)

Tracy, Sally June; Turneaure, Stefan J.; Duffy, Thomas S.

2018-03-01

Because of its widespread applications in materials science and geophysics, SiO2 has been extensively examined under shock compression. Both quartz and fused silica transform through a so-called "mixed-phase region" to a dense, low compressibility high-pressure phase. For decades, the nature of this phase has been a subject of debate. Proposed structures include crystalline stishovite, another high-pressure crystalline phase, or a dense amorphous phase. Here we use plate-impact experiments and pulsed synchrotron x-ray diffraction to examine the structure of fused silica shock compressed to 63 GPa. In contrast to recent laser-driven compression experiments, we find that fused silica adopts a dense amorphous structure at 34 GPa and below. When compressed above 34 GPa, fused silica transforms to untextured polycrystalline stishovite. Our results can explain previously ambiguous features of the shock-compression behavior of fused silica and are consistent with recent molecular dynamics simulations. Stishovite grain sizes are estimated to be ˜5 - 30 nm for compression over a few hundred nanosecond time scale.

Forced wave induced by an atmospheric pressure disturbance moving towards shore

NASA Astrophysics Data System (ADS)

Chen, Yixiang; Niu, Xiaojing

2018-05-01

Atmospheric pressure disturbances moving over a vast expanse of water can induce different wave patterns, which can be determined by the Froude number Fr. Generally, Fr = 1 is a critical value for the transformation of the wave pattern and the well-known Proudman resonance happens when Fr = 1. In this study, the forced wave induced by an atmospheric pressure disturbance moving over a constant slope from deep sea to shore is numerically investigated. The wave pattern evolves from a concentric-circle type into a triangular type with the increase of the Froude number, as the local water depth decreases, which is in accord with the analysis in the unbounded flat-bottom cases. However, a hysteresis effect has been observed, which implies the obvious amplification of the forced wave induced by a pressure disturbance can not be simply predicted by Fr = 1. The effects of the characteristic parameters of pressure disturbances and slope gradient have been discussed. The results show that it is not always possible to observe significant peak of the maximum water elevation before the landing of pressure disturbances, and a significant peak can be generated by a pressure disturbance with small spatial scale and fast moving velocity over a milder slope. Besides, an extremely high run-up occurs when the forced wave hits the shore, which is an essential threat to coastal security. The results also show that the maximum run-up is not monotonously varying with the increase of disturbance moving speed and spatial scale. There exists a most dangerous speed and scale which may cause disastrous nearshore surge.

Ground state structure of high-energy-density polymeric carbon monoxide

NASA Astrophysics Data System (ADS)

Xia, Kang; Sun, Jian; Pickard, Chris J.; Klug, Dennis D.; Needs, Richard J.

2017-04-01

Crystal structure prediction methods and first-principles calculations have been used to explore low-energy structures of carbon monoxide (CO). Contrary to the standard wisdom, the most stable structure of CO at ambient pressure was found to be a polymeric structure of P n a 21 symmetry rather than a molecular solid. This phase is formed from six-membered (four carbon + two oxygen) rings connected by C=C double bonds with two double-bonded oxygen atoms attached to each ring. Interestingly, the polymeric P n a 21 phase of CO has a much higher energy density than trinitrotoluene (TNT). On compression to about 7 GPa, P n a 21 is found to transform into another chainlike phase of C c symmetry which has similar ring units to P n a 21 . On compression to 12 GPa, it is energetically favorable for CO to polymerize into a purely single bonded C m c a phase, which is stable over a wide pressure range and transforms into the previously known C m c m phase at around 100 GPa. Thermodynamic stability of these structures was verified using calculations with different density functionals, including hybrid and van der Waals corrected functionals.

Pressure-induced phase transitions and templating effect in three-dimensional organic-inorganic hybrid perovskites

NASA Astrophysics Data System (ADS)

Lee, Yongjae; Mitzi, David; Barnes, Paris; Vogt, Thomas

2003-07-01

Pressure-induced structural changes of conducting halide perovskites (CH3NH3)SnI3, (CH3NH3)0.5(NH2CH=NH2)0.5SnI3, and (NH2CH=NH2)SnI3, have been investigated using synchrotron x-ray powder diffraction. In contrast to low-temperature structural changes, no evidence of an increased ordering of the organic cations was observed under pressure. Instead, increase in pressure results first in a ReO3-type doubling of the primitive cubic unit cell, followed by a symmetry distortion, and a subsequent amorphization above 4 GPa. This process is reversible and points towards a pressure-induced templating role of the organic cation. Bulk compressions are continuous across the phase boundaries. The compressibilities identify these hybrids as the most compressible perovskite system ever reported. However, the Sn-I bond compressibility in (CH3NH3)SnI3 shows a discontinuity within the supercell phase. This is possibly due to an electronic localization.

Decompression-Driven Superconductivity Enhancement in In2 Se3.

PubMed

Ke, Feng; Dong, Haini; Chen, Yabin; Zhang, Jianbo; Liu, Cailong; Zhang, Junkai; Gan, Yuan; Han, Yonghao; Chen, Zhiqiang; Gao, Chunxiao; Wen, Jinsheng; Yang, Wenge; Chen, Xiao-Jia; Struzhkin, Viktor V; Mao, Ho-Kwang; Chen, Bin

2017-09-01

An unexpected superconductivity enhancement is reported in decompressed In 2 Se 3 . The onset of superconductivity in In 2 Se 3 occurs at 41.3 GPa with a critical temperature (T c ) of 3.7 K, peaking at 47.1 GPa. The striking observation shows that this layered chalcogenide remains superconducting in decompression down to 10.7 GPa. More surprisingly, the highest T c that occurs at lower decompression pressures is 8.2 K, a twofold increase in the same crystal structure as in compression. It is found that the evolution of T c is driven by the pressure-induced R-3m to I-43d structural transition and significant softening of phonons and gentle variation of carrier concentration combined in the pressure quench. The novel decompression-induced superconductivity enhancement implies that it is possible to maintain pressure-induced superconductivity at lower or even ambient pressures with better superconducting performance. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanoclusters first: a hierarchical phase transformation in a novel Mg alloy

NASA Astrophysics Data System (ADS)

Okuda, Hiroshi; Yamasaki, Michiaki; Kawamura, Yoshihito; Tabuchi, Masao; Kimizuka, Hajime

2015-09-01

The Mg-Y-Zn ternary alloy system contains a series of novel structures known as long-period stacking ordered (LPSO) structures. The formation process and its key concept from a viewpoint of phase transition are not yet clear. The current study reveals that the phase transformation process is not a traditional spinodal decomposition or structural transformation but, rather a novel hierarchical phase transformation. In this transformation, clustering occurs first, and the spatial rearrangement of the clusters induce a secondary phase transformation that eventually lead to two-dimensional ordering of the clusters. The formation process was examined using in situ synchrotron radiation small-angle X-ray scattering (SAXS). Rapid quenching from liquid alloy into thin ribbons yielded strongly supersaturated amorphous samples. The samples were heated at a constant rate of 10 K/min. and the scattering patterns were acquired. The SAXS analysis indicated that small clusters grew to sizes of 0.2 nm after they crystallized. The clusters distributed randomly in space grew and eventually transformed into a microstructure with two well-defined cluster-cluster distances, one for the segregation periodicity of LPSO and the other for the in-plane ordering in segregated layer. This transformation into the LPSO structure concomitantly introduces the periodical stacking fault required for the 18R structures.

Combined Determination of Elastic Properties and Structure of Coesite under Simulated Mantle Conditions

NASA Astrophysics Data System (ADS)

Mueller, H. J.; Schilling, F. R.; Lauterjung, J.; Lathe, C.

2001-12-01

The high pressure SiO2-polymorph coesite seems to be an important mineral in the subduction process including crustal material (Chopin, 1984; Schreyer, 1995). The quartz to coesite transition is thus of fundamental importance to understand the processes within a subducting crust. Furthermore, the nature of the quartz to coesite transition is discussed controversially, because high pressure XRD-studies suggest an intermediate phase during the transformation process (Zinn et al., 1997). For the combined determination of elastic properties and structure a cubic multi-anvil high pressure apparatus (MAX80) was used. For the maximum sample volume of 20 mm3 the pressure limit is about 7GPa. The pressure is measured by use of NaCl as an internal pressure marker with calibrated PVT-data. The maximum temperature of about 2,000K is generated by an internal graphite heater and controlled by a thermocouple. The synchrotron beam (100x100 microns) is guided by a collimator through the sample between the anvils. For energy-dispersive X-ray diffraction, a Ge-solid state detector analyses the diffracted white beam at a fixed angle. The compressional and shear wave velocities were determined simultaneously by ultrasonic interferometry inside MAX80. Two of the six anvils are equipped with overtone polished lithium niobate transducers at their rear side, outside the volume under pressure, for generation and detection of ultrasonic waves between 10 and 60 MHz. Different buffer - reflector combinations and transducer arrangements were used to optimize the critical interference between both sample echoes. Therefore MAX80 is equipped for asymmetrical and symmetrical interferometric set-ups, i.e. compressional and shear waves are generated from the same or from two anvils, opposite to each other. We used for our transient measurements 3 natural fine-grained quartzites from Turkey and Germany. As a first step the pressure was increased gradually up to 4GPa at ambient temperature. At each pressure Vp and Vs was measured by ultrasonic interferometry. After reaching a given pressure, temperature was increased. At 4.5GPa and 800\\deg C the phase transition to coesite took place in less than 2 minutes. The fast kinetic of transformation was observed by synchrotron radiation. The compressional wave velocity increased by 30% and the shear wave velocity by 10% during the phase transition. The kinetic of the transition was varied by choosing different pressure and temperature conditions. The transformation with lower kinetic was studied in detail by XRD and ultrasonic interferometry. At 4.2 GPa the transformation could not be observed even above 950\\deg C. At 4.5 GPa and 750\\deg C the transition stopped at about 50% transformation, but transforms complete while increasing temperature to 800\\deg C. After the phase transition monitored by X-ray scattering the sample was quenched and Vp and Vs of coesite was measured at ambient temperatures up to the maximum pressure. Small differences in grain size, shape and in minor graphite contents did not change systematically the PT-conditions and kinetics. In addition to the kinetic and change of elastic properties the pressure and temperature derivatives of elastic properties of coesite will be presented.\\Chopin, C., Contr. Min. Petrol., 86 (1984), 107-118\\Schreyer, W., J. Geophys. Res., 100 (1995), 8,353-8,366\\Zinn P., Lauterjung J., Wirth R. & Hinze E. Zeitschrift für Kristallographie, 212 (1997), 691-698.

The high-pressure phase transitions of hydroxides

NASA Astrophysics Data System (ADS)

Nishi, M.; Kuwayama, Y.; Tsuchiya, J.; Tsuchiya, T.; Irifune, T.

2017-12-01

The discovery of new high-pressure hydrous minerals has important implications for understanding the structure, dynamics, and evolution of the Earth, since hydrogen significantly affects the physical properties and stabilities of Earth's constituent minerals. Whereas hydrous minerals commonly dehydrate under pressures of around a few tens of gigapascals (GPa) and at temperature around 1,500 K, those with CaCl2-type crystal structure, MgSiO4H2 phase H, δ-AlOOH and ɛ-FeOOH, are known to be stable at pressures corresponding to the lower mantle. However, although the CaCl2-type hydroxides were suggested to form a solid solution owing to their similar crystal structure, there are few experimental studies on the stability of the hydroxide in such multicomponent. Moreover, ab initio calculations have predicted that some CaCl2-type hydroxides transform to pyrite-type structure at higher pressures. Here, we conducted high pressure-temperature experiments on pure AlOOH, FeOOH, and their solid solutions, with the aid of these first-principles predictions. We use in situ X-ray measurements in conjunction with a multi-anvil apparatus to study the high-pressure behaviour of hydroxides in the multicomponent system under middle lower mantle conditions. Solid solutions in wide compositional ranges between CaCl2-type δ-AlOOH and ɛ-FeOOH were recognized from X-ray diffraction patterns. Also, unit cell volume of FeOOH and (Al,Fe)OOH significantly decreased accompanied with the spin transition of iron at 50 GPa. Thus, the wide compositional ranges in CaCl2-type hydroxide are maintained beyond the depth of the middle lower mantle, where the spin transition of iron occurs. We used a laser-heated diamond anvil cell in order to study the stability of AlOOH and FeOOH at higher pressures above 70 GPa. We observed that ɛ-FeOOH transforms to the pyrite-type structure at above 80 GPa, which is consistent with the theoretical prediction. At conditions above 190 GPa and 2,500 K, we observed the phase transition of δ-AlOOH to its higher pressure phase at above 170 GPa although further experimental study should be required to determine the precise structure. Based on these experimental and theoretical results, the stability and phase transitions of hydrous phases in the lower mantle will be discussed.

Analysis and Modeling of a Two-Phase Jet Pump of a Thermal Management System for Aerospace Applications

NASA Technical Reports Server (NTRS)

Sherif, S.A.; Hunt, P. L.; Holladay, J. B.; Lear, W. E.; Steadham, J. M.

1998-01-01

Jet pumps are devices capable of pumping fluids to a higher pressure by inducing the motion of a secondary fluid employing a high speed primary fluid. The main components of a jet pump are a primary nozzle, secondary fluid injectors, a mixing chamber, a throat, and a diffuser. The work described in this paper models the flow of a two-phase primary fluid inducing a secondary liquid (saturated or subcooled) injected into the jet pump mixing chamber. The model is capable of accounting for phase transformations due to compression, expansion, and mixing. The model is also capable of incorporating the effects of the temperature and pressure dependency in the analysis. The approach adopted utilizes an isentropic constant pressure mixing in the mixing chamber and at times employs iterative techniques to determine the flow conditions in the different parts of the jet pump.

Pressure induced enhancement of the magnetic ordering temperature in rhenium(IV) monomers

NASA Astrophysics Data System (ADS)

Woodall, Christopher H.; Craig, Gavin A.; Prescimone, Alessandro; Misek, Martin; Cano, Joan; Faus, Juan; Probert, Michael R.; Parsons, Simon; Moggach, Stephen; Martínez-Lillo, José; Murrie, Mark; Kamenev, Konstantin V.; Brechin, Euan K.

2016-12-01

Materials that demonstrate long-range magnetic order are synonymous with information storage and the electronics industry, with the phenomenon commonly associated with metals, metal alloys or metal oxides and sulfides. A lesser known family of magnetically ordered complexes are the monometallic compounds of highly anisotropic d-block transition metals; the `transformation' from isolated zero-dimensional molecule to ordered, spin-canted, three-dimensional lattice being the result of through-space interactions arising from the combination of large magnetic anisotropy and spin-delocalization from metal to ligand which induces important intermolecular contacts. Here we report the effect of pressure on two such mononuclear rhenium(IV) compounds that exhibit long-range magnetic order under ambient conditions via a spin canting mechanism, with Tc controlled by the strength of the intermolecular interactions. As these are determined by intermolecular distance, `squeezing' the molecules closer together generates remarkable enhancements in ordering temperatures, with a linear dependence of Tc with pressure.

FeRh ground state and martensitic transformation

DOE PAGES

Zarkevich, Nikolai A.; Johnson, Duane D.

2018-01-09

Cubic B2 FeRh exhibits a metamagnetic transition [(111) antiferromagnet (AFM) to ferromagnet (FM)] around 353 K and remains structurally stable at higher temperatures. However, the calculated zero-Kelvin phonons of AFM FeRh exhibit imaginary modes at M points in the Brillouin zone, indicating a premartensitic instability, which is a precursor to a martensitic transformation at low temperatures. Combining electronic-structure calculations with ab initio molecular dynamics, conjugate gradient relaxation, and the solid-state nudged-elastic band methods, we predict that AFM B2 FeRh becomes unstable at ambient pressure and transforms without a barrier to an AFM(111) orthorhombic (martensitic) ground state below 90±10K. In conclusion,more » we also consider competing structures, in particular, a tetragonal AFM(100) phase that is not the global ground state, as proposed, but a constrained solution.« less

Ab initio study on structural stability of uranium carbide

NASA Astrophysics Data System (ADS)

Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.

2013-06-01

First principles calculations have been performed using plane wave pseudopotential and full potential linearized augmented plane wave (FP-LAPW) methods to analyze structural, elastic and dynamic stability of UC under hydrostatic compression. Our calculations within pseudopotential method suggest that the rocksalt (B1) structure will transform to body centered orthorhombic (bco) structure at ˜21.5 GPa. The FP-LAPW calculations put this transition at 23 GPa. The transition pressures determined from our calculations though agree reasonably with the experimental value of 27 GPa, the high pressure bco structure suggested by theory differs slightly from the experimentally reported pseudo bco phase. The elastic stability analysis of B1 phase suggests that the B1 to bco transition is driven by the failure of C44 modulus. This finding is further substantiated by the lattice dynamic calculations which demonstrate that the B1 phase becomes dynamically unstable around the transition pressure and the instability is of long wavelength nature.

Highly efficient and selective pressure-assisted photon-induced polymerization of styrene

NASA Astrophysics Data System (ADS)

Guan, Jiwen; Song, Yang

2016-06-01

The polymerization process of condensed styrene to produce polystyrene as an industrially important polymeric material was investigated using a novel approach by combining external compression with ultraviolet radiation. The reaction evolution was monitored as a function of time and the reaction products were characterized by in situ Fourier transform infrared spectroscopy. By optimizing the loading pressures, we observed highly efficient and selective production of polystyrene of different tacticities. Specifically, at relatively low loading pressures, infrared spectra suggest that styrene monomers transform to amorphous atactic polystyrene (APS) with minor crystalline isotactic polystyrene. In contrast, APS was found to be the sole product when polymerization occurs at relatively higher loading pressures. The time-dependent reaction profiles allow the examination of the polymerization kinetics by analyzing the rate constant and activation volume as a function of pressure. As a result, an optimized pressure condition, which allows a barrierless reaction to proceed, was identified and attributed to the very desirable reaction yield and kinetics. Finally, the photoinitiated reaction mechanism and the growth geometry of the polymer chains were investigated from the energy diagram of styrene and by the topology analysis of the crystal styrene. This study shows strong promise to produce functional polymeric materials in a highly efficient and controlled manner.

Skeletal adaptation to intramedullary pressure-induced interstitial fluid flow is enhanced in mice subjected to targeted osteocyte ablation.

PubMed

Kwon, Ronald Y; Meays, Diana R; Meilan, Alexander S; Jones, Jeremiah; Miramontes, Rosa; Kardos, Natalie; Yeh, Jiunn-Chern; Frangos, John A

2012-01-01

Interstitial fluid flow (IFF) is a potent regulatory signal in bone. During mechanical loading, IFF is generated through two distinct mechanisms that result in spatially distinct flow profiles: poroelastic interactions within the lacunar-canalicular system, and intramedullary pressurization. While the former generates IFF primarily within the lacunar-canalicular network, the latter generates significant flow at the endosteal surface as well as within the tissue. This gives rise to the intriguing possibility that loading-induced IFF may differentially activate osteocytes or surface-residing cells depending on the generating mechanism, and that sensation of IFF generated via intramedullary pressurization may be mediated by a non-osteocytic bone cell population. To begin to explore this possibility, we used the Dmp1-HBEGF inducible osteocyte ablation mouse model and a microfluidic system for modulating intramedullary pressure (ImP) to assess whether structural adaptation to ImP-driven IFF is altered by partial osteocyte depletion. Canalicular convective velocities during pressurization were estimated through the use of fluorescence recovery after photobleaching and computational modeling. Following osteocyte ablation, transgenic mice exhibited severe losses in bone structure and altered responses to hindlimb suspension in a compartment-specific manner. In pressure-loaded limbs, transgenic mice displayed similar or significantly enhanced structural adaptation to Imp-driven IFF, particularly in the trabecular compartment, despite up to ∼50% of trabecular lacunae being uninhabited following ablation. Interestingly, regression analysis revealed relative gains in bone structure in pressure-loaded limbs were correlated with reductions in bone structure in unpressurized control limbs, suggesting that adaptation to ImP-driven IFF was potentiated by increases in osteoclastic activity and/or reductions in osteoblastic activity incurred independently of pressure loading. Collectively, these studies indicate that structural adaptation to ImP-driven IFF can proceed unimpeded following a significant depletion in osteocytes, consistent with the potential existence of a non-osteocytic bone cell population that senses ImP-driven IFF independently and potentially parallel to osteocytic sensation of poroelasticity-derived IFF.

In situ CF3 Detection in Low Pressure Inductive Discharges by Fourier Transform Infrared Spectroscopy

NASA Technical Reports Server (NTRS)

Kim, J. S.; Cappelli, M. A.; Sharma, S. P.; Arnold, J. O. (Technical Monitor)

1998-01-01

The detection of CF(x) (x=1-3) radicals in low pressure discharges using source gases such as CF4 and CHF3 is of importance to the understanding of their chemical structure and relevance in plasma based etching processes. These radicals are known to contribute to the formation of fluorocarbon polymer films, which affect the selectivity and anisotropy of etching. In this study, we present preliminary results of the quantitative measurement of trifluoromethyl radicals, CF3, in low pressure discharges. The discharge studied here is an inductively (transformer) coupled plasma (ICP) source in the GEC reference cell, operating on pure CF4 at pressures ranging from 10 - 100 mTorr, This plasma source generates higher electron number densities at lower operating pressures than obtainable with the parallel-plate capacitively coupled version of the GEC reference cell. Also, this expanded operating regime is more relevant to new generations of industrial plasma reactors being used by the microelectronics industry. Fourier transform infrared (FTIR) spectroscopy is employed to observe the absorption band of CF3 radicals in the electronic ground state X2Al in the region of 1233-1270/cm. The spectrometer is equipped with a high sensitivity HgCdTe (MCT) detector and has a fixed resolution of 0.125/cm. The CF3 concentrations are measured for a range of operating pressures and discharge power levels.

Influence of xanthan gum on the structural characteristics of myofibrillar proteins treated by high pressure.

PubMed

Villamonte, Gina; Jury, Vanessa; Jung, Stéphanie; de Lamballerie, Marie

2015-03-01

The effects of xanthan gum on the structural modifications of myofibrillar proteins (0.3 M NaCl, pH 6) induced by high pressure (200, 400, and 600 MPa, 6 min) were investigated. The changes in the secondary and tertiary structures of myofibrillar proteins were analyzed by circular dichroism. The protein denaturation was also evaluated by differential scanning calorimetry. Likewise, the protein surface hydrophobicity and the solubility of myofibrillar proteins were measured. High pressure (600 MPa) induced the loss of α-helix structures and an increase of β-sheet structures. However, the presence of xanthan gum hindered the former mechanism of protein denaturation by high pressure. In fact, changes in the secondary (600 MPa) and the tertiary structure fingerprint of high-pressure-treated myofibrillar proteins (400 to 600 MPa) were observed in the presence of xanthan gum. These modifications were confirmed by the thermal analysis, the thermal transitions of high-pressure (400 to 600 MPa)-treated myofibrillar proteins were modified in systems containing xanthan gum. As consequence, the high-pressure-treated myofibrillar proteins with xanthan gum showed increased solubility from 400 MPa, in contrast to high-pressure treatment (600 MPa) without xanthan gum. Moreover, the surface hydrophobicity of high-pressure-treated myofibrillar proteins was enhanced in the presence of xanthan gum. These effects could be due to the unfolding of myofibrillar proteins at high-pressure levels, which exposed sites that most likely interacted with the anionic polysaccharide. This study suggests that the role of food additives could be considered for the development of meat products produced by high-pressure processing. © 2015 Institute of Food Technologists®

Transformations in methane hydrates

USGS Publications Warehouse

Chou, I.-Ming; Sharma, A.; Burruss, R.C.; Shu, J.; Mao, Ho-kwang; Hemley, R.J.; Goncharov, A.F.; Stern, L.A.; Kirby, S.H.

2000-01-01

Detailed study of pure methane hydrate in a diamond cell with in situ optical, Raman, and x-ray microprobe techniques reveals two previously unknown structures, structure II and structure H, at high pressures. The structure II methane hydrate at 250 MPa has a cubic unit cell of a = 17.158(2) A?? and volume V = 5051.3(13) A??3; structure H at 600 MPa has a hexagonal unit cell of a = 11.980(2) A??, c = 9.992(3) A??, and V = 1241.9(5) A??3. The compositions of these two investigated phases are still not known. With the effects of pressure and the presence of other gases in the structure, the structure II phase is likely to dominate over the known structure I methane hydrate within deep hydrate-bearing sediments underlying continental margins.

On the brittle nature of rare earth pnictides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shriya, S.; Sapkale, R.; Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com, E-mail: sapkale.raju@rediffmail.com

The high-pressure structural phase transition and pressure as well temperature induced elastic properties in ReY; (Re = La, Sc, Pr; Y = N, P, As, Sb, Bi) pnictides have been performed using effective interionic interaction potential with emphasis on charge transfer interactions and covalent contribution. Estimated values of phase transition pressure and the volume discontinuity in pressure-volume phase diagram indicate the structural phase transition from NaCl to CsCl structure. From the investigations of elastic constants the pressure (temperature) dependent volume collapse/expansion, second order Cauchy discrepancy, anisotropy, hardness and brittle/ductile nature of rare earth pnictides are computed.

Electrical resistance of single-crystal magnetite (Fe 3 O 4 ) under quasi-hydrostatic pressures up to 100 GPa

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muramatsu, Takaki; Gasparov, Lev V.; Berger, Helmuth

2016-04-07

We measured the pressure dependence of electrical resistance of single-crystal magnetite (Fe 3O 4) under quasi-hydrostatic conditions to 100 GPa using low-temperature, megabar diamond-anvil cell techniques in order to gain insight into the anomalous behavior of this material that has been reported over the years in different high-pressure experiments. The measurements under nearly hydrostatic pressure conditions allowed us to detect the clear Verwey transition and the high-pressure structural phase. Furthermore, the appearance of a metallic ground state after the suppression of the Verwey transition around 20 GPa and the concomitant enhancement of electrical resistance caused by the structural transformation tomore » the high-pressure phase form reentrant semiconducting-metallic-semiconducting behavior, though the appearance of the metallic phase is highly sensitive to stress conditions and details of the measurement technique.« less

Bio-inspired metal ions regulate the structure evolution of self-assembled peptide-based nanoparticles

NASA Astrophysics Data System (ADS)

Xu, An-Ping; Yang, Pei-Pei; Yang, Chao; Gao, Yu-Juan; Zhao, Xiao-Xiao; Luo, Qiang; Li, Xiang-Dan; Li, Li-Zhong; Wang, Lei; Wang, Hao

2016-07-01

We report an assembly and transformation process of a supramolecular module, BP-KLVFF-RGD (BKR) in solution and on specific living cell surfaces for imaging and treatment. The BKR self-assembled into nanoparticles, which further transformed into nanofibers in situ induced by coordination with Ca2+ ions.We report an assembly and transformation process of a supramolecular module, BP-KLVFF-RGD (BKR) in solution and on specific living cell surfaces for imaging and treatment. The BKR self-assembled into nanoparticles, which further transformed into nanofibers in situ induced by coordination with Ca2+ ions. Electronic supplementary information (ESI) available: Experimental details; Fig. S1-S9. See DOI: 10.1039/c6nr03580a

Electrostrictive Mechanism of Nanostructure Formation at Solid Surfaces Irradiated by Femtosecond Laser Pulses.

PubMed

Pavlyniuk, Oleg R; Datsyuk, Vitaly V

2016-12-01

The significance of the mechanical pressure of light in creation of laser-induced periodic surface structures (LIPSSs) is investigated. Distributions of the electrically induced normal pressure and tangential stress at the illuminated solid surface, as well as the field of volume electrostrictive forces, are calculated taking into account surface plasmon polariton (SPP) excitation. Based on these calculations, we predict surface destruction and structure formation due to inelastic deformations during single femtosecond pulses. The calculated fields of the electromagnetic forces are found to agree well with the experimental ripple structures. We thus conclude that the electrostrictive forces can explain the origin of the periodic ripple structures.

Synthesis and Characterization of A2Mo3O 12 Materials

NASA Astrophysics Data System (ADS)

Young, Lindsay Kay

Negative thermal expansion (NTE) materials have attracted considerable research interest in recent decades. These unique materials shrink when heated, offering a potential means to control the overall thermal expansion of composites. Several families of materials display this behavior, the largest of which is the A2Mo3O12 family (also called the scandium tungstate family), in which A is a trivalent cation and M is molybdenum or tungsten. These materials show NTE in an orthorhombic structure, but many members transform to a monoclinic structure with positive expansion at low temperatures. Many properties of these materials are dependent on their elemental composition, especially the identity of the A3+ cation. This includes the magnitude of NTE, as well as the phase transition behavior as a function of temperature and pressure. It is also possible to create "mixed site" cation A2Mo3O12 materials, in which the A site is occupied by two different cations. These are described as AxA'2-xM3O12 materials, as the composition A:A' can vary. Creating these new compositions may result in different phase transition properties or the ability to tune the NTE properties of these materials. In this work, the focus was on synthesis and characterization of indium gallium molybdate (InxGa2-xM3O12). The non-hydrolytic sol-gel (NHSG) method was used to synthesize indium gallium molybdate while exploring a variety of reaction parameters. While the goal was to create stoichiometric, homogenous materials, it was found that this could not be accomplished using easily accessible parameters during NHSG reactions. However, it was discovered that certain conditions allowed unusually low temperature (230 °C) crystallization of these materials. Similar conditions were explored for single cation A2Mo3O12 materials, and it was determined that crystallization of indium molybdate, iron molybdate, and scandium molybdate was possible at temperatures of 230 or 300 °C. This extremely low temperature crystallization may provide the opportunity for exploring the in situ synthesis of polymer composites containing these materials, as the crystallization temperatures are compatible with many polymer systems. In the second part of this thesis, the high pressure behavior of a number of A2Mo3O12 and AA'Mo3O12 materials was studied. The open frameworks of NTE compounds are generally prone to pressure induced phase transitions. NTE materials may have to withstand high pressures during production or regular use of composites, thus understanding the high pressure behavior of these materials is necessary for effective application. Irreversible transitions to new phases or amorphization at high pressures could lead to failure of composites, as these phases are not expected to exhibit any NTE properties. Studies were carried out at the Advanced Photon Source at Argonne National Laboratory at pressures up to 5-7 GPa using a diamond anvil cell. The materials investigated could be divided into three groups based on distinct types of high pressure behavior. The room temperature monoclinic Group1 compounds (A2 = Al2, Fe2, FeAl, AlGa) underwent a similar sequence of reversible subtle phase transitions before undergoing a major structural transition to a common high pressure structure. The unit cell of this high pressure phase was successfully indexed, and the transition was found to be reversible upon decompression. Phase transition pressures increased with decreasing A-site cation radius. In contrast, Group2 materials (A = Cr, Y) retained their low temperature monoclinic structures up to the highest pressures investigated. The remaining materials (A2 = In2, InGa) underwent a different sequence of subtle transitions followed by an irreversible transition at higher pressures. The patterns belonging to these high pressure phases are unlike those of the first group. No patterns similar to InGaMo3O12 were found in the literature, while In2Mo3O12 may transform to the same high pressure polymorph as In2W3O12. The classification of A2Mo3O12 materials into several groups with distinct high pressure behavior adds pertinent knowledge to the field that may help elucidate the structures of previously studied materials, and ultimately may help predict the behavior of compositions that have not yet been explored.

Structural changes of deposited casein micelles induced by membrane filtration.

PubMed

Gebhardt, R; Steinhauer, T; Meyer, P; Sterr, J; Perlich, J; Kulozik, U

2012-01-01

Casein micelles undergo shape changes when subjected to frontal filtration forces. Grazing incidence small angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) allow a quantification of such structural changes on filtration cakes deposited on smooth silicon micro-sieves. A trans-membrane pressure of deltap = 400 mbar across the micro-sieve leads to an immediate film formation after deposition of casein solution. We observe significant changes in the GISAXS pattern depending on how many layers are stacked on top of each other. Compared to a deposit formed by one layer, GISAXS on a deposit formed by three layers of casein micelles leads to less scattering in the vertical and more scattering in the horizontal direction. Simulations show that the experimental results can be interpreted by a structural transformation from an originally spherical micelle shape to an ellipsoidal-deformed shape. The results are supported by AFM measurements showing a reduced lateral size of casein micelles deposited on top of a membrane pore. The observed shape changes could be due to filtration forces acting on densely packed deposits confining the micelles into ellipsoidal shapes.

Absence of pressure-induced amorphization in LiKSO4.

PubMed

Machon, D; Pinheiro, C B; Bouvier, P; Dmitriev, V P; Crichton, W A

2010-08-11

Angle-resolved synchrotron radiation diffraction was used to investigate lithium potassium sulfate (LiKSO(4)) crystals under high pressure. We confirm that the title compound undergoes three phase transitions, α →β, β → γ and γ →δ, observed at around 0.8 GPa, 4.0 GPa and 7.0 GPa, respectively. Two competitive structures are proposed for the β-phase after powder diffraction data Rietveld refinements: an orthorhombic (space group Cmc 2(1)) or a monoclinic (space group Cc) structure. These structures correspond to the models of the low temperature phases. The γ-phase is indexed by a monoclinic structure. Finally, the δ-phase is found to be highly disordered. No evidence of any pressure-induced amorphous phase was observed up to 24 GPa, even under imposed highly non-hydrostatic conditions, contrary to previous propositions.

Pressure-induced structural phase transition in transition metal carbides TMC (TM = Ru, Rh, Pd, Os, Ir, Pt): a DFT study

NASA Astrophysics Data System (ADS)

Manikandan, M.; Rajeswarapalanichamy, R.; Iyakutti, K.

2018-03-01

First-principles calculations based on density functional theory was performed to analyse the structural stability of transition metal carbides TMC (TM = Ru, Rh, Pd, Os, Ir, Pt). It is observed that zinc-blende phase is the most stable one for these carbides. Pressure-induced structural phase transition from zinc blende to NiAs phase is predicted at the pressures of 248.5 GPa, 127 GPa and 142 GPa for OsC, IrC and PtC, respectively. The electronic structure reveals that RuC exhibits a semiconducting behaviour with an energy gap of 0.7056 eV. The high bulk modulus values of these carbides indicate that these metal carbides are super hard materials. The high B/G value predicts that the carbides are ductile in their most stable phase.

Pressure-induced electronic topological transitions in the charge-density-wave material In 4 Se 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yuhang; Song, Liyan; Shao, Xuecheng

2017-08-01

High-pressure in situ angle dispersive X-ray diffraction (ADXRD) measurements were performed on the charge-density-wave (CDW) material In4Se3 up to 48.8 GPa. Pressure-induced structural changes were observed at 7.0 and 34.2 GPa, respectively. Using the CALYPSO methodology, the first high-pressure phase was solved as an exotic Pca21 structure. The compressional behaviors of the initial Pnnm and the Pca21 phases were all determined. Combined with first-principle calculations, we find that, unexpectedly, the Pnnm phase probably experiences twice electronic topological transitions (ETTs), from the initial possible CDW state to a semimetallic state at about 2.3 GPa and then back to a possible CDWmore » state at around 3.5 GPa, which was uncovered for the first time in CDW systems. In the both possible CDW states, pressure provokes a decrease of band-gap. The observation of a bulk metallic state was ascribed to structural transition to the Pca21 phase. Besides, based on electronic band structure calculations, the thermoelectric property of the Pnnm phase under compression was discussed. Our results show that pressure play a dramatic role in tuning In4Se3's structure and transport properties.« less

High-pressure phase transition in silicon carbide under shock loading using ultrafast x-ray diffraction

NASA Astrophysics Data System (ADS)

Tracy, S. J.; Smith, R. F.; Wicks, J. K.; Fratanduono, D. E.; Gleason, A. E.; Bolme, C.; Speziale, S.; Appel, K.; Prakapenka, V. B.; Fernandez Panella, A.; Lee, H. J.; MacKinnon, A.; Eggert, J.; Duffy, T. S.

2017-12-01

The behavior of silicon carbide (SiC) under shock loading was investigated through a series of time-resolved pump-probe x-ray diffraction (XRD) measurements. SiC is found at impact sites and has been put forward as a possible constituent in the proposed class of extra-solar planets known as carbon planets. Previous studies have used wave profile measurements to identify a phase transition under shock loading near 1 Mbar, but crystal structure information was not obtained. We have carried out an in situ XRD study of shock-compressed SiC using the Matter in Extreme Conditions instrument of the Linac Coherent Light Source. The femtosecond time resolution of the x-ray free electron laser allows for the determination of time-dependent atomic arrangements during shock loading and release. Two high-powered lasers were used to generate ablation-driven compression waves in the samples. Time scans were performed using the same drive conditions and nominally identical targets. For each shot in a scan, XRD data was collected at a different probe time after the shock had entered the SiC. Probe times extended up to 40 ns after release. Scans were carried out for peak pressures of 120 and 185 GPa. Our results demonstrate that SiC transforms directly from the ambient tetrahedrally-coordinated phase to the octahedral B1 structure on the nanosecond timescale of laser-drive experiments and reverts to the tetrahedrally coordinated ambient phase within nanoseconds of release. The data collected at 120 GPa exhibit diffraction peaks from both compressed ambient phase and transformed B1 phase, while the data at 185 GPa show a complete transformation to the B1 phase. Densities determined from XRD peaks are in agreement with an extrapolation of previous continuum data as well as theoretical predictions. Additionally, a high degree of texture was retained in both the high-pressure phase as well as on back transformation. Two-dimensional fits to the XRD data reveal details of the orientational relationships between the low- and high-pressure phases that can be interpreted to provide information about transformation pathways between tetrahedral and octahedral coordination structures. We acknowledge support for this work from SLAC National Accelerator Laboratory, Lawrence Livermore National Laboratory, and Los Alamos National Laboratory.

Giant Pressure-Induced Enhancement of Seebeck Coefficient and Thermoelectric Efficiency in SnTe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Jason; Kumar, Ravhi; Park, Changyong

The thermoelectric properties of polycrystalline SnTe have been measured up to 4.5 GPa at 330 K. SnTe shows an enormous enhancement in Seebeck coefficient, greater than 200 % after 3 GPa, which correlates to a known pressure-induced structural phase transition that is observed through simultaneous in situ X-ray diffraction measurement. We also measured electrical resistance and relative changes to the thermal conductivity, enabling the determination of relative changes in the dimensionless figure of merit (ZT), which increases dramatically after 3 GPa, reaching 350 % of the lowest pressure ZT value. Our results demonstrate a fundamental relationship between structure and thermoelectricmore » behaviours and suggest that pressure is an effective tool to control them.« less

Giant Pressure-Induced Enhancement of Seebeck Coefficient and Thermoelectric Efficiency in SnTe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Jason; Kumar, Ravhi; Park, Changyong

The thermoelectric properties of polycrystalline SnTe have been measured up to 4.5 GPa at 330 K. SnTe shows an enormous enhancement in Seebeck coefficient, greater than 200 % after 3 GPa, which correlates to a known pressure-induced structural phase transition that is observed through simultaneous in situ X-ray diffraction measurement. Electrical resistance and relative changes to the thermal conductivity were also measured, enabling the determination of relative changes in the dimensionless figure of merit (ZT), which increases dramatically after 3 GPa, reaching 350 % of the lowest pressure ZT value. The results demonstrate a fundamental relationship between structure and thermoelectricmore » behaviours and suggest that pressure is an effective tool to control them.« less

Giant Pressure-Induced Enhancement of Seebeck Coefficient and Thermoelectric Efficiency in SnTe

DOE PAGES

Baker, Jason; Kumar, Ravhi; Park, Changyong; ...

2017-10-30

The thermoelectric properties of polycrystalline SnTe have been measured up to 4.5 GPa at 330 K. SnTe shows an enormous enhancement in Seebeck coefficient, greater than 200 % after 3 GPa, which correlates to a known pressure-induced structural phase transition that is observed through simultaneous in situ X-ray diffraction measurement. We also measured electrical resistance and relative changes to the thermal conductivity, enabling the determination of relative changes in the dimensionless figure of merit (ZT), which increases dramatically after 3 GPa, reaching 350 % of the lowest pressure ZT value. Our results demonstrate a fundamental relationship between structure and thermoelectricmore » behaviours and suggest that pressure is an effective tool to control them.« less

Three-dimensional imaging of dislocation dynamics during the hydriding phase transformation

NASA Astrophysics Data System (ADS)

Ulvestad, A.; Welland, M. J.; Cha, W.; Liu, Y.; Kim, J. W.; Harder, R.; Maxey, E.; Clark, J. N.; Highland, M. J.; You, H.; Zapol, P.; Hruszkewycz, S. O.; Stephenson, G. B.

2017-05-01

Crystallographic imperfections significantly alter material properties and their response to external stimuli, including solute-induced phase transformations. Despite recent progress in imaging defects using electron and X-ray techniques, in situ three-dimensional imaging of defect dynamics remains challenging. Here, we use Bragg coherent diffractive imaging to image defects during the hydriding phase transformation of palladium nanocrystals. During constant-pressure experiments we observe that the phase transformation begins after dislocation nucleation close to the phase boundary in particles larger than 300 nm. The three-dimensional phase morphology suggests that the hydrogen-rich phase is more similar to a spherical cap on the hydrogen-poor phase than to the core-shell model commonly assumed. We substantiate this using three-dimensional phase field modelling, demonstrating how phase morphology affects the critical size for dislocation nucleation. Our results reveal how particle size and phase morphology affects transformations in the PdH system.

Origin of Pressure-induced Superconducting Phase in K xFe 2-ySe 2 studied by Synchrotron X-ray Diffraction and Spectroscopy

DOE PAGES

Yamamoto, Yoshiya; Yamaoka, Hitoshi; Tanaka, Masashi; ...

2016-08-08

Pressure dependence of the electronic and crystal structures of K xFe 2–ySe 2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change ofmore » Fermi surface topology. Lastly, our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.« less

Origin of Pressure-induced Superconducting Phase in KxFe2-ySe2 studied by Synchrotron X-ray Diffraction and Spectroscopy

NASA Astrophysics Data System (ADS)

Yamamoto, Yoshiya; Yamaoka, Hitoshi; Tanaka, Masashi; Okazaki, Hiroyuki; Ozaki, Toshinori; Takano, Yoshihiko; Lin, Jung-Fu; Fujita, Hidenori; Kagayama, Tomoko; Shimizu, Katsuya; Hiraoka, Nozomu; Ishii, Hirofumi; Liao, Yen-Fa; Tsuei, Ku-Ding; Mizuki, Jun'Ichiro

2016-08-01

Pressure dependence of the electronic and crystal structures of KxFe2-ySe2, which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change of Fermi surface topology. Our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.

Free microparticles—An inducing mechanism of pre-firing in high pressure gas switches for fast linear transformer drivers

NASA Astrophysics Data System (ADS)

Li, Xiaoang; Pei, Zhehao; Wu, Zhicheng; Zhang, Yuzhao; Liu, Xuandong; Li, Yongdong; Zhang, Qiaogen

2018-03-01

Microparticle initiated pre-firing of high pressure gas switches for fast linear transformer drivers (FLTDs) is experimentally and theoretically verified. First, a dual-electrode gas switch equipped with poly-methyl methacrylate baffles is used to capture and collect the microparticles. By analyzing the electrode surfaces and the collecting baffles by a laser scanning confocal microscope, microparticles ranging in size from tens of micrometers to over 100 μm are observed under the typical working conditions of FLTDs. The charging and movement of free microparticles in switch cavity are studied, and the strong DC electric field drives the microparticles to bounce off the electrode. Three different modes of free microparticle motion appear to be responsible for switch pre-firing. (i) Microparticles adhere to the electrode surface and act as a fixed protrusion which distorts the local electric field and initiates the breakdown in the gap. (ii) One particle escapes toward the opposite electrode and causes a near-electrode microdischarge, inducing the breakdown of the residual gap. (iii) Multiple moving microparticles are occasionally in cascade, leading to pre-firing. Finally, as experimental verification, repetitive discharges at ±90 kV are conducted in a three-electrode field-distortion gas switch, with two 8 mm gaps and pressurized with nitrogen. An ultrasonic probe is employed to monitor the bounce signals. In pre-firing incidents, the bounce is detected shortly before the collapse of the voltage waveform, which demonstrates that free microparticles contribute significantly to the mechanism that induces pre-firing in FLTD gas switches.

Free microparticles-An inducing mechanism of pre-firing in high pressure gas switches for fast linear transformer drivers.

PubMed

Li, Xiaoang; Pei, Zhehao; Wu, Zhicheng; Zhang, Yuzhao; Liu, Xuandong; Li, Yongdong; Zhang, Qiaogen

2018-03-01

Microparticle initiated pre-firing of high pressure gas switches for fast linear transformer drivers (FLTDs) is experimentally and theoretically verified. First, a dual-electrode gas switch equipped with poly-methyl methacrylate baffles is used to capture and collect the microparticles. By analyzing the electrode surfaces and the collecting baffles by a laser scanning confocal microscope, microparticles ranging in size from tens of micrometers to over 100 μm are observed under the typical working conditions of FLTDs. The charging and movement of free microparticles in switch cavity are studied, and the strong DC electric field drives the microparticles to bounce off the electrode. Three different modes of free microparticle motion appear to be responsible for switch pre-firing. (i) Microparticles adhere to the electrode surface and act as a fixed protrusion which distorts the local electric field and initiates the breakdown in the gap. (ii) One particle escapes toward the opposite electrode and causes a near-electrode microdischarge, inducing the breakdown of the residual gap. (iii) Multiple moving microparticles are occasionally in cascade, leading to pre-firing. Finally, as experimental verification, repetitive discharges at ±90 kV are conducted in a three-electrode field-distortion gas switch, with two 8 mm gaps and pressurized with nitrogen. An ultrasonic probe is employed to monitor the bounce signals. In pre-firing incidents, the bounce is detected shortly before the collapse of the voltage waveform, which demonstrates that free microparticles contribute significantly to the mechanism that induces pre-firing in FLTD gas switches.

Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, L.; Cong, D. Y.; Wang, Z. L.

2015-07-08

The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels.more » The present study is instructive for designing advanced multifunctional alloys with easy actuation.« less

Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy

NASA Astrophysics Data System (ADS)

Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Y.; Wang, Y. D.

2015-07-01

The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.

Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, L.; Cong, D. Y.; Wang, Z. L.

2015-06-03

The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels.more » The present study is instructive for designing advanced multifunctional alloys with easy actuation.« less

Effects of internal structure on equilibrium of field-reversed configuration plasma sustained by rotating magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yambe, Kiyoyuki; Inomoto, Michiaki; Okada, Shigefumi

The effects of an internal structure on the equilibrium of a field-reversed configuration (FRC) plasma sustained by rotating magnetic field is investigated by using detailed electrostatic probe measurements in the FRC Injection Experiment apparatus [S. Okada, et al., Nucl. Fusion. 45, 1094 (2005)]. An internal structure installed axially on the geometrical axis, which simulates Ohmic transformer or external toroidal field coils on the FRC device, brings about substantial changes in plasma density profile. The internal structure generates steep density-gradients not only on the inner side but on the outer side of the torus. The radial electric field is observed tomore » sustain the ion thermal pressure-gradient in the FRC without the internal structure; however, the radial electric field is not sufficient to sustain the increased ion thermal pressure-gradient in the FRC with the internal structure. Spontaneously driven azimuthal ion flow will be accountable for the imbalance of the radial pressure which is modified by the internal structure.« less

The effect of high hydrostatic pressure treatment on the molecular structure of starches with different amylose content.

PubMed

Szwengiel, Artur; Lewandowicz, Grażyna; Górecki, Adrian R; Błaszczak, Wioletta

2018-02-01

The effect of high hydrostatic pressure processing (650MPa/9min) on molecular mass distribution, and hydrodynamic and structural parameters of amylose (maize, sorghum, Hylon VII) and amylopectin (waxy maize, amaranth) starches was studied. The starches were characterized by high-performance size-exclusion chromatography (HPSEC) equipped with static light scattering and refractive index detectors and by Fourier Transform Infrared (FTIR) spectroscopy. Significant changes were observed in molecular mass distribution of pressurized waxy maize starch. Changes in branches/branch frequency, intrinsic viscosity, and radius of gyration were observed for all treated starches. The combination of SEC and FTIR data showed that α-1,6-glycosidic bonds are more frequently split in pressurized amaranth, Hylon VII, and waxy maize starch, while in sorghum and maize starches, the α-1,4 bonds are most commonly split. Our results show that the structural changes found for pressurized starches were more strongly determined by the starch origin than by the processing applied. Copyright © 2017 Elsevier Ltd. All rights reserved.

Structural transformations in Ge{sub 2}Sb{sub 2}Te{sub 5} under high pressure and temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mio, A. M.; Privitera, S., E-mail: stefania.privitera@imm.cnr.it; D'Arrigo, G.

2015-08-14

The structural transformations occurring in Ge{sub 2}Sb{sub 2}Te{sub 5} films heated at temperature up to 400 °C, and under hydrostatic pressure up to 12 GPa, have been investigated through in-situ X ray diffraction measurements. The adopted experimental conditions are close to those experienced by the phase change material during the SET (crystallization)/RESET (amorphization) processes in a nonvolatile memory device. The compression enhances the thermal stability of the amorphous phase, which remains stable up to 180 °C at 8 GPa and to 230 °C at 12 GPa. The structure of the crystalline phases is also modified, with the formation of a CsCl-type structure instead of rock-salt andmore » of a GeS-type structure at the temperature at which usually the trigonal stable phase is formed. Overall, the stability of the stable phase appears to be more affected by the compression. We argue that the presence of weak bonds associated to the van der Waals gaps is a determining factor for the observed reduced stability.« less

Transient porosity pulses and microfracturing during a stress-generating retrograde metamorphic reaction

NASA Astrophysics Data System (ADS)

Renard, F.; Zheng, X.; Cordonnier, B.; Zhu, W.; Jamtveit, B.

2017-12-01

Several geological processes involve mineral transformations where nominally dry rocks transform into hydrated ones when left in contact with water (i.e. eclogitization, serpentinization). In these systems, the transformation induces stress if the rock is confined, and the new minerals create a so-called force of crystallization. Here, we study a model retrograde metamorphic reaction, the hydration of periclase, MgO, into brucite, Mg(OH)2, to quantify the coupling between reaction, stress generation, porosity evolution and fracturing. This hydration reaction generates a volume increase of 110%, and a density decrease of 33.8% of the solid. Samples of a microporous MgO ceramics were reacted at 170-211°C, 5-80 MPa confining pressure, 6-95 MPa differential stress and 5 MPa pore fluid pressure. They were installed into an X-ray transparent triaxial deformation rig, called Hades, and mounted on a synchrotron microtomography stage. Each experiment lasted between 2 and 5 hours, during which between 35 and 130 three-dimensional images were acquired, allowing to follow the chemical transformation and the deformation of the sample. Below 30 MPa mean pressure, the hydration reaction was coupled to fracturing of the MgO ceramics, and the transformation rate followed a sigmoidal kinetics curve with a slow initiation, a fast reaction coupled to fracturing and the generation of a transient porosity pulse, and a slow-down until an almost complete transformation of periclase into brucite.. Conversely, above 30 MPa, the reaction kinetics was very slow, without fracturing over the time scale of the experiment. When considering the driving force of the hydration reaction, stress generation should be several hundreds MPa, whereas the present experiments show that fracturing occurred only below 30 MPa. This indicates that the potential energy due to phase transformation generates much lower stress than what is estimated from non-equilibrium thermodynamics. A possible interpretation of this observation is that the stress created by the reaction may overcome the disjoining pressure at the grain-grain interface, expelling the water film trapped there and reducing the kinetics of reaction. As a consequence, only a fraction of the available potential driving force was used to accelerate the reaction by microfracturing.

Pressure induced polymerization of acetylide anions in CaC 2 and 10 7 fold enhancement of electrical conductivity

DOE PAGES

Zheng, Haiyan; Wang, Lijuan; Li, Kuo; ...

2016-08-17

Transformation between different types of carbon–carbon bonding in carbides often results in a dramatic change of physical and chemical properties. Under external pressure, unsaturated carbon atoms form new covalent bonds regardless of the electrostatic repulsion. It was predicted that calcium acetylide (also known as calcium carbide, CaC 2) polymerizes to form calcium polyacetylide, calcium polyacenide and calcium graphenide under high pressure. In this work, the phase transitions of CaC 2 under external pressure were systematically investigated, and the amorphous phase was studied in detail for the first time. Polycarbide anions like C 6 6– are identified with gas chromatography-mass spectrometrymore » and several other techniques, which evidences the pressure induced polymerization of the acetylide anions and suggests the existence of the polyacenide fragment. Additionally, the process of polymerization is accompanied with a 10 7 fold enhancement of the electrical conductivity. As a result, the polymerization of acetylide anions demonstrates that high pressure compression is a viable route to synthesize novel metal polycarbides and materials with extended carbon networks, while shedding light on the synthesis of more complicated metal organics.« less

Influence of hydrostatic pressure on the built-in electric field in ZnO/ZnMgO quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teisseyre, Henryk, E-mail: teiss@ifpan.edu.pl; Institute of High Pressure, Polish Academy of Sciences, Sokołowska 29/37, 01-142 Warsaw; Kaminska, Agata

We used high hydrostatic pressure to perform photoluminescence measurements on polar ZnO/ZnMgO quantum well structures. Our structure oriented along the c-direction (polar direction) was grown by plasma-assisted molecular beam epitaxy on a-plane sapphire. Due to the intrinsic electric field, which exists in polar wurtzite structure at ambient pressure, we observed a red shift of the emission related to the quantum-confined Stark effect. In the high hydrostatic pressure experiment, we observed a strong decrease of the quantum well pressure coefficients with increased thickness of the quantum wells. Generally, a narrower quantum well gave a higher pressure coefficient, closer to the band-gapmore » pressure coefficient of bulk material 20 meV/GPa for ZnO, while for wider quantum wells it is much lower. We observed a pressure coefficient of 19.4 meV/GPa for a 1.5 nm quantum well, while for an 8 nm quantum well the pressure coefficient was equal to 8.9 meV/GPa only. This is explained by taking into account the pressure-induced increase of the strain in our structure. The strain was calculated taking in to account that in-plane strain is not equal (due to fact that we used a-plane sapphire as a substrate) and the potential distribution in the structure was calculated self-consistently. The pressure induced increase of the built-in electric field is the same for all thicknesses of quantum wells, but becomes more pronounced for thicker quantum wells due to the quantum confined Stark effect lowering the pressure coefficients.« less

Over 7% magnetic field-induced strain in a Ni-Mn-Ga five-layered martensite

NASA Astrophysics Data System (ADS)

Pagounis, E.; Chulist, R.; Szczerba, M. J.; Laufenberg, M.

2014-08-01

A Ni-Mn-Ga single crystal with a modulated five-layered martensite structure is reported, demonstrating giant magnetic field induced strain (MFIS) of 7.1% at room temperature and of 6% at temperatures close to the austenite transformation (TA = 71 °C). The room temperature MFIS clearly exceeds the best results of around 6% measured earlier in 10M martensites. The larger MFIS is connected to the huge (>1%) change in the lattice distortion of the 10M structure, obtained within a narrow temperature interval of 47 K, which has been previously observed only during intermartensitic transformation. The present material shall effectively reduce the size of magnetic shape memory actuators.