Pressure-induced collapsed-tetragonal phase in SrCo2As2

NASA Astrophysics Data System (ADS)

Jayasekara, W. T.; Kaluarachchi, U. S.; Ueland, B. G.; Pandey, Abhishek; Lee, Y. B.; Taufour, V.; Sapkota, A.; Kothapalli, K.; Sangeetha, N. S.; Fabbris, G.; Veiga, L. S. I.; Feng, Yejun; dos Santos, A. M.; Bud'ko, S. L.; Harmon, B. N.; Canfield, P. C.; Johnston, D. C.; Kreyssig, A.; Goldman, A. I.

2015-12-01

We present high-energy x-ray diffraction data under applied pressures up to p =29 GPa , neutron diffraction measurements up to p =1.1 GPa , and electrical resistance measurements up to p =5.9 GPa , on SrCo2As2 . Our x-ray diffraction data demonstrate that there is a first-order transition between the tetragonal (T) and collapsed-tetragonal (cT) phases, with an onset above approximately 6 GPa at T =7 K . The pressure for the onset of the cT phase and the range of coexistence between the T and cT phases appears to be nearly temperature independent. The compressibility along the a axis is the same for the T and cT phases, whereas, along the c axis, the cT phase is significantly stiffer, which may be due to the formation of an As-As bond in the cT phase. Our resistivity measurements found no evidence of superconductivity in SrCo2As2 for p ≤5.9 GPa and T ≥ 1.8 K. The resistivity data also show signatures consistent with a pressure-induced phase transition for p ≳5.5 GPa. Single-crystal neutron diffraction measurements performed up to 1.1 GPa in the T phase found no evidence of stripe-type or A-type antiferromagnetic ordering down to 10 K. Spin-polarized total-energy calculations demonstrate that the cT phase is the stable phase at high pressure with a c/a ratio of 2.54. Furthermore, these calculations indicate that the cT phase of SrCo2As2 should manifest either A-type antiferromagnetic or ferromagnetic order.

Conventional empirical law reverses in the phase transitions of 122-type iron-based superconductors

DOE PAGES

Yu, Zhenhai; Wang, Lin; Wang, Luhong; ...

2014-11-24

Phase transition of solid-state materials is a fundamental research topic in condensed matter physics, materials science and geophysics. It has been well accepted and widely proven that isostructural compounds containing different cations undergo same pressure-induced phase transitions but at progressively lower pressures as the cation radii increases. However, we discovered that this conventional law reverses in the structural transitions in 122-type iron-based superconductors. In this report, a combined low temperature and high pressure X-ray diffraction (XRD) measurement has identified the phase transition curves among the tetragonal (T), orthorhombic (O) and the collapsed-tetragonal (cT) phases in the structural phase diagram ofmore » the iron-based superconductor AFe 2As 2 (A = Ca, Sr, Eu, and Ba). As a result, the cation radii dependence of the phase transition pressure (T → cT) shows an opposite trend in which the compounds with larger ambient radii cations have a higher transition pressure.« less

Pressure induced phase transition and elastic properties of cerium mono-nitride (CeN)

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

Yaduvanshi, Namrata, E-mail: namrata-yaduvanshi@yahoo.com; Singh, Sadhna

2016-05-23

In the present paper, we have investigated the high-pressure structural phase transition and elastic properties of cerium mono-nitride. We studied theoretically the structural properties of this compound (CeN) by using the improved interaction potential model (IIPM) approach. This compound exhibits first order crystallographic phase transition from NaCl (B{sub 1}) to tetragonal (BCT) phase at 37 GPa. The phase transition pressures and associated volume collapse obtained from present potential model (IIPM) show a good agreement with available theoretical data.

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.

Publisher's Note: High-temperature superconductivity stabilized by electron-hole interband coupling in collapsed tetragonal phase of KFe 2 As 2 under high pressure [Phys. Rev. B 91 , 060508(R) (2015)

DOE PAGES

Nakajima, Yasuyuki; Wang, Renxiong; Metz, Tristin; ...

2015-03-09

Here, we report a high-pressure study of simultaneous low-temperature electrical resistivity and Hall effect measurements on high quality single-crystalline KFe 2As 2 using designer diamond anvil cell techniques with applied pressures up to 33 GPa. In the low pressure regime, we show that the superconducting transition temperature T c finds a maximum onset value of 7 K near 2 GPa, in contrast to previous reports that find a minimum T c and reversal of pressure dependence at this pressure. Upon applying higher pressures, this T c is diminished until a sudden drastic enhancement occurs coincident with a first-order structural phasemore » transition into a collapsed tetragonal phase. The appearance of a distinct superconducting phase above 13 GPa is also accompanied by a sudden reversal of dominant charge carrier sign, from hole- to electron-like, which agrees with our band calculations predicting the emergence of an electron pocket and diminishment of hole pockets upon Fermi surface reconstruction. Our results suggest the high-temperature superconducting phase in KFe 2As 2 is substantially enhanced by the presence of nested electron and hole pockets, providing the key ingredient of high-T c superconductivity in iron pnictide superconductors.« less

Influence of growth flux solvent on anneal-tuning of ground states in CaFe2As2

NASA Astrophysics Data System (ADS)

Roncaioli, Connor; Drye, Tyler; Saha, Shanta R.; Paglione, Johnpierre

2018-04-01

The effects of anneal-tuning of single-crystalline samples of CaFe2As2 synthesized via a molten Sn-flux method are investigated using x-ray diffraction, chemical composition, electrical transport, and magnetic susceptibility measurements in order to understand the role of growth conditions on the resultant phase diagram. Previous studies of CaFe2As2 crystals synthesized using a self-flux (FeAs) method revealed an ability to tune the structural and magnetic properties of this system by control of post-synthesis annealing conditions, resulting in an ambient pressure phase diagram that spans from tetragonal/orthorhombic antiferromagnetism to the collapsed tetragonal phase of this system. In this work, we compare previous results to those obtained on crystals synthesized via Sn flux, finding similar tunability in both self- and Sn-flux cases, but less sensitivity to annealing temperatures in the latter case, resulting in a temperature-shifted phase diagram.

Combined effects of Sr substitution and pressure on the ground states in CaFe2As2

NASA Astrophysics Data System (ADS)

Knöner, S.; Gati, E.; Köhler, S.; Wolf, B.; Tutsch, U.; Ran, S.; Torikachvili, M. S.; Bud'ko, S. L.; Canfield, P. C.; Lang, M.

2016-10-01

We present a detailed study of the combined effects of Sr substitution and hydrostatic pressure on the ground-state properties of CaFe2As2 . Measurements of the electrical resistance and magnetic susceptibility, both at ambient and finite pressure P ≤2 GPa, were performed on Ca1 -xSrxFe2As2 single crystals grown out of Sn flux. We find that by Sr substitution the transition temperature to the magnetic/structural phase is enhanced and therefore a higher pressure is needed to suppress the transition to lowest temperature. In addition, the transition to the collapsed tetragonal phase is found at a pressure, which is distinctly higher than in the pure compound. This implies that the stability ranges of both phases shift on the pressure-axis upon doping, but the latter one with a higher rate. These observations suggest the possibility of separating the two phase lines, which intersect already at elevated temperatures for x =0 and low Sr concentration levels. For x =0.177 , we find strong evidence that both phases remain separated down to the lowest temperature and that a zero-resistance state emerges in this intermediate pressure window. This observation indicates that Sr substitution combined with hydrostatic pressure provides another route for stabilizing superconductivity in CaFe2As2 . Our results are consistent with the notion that (i) preserving the fluctuations associated with the structural-magnetic transition to low temperatures is vital for superconductivity to form in this material and that (ii) the nonmagnetic collapsed tetragonal phase is detrimental for superconductivity.

Combined effects of Sr substitution and pressure on the ground states in CaFe 2 As 2

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

Knoner, S.; Gati, E.; Kohler, S.

2016-10-21

Here, we present a detailed study of the combined effects of Sr substitution and hydrostatic pressure on the ground-state properties of CaFe 2As 2. Measurements of the electrical resistance and magnetic susceptibility, both at ambient and finite pressure P ≤ 2 GPa, were performed on Ca 1–xSr xFe 2As 2 single crystals grown out of Sn flux. We find that by Sr substitution the transition temperature to the magnetic/structural phase is enhanced and therefore a higher pressure is needed to suppress the transition to lowest temperature. In addition, the transition to the collapsed tetragonal phase is found at a pressure,more » which is distinctly higher than in the pure compound. This implies that the stability ranges of both phases shift on the pressure-axis upon doping, but the latter one with a higher rate. These observations suggest the possibility of separating the two phase lines, which intersect already at elevated temperatures for x = 0 and low Sr concentration levels. For x = 0.177, we find strong evidence that both phases remain separated down to the lowest temperature and that a zero-resistance state emerges in this intermediate pressure window. This observation indicates that Sr substitution combined with hydrostatic pressure provides another route for stabilizing superconductivity in CaFe 2As 2. Lastly, our results are consistent with the notion that (i) preserving the fluctuations associated with the structural-magnetic transition to low temperatures is vital for superconductivity to form in this material and that (ii) the nonmagnetic collapsed tetragonal phase is detrimental for superconductivity.« less

Complex structures of different CaFe2As2 samples

PubMed Central

Saparov, Bayrammurad; Cantoni, Claudia; Pan, Minghu; Hogan, Thomas C.; II, William Ratcliff; Wilson, Stephen D.; Fritsch, Katharina; Gaulin, Bruce D.; Sefat, Athena S.

2014-01-01

The interplay between magnetism and crystal structures in three CaFe2As2 samples is studied. For the nonmagnetic quenched crystals, different crystalline domains with varying lattice parameters are found, and three phases (orthorhombic, tetragonal, and collapsed tetragonal) coexist between TS = 95 K and 45 K. Annealing of the quenched crystals at 350°C leads to a strain relief through a large (~1.3%) expansion of the c-parameter and a small (~0.2%) contraction of the a-parameter, and to local ~0.2 Å displacements at the atomic-level. This annealing procedure results in the most homogeneous crystals for which the antiferromagnetic and orthorhombic phase transitions occur at TN/TS = 168(1) K. In the 700°C-annealed crystal, an intermediate strain regime takes place, with tetragonal and orthorhombic structural phases coexisting between 80 to 120 K. The origin of such strong shifts in the transition temperatures are tied to structural parameters. Importantly, with annealing, an increase in the Fe-As length leads to more localized Fe electrons and higher local magnetic moments on Fe ions. Synergistic contribution of other structural parameters, including a decrease in the Fe-Fe distance, and a dramatic increase of the c-parameter, which enhances the Fermi surface nesting in CaFe2As2, are also discussed. PMID:24844399

Suppression of magnetic order in CaCo1.86As2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca (Co1-xFex) yAs2

NASA Astrophysics Data System (ADS)

Jayasekara, W. T.; Pandey, Abhishek; Kreyssig, A.; Sangeetha, N. S.; Sapkota, A.; Kothapalli, K.; Anand, V. K.; Tian, W.; Vaknin, D.; Johnston, D. C.; McQueeney, R. J.; Goldman, A. I.; Ueland, B. G.

2017-02-01

Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca (Co1-xFex) yAs2 , 0 ≤x ≤1 , 1.86 ≤y ≤2 , are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲0.12 (1 ) . The antiferromagnetic order is smoothly suppressed with increasing x , with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤0.25 , nor does ferromagnetic order for x up to at least x =0.104 , and a smooth crossover from the collapsed-tetragonal (cT) phase of CaCo1.86As2 to the tetragonal (T) phase of CaFe2As2 occurs. These results suggest that hole doping CaCo1.86As2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.

Probing mixed tetragonal/rhombohedral-like monoclinic phases in strained bismuth ferrite films by optical second harmonic generation

NASA Astrophysics Data System (ADS)

Kumar, Amit; Denev, Sava; Zeches, Robert J.; Vlahos, Eftihia; Podraza, Nikolas J.; Melville, Alexander; Schlom, Darrell G.; Ramesh, R.; Gopalan, Venkatraman

2010-09-01

Epitaxial strain can induce the formation of morphotropic phase boundary in lead free ferroelectrics like bismuth ferrite, thereby enabling the coexistence of tetragonal and rhombohedral phases in the same film. The relative ratio of these phases is governed by the film thickness and theoretical studies suggest that there exists a monoclinic distortion of both the tetragonal as well as the rhombohedral unit cells due to imposed epitaxial strain. In this work we show that optical second harmonic generation can distinguish the tetragonal-like phase from the rhombohedral-like phase and enable detection of monoclinic distortion in only a pure tetragonal-like phase.

Phase Transitions and Domain Structure in Mixed Tetragonal-Rhombohedral BiFeO3 thin films using Raman Spectroscopy and Nonlinear Optics

NASA Astrophysics Data System (ADS)

Vlahos, E.; Kumar, A.; Denev, S.; Melville, A.; Adamo, C.; Ihlefeld, J. F.; Sheng, G.; Zeches, R. J.; Zhang, J. X.; He, Q.; Yang, C. H.; Erni, R.; Rossell, M. D.; J, A.; Hatt; Chu, Y.-H.; Wang, C. H.; Ederer, C.; Gopalan, V.; Chen, L. Q.; Schlom, D. G.; Spaldin, N. A.; Martin, L. W.; Ramesh, R.; Tenne, Dmitri

2010-03-01

We have shown that biaxially strained BiFeO3 thin films can undergo an isosymmetric phase transition from a rhombohedral-like to a tetragonal-like phase. This talk discusses the evolution of the tetragonal and the mixed phases in BiFeO3/YAlO3 thin films with varying film thickness using optical second harmonic generation (SHG) and Raman spectroscopy. 25nm, 75nm, and 225 nm thick films were studied; thinner films are dominated by the tetragonal phase, whereas thicker films exhibit both tetragonal and rhombohedral phases. The evolution of these phases as function of film thickness and temperature was experimentally determined.

Suppression of magnetic order in CaCo 1.86 As 2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca ( Co 1 – x Fe x ) y As 2

DOE PAGES

Jayasekara, W. T.; Pandey, Abhishek; Kreyssig, A.; ...

2017-02-23

Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca(Co 1–xFe x) yAs 2, 0 ≤ x ≤ 1, 1.86 ≤ y ≤ 2, are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲ 0.12(1). The antiferromagnetic order is smoothly suppressed with increasing x, with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤ 0.25, nor does ferromagnetic order for x up to at least x = 0.104, and a smooth crossover from the collapsed-tetragonal (cT)more » phase of CaCo 1.86As 2 to the tetragonal (T) phase of CaFe 2As 2 occurs. Furthermore, these results suggest that hole doping CaCo 1.86As 2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.« less

Suppression of magnetic order in CaCo 1.86 As 2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca ( Co 1 – x Fe x ) y As 2

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

Jayasekara, W. T.; Pandey, Abhishek; Kreyssig, A.

Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca(Co 1–xFe x) yAs 2, 0 ≤ x ≤ 1, 1.86 ≤ y ≤ 2, are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲ 0.12(1). The antiferromagnetic order is smoothly suppressed with increasing x, with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤ 0.25, nor does ferromagnetic order for x up to at least x = 0.104, and a smooth crossover from the collapsed-tetragonal (cT)more » phase of CaCo 1.86As 2 to the tetragonal (T) phase of CaFe 2As 2 occurs. Furthermore, these results suggest that hole doping CaCo 1.86As 2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.« less

Investigation of structural and mechanical properties of rare-earth bismuthide (RBi, R=Ce & Pr) with the NaCl structure at high pressure

NASA Astrophysics Data System (ADS)

Yaduvanshi, Namrata; Kapoor, Shilpa; Singh, Sadhna

2018-05-01

We have investigated the structural and mechanical properties of Cerium and Praseodymium Bismuthides under pressure by means of a three body interaction potential model which includes long range columbic interaction, three body interactions and short range overlap repulsive interaction operative up to second nearest neighbor. These compounds shows transition from NaCl structure to body-centered tetragonal (BCT) structure (distorted CsCl-type P4/mmm). The elastic constants and their properties are also reported. Our calculated results of phase transitions and volume collapses of these compounds show a good agreement with available theoretical and experimental results.

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

Sypek, John T.; Yu, Hang; Dusoe, Keith J.

Shape memory materials have the ability to recover their original shape after a significant amount of deformation when they are subjected to certain stimuli, for instance, heat or magnetic fields. But, their performance is often limited by the energetics and geometry of the martensitic-austenitic phase transformation. We report a unique shape memory behavior in CaFe 2As 2, which exhibits superelasticity with over 13% recoverable strain, over 3 GPa yield strength, repeatable stress–strain response even at the micrometer scale, and cryogenic linear shape memory effects near 50 K. These properties are acheived through a reversible uni-axial phase transformation mechanism, the tetragonal/orthorhombic-to-collapsed-tetragonalmore » phase transformation. These results offer the possibility of developing cryogenic linear actuation technologies with a high precision and high actuation power per unit volume for deep space exploration, and more broadly, suggest a mechanistic path to a class of shape memory materials, ThCr 2Si 2-structured intermetallic compounds.« less

Interface-induced superconductivity at ∼25 K at ambient pressure in undoped CaFe2As2 single crystals

PubMed Central

Zhao, Kui; Lv, Bing; Deng, Liangzi; Huyan, Shu-Yuan; Xue, Yu-Yi; Chu, Ching-Wu

2016-01-01

Superconductivity has been reversibly induced/suppressed in undoped CaFe2As2 (Ca122) single crystals through proper thermal treatments, with Tc at ∼25 K at ambient pressure and up to 30 K at 1.7 GPa. We found that Ca122 can be stabilized in two distinct tetragonal (T) phases at room temperature and ambient pressure: PI with a nonmagnetic collapsed tetragonal (cT) phase at low temperature and PII with an antiferromagnetic orthorhombic (O) phase at low temperature, depending on the low-temperature annealing condition. Neither phase at ambient pressure is superconducting down to 2 K. However, systematic annealing for different time periods at 350 °C on the as-synthesized crystals, which were obtained by quenching the crystal ingot from 850 °C, reveals the emergence of superconductivity over a narrow time window. Whereas the onset Tc is insensitive to the anneal time, the superconductive volume fraction evolves with the time in a dome-shaped fashion. Detailed X-ray diffraction profile analyses further reveal mesoscopically stacked layers of the PI and the PII phases. The deduced interface density correlates well with the superconducting volume measured. The transport anomalies of the T–cT transition, which is sensitive to lattice strain, and the T–O transition, which is associated with the spin-density-wave (SDW) transition, are gradually suppressed over the superconductive region, presumably due to the interface interactions between the nonmagnetic metallic cT phase and the antiferromagnetic O phase. The results provide the most direct evidence to date for interface-enhanced superconductivity in undoped Ca122, consistent with the recent theoretical prediction. PMID:27799564

Room Temperature Monoclinic Phase in BaTiO3 Single Crystals

NASA Astrophysics Data System (ADS)

Denev, Sava; Kumar, Amit; Barnes, Andrew; Vlahos, Eftihia; Shepard, Gabriella; Gopalan, Venkatraman

2010-03-01

BaTiO3 is a well studied ferroelectric material for the last half century. It is well known to show phase transitions to tetragonal, orthorhombic and rhombohedral phases upon cooling. Yet, some old and some recent studies have argued that all these phases co-exist with a second phase with monoclinic distortion. Using optical second harmonic generation (SHG) at room temperature we directly present evidence for such monoclininc phase co-existing with tetragonal phase at room temperature. We observe domains with the expected tetragonal symmetry exhibiting 90^o and 180^o domain walls. However, at points of higher stress at the tips of the interpenetrating tetragonal domains we observe a well pronounced metastable ``staircase pattern'' with a micron-scale fine structure. Polarization studies show that this phase can be explained only by monoclinic symmetry. This phase is very sensitive to external perturbations such as temperature and fields, hence stabilizing this phase at room temperature could lead to large properties' tunability.

Structural stability, electronic structure and mechanical properties of alkali gallium hydrides AGaH{sub 4} (A = Li, Na)

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

Santhosh, M.; Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com; Manikandan, M.

2016-05-06

Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of alkali gallium hydrides AGaH{sub 4} (A = Li, Na) for three different crystal structures, namely tetragonal (P42{sub 1}c), tetragonal (P4{sub 2}/nmc) and monoclinic (P2{sub 1}/c). Among the considered structures, tetragonal (P42{sub 1}c) phase is found to be the most stable phase for these hydrides at normal pressure. A pressure induced structural phase transition from tetragonal (P42{sub 1}c) to tetragonal (P4{sub 2}/nmc) is observed. The electronic structure reveals that these hydrides are insulators. The calculated elastic constants indicate that these ternary imides are mechanically stablemore » at normal pressure.« less

Enhancement of tetragonal anisotropy and stabilisation of the tetragonal phase by Bi/Mn-double-doping in BaTiO3 ferroelectric ceramics

PubMed Central

Yabuta, Hisato; Tanaka, Hidenori; Furuta, Tatsuo; Watanabe, Takayuki; Kubota, Makoto; Matsuda, Takanori; Ifuku, Toshihiro; Yoneda, Yasuhiro

2017-01-01

To stabilise ferroelectric-tetragonal phase of BaTiO3, the double-doping of Bi and Mn up to 0.5 mol% was studied. Upon increasing the Bi content in BaTiO3:Mn:Bi, the tetragonal crystal-lattice-constants a and c shrank and elongated, respectively, resulting in an enhancement of tetragonal anisotropy, and the temperature-range of the ferroelectric tetragonal phase expanded. X-ray absorption fine structure measurements confirmed that Bi and Mn were located at the A(Ba)-site and B(Ti)-site, respectively, and Bi was markedly displaced from the centrosymmetric position in the BiO12 cluster. This A-site substitution of Bi also caused fluctuations of B-site atoms. Magnetic susceptibility measurements revealed a change in the Mn valence from +4 to +3 upon addition of the same molar amount of Bi as Mn, probably resulting from a compensating behaviour of the Mn at Ti4+ sites for donor doping of Bi3+ into the Ba2+ site. Because addition of La3+ instead of Bi3+ showed neither the enhancement of the tetragonal anisotropy nor the stabilisation of the tetragonal phase, these phenomena in BaTiO3:Mn:Bi were not caused by the Jahn-Teller effect of Mn3+ in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi3+. PMID:28367973

Effects of poling over the orthorhombic-tetragonal phase transition temperature in compositionally homogeneous (K,Na)NbO3-based ceramics

NASA Astrophysics Data System (ADS)

Morozov, M. I.; Kungl, H.; Hoffmann, M. J.

2011-03-01

Li-, Ta-, and Mn-modified (K,Na)NbO3 ceramics with various compositional homogeneity have been prepared by conventional and precursor methods. The homogeneous ceramic has demonstrated a sharper peak in temperature dependent piezoelectric response. The dielectric and piezoelectric properties of the homogeneous ceramics have been characterized at the experimental subcoercive electric fields near the temperature of the orthorhombic-tetragonal phase transition with respect to poling in both phases. Poling in the tetragonal phase is shown to enhance the low-signal dielectric and piezoelectric properties in the orthorhombic phase.

Superelasticity and cryogenic linear shape memory effects of CaFe 2As 2

DOE PAGES

Sypek, John T.; Yu, Hang; Dusoe, Keith J.; ...

2017-10-20

Shape memory materials have the ability to recover their original shape after a significant amount of deformation when they are subjected to certain stimuli, for instance, heat or magnetic fields. But, their performance is often limited by the energetics and geometry of the martensitic-austenitic phase transformation. We report a unique shape memory behavior in CaFe 2As 2, which exhibits superelasticity with over 13% recoverable strain, over 3 GPa yield strength, repeatable stress–strain response even at the micrometer scale, and cryogenic linear shape memory effects near 50 K. These properties are acheived through a reversible uni-axial phase transformation mechanism, the tetragonal/orthorhombic-to-collapsed-tetragonalmore » phase transformation. These results offer the possibility of developing cryogenic linear actuation technologies with a high precision and high actuation power per unit volume for deep space exploration, and more broadly, suggest a mechanistic path to a class of shape memory materials, ThCr 2Si 2-structured intermetallic compounds.« less

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

Raman scattering in HfxZr1-xO2 nanoparticles

NASA Astrophysics Data System (ADS)

Robinson, Richard D.; Tang, Jing; Steigerwald, Michael L.; Brus, Louis E.; Herman, Irving P.

2005-03-01

Raman spectroscopy demonstrates that ˜5nm dimension HfxZr1-xO2 nanocrystals prepared by a nonhydrolytic sol-gel synthesis method are solid solutions of hafnia and zirconia, with no discernable segregation within the individual nanoparticles. Zirconia-rich particles are tetragonal and ensembles of hafnia-rich particles show mixed tetragonal/monoclinic phases. Sintering at 1200 °C produces larger particles (20-30 nm) that are monoclinic. A simple lattice dynamics model with composition-averaged cation mass and scaled force constants is used to understand how the Raman mode frequencies vary with composition in the tetragonal HfxZr1-xO2 nanoparticles. Background luminescence from these particles is minimized after oxygen treatment, suggesting possible oxygen defects in the as-prepared particles. Raman scattering is also used to estimate composition and the relative fractions of tetragonal and monoclinic phases. In some regimes there are mixed phases, and Raman analysis suggests that in these regimes the tetragonal phase particles are relatively rich in zirconium and the monoclinic phase particles are relatively rich in hafnium.

Phase field modeling of tetragonal to monoclinic phase transformation in zirconia

NASA Astrophysics Data System (ADS)

Mamivand, Mahmood

Zirconia based ceramics are strong, hard, inert, and smooth, with low thermal conductivity and good biocompatibility. Such properties made zirconia ceramics an ideal material for different applications form thermal barrier coatings (TBCs) to biomedicine applications like femoral implants and dental bridges. However, this unusual versatility of excellent properties would be mediated by the metastable tetragonal (or cubic) transformation to the stable monoclinic phase after a certain exposure at service temperatures. This transformation from tetragonal to monoclinic, known as LTD (low temperature degradation) in biomedical application, proceeds by propagation of martensite, which corresponds to transformation twinning. As such, tetragonal to monoclinic transformation is highly sensitive to mechanical and chemomechanical stresses. It is known in fact that this transformation is the source of the fracture toughening in stabilized zirconia as it occurs at the stress concentration regions ahead of the crack tip. This dissertation is an attempt to provide a kinetic-based model for tetragonal to monoclinic transformation in zirconia. We used the phase field technique to capture the temporal and spatial evolution of monoclinic phase. In addition to morphological patterns, we were able to calculate the developed internal stresses during tetragonal to monoclinic transformation. The model was started form the two dimensional single crystal then was expanded to the two dimensional polycrystalline and finally to the three dimensional single crystal. The model is able to predict the most physical properties associated with tetragonal to monoclinic transformation in zirconia including: morphological patterns, transformation toughening, shape memory effect, pseudoelasticity, surface uplift, and variants impingement. The model was benched marked with several experimental works. The good agreements between simulation results and experimental data, make the model a reliable tool for predicting tetragonal to monoclinic transformation in the cases we lack experimental observations.

Thickness-dependent electrocaloric effect in mixed-phase Pb0.87Ba0.1 La0.02(Zr0.6Sn0.33Ti0.07)O3 thin films

PubMed Central

Correia, T. M.

2016-01-01

Full-perovskite Pb0.87Ba0.1La0.02(Zr0.6Sn0.33Ti0.07)O3 (PBLZST) thin films were fabricated by a sol–gel method. These revealed both rhombohedral and tetragonal phases, as opposed to the full-tetragonal phase previously reported in ceramics. The fractions of tetragonal and rhombohedral phases are found to be strongly dependent on film thickness. The fraction of tetragonal grains increases with increasing film thickness, as the substrate constraint throughout the film decreases with film thickness. The maximum of the dielectric constant (εm) and the corresponding temperature (Tm) are thickness-dependent and dictated by the fraction of rhombohedral and tetragonal phase, with εm reaching a minimum at 400 nm and Tm shifting to higher temperature with increasing thickness. With the thickness increase, the breakdown field decreases, but field-induced antiferroelectric–ferroelectric (EAFE−FE) and ferroelectric–antiferroelectric (EFE−AFE) switch fields increase. The electrocaloric effect increases with increasing film thickness. This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’. PMID:27402937

Y-TZP zirconia regeneration firing: Microstructural and crystallographic changes after grinding.

PubMed

Ryan, Daniel Patrick Obelenis; Fais, Laiza Maria Grassi; Antonio, Selma Gutierrez; Hatanaka, Gabriel Rodrigues; Candido, Lucas Miguel; Pinelli, Ligia Antunes Pereira

2017-07-26

This study evaluated microstructural and crystallographic phase changes after grinding (G) and regeneration firing/anneling (R) of Y-TZP ceramics. Thirty five bars (Lava TM and Ice Zirkon) were divided: Y-TZP pre-sintered, control (C), regeneration firing (R), dry grinding (DG), dry grinding+regeneration firing (DGR), wet grinding (WG) and wet grinding+regeneration firing (WGR). Grinding was conducted using a diamond bur and annealing at 1,000°C. The microstructure was analyzed by SEM and the crystalline phases by X-ray diffraction (XRD). XRD showed that pre-sintered specimens contained tetragonal and monoclinic phases, while groups C and R showed tetragonal, cubic and monoclinic phases. After grinding, the cubic phase was eliminated in all groups. Annealing (DGR and WGR) resulted in only tetragonal phase. SEM showed semi-circular cracks after grinding and homogenization of particles after annealing. After grinding, surfaces show tetragonal and monoclinic phases and R can be assumed to be necessary prior to porcelain layering when grinding is performed.

Phase transition in a tetragonal In90Pb10 alloy under high pressure: a switch from c/a > 1 to c/a < 1

NASA Astrophysics Data System (ADS)

Degtyareva, V. F.; Bdikin, I. K.; Porsch, F.; Novokhatskaya, N. I.

2003-03-01

The effect of pressure on tetragonal In-Pb alloys with 10, 15, and 22 at.% Pb has been studied up to pressure 30 GPa with diamond anvil cells using synchrotron radiation. The In-type face-centred tetragonal phase of the In alloy with 10 at.% Pb undergoes under pressure a phase transition with a discontinuous jump of the axial ratio from c/a > 1 to c/a < 1 via a two-phase region from 7 to 20 GPa. The tetragonal phases of the In alloys with 15 and 22 at.% Pb with c/a < 1 at ambient pressure show only a slight decrease in c/a with pressure increase. The correlation of the axial ratio with the alloy content and its change with pressure in In alloys and In itself are attributed to Brillouin-zone-Fermi-sphere interactions.

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

A comparison study of the Born effective charges and dielectric properties of the cubic, tetragonal, monoclinic, ortho-I, ortho-II and ortho-III phases of zirconia

NASA Astrophysics Data System (ADS)

Zhang, Yan; Chen, Hua-Xin; Duan, Li; Fan, Ji-Bin; Ni, Lei; Ji, Vincent

2018-07-01

Using density-functional perturbation theory, we systematically investigate the Born effective charges and dielectric properties of cubic, tetragonal, monoclinic, ortho-I (Pbca), ortho-II (Pnma) and ortho-III (Pca21) phases of ZrO2. The magnitudes of the Born effective charges of the Zr and oxygen atoms are greater than their nominal ionic valences (+4 for Zr and -2 for oxygen), indicating a strong dynamic charge transfer from Zr atoms to O atoms and a mixed covalent-ionic bonding in six phases of ZrO2. For all six phases of ZrO2, the electronic contributions εij∞ to the static dielectric constant are rather small (range from 5 to 6.5) and neither strongly anisotropic nor strongly dependent on the structural phase, while the ionic contributions εijion to the static dielectric constant are large and not only anisotropic but also dependent on the structural phase. The average dielectric constant εbar0 of the six ZrO2 phases decreases in the sequence of tetragonal, cubic, ortho-II (Pnma), ortho-I (Pbca), ortho-III (Pca21) and monoclinic. So among six phases of ZrO2, the tetragonal and cubic phases are two suitable phases to replace SiO2 as the gate dielectric material in modern integrated-circuit technology. Furthermore, for the tetragonal ZrO2 the best orientation is [100].

Evolution of structure and superconductivity in Ba(Ni 1 -xCox)2As2

NASA Astrophysics Data System (ADS)

Eckberg, Chris; Wang, Limin; Hodovanets, Halyna; Kim, Hyunsoo; Campbell, Daniel J.; Zavalij, Peter; Piccoli, Philip; Paglione, Johnpierre

2018-06-01

The effects of Co substitution on Ba (Ni1-xCox) 2As2 (0 ≤x ≤0.251 ) single crystals grown out of Pb flux are investigated via transport, magnetic, and thermodynamic measurements. BaNi2As2 exhibits a first-order tetragonal to triclinic structural phase transition at Ts=137 K upon cooling, and enters a superconducting phase below Tc=0.7 K. The structural phase transition is sensitive to cobalt content and is suppressed completely by x ≥0.133 . The superconducting critical temperature, Tc, increases continuously with x , reaching a maximum of Tc=2.3 K at x =0.083 and then decreases monotonically until superconductivity is no longer observable well into the tetragonal phase. In contrast to similar BaNi2As2 substitutional studies, which show an abrupt change in Tc at the triclinic-tetragonal boundary that extends far into the tetragonal phase, Ba (Ni1-xCox) 2As2 exhibits a domelike phase diagram centered around the zero-temperature tetragonal-triclinic boundary. Together with an anomalously large heat capacity jump Δ Ce/γ T ˜2.2 near optimal doping, the smooth evolution of Tc in the Ba (Ni1-xCox) 2As2 system suggests a mechanism for pairing enhancement other than phonon softening.

Effects of Zr/Ce molar ratio and water content on thermal stability and structure of ZrO{sub 2}–CeO{sub 2} mixed oxides prepared via sol–gel process

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

Huang, Wenzhi; Yang, Jili; Wang, Chunjie

2012-09-15

Highlights: ► Tetragonal t″ phase was stabilized in Zr{sub 0.5}Ce{sub 0.5}O{sub 2} solid solution at temperature as high as 1000 °C. ► Specific surface area of powders decreased with the increase of water addition and the Ce content. ► The single stable phase was controlled by adjusting the volume ratio of water and ethanol. ► Tetragonal (t″) phase dissociated into cubic and tetragonal (t′) phases at 1200 °C. -- Abstract: ZrO{sub 2}–CeO{sub 2} mixed oxides were synthesized via sol–gel process. Thermal stability, structure and morphology of samples were investigated by powder X-ray diffraction, FT-Raman spectroscopy, X-ray photoelectron spectroscopy and scanningmore » electron microscopy. In this approach, the solvent composition and Zr/Ce molar ratio have great influences on the structure and morphology of final products. With decreasing water content in the mixed solvent, specific surface area of powders increased and the single tetragonal phase was obtained. Only when the volume ratio of water and ethanol and the Zr/Ce molar ratio were 1:1, tetragonal t″-Zr{sub 0.5}Ce{sub 0.5}O{sub 2} could be stabilized in powders at temperature as high as 1000 °C. Meanwhile, tetragonal (t′) and (t″) phases coexisted in Zr{sub 0.5}Ce{sub 0.5}O{sub 2} solid solution without peak splitting after calcination at 1100 °C, further transforming into cubic and tetragonal (t′) phases at 1200 °C. The effective activation energy for Zr{sub 0.5}Ce{sub 0.5}O{sub 2} nanocrystallite growth during annealing is about 5.24 ± 0.15 kJ/mol.« less

Ultrafast optical snapshots of hybrid perovskites reveal the origin of multiband electronic transitions

DOE PAGES

Appavoo, Kannatassen; Nie, Wanyi; Blancon, Jean -Christophe; ...

2017-11-15

In this paper, connecting the complex electronic excitations of hybrid perovskites to their intricate organic-inorganic lattice structure has critical implications for energy conversion and optoelectronic technologies. Here we detail the multiband, multivalley electronic structure of a halide hybrid perovskite by measuring the absorption transients of a millimeter-scale-grain thin film as it undergoes a thermally controlled reversible tetragonal-to-orthogonal phase transition. Probing nearly single grains of this hybrid perovskite, we observe an unreported energy splitting (degeneracy lifting) of the high-energy 2.6 eV band in the tetragonal phase that further splits as the rotational degrees of freedom of the disordered CH 3NH 3more » + molecules are reduced when the sample is cooled. This energy splitting drastically increases during an extended phase-transition coexistence region that persists from 160 to 120 K, becoming more pronounced in the orthorhombic phase. By tracking the temperature-dependent optical transition energies and using symmetry analysis that describes the evolution of electronic states from the tetragonal phase to the orthorhombic phase, we assign this energy splitting to the nearly degenerate transitions in the tetragonal phase from both the R- and M-point-derived states. Importantly, these assignments explain how momentum conservation effects lead to long hot-carrier lifetimes in the room-temperature tetragonal phase, with faster hot-carrier relaxation when the hybrid perovskite structurally transitions to the orthorhombic phase due to enhanced scattering at the Γ point.« less

Ultrafast optical snapshots of hybrid perovskites reveal the origin of multiband electronic transitions

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

Appavoo, Kannatassen; Nie, Wanyi; Blancon, Jean -Christophe

In this paper, connecting the complex electronic excitations of hybrid perovskites to their intricate organic-inorganic lattice structure has critical implications for energy conversion and optoelectronic technologies. Here we detail the multiband, multivalley electronic structure of a halide hybrid perovskite by measuring the absorption transients of a millimeter-scale-grain thin film as it undergoes a thermally controlled reversible tetragonal-to-orthogonal phase transition. Probing nearly single grains of this hybrid perovskite, we observe an unreported energy splitting (degeneracy lifting) of the high-energy 2.6 eV band in the tetragonal phase that further splits as the rotational degrees of freedom of the disordered CH 3NH 3more » + molecules are reduced when the sample is cooled. This energy splitting drastically increases during an extended phase-transition coexistence region that persists from 160 to 120 K, becoming more pronounced in the orthorhombic phase. By tracking the temperature-dependent optical transition energies and using symmetry analysis that describes the evolution of electronic states from the tetragonal phase to the orthorhombic phase, we assign this energy splitting to the nearly degenerate transitions in the tetragonal phase from both the R- and M-point-derived states. Importantly, these assignments explain how momentum conservation effects lead to long hot-carrier lifetimes in the room-temperature tetragonal phase, with faster hot-carrier relaxation when the hybrid perovskite structurally transitions to the orthorhombic phase due to enhanced scattering at the Γ point.« less

Ultrafast optical snapshots of hybrid perovskites reveal the origin of multiband electronic transitions

NASA Astrophysics Data System (ADS)

Appavoo, Kannatassen; Nie, Wanyi; Blancon, Jean-Christophe; Even, Jacky; Mohite, Aditya D.; Sfeir, Matthew Y.

2017-11-01

Connecting the complex electronic excitations of hybrid perovskites to their intricate organic-inorganic lattice structure has critical implications for energy conversion and optoelectronic technologies. Here we detail the multiband, multivalley electronic structure of a halide hybrid perovskite by measuring the absorption transients of a millimeter-scale-grain thin film as it undergoes a thermally controlled reversible tetragonal-to-orthogonal phase transition. Probing nearly single grains of this hybrid perovskite, we observe an unreported energy splitting (degeneracy lifting) of the high-energy 2.6 eV band in the tetragonal phase that further splits as the rotational degrees of freedom of the disordered C H3N H3 + molecules are reduced when the sample is cooled. This energy splitting drastically increases during an extended phase-transition coexistence region that persists from 160 to 120 K, becoming more pronounced in the orthorhombic phase. By tracking the temperature-dependent optical transition energies and using symmetry analysis that describes the evolution of electronic states from the tetragonal phase to the orthorhombic phase, we assign this energy splitting to the nearly degenerate transitions in the tetragonal phase from both the R - and M -point-derived states. Importantly, these assignments explain how momentum conservation effects lead to long hot-carrier lifetimes in the room-temperature tetragonal phase, with faster hot-carrier relaxation when the hybrid perovskite structurally transitions to the orthorhombic phase due to enhanced scattering at the Γ point.

Defect-induced local variation of crystal phase transition temperature in metal-halide perovskites.

PubMed

Dobrovolsky, Alexander; Merdasa, Aboma; Unger, Eva L; Yartsev, Arkady; Scheblykin, Ivan G

2017-06-26

Solution-processed organometal halide perovskites are hybrid crystalline semiconductors highly interesting for low-cost and efficient optoelectronics. Their properties are dependent on the crystal structure. Literature shows a variety of crystal phase transition temperatures and often a spread of the transition over tens of degrees Kelvin. We explain this inconsistency by demonstrating that the temperature of the tetragonal-to-orthorhombic phase transition in methylammonium lead triiodide depends on the concentration and nature of local defects. Phase transition in individual nanowires was studied by photoluminescence microspectroscopy and super-resolution imaging. We propose that upon cooling from 160 to 140 K, domains of the crystal containing fewer defects stay in the tetragonal phase longer than highly defected domains that readily transform to the high bandgap orthorhombic phase at higher temperatures. The existence of relatively pure tetragonal domains during the phase transition leads to drastic photoluminescence enhancement, which is inhomogeneously distributed across perovskite microcrystals.Understanding crystal phase transition in materials is of fundamental importance. Using luminescence spectroscopy and super-resolution imaging, Dobrovolsky et al. study the transition from the tetragonal to orthorhombic crystal phase in methylammonium lead triiodide nanowires at low temperature.

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.

Structure Evolution of BaTiO3 on Co Doping: X-ray diffraction and Raman study

NASA Astrophysics Data System (ADS)

Mansuri, Amantulla; Mishra, Ashutosh

2016-10-01

In the present study, we have synthesize polycrystalline samples of BaTi1-xCoxO3 (x = 0, 0.05 and 0.1) with standard solid state reaction technique. The obtained samples are characterized by X-ray diffraction (XRD) and Raman spectroscopy. The detail structural analysis has been performed by Rietveld refinement using Fullprof program. The structural analysis reveal the samples are chemical pure and crystallize in tetragonal phase with space group Pm3m. We observe an increase in lattice parameters which results due to substitution of Co2+ with large ionic radii (0.9) for smaller ionic radii (0.6) Ti4+. Moreover peak at 45.5° shift to 45° on Co doping, which is due to structure phase transition from tetragonal to cubic. Raman study infers that the intensity of characteristic peaks decreases and linewidth increases with Co doping. The bands linked with the tetragonal structure (307 cm1) decreased due to the tetragonal-towards-cubic phase transition with Co doping. Our structural study reveals the expansion of BTO unit cell and tetragonal-to-cubic phase transformation takes place, results from different characterization techniques are conclusive and show structural evolution with Co doping.

A comprehensive study on the structural evolution of HfO 2 thin films doped with various dopants

DOE PAGES

Park, Min Hyuk; Schenk, Tony; Fancher, Christopher M.; ...

2017-04-19

The origin of the unexpected ferroelectricity in doped HfO 2 thin films is now considered to be the formation of a non-centrosymmetric Pca2 1 orthorhombic phase. Due to the polycrystalline nature of the films as well as their extremely small thickness (~10 nm) and mixed orientation and phase composition, structural analysis of doped HfO 2 thin films remains a challenging task. As a further complication, the structural similarities of the orthorhombic and tetragonal phase are difficult to distinguish by typical structural analysis techniques such as X-ray diffraction. To resolve this issue, the changes in the grazing incidence X-ray diffraction (GIXRD)more » patterns of HfO 2 films doped with Si, Al, and Gd are systematically examined. For all dopants, the shift of o111/ t101 diffraction peak is observed with increasing atomic layer deposition (ALD) cycle ratio, and this shift is thought to originate from the orthorhombic to P4 2/ nmc tetragonal phase transition with decreasing aspect ratio (2 a/(b + c) for orthorhombic and c/a for the tetragonal phase). For quantitative phase analysis, Rietveld refinement is applied to the GIXRD patterns. A progressive phase transition from P2 1/c monoclinic to orthorhombic to tetragonal is confirmed for all dopants, and a strong relationship between orthorhombic phase fraction and remanent polarization value is uniquely demonstrated. The concentration range for the ferroelectric properties was the narrowest for the Si-doped HfO 2 films. As a result, the dopant size is believed to strongly affect the concentration range for the ferroelectric phase stabilization, since small dopants can strongly decrease the free energy of the tetragonal phase due to their shorter metal–oxygen bonds.« less

A comprehensive study on the structural evolution of HfO 2 thin films doped with various dopants

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

Park, Min Hyuk; Schenk, Tony; Fancher, Christopher M.

The origin of the unexpected ferroelectricity in doped HfO 2 thin films is now considered to be the formation of a non-centrosymmetric Pca2 1 orthorhombic phase. Due to the polycrystalline nature of the films as well as their extremely small thickness (~10 nm) and mixed orientation and phase composition, structural analysis of doped HfO 2 thin films remains a challenging task. As a further complication, the structural similarities of the orthorhombic and tetragonal phase are difficult to distinguish by typical structural analysis techniques such as X-ray diffraction. To resolve this issue, the changes in the grazing incidence X-ray diffraction (GIXRD)more » patterns of HfO 2 films doped with Si, Al, and Gd are systematically examined. For all dopants, the shift of o111/ t101 diffraction peak is observed with increasing atomic layer deposition (ALD) cycle ratio, and this shift is thought to originate from the orthorhombic to P4 2/ nmc tetragonal phase transition with decreasing aspect ratio (2 a/(b + c) for orthorhombic and c/a for the tetragonal phase). For quantitative phase analysis, Rietveld refinement is applied to the GIXRD patterns. A progressive phase transition from P2 1/c monoclinic to orthorhombic to tetragonal is confirmed for all dopants, and a strong relationship between orthorhombic phase fraction and remanent polarization value is uniquely demonstrated. The concentration range for the ferroelectric properties was the narrowest for the Si-doped HfO 2 films. As a result, the dopant size is believed to strongly affect the concentration range for the ferroelectric phase stabilization, since small dopants can strongly decrease the free energy of the tetragonal phase due to their shorter metal–oxygen bonds.« less

Instability of the layered orthorhombic post-perovskite phase of SrTiO3 and other candidate orthorhombic phases under pressure

NASA Astrophysics Data System (ADS)

Bhandari, Churna; Lambrecht, Walter R. L.

2018-06-01

While the tetragonal antiferro-electrically distorted (AFD) phase with space group I 4 / mcm is well known for SrTiO3 to occur below 105 K, there are also some hints in the literature of an orthorhombic phase, either at the lower temperature or at high pressure. A previously proposed orthorhombic layered structure of SrTiO3, known as the post-perovskite or CaIrO3 structure with space group Cmcm is shown to have significantly higher energy than the cubic or tetragonal phase and to have its minimum volume at larger volume than cubic perovskite. The Cmcm structure is thus ruled out. We also study an alternative Pnma phase obtained by two octahedral rotations about different axes. This phase is found to have slightly lower energy than the I 4 / mcm phase in spite of the fact that its parent, in-phase tilted P 4 / mbm phase is not found to occur. Our calculated enthalpies of formation show that the I 4 / mcm phase occurs at slightly higher volume than the cubic phase and has a negative transition pressure relative to the cubic phase, which suggests that it does not correspond to the high-pressure tetragonal phase. The enthalpy of the Pnma phase is almost indistinguishable from the I 4 / mcm phase. Alternative ferro-electric tetragonal and orthorhombic structures previously suggested in literature are discussed.

Local Orthorhombicity in the Magnetic C 4 Phase of the Hole-Doped Iron-Arsenide Superconductor Sr 1 - x Na x Fe 2 As 2

DOE PAGES

Frandsen, Benjamin A.; Taddei, Keith M.; Yi, Ming; ...

2017-10-30

We report on temperature-dependent pair distribution function measurements of Sr 1-xNa xFe 2As 2, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic C 4 phase. Quantitative refinements indicate that the instantaneous local structure in the C 4 phase comprises fluctuating orthorhombic regions with a length scale of similar to 2 nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the paramagnetic tetragonal phase. Furthermore, these results highlight the exceptionally large nematic susceptibility of iron-based superconductors andmore » have significant implications for the magnetic C 4 phase and the neighboring C 2 and superconducting phases.« less

Local Orthorhombicity in the Magnetic C 4 Phase of the Hole-Doped Iron-Arsenide Superconductor Sr 1 - x Na x Fe 2 As 2

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

Frandsen, Benjamin A.; Taddei, Keith M.; Yi, Ming

We report on temperature-dependent pair distribution function measurements of Sr 1-xNa xFe 2As 2, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic C 4 phase. Quantitative refinements indicate that the instantaneous local structure in the C 4 phase comprises fluctuating orthorhombic regions with a length scale of similar to 2 nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the paramagnetic tetragonal phase. Furthermore, these results highlight the exceptionally large nematic susceptibility of iron-based superconductors andmore » have significant implications for the magnetic C 4 phase and the neighboring C 2 and superconducting phases.« less

Glass ceramic toughened with tetragonal zirconia

DOEpatents

Keefer, K.D.

1984-02-10

A phase transformation-toughened glass ceramic and a process for making it are disclosed. A mixture of particulate network-forming oxide, network-modifying oxide, and zirconium oxide is heated to yield a homogeneous melt, and this melt is then heat treated to precipitate an appreciable quantity of tetragonal zirconia, which is retained at ambient temperature to form a phase transformation-toughened glass ceramic. Nuclearing agents and stabilizing agents may be added to the mixture to facilitate processing and improve the ceramic's properties. Preferably, the mixture is first melted at a temperature from 1200 to 1700/sup 0/C and is then heat-treated at a temperature within the range of 800 to 1200/sup 0/C in order to precipitate tetragonal ZrO/sub 2/. The composition, as well as the length and temperature of the heat treatment, must be carefully controlled to prevent solution of the precipitated tetragonal zirconia and subsequent conversion to the monoclinic phase.

Glass ceramic toughened with tetragonal zirconia

DOEpatents

Keefer, Keith D.; Michalske, Terry A.

1986-01-01

A phase transformation-toughened glass ceramic and a process for making it are disclosed. A mixture of particulate network-forming oxide, network-modifying oxide, and zirconium oxide is heated to yield a homogeneous melt, and this melt is then heat-treated to precipitate an appreciable quantity of tetragonal zirconia, which is retained at ambient temperature to form a phase transformation-toughened glass ceramic. Nucleating agents and stabilizing agents may be added to the mixture to facilitate processing and improve the ceramic's properties. Preferably, the mixture is first melted at a temperature from 1200.degree. to 1700.degree. C. and is then heat-treated at a temperature within the range of 800.degree. to 1200.degree. C. in order to precipitate tetragonal ZrO.sub.2. The composition, as well as the length and temperature of the heat-treatment, must be carefully controlled to prevent solution of the precipitated tetragonal zirconia and subsequent conversion to the monoclinic phase.

Structural crossover from nonmodulated to long-period modulated tetragonal phase and anomalous change in ferroelectric properties in the lead-free piezoelectric N a1 /2B i1 /2Ti O3-BaTi O3

NASA Astrophysics Data System (ADS)

Rao, Badari Narayana; Khatua, Dipak Kumar; Garg, Rohini; Senyshyn, Anatoliy; Ranjan, Rajeev

2015-06-01

The highly complex structure-property interrelationship in the lead-free piezoelectric (x )N a1 /2B i1 /2Ti O3- (1 -x ) BaTi O3 is a subject of considerable contemporary debate. Using comprehensive x-ray, neutron diffraction, dielectric, and ferroelectric studies, we have shown the existence of a new criticality in this system at x =0.80 , i.e., well within the conventional tetragonal phase field. This criticality manifests as a nonmonotonic variation of the tetragonality and coercivity and is shown to be associated with a crossover from a nonmodulated tetragonal phase (for x <0.8 ) to a long-period modulated tetragonal phase (for x >0.80 ). It is shown that the stabilization of long-period modulation introduces a characteristic depolarization temperature in the system. While differing qualitatively from the two-phase model often suggested for the critical compositions of this system, our results support the view with regard to the tendency in perovskites to stabilize long-period modulated structures as a result of complex interplay of antiferrodistortive modes [Bellaiche and Iniguez, Phys. Rev. B 88, 014104 (2013), 10.1103/PhysRevB.88.014104; Prosandeev, Wang, Ren, Iniguez, ands Bellaiche, Adv. Funct. Mater. 23, 234 (2013), 10.1002/adfm.201201467].

Raman spectroscopy analysis of air grown oxide scale developed on pure zirconium substrate

NASA Astrophysics Data System (ADS)

Kurpaska, L.; Favergeon, J.; Lahoche, L.; El-Marssi, M.; Grosseau Poussard, J.-L.; Moulin, G.; Roelandt, J.-M.

2015-11-01

Using Raman spectroscopy technique, external and internal parts of zirconia oxide films developed at 500 °C and 600 °C on pure zirconium substrate under air at normal atmospheric pressure have been examined. Comparison of Raman peak positions of tetragonal and monoclinic zirconia phases, recorded during the oxide growth at elevated temperature, and after cooling at room temperature have been presented. Subsequently, Raman peak positions (or shifts) were interpreted in relation with the stress evolution in the growing zirconia scale, especially closed to the metal/oxide interface, where the influence of compressive stress in the oxide is the biggest. Reported results, for the first time show the presence of a continuous layer of tetragonal zirconia phase developed in the proximity of pure zirconium substrate. Based on the Raman peak positions we prove that this tetragonal layer is stabilized by the high compressive stress and sub-stoichiometry level. Presence of the tetragonal phase located in the outer part of the scale have been confirmed, yet its Raman characteristics suggest a stress-free tetragonal phase, therefore different type of stabilization mechanism. Presented study suggest that its stabilization could be related to the lattice defects introduced by highstoichiometry of zirconia or presence of heterovalent cations.

Thermodynamic theory of intrinsic finite-size effects in PbTiO3 nanocrystals. I. Nanoparticle size-dependent tetragonal phase stability

NASA Astrophysics Data System (ADS)

Akdogan, E. K.; Safari, A.

2007-03-01

We propose a phenomenological intrinsic finite-size effect model for single domain, mechanically free, and surface charge compensated ΔG-P ⃗s-ξ space, which describes the decrease in tetragonal phase stability with decreasing ξ rigorously.

Temperature controlled evolution of monoclinic to super-tetragonal phase of epitaxial BiFeO3 thin films on La0.67Sr0.33MnO3 buffered SrTiO3 substrate

NASA Astrophysics Data System (ADS)

Singh, Anar; Kaifeng, Dong; Chen, Jing-Sheng

2018-03-01

Epitaxial BiFeO3 thin films of 130nm were deposited by pulsed laser deposition (PLD) technique on La0.67Sr0.33MnO3 buffered SrTiO3 (001) substrate at various temperatures under different ambient oxygen pressures. Reciprocal space mapping reveals that, with decreasing temperature and oxygen pressure, the broadly reported monoclinic phase (MA) of BiFeO3 thin film initially transforms to a tetragonal phase (T1) with c/a =1.05 (1) in a narrow girth of deposition condition and then to a super-tetragonal phase (T2) with giant c/a = 1.24 (1), as confirmed by reciprocal space mapping using high resolution x-ray diffraction. The surface morphology of the films reveals the island growth of the BiFeO3 films deposited at low temperatures. We propose that the transformation from monoclinic to the super-tetragonal phase is essentially due to the manifestation of excess local strain as a result of the island growth. This study offers a recipe to grow the super-tetragonal phase of BiFeO3, with giant c/a =1.24 (1) which exhibits exceptionally large ferroelectric polarization, on ferromagnetic layer La0.67Sr0.33MnO3. This phase of BiFeO3 can be utilized for the ferroelectric control of magnetism at the interface of BiFeO3 and La0.67Sr0.33MnO3.

The p- T phase diagram of KNbO 3 by a dielectric constant measurement

NASA Astrophysics Data System (ADS)

Kobayashi, Y.; Endo, S.; Deguchi, K.; Ming, L. C.; Zou, G.

2001-11-01

A dielectric constant measurement was carried out on perovskite-type ferroelectrics KNbO 3 over a wide range of temperature under high pressure. The temperature- and pressure-dependence of the dielectric constant clarified that all temperatures of the transitions from the ferroelectric rhombohedral to orthorhombic, to tetragonal and then to the paraelectric cubic phase, decrease with increasing pressure. These results indicate that the orthorhombic-tetragonal transition takes place at 8.5 GPa and the tetragonal-cubic transition at 11 GPa, at room temperature.

Template assisted strain tuning and phase stabilization in epitaxial BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Saj Mohan M., M.; Ramadurai, Ranjith

2018-04-01

Strain engineering is a key to develop novel properties in functional materials. We report a strain mediated phase stabilization and epitaxial growth of bismuth ferrite(BiFeO3) thin films on LaAlO3 (LAO) substrates. The strain in the epitaxial layer is controlled by controlling the thickness of bottom electrode where the thickness of the BFO is kept constant. The thickness of La0.7Sr0.3MnO3(LSMO) template layer was optimized to grow completely strained tetragonal, tetragonal/rhombohedral mixed phase and fully relaxed rhombohedral phase of BFO layers. The results were confirmed with coupled-θ-2θ scan, and small area reciprocal space mapping. The piezoelectric d33 (˜ 45-48 pm/V) coefficient of the mixed phase was relatively larger than the strained tetragonal and relaxed rhombohedral phase for a given thickness.

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

Wang, Peigong; Fan, Caimei, E-mail: fancm@163.com; Wang, Yawen

Graphical abstract: The cubic phase BaTiO{sub 3} nanoparticles can be obtained at 600 °C and changed into tetragonal phase at 900 °C by a dual chelating sol–gel method, and the photocatalytic activities of the photocatalysts calcined at different temperatures were investigated by the removal of humic acid (HA) from water under UV light irradiation. Highlights: ► The humic acid in water was firstly degradated by BaTiO{sub 3} photocatalyst. ► The cubic BaTiO{sub 3} was obtained and changed into tetragonal phase at lower temperature. ► The chelating agents had an important influence on the phase formation of BaTiO{sub 3}. ► Themore » tetragonal phase BaTiO{sub 3} calcined at 900 °C exhibited higher photocatalytic activity under UV irradiation. -- Abstract: In this paper, a dual chelating sol–gel method was used to synthesize BaTiO{sub 3} nanoparticles by using acetylacetone and citric acid as chelating agents. The samples calcined at different temperatures were analyzed by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), scanning electron microscope (SEM) and UV–vis diffuse reflectance spectra (UV–vis). The results indicated that cubic phase BaTiO{sub 3} nanoparticles about 19.6 nm can be obtained at 600 °C and changed into tetragonal phase at 900 °C about 97.1 nm. All the BaTiO{sub 3} nanoparticles showed effective photocatalytic activities on the removal of humic acid (HA) under UV light irradiation. A comparison of single (acetylacetone or citric acid) and dual chelating (acetylacetone and citric acid) synthetic processes was also studied and the results demonstrated that the dual chelating agents indeed reduced phase transformation temperature from cubic to tetragonal BaTiO{sub 3}.« less

Continuous-wave lasing in an organic-inorganic lead halide perovskite semiconductor

NASA Astrophysics Data System (ADS)

Jia, Yufei; Kerner, Ross A.; Grede, Alex J.; Rand, Barry P.; Giebink, Noel C.

2017-12-01

Hybrid organic-inorganic perovskites have emerged as promising gain media for tunable, solution-processed semiconductor lasers. However, continuous-wave operation has not been achieved so far1-3. Here, we demonstrate that optically pumped continuous-wave lasing can be sustained above threshold excitation intensities of 17 kW cm-2 for over an hour in methylammonium lead iodide (MAPbI3) distributed feedback lasers that are maintained below the MAPbI3 tetragonal-to-orthorhombic phase transition temperature of T ≈ 160 K. In contrast with the lasing death phenomenon that occurs for pure tetragonal-phase MAPbI3 at T > 160 K (ref. 4), we find that continuous-wave gain becomes possible at T ≈ 100 K from tetragonal-phase inclusions that are photogenerated by the pump within the normally existing, larger-bandgap orthorhombic host matrix. In this mixed-phase system, the tetragonal inclusions function as carrier recombination sinks that reduce the transparency threshold, in loose analogy to inorganic semiconductor quantum wells, and may serve as a model for engineering improved perovskite gain media.

Electronic properties of two-dimensional zinc oxide in hexagonal, (4,4)-tetragonal, and (4,8)-tetragonal structures by using Hybrid Functional calculation

NASA Astrophysics Data System (ADS)

Supatutkul, C.; Pramchu, S.; Jaroenjittichai, A. P.; Laosiritaworn, Y.

2017-09-01

This work reports the structures and electronic properties of two-dimensional (2D) ZnO in hexagonal, (4,8)-tetragonal, and (4,4)-tetragonal monolayer using GGA and HSE-hybrid functional. The calculated results show that the band gaps of 2D ZnO sheets are wider than those of the bulk ZnO. The hexagonal and (4,8)-tetragonal phases yield direct band gaps, which are 4.20 eV, and 4.59 eV respectively, while the (4,4)-tetragonal structure has an indirect band gap of 3.02 eV. The shrunken Zn-O bond lengths in the hexagonal and (4,8)-tetragonal indicate that they become more ionic in comparison with the bulk ZnO. In addition, the hexagonal ZnO sheet is the most energetically favourable. The total energy differences of (4,8)-tetragonal and (4,4)-tetragonal sheets from that of hexagonal monolayer (per formula unit) are 197 meV and 318 meV respectively.

Structures, Phase Transitions and Tricritical Behavior of the Hybrid Perovskite Methyl Ammonium Lead Iodide

DOE PAGES

Whitfield, P. S.; Herron, N.; Guise, W. E.; ...

2016-10-21

Here, we examine the crystal structures and structural phase transitions of the deuterated, partially deuterated and hydrogenous organic-inorganic hybrid perovskite methyl ammonium lead iodide (MAPbI 3) using time-of-flight neutron and synchrotron X-ray powder diffraction. Near 330 K the high temperature cubic phases transformed to a body-centered tetragonal phase. The variation of the order parameter Q for this transition scaled with temperature T as Q (T c-T) , where T c is the critical temperature and the exponent was close to , as predicted for a tricritical phase transition. We also observed coexistence of the cubic and tetragonal phases over amore » range of temperature in all cases, demonstrating that the phase transition was in fact first-order, although still very close to tricritical. Upon cooling further, all the tetragonal phases transformed into a low temperature orthorhombic phase around 160 K, again via a first-order phase transition. Finally, based upon these results, we discuss the impact of the structural phase transitions upon photovoltaic performance of MAPbI 3 based solar cells.« less

Domain wall and interphase boundary motion in (1-x)Bi(Mg 0.5 Ti 0.5 )O 3 –xPbTiO 3 near the morphotropic phase boundary

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

Tutuncu, Goknur; Chen, Jun; Fan, Longlong

Electric field-induced changes in the domain wall motion of (1-x)Bi(Mg 0.5Ti 0.5)O 3–xPbTiO 3 (BMT-xPT) near the morphotropic phase boundary (MPB) where x = 0.37 (BMT-37PT) and x =0.38 (BMT-38PT), are studied by means of synchrotron x-ray diffraction. Through Rietveld analysis and profile fitting, a mixture of coexisting monoclinic (Cm) and tetragonal (P4mm) phases is identified at room temperature. Extrinsic contributions to the property coefficients are evident from electric-field-induced domain wall motion in both the tetragonal and monoclinic phases, as well as through the interphase boundary motion between the two phases. Domain wall motion in the tetragonal and monoclinic phasesmore » for BMT-37PT is larger than that of BMT-38PT, possibly due to this composition's closer proximity to the MPB. Increased interphase boundary motion was also observed in BMT-37PT. Lattice strain, which is a function of both intrinsic piezoelectric strain and elastic interactions of the grains (the latter originating from domain wall and interphase boundary motion), is similar for the respective tetragonal and monoclinic phases.« less

Size-dependent phase transition in methylammonium lead iodide perovskite microplate crystals

PubMed Central

Li, Dehui; Wang, Gongming; Cheng, Hung-Chieh; Chen, Chih-Yen; Wu, Hao; Liu, Yuan; Huang, Yu; Duan, Xiangfeng

2016-01-01

Methylammonium lead iodide perovskite has attracted considerable recent interest for solution processable solar cells and other optoelectronic applications. The orthorhombic-to-tetragonal phase transition in perovskite can significantly alter its optical, electrical properties and impact the corresponding applications. Here, we report a systematic investigation of the size-dependent orthorhombic-to-tetragonal phase transition using a combined temperature-dependent optical, electrical transport and transmission electron microscopy study. Our studies of individual perovskite microplates with variable thicknesses demonstrate that the phase transition temperature decreases with reducing microplate thickness. The sudden decrease of mobility around phase transition temperature and the presence of hysteresis loops in the temperature-dependent mobility confirm that the orthorhombic-to-tetragonal phase transition is a first-order phase transition. Our findings offer significant fundamental insight on the temperature- and size-dependent structural, optical and charge transport properties of perovskite materials, and can greatly impact future exploration of novel electronic and optoelectronic devices from these materials. PMID:27098114

Size-dependent phase transition in methylammonium lead iodide perovskite microplate crystals

DOE PAGES

Li, Dehui; Wang, Gongming; Cheng, Hung -Chieh; ...

2016-04-21

Methylammonium lead iodide perovskite has attracted considerable recent interest for solution processable solar cells and other optoelectronic applications. The orthorhombic-to-tetragonal phase transition in perovskite can significantly alter its optical, electrical properties and impact the corresponding applications. Here, we report a systematic investigation of the size-dependent orthorhombic-to-tetragonal phase transition using a combined temperature-dependent optical, electrical transport and transmission electron microscopy study. Our studies of individual perovskite microplates with variable thicknesses demonstrate that the phase transition temperature decreases with reducing microplate thickness. The sudden decrease of mobility around phase transition temperature and the presence of hysteresis loops in the temperature-dependent mobility confirmmore » that the orthorhombic-to-tetragonal phase transition is a first-order phase transition. Lastly, our findings offer significant fundamental insight on the temperature-and size-dependent structural, optical and charge transport properties of perovskite materials, and can greatly impact future exploration of novel electronic and optoelectronic devices from these materials.« less

Revealing the hidden structural phases of FeRh

NASA Astrophysics Data System (ADS)

Kim, Jinwoong; Ramesh, R.; Kioussis, Nicholas

2016-11-01

Ab initio electronic structure calculations reveal that tetragonal distortion has a dramatic effect on the relative stability of the various magnetic structures (C-, A-, G-, A'-AFM, and FM) of FeRh giving rise to a wide range of novel stable/metastable structures and magnetic phase transitions between these states. We predict that the cubic G-AFM structure, which was believed thus far to be the ground state, is metastable and that the tetragonally expanded G-AFM is the stable structure. The low energy barrier separating these states suggests phase coexistence at room temperature. We propose an A'-AFM phase to be the global ground state among all magnetic phases which arises from the strain-induced tuning of the exchange interactions. The results elucidate the underlying mechanism for the recent experimental findings of electric-field control of magnetic phase transition driven via tetragonal strain. The magnetic phase transitions open interesting prospects for exploiting strain engineering for the next-generation memory devices.

Temperature-dependent electron paramagnetic resonance detect oxygen vacancy defects and Cr valence of tetragonal Ba(Ti1-xCrx)O3 ceramics

NASA Astrophysics Data System (ADS)

Han, Dan-Dan; Lu, Da-Yong; Meng, Fan-Ling; Yu, Xin-Yu

2018-03-01

Temperature-dependent electron paramagnetic resonance (EPR) study was employed to detect oxygen vacancy defects in the tetragonal Ba(Ti1-xCrx)O3 (x = 5%) ceramic for the first time. In the rhombohedral phase below -150 °C, an EPR signal at g = 1.955 appeared in the insulating Ba(Ti1-xCrx)O3 (x = 5%) ceramic with an electrical resistivity of 108 Ω cm and was assigned to ionized oxygen vacancy defects. Ba(Ti1-xCrx)O3 ceramics exhibited a tetragonal structure except Ba(Ti1-xCrx)O3 (x = 10%) with a tetragonal-hexagonal mixed phase and a first-order phase transition dielectric behavior (ε‧m > 11,000). Mixed valence Cr ions could coexist in ceramics, form CrTi‧-VOrad rad or CrTirad-TiTi‧ defect complexes and make no contribution to a dielectric peak shift towards low temperature.

Enhanced piezoelectricity in A B O3 ferroelectrics via intrinsic stress-driven flattening of the free-energy profile

NASA Astrophysics Data System (ADS)

Feng, Yu; Li, Wei-Li; Yu, Yang; Jia, He-Nan; Qiao, Yu-Long; Fei, Wei-Dong

2017-11-01

An approach to greatly enhance the piezoelectric properties (˜4 00 pC/N) of the tetragonal BaTi O3 polycrystal using a small number of A -site acceptor-donor substitutions [D. Xu et al., Acta Mater. 79, 84 (2014), 10.1016/j.actamat.2014.07.023] has been proposed. In this study, Pb (ZrTi ) O3 (PZT) based polycrystals with various crystal symmetries (tetragonal, rhombohedral, and so on) were chosen to investigate the piezoelectricity enhancement mechanism. X-ray diffraction results show that doping generates an intrinsic uniaxial compressive stress along the [001] pc direction in the A B O3 lattices. Piezoelectric maps in the parameter space of temperature and Ti concentration in the PZT and doped system show a more significant enhancement effect of L i+-A l3 + codoping in tetragonal PZT than in the rhombohedral phase. Phenomenological thermodynamic analysis indicates that the compressive stress results in more serious flattening of the free-energy profile in tetragonal PZT, compared with that in the rhombohedral phase. The chemical stress obtained by this acceptor-donor codoping can be utilized to optimize the piezoelectric performance on the tetragonal-phase site of the morphotropic phase boundary in the PZT system. The present study provides a promising route to the large piezoelectric effect induced by chemical-stress-driven flattening of the free-energy profile.

Direct synthesis of ultrafine tetragonal BaTiO3 nanoparticles at room temperature

PubMed Central

2011-01-01

A large quantity of ultrafine tetragonal barium titanate (BaTiO3) nanoparticles is directly synthesized at room temperature. The crystalline form and grain size are checked by both X-ray diffraction and transmission electron microscopy. The results revealed that the perovskite nanoparticles as fine as 7 nm have been synthesized. The phase transition of the as-prepared nanoparticles is investigated by the temperature-dependent Raman spectrum and shows the similar tendency to that of bulk BaTiO3 materials. It is confirmed that the nanoparticles have tetragonal phase at room temperature. PMID:21781339

Domain wall and interphase boundary motion in (1−x)Bi(Mg{sub 0.5}Ti{sub 0.5})O{sub 3}–xPbTiO{sub 3} near the morphotropic phase boundary

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

Tutuncu, Goknur; Chen, Jun; Fan, Longlong

Electric field-induced changes in the domain wall motion of (1−x)Bi(Mg{sub 0.5}Ti{sub 0.5})O{sub 3}–xPbTiO{sub 3} (BMT-xPT) near the morphotropic phase boundary (MPB) where x = 0.37 (BMT-37PT) and x = 0.38 (BMT-38PT), are studied by means of synchrotron x-ray diffraction. Through Rietveld analysis and profile fitting, a mixture of coexisting monoclinic (Cm) and tetragonal (P4mm) phases is identified at room temperature. Extrinsic contributions to the property coefficients are evident from electric-field-induced domain wall motion in both the tetragonal and monoclinic phases, as well as through the interphase boundary motion between the two phases. Domain wall motion in the tetragonal and monoclinic phases for BMT-37PT ismore » larger than that of BMT-38PT, possibly due to this composition's closer proximity to the MPB. Increased interphase boundary motion was also observed in BMT-37PT. Lattice strain, which is a function of both intrinsic piezoelectric strain and elastic interactions of the grains (the latter originating from domain wall and interphase boundary motion), is similar for the respective tetragonal and monoclinic phases.« less

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

Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co substituted CaFe 2As 2. We use Atomic Force, Magnetic Force and Scanning Tunneling Microscopy (AFM, MFM and STM) to identify the domains and characterize their properties, nding in particular that tetragonal superconducting domains are very elongated, more than several tens of μm long and about 30 nm wide, have the same Tc than unstrained samples and hold vortices in a magnetic eld. Thus, biaxial strain produces a phase separated state, where each phase is equivalent to what is found at either side of the rstmore » order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first order quantum phase transitions lead to nanometric size phase separation under the influence of strain.« less

A sol-powder coating technique for fabrication of yttria stabilised zirconia

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

Wattanasiriwech, Darunee; Wattanasiriwech, Suthee; Stevens, Ron

Yttria stabilised zirconia has been prepared using a simple sol-powder coating technique. The polymeric yttria sol, which was prepared using 1,3 propanediol as a network modifier, was homogeneously mixed with nanocrystalline zirconia powder and it showed a dual function: as a binder which promoted densification and a phase modifier which stabilised zirconia in the tetragonal and cubic phases. Thermal analysis and X-ray diffraction revealed that the polymeric yttria sol which decomposed at low temperature into yttrium oxide could change the m {sup {yields}} t phase transformation behaviour of the zirconia, possibly due to the small particle size and very highmore » surface area of both yttria and zirconia particles allowing rapid alloying. The sintered samples exhibited three crystalline phases: monoclinic, tetragonal and cubic, in which cubic and tetragonal are the major phases. The weight fractions of the individual phases present in the selected specimens were determined using quantitative Rietveld analysis.« less

Opportunities for functional oxides in yttrium oxide-titanium oxide-zirconium oxide system: Applications for novel thermal barrier coatings

NASA Astrophysics Data System (ADS)

Francillon, Wesley

This dissertation is an investigation of materials and processed under consideration for next generation thermal structural oxides with potential applications as thermal barrier coatings; wherein, high temperature stability and mechanical properties affect durability. Two notable next generation materials systems under investigation are pyrochlore and co-doped zirconia oxides. The motivation for this work is based on current limitations of the currently used thermal barrier material of yttria stabilized zirconia (YSZ) deposited by the plasma spray processes. The rapid quenching associated with the plasma spray process, results in a metastable structure that is a non-transformable tetragonal structure in the yttria partially stabilized zirconia system rather than the equilibrium anticipated two phase mixture of cubic and monoclinic phases. It has been shown that this metastable structure offers enhanced toughness and thus durability during thermomechanical cycling from the operating temperatures in excess of 1000C to ambient. However, the metastable oxides are susceptible to partitioning at temperatures greater than 1200C, thus resulting in a transformation of the tetragonal phase oxides. Transformations of the tetragonal prime phase into the parent cubic and tetragonal prime phase result in coating degradation. Several of the emerging oxides are based on rare earth additions to zirconia. However, there is limited information of the high temperature stability of these oxide coatings and more notably these compositions exhibit limited toughness for durable performance. A potential ternary composition based on the YSZ system that offers the ability to tailor the phase structure is based YO1.5-TiO2 -ZrO2. The ternary of YO1.5-TiO2-ZrO 2 has the current TBC composition of seven molar percent yttria stabilized zirconia, pyrochlore phase oxide and zirconia doped with yttria and titania additions (Ti-YSZ). The Ti-YSZ phase field is of interest because at equilibrium it is a single tetragonal phase. Thus, compositions are of single phase tetragonal phase, theoretically, should not undergo high temperature partitioning. Single Tetragonal phase oxides of Ti-YSZ also offer the possibility of enhanced toughness and higher temperature stability akin to those observed in yttria partially stabilized zirconia. Many pyrochlore oxides are under review because they have shown to have lower thermal conductivity than YSZ oxides. This study focused on chemically synthesizing homogeneous starting material compositions in a metastable state (preferably amorphous), following its evolution according to the phase hierarchy under conditions of kinetic constraints. The current equilibrium diagram of YO1.5-TiO2-ZrO 2 is based on theoretical calculations. One of the contributions of this work is the redefined phase fields in YO1.5-TiO2-ZrO 2 based on our experimental results. Investigated compositions were based on tie lines of Y2-xTi2ZrxO7+x/2 and Y2Ti2-yZryO7 representing substitution of Zr4+ for Y3+ and Zr4+ for Ti4+ respectively. More notably, we observed extended metastable phases in pyrochlore and fluorite oxides at low temperature. The significance of this result is that it offers a larger compositional range for investing pyrochlore oxides with associated high temperature phase stability for TBC applications. In tetragonal oxides, our results showed that Ti-YSZ results have slower partitioning kinetics in comparison to YSZ at high temperature. This study also emphasized the deposition of advanced ceramic coatings by plasma spray for tetragonal and pyrochlore systems, compositionally complex functional oxides that may potentially have lower thermal conductivity values compared to current YSZ oxides. Next generation thermal barrier coatings require powders with high chemical purity, chemical homogeneity, controlled particle size/shape and pertinent phase state. Thermal spray offers an avenue to create novel materials and deposits directly from the precursor and compositionally controlled powder feedstock. This study contributed to investigating an unexplored field that offers a variety of opportunities in materials synthesis that would not be possible by conventional methods. Understanding processing-microstructure-property correlations is of considerable importance in thermal spray of functional oxide materials. This thesis demonstrated by radio-frequency thermal spray that the complex pyrochlore oxide Y 2Ti2O7 could be deposited by directly injecting molecularly mixed precursors to form oxide coatings. Structural analysis revealed the metastable fluorite phase; however, with thermal treatments at relatively low temperature of 700°C the pyrochlore phase was obtained. For Ti-YSZ coatings, the tetragonal phase oxides were obtained with unique microstructures, however, the tetragonal prime destabilized at 1200°C. This dissertation explored novel oxide compositions through detailed structural analysis. The approach presented a comprehensive and integrated investigation as it pertains to phase evolution of oxides in powder feedstock to coating characteristics (phase/properties).

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.

Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe2As2 close to a first-order phase transition

NASA Astrophysics Data System (ADS)

Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.; Kreyssig, Andreas; Ran, S.; Bud'ko, Sergey L.; Canfield, Paul C.; Mompean, Federico J.; García-Hernández, Mar; Munuera, Carmen; Guillamón, Isabel; Suderow, Hermann

2018-01-01

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co-substituted CaFe2As2 . We use atomic force, magnetic force, and scanning tunneling microscopy to identify the domains and characterize their properties, finding in particular that tetragonal superconducting domains are very elongated, more than several tens of micrometers long and about 30 nm wide; have the same Tc as unstrained samples; and hold vortices in a magnetic field. Thus, biaxial strain produces a phase-separated state, where each phase is equivalent to what is found on either side of the first-order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of the order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first-order quantum phase transitions lead to nanometric-size phase separation under the influence of strain.

Direct visualization of phase separation between superconducting and nematic domains in Co-doped CaFe 2 As 2 close to a first-order phase transition

DOE PAGES

Fente, Antón; Correa-Orellana, Alexandre; Böhmer, Anna E.; ...

2018-01-09

We show that biaxial strain induces alternating tetragonal superconducting and orthorhombic nematic domains in Co substituted CaFe 2As 2. We use Atomic Force, Magnetic Force and Scanning Tunneling Microscopy (AFM, MFM and STM) to identify the domains and characterize their properties, nding in particular that tetragonal superconducting domains are very elongated, more than several tens of μm long and about 30 nm wide, have the same Tc than unstrained samples and hold vortices in a magnetic eld. Thus, biaxial strain produces a phase separated state, where each phase is equivalent to what is found at either side of the rstmore » order phase transition between antiferromagnetic orthorhombic and superconducting tetragonal phases found in unstrained samples when changing Co concentration. Having such alternating superconducting domains separated by normal conducting domains with sizes of order of the coherence length opens opportunities to build Josephson junction networks or vortex pinning arrays and suggests that first order quantum phase transitions lead to nanometric size phase separation under the influence of strain.« less

Thermal Aging Behavior of Axial Suspension Plasma-Sprayed Yttria-Stabilized Zirconia (YSZ) Thermal Barrier Coatings

NASA Astrophysics Data System (ADS)

Zhao, Yuexing; Wang, Liang; Yang, Jiasheng; Li, Dachuan; Zhong, Xinghua; Zhao, Huayu; Shao, Fang; Tao, Shunyan

2015-02-01

7.5YSZ thermal barrier coatings (TBCs) were deposited onto the stainless steel substrates using axial suspension plasma spraying (ASPS). Free-standing coatings were isothermally aged in air from 1200 to 1600 °C for 24 h and at 1550 °C for 20 to 100 h, respectively. Thermal aging behavior such as phase composition, microstructure evolutions, grain growth, and mechanical properties for thermal-aged coatings were investigated. Results show that the as-sprayed metastable tetragonal (t'-ZrO2) phase decomposes into equilibrium tetragonal (t-ZrO2) and cubic (c-ZrO2) phases during high-temperature exposures. Upon further cooling, the c-ZrO2 may be retained or transform into another metastable tetragonal (t″-ZrO2) phase, and tetragonal → monoclinic phase transformation occurred after 1550 °C/40 h aging treatment. The coating exhibits a unique structure with segmentation cracks and micro/nano-size grains, and the grains grow gradually with increasing aging temperature and time. In addition, the hardness ( H) and Young's modulus ( E) significantly increased as a function of temperature due to healing of pores or cracks and grain growth of the coating. And a nonmonotonic variation is found in the coatings thermal aged at a constant temperature (1550 °C) with prolonged time, this is a synergetic effect of coating sintering and m-ZrO2 phase formation.

Expansion of the tetragonal magnetic phase with pressure in the iron arsenide superconductor Ba 1 - x K x Fe 2 As 2

DOE PAGES

Hassinger, Elena; Gredat, G.; Valade, F.; ...

2016-04-01

In the temperature-concentration phase diagram of most iron-based superconductors, antiferromagnetic order is gradually suppressed to zero at a critical point, and a dome of superconductivity forms around that point. The nature of the magnetic phase and its fluctuations is of fundamental importance for elucidating the pairing mechanism. In Ba 1–xK xFe 2As 2 and Ba 1–xNa xFe 2As 2, it has recently become clear that the usual stripelike magnetic phase, of orthorhombic symmetry, gives way to a second magnetic phase, of tetragonal symmetry, near the critical point, in the range from x = 0.24 to x = 0.28 for Bamore » 1–xK xFe 2As 2. In a prior study, an unidentified phase was discovered for x < 0.24 but under applied pressure, whose onset was detected as a sharp anomaly in the resistivity. Here we report measurements of the electrical resistivity of Ba 1–xK xFe 2As 2 under applied hydrostatic pressures up to 2.75 GPa, for x = 0.22, 0.24, and 0.28. The critical pressure above which the unidentified phase appears is seen to decrease with increasing x and vanish at x = 0.24, thereby linking the pressure-induced phase to the tetragonal magnetic phase observed at ambient pressure. In the temperature-concentration phase diagram of Ba 1–xK xFe 2As 2, we find that pressure greatly expands the tetragonal magnetic phase, while the stripelike phase shrinks. As a result, this reveals that pressure may be a powerful tuning parameter with which to explore the interplay between magnetism and superconductivity in this material.« less

Lattice parameters and structural phase transition of lanthanum titanate perovskite, La0.68(Ti0.95,Al0.05)O3.

PubMed

Ali, Roushown; Yashima, Masatomo

2003-05-01

Lattice parameters and the structural phase transition of La(0.68)(Ti(0.95),Al(0.05))O(3) have been investigated in situ in the temperature range 301-689 K by the synchrotron radiation powder diffraction (SR-PD) technique. High-angular-resolution SR-PD is confirmed to be a powerful technique for determining precise lattice parameters around a phase-transition temperature. The title compound exhibits a reversible phase transition between orthorhombic and tetragonal phases at 622.3 +/- 0.6 K. The following results were obtained: (i) the lattice parameters increased continuously with temperature, while the b/a ratio decreased continuously with temperature and became unity at the orthorhombic-tetragonal transition point; (ii) no hysteresis was observed between the lattice-parameter values measured on heating and on cooling. Results (i) and (ii) indicate that the orthorhombic-tetragonal phase transition is continuous and reversible. The b/a ratio is found to exhibit a more continuous temperature evolution than does the order parameter for a typical second-order phase transition based on Landau theory.

Demonstration of Ru as the 4th ferromagnetic element at room temperature.

PubMed

Quarterman, P; Sun, Congli; Garcia-Barriocanal, Javier; Dc, Mahendra; Lv, Yang; Manipatruni, Sasikanth; Nikonov, Dmitri E; Young, Ian A; Voyles, Paul M; Wang, Jian-Ping

2018-05-25

Development of novel magnetic materials is of interest for fundamental studies and applications such as spintronics, permanent magnetics, and sensors. We report on the first experimental realization of single element ferromagnetism, since Fe, Co, and Ni, in metastable tetragonal Ru, which has been predicted. Body-centered tetragonal Ru phase is realized by use of strain via seed layer engineering. X-ray diffraction and electron microscopy confirm the epitaxial mechanism to obtain tetragonal phase Ru. We observed a saturation magnetization of 148 and 160 emu cm -3 at room temperature and 10 K, respectively. Control samples ensure the ferromagnetism we report on is from tetragonal Ru and not from magnetic contamination. The effect of thickness on the magnetic properties is also studied, and it is observed that increasing thickness results in strain relaxation, and thus diluting the magnetization. Anomalous Hall measurements are used to confirm its ferromagnetic behavior.

Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO3

NASA Astrophysics Data System (ADS)

Rosenberg, Aaron J.; Katmis, Ferhat; Kirtley, John R.; Gedik, Nuh; Moodera, Jagadeesh S.; Moler, Kathryn A.

2017-12-01

The combination of ferromagnets with topological superconductors or insulators allows for new phases of matter that support excitations such as chiral edge modes and Majorana fermions. EuS, a wide-bandgap ferromagnetic insulator with a Curie temperature around 16 K, and SrTiO3 (STO), an important substrate for engineering heterostructures, may support these phases. We present scanning superconducting quantum interference device measurements of EuS grown epitaxially on STO that reveal micron-scale variations in ferromagnetism and paramagnetism. These variations are oriented along the STO crystal axes and only change their configuration upon thermal cycling above the STO cubic-to-tetragonal structural transition temperature at 105 K, indicating that the observed magnetic features are due to coupling between EuS and the STO tetragonal structure. We speculate that the STO tetragonal distortions may strain the EuS, altering the magnetic anisotropy on a micron scale. This result demonstrates that local variation in the induced magnetic order from EuS grown on STO needs to be considered when engineering new phases of matter that require spatially homogeneous exchange.

Nanotwin and phase transformation in tetragonal Pb(Fe1/2Nb1/2)1-xTixO3 single crystal

NASA Astrophysics Data System (ADS)

Tu, C.-S.; Tseng, C.-T.; Chien, R. R.; Schmidt, V. Hugo; Hsieh, C.-M.

2008-09-01

This work is a study of phase transformation in (001)-cut Pb(Fe1/2Nb1/2)1-xTixO3 (x =48%) single crystals by means of dielectric permittivity, domain structure, and in situ x-ray diffraction. A first-order T(TNT)-C(TNT) phase transition was observed at the Curie temperature TC≅518 K upon zero-field heating. T, TNT, and C are tetragonal, tetragonal nanotwin, and cubic phases, respectively. T(TNT) and C(TNT) indicate that minor TNT domains reside in the T and C matrices. Nanotwins, which can cause broad diffraction peak, remain above TC≅518 K and give an average microscopic cubic symmetry in the polarizing microscopy. Colossal dielectric permittivity (>104) was observed above room temperature with strong frequency dispersion. This study suggests that nanotwins can play an important role in relaxor ferroelectric crystals while phase transition takes place. The Fe ion is a potential candidate as a B-site dopant for enhancing dielectric permittivity.

Ionic and Optical Properties of Methylammonium Lead Iodide Perovskite across the Tetragonal-Cubic Structural Phase Transition

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

Hoque, Md Nadim Ferdous; Islam, Nazifah; Li, Zhen

Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3). However, the ionic and optical properties of MAPbI3 in such a temperature range, and particularly, dramatic changes in these properties resulting from a structural phase transition, are not well studied. Herein, we report a striking contrast at approximately 45 degrees C in the ionic/electrical properties of MAPbl3 owing to a change of the ion activation energy from 0.7 to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. Thesemore » observations can be explained by the 'continuous' nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature as when tetragonal-cubic structural phase transition occurs.« less

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase

NASA Technical Reports Server (NTRS)

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar; Curreri, Peter A. (Technical Monitor)

2002-01-01

Experimental evidence indicates a dominant role of solution phase interactions in nucleating and growing tetragonal lysozyme crystals. These interactions are extensive, even at saturation, and may be a primary cause of misoriented regions in crystals grown on Earth. Microgravity, by limiting interfacial concentrations to diffusion-controlled levels, may benefit crystal quality by also reducing the extent of associated species present at the interface.

Atomistic simulation of cubic and tetragonal phases of U-Mo alloy: Structure and thermodynamic properties

NASA Astrophysics Data System (ADS)

Starikov, S. V.; Kolotova, L. N.; Kuksin, A. Yu.; Smirnova, D. E.; Tseplyaev, V. I.

2018-02-01

We studied structure and thermodynamic properties of cubic and tetragonal phases of pure uranium and U-Mo alloys using atomistic simulations: molecular dynamics and density functional theory. The main attention was paid to the metastable γ0 -phase that is formed in U-Mo alloys at low temperature. Structure of γ0 -phase is similar to body-centered tetragonal (bct) lattice with displacement of a central atom in the basic cell along [ 001 ] direction. Such displacements have opposite orientations for part of the neighbouring basic cells. In this case, such ordering of the displacements can be designated as antiferro-displacement. Formation of such complex structure may be interpreted through forming of short U-U bonds. At heating, the tetragonal structure transforms into cubic γs -phase, still showing ordering of central atom displacements. With rise in temperature, γs -phase transforms to γ-phase with a quasi body-centered cubic (q-bcc) lattice. The local positions of uranium atoms in γ-phase correspond to γs -phase, however, orientations of the central atom displacements become disordered. Transition from γ0 to γ can be considered as antiferro-to paraelastic transition of order-disorder type. This approach to the structure description of uranium alloy allows to explain a number of unusual features found in the experiments: anisotropy of lattice at low temperature; remarkably high self-diffusion mobility in γ-phase; decreasing of electrical resistivity at heating for some alloys. In addition, important part of this work is the development of new interatomic potential for U-Mo system made with taking into account details of studied structures.

Grain size dependent phase stabilities and presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of (1-x)Bi(Mg1/2Ti1/2)O3-xPbTiO3 piezoceramics

NASA Astrophysics Data System (ADS)

Upadhyay, Ashutosh; Singh, Akhilesh Kumar

2015-04-01

Results of the room temperature structural studies on (1-x)Bi(Mg1/2Ti1/2)O3-xPbTiO3 ceramics using Rietveld analysis of the powder x-ray diffraction data in the composition range 0.28 ≤ x ≤ 0.45 are presented. The morphotropic phase boundary region exhibits coexistence of monoclinic (space group Pm) and tetragonal (space group P4 mm) phases in the composition range 0.33 ≤ x ≤ 0.40. The structure is nearly single phase monoclinic (space group Pm) in the composition range 0.28 ≤ x ≤ 0.32. The structure for the compositions with x ≥ 0.45 is found to be predominantly tetragonal with space group P4 mm. Rietveld refinement of the structure rules out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase boundary region reported by earlier authors. The Rietveld structure analysis for the sample x = .35 calcined at various temperatures reveals that phase fraction of the coexisting phases in the morphotropic phase boundary region varies with grain size. The structural parameters of the two coexisting phases also change slightly with changing grain size.

Composition-dependent properties and phase stability of Fe-Pd ferromagnetic shape memory alloys: A first-principles study

NASA Astrophysics Data System (ADS)

Li, Chun-Mei; Hu, Yan-Fei

2017-12-01

The composition-dependent properties and their correlation with the phase stability of Fe75+xPd25-x (- 10.0 ≤x ≤10.0 ) alloys are systematically investigated by using first-principles exact muffin-tin orbitals (EMTO)-coherent potential approximation (CPA) calculations. It is shown that the martensitic transformation (MT) from L 12 to body-centered-tetragonal (bct) occurs in the ordered alloys with about -5.0 ≤x ≤10.0 . In both the L 12 and bct phases, the evaluated a and c/a agree well with the available experimental data; the average magnetic moment per atom increases whereas the local magnetic moments of Fe atoms, dependent on both their positions and the structure of the alloy, decrease with increasing x. The tetragonal shear elastic constant of the L 12 phase ( C ' ) decreases whereas that of the bct phase (Cs) increases with x. The tetragonality of the martensite ( |1 -c /a | ) increases whereas its energy relative to the austenite with a negative value decreases with Fe addition. All these effects account for the increase of MT temperature (TM) with x. The MT from L 12 to bct is finally confirmed originating from the splitting of Fe 3d Eg and T2 g bands upon tetragonal distortion due to the Jahn-Teller effect.

Finite element analysis of the tetragonal to monoclinic phase transformation during oxidation of zirconium alloys

NASA Astrophysics Data System (ADS)

Platt, P.; Frankel, P.; Gass, M.; Howells, R.; Preuss, M.

2014-11-01

Corrosion is a key limiting factor in the degradation of zirconium alloys in light water reactors. Developing a mechanistic understanding of the corrosion process offers a route towards improving safety and efficiency as demand increases for higher burn-up of fuel. Oxides formed on zirconium alloys are composed of both monoclinic and meta-stable tetragonal phases, and are subject to a number of potential mechanical degradation mechanisms. The work presented investigates the link between the tetragonal to monoclinic oxide phase transformation and degradation of the protective character of the oxide layer. To achieve this, Abaqus finite element analysis of the oxide phase transformation has been carried out. Study of the change in transformation strain energy shows how relaxation of oxidation induced stress and fast fracture at the metal-oxide interface could destabilise the tetragonal phase. Central to this is the identification of the transformation variant most likely to form, and understanding why twinning of the transformed grain is likely to occur. Development of transformation strain tensors and analysis of the strain components allows some separation of dilatation and shear effects. Maximum principal stress is used as an indication of fracture in the surrounding oxide layer. Study of the stress distributions shows the way oxide fracture is likely to occur and the differing effects of dilatation and shape change. Comparison with literature provides qualitative validation of the finite element simulations.

Building Materials from Colloidal Nanocrystal Assemblies: Molecular Control of Solid/Solid Interfaces in Nanostructured Tetragonal ZrO 2

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

Shaw, Santosh; Silva, Tiago F.; Bobbitt, Jonathan M.

We describe in this paper a bottom-up approach to control the composition of solid/solid interfaces in nanostructured materials, and we test its effectiveness on tetragonal ZrO 2, an inorganic phase of great technological significance. Colloidal nanocrystals capped with trioctylphosphine oxide (TOPO) or oleic acid (OA) are deposited, and the organic fraction of the ligands is selectively etched with O 2 plasma. The interfaces in the resulting all-inorganic colloidal nanocrystal assemblies are either nearly bare (for OA-capped nanocrystals) or terminated with phosphate groups (for TOPO-capped nanocrystals) resulting from the reaction of phosphine oxide groups with plasma species. The chemical modification ofmore » the interfaces has extensive effects on the thermodynamics and kinetics of the material. Different growth kinetics indicate different rate limiting processes of growth (surface diffusion for the phosphate-terminated surfaces and dissolution for the “bare” surfaces). Phosphate termination led to a higher activation energy of growth, and a 3-fold reduction in interfacial energy, and facilitated significantly the conversion of the tetragonal phase into the monoclinic phase. Finally, films devoid of residual ligands persisted in the tetragonal phase at temperatures as high as 900 °C for 24 h.« less

Building Materials from Colloidal Nanocrystal Assemblies: Molecular Control of Solid/Solid Interfaces in Nanostructured Tetragonal ZrO 2

DOE PAGES

Shaw, Santosh; Silva, Tiago F.; Bobbitt, Jonathan M.; ...

2017-08-28

We describe in this paper a bottom-up approach to control the composition of solid/solid interfaces in nanostructured materials, and we test its effectiveness on tetragonal ZrO 2, an inorganic phase of great technological significance. Colloidal nanocrystals capped with trioctylphosphine oxide (TOPO) or oleic acid (OA) are deposited, and the organic fraction of the ligands is selectively etched with O 2 plasma. The interfaces in the resulting all-inorganic colloidal nanocrystal assemblies are either nearly bare (for OA-capped nanocrystals) or terminated with phosphate groups (for TOPO-capped nanocrystals) resulting from the reaction of phosphine oxide groups with plasma species. The chemical modification ofmore » the interfaces has extensive effects on the thermodynamics and kinetics of the material. Different growth kinetics indicate different rate limiting processes of growth (surface diffusion for the phosphate-terminated surfaces and dissolution for the “bare” surfaces). Phosphate termination led to a higher activation energy of growth, and a 3-fold reduction in interfacial energy, and facilitated significantly the conversion of the tetragonal phase into the monoclinic phase. Finally, films devoid of residual ligands persisted in the tetragonal phase at temperatures as high as 900 °C for 24 h.« less

Effect of Cs content on K1-xCsxAlSi2O6 ceramic solidification forms

NASA Astrophysics Data System (ADS)

Li, Jun; Duan, Jianxia; Hou, Li; Lu, Zhongyuan

2018-02-01

K1-xCsx-geopolymers with chemical compositions of about K1-xCsxAlSi2O6·nH2O were used as precursors to prepare K1-xCsxAlSi2O6 ceramic solidification forms through the thermal treatment method. The structures of K1-xCsxAlSi2O6 ceramic solidification forms obtained at different sintering temperatures have been characterized by X-ray diffraction, scanning electron microscopy and fourier transform infrared spectroscopy. It has been observed that the crystallization temperature and phase of K1-xCsxAlSi2O6 ceramic were significantly influenced by the Cs content. An increase in the Cs content resulted in a decrease in the crystallization temperature of the K1-xCsxAlSi2O6 cubic phase. K1-xCsxAlSi2O6 ceramic obtained at 850 °C was lecucite cubic or pollucite cubic phase when x ≥ 0.2, and the lattice parameters of cubic phase increased with increasing of Cs content. However, leucite tetragonal phase formed at elevated heating temperature (1100 °C and 1300 °C) except for the case x = 0.3, 0.4, 0.5 and 1. The c/a ratio of leucite tetragonal phase obtained at 1100 °C and 1300 °C was much more closed to 1 with Cs content increased, which made it hard to be indexed between cubic and tetragonal phase. In this case, leucite tetragonal phase could also be considered as pseudo-cubic phase. Additionally, the product consistency test leaching results showed that K1-xCsxAlSi2O6 ceramics possessed superior chemical durability.

Mechanical properties of metal dihydrides

DOE PAGES

Schultz, Peter A.; Snow, Clark S.

2016-02-04

First-principles calculations are used to characterize the bulk elastic properties of cubic and tetragonal phase metal dihydrides,more » $$\\text{M}{{\\text{H}}_{2}}$$ {$$\\text{M}$$ = Sc, Y, Ti, Zr, Hf, lanthanides} to gain insight into the mechanical properties that govern the aging behavior of rare-earth di-tritides as the constituent 3H, tritium, decays into 3He. As tritium decays, helium is inserted in the lattice, the helium migrates and collects into bubbles, that then can ultimately create sufficient internal pressure to rupture the material. The elastic properties of the materials are needed to construct effective mesoscale models of the process of bubble growth and fracture. Dihydrides of the scandium column and most of the rare-earths crystalize into a cubic phase, while dihydrides from the next column, Ti, Zr, and Hf, distort instead into the tetragonal phase, indicating incipient instabilities in the phase and potentially significant changes in elastic properties. We report the computed elastic properties of these dihydrides, and also investigate the off-stoichiometric phases as He or vacancies accumulate. As helium builds up in the cubic phase, the shear moduli greatly soften, converting to the tetragonal phase. Conversely, the tetragonal phases convert very quickly to cubic with the removal of H from the lattice, while the cubic phases show little change with removal of H. Finally, the source and magnitude of the numerical and physical uncertainties in the modeling are analyzed and quantified to establish the level of confidence that can be placed in the computational results, and this quantified confidence is used to justify using the results to augment and even supplant experimental measurements.« less

Cubic-to-tetragonal structural phase transition in Rb1-xCsxCaF3 solid solutions: Thermal expansion and EPR studies

NASA Astrophysics Data System (ADS)

Lahoz, F.; Villacampa, B.; Alcalá, R.; Marquina, C.; Ibarra, M. R.

1997-04-01

The influence of crystal mixing on the structural phase transitions in Rb1-xCsxCaF3 (0=0.44. This transition shows a weak first-order component in the x=0 and 0.1 samples, which is progressively smeared out for x>0.1, indicating a spatial distribution of the critical temperature in those crystals with high ionic substitution rate. In RbCaF3 , another structural phase transition was observed at 20 K with a thermal hysteresis between 20 and 40 K. This transition has not been found in any of the mixed crystals.

Real-time atomistic observation of structural phase transformations in individual hafnia nanorods

DOE PAGES

Hudak, Bethany M.; Depner, Sean W.; Waetzig, Gregory R.; ...

2017-05-12

High-temperature phases of hafnium dioxide have exceptionally high dielectric constants and large bandgaps, but quenching them to room temperature remains a challenge. Scaling the bulk form to nanocrystals, while successful in stabilizing the tetragonal phase of isomorphous ZrO 2, has produced nanorods with a twinned version of the room temperature monoclinic phase in HfO 2. Here we use in situ heating in a scanning transmission electron microscope to observe the transformation of an HfO 2 nanorod from monoclinic to tetragonal, with a transformation temperature suppressed by over 1000°C from bulk. When the nanorod is annealed, we observe with atomic-scale resolutionmore » the transformation from twinned-monoclinic to tetragonal, starting at a twin boundary and propagating via coherent transformation dislocation; the nanorod is reduced to hafnium on cooling. Unlike the bulk displacive transition, nanoscale size-confinement enables us to manipulate the transformation mechanism, and we observe discrete nucleation events and sigmoidal nucleation and growth kinetics.« less

Phase Transition and Structure of Silver Azide at High Pressure

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

D Hou; F Zhang; C Ji

2011-12-31

Silver azide (AgN{sub 3}) was compressed up to 51.3 GPa. The results reveal a reversible second-order orthorhombic-to-tetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters a and b, a 3{sup o} rotation of azide anions, and a change of coordination number from 4-4 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be in I4/mcm space group, with Ag at 4a, N{sub 1} at 4d, and N{sub 2} at 8h Wyckoff positions. Both of the two phasesmore » have anisotropic compressibility: the orthorhombic phase exhibits an anomalous expansion under compression along a-axis and is more compressive along b-axis than c-axis; the tetragonal phase is more compressive along the interlayer direction than the intralayer directions. The bulk moduli of the orthorhombic and tetragonal phases are determined to be K{sub OT} = 39{+-}5 GPa with K{sub OT'} = 10{+-}7 and K{sub OT} = 57 {+-}2 GPa with K{sub OT'} = 6.6{+-}0.2, respectively.« less

Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO 3

DOE PAGES

Rosenberg, Aaron J.; Katmis, Ferhat; Kirtley, John R.; ...

2017-12-15

The combination of ferromagnets with topological superconductors or insulators allows for new phases of matter that support excitations such as chiral edge modes and Majorana fermions. EuS, a wide-bandgap ferromagnetic insulator with a Curie temperature around 16K, and SrTiO 3 (STO), an important substrate for engineering heterostructures, may support these phases. We present scanning superconducting quantum interference device measurements of EuS grown epitaxially on STO that reveal micron-scale variations in ferromagnetism and paramagnetism. These variations are oriented along the STO crystal axes and only change their configuration upon thermal cycling above the STO cubic-to-tetragonal structural transition temperature at 105 K,more » indicating that the observed magnetic features are due to coupling between EuS and the STO tetragonal structure. Here, we speculate that the STO tetragonal distortions may strain the EuS, altering the magnetic anisotropy on a micron scale. This result demonstrates that local variation in the induced magnetic order from EuS grown on STO needs to be considered when engineering new phases of matter that require spatially homogeneous exchange.« less

Ferroelectricity of strained SrTiO3 in lithium tetraborate glass-nanocomposite and glass-ceramic

NASA Astrophysics Data System (ADS)

Abdel-Khalek, E. K.; Mohamed, E. A.; Kashif, I.

2018-02-01

Glass-nanocomposite (GNCs) sample of the composition [90Li2B4O7-10SrTiO3] (mol %) was prepared by conventional melt quenching technique. The glassy phase and the amorphous nature of the GNCs sample were identified by Differential thermal analysis (DTA) and X-ray diffraction (XRD) studies, respectively. DTA of the GNCs exhibits sharp and broad exothermic peaks which represent the crystallization of Li2B4O7 and SrTiO3, respectively. The tetragonal Li2B4O7 and tetragonal SrTiO3 crystalline phases in glass-ceramic (GC) were identified by XRD and scanning electron microscopic (SEM). The strain tetragonal SrTiO3 phase in GNCs and GC has been confirmed by SEM. The values of crystallization activation energies (Ec1 and Ec2) for the first and second exothermic peaks are equal to 174 and 1452 kJ/mol, respectively. The Ti3+ ions in tetragonal distorted octahedral sites in GNCs were identified by optical transmission spectrum. GNCs and GC samples exhibit broad dielectric anomalies at 303 and 319 K because of strained SrTiO3 ferroelectric, respectively.

Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO 3

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

Rosenberg, Aaron J.; Katmis, Ferhat; Kirtley, John R.

The combination of ferromagnets with topological superconductors or insulators allows for new phases of matter that support excitations such as chiral edge modes and Majorana fermions. EuS, a wide-bandgap ferromagnetic insulator with a Curie temperature around 16K, and SrTiO 3 (STO), an important substrate for engineering heterostructures, may support these phases. We present scanning superconducting quantum interference device measurements of EuS grown epitaxially on STO that reveal micron-scale variations in ferromagnetism and paramagnetism. These variations are oriented along the STO crystal axes and only change their configuration upon thermal cycling above the STO cubic-to-tetragonal structural transition temperature at 105 K,more » indicating that the observed magnetic features are due to coupling between EuS and the STO tetragonal structure. Here, we speculate that the STO tetragonal distortions may strain the EuS, altering the magnetic anisotropy on a micron scale. This result demonstrates that local variation in the induced magnetic order from EuS grown on STO needs to be considered when engineering new phases of matter that require spatially homogeneous exchange.« less

Abnormal cubic-tetragonal phase transition of barium strontium titanate nanoparticles studied by in situ Raman spectroscopy and transmission electron microscopy heating experiments

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

Zhang, Yin; Chen, Chen; Gao, Ran

2015-11-02

Phase stability of the ferroelectric materials at high temperature is extremely important to their device performance. Ba{sub x}Sr{sub 1−x}TiO{sub 3} (BST) nanoparticles with different Sr contents (x = 1, 0.91, 0.65, 0.4, and 0) are prepared by a facile hydrothermal method. Using Raman spectroscopy and transmission electron microscopy (TEM) analyses under in situ heating conditions (up to 300 °C), the phase transitions of BST nanoparticles between 25 °C and 280 °C are comprehensively investigated. The original Curie temperature of BST nanoparticles decreases abruptly with the increase in Sr content, which is more obvious than in the bulk or film material. Besides, an abnormal phase transitionmore » from cubic to tetragonal structure is observed from BST nanoparticles and the transition temperature rises along with the increase in Sr content. Direct TEM evidences including a slight lattice distortion have been provided. Differently, BaTiO{sub 3} nanoparticles remained in the tetragonal phase during the above temperature ranges.« less

Raman spectroscopic studies of defect structures and phase transition in hyper-stoichiometric UO(2+x).

PubMed

He, Heming; Shoesmith, David

2010-07-28

A method to determine the defect structures in hyper-stoichiometric UO(2+x) using a combination of XRD and Raman spectroscopy has been developed. A sequence of phase transitions, from cubic to tetragonal symmetry, occurs with increasing degree of non-stoichiometry. This sequence proceeds from a cubic phase through an intermediate t''-type tetragonal (axial ratio c/a = 1) phase to a final t-type tetragonal (c/a not = 1) phase. Four distinct structural defect regions can be identified in the stoichiometry range, UO(2) to U(3)O(7): (i) a random point defect structure (x (in UO(2+x)) < or = 0.05); (ii) a non-stoichiometry region (0.05 < or = x < or = 0.15) over which point defects are gradually eliminated and replaced by the Willis 2:2:2 cluster; (iii) a mixture of Willis and cuboctahedral clusters (0.15 < or = x < or = 0.23); (iv) the cuboctahedral cluster (x > or = 0.23). The geometry and steric arrangement of these defects is primarily determined by the concentration of the excess-oxygen interstitials.

Thermodynamic analysis of the formation of tetragonal bainite in steels

NASA Astrophysics Data System (ADS)

Mirzayev, D. A.; Mirzoev, A. A.; Buldashev, I. V.; Okishev, K. Yu.

2017-06-01

In the articles of Bkhadeshia, a new class of high-strength steels based on the structure of carbidefree bainite with an enhanced carbon content has been developed. According to Bkhadeshia, the main factor responsible for the high solubility of carbon is the occurrence of a tetragonality of the bainite lattice. To check this effect, in this article, the theory of tetragonality of martensite of iron alloys developed by Zener and Khachaturyan was applied to bainite under the assumption that the precipitation of carbides is prohibited. Equations for the chemical potentials of carbon and iron in austenite and in tetragonal ferrite have been derived. The equilibrium of these phases has been considered, and the calculations of the boundary concentrations of carbon and iron at different temperatures (300-1000 K) and at different parameters of the deformation interaction λ0 have been performed. The rigorous calculations confirmed Bkhadeshia's hypothesis that the suppression of the carbide formation during the formation of bainite leads to an increase in the carbon solubility in the bcc phase.

Investigation of La and Al substitution on the spontaneous polarization and lattice dynamics of the Pb(1-x)LaxTi(1-x)AlxO3 ceramics

NASA Astrophysics Data System (ADS)

Yadav, Arun Kumar; Verma, Anita; Kumar, Sunil; Srihari, Velaga; Sinha, A. K.; Reddy, V. Raghavendra; Liu, Shun Wei; Biring, Sajal; Sen, Somaditya

2018-03-01

The phase purity and crystal structure of Pb(1-x)LaxTi(1-x)AlxO3 (0 ≤ x ≤ 0.25) samples (synthesized via the sol-gel process) were confirmed using synchrotron x-ray powder diffraction (XRD) (wavelength, λ = 0.44573 Å). Rietveld analyses of powder x-ray diffraction data confirmed the tetragonal structure for compositions with x ≤ 0.18 and cubic structure for the sample with x = 0.25. Temperature-dependent XRD was performed to investigate the structural change from tetragonal to cubic structure phase transition. Raman spectroscopy at room temperature also confirmed this phase transition with compositions. Field emission scanning electron microscopy (FESEM) provided information about the surface morphology while an energy dispersive x-ray spectrometer attached with FESEM confirmed the chemical compositions of samples. Temperature and frequency dependent dielectric studies showed that the tetragonal to cubic phase transition decreased from 680 K to 175 K with an increase in the x from 0.03 to 0.25, respectively. This is correlated with the structural studies. Electric field dependent spontaneous polarization showed a proper ferroelectric loop for 0.06 ≤ x ≤ 0.18 belonging to a tetragonal phase, while for x ≥ 0.25, the spontaneous polarization vanishes. Bipolar strain versus electric field revealed a butterfly loop for 0.06 ≤ x ≤ 0.18 compositions. Energy storage efficiency initially increases nominally with substitution but beyond x = 0.18 enhances considerably.

Synthesis and thermal stability of zirconia and yttria-stabilized zirconia microspheres.

PubMed

Leib, Elisabeth W; Vainio, Ulla; Pasquarelli, Robert M; Kus, Jonas; Czaschke, Christian; Walter, Nils; Janssen, Rolf; Müller, Martin; Schreyer, Andreas; Weller, Horst; Vossmeyer, Tobias

2015-06-15

Zirconia microparticles produced by sol-gel synthesis have great potential for photonic applications. To this end, identifying synthetic methods that yield reproducible control over size uniformity is important. Phase transformations during thermal cycling can disintegrate the particles. Therefore, understanding the parameters driving these transformations is essential for enabling high-temperature applications. Particle morphology is expected to influence particle processability and stability. Yttria-doping should improve the thermal stability of the particles, as it does in bulk zirconia. Zirconia and YSZ particles were synthesized by improved sol-gel approaches using fatty acid stabilizers. The particles were heated to 1500 °C, and structural and morphological changes were monitored by SEM, ex situ XRD and high-energy in situ XRD. Zirconia particles (0.4-4.3 μm in diameter, 5-10% standard deviation) synthesized according to the modified sol-gel approaches yielded significantly improved monodispersities. As-synthesized amorphous particles transformed to the tetragonal phase at ∼450 °C with a volume decrease of up to ∼75% and then to monoclinic after heating from ∼650 to 850 °C. Submicron particles disintegrated at ∼850 °C and microparticles at ∼1200 °C due to grain growth. In situ XRD revealed that the transition from the amorphous to tetragonal phase was accompanied by relief in microstrain and the transition from tetragonal to monoclinic was correlated with the tetragonal grain size. Early crystallization and smaller initial grain sizes, which depend on the precursors used for particle synthesis, coincided with higher stability. Yttria-doping reduced grain growth, stabilized the tetragonal phase, and significantly improved the thermal stability of the particles. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

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

Adaptive modulations of martensites.

PubMed

Kaufmann, S; Rössler, U K; Heczko, O; Wuttig, M; Buschbeck, J; Schultz, L; Fähler, S

2010-04-09

Modulated phases occur in numerous functional materials like giant ferroelectrics and magnetic shape-memory alloys. To understand the origin of these phases, we employ and generalize the concept of adaptive martensite. As a starting point, we investigate the coexistence of austenite, adaptive 14M phase, and tetragonal martensite in Ni-Mn-Ga magnetic shape-memory alloy epitaxial films. We show that the modulated martensite can be constructed from nanotwinned variants of the tetragonal martensite phase. By combining the concept of adaptive martensite with branching of twin variants, we can explain key features of modulated phases from a microscopic view. This includes metastability, the sequence of 6M-10M-14M-NM intermartensitic transitions, and the magnetocrystalline anisotropy.

Determination of the electric field gradient in RbCaF3 near the phase transition

NASA Astrophysics Data System (ADS)

Hepp, M. A.; Man, P. P.; Trokiner, A.; Zanni, H.; Fraissard, J.

1992-12-01

The fluoroperovskite, RbCaF 3 undergoes a phase transition at 195.5K from a cubic to a tetragonal phase. The order parameter for this transition is directly related to the electric field gradient which arises in the tetragonal phase. In this work, we have used three NMR methods to measure the electric field gradient at the 87Rb site in a single crystal of RbCaF 3, very near this transition. These experiments are based on recent theoretical developments which allow the measurement of quadrupole parameters even for nuclei in a weak electric field gradient.

Electron microscopy of a Gd-Ba-Cu-O superconductor

NASA Technical Reports Server (NTRS)

Ramesh, R.; Thomas, G.; Meng, R. L.; Hor, P. H.; Chu, C. W.

1989-01-01

An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd-Ba-Cu-O superconductor alloy. The GdBa2Cu3O(7-x) phase in the oxygen annealed sample is orthorhombic, while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the 001-line zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.

Phase transformation in (0.90- x)Pb(Mg 1/3Nb 2/3)O 3- xPbTiO 3-0.10PbZrO 3 piezoelectric ceramic: X-ray diffraction and Raman investigation

NASA Astrophysics Data System (ADS)

Xia, Zhiguo; Li, Qiang

2007-05-01

Piezoelectric ceramics with compositions of (0.90- x)Pb(Mg 1/3Nb 2/3)O 3- xPbTiO 3-0.10PbZrO 3, x=0.28, 0.31, 0.34, 0.37, 0.40 and 0.43, were prepared using the conventional columbite precursor method, and their structural phase transformation and piezoelectric behaviors near the morphotropic phase boundary (MPB) have been systematically investigated as a function of PbTiO 3 content. X-ray diffraction (XRD) results demonstrate that the structure of the ceramics experiences a gradual transition process from rhombohedral phase to tetragonal phase with the increasing of PbTiO 3 content, and that compositions with x=0.34-0.40 lie in the MPB region of this ternary system. A Raman spectra investigation of the ceramic samples testified to the transformation process of rhombohedral phase to tetragonal phase by comparing the relative intensities of tetragonal E(2TO 1) mode and rhombohedral phase R h mode. The structure information was also correlated to the parabola change of the piezoelectric constant; the maximum piezoelectric constants were obtained near the MPB region.

[Structure and properties of colored dental tetragonal zirconia stabilized by yttrium ceramics].

PubMed

Yi, Yuan-fu; Wang, Chen; Wen, Ning; Lin, Yong-zhao; Tian, Jie-mo

2009-10-01

To investigate the structure, mechanical and low temperature aging properties of colored dental zirconia ceramics. 5 graded colored dental zirconia ceramics were made by adding colorants and their combinations into a 3Y-TZP (tetragonal zirconia stabilized by 3mol% yttrium) powder, the green body were compacted at 200 MPa, pre-sinter at 1,050 degrees C and maintained for 2 h, then densely sintered at 1,500 degrees C for 2 h. Specimens were cut from each of the 5 graded colored blocks. Physical, mechanical properties as well as chemical stability were tested, microstructure were observed, crystalline phase were identified by X-ray diffraction (XRD), aging properties were assessed by measurement of the relative content of monoclinic phase and bending strength testing. The overall density of colored zirconia ceramics was over 99.7%, linear shrinkage was about 20%, while thermal expansion coefficient was about 11 x 10(-6) x degrees C(-1), the crystalline phase was tetragonal, bending strength was over 900 MPa which was slightly lowered than that of the uncolored zirconia, fracture toughness was slightly higher. Good chemical stability in acetic acid was observed. After aging treatment, tetragonal-to-monoclinic phase transformation was detected up to 40%, while bending strength was not significantly degraded. The results showed that colored 3Y-TZP ceramics presented good mechanical properties even after aging treatments, and was suitable for dental clinical use.

Effect of pressure on the tetragonal distortion in TiH2: a first-principles study

NASA Astrophysics Data System (ADS)

de Coss, R.; Quijano, R.; Singh, D. J.

2009-03-01

The transition metal dihydride TiH2 present the fluorite structure (CaF2) at high temperature but undergoes a tetragonal distortion with c/a<1 at low temperature. Early electronic band structure calculations have shown that TiH2 in the cubic phase display a nearly flat double degenerated band at the Fermi level. Thus the low temperature tetragonal distortion has been associated to a Jahn-Teller effect. Nevertheless, recently we have show that the instability of fcc-TiH2 is likely to be related with a van Hove singularity. In the present work, we have performed ab-initio calculations of the electronic structure and the tetragonal distortion for TiH2 under pressure (0-30 GPa). We found that the fcc-fct energy barrier and the tetragonal distortion increases with pressure. The evolution of the tetragonal distortion is analyzed in terms of the electronic band structure. This research was supported by Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grant No. 49985.

Pressure-temperature phase diagrams of CaK(Fe1 -xNix)4As4 superconductors

NASA Astrophysics Data System (ADS)

Xiang, Li; Meier, William R.; Xu, Mingyu; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; Canfield, Paul C.

2018-05-01

The pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK (Fe1-xNix) 4As4 , the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels (x =0.033 ,0.050 ) under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures TN are suppressed upon applying pressure; the superconducting transition temperatures Tc are suppressed by pressure as well, except for x =0.050 in the pressure region where TN and Tc cross. Furthermore, the pressure associated with the crossing of the TN and Tc lines also coincides with a minimum in the normalized slope of the superconducting upper critical field, consistent with a likely Fermi-surface reconstruction associated with the loss of magnetic ordering. Finally, at p ˜4 GPa, both Ni-substituted CaK (Fe1-xNix) 4As4 samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound CaKFe4As4 .

Ferroelastic phase transitions in (NH4)2TaF7

NASA Astrophysics Data System (ADS)

Pogorel'tsev, E. I.; Mel'nikova, S. V.; Kartashev, A. V.; Molokeev, M. S.; Gorev, M. V.; Flerov, I. N.; Laptash, N. M.

2013-03-01

The heat capacity, unit cell parameters, permittivity, optical properties, and thermal expansion of the (NH4)2TaF7 compound with a seven-coordinated anion polyhedron have been measured. It has been found that the compound undergoes two successive phase transitions with the symmetry change: tetragonal → ( T 1 = 174 K) orthorhombic → ( T 2 = 156 K) tetragonal. The ferroelastic nature of structural transformations has been established, and their entropy and susceptibility to hydrostatic pressure have been determined.

Temperature dependence of field-responsive mechanisms in lead zirconate titanate

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

Chung, Ching-Chang; Fancher, Chris M.; Isaac, Catherine

2017-05-17

An electric field loading stage was designed for use in a laboratory diffractometer that enables in situ investigations of the temperature dependence in the field response mechanisms of ferroelectric materials. The stage was demonstrated in this paper by measuring PbZr 1-xTi xO 3 (PZT) based materials—a commercially available PZT and a 1% Nb-doped PbZr 0.56Ti 0.44O 3 (PZT 56/44)—over a temperature range of 25°C to 250°C. The degree of non-180° domain alignment (η 002) of the PZT as a function of temperature was quantified. η 002 of the commercially available PZT increases exponentially with temperature, and was analyzed as amore » thermally activated process as described by the Arrhenius law. The activation energy for thermally activated domain wall depinning process in PZT was found to be 0.47 eV. Additionally, a field-induced rhombohedral to tetragonal phase transition was observed 5°C below the rhombohedral-tetragonal transition in PZT 56/44 ceramic. The field-induced tetragonal phase fraction was increased 41.8% after electrical cycling. Finally, a large amount of domain switching (η 002=0.45 at 1.75 kV/mm) was observed in the induced tetragonal phase.« less

Tunable magnetic and transport properties of Mn3Ga thin films on Ta/Ru seed layer

NASA Astrophysics Data System (ADS)

Hu, Fang; Xu, Guizhou; You, Yurong; Zhang, Zhi; Xu, Zhan; Gong, Yuanyuan; Liu, Er; Zhang, Hongguo; Liu, Enke; Wang, Wenhong; Xu, Feng

2018-03-01

Hexagonal D019-type Mn3Z alloys that possess large anomalous and topological-like Hall effects have attracted much attention due to their great potential in antiferromagnetic spintronic devices. Herein, we report the preparation of Mn3Ga films in both tetragonal and hexagonal phases with a tuned Ta/Ru seed layer on a thermally oxidized Si substrate. Large coercivity together with large anomalous Hall resistivity is found in the Ta-only sample with a mixed tetragonal phase. By increasing the thickness of the Ru layer, the tetragonal phase gradually disappears and a relatively pure hexagonal phase is obtained in the Ta(5)/Ru(30) buffered sample. Further magnetic and transport measurements revealed that the anomalous Hall conductivity nearly vanishes in the pure hexagonal sample, while an abnormal asymmetric hump structure emerges in the low field region. The extracted additional Hall term is robust in a large temperature range and presents a sign reversal above 200 K. The abnormal Hall properties are proposed to be closely related to the frustrated spin structure of D019 Mn3Ga.

Hybrid-exchange density-functional theory study of the electronic structure of MnV2O4 : Exotic orbital ordering in the cubic structure

NASA Astrophysics Data System (ADS)

Wu, Wei

2015-05-01

The electronic structures of cubic and tetragonal MnV2O4 have been studied using hybrid-exchange density-functional theory. The computed electronic structure of the tetragonal phase shows an antiferro-orbital ordering on V sites and a ferrimagnetic ground state (the spins on V and Mn are antialigned). These results are in good agreement with the previous theoretical result obtained from the local-density approximation + U methods [S. Sarkar et al., Phys. Rev. Lett. 102, 216405 (2009), 10.1103/PhysRevLett.102.216405]. Moreover, the electronic structure, especially the projected density of states of the cubic phase, has been predicted with good agreement with the recent soft x-ray spectroscopy experiment. Similar to the tetragonal phase, the spins on V and Mn in the cubic structure favor a ferrimagnetic configuration. Most interesting is that the computed charge densities of the spin-carrying orbitals on V in the cubic phase show an exotic orbital ordering, i.e., a ferro-orbital ordering along [110] but an antiferro-orbital ordering along [1 ¯10 ] .

The Effects of Thermal History on Nucleation of Tetragonal Lysozyme Crystals, or Hot Protein and Cold Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael; Judge, Russell; Pusey, Marc

2000-01-01

Chicken egg white lysozyme has a well characterized thermally driven phase transition. Between pH 4.2 and 5.2, the transition temperature, as defined by the point where the tetragonal and orthorhombic solubilities are equal, is a function of the pH, salt (precipitant) type and concentration, and most likely of the buffer concentration as well. This phase transition can be carried out with protein solution alone, prior to addition of precipitant solution. Warming a lysozyme solution above the phase transition point, then cooling it back below this point, has been shown to affect the subsequent nucleation rate, as determined by the numbers and size of crystals formed, but not the growth rate for the tetragonal crystal form . We have now measured the kinetics of this process and investigated its reversibility. The transition effects are progressive with temperature, having a half time of about 1 hour at 37C at pH 4.8. After holding a lysozyme solution at 37C (prior to addition of precipitant) for 16 hours, then cooling it back to 4C no return to the pre-warmed nucleation kinetics are observed after at least 4 weeks. Orthorhombic lysozyme crystals apparently do not undergo the flow-induced growth cessation of tetragonal lysozyme crystals. Putting the protein in the orthorhombic form does not affect the averaged face growth kinetics, only nucleation, for tetragonal crystals. This differential behaviour may be exploited to elucidate how and where flow affects the lysozyme crystal growth process. The presentation will focus on the results of these and ongoing studies in this area.

Grain size dependent phase stabilities and presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of (1−x)Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} piezoceramics

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

Upadhyay, Ashutosh; Singh, Akhilesh Kumar, E-mail: akhilesh-bhu@yahoo.com, E-mail: aksingh.mst@itbhu.ac.in

2015-04-14

Results of the room temperature structural studies on (1−x)Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} ceramics using Rietveld analysis of the powder x-ray diffraction data in the composition range 0.28 ≤ x ≤ 0.45 are presented. The morphotropic phase boundary region exhibits coexistence of monoclinic (space group Pm) and tetragonal (space group P4 mm) phases in the composition range 0.33 ≤ x ≤ 0.40. The structure is nearly single phase monoclinic (space group Pm) in the composition range 0.28 ≤ x ≤ 0.32. The structure for the compositions with x ≥ 0.45 is found to be predominantly tetragonal with space group P4 mm. Rietveld refinement of the structure rules out the coexistence of rhombohedral and tetragonal phases inmore » the morphotropic phase boundary region reported by earlier authors. The Rietveld structure analysis for the sample x = .35 calcined at various temperatures reveals that phase fraction of the coexisting phases in the morphotropic phase boundary region varies with grain size. The structural parameters of the two coexisting phases also change slightly with changing grain size.« less

Thermal stability and phase transformation in fully indium oxide (InO{sub 1.5}) stabilized zirconia

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

Piva, R.H., E-mail: honorato.piva@ua.pt; Piva, D.H

2017-01-15

Indium oxide (InO{sub 1.5}) stabilized zirconia (InSZ) is an attractive material as electrolyte, or electrode, in solid oxide fuel cells (SOFCs), and as corrosion resistant top coat in thermal barrier coatings. However, little is known about the phase stability of cubic InSZ at temperatures that simulate the conditions in an operating SOFC or turbine. This article provides an investigation of the phase stability and phase transformations in cubic InSZ after heat treatments at 800, 1000, and 1200 °C for periods up to 2000 h. The results revealed that cubic InSZ is not stable during annealing at 1000 and 1200 °C,more » owing to a fast destabilization of the initial cubic phase to tetragonal, and eventually to monoclinic (c → t → m). The c → t → m transition in InSZ is intimately associated with the indium volatilization. On the other hand, cubic InSZ remained stable for 2000 h at 800 °C, although the partial formation of the tetragonal phase was observed along with a 0.25% contraction in the unit cell volume of the cubic phase, caused by short-range ordering. These results demonstrate that technological applications of cubic InSZ are restricted to temperatures at which the volatilization of the InO{sub 1.5} stabilizer does not occur. - Highlights: •Phase stability of fully InO{sub 1.5} stabilized zirconia (cubic InSZ) was evaluated. •Cubic InSZ is instable at temperatures ≥ 1000 °C, owing to the cubic-to-tetragonal-to-monoclinic destabilization. •Cubic InSZ undergoes the cubic-to-tetragonal transformation at ~ 800 °C. •Owing to the low phase stability, applications of cubic InSZ in TBCs or SOFCs are restricted.« less

The Effect of Poling on the Properties of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 Ceramics

NASA Astrophysics Data System (ADS)

Uršič, Hana; Tellier, Jenny; Hrovat, Marko; Holc, Janez; Drnovšek, Silvo; Bobnar, Vid; Alguero, Miguel; Kosec, Marija

2011-03-01

The effects of the poling field on the structural and electrical properties of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (0.65PMN-0.35PT) ceramics were investigated. The highest piezoelectric coefficient d33, coupling coefficients kp, kt, and mechanical quality factor Qm were achieved for ceramics poled at electric fields between 2 and 3.5 kV/mm, whereas the d33, kp, kt, and Qm of ceramics poled at higher electric fields, i.e., 4 and 4.5 kV/mm, were lower. The non-poled ceramics contained 86% of the monoclinic phase with the space group Pm and 14% of the tetragonal phase with the space group P4mm. However, the ceramics poled at 2.5 kV/mm contained 99% of the monoclinic phase and the rest is the tetragonal phase. The results show that the ratio of the monoclinic to the tetragonal phases can be changed by the application of a poling electric field and that the extent of this change is dependent on the field strength.

Prediction of the wetting-induced collapse behaviour using the soil-water characteristic curve

NASA Astrophysics Data System (ADS)

Xie, Wan-Li; Li, Ping; Vanapalli, Sai K.; Wang, Jia-Ding

2018-01-01

Collapsible soils go through three distinct phases in response to matric suction decrease during wetting: pre-collapse phase, collapse phase and post-collapse phase. It is reasonable and conservative to consider a strain path that includes a pre-collapse phase in which constant volume is maintained and a collapse phase that extends to the final matric suction to be experienced by collapsible soils during wetting. Upon this assumption, a method is proposed for predicting the collapse behaviour due to wetting. To use the proposed method, two parameters, critical suction and collapse rate, are required. The former is the suction value below which significant collapse deformations take place in response to matric suction decease, and the later is the rate at which void ratio reduces with matric suction in the collapse phase. The value of critical suction can be estimated from the water-entry value taking account of both the microstructure characteristics and collapse mechanism of fine-grained collapsible soils; the wetting soil-water characteristic curve thus can be used as a tool. Five sets of data of wetting tests on both compacted and natural collapsible soils reported in the literature were used to validate the proposed method. The critical suction values were estimated from the water-entry value with parameter a that is suggested to vary between 0.10 and 0.25 for compacted soils and to be lower for natural collapsible soils. The results of a field permeation test in collapsible loess soils were also used to validate the proposed method. The relatively good agreement between the measured and estimated collapse deformations suggests that the proposed method can provide reasonable prediction of the collapse behaviour due to wetting.

Barium Titanate Nanoparticles for Biomarker Applications

NASA Astrophysics Data System (ADS)

Matar, O.; Posada, O. M.; Hondow, N. S.; Wälti, C.; Saunders, M.; Murray, C. A.; Brydson, R. M. D.; Milne, S. J.; Brown, A. P.

2015-10-01

A tetragonal crystal structure is required for barium titanate nanoparticles to exhibit the nonlinear optical effect of second harmonic light generation (SHG) for use as a biomarker when illuminated by a near-infrared source. Here we use synchrotron XRD to elucidate the tetragonal phase of commercially purchased tetragonal, cubic and hydrothermally prepared barium titanate (BaTiO3) nanoparticles by peak fitting with reference patterns. The local phase of individual nanoparticles is determined by STEM electron energy loss spectroscopy (EELS), measuring the core-loss O K-edge and the Ti L3-edge energy separation of the t2g, eg peaks. The results show a change in energy separation between the t2g and eg peak from the surface and core of the particles, suggesting an intraparticle phase mixture of the barium titanate nanoparticles. HAADF-STEM and bright field TEM-EDX show cellular uptake of the hydrothermally prepared BaTiO3 nanoparticles, highlighting the potential for application as biomarkers.

Ferroelastic domain structure and phase transition in single-crystalline [PbZn 1/3Nb 2/3O 3] 1-x[PbTiO 3] x observed via in situ x-ray microbeam

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

Li, Tao; Du, Zehui; Tamura, Nobumichi

(1-x)Pb(Zn 1/3Nb 2/3)O 3-xPbTiO 3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this study, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25°C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in xmore » = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (T C), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient.« less

Ferroelastic domain structure and phase transition in single-crystalline [PbZn 1/3Nb 2/3O 3] 1-x[PbTiO 3] x observed via in situ x-ray microbeam

DOE PAGES

Li, Tao; Du, Zehui; Tamura, Nobumichi; ...

2017-11-10

(1-x)Pb(Zn 1/3Nb 2/3)O 3-xPbTiO 3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this study, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25°C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in xmore » = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (T C), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient.« less

Monitoring a Silent Phase Transition in CH 3NH 3PbI 3 Solar Cells via Operando X-ray Diffraction

DOE PAGES

Schelhas, Laura T.; Christians, Jeffrey A.; Berry, Joseph J.; ...

2016-10-13

The relatively modest temperature of the tetragonal-to-cubic phase transition in CH 3NH 3PbI 3 perovskite is likely to occur during real world operation of CH 3NH 3PbI 3 solar cells. In this work, we simultaneously monitor the structural phase transition of the active layer along with solar cell performance as a function of the device operating temperature. The tetragonal to cubic phase transition is observed in the working device to occur reversibly at temperatures between 60.5 and 65.4 degrees C. In these operando measurements, no discontinuity in the device performance is observed, indicating electronic behavior that is insensitive to themore » structural phase transition. Here, this decoupling of device performance from the change in long-range order across the phase transition suggests that the optoelectronic properties are primarily determined by the local structure in CH 3NH 3PbI 3. That is, while the average crystal structure as probed by X-ray diffraction shows a transition from tetragonal to cubic, the local structure generally remains well characterized by uncorrelated, dynamic octahedral rotations that order at elevated temperatures but are unchanged locally.« less

Non-Congruence of Thermally Induced Structural and Electronic Transitions in VO2

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

Nag, Joyeeta; HaglundJr., Richard F; Payzant, E Andrew

2012-01-01

The multifunctional properties of vanadium dioxide (VO2) arise from coupled first-order phase transitions: an insulator-to-metal transition (IMT) and a structural phase transition (SPT) from monoclinic to tetragonal. The characteristic signatures of the IMT and SPT are the hysteresis loops that track the phase transition from nucleation to stabilization of a new phase and back. A long-standing question about the mechanism of the VO2 phase transition is whether and how the almost-simultaneous electronic and structural transitions are related. Here we report independent measurements of the IMT and SPT hystereses in epitaxial VO2 films with differing morphologies. We show that, in bothmore » cases, the hystereses are not congruent, that the structural change requires more energy to reach completion. This result is independent of nanoscale morphology, so that the non- congruence is an intrinsic property of the VO2 phase transition. Our conclusion is supported by effective-medium calculations of the dielectric function incorporating the measured volume fractions of the monoclinic and tetragonal states. The results are consistent with the existence of an monoclinic correlated metallic state in which the electron- electron correlations characteristic of the monoclinic state begin to disappear before the transition to the tetragonal structural state.« less

Monitoring a Silent Phase Transition in CH 3NH 3PbI 3 Solar Cells via Operando X-ray Diffraction

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

Schelhas, Laura T.; Christians, Jeffrey A.; Berry, Joseph J.

The relatively modest temperature of the tetragonal-to-cubic phase transition in CH 3NH 3PbI 3 perovskite is likely to occur during real world operation of CH 3NH 3PbI 3 solar cells. In this work, we simultaneously monitor the structural phase transition of the active layer along with solar cell performance as a function of the device operating temperature. The tetragonal to cubic phase transition is observed in the working device to occur reversibly at temperatures between 60.5 and 65.4 degrees C. In these operando measurements, no discontinuity in the device performance is observed, indicating electronic behavior that is insensitive to themore » structural phase transition. Here, this decoupling of device performance from the change in long-range order across the phase transition suggests that the optoelectronic properties are primarily determined by the local structure in CH 3NH 3PbI 3. That is, while the average crystal structure as probed by X-ray diffraction shows a transition from tetragonal to cubic, the local structure generally remains well characterized by uncorrelated, dynamic octahedral rotations that order at elevated temperatures but are unchanged locally.« less

Atomic Origins of Monoclinic-Tetragonal (Rutile) Phase Transition in Doped VO2 Nanowires.

PubMed

Asayesh-Ardakani, Hasti; Nie, Anmin; Marley, Peter M; Zhu, Yihan; Phillips, Patrick J; Singh, Sujay; Mashayek, Farzad; Sambandamurthy, Ganapathy; Low, Ke-Bin; Klie, Robert F; Banerjee, Sarbajit; Odegard, Gregory M; Shahbazian-Yassar, Reza

2015-11-11

There has been long-standing interest in tuning the metal-insulator phase transition in vanadium dioxide (VO2) via the addition of chemical dopants. However, the underlying mechanisms by which doping elements regulate the phase transition in VO2 are poorly understood. Taking advantage of aberration-corrected scanning transmission electron microscopy, we reveal the atomistic origins by which tungsten (W) dopants influence the phase transition in single crystalline WxV1-xO2 nanowires. Our atomically resolved strain maps clearly show the localized strain normal to the (122̅) lattice planes of the low W-doped monoclinic structure (insulator). These strain maps demonstrate how anisotropic localized stress created by dopants in the monoclinic structure accelerates the phase transition and lead to relaxation of structure in tetragonal form. In contrast, the strain distribution in the high W-doped VO2 structure is relatively uniform as a result of transition to tetragonal (metallic) phase. The directional strain gradients are furthermore corroborated by density functional theory calculations that show the energetic consequences of distortions to the local structure. These findings pave the roadmap for lattice-stress engineering of the MIT behavior in strongly correlated materials for specific applications such as ultrafast electronic switches and electro-optical sensors.

Ultra-flexible framework breathing in response to dehydration in liskeardite, [(Al,Fe){sub 16}(AsO{sub 4}){sub 9}(OH){sub 21}(H{sub 2}O){sub 11}]·26H{sub 2}O, a natural open-framework compound

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

Grey, Ian. E., E-mail: Ian.Grey@csiro.au; Brand, Helen E.A.; Rumsey, Michael S.

Dehydration of the natural open-framework compound, liskeardite, [(Al,Fe){sub 16}(AsO{sub 4}){sub 9}(OH){sub 21}(H{sub 2}O){sub 11}]·26H{sub 2}O, is accompanied by a change in the sign of the thermal expansion from positive to negative above room temperature, and at ~100 °C the structure undergoes a dramatic 2D contraction by co-operative rotation of heteropolyhedral columns that constitute the framework walls. Monoclinic liskeardite, I112 with a≈b≈24.7 Å, c ≈7.8 Å and β≈90° is transformed to a tetragonal phase, I-4 with a≈20.6 Å, c ≈7.7 Å. The associated 30% decrease in volume is unprecedented in inorganic microporous compounds. The flexibility of the contraction is related tomore » the double-hinged nature of the column rotations about [001]. Octahedra in adjacent columns are interconnected by corner-sharing with the two pairs of anions forming opposing edges of AsO{sub 4} tetrahedra, so a double-hinged rotation mechanism operates. Thermal analysis and mass spectroscopic results for liskeardite show that the phase transition at ~100 °C is related to removal of the channel water. The tetragonal phase shows exceptionally large NTE behaviour. Over the temperature range 148–178 the NTE along a and b is close to linear with a magnitude of the order of −900×10{sup −6} °C{sup −1}. The contraction along the channel direction is smaller but still appreciable at −200×10{sup −6} °C{sup −1}. - Graphical abstract: Structure of the collapsed liskeardite framework, formed on dehydration above 100 °C. - Highlights: • The thermal expansion of the mineral liskeardite changes + to − above ambient. • Dehydration at 100 °C results in a record reversible 30% volume reduction. • In situ synchrotron XRD has led to a structural model for the dehydrated phase. • Framework breathing flexibility is attributed to a double-hinge rotation mechanism. • The dehydrated phase shows unprecedented -ve expansion for inorganic materials.« less

Surface crystalline phases and nanoindentation hardness of explanted zirconia femoral heads.

PubMed

Catledge, Shane A; Cook, Monique; Vohra, Yogesh K; Santos, Erick M; McClenny, Michelle D; David Moore, K

2003-10-01

One new and nine explanted zirconia femoral heads were studied using glancing angle X-ray diffraction, scanning electron microscopy, and nanoindentation hardness techniques. All starting zirconia implants consisted only of tetragonal zirconia polycrystals (TZP). For comparison, one explanted alumina femoral head was also studied. Evidence for a surface tetragonal-to-monoclinic zirconia phase transformation was observed in some implants, the extent of which was varied for different in-service conditions. A strong correlation was found between increasing transformation to the monoclinic phase and decreasing surface hardness. Microscopic investigations of some of the explanted femoral heads revealed ultra high molecular weight polyethylene and metallic transfer wear debris.

Phase stability of zirconium oxide films during focused ion beam milling

NASA Astrophysics Data System (ADS)

Baxter, Felicity; Garner, Alistair; Topping, Matthew; Hulme, Helen; Preuss, Michael; Frankel, Philipp

2018-06-01

Focused ion beam (FIB) is a widely used technique for preparation of electron transparent samples and so it is vital to understand the potential for introduction of FIB-induced microstructural artefacts. The bombardment of both Xe+ and Ga+ ions is observed to cause extensive monoclinic to tetragonal phase transformation in ZrO2 corrosion films, however, this effect is diminished with reduced energy and is not observed below 5 KeV. This study emphasises the importance of careful FIB sample preparation with a low energy cleaning step, and also gives insight into the stabilisation mechanism of the tetragonal phase during oxidation.

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

Low temperature anomalous field effect in SrxBa1-xNb2O6 uniaxial relaxor ferroelectric seen via acoustic emission

NASA Astrophysics Data System (ADS)

Dul'kin, E.; Kojima, S.; Roth, M.

2012-04-01

Sr0.75Ba0.25Nb2O6 [100]-oriented uniaxial tungsten bronze relaxor crystals have been studied by means of dedicated acoustic emission during their thermal cycling in 150-300 K temperature range under dc electric field (E). A 1st order transition in a modulated incommensurate tetragonal phase has been successfully detected at Tmi = 198 K on heating and Tmi = 184 K on cooling, respectively. As field E enhances, a thermal hysteresis gradually narrows and vanishes in the critical point at Eth = 0.31 kV/cm, above which a phase transition becomes to 2nd order. The Tmi(E) dependence looks as a V-shape dip, not similar that previously has been looked as a smeared minimum between both the two polar and nonpolar tetragonal phases near Tm = 220 ÷ 230 K in the same crystals (Dul'kin et al., J Appl. Phys. 110, 044106 (2011)). Due to such a V-shape dip is characteristic for Pb-based multiaxial perovskite relaxor, a rhombohedral phase is waited to be induced by a field E in the critical point temperature range. The emergence of this rhombohedral phase as a crucial evidence of an orthorhombic phase presumably existing within the modulated incommensurate tetragonal phase in tungsten bronze SrxBa1-xNb2O6 relaxor is discussed.

Crystal structure and phase transitions of sodium potassium niobate perovskites

NASA Astrophysics Data System (ADS)

Tellier, J.; Malic, B.; Dkhil, B.; Jenko, D.; Cilensek, J.; Kosec, M.

2009-02-01

This paper presents the crystal structure and the phase transitions of K xNa 1- xNbO 3 (0.4 ≤ x ≤ 0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100-800 K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32° ≤ β ≤ 90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic-tetragonal and tetragonal-cubic transitions. Only the potassium-rich phases were rhombohedral at 100 K.

Ferroic phase transition of tetragonal Pb0.6-xCaxBi0.4(Ti0.75Zn0.15Fe0.1)O3 ceramics: Factors determining Curie temperature

NASA Astrophysics Data System (ADS)

Yu, Jian; An, Fei-fei; Cao, Fei

2014-05-01

In this paper, ferroelectric phase transitions of Pb0.6-xCaxBi0.4(Ti0.75Zn0.15Fe0.1)O3 with x ≤ 0.20 ceramics were experimentally measured and a change from first-order to relaxor was found at a critical composition x ˜ 0.19. With increasing Ca content of x ≤ 0.18, Curie temperature and tetragonality was found decrease but piezoelectric constant and dielectric constant increase in a quadratic polynomial relationship as a function of x, while the ferroic Curie temperature and ferroelastic ordering parameter of tetragonality are correlated in a quadratic polynomial relationship. Near the critical composition of ferroic phase transition from first-order to relaxor, the Pb0.42Ca0.18Bi0.4(Ti0.75Zn0.15Fe0.1)O3 and 1 mol % Nb + 0.5 mol % Mg co-doped Pb0.44Ca0.16Bi0.4(Ti0.75Zn0.15Fe0.1)O3 ceramics exhibit a better anisotropic piezoelectric properties than those commercial piezoceramics of modified-PbTiO3 and PbNb2O6. At last, those factors including reduced mass of unit cell, mismatch between cation size and anion cage size, which affect ferroic Curie temperature and ferroelastic ordering parameter (tetragonality) of tetragonal ABO3 perovskites, are analyzed on the basis of first principle effective Hamiltonian and the reduced mass of unit cell is argued a more universal variable than concentration to determine Curie temperature in a quadratic polynomial relationship over various perovskite-structured solid solutions.

Cubic-to-tetragonal structural phase transition in Rb{sub 1{minus}x}Cs{sub x}CaF{sub 3} solid solutions: Thermal expansion and EPR studies

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

Lahoz, F.; Villacampa, B.; Alcala, R.

1997-04-01

The influence of crystal mixing on the structural phase transitions in Rb{sub 1{minus}x}Cs{sub x}CaF{sub 3} (0{lt}x{lt}1) fluoroperovskite crystals has been studied by thermal expansion and EPR measurements of Ni{sup 2+} and Ni{sup 3+} paramagnetic probes. A cubic-to-tetragonal phase transition has been detected in crystals with x=0, 0.1, 0.21, 0.27, and 0.35. The critical temperature and the tetragonal distortion decrease as x increases. No transition was observed for x{ge}0.44. This transition shows a weak first-order component in the x=0 and 0.1 samples, which is progressively smeared out for x{gt}0.1, indicating a spatial distribution of the critical temperature in those crystals withmore » high ionic substitution rate. In RbCaF{sub 3}, another structural phase transition was observed at 20 K with a thermal hysteresis between 20 and 40 K. This transition has not been found in any of the mixed crystals.« 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.

Microstructure and mechanical properties of bulk yttria-partially-stabilized zirconia

NASA Technical Reports Server (NTRS)

Valentine, P. G.; Maier, R. D.; Mitchell, T. E.

1981-01-01

A commercially available bulk 4.5 mole percent yttria-(Y2O3) partially stabilized zirconia (PSZ) was studied by light microscopy, X-ray analysis, microhardness measurement, and fracture toughness testing. The growth of the precipitates and the phase transformations were studied as a function of aging in air at 1500 C. Aging curves were constructed for both the as received and the solution annealed and quenched materials; the curves showed hardness peaks at 1397 and 1517 Kg/sq mm respectively. The rectangular plate shaped tetragonal precipitates were found to have a 110 habit plane. A total of twelve different types of tetragonal precipitates were found. Grinding of the Y2O3 PSZ into powder did not cause a significant amount of metastable tetragonal precipitates to transform into the monoclinc phase, thus indicating that transformation toughening is not a significant mechanism for the material.

Ternary ceramic alloys of ZR-CE-HF oxides

DOEpatents

Becher, Paul F.; Funkenbusch, Eric F.

1990-01-01

A ternary ceramic alloy which produces toughening of zirconia and zirconia composites through the stress transformation from tetragonal phase to monoclinic phase. This alloy, having the general formula Ce.sub.x Hf.sub.y Zn.sub.1-x-y O.sub.2, is produced through the addition of appropriate amounts of ceria and hafnia to the zirconia. Typically, improved toughness is achieved with about 5 to about 15 mol % ceria and up to about 40 mol % hafnia. The preparation of alloys of these compositions are given together with data as to the densities, tetragonal phase content, hardness and fracture toughness. The alloys are useful in preparing zirconia bodies as well as reinforcing ceramic composites.

Synchrotron x-ray scattering investigations of oxygen-induced nucleation in a Zr-based glass-forming alloy.

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

Wall, J. J.; Almer, J. D.; Vogel, S. C.

The metallic glass-forming alloy VIT-105 (Zr{sub 52.5}Cu{sub 17.9}Ni{sub 14.6}Al{sub 10}Ti{sub 5}) was used to study the effect of oxygen on nucleation. Ex situ synchrotron X-ray scattering experiments performed on as-cast samples showed that oxygen leads to the formation of tetragonal and/or cubic phases, depending on oxygen content. The samples crystallized into either a primitive tetragonal phase or the so-called fcc 'big cube' phase in a glassy matrix. A subsequent discussion on the role of oxygen in heterogeneous nucleation in Zr-based bulk metallic glasses is presented.

Local and average structures of BaTiO 3-Bi(Zn 1/2Ti 1/2)O 3

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

Usher, Tedi-Marie; Iamsasri, Thanakorn; Forrester, Jennifer S.

The complex crystallographic structures of (1-x)BaTiO 3-xBi(Zn 1/2Ti 1/2)O 3 (BT-xBZT) are examined using high resolution synchrotron X-ray diffraction, neutron diffraction, and neutron pair distribution function (PDF) analyses. The short-range structures are characterized from the PDFs, and a combined analysis of the X-ray and neutron diffraction patterns is used to determine the long-range structures. Our results demonstrate that the structure appears different when averaged over different length scales. In all compositions, the local structures determined from the PDFs show local tetragonal distortions (i.e., c/a > 1). But, a box-car fitting analysis of the PDFs reveals variations at different length scales.more » For 0.80BT-0.20BZT and 0.90BT-0.10BZT, the tetragonal distortions decrease at longer atom-atom distances (e.g., 30 vs. 5 ). When the longest distances are evaluated (r > 40 ), the lattice parameters approach cubic. Neutron and X-ray diffraction yield further information about the long-range structure. Compositions 0.80BT-0.20BZT and 0.90BT-0.10BZT appear cubic by Bragg diffraction (no peak splitting), consistent with the PDFs at long distances. However, these patterns cannot be adequately fit using a cubic lattice model; modeling their structures with the P4mm space group allows for a better fit to the patterns because the space group allows for c-axis atomic displacements that occur at the local scale. Furthermore, for the compositions 0.92BT-0.08BZT and 0.94BT-0.06BZT, strong tetragonal distortions are observed at the local scale and a less-distorted tetragonal structure is observed at longer length scales. In Rietveld refinements, the latter is modeled using a tetragonal phase. Since the peak overlap in these two-phase compositions limits the ability to model the local-scale structures as tetragonal, it is approximated in the refinements as a cubic phase. These results demonstrate that alloying BT with BZT results in increased disorder and disrupts the long-range ferroelectric symmetry present in BT, while the large tetragonal distortion present in BZT persists at the local scale.« less

Local and average structures of BaTiO 3-Bi(Zn 1/2Ti 1/2)O 3

DOE PAGES

Usher, Tedi-Marie; Iamsasri, Thanakorn; Forrester, Jennifer S.; ...

2016-11-11

The complex crystallographic structures of (1-x)BaTiO 3-xBi(Zn 1/2Ti 1/2)O 3 (BT-xBZT) are examined using high resolution synchrotron X-ray diffraction, neutron diffraction, and neutron pair distribution function (PDF) analyses. The short-range structures are characterized from the PDFs, and a combined analysis of the X-ray and neutron diffraction patterns is used to determine the long-range structures. Our results demonstrate that the structure appears different when averaged over different length scales. In all compositions, the local structures determined from the PDFs show local tetragonal distortions (i.e., c/a > 1). But, a box-car fitting analysis of the PDFs reveals variations at different length scales.more » For 0.80BT-0.20BZT and 0.90BT-0.10BZT, the tetragonal distortions decrease at longer atom-atom distances (e.g., 30 vs. 5 ). When the longest distances are evaluated (r > 40 ), the lattice parameters approach cubic. Neutron and X-ray diffraction yield further information about the long-range structure. Compositions 0.80BT-0.20BZT and 0.90BT-0.10BZT appear cubic by Bragg diffraction (no peak splitting), consistent with the PDFs at long distances. However, these patterns cannot be adequately fit using a cubic lattice model; modeling their structures with the P4mm space group allows for a better fit to the patterns because the space group allows for c-axis atomic displacements that occur at the local scale. Furthermore, for the compositions 0.92BT-0.08BZT and 0.94BT-0.06BZT, strong tetragonal distortions are observed at the local scale and a less-distorted tetragonal structure is observed at longer length scales. In Rietveld refinements, the latter is modeled using a tetragonal phase. Since the peak overlap in these two-phase compositions limits the ability to model the local-scale structures as tetragonal, it is approximated in the refinements as a cubic phase. These results demonstrate that alloying BT with BZT results in increased disorder and disrupts the long-range ferroelectric symmetry present in BT, while the large tetragonal distortion present in BZT persists at the local scale.« less

Electronic structure and electron-phonon coupling in TiH$$_2$$

DOE PAGES

Shanavas, Kavungal Veedu; Lindsay, Lucas R.; Parker, David S.

2016-06-15

Calculations using first principles methods and strong coupling theory are carried out to understand the electronic structure and superconductivity in cubic and tetragonal TiHmore » $$_2$$. A large electronic density of states at the Fermi level in the cubic phase arises from Ti-$$t_{2g}$$ states and leads to a structural instability against tetragonal distortion at low temperatures. However, constraining the in-plane lattice constants diminishes the energy gain associated with the tetragonal distortion, allowing the cubic phase to be stable at low temperatures. Furthermore, calculated phonon dispersions show decoupled acoustic and optic modes arising from Ti and H vibrations, respectively and frequencies of optic modes to be rather high. The cubic phase has a large electron-phonon coupling parameter $$\\lambda$$ and critical temperature of several K. Contribution of the hydrogen sublattice to $$\\lambda$$ is found to be small in this material, which we understand from strong coupling theory to be due to the small H-$s$ DOS at the Fermi level and high energy of hydrogen modes at the tetrahedral sites.« less

Cubic to tetragonal phase transition of Tm{sup 3+} doped nanocrystals in oxyfluoride glass ceramics

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

Li, Yiming; Fu, Yuting; Shi, Yahui

2016-02-15

Tm{sup 3+} ions doped β-PbF{sub 2} nanocrystals in oxyfluoride glass ceramics with different doping concentrations and thermal temperatures are prepared by a traditional melt-quenching and thermal treatment method to investigate the structure and the phase transition of Tm{sup 3+} doped nanocrystals. The structures are characterized by X-ray diffraction Rietveld analysis and confirmed with numerical simulation. The phase transitions are proved further by the emission spectra. Both of the doping concentration and thermal temperature can induce an O{sub h} to D{sub 4h} site symmetry distortion and a cubic to tetragonal phase transition. The luminescence of Tm{sup 3+} doped nanocrystals at 800more » nm was modulated by the phase transition of the surrounding crystal field.« less

High pressure ferroelastic phase transition in SrTiO3

NASA Astrophysics Data System (ADS)

Salje, E. K. H.; Guennou, M.; Bouvier, P.; Carpenter, M. A.; Kreisel, J.

2011-07-01

High pressure measurements of the ferroelastic phase transition of SrTiO3 (Guennou et al 2010 Phys. Rev. B 81 054115) showed a linear pressure dependence of the transition temperature between the cubic and tetragonal phase. Furthermore, the pressure induced transition becomes second order while the temperature dependent transition is near a tricritical point. The phase transition mechanism is characterized by the elongation and tilt of the TiO6 octahedra in the tetragonal phase, which leads to strongly nonlinear couplings between the structural order parameter, the volume strain and the applied pressure. The phase diagram is derived from the Clausius-Clapeyron relationship and is directly related to a pressure dependent Landau potential. The nonlinearities of the pressure dependent strains lead to an increase of the fourth order Landau coefficient with increasing pressure and, hence, to a tricritical-second order crossover. This behaviour is reminiscent of the doping related crossover in isostructural KMnF3.

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.

Structural studies of degradation process of zirconium dioxide tetragonal phase induced by grinding with dental bur

NASA Astrophysics Data System (ADS)

Piosik, A.; Żurowski, K.; Pietralik, Z.; Hędzelek, W.; Kozak, M.

2017-11-01

Zirconium dioxide has been widely used in dental prosthetics. However, the improper mechanical treatment can induce changes in the microstructure of zirconium dioxide. From the viewpoint of mechanical properties and performance, the phase transitions of ZrO2 from the tetragonal to the monoclinic phase induced by mechanical processing, are particularly undesirable. In this study, the phase transitions of yttrium stabilized zirconium dioxide (Y-TZP) induced by mechanical treatment are investigated by the scanning electron microscopy (SEM), atomic force microscopy (AFM) and powder diffraction (XRD). Mechanical stress was induced by different types of drills used presently in dentistry. At the same time the surface temperature was monitored during milling using a thermal imaging camera. Diffraction analysis allowed determination of the effect of temperature and mechanical processing on the scale of induced changes. The observed phase transition to the monoclinic phase was correlated with the methods of mechanical processing.

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.

Giant electric-field-induced strain in lead-free piezoelectric materials

PubMed Central

Chen, Lan; Yang, Yurong; Meng, X. K.

2016-01-01

First-principles calculations are performed to investigate the structures, electrical, and magnetic properties of compressive BiFeO3 films under electric-field and pressure perpendicular to the films. A reversible electric-field-induced strain up 10% is achieved in the compressive BiFeO3 films. The giant strain originates from rhombohedral-tetragonal (R-T) phase transition under electric-filed, and is recoverable from tetragonal-rhombohedral (T-R) phase transition by compressive stress. Additionally, the weak ferromagnetism in BiFeO3 films is largely changed in R-T phase transition under electric-filed and T-R phase transition under pressure – reminiscent of magnetoelectric effect and magnetoelastic effect. These results suggest exciting device opportunities arising from the giant filed-induced strain, large magnetoelectric effect and magnetoelastic effect. PMID:27139526

Sigma-phase packing of icosahedral clusters in 780-atom tetragonal crystals of Cr5Ni3Si2 and V15Ni10Si that by twinning achieve 8-fold rotational point-group symmetry

PubMed Central

Pauling, Linus

1988-01-01

A 780-atom primitive tetragonal unit with edges 27.3, 27.3, and 12.6 Å is assigned to rapidly solidified Cu5Ni3Si2 and V15Ni10Si by analysis of electron diffraction photographs with the assumption that the crystals contain icosahedral clusters. There are thirty 26-atom clusters at the sigma-phase positions. Apparent 8-fold symmetry results from 45° twinning on the basal plane. PMID:16593915

Sigma-phase packing of icosahedral clusters in 780-atom tetragonal crystals of Cr(5)Ni(3)Si(2) and V(15)Ni(10)Si that by twinning achieve 8-fold rotational point-group symmetry.

PubMed

Pauling, L

1988-04-01

A 780-atom primitive tetragonal unit with edges 27.3, 27.3, and 12.6 A is assigned to rapidly solidified Cu(5)Ni(3)Si(2) and V(15)Ni(10)Si by analysis of electron diffraction photographs with the assumption that the crystals contain icosahedral clusters. There are thirty 26-atom clusters at the sigma-phase positions. Apparent 8-fold symmetry results from 45 degrees twinning on the basal plane.

Electronic properties and structural phase transition in A4 [M4O4] (A=Li, Na, K and Rb; M=Ag and Cu): A first principles study

NASA Astrophysics Data System (ADS)

Umamaheswari, R.; Yogeswari, M.; Kalpana, G.

2013-02-01

Self-consistent scalar relativistic band structure calculations for AMO (A=Li, Na, K and Rb; M=Ag and Cu) compounds have been performed using the tight-binding linear muffin-tin orbital (TB-LMTO) method within the local density approximation (LDA). At ambient conditions, these compounds are found to crystallize in tetragonal KAgO-type structure with two different space group I-4m2 and I4/mmm. Nowadays, hypothetical structures are being considered to look for new functional materials. AMO compounds have stoichiometry similar to eight-electron half-Heusler materials of type I-I-VI which crystallizes in cubic (C1b) MgAgAs-type structure with space group F-43m. For all these compounds, by interchanging the positions of atoms in the hypothetical cubic structure, three phases (α, β and γ) are formed. The energy-volume relation for these compounds in tetragonal KAgO-type structure and cubic α, β and γ phases of related structure have been obtained. Under ambient conditions these compounds are more stable in tetragonal KAgO-type (I4/mmm) structure. The total energies calculated within the atomic sphere approximation (ASA) were used to determine the ground state properties such as equilibrium lattice parameters, c/a ratio, bulk modulus, cohesive energy and are compared with the available experimental results. The results of the electronic band structure calculations at ambient condition show that LiCuO and NaMO are indirect band gap semiconductors whereas KMO and RbMO are direct band gap semiconductors. At high pressure the band gap decreases and the phenomenon of band overlap metallization occur. Also these compounds undergo structural phase transition from tetragonal I-4m2 phase to cubic α-phase and transition pressures were calculated.

Pressure-temperature phase diagrams of CaK ( Fe 1 – x Ni x ) 4 As 4 superconductors

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

Xiang, Li; Meier, William R.; Xu, Mingyu

Here, the pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK(Fe 1–xNi x) 4As 4, the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels (x = 0.033,0.050) under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures T N are suppressed upon applying pressure; the superconducting transition temperatures T c are suppressed by pressure as well, except for x = 0.050more » in the pressure region where T N and T c cross. Furthermore, the pressure associated with the crossing of the T N and T c lines also coincides with a minimum in the normalized slope of the superconducting upper critical field, consistent with a likely Fermi-surface reconstruction associated with the loss of magnetic ordering. Lastly, at p ~ 4 GPa, both Ni-substituted CaK(Fe 1–xNi x) 4As 4 samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound CaKFe 4As 4.« less

Pressure-temperature phase diagrams of CaK ( Fe 1 – x Ni x ) 4 As 4 superconductors

DOE PAGES

Xiang, Li; Meier, William R.; Xu, Mingyu; ...

2018-05-22

Here, the pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK(Fe 1–xNi x) 4As 4, the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels (x = 0.033,0.050) under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures T N are suppressed upon applying pressure; the superconducting transition temperatures T c are suppressed by pressure as well, except for x = 0.050more » in the pressure region where T N and T c cross. Furthermore, the pressure associated with the crossing of the T N and T c lines also coincides with a minimum in the normalized slope of the superconducting upper critical field, consistent with a likely Fermi-surface reconstruction associated with the loss of magnetic ordering. Lastly, at p ~ 4 GPa, both Ni-substituted CaK(Fe 1–xNi x) 4As 4 samples likely go through a half-collapsed-tetragonal phase transition, similar to the parent compound CaKFe 4As 4.« less

Presence of a monoclinic (Pm) phase in the morphotropic phase boundary region of multiferroic (1 − x)Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} solid solution: A Rietveld study

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

Pandey, Rishikesh, E-mail: akhilesh-bhu@yahoo.com, E-mail: aksingh.mst@itbhu.ac.in; Singh, Akhilesh Kumar, E-mail: akhilesh-bhu@yahoo.com, E-mail: aksingh.mst@itbhu.ac.in

2014-07-28

We present here the results of structural studies on multiferroic (1 − x)Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} solid solution using Rietveld analysis on powder x-ray diffraction data in the composition range 0.35 ≤ x ≤ 0.55. The stability region of various crystallographic phases at room temperature for (1 − x)Bi(Ni{sub 1/2}Ti{sub 1/2})O{sub 3}-xPbTiO{sub 3} is determined precisely. Structural transformation from pseudo-cubic (x ≤ 0.40) to tetragonal (x ≥ 0.50) phase is observed via phase coexistence region demarcating the morphotropic phase boundary. The morphotropic phase boundary region consists of coexisting tetragonal and monoclinic structures with space group P4mm and Pm, respectively, stable in composition range 0.41 ≤ x ≤ 0.49 as confirmed by Rietveld analysis. The resultsmore » of Rietveld analysis completely rule out the coexistence of rhombohedral and tetragonal phases in the morphotropic phase boundary region reported by earlier workers. A comparison between the bond lengths for “B-site cations-oxygen anions” obtained after Rietveld refinement, with the bond length calculated using Shannon-Prewitt ionic radii, reveals the ionic nature of B-O (Ni/Ti-O) bonds for the cubic phase and partial covalent character for the other crystallographic phases.« less

Ternary ceramic alloys of Zr-Ce-Hf oxides

DOEpatents

Becher, P.F.; Funkenbusch, E.F.

1990-11-20

A ternary ceramic alloy is described which produces toughening of zirconia and zirconia composites through the stress transformation from tetragonal phase to monoclinic phase. This alloy, having the general formula Ce[sub x]Hf[sub y]Zr[sub 1[minus]x[minus]y]O[sub 2], is produced through the addition of appropriate amounts of ceria and hafnia to the zirconia. Typically, improved toughness is achieved with about 5 to about 15 mol % ceria and up to about 40 mol % hafnia. The preparation of alloys of these compositions are given together with data as to the densities, tetragonal phase content, hardness and fracture toughness. The alloys are useful in preparing zirconia bodies as well as reinforcing ceramic composites. 1 fig.

X-ray and dielectric characterization of Co doped tetragonal BaTiO3 ceramics

NASA Astrophysics Data System (ADS)

Bujakiewicz-Koronska, R.; Vasylechko, L.; Markiewicz, E.; Nalecz, D. M.; Kalvane, A.

2017-01-01

The crystal structure modifications of BaTiO3 induced by cobalt doping were studied. The polycrystalline (1 - x)BaTiO3 + xCo2O3 samples, with x ≤ 10 wt.%, were prepared by high temperature sintering conventional method. According to X-ray phase and structural characterization, performed by full-profile Rietveld refinement technique, all synthesized samples showed tetragonal symmetry perovskite structure with minor amount of parasitic phases. Pure single-phase composition has been detected only in the low level of doping BaTiO3. It was indicated that substitution of Co for the Ti sites in the (1 - x)BaTiO3 + xCo2O3 series led to decrease of tetragonality (c/a) of the BaTiO3 perovskite structure. This effect almost vanished in the (1 - x)BaTiO3 + xCo2O3 samples with nominal Co content higher than ∼1 wt.%, in which precipitation of parasitic Co-containing phases CoO and Co2TiO4 has been observed. Based on the results, the solubility limit of Co in Ti sub-lattice in the (1 - x)BaTiO3 + xCo2O3 series is estimated as x = 0.75 wt.%.

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.

Room temperature metastable monoclinic phase in BaTiO3 crystals

NASA Astrophysics Data System (ADS)

Lummen, Tom; Wang, Jianjun; Holt, Martin; Kumar, Amit; Vlahos, Eftihia; Denev, Sava; Chen, Long-Qing; Gopalan, Venkatraman

2011-03-01

Low-symmetry monoclinic phases in ferroelectric materials are of considerable interest, due to their associated enhanced electromechanical coupling. Such phases have been found in Pb-based perovskite solid solutions such as lead zirconate titanate (PZT), where they form structural bridges between the rhombohedral and tetragonal ground states in compositional space. In this work, we directly image such a monoclinic phase in BaTi O3 crystals at room-temperature, using optical second harmonic generation, Raman, and X-ray microscopic imaging techniques. Phase-field modeling indicates that ferroelectric domain microstructures in BaTi O3 induce local inhomogeneous stresses in the crystals, which can effectively trap the transient intermediate monoclinic structure that occurs across the thermal orthorhombic-tetragonal phase boundary. The induced metastable monoclinic domains are ferroelectrically soft, being easily moved by electric fields as low as 0.5 kV cm-1 . Stabilizing such intermediate low-symmetry phases could very well lead to Pb-free materials with enhanced piezoelectric properties.

Phonon Mode Transformation across the Orthohombic-Tetragonal Phase Transition in a Lead-Iodide Perovskite CH3NH3PbI3: a Terahertz Time-Domain Spectroscopy Approach

NASA Astrophysics Data System (ADS)

Chia, Elbert E. M.; La-O-Vorakiat, Chan; Kadro, Jeannette; Salim, Teddy; Zhao, Daming; Ahmed, Towfiq; Lam, Yeng Ming; Zhu, Jian-Xin; Marcus, Rudolph; Michel-Beyerle, Maria-Elisabeth

Using terahertz time-domain spectroscopy (THz-TDS), we study the temperature-dependent phonon modes of the organometallic lead iodide perovskite CH3NH3PbI3 thin film across the terahertz (0.5-3 THz) and temperature (20-300 K) ranges. These modes are related to the vibration of the Pb-I bonds. We found that two phonon modes in the tetragonal phase at room temperature split into four modes in the low-temperature orthorhombic phase. By use of the Lorentz model fitting, we analyze the critical behavior of this phase transition. King Mongkut's University of Technology Thonburi (Grant No. SCI58-003), Singapore MOE Tier 1 (RG13/12, RG123/14), ONR, ARO, NTU Biophysics Center, LANL LDRD, LANL CINT.

Antiferroelectricity in lanthanum doped zirconia without metallic capping layers and post-deposition/-metallization anneals

NASA Astrophysics Data System (ADS)

Wang, Zheng; Gaskell, Anthony Arthur; Dopita, Milan; Kriegner, Dominik; Tasneem, Nujhat; Mack, Jerry; Mukherjee, Niloy; Karim, Zia; Khan, Asif Islam

2018-05-01

We report the effects of lanthanum doping/alloying on antiferroelectric (AFE) properties of ZrO2. Starting with pure ZrO2, an increase in La doping leads to the narrowing of the AFE double hysteresis loops and an increase in the critical voltage/electric field for AFE → ferroelectric transition. At higher La contents, the polarization-voltage characteristics of doped/alloyed ZrO2 resemble that of a non-linear dielectric without any discernible AFE-type hysteresis. X-ray diffraction based analysis indicates that the increased La content while preserving the non-polar, parent AFE, tetragonal P42/nmc phase leads to a decrease in tetragonality and the (nano-)crystallite size and an increase in the unit cell volume. Furthermore, antiferroelectric behavior is obtained in the as-deposited thin films without requiring any capping metallic layers and post-deposition/-metallization anneals due to which our specific atomic layer deposition system configuration crystallizes and stabilizes the AFE tetragonal phase during growth.

Microstructure and mechanical properties of bulk yttria-partially-stabilized zirconia

NASA Technical Reports Server (NTRS)

Valentine, P. G.; Maier, R. D.; Mitchell, T. E.

1981-01-01

A commercially available bulk 4.5 mole percent yttria-Y2O3)-partially-stabilized zirconia (PSZ) was studied by light microscopy, X-ray analysis, microhardness measurement, and fracture toughness testing. The growth of the precipitates and the phase transformations were studied as a function of aging in air at 1500 C. Aging cuves were constructed for both the as-received and the solution-annealed-and-quenched materials; the curves showed hardness peaks at 1397 and 1517 kg/sq mm, respectively. A total of twelve different types of tetragonal precipitates were found. The rectangular plate-shaped tetragonal precipitates were found to have a (110) habit plane. Grinding of the Y2O3 PSZ into powder did not cause a significant amount of metastable tetragonal precipitates to transform into the monoclinic phase, thus indicating that transformation toughening is not a significant mechanism for the material. The fracture toughness of the aged and of the unaged solution-annealed-and-quenched PSZ was found to be between 2 and 3 MN/cu m/2.

Orthorhombic-tetragonal phase coexistence and enhanced piezo-response at room temperature in Zr, Sn, and Hf modified BaTiO{sub 3}

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

Kalyani, Ajay Kumar; Brajesh, Kumar; Ranjan, Rajeev, E-mail: rajeev@materials.iisc.ernet.in

2014-06-23

The effect of Zr, Hf, and Sn in BaTiO{sub 3} has been investigated at close composition intervals in the dilute concentration limit. Detailed structural analysis by x-ray and neutron powder diffraction revealed that merely 2 mol. % of Zr, Sn, and Hf stabilizes a coexistence of orthorhombic (Amm2) and tetragonal (P4mm) phases at room temperature. As a consequence, all the three systems show substantial enhancement in the longitudinal piezoelectric coefficient (d{sub 33}), with Sn modification exhibiting the highest value ∼425 pC/N.

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.

Influence of frequency on the structure of zirconium oxide coatings deposited from aqueous electrolytes under microplasma oxidation

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

Gubaidulina, Tatiana A., E-mail: goub2002@mail.ru; Sergeev, Viktor P., E-mail: vserg@mail.tomsknet.ru; Fedorischeva, Marina V., E-mail: fmw@ispms.tsc.ru

2015-10-27

The work describes the microplasma oxidation (MPO) of zirconium surface resulting in the formation of zirconium oxide Zr-Al-Nb-O. We have used novel power supply to deposit oxide ceramic coatings by MPO and studied the effect of current density on the phase structure of oxide ceramic coatings. The size of microcracks in the coatings was determined at different frequencies. We have also used EVO50c scanning election microscope with an attachment for elemental analysis to study the morphology and elemental composition of oxide ceramic coating. In addition, we have established the influence of the frequency on the phase composition of the coating:more » at the frequency of 2500 Hz, the fraction of monoclinic phase was 18%, while the fraction of tetragonal phase amounted to 72%. The oxide ceramic coating produced at 250 Hz contained 38% of monoclinic phase and 62% of tetragonal phase; in addition, it had no buildups and craters.« less

Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide.

PubMed

Fabini, Douglas H; Stoumpos, Constantinos C; Laurita, Geneva; Kaltzoglou, Andreas; Kontos, Athanassios G; Falaras, Polycarpos; Kanatzidis, Mercouri G; Seshadri, Ram

2016-12-05

The structure of the hybrid perovskite HC(NH 2 ) 2 PbI 3 (formamidinium lead iodide) reflects competing interactions associated with molecular motion, hydrogen bonding tendencies, thermally activated soft octahedral rotations, and the propensity for the Pb 2+ lone pair to express its stereochemistry. High-resolution synchrotron X-ray powder diffraction reveals a continuous transition from the cubic α-phase (Pm3‾ m, #221) to a tetragonal β-phase (P4/mbm, #127) at around 285 K, followed by a first-order transition to a tetragonal γ-phase (retaining P4/mbm, #127) at 140 K. An unusual reentrant pseudosymmetry in the β-to-γ phase transition is seen that is also reflected in the photoluminescence. Around room temperature, the coefficient of volumetric thermal expansion is among the largest for any extended crystalline solid. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Parlinski, K.; Hashi, Y.; Tsunekawa, S.

A model of lanthanum orthoniobate which possesses a ferroelastic tetragonal-monoclinic phase transition is proposed. It contains only one particle per unit cell, but it is constructed consistently with symmetry changes at the phase transition. The model parameters are chosen to reproduce the bare soft mode, degree of deformation of the tetragonal unit cell to monoclinic one, and the phase transition temperature. The ferroelastic system with free boundary conditions was simulated by the molecular dynamics technique, and the second order phase transition was reproduced. The studied annealing process shows formation of the stripe lenticular domain pattern, which has been interrupted bymore » appearance of a temporary band of perpendicularly oriented lenticular domains. The maps contain W{sup {prime}}-type domain walls whose orientations are fixed only by interplay of potential parameters and not by symmetry elements. The simulated domain pattern has the same features as those observed by transmission electron microscopy. {copyright} {ital 1997 Materials Research Society.}« less

Phase transitions in heated Sr{sub 2}MgTeO{sub 6} double perovskite oxide probed by X-ray diffraction and Raman spectroscopy

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

Manoun, Bouchaib, E-mail: manounb@gmail.com; Tamraoui, Y.; Lazor, P.

2013-12-23

Double-perovskite oxide Sr{sub 2}MgTeO{sub 6} has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550 °C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100 °C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300 °C, changes in the slopes of temperature dependencies of external and O–Te–O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) tomore » the cubic (Fm-3m) structure.« less

S = 1 on a Diamond Lattice in NiRh2O4

NASA Astrophysics Data System (ADS)

Chamorro, Juan; McQueen, Tyrel

An S = 1 system has the potential of rich physics, and has been the subject of intense theoretical work. Extensive work has been done on one-dimensional and two-dimensional S = 1 systems, yet three dimensional systems remain elusive. Experimental realizations of three-dimensional S = 1, however, are limited, and no system to date has been found to genuinely harbor this. Recent theoretical work suggests that S = 1 on a diamond lattice would enable a novel topological paramagnet state, generated by fluctuating Haldane chains within the structure, with topologically protected end states. Here we present data on NiRh2O4, a tetragonal spinel that has a structural phase transition from cubic to tetragonal at T = 380 K. High resolution XRD shows it to have a tetragonally distorted spinel structure, with Ni2+ (d8, S = 1) on the tetrahedral, diamond sublattice site. Magnetic susceptibility and specific heat measurements show that it does not order magnetically down to T = 0.1 K. Nearest neighbor interactions remain the same despite the cubic to tetragonal phase transition. Comparison to theoretical models indicate that this system might fulfill the requirements necessary to have both highly entangled and topological behaviors. IQM Is Funded by US Department of Energy, Office of Basic Energy Sciences, Division of Material Sciences and Engineering, under Grant No. DE-FG02-08ER46544.

Anisotropic physical properties of single-crystal U2Rh2Sn in high magnetic fields

NASA Astrophysics Data System (ADS)

Prokeš, K.; Gorbunov, D. I.; Reehuis, M.; Klemke, B.; Gukasov, A.; Uhlířová, K.; Fabrèges, X.; Skourski, Y.; Yokaichiya, F.; Hartwig, S.; Andreev, A. V.

2017-05-01

We report on the crystal and magnetic structures, magnetic, transport, and thermal properties of U2Rh2Sn single crystals studied in part in high magnetic fields up to 58 T. The material adopts a U3Si2 -related tetragonal crystal structure and orders antiferromagnetically below TN=25 K. The antiferromagnetic structure is characterized by a propagation vector k =(00 1/2 ) . The magnetism in U2Rh2Sn is found to be associated mainly with 5 f states. However, both unpolarized and polarized neutron experiments reveal at low temperatures in zero field non-negligible magnetic moments also on Rh sites. U moments of 0.50(2) μB are directed along the tetragonal axis while Rh moments of 0.06(4) μB form a noncollinear arrangement confined to the basal plane. The response to applied magnetic field is highly anisotropic. Above ˜15 K the easy magnetization direction is along the tetragonal axis. At lower temperatures, however, a stronger response is found perpendicular to the c axis. While for the a axis no magnetic phase transition is observed up to 58 T, for the field applied at 1.8 K along the tetragonal axis we observe above 22.5 T a field-polarized state. A magnetic phase diagram for the field applied along the c axis is presented.

Fabrication of dense and porous Li2ZrO3 nanofibers with electrospinning method

NASA Astrophysics Data System (ADS)

Yuan, Kangkang; Jin, Xiaotong; Xu, Chonghe; Wang, Xinqiang; Zhang, Guanghui; Zhu, Luyi; Xu, Dong

2018-06-01

Lithium zirconate (Li2ZrO3) has been extensively studied as CO2 capture material, electrolyte material and coating material. Most of the previous studies were focused on the powder structure, while seldom taking a consideration of fiber structure. In the present work, dense and porous Li2ZrO3 nanofibers with surface area of 16 m2 g-1 were prepared by electrospinning method. IR spectral results showed that lithium carbonate was the intermediate for the formation of Li2ZrO3. The phase transformation of Li2ZrO3 underwent the pathway of amorphous precursor fibers, tetragonal zirconia and Li2CO3, tetragonal Li2ZrO3, and monoclinic Li2ZrO3. XRD and XPS results further suggested that Li2O diffusion from the fiber body to surface occurred for Li2ZrO3 nanofibers when heat-treated above 900 °C, and the tetragonal Li2ZrO3 with high surface area could be obtained at 800 °C. Bamboo structure appeared both for the dense and porous nanofibers heat-treated at 1000 °C. The high surface area and high thermal stability of tetragonal phase of Li2ZrO3 make it a promising candidate in CO2 absorption, electrolyte and coating material.

On the bulk degradation of yttria-stabilized nanocrystalline zirconia dental implant abutments: an electron backscatter diffraction study.

PubMed

Ocelík, V; Schepke, U; Rasoul, H Haji; Cune, M S; De Hosson, J Th M

2017-08-01

Degradation of yttria-stabilized zirconia dental implants abutments due to the tetragonal to monoclinic phase transformation was studied in detail by microstructural characterization using Electron Back Scatter Diffraction (EBSD). The amount and distribution of the monoclinic phase, the grain-size distribution and crystallographic orientations between tetragonal and monoclinic crystals in 3 mol.% yttria-stabilized polycrystalline zirconia (3Y-TZP) were determined in two different types of nano-crystalline dental abutments, even for grains smaller than 400 nm. An important and novel conclusion is that no substantial bulk degradation of 3Y-TZP dental implant abutments was detected after 1 year of clinical use.

Tetragonal Almandine, (Fe,Mg,Ca,Na)3(Al,Si,Mg)2Si3O12, a New High-Pressure Mineral from the Shergotty Impact on Mars: an Integrated FESEM-EPMA-Synchrotron Diffraction Investigation

NASA Astrophysics Data System (ADS)

Ma, C.; Tschauner, O. D.

2016-12-01

The combination of FESEM-EDS-EBSD, EPMA, and synchrotron microdiffraction is developing into a powerful tool for identification of micron-scale minerals in rocks such as high-pressure phases in shocked meteorites. During a nanomineralogy investigation of the Shergotty meteorite using this approach, we have identified a new shock-induced high-pressure silicate, majoritic almandine with a tetragonal I41/a structure, in an impact melt pocket. The Shergotty meteorite, which fell in the Gaya district, Bihar, India in 1865, is a Martian basaltic shergottite with shock features. Tetragonal almandine in Shergotty occurs as aggregates of subhedral crystals, 0.8 - 2.5 µm in diameter, along with stishovite in the central region of a shock melt pocket, showing an empirical formula of (Fe1.16Ca0.75Mg0.61Na0.42Mn0.03K0.01)(Al1.16Si0.63Mg0.19Ti0.02)Si3O12. Its general formula is (Fe,Mg,Ca,Na)3(Al,Si,Mg)2Si3O12. EBSD indicated this phase has a garnet-related structure. Synchrotron X-ray diffraction revealed that this garnet has actually a tetragonal structure (I41/a) with unit cell dimensions: a = 11.585(9) Å, c = 11.63(4) Å, V = 1561(7) Å3, and Z = 8. Tetragonal almandine is the polymorph of cubic almandine, a new high-pressure garnet mineral, formed by shock metamorphism via the Shergotty impact event on Mars. It apparently crystallized from Fe-rich shock-induced melt under high-pressure and high-temperature conditions.

Origin of thickness dependence of structural phase transition temperatures in BiFeO 3 thin films

DOE PAGES

Yang, Yongsoo; Beekman, Christianne; Siemons, Wolter; ...

2016-03-28

In this study, two structural phase transitions are investigated in highly strained BiFeO 3 thin films grown on LaAlO 3 substrates, as a function of film thickness and temperature via synchrotron x-ray diffraction. Both transition temperatures (upon heating: monoclinic MC to monoclinic MA, and MA to tetragonal) decrease as the film becomes thinner. The existence of an interface layer at the film-substrate interface, deduced from half-order peak intensities, contributes to this behavior only for the thinnest samples; at larger thicknesses (above a few nanometers) the temperature dependence can be understood in terms of electrostatic considerations akin to size effects inmore » ferroelectric phase transitions, but observed here for structural phase transitions within the ferroelectric phase and related to the rearrangement rather than the formation of domains. For ultra-thin films, the tetragonal structure is stable at all investigated temperatures (down to 30 K).« less

Variable-temperature single-crystal X-ray diffraction study of tetragonal and cubic perovskite-type barium titanate phases.

PubMed

Nakatani, Tomotaka; Yoshiasa, Akira; Nakatsuka, Akihiko; Hiratoko, Tatsuya; Mashimo, Tsutomu; Okube, Maki; Sasaki, Satoshi

2016-02-01

A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3 perovskite has been performed over the temperature range 298-778 K. A transition from a tetragonal (P4mm) to a cubic (Pm3m) phase has been revealed near 413 K. In the non-centrosymmetric P4mm symmetry group, both Ti and O atoms are displaced along the c-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti(4+) and Ba(2+) cations occupy off-center positions in the TiO6 and BaO12 polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.

Order-disorder phenomena in the low-temperature phase of BaTiO3

NASA Astrophysics Data System (ADS)

Völkel, G.; Müller, K. A.

2007-09-01

X - and Q -band electron paramagnetic resonance measurements are reported on Mn4+ -doped BaTiO3 single crystals in the rhombohedral low-temperature phase. The Mn4+ probe ion is statistically substitute for the isovalent Ti4+ ion. The critical line broadening observed when approaching the phase transition to the orthorhombic phase demonstrates the presence of order-disorder processes within the off-center Ti subsystem and the formation of dynamic precursor clusters with a structure compatible with one of the orthorhombic phase. From the data it is concluded that BaTiO3 shows a special type of phase transition where displacive and order-disorder character are not only present at the cubic-tetragonal transition, but also at the orthorhombic-rhombohedral transition at low temperatures. The disappearance of the Mn4+ spectrum in the orthorhombic, tetragonal, and cubic phases can be interpreted as the consequence of the strong line broadening caused by changes of the instantaneous off-center positions in time around the averaged off-center position along a body diagonal.

Improvement of the piezoelectric properties in (K,Na)NbO3-based lead-free piezoelectric ceramic with two-phase co-existing state

NASA Astrophysics Data System (ADS)

Yamada, H.; Matsuoka, T.; Kozuka, H.; Yamazaki, M.; Ohbayashi, K.; Ida, T.

2015-06-01

Two phases of (K,Na)NbO3 (KNN) co-exist in a KNN-based composite lead-free piezoelectric ceramic 0.910(K1-xNax)0.86Ca0.04Li0.02Nb0.85O3-δ-0.042K0.85Ti0.85Nb1.15O5-0.036BaZrO3-0.0016Co3O4- 0.0025Fe2O3-0.0069ZnO system, over a wide range of Na fractions, where 0.56 ≤ x ≤ 0.75. The crystal systems of the two KNN phases are identified to tetragonal and orthorhombic by analyzing the synchrotron powder X-ray diffraction (XRD) data, high-resolution transmission electron microscopy (HR-TEM), and selected-area electron diffraction (SAD). In the range 0.33 ≤ x ≤ 0.50, the main component of the composite system is found to be single-phase KNN with a tetragonal structure. Granular nanodomains of the orthorhombic phase dispersed in the tetragonal matrix have been identified by HR-TEM and SAD for 0.56 ≤ x ≤ 0.75. Only a trace amount of the orthorhombic phase has been found in the SAD patterns at the composition x = 0.56. However, the number of orthorhombic nanodomains gradually increases with increasing Na content up to x < 0.75, as observed from the HR-TEM images. An abrupt increase and agglomeration of the nanodomains are observed at x = 0.75, where weak diffraction peaks of the orthorhombic phase have also become detectable from the XRD data. The maximum value of the electromechanical coupling coefficient, kp = 0.56, has been observed at the composition x = 0.56.

Phase coexistence and high electrical properties in (KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 piezoelectric ceramics

NASA Astrophysics Data System (ADS)

Chang, Yunfei; Yang, Zupei; Ma, Difei; Liu, Zonghuai; Wang, Zenglin

2009-03-01

(KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 lead-free piezoelectric ceramics were produced by conventional solid-state reaction method. The effects of K/Na ratio on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics have been investigated. The phase structure of the ceramics undergoes a transition from orthorhombic to tetragonal phase with increasing x. A double-degenerate symmetric O-Nb-O stretching vibration v1 and a triply degenerate symmetric O-Nb-O bending vibration v5 are detected as relatively strong scattering in the Raman spectra. The peak shifts of v5 and v1 modes all have a discontinuity with x between 0.42 and 0.46, which may suggest the coexistence of orthorhombic and tetragonal phases in this range. Properly modifying x reduces the sintering temperature, promotes the grain growth behavior, and improves the density of the ceramics. The polymorphic phase transition (at To -t) is shifted to near room temperature by increasing x to 0.44 (K/Na ratio of about 0.85:1), and the coexistence of orthorhombic and tetragonal phases in the ceramics at x =0.44 results in the optimized electrical properties (d33=291 pC/N, kp=0.54, ɛr=1167, tan δ=0.018, To -t=35 °C, TC=351 °C, Pr=27.65 μC/cm2, and Ec=8.63 kV/cm). The results show that the equal K/Na ratio is not an essential condition in obtaining optimized electrical properties in (KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 ceramics.

Role of Y2O3, CaO, MgO additives on structural and microstructural behavior of zirconia/mullite aggregates

NASA Astrophysics Data System (ADS)

Mishra, D. K.; Prusty, Sasmita; Mohapatra, B. K.; Singh, S. K.; Behera, S. N.

2012-07-01

Zirconia mullite (MUZ), Y2O3-MUZ, CaO-MUZ and MgO-MUZ composites, synthesized through plasma fusion technique, are becoming important due to their commercial scale of production within five minutes of plasma treatment from sillimanite, zircon and alumina mixture. The X-ray diffraction studies reveal the monoclinic zirconia phase in MUZ composite whereas mixed monoclinic, tetragonal and cubic phases of zirconia have been observed in Y2O3, CaO, MgO added MUZ composites. The Y2O3, CaO and MgO additives act as sintering aids to favour the transformation and stabilisation of tetragonal and cubic zirconia phases at room temperature. These additives also play a key role in the development of various forms of microstructure to achieve dense MUZ composites.

One pot synthesis of pure micro/nano photoactive α-PbO crystals

NASA Astrophysics Data System (ADS)

Bhagat, Dharini; Waldiya, Manmohansingh; Vanpariya, Anjali; Mukhopadhyay, Indrajit

2018-05-01

The present study reports a simple, fast and cost effective precipitation technique for synthesis of pure α-PbO powder. Lead monoxide powder with tetragonal structure was synthesized chemically at an elevated temperature using lead acetate and sodium hydroxide solution bath. XRD powder diffraction was used to find the structural properties as well as phase transition from alpha to beta. Study revealed that synthesized PbO powder was crystalline with tetragonal symmetry, having an average crystallite size of 70 nm and lattice constants; a=3.97Å, b=3.97Å, and c=5.02Å. Phase transition from tetragonal to orthorhombic structure was studied by comparing the XRD data of the annealed samples in the temperature range from 200 °C to 600 °C. UV-Visible spectroscopy was used to find out the optical properties of prepared PbO powder. Diffuse reflectance and absorbance spectra confirmed the formation of α-PbO with obtained direct band gap of 1.9 eV. Synthesized lead monoxide (α-PbO) powder has promising application in energy conversion as well as energy storage applications.

Metal-organic chemical vapour deposition of polycrystalline tetragonal indium sulphide (InS) thin films

NASA Technical Reports Server (NTRS)

Macinnes, Andrew N.; Cleaver, William M.; Barron, Andrew R.; Power, Michael B.; Hepp, Aloysius F.

1992-01-01

The dimeric indium thiolate /(t Bu)2In(mu-S sup t Bu)/2 has been used as a single-source precursor for the MOCVD of InS thin films. The dimeric In2S2 core is proposed to account for the formation of the nonequilibrium high-pressure tetragonal phase in the deposited films. Analysis of the deposited films has been obtained by TEM, with associated energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy.

Elastic excitations in BaTiO3 single crystals and ceramics: Mobile domain boundaries and polar nanoregions observed by resonant ultrasonic spectroscopy

NASA Astrophysics Data System (ADS)

Salje, Ekhard K. H.; Carpenter, Michael A.; Nataf, Guillaume F.; Picht, Gunnar; Webber, Kyle; Weerasinghe, Jeevaka; Lisenkov, S.; Bellaiche, L.

2013-01-01

The dynamic properties of elastic domain walls in BaTiO3 were investigated using resonance ultrasonic spectroscopy (RUS). The sequence of phase transitions is characterized by minima in the temperature dependence of RUS resonance frequencies and changes in Q factors (resonance damping). Damping is related to the friction of mobile twin boundaries (90° ferroelectric walls) and distorted polar nanoregions (PNRs) in the cubic phase. Damping is largest in the tetragonal phase of ceramic materials but very low in single crystals. Damping is also small in the low-temperature phases of the ceramic sample and slightly increases with decreasing temperature in the single crystal. The phase angle between the real and imaginary part of the dynamic response function changes drastically in the cubic and tetragonal phases and remains constant in the orthorhombic phase. Other phases show a moderate dependence of the phase angle on temperature showing systematic changes of twin microstructures. Mobile twin boundaries (or sections of twin boundaries such as kinks inside twin walls) contribute strongly to the energy dissipation of the forced oscillation while the reduction in effective modulus due to relaxing twin domains is weak. Single crystals and ceramics show strong precursor softening in the cubic phase related to polar nanoregions (PNRs). The effective modulus decreases when the transition point of the cubic-tetragonal transformation is approached from above. The precursor softening follows temperature dependence very similar to recent results from Brillouin scattering. Between the Burns temperature (≈586 K) and Tc at 405 K, we found a good fit of the squared RUS frequency [˜Δ (C11-C12)] to a Vogel-Fulcher process with an activation energy of ˜0.2 eV. Finally, some first-principles-based effective Hamiltonian computations were carried out in BaTiO3 single domains to explain some of these observations in terms of the dynamics of the soft mode and central mode.

Identification and properties of the non-cubic phases of Mg 2Pb

DOE PAGES

Li, Yuwei; Bian, Guang; Singh, David J.

2016-12-20

Mg 2Pb occurs in the cubic fluorite structure and is a semimetal with a band structure strongly affected by spin-orbit interaction on the Pb p states. Its properties are therefore of interest in the context of topological materials. In addition a different phase of Mg 2Pb was experimentally reported, but its crystal structure and properties remain unknown. Here we determine the structure of this phase using ab initio evolutionary methods and report its properties. The energy of one tetragonal phase, space group P4/ nmm, is 2 meV per atom higher than that of the ground state structure supporting the experimentalmore » observation. We find this tetragonal phase to be a compenstated anisotropic metal with strong spin orbit effects. As a result, many other metastable structures have also been identified, especially one orthorhombic structure, space group Pnma, of which energy is 17 meV per atom higher than that of ground state structure and which perhaps could be the phase that was reported based on similarity of lattice parameters.« less

Epitaxial bain paths and metastable phases of tetragonal iron and manganese

NASA Astrophysics Data System (ADS)

Ma, Hong

2002-04-01

Epitaxial Bain paths and metastable states of tetragonal Fe and Mn have been studied by first-principles total-energy calculations using the full-potential linearized-augmented-plane-wave method. The main accomplishments are as follows. (1) We have performed the first ever EBP calculation of tetragonal antiferromagnetic (AF) Mn showing that when grown epitaxially on Pd(001), the AF Mn film is strained gamma-Mn, but grown on V(001) the film is strained delta-Mn, which could not be determined using the available crystallographic and elastic data because they were obtained from unstrained states. (2) We have calculated the EBP's of Fe at zero pressure in four magnetic phases, i.e., ferromagnetic (FM), nonmagnetic (NM), type-I antiferromagnetic (AF1), and type-II antiferromagnetic (AF2), which show that the AF2 is the phase of the bulk of epitaxial Fe films on Cu(001) and it is unstable for [110] and [010] shears in the (001) plane, but it can be stabilized by epitaxy on Cu(001). (3)We have unified and simplified the theory of elasticity under hydrostatic pressure p at zero temperature using the Gibbs free energy G, rather than the energy E. The minima of G, but not E, with respect to strains at the equilibrium structure give the zero temperature elastic constants; the stability of a phase at p is then determined by the same Born stability conditions used at p = 0 when applied to the elastic constants from G. The EBP's of FM Fe under hydrostatic pressure show that the bcc phase exists up to 1500 kbar. A bct phase is shown to come into existence at 1300 kbar and becomes stable at 1825 kbar and above. (4) Based on this dissertation research five papers have been published in refereed journals.

Nematic fluctuations in iron arsenides NaFeAs and LiFeAs probed by 75As NMR

NASA Astrophysics Data System (ADS)

Toyoda, Masayuki; Kobayashi, Yoshiaki; Itoh, Masayuki

2018-03-01

75As NMR measurements have been made on single crystals to study the nematic state in the iron arsenides NaFeAs, which undergoes a structural transition from a high-temperature (high-T ) tetragonal phase to a low-T orthorhombic phase at Ts=57 K and an antiferromagnetic transition at TN=42 K, and LiFeAs having a superconducting transition at Tc=18 K. We observe the in-plane anisotropy of the electric field gradient η even in the tetragonal phase of NaFeAs and LiFeAs, showing the local breaking of tetragonal C4 symmetry. Then, η is found to obey the Curie-Weiss (CW) law as well as in Ba (Fe1-xCox) 2As2 . The good agreement between η and the nematic susceptibility obtained by electronic Raman spectroscopy indicates that η is governed by the nematic susceptibility. From comparing η in NaFeAs and LiFeAs with η in Ba (Fe1-xCox) 2As2 , we discuss the carrier-doping dependence of the nematic susceptibility. The spin contribution to nematic susceptibility is also discussed from comparing the CW terms in η with the nuclear spin-lattice relaxation rate divided by temperature 1 /T1T . Finally, we discuss the nematic transition in the paramagnetic orthorhombic phase of NaFeAs from the in-plane anisotropy of 1 /T1T .

Tetragonal zirconia quantum dots in silica matrix prepared by a modified sol-gel protocol

NASA Astrophysics Data System (ADS)

Verma, Surbhi; Rani, Saruchi; Kumar, Sushil

2018-05-01

Tetragonal zirconia quantum dots (t-ZrO2 QDs) in silica matrix with different compositions ( x)ZrO2-(100 - x)SiO2 were fabricated by a modified sol-gel protocol. Acetylacetone was added as a chelating agent to zirconium propoxide to avoid precipitation. The powders as well as thin films were given thermal treatment at 650, 875 and 1100 °C for 4 h. The silica matrix remained amorphous after thermal treatment and acted as an inert support for zirconia quantum dots. The tetragonal zirconia embedded in silica matrix transformed into monoclinic form due to thermal treatment ≥ 1100 °C. The stability of tetragonal phase of zirconia is found to enhance with increase in silica content. A homogenous dispersion of t-ZrO2 QDs in silica matrix was indicated by the mapping of Zr, Si and O elements obtained from scanning electron microscope with energy dispersive X-ray analyser. The transmission electron images confirmed the formation of tetragonal zirconia quantum dots embedded in silica. The optical band gap of zirconia QDs (3.65-5.58 eV) was found to increase with increase in zirconia content in silica. The red shift of PL emission has been exhibited with increase in zirconia content in silica.

A study of suppressed formation of low-conductivity phases in doped Li 7La 3Zr 2O 12 garnets by in situ neutron diffraction

DOE PAGES

Chen, Yan; Rangasamy, Ezhiylmurugan; dela Cruz, Clarina R.; ...

2015-09-28

Doped Li 7La 3Zr 2O 12 garnets, oxide-based solids with good Li + conductivity and compatibility, show great potential as leading electrolyte material candidates for all-solid-state lithium ion batteries. Still yet, the conductive bulk usually suffers from the presence of secondary phases and the transition towards a low-conductivity tetragonal phase during synthesis. Dopants are designed to stabilize the high-conductive cubic phase and suppress the formation of the low-conductivity phases. In situ neutron diffraction enables a direct observation of the doping effects by monitoring the phase evolutions during garnet synthesis. It reveals the reaction mechanism involving the temporary presence of intermediatemore » phases. The off-stoichiometry due to the liquid Li 2CO 3 evaporation leads to the residual of the low-conductivity intermediate phase in the as-synthesized bulk. Appropriate doping of an active element may alter the component of the intermediate phases and promote the completion of the reaction. While the dopants aid to stabilize most of the cubic phase, a small amount of tetragonal phase tends to form under a diffusion process. Lastly, the in situ observations provide the guideline of process optimization to suppress the formation of unwanted low-conductivity phases.« less

Twin and habit plane microstructures due to the tetragonal to monoclinic transformation of zirconia

NASA Astrophysics Data System (ADS)

Simha, N. K.

1997-02-01

We first construct Bain strains for the tetragonal to monoclinic ( t → m) transformation of zirconia (ZrO 2), and then examine the resulting twin and habit plane microstructures. The ( t → m) transformation in zirconia occurs via two paths; transformation along path I has two Bain strains that involve shearing of a rectangular face of the tetragonal unit cell, and shearing of the square base corresponds to path II. The monoclinic variants resulting from each of the three Bain strains can form 12 twins, and four of the twins corresponding to path II are neither of type I nor of type II. Habit planes do not exist for the transformation along path I, whereas transformation along path II has: (± 0.8139, ± 0.3898, - 0.4309) t, (± 0.6489, ± 0.6271, - 0.4309) t, (± 0.7804, ± 0.4530, - 0.4309) t. We predict the exact twin planes observed by Bailey [(1964) Phase transformation at high temperatures in hafnia and zirconia. Proc. Roy. Soc.279A, 395-412], Bansal and Heuer [(1972) On a martensitic phase transformation in Zirconia ZrO 2—I. Metallographic evidence. Acta Metall.20, 1281-1289] and Buljan et al. [(1976) Optical and X-ray single crystal studies of the monoclinic ↔ tetragonal transition in ZrO 2. J. Am. Ceram. Soc.59, 351-354]; additional twins and habit planes that we predict have not yet been observed.

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

Guo, Peijun; Xia, Yi; Gong, Jue

Solution-processable metal-halide perovskites (MHPs) offer great promise for efficient light harvesting and emitting devices due to their long carrier lifetime and superior carrier transport characteristics. Ferroelectric effects, a hallmark of traditional oxide perovskites, was proposed to be a mechanism to suppress carrier recombination and enhance charge transport in MHPs, but the existence and influence of such polar order is still of considerable debate. Here we performed transient reflection measurements on single crystals of both inorganic and organic-inorganic (hybrid) MHPs over a range of temperatures, and demonstrate significant phonon softening in the cubic phases close to the cubic-to-tetragonal phase transition temperatures.more » Such phonon softening indicates the formation of polar domains, which grow in size upon cooling and can persist in the low-temperature tetragonal and orthorhombic phases. Our results link the extraordinary electronic properties of MHPs to the spontaneous polarizations which can contribute to more efficient charge separation and characteristics of an indirect bandgap.« less

Large scale synthesis of nanostructured zirconia-based compounds from freeze-dried precursors

NASA Astrophysics Data System (ADS)

Gómez, A.; Villanueva, R.; Vie, D.; Murcia-Mascaros, S.; Martínez, E.; Beltrán, A.; Sapiña, F.; Vicent, M.; Sánchez, E.

2013-01-01

Nanocrystalline zirconia powders have been obtained at the multigram scale by thermal decomposition of precursors resulting from the freeze-drying of aqueous acetic solutions. This technique has equally made possible to synthesize a variety of nanostructured yttria or scandia doped zirconia compositions. SEM images, as well as the analysis of the XRD patterns, show the nanoparticulated character of those solids obtained at low temperature, with typical particle size in the 10-15 nm range when prepared at 673 K. The presence of the monoclinic, the tetragonal or both phases depends on the temperature of the thermal treatment, the doping concentration and the nature of the dopant. In addition, Rietveld refinement of the XRD profiles of selected samples allows detecting the coexistence of the tetragonal and the cubic phases for high doping concentration and high thermal treatment temperatures. Raman experiments suggest the presence of both phases also at relatively low treatment temperatures.

Frustrated spin one on a diamond lattice in NiRh2O4

NASA Astrophysics Data System (ADS)

Chamorro, J. R.; Ge, L.; Flynn, J.; Subramanian, M. A.; Mourigal, M.; McQueen, T. M.

2018-03-01

We report the discovery of a spin one diamond lattice in NiRh2O4 . This spinel undergoes a cubic to tetragonal phase transition at T =440 K that leaves all nearest neighbor interactions equivalent. In the tetragonal phase, magnetization measurements show a Ni2 + effective moment of peff=3.3 (1 ) and dominant antiferromagnetic interactions with ΘCW=-11.3 (7 ) K. No phase transition to a long-range magnetically ordered state is observed by specific heat measurements down to T =0.1 K. Inelastic neutron scattering measurements on substoichiometric NiRh2O4 reveal possible valence-bond behavior and show no visible signs of magnetic ordering. NiRh2O4 provides a platform on which to explore the previously unknown and potentially rich physics of spin one interacting on the diamond lattice, including the realization of theoretically predicted quantum spin liquid and topological paramagnet states.

Momentum-resolved hidden-order gap reveals symmetry breaking and origin of entropy loss in URu2Si2

NASA Astrophysics Data System (ADS)

Bareille, C.; Boariu, F. L.; Schwab, H.; Lejay, P.; Reinert, F.; Santander-Syro, A. F.

2014-07-01

Spontaneous symmetry breaking in physical systems leads to salient phenomena at all scales, from the Higgs mechanism and the emergence of the mass of the elementary particles, to superconductivity and magnetism in solids. The hidden-order state arising below 17.5 K in URu2Si2 is a puzzling example of one of such phase transitions: its associated broken symmetry and gap structure have remained longstanding riddles. Here we directly image how, across the hidden-order transition, the electronic structure of URu2Si2 abruptly reconstructs. We observe an energy gap of 7 meV opening over 70% of a large diamond-like heavy-fermion Fermi surface, resulting in the formation of four small Fermi petals, and a change in the electronic periodicity from body-centred tetragonal to simple tetragonal. Our results explain the large entropy loss in the hidden-order phase, and the similarity between this phase and the high-pressure antiferromagnetic phase found in quantum-oscillation experiments.

Morphological Evolution and Weak Interface Development within CVD-Zirconia Coating Deposited on Hi-Nicalon Fiber

NASA Technical Reports Server (NTRS)

Li, Hao; Lee, Jinil; Libera, Matthew R.; Lee, Woo Y.; Kebbede, Anteneh; Lance, Michael J.; Wang, Hongyu; Morscher, Gregory N.; Gray, Hugh R. (Technical Monitor)

2002-01-01

The phase contents and morphology of a ZrO2 fiber coating deposited at 1050 C on Hi-Nicalon(Tm) by chemical vapor deposition were examined as a function of deposition time from 5 to 120 min. The morphological evolution in the ZrO2 coating was correlated to the development of delamination within the ZrO2 coating. The delamination appears to occur as a result of: (1) continuous formation of tetragonal ZrO2 nuclei on the deposition surface; (2) martensitic transformation of the tetragonal phase to a monoclinic phase upon reaching a critical grain size; and (3) development of significant compressive hoop stresses due to the volume dilation associated with the transformation. Our observations suggest that it will be of critical importance to further understand and eventually control the nucleation and grain growth behavior of CVD ZrO2 and its phase transformation behavior for its potential applications for composites.

Ferroelectric, elastic, piezoelectric, and dielectric properties of Ba(Ti0.7Zr0.3)O3-x(Ba0.82Ca0.18)TiO3 Pb-free ceramics

NASA Astrophysics Data System (ADS)

Yuan, Ruihao; Xue, Deqing; Zhou, Yumei; Ding, Xiangdong; Sun, Jun; Xue, Dezhen

2017-07-01

We designed and synthesized a pseudo-binary Pb-free system, Ba(Ti0.7Zr0.3)O3-x(Ba0.82Ca0.18)TiO3, by combining a rhombohedral end (with only cubic to rhombohedral ferroelectric phase transition) and a tetragonal end (with only cubic to tetragonal ferroelectric phase transition). The established composition-temperature phase diagram is characterized by a tricritical point type morphotropic phase boundary (MPB), and the MPB composition has better ferroelectric, piezoelectric, and dielectric properties than the compositions deviating from MPB. Moreover, a full set of material constants (including elastic stiffness constants, elastic compliance constants, piezoelectric constants, dielectric constants, and electromechanical coupling factors) of the MPB composition are determined using a resonance method. The good piezoelectric performance of the MPB composition can be ascribed to the high dielectric constants, elastic softening, and large electromechanical coupling factor.

Neutron and X-ray diffraction of plasma-sprayed zirconia-yttria thermal barrier coatings

NASA Technical Reports Server (NTRS)

Shankar, N. R.; Herman, H.; Singhal, S. P.; Berndt, C. C.

1984-01-01

ZrO2-7.8mol. pct. YO1.5, a fused powder, and ZrO2-8.7mol. pct. YO1.5, a prereacted powder, were plasma-sprayed onto steel substrates. Neutron diffraction and X-ray diffraction of the as-received powder, the powder plasma sprayed into water, as-sprayed coatings, and coatings heat-treated for 10 and 100 h were carried out to study phase transformations and ordering of the oxygen ions on the oxygen sublattice. The as-received fused powder has a much lower monoclinic percentage than does the pre-reacted powder, this resulting in a much lower monoclinic percentage in the coating. Heat treatment increases the percentages of the cubic and monoclinic phases, while decreasing the tetragonal content. An ordered tetragonal phase is detected by the presence of extra neutron diffraction peaks. These phase transformations and ordering will result in volume changes. The implications of these transformations on the performance of partially stabilized zirconia thermal barrier coatings is discussed.

Phase transition in lithium garnet oxide ionic conductors Li7La3Zr2O12: The role of Ta substitution and H2O/CO2 exposure

NASA Astrophysics Data System (ADS)

Wang, Yuxing; Lai, Wei

2015-02-01

High Li-content lithium garnet oxides are promising solid electrolyte materials for lithium batteries. Being the highest Li-content lithium garnet oxides, Li7La3Zr2O12 has been reported to crystallize in either the tetragonal or cubic phase with no consensus on the exact conditions under which these two phases are formed, which may be due to unintentional Al contamination and air exposure. In this work, the effects of Ta substitution and H2O/CO2 exposure have been studied under Al-contamination free conditions with minimal air exposure. We showed that 1) the Ta-substitution induced phase transition occurred through a two-phase mechanism and a minimum 0.6 mol of Ta substitution to Zr is needed to stabilize the cubic phase; 2) H2O and CO2 can individually induce the tetragonal-cubic phase transition in Li7La3Zr2O12 through proton exchange and Li extraction, respectively, which can have great influence on the transport properties of Li7La3Zr2O12.

The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.

2001-01-01

Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study, we show that possible conformational changes induced by heating are stable and apparently non-reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for four weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 hours at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.

The Effect of Solution Thermal History on Chicken Egg White Lysozyme Nucleation

NASA Technical Reports Server (NTRS)

Burke, Michael W.; Judge, Russell A.; Pusey, Marc L.; Rose, M. Franklin (Technical Monitor)

2000-01-01

Proteins are highly flexible molecules and often exhibit defined conformational changes in response to changes in the ambient temperature. Chicken egg white lysozyme has been previously shown to undergo an apparent structural change when warmed above the tetragonal/orthorhombic phase transition temperature. This is reflected by a change in the habit of the tetragonal and orthorhombic crystals so formed. In this study we show that possible conformational changes induced by heating are stable and apparently non- reversible by simple cooling. Exposure of protein solutions to temperatures above the phase change transition temperature, before combining with precipitant solution to begin crystallization, reduces final crystal numbers. Protein that is briefly warmed to 37 C, then cooled shows no sign of reversal to the unheated nucleation behavior even after storage for 4 weeks at 4 C. The change in nucleation behavior of tetragonal lysozyme crystals, attributed to a structural shift, occurs faster the greater the exposure to temperature above the equi-solubility point for the two phases. Heating for 2 h at 48 C reduces crystal numbers by 20 fold in comparison to the same solution heated for the same time at 30 C. Thermal treatment of solutions is therefore a possible tool to reduce crystal numbers and increase crystal size. The effects of a protein's previous thermal history are now shown to be a potentially critical factor in subsequent macromolecule crystal nucleation and growth studies.

Energy shifts in photoemission lines during the tetragonal- to cubic-phase transition in BaTiO3 single crystals and systems with CoFe2O4 and NiFe2O4 overlayers

NASA Astrophysics Data System (ADS)

Welke, M.; Huth, P.; Dabelow, K.; Gorgoi, M.; Schindler, K.-M.; Chassé, A.; Denecke, R.

2018-05-01

In BaTiO3 the phase transition from tetragonal to cubic is connected with the disappearance of the ferroelectric polarization. In photoelectron spectroscopy huge transient shifts in the binding energies of all core-level photoemission lines have been observed while heating and cooling through the Curie temperature. Excitation energies from 2 keV to 6 keV have been used to show this to be a bulk effect and not a surface effect alone. These observations are discussed in terms of charging, which results from the disappearance of the ferroelectric polarization. This mechanism has previously been proposed as the origin of electron emission in ferroelectric materials. Besides the jump-like shifts, additional permanent shifts in binding energies have been observed for the tetragonal and the cubic phase. These experimental shifts have been related to theoretical ones from ab initio calculations. In addition to BaTiO3 single crystals, systems with CoFe2O4 and NiFe2O4 overlayers on BaTiO3 have been investigated. The low conductivity of these layers sets them apart from metallic overlayers like Fe or Co, where the shifts are suppressed. This difference adds further support for charging as the origin of the effect.

Self-Organized Superlattice and Phase Coexistence inside Thin Film Organometal Halide Perovskite.

PubMed

Kim, Tae Woong; Uchida, Satoshi; Matsushita, Tomonori; Cojocaru, Ludmila; Jono, Ryota; Kimura, Kohei; Matsubara, Daiki; Shirai, Manabu; Ito, Katsuji; Matsumoto, Hiroaki; Kondo, Takashi; Segawa, Hiroshi

2018-02-01

Organometal halide perovskites have attracted widespread attention as the most favorable prospective material for photovoltaic technology because of their high photoinduced charge separation and carrier transport performance. However, the microstructural aspects within the organometal halide perovskite are still unknown, even though it belongs to a crystal system. Here direct observation of the microstructure of the thin film organometal halide perovskite using transmission electron microscopy is reported. Unlike previous reports claiming each phase of the organometal halide perovskite solely exists at a given temperature range, it is identified that the tetragonal and cubic phases coexist at room temperature, and it is confirmed that superlattices composed of a mixture of tetragonal and cubic phases are self-organized without a compositional change. The organometal halide perovskite self-adjusts the configuration of phases and automatically organizes a buffer layer at boundaries by introducing a superlattice. This report shows the fundamental crystallographic information for the organometal halide perovskite and demonstrates new possibilities as promising materials for various applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influences of PZT addition on phase formation and magnetic properties of perovskite Pb(Fe0.5Nb0.5)O3-based ceramics

NASA Astrophysics Data System (ADS)

Amonpattaratkit, P.; Jantaratana, P.; Ananta, S.

2015-09-01

In this work, the investigation of phase formation, crystal structure, microstructure, microchemical composition and magnetic properties of perovskite (1-x)PFN-xPZT (x=0.1-0.5) multiferroic ceramics derived from a combination of perovskite stabilizer PZT and a wolframite-type FeNbO4 B-site precursor was carried out by using a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analyzer and vibrating sample magnetometer (VSM) techniques. The addition of PZT phase and its concentration have been found to have pronounced effects on the perovskite phase formation, densification, grain growth and magnetic properties of the sintered ceramics. XRD spectra from these ceramics reveal transformation of the (pseudo) cubic into the tetragonal perovskite structure. When increasing PZT content, the degree of perovskite phase formation and the tetragonality value of the ceramics increase gradually accompanied with the variation of cell volume, the M-H hysteresis loops, however, become narrower accompanied by the decrease of maximum magnetization (Mmax), remanent polarization (Mr), and coercive field (HC).

Phase Stabilization of Zirconia.

DTIC Science & Technology

1997-01-30

preparing stabilized zirconia pursuant to this disclosure, an insoluble alumina powder is mixed with zirconia powder using a liquid dispersant, such...in a drying oven or a furnace. When mixing the alumina and zirconia powders , it is not necessary to have zirconia in any particular phase to achieve...phase stabilization, as disclosed herein. When mixed with alumina powder, zirconia powder can be in cubic, tetragonal or 20 monoclinic phases

Variational method of determining effective moduli of polycrystals with tetragonal symmetry

USGS Publications Warehouse

Meister, R.; Peselnick, L.

1966-01-01

Variational principles have been applied to aggregates of randomly oriented pure-phase polycrystals having tetragonal symmetry. The bounds of the effective elastic moduli obtained in this way show a substantial improvement over the bounds obtained by means of the Voigt and Reuss assumptions. The Hill average is found to be a good approximation in most cases when compared to the bounds found from the variational method. The new bounds reduce in their limits to the Voigt and Reuss values. ?? 1966 The American Institute of Physics.

Domain wall motion and electromechanical strain in lead-free piezoelectrics: Insight from the model system (1 - x)Ba(Zr 0.2Ti 0.8)O 3-x(Ba 0.7Ca 0.3)TiO 3 using in situ high-energy X-ray diffraction during application of electric fields

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

Tutuncu, Goknur; Li, Binzhi; Bowman, Keith

The piezoelectric compositions (1 - x)Ba(Zr 0.2Ti 0.8)O 3–x(Ba 0.7Ca 0.3)TiO 3 (BZT-xBCT) span a model lead-free morphotropic phase boundary (MPB) between room temperature rhombohedral and tetragonal phases at approximately x = 0.5. In the present work, in situ X-ray diffraction measurements during electric field application are used to elucidate the origin of electromechanical strain in several compositions spanning the tetragonal compositional range 0.6 ≤ x ≤ 0.9. As BCT concentration decreases towards the MPB, the tetragonal distortion (given by c/a-1) decreases concomitantly with an increase in 90° domain wall motion. The increase in observed macroscopic strain is predominantly attributedmore » to the increased contribution from 90° domain wall motion. The results demonstrate that domain wall motion is a significant factor in achieving high strain and piezoelectric coefficients in lead-free polycrystalline piezoelectrics.« less

Reversible pressure pre-amorphization of a piezochromic metal-organic framework.

PubMed

Andrzejewski, M; Casati, N; Katrusiak, A

2017-11-07

The piezochromic metal-organic framework Co 2 (Bdc) 2 Dabco·4DMF·H 2 O (Bdc denotes 1,4-benzenedicarboxylate, Dabco - 1,4-diazabicyclo[2.2.2]octane, and DMF - dimethylformamide) under ambient conditions is tetragonal (phase α) and at about 1.9 GPa undergoes a strong pressure-induced shortening of translational correlations in the sample. A broad gradual pre-amorphization process starting at about 0.7 GPa reduces the tetragonal symmetry and is described as phase β. The pre-amorphization mechanism involves several competing distortions of the Bdc linkers and Co(ii)-coordination schemes. These in turn, affect the crystal field around the cations and their optical absorption. The compression strongly affects the VIS absorption of this piezochromic compound visibly changing its colour from blue to red.

Synthesis and structural properties of Ba(1-x)LaxTiO3 perovskite nanoparticles fabricated by solvothermal synthesis route

NASA Astrophysics Data System (ADS)

Puli, Venkata Sreenivas; Adireddy, Shiva; Elupula, Ravinder; Molugu, Sudheer; Shipman, Josh; Chrisey, Douglas B.

2017-05-01

We report the successful synthesis and structural characterization of barium lanthanum titanate Ba(1-x)LaxTiO3 (x=0.003,0.006,0.010) nanoparticles. The colloidal nanoparticles were prepared with high yield by a solvothermal method at temperatures as low as 150°C for 24h. The as-prepared nanopowders were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. The XRD studies revealed pseudo-cubic crystalline structure, with no impurity phases at room temperature. However ferroelectric tetragonal modes were clearly observed using Raman spectroscopy measurements. From TEM measurements, uniformly sized BLT nanoparticles were observed. Selected area diffraction TEM images revealed polycrystalline perovskite ring patterns, identified as corresponding to the tetragonal phase.

Phase control of Mn-based spinel films via pulsed laser deposition

DOE PAGES

Feng, Zhenxing; Chen, Xiao; Fister, Timothy T.; ...

2016-07-06

Phase transformations in battery cathode materials during electrochemical-insertion reactions lead to capacity fading and low cycle life. One solution is to keep the same phase of cathode materials during cation insertion-extraction processes. Here, we demonstrate a novel strategy to control the phase and composition of Mn-based spinel oxides for magnesium-ion battery applications through the growth of thin films on lattice-matched substrates using pulsed laser deposition. Materials at two extreme conditions are considered: fully discharged cathode MgMn 2O 4 and fully charged cathode Mn 2O 4. The tetragonal MgMn 2O 4 (MMO) phase is obtained on MgAl 2O 4 substrates, whilemore » the cubic MMO phase is obtained on MgO substrates. Similarly, growth of the empty Mn 2O 4 spinel in the cubic phase is obtained on an MgO substrate. These results demonstrate the ability to control separately the phase of spinel thin films (e.g., tetragonal vs. cubic MMO) at nominally fixed composition, and to maintain a fixed (cubic) phase while varying its composition (MgxMn 2O 4, for x = 0, 1). As a result, this capability provides a novel route to gain insights into the operation of battery electrodes for energy storage applications.« less

Phase control of Mn-based spinel films via pulsed laser deposition

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

Feng, Zhenxing; Chen, Xiao; Fister, Timothy T.

Phase transformations in battery cathode materials during electrochemical-insertion reactions lead to capacity fading and low cycle life. One solution is to keep the same phase of cathode materials during cation insertion-extraction processes. Here, we demonstrate a novel strategy to control the phase and composition of Mn-based spinel oxides for magnesium-ion battery applications through the growth of thin films on lattice-matched substrates using pulsed laser deposition. Materials at two extreme conditions are considered: fully discharged cathode MgMn 2O 4 and fully charged cathode Mn 2O 4. The tetragonal MgMn 2O 4 (MMO) phase is obtained on MgAl 2O 4 substrates, whilemore » the cubic MMO phase is obtained on MgO substrates. Similarly, growth of the empty Mn 2O 4 spinel in the cubic phase is obtained on an MgO substrate. These results demonstrate the ability to control separately the phase of spinel thin films (e.g., tetragonal vs. cubic MMO) at nominally fixed composition, and to maintain a fixed (cubic) phase while varying its composition (MgxMn 2O 4, for x = 0, 1). As a result, this capability provides a novel route to gain insights into the operation of battery electrodes for energy storage applications.« less

Anomalous magnetoelastic behaviour near morphotropic phase boundary in ferromagnetic Tb 1-xNd xCo 2 system

DOE PAGES

Murtaza, Adil; Yang, Sen; Zhou, Chao; ...

2016-08-04

In this study, we report a morphotropic phase boundary (MPB) involved ferromagnetic system Tb 1-xNd xCo 2 and reveal the corresponding structural and magnetoelastic properties of this system. With high resolution synchrotron X-ray diffractometry, the crystal structure of the TbCo 2-rich side is detected to be rhombohedral and that of NdCo 2-rich side is tetragonal below their respective Curie temperatures TC. The MPB composition Tb 0.35Nd 0.65Co 2 corresponds to the coexistence of the rhombohedral phase (R-phase) and tetragonal phase ( T-phase). Contrary to previously reported MPB involved ferromagnetic systems, the MPB composition of Tb 0.35Nd 0.65Co 2 shows minimummore » magnetization which can be understood as compensation of sublattice moments between the R-phase and the T-phase. Furthermore, magnetostriction of Tb 1-xNd xCo 2 decreases with increasing Nd concentration until x = 0.8 and then increases in the negative direction with further increasing Nd concentration; the optimum point for magnetoelastic properties lies towards the rhombohedral phase. Finally, our work not only shows an anomalous type of ferromagnetic MPB but also provides an effective way to design functional materials.« less

Effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain.

PubMed

Li, Kai Chun; Waddell, J Neil; Prior, David J; Ting, Stephanie; Girvan, Liz; van Vuuren, Ludwig Jansen; Swain, Michael V

2013-11-01

To investigate the effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain. The strain energy release rate using a four-point bending stable fracture test was evaluated for two different porcelains [leucite containing (VM9) and glass (Zirox) porcelain] veneered to zirconia. Prior to veneering the zirconia had been subjected to 0 (control), 1, 5, 10 and 20 autoclave cycles. The specimens were manufactured to a total bi-layer dimension of 30 mm × 8 mm × 3 mm. Subsequent scanning electron microscopy/energy dispersive spectrometry, electron backscatter diffraction and X-ray diffraction analysis were performed to identify the phase transformation and fracture behavior. The strain energy release rate for debonding of the VM9 specimens were significantly higher (p<0.05) compared to the Zirox specimens across all test groups. Increasing autoclave cycles lowered the strain energy release rate significantly (p<0.05) from 18.67 J/m(2) (control) to the lowest of 12.79 J/m(2) (cycle 10) for only the VM9 specimens. SEM analyses showed predominant cohesive fracture within the porcelain for all cycle groups. XRD analysis of the substrate prior to veneering confirmed a tetragonal to monoclinic phase transformation with increasing the number of autoclave cycles between 5 and 20. The monoclinic phase reverted back to tetragonal phase after undergoing conventional porcelain firing cycles. EBSD data showed significant changes of the grain size distribution between the control and autoclaved specimen (cycle 20). Increasing autoclave cycles only significantly decreased the adhesion of the VM9 layered specimens. In addition, a conventional porcelain firing schedule completely reverted the monoclinic phase back to tetragonal. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Characterization of a Diamond Ground Y-TZP and Reversion of the Tetragonal to Monoclinic Transformation.

PubMed

Candido, L M; Fais, Lmg; Ferreira, E B; Antonio, S G; Pinelli, Lap

To characterize the surface of an yttria-stabilized zirconia (Y-TZP) ceramic after diamond grinding in terms of its crystalline phase, morphology, mean roughness (Ra), and wettability as well as to determine a thermal treatment to reverse the resulting tetragonal to monoclinic (t-m) transformation. Y-TZP specimens were distributed into different groups according to the actions (or no action) of grinding and irrigation. Grinding was accomplished using a diamond stone at a low speed. The samples were characterized by x-ray diffraction (XRD), scanning electron microscopy, goniometry, and profilometry. In situ high-temperature XRD was used to determine an annealing temperature to reverse the t-m transformation. Ra was submitted to the Kruskal-Wallis test, followed by the Dunn test (α=0.05). The volume fraction of the monoclinic phase and contact angle were submitted to one-way analysis of variance, followed by the Tukey test (α=0.05). Monoclinic zirconia was observed on the surface of samples after dry and wet grinding with a diamond stone. The volume fraction of the monoclinic phase was smaller on the dry ground samples (3.6%±0.3%) than on the wet ground samples (5.6%±0.3%). High-temperature XRD showed reversion of the t-m phase transformation, which started at 700°C and completed at 800°C in a conventional oven. Grinding with a diamond stone partially transformed the crystalline phase on the surface of a Y-TZP ceramic from tetragonal to monoclinic zirconia while simultaneously increasing the surface roughness and wettability. The t-m transformation could be reversed by heat treatment at 800°C or 900°C for 60 minutes or 1000°C for 30 minutes.

Electronic structure and energetics of the tetragonal distortion for TiH2, ZrH2 and HfH2: a first principles study

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

Quijano, Ramiro; DeCoss, Romeo; Singh, David J

2009-01-01

The electronic structure and energetics of the tetragonal distortion for the fluorite-type dihydrides TiH{sub 2}, ZrH{sub 2}, and HfH{sub 2} are studied by means of highly accurate first-principles total-energy calculations. For HfH{sub 2}, in addition to the calculations using the scalar relativistic (SR) approximation, calculations including the spin-orbit coupling have also been performed. The results show that TiH{sub 2}, ZrH{sub 2}, and HfH{sub 2} in the cubic phase are unstable against tetragonal strain. For the three systems, the total energy shows two minima as a function of the c/a ratio with the lowest-energy minimum at c/a < 1 in agreementmore » with the experimental observations. The band structure of TiH{sub 2}, ZrH{sub 2}, and HfH{sub 2} (SR) around the Fermi level shows two common features along the two major symmetry directions of the Brillouin zone, {Lambda}?L and {Lambda}?K, a nearly flat doubly degenerate band, and a van Hove singularity, respectively. In cubic HfH{sub 2} the spin-orbit coupling lifts the degeneracy of the partially filled bands in the {Lambda}?L path, while the van Hove singularity in the {Lambda}?K path remains unchanged. The density of states of the three systems in the cubic phase shows a sharp peak at the Fermi level. We found that the tetragonal distortion produces a strong reduction in the density of states at the Fermi level resulting mainly from the splitting of the doubly-degenerate bands in the {Lambda}?L direction and the shift of the van Hove singularity to above the Fermi level. The validity of the Jahn-Teller model in explaining the tetragonal distortion in this group of dihydrides is discussed.« less

Structural and relaxor-like dielectric properties of unfilled tungsten bronzes Ba5-5xSm5xTi5xNb10-5xO30

NASA Astrophysics Data System (ADS)

Wei, T.; Dong, Z.; Zhao, C. Z.; Guo, Y. Y.; Zhou, Q. J.; Li, Z. P.

2016-03-01

New unfilled tetragonal tungsten bronze (TTB) oxides, Ba5-5xSm5xTi5xNb10-5xO30 (BSTN-x), where 0.10 ≤ x ≤ 0.35, have been synthesized in this work. Their crystal structure was determined and analyzed based on Rietveld structural refinement. It is found that single TTB phase can be formed in a particular x range (i.e., 0.15 ≤ x ≤ 0.3) due to the competition interaction between tolerance factor and electronegativity difference. Furthermore, dielectric and ferroelectric results indicate that phase transitions and ferroelectric states are sensitive to x. Referring to the local chemistry, we suggest that the raise of vacancies at the A2-site compared with that of A1-site will intensely depress the normal ferroelectric phase and is in favor of relaxor ferroelectric state. Macroscopically, previous A-site size difference standpoint on fill TTB compounds cannot give a reasonable explanation about the variation of dielectric maximum temperature (Tm) for present BSTN-x compounds. Alternatively, tetragonality (c/a) is adopted which can well describe the variation of Tm in whole x range. In addition, one by one correspondence between tetragonality and electrical features can be found, and the compositions involving high c/a are usually stabilized in normal ferroelectric phase. It is believed that c/a is a more appropriate parameter to illustrate the variation of ferroelectric properties for unfilled TTB system.

Phonon Mode Transformation Across the Orthohombic–Tetragonal Phase Transition in a Lead Iodide Perovskite CH 3 NH 3 PbI 3 : A Terahertz Time-Domain Spectroscopy Approach

DOE PAGES

La-o-vorakiat, Chan; Xia, Huanxin; Kadro, Jeannette; ...

2015-12-03

Here, we study the temperature-dependent phonon modes of the organometallic lead iodide perovskite CH 3NH 3PbI 3 thin film across the terahertz (0.5–3 THz) and temperature (20–300 K) ranges. These modes are related to the vibration of the Pb–I bonds. We found that two phonon modes in the tetragonal phase at room temperature split into four modes in the low-temperature orthorhombic phase. By use of the Lorentz model fitting, we also analyze the critical behavior of this phase transition. The carrier mobility values calculated from the low-temperature phonon mode frequencies, via two theoretical approaches, are found to agree reasonably withmore » the experimental value (~2000 cm 2 V –1 s –1) from a previous time-resolved THz spectroscopy work. Thus, we have established a possible link between terahertz phonon modes and the transport properties of perovskite-based solar cells.« less

Electronic and magnetic properties of iron doped zirconia: Theory and experiment

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

Debernardi, A., E-mail: alberto.debernardi@mdm.imm.cnr.it; Sangalli, D.; Lamperti, A.

We systematically investigated, both theoretically and experimentally, Zr{sub 1−x}Fe{sub x}O{sub 2−y} ranging from diluted (x ≈ 0.05) up to large (x ≈ 0.25) Fe concentration. By atomic layer deposition, we grew thin films of high-κ zirconia in cubic phase with Fe uniformly distributed in the film, as proven by time of flight secondary ion mass spectrometry and transmission electron microscopy measurements. Iron is in Fe{sup 3+} oxidation state suggesting the formation of oxygen vacancies with y concentration close to x/2. By ab-initio simulations, we studied the phase diagram relating the stability of monoclinic vs. tetragonal phase as a function of Fe doping and filmmore » thickness: the critical thickness at which the pure zirconia is stabilized in the tetragonal phase is estimated ranging from 2 to 6 nm according to film morphology. Preliminary results by X-ray magnetic circular dichroism and alternating gradient force magnetometry are discussed in comparison to ab initio data enlightening the role of oxygen vacancies in the magnetic properties of the system.« less

Bone-Inspired Spatially Specific Piezoelectricity Induces Bone Regeneration

PubMed Central

Yu, Peng; Ning, Chengyun; Zhang, Yu; Tan, Guoxin; Lin, Zefeng; Liu, Shaoxiang; Wang, Xiaolan; Yang, Haoqi; Li, Kang; Yi, Xin; Zhu, Ye; Mao, Chuanbin

2017-01-01

The extracellular matrix of bone can be pictured as a material made of parallel interspersed domains of fibrous piezoelectric collagenous materials and non-piezoelectric non-collagenous materials. To mimic this feature for enhanced bone regeneration, a material made of two parallel interspersed domains, with higher and lower piezoelectricity, respectively, is constructed to form microscale piezoelectric zones (MPZs). The MPZs are produced using a versatile and effective laser-irradiation technique in which K0.5Na0.5NbO3 (KNN) ceramics are selectively irradiated to achieve microzone phase transitions. The phase structure of the laser-irradiated microzones is changed from a mixture of orthorhombic and tetragonal phases (with higher piezoelectricity) to a tetragonal dominant phase (with lower piezoelectricity). The microzoned piezoelectricity distribution results in spatially specific surface charge distribution, enabling the MPZs to bear bone-like microscale electric cues. Hence, the MPZs induce osteogenic differentiation of stem cells in vitro and bone regeneration in vivo even without being seeded with stem cells. The concept of mimicking the spatially specific piezoelectricity in bone will facilitate future research on the rational design of tissue regenerative materials. PMID:28900517

Double-Q spin-density wave in iron arsenide superconductors

DOE PAGES

Allred, J. M.; Taddei, K. M.; Bugaris, D. E.; ...

2016-01-25

Elucidating the nature of the magnetic ground state of iron-based superconductors is of paramount importance in unveiling the mechanism behind their high temperature superconductivity. Until recently, it was thought that superconductivity emerges only from an orthorhombic antiferromagnetic stripe phase, which can in principle be described in terms of either localized or itinerant spins. However, we recently reported that tetragonal symmetry is restored inside the magnetically ordered state of certain hole-doped compounds, revealing the existence of a new magnetic phase at compositions close to the onset of superconductivity. Here, we present Mossbauer data that show that half of the iron sitesmore » in this tetragonal phase are non-magnetic, establishing conclusively the existence of a novel magnetic ground state with a non-uniform magnetization that is inconsistent with localized spins. Instead, this state is naturally explained as the interference between two commensurate spin density waves, a rare example of collinear double-Q magnetic order. Finally, our results demonstrate the itinerant character of the magnetism of the iron pnictides, and the primary role played by magnetic degrees of freedom in determining their phase diagram.« less

Polar Fluctuations in Metal Halide Perovskites Uncovered by Acoustic Phonon Anomalies

DOE PAGES

Guo, Peijun; Xia, Yi; Gong, Jue; ...

2017-09-28

Solution-processable metal-halide perovskites (MHPs) offer great promise for efficient light harvesting and emitting devices due to their long carrier lifetime and superior carrier transport characteristics. Ferroelectric effects, a hallmark of traditional oxide perovskites, was proposed to be a mechanism to suppress carrier recombination and enhance charge transport in MHPs, but the existence and influence of such polar order is still of considerable debate. Here we performed transient reflection measurements on single crystals of both inorganic and organic-inorganic (hybrid) MHPs over a range of temperatures, and demonstrate significant phonon softening in the cubic phases close to the cubic-to-tetragonal phase transition temperatures.more » Such phonon softening indicates the formation of polar domains, which grow in size upon cooling and can persist in the low-temperature tetragonal and orthorhombic phases. Our results link the extraordinary electronic properties of MHPs to the spontaneous polarizations which can contribute to more efficient charge separation and characteristics of an indirect bandgap.« less

Influence of Sn doping in BaSnxTi1-xO3 ceramics on microstructural and dielectric properties

NASA Astrophysics Data System (ADS)

Ansari, Mohd. Azaj; Sreenivas, K.

2018-05-01

BaSnxTi1-x O3 solid solutions with varying Sn content (x = 0.00, 0.05, 0.15, 0.25) prepared by solid state reaction method have been studied for their structural and dielectric properties. X-ray diffraction and Raman spectroscopic analysis show composition induced modifications in the crystallographic structure, and with increasing Sn content the structure changes from tetragonal to cubic structure. The tetragonal distortion decreases with increasing Sn, and the structure becomes purely cubic for x =0.25. Changes in the structure are reflected in the temperature dependent dielectric properties. For increasing Sn content the peak dielectric constant is found to increase and the phase transition temperature (Tc) decreases to lower temperature. The purely cubic structure with x=0.25 shows a diffused phased transition.

Stable tetragonal phase and magnetic properties of Fe-doped HfO2 nanoparticles

NASA Astrophysics Data System (ADS)

Sales, T. S. N.; Cavalcante, F. H. M.; Bosch-Santos, B.; Pereira, L. F. D.; Cabrera-Pasca, G. A.; Freitas, R. S.; Saxena, R. N.; Carbonari, A. W.

2017-05-01

In this paper, the effect in structural and magnetic properties of iron doping with concentration of 20% in hafnium dioxide (HfO2) nanoparticles is investigated. HfO2 is a wide band gap oxide with great potential to be used as high-permittivity gate dielectrics, which can be improved by doping. Nanoparticle samples were prepared by sol-gel chemical method and had their structure, morphology, and magnetic properties, respectively, investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with electron back scattering diffraction (EBSD), and magnetization measurements. TEM and SEM results show size distribution of particles in the range from 30 nm to 40 nm with small dispersion. Magnetization measurements show the blocking temperature at around 90 K with a strong paramagnetic contribution. XRD results show a major tetragonal phase (94%).

Electric-field-induced structural changes in multilayer piezoelectric actuators during electrical and mechanical loading

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

Esteves, Giovanni; Fancher, Chris M.; Röhrig, Sören

The effects of electrical and mechanical loading on the behavior of domains and phases in Multilayer Piezoelectric Actuators (MAs) is studied using in situ high-energy X-ray diffraction (XRD) and macroscopic property measurements. Rietveld refinement is carried out on measured diffraction patterns using a two-phase tetragonal (P4mm) and rhombohedral (R3m) model. Applying an electric field promotes the rhombohedral phase, while increasing compressive uniaxial pre-stress prior to electric field application favors the tetragonal phase. The competition between electrical and mechanical energy leads to a maximal difference between electric-field-induced phase fractions at 70 MPa pre-stress. Additionally, the available volume fraction of non-180° domainmore » reorientation that can be accessed during electric field application increases with compressive pre-stress up to 70 MPa. The origin for enhanced strain and polarization with applied pre-stress is attributed to a combination of enhanced non-180° domain reorientation and electric-field-induced phase transitions. The suppression of both the electric-field-induced phase transitions and domain reorientation at high pre-stresses (>70 MPa) is attributed to a large mechanical energy barrier, and alludes to the competition of the electrical and mechanical energy within the MA during applied stimuli.« less

Thermal stability of simple tetragonal and hexagonal diamond germanium

DOE PAGES

Huston, Larissa Q.; Johnson, Brett C.; Haberl, Bianca; ...

2017-11-07

Here, exotic phases of germanium, that form under high pressure but persist under ambient conditions, are of technological interest due to their unique optical and electrical properties. The thermal evolution and stability of two of these exotic Ge phases, the simple tetragonal (st12) and hexagonal diamond (hd) phases, are investigated in detail. These metastable phases, formed by high pressure decompression in either a diamond anvil cell or by nanoindentation, are annealed at temperatures ranging from 280 to 320 °C for st12-Ge and 200 to 550 °C for hd-Ge. In both cases, the exotic phases originated from entirely pure Ge precursormore » materials. Raman microspectroscopy is used to monitor the phase changes ex situ following annealing. Our results show that hd-Ge synthesized via a pure form of a-Ge first undergoes a subtle change in structure and then an irreversible phase transformation to dc-Ge with an activation energy of (4.3 ± 0.2) eV at higher temperatures. St12-Ge was found to transform to dc-Ge with an activation energy of (1.44 ± 0.08) eV. Taken together with results from previous studies, this study allows for intriguing comparisons with silicon and suggests promising technological applications.« less

Thermal stability of simple tetragonal and hexagonal diamond germanium

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

Huston, Larissa Q.; Johnson, Brett C.; Haberl, Bianca

Here, exotic phases of germanium, that form under high pressure but persist under ambient conditions, are of technological interest due to their unique optical and electrical properties. The thermal evolution and stability of two of these exotic Ge phases, the simple tetragonal (st12) and hexagonal diamond (hd) phases, are investigated in detail. These metastable phases, formed by high pressure decompression in either a diamond anvil cell or by nanoindentation, are annealed at temperatures ranging from 280 to 320 °C for st12-Ge and 200 to 550 °C for hd-Ge. In both cases, the exotic phases originated from entirely pure Ge precursormore » materials. Raman microspectroscopy is used to monitor the phase changes ex situ following annealing. Our results show that hd-Ge synthesized via a pure form of a-Ge first undergoes a subtle change in structure and then an irreversible phase transformation to dc-Ge with an activation energy of (4.3 ± 0.2) eV at higher temperatures. St12-Ge was found to transform to dc-Ge with an activation energy of (1.44 ± 0.08) eV. Taken together with results from previous studies, this study allows for intriguing comparisons with silicon and suggests promising technological applications.« less

Electric-field-induced structural changes in multilayer piezoelectric actuators during electrical and mechanical loading

DOE PAGES

Esteves, Giovanni; Fancher, Chris M.; Röhrig, Sören; ...

2017-04-08

The effects of electrical and mechanical loading on the behavior of domains and phases in Multilayer Piezoelectric Actuators (MAs) is studied using in situ high-energy X-ray diffraction (XRD) and macroscopic property measurements. Rietveld refinement is carried out on measured diffraction patterns using a two-phase tetragonal (P4mm) and rhombohedral (R3m) model. Applying an electric field promotes the rhombohedral phase, while increasing compressive uniaxial pre-stress prior to electric field application favors the tetragonal phase. The competition between electrical and mechanical energy leads to a maximal difference between electric-field-induced phase fractions at 70 MPa pre-stress. Additionally, the available volume fraction of non-180° domainmore » reorientation that can be accessed during electric field application increases with compressive pre-stress up to 70 MPa. The origin for enhanced strain and polarization with applied pre-stress is attributed to a combination of enhanced non-180° domain reorientation and electric-field-induced phase transitions. The suppression of both the electric-field-induced phase transitions and domain reorientation at high pre-stresses (>70 MPa) is attributed to a large mechanical energy barrier, and alludes to the competition of the electrical and mechanical energy within the MA during applied stimuli.« less

Rotational Rehybridization and the High Temperature Phase of UC2

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

Wen, Xiaodong; Rudin, Sven P.; Batista, Enrique R.

2012-12-03

The screened hybrid approximation (HSE) of density functional theory (DFT) is used to examine the structural, optical, and electronic properties of the high temperature phase, cubic UC(2). This phase contains C(2) units with a computed C-C distance of 1.443 Å which is in the range of a CC double bond; U is formally 4+, C(2) 4-. The closed shell paramagnetic state (NM) was found to lie lowest. Cubic UC(2) is found to be a semiconductor with a narrow gap, 0.4 eV. Interestingly, the C(2) units connecting two uranium sites can rotate freely up to an angle of 30°, indicating amore » hindered rotational solid. Ab-initio molecular dynamic simulations (HSE) show that the rotation of C(2) units in the low temperature phase (tetragonal UC(2)) occurs above 2000 K, in good agreement with experiment. The computed energy barrier for the phase transition from tetragonal UC(2) to cubic UC(2) is around 1.30 eV per UC(2). What is fascinating about this system is that at high temperature, the phase transformation to the cubic phase is associated with a rehybridization of the C atoms from sp to sp(3).« less

Correlation and the mechanism of lithium ion diffusion with the crystal structure of Li7La3Zr2O12 revealed by an internal friction technique.

PubMed

Wang, X P; Gao, Y X; Xia, Y P; Zhuang, Z; Zhang, T; Fang, Q F

2014-04-21

The correlation and transport mechanism of lithium ions with the crystal structure of a fast lithium ion conductor Li7La3Zr2O12 are mainly investigated by internal friction (IF) and AC impedance spectroscopy techniques. Compared with the poor conductivity of tetragonal Li7La3Zr2O12, the Al stabilized cubic phase exhibits a good ionic conductivity that can be up to 1.9 × 10(-4) S cm(-1) at room temperature, which can be ascribed to the disordered distribution of lithium ions in the cubic phase. A well-pronounced relaxation IF peak (labeled as peak PC) is observed in the cubic phase while a very weak IF peak (labeled as PT) is observed in the tetragonal phase, further evidencing the difference in lithium ion migration in the two phases. Peak PC can be decomposed into two sub-peaks with the activation energy and the pre-exponential factor of relaxation time being E1 = 0.41 eV and τ01 = 1.2 × 10(-14) s for the lower temperature peak PC1 and E2 = 0.35 eV and τ02 = 1.9 × 10(-15) s for the higher temperature PC2 peak, respectively. Based on the crystalline structure of a cubic garnet-type Li7La3Zr2O12 compound, an atomistic mechanism of lithium ion diffusion via vacancies is suggested, i.e. 48g(96h) ↔ 48g(96h) for peak PC1 and 48g(96h) ↔ 24d for peak PC2, respectively. The weak PT peak in the tetragonal phase is preliminarily interpreted as due to the short jump process among neighboring octahedral sites and vacant tetrahedral sites.

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

Yamada, H., E-mail: hide-yamada@mg.ngkntk.co.jp; Matsuoka, T.; Kozuka, H.

Two phases of (K,Na)NbO{sub 3} (KNN) co-exist in a KNN-based composite lead-free piezoelectric ceramic 0.910(K{sub 1−x}Na{sub x}){sub 0.86}Ca{sub 0.04}Li{sub 0.02}Nb{sub 0.85}O{sub 3−δ}–0.042K{sub 0.85}Ti{sub 0.85}Nb{sub 1.15}O{sub 5} –0.036BaZrO{sub 3}–0.0016Co{sub 3}O{sub 4}– 0.0025Fe{sub 2}O{sub 3}–0.0069ZnO system, over a wide range of Na fractions, where 0.56 ≤ x ≤ 0.75. The crystal systems of the two KNN phases are identified to tetragonal and orthorhombic by analyzing the synchrotron powder X-ray diffraction (XRD) data, high-resolution transmission electron microscopy (HR-TEM), and selected-area electron diffraction (SAD). In the range 0.33 ≤ x ≤ 0.50, the main component of the composite system is found to be single-phase KNN with a tetragonal structure. Granular nanodomains ofmore » the orthorhombic phase dispersed in the tetragonal matrix have been identified by HR-TEM and SAD for 0.56 ≤ x ≤ 0.75. Only a trace amount of the orthorhombic phase has been found in the SAD patterns at the composition x = 0.56. However, the number of orthorhombic nanodomains gradually increases with increasing Na content up to x < 0.75, as observed from the HR-TEM images. An abrupt increase and agglomeration of the nanodomains are observed at x = 0.75, where weak diffraction peaks of the orthorhombic phase have also become detectable from the XRD data. The maximum value of the electromechanical coupling coefficient, k{sub p} = 0.56, has been observed at the composition x = 0.56.« less

Structural phase transition, Néel temperature enhancement, and persistent magneto-dielectric coupling in Cr-substituted Mn3O4

NASA Astrophysics Data System (ADS)

Dwivedi, G. D.; Kumar, Abhishek; Yang, K. S.; Chen, B. Y.; Liu, K. W.; Chatterjee, Sandip; Yang, H. D.; Chou, H.

2016-05-01

Structural phase transition and Néel temperature (TN) enhancement were observed in Cr-substituted Mn3O4 spinels. Structural, magnetic, and dielectric properties of (Mn1-xCrx)3O4 (where x = 0.00, 0.10, 0.20, 0.25, 0.30, 0.40, and 0.50) were investigated. Cr-substitution induces room temperature structural phase transition from tetragonally distorted I41/amd (x = 0.00) to cubic Fd 3 ¯ m (x = 0.50). TN is found to increase from 43 K (x = 0.00) to 58 K (x = 0.50) with Cr-substitution. The spin ordering-induced dielectric anomaly near TN ensures that magneto-dielectric coupling persists in the cubic x = 0.50 system. X-ray absorption spectra reveal that Cr exists in a trivalent oxidation state and prefers the octahedral (Oh)-site, replacing Mn3+. Due to a reduction in the Jahn-Teller active Mn3+ cation and an increase in the smaller Cr3+ cation, the system begins to release the geometrical frustration by lowering its degeneracy. Consequently, a phase transition, from distorted tetragonal structure to the more symmetric cubic phase, occurs.

Thermal analysis of 3-mol%-yttria-stabilized tetragonal zirconia powder doped with copper oxide

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

Seidensticker, J.R.; Mayo, M.J.

Thermal analysis was performed upon 3-mol%-yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) which had been doped with CuO using an aqueous adsorption technique. Cyclic differential thermal analysis (DTA) scans indicated that the CuO present on the powder surfaces first transforms to Cu{sub 2}O and then melts. The molten Cu{sub 2}O then reacts with yttria at the powder surfaces to form a new phase containing Y, Cu, and O. Because Y takes time to diffuse to the particle surfaces, the apparent melting point of this new phase appears at higher temperatures in initial DTA scans than in subsequent scans. Vaporization of the moltenmore » copper-oxide-rich phase at the temperatures studied causes a gradual shift in composition from Y{sub 2}Cu{sub 4}O{sub 5} to the less copper-rich Y{sub 2}Cu{sub 2}O{sub 5} phase. The presence of the Y{sub 2}Cu{sub 2}O{sub 5} phase in CuO-doped 3Y-TZP allows for previous sintering and superplasticity results to be explained.« less

Study of a structural phase transition by two dimensional Fourier transform NMR method

NASA Astrophysics Data System (ADS)

Trokiner, A.; Man, P. P.; Théveneau, H.; Papon, P.

1985-09-01

The fluoroperovskite RbCaF 3 undergoes a structural phase transition at 195.5 K, from a cubic phase where the 87Rb nuclei have no quadrupolar interaction ( ωQ= 0) to a tetragonal phase where ω Q ≠ O. The transition is weakly first-order. A two-dimensional FT NMR experiment has been performed on 87Rb ( I = {3}/{2}) in a single crystal in both phases and in the vicinity of the phase transition. Our results show the coexistence of the two phases at the phase transition.

Anomalous magnetoelastic behaviour near morphotropic phase boundary in ferromagnetic Tb{sub 1-x}Nd{sub x}Co{sub 2} system

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

Murtaza, Adil; Yang, Sen, E-mail: yang.sen@mail.xjtu.edu.cn; Zhou, Chao

2016-08-01

In this work, we report a morphotropic phase boundary (MPB) involved ferromagnetic system Tb{sub 1-x}Nd{sub x}Co{sub 2} and reveal the corresponding structural and magnetoelastic properties of this system. With high resolution synchrotron X-ray diffractometry, the crystal structure of the TbCo{sub 2}-rich side is detected to be rhombohedral and that of NdCo{sub 2}-rich side is tetragonal below their respective Curie temperatures T{sub C}. The MPB composition Tb{sub 0.35}Nd{sub 0.65}Co{sub 2} corresponds to the coexistence of the rhombohedral phase (R-phase) and tetragonal phase (T-phase). Contrary to previously reported MPB involved ferromagnetic systems, the MPB composition of Tb{sub 0.35}Nd{sub 0.65}Co{sub 2} shows minimummore » magnetization which can be understood as compensation of sublattice moments between the R-phase and the T-phase. Furthermore, magnetostriction of Tb{sub 1-x}Nd{sub x}Co{sub 2} decreases with increasing Nd concentration until x = 0.8 and then increases in the negative direction with further increasing Nd concentration; the optimum point for magnetoelastic properties lies towards the rhombohedral phase. Our work not only shows an anomalous type of ferromagnetic MPB but also provides an effective way to design functional materials.« less

Domain wall motion and electromechanical strain in lead-free piezoelectrics: Insight from the model system (1 − x)Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}–x(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} using in situ high-energy X-ray diffraction during application of electric fields

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

Tutuncu, Goknur; Li, Binzhi; Bowman, Keith

The piezoelectric compositions (1 − x)Ba(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}–x(Ba{sub 0.7}Ca{sub 0.3})TiO{sub 3} (BZT-xBCT) span a model lead-free morphotropic phase boundary (MPB) between room temperature rhombohedral and tetragonal phases at approximately x = 0.5. In the present work, in situ X-ray diffraction measurements during electric field application are used to elucidate the origin of electromechanical strain in several compositions spanning the tetragonal compositional range 0.6 ≤ x ≤ 0.9. As BCT concentration decreases towards the MPB, the tetragonal distortion (given by c/a-1) decreases concomitantly with an increase in 90° domain wall motion. The increase in observed macroscopic strain is predominantly attributed to the increased contribution from 90°more » domain wall motion. The results demonstrate that domain wall motion is a significant factor in achieving high strain and piezoelectric coefficients in lead-free polycrystalline piezoelectrics.« less

Methodical thermolysis of [Ba2Ti2(thd)4(OnPr)8(nPrOH)2] under autogenous pressure followed by combustion for the synthesis of dielectric tetragonal BaTiO3 nanopowder.

PubMed

Pol, Vilas G; Thiyagarajan, P; Moreno, Jose M Calderon; Popa, Monica; Kessler, Vadim G; Gohil, Suresh; Seisenbaeva, Gulaim A

2009-07-06

The tetragonal BaTiO(3) nanopowder is synthesized in a solvent-less, efficient process by the thermolysis of a single [Ba(2)Ti(2)(thd)(4)(OnPr)(8)(nPrOH)(2)] precursor in a closed reactor at 700 degrees C under autogenous pressure, followed by combustion. This paper compiles the synthesis of the [Ba(2)Ti(2)(thd)(4)(OnPr)(8)(nPrOH)(2)] precursor, its analysis by mass spectrometry, and implementation for the fabrication of dielectric tetragonal BaTiO(3) nanopowder by controlled efficient thermal decomposition. The as-prepared, intermediate, and final forms of the obtained nanomaterials are systematically analysed by XRD, Raman, and EDS measurements to gain structural and compositional information. Employing HR-SEM, TEM, and HR-TEM techniques, the morphological changes during the structural evolution of all the phases are pursued. The mechanistic elucidation for the fabrication of BaTiO(3) nanopowder is developed on the basis of TGA and DTA data obtained for the initial [Ba(2)Ti(2)(thd)(4)(OnPr)(8)(nPrOH)(2)] reactant as well as the as-prepared BaCO(3) with amorphous Ti phase.

First determination of the valence band dispersion of CH3NH3PbI3 hybrid organic-inorganic perovskite

NASA Astrophysics Data System (ADS)

Lee, Min-I.; Barragán, Ana; Nair, Maya N.; Jacques, Vincent L. R.; Le Bolloc'h, David; Fertey, Pierre; Jemli, Khaoula; Lédée, Ferdinand; Trippé-Allard, Gaëlle; Deleporte, Emmanuelle; Taleb-Ibrahimi, Amina; Tejeda, Antonio

2017-07-01

The family of hybrid organic-inorganic halide perovskites is in the limelight because of their recently discovered high photovoltaic efficiency. These materials combine photovoltaic energy conversion efficiencies exceeding 22% and low-temperature and low-cost processing in solution; a breakthrough in the panorama of renewable energy. Solar cell operation relies on the excitation of the valence band electrons to the conduction band by solar photons. One factor strongly impacting the absorption efficiency is the band dispersion. The band dispersion has been extensively studied theoretically, but no experimental information was available. Herein, we present the first experimental determination of the valence band dispersion of methylammonium lead halide in the tetragonal phase. Our results pave the way for contrasting the electronic hopping or the electron effective masses in different theories by comparing to our experimental bands. We also show a significant broadening of the electronic states, promoting relaxed conditions for photon absorption, and demonstrate that the tetragonal structure associated to the octahedra network distortion below 50 °C induces only a minor modification of the electronic bands, with respect to the cubic phase at high temperature, thus minimizing the impact of the cubic-tetragonal transition on solar cell efficiencies.

[Raman studies of nanocrystalline BaTiO3 ceramics].

PubMed

Xiao, Chang-jiang; Jin, Chang-qing; Wang, Xiao-hui

2008-12-01

High pressure can significantly increase the densification. Further, during the high pressure assisted sintering, the nucleation rate is increased due to reduced energy barrier and the growth rate is suppressed due to the decreased diffusivity. Thus high pressure enables the specimen to be fabricated with relatively lower temperature and shorter sintering period that assures to obtain dense nanocrystalline ceramics. Dense nanocrystalline BaTiO3 ceramics with uniform grain sizes of 60 and 30 nm, respectively, were obtained by pressure assisted sintering. The crystal structure and phase transitions were investigated by Raman scattering at temperatures ranging from -190 to 200 degrees C. The Raman results indicated that the evolution of Raman spectrum with grain size is characterized by an intensity decrease, a broadening of the line width, a frequency shift, and the disappearance of the Raman mode. With increasing temperature, similar to 3 mm BaTiO3 normal ceramics, the successive phase transitions from rhombohedral to orthorhombic, orthorhombic to tetragonal, and tetragonal to cubic were also observed in nanocrystalline BaTiO3 ceramics. In addition, when particle size is reduced to the nanoscale, one will find some unusual physical properties in nanocrystalline ceramics, compared with those of coarse-grained BaTiO3 ceramics. The different coexistences of multiphase were found at different temperature. Especially, the ferroelectric tetragonal and orthorhombic phase can coexist at room temperature in nanocrystalline BaTiO3 ceramics. The phenomenon can be explained by the internal stress. The coexistences of different ferroelectric phases at room temperature indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm.

Structural and relaxor-like dielectric properties of unfilled tungsten bronzes Ba{sub 5−5x}Sm{sub 5x}Ti{sub 5x}Nb{sub 10−5x}O{sub 30}

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

Wei, T., E-mail: weitong.nju@gmail.com, E-mail: weitong-nju@163.com; Dong, Z.; Zhou, Q. J.

2016-03-28

New unfilled tetragonal tungsten bronze (TTB) oxides, Ba{sub 5−5x}Sm{sub 5x}Ti{sub 5x}Nb{sub 10−5x}O{sub 30} (BSTN-x), where 0.10 ≤ x ≤ 0.35, have been synthesized in this work. Their crystal structure was determined and analyzed based on Rietveld structural refinement. It is found that single TTB phase can be formed in a particular x range (i.e., 0.15 ≤ x ≤ 0.3) due to the competition interaction between tolerance factor and electronegativity difference. Furthermore, dielectric and ferroelectric results indicate that phase transitions and ferroelectric states are sensitive to x. Referring to the local chemistry, we suggest that the raise of vacancies at the A{sub 2}-site compared with that of A{sub 1}-sitemore » will intensely depress the normal ferroelectric phase and is in favor of relaxor ferroelectric state. Macroscopically, previous A-site size difference standpoint on fill TTB compounds cannot give a reasonable explanation about the variation of dielectric maximum temperature (T{sub m}) for present BSTN-x compounds. Alternatively, tetragonality (c/a) is adopted which can well describe the variation of T{sub m} in whole x range. In addition, one by one correspondence between tetragonality and electrical features can be found, and the compositions involving high c/a are usually stabilized in normal ferroelectric phase. It is believed that c/a is a more appropriate parameter to illustrate the variation of ferroelectric properties for unfilled TTB system.« less

Crystal structure and properties of tetragonal EuAg{sub 4}In{sub 8} grown by metal flux technique

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

Subbarao, Udumula; Sarkar, Sumanta; Peter, Sebastian C., E-mail: sebastiancp@jncasr.ac.in

The compound EuAg{sub 4}In{sub 8} has been obtained as single crystals in high yield from reactions run in liquid indium. X-ray diffraction on single crystals suggests that EuAg{sub 4}In{sub 8} crystallizes in the CeMn{sub 4}Al{sub 8} structure type, tetragonal space group I4/mmm with lattice constants a=b=9.7937(2) Å and c=5.7492(2) Å. Crystal structure of EuAg{sub 4}In{sub 8} is composed of pseudo Frank–Kasper cages occupied by one europium atom in each ring, which are shared through the corner along the ab plane resulting in a three dimensional network. The magnetic susceptibility of EuAg{sub 4}In{sub 8} was measured in the temperature range 2–300more » K, which obeyed Curie–Weiss law above 50 K. Magnetic moment value calculated from the fitting indicates the presence of divalent europium, which was confirmed by X-ray absorption near edge spectroscopy. Electrical resistivity measurements suggest that EuAg{sub 4}In{sub 8} is metallic in nature with a probable Fermi liquid behavior at low temperature. - Graphical abstract: The tetragonal EuAg{sub 4}In{sub 8} has been grown as single crystals from reactions run in liquid indium. Magnetic and XANES measurements suggest divalent nature of Eu and resistivity measurements suggest metallic nature. - Highlights: • EuAg{sub 4}In{sub 8} phase having tetragonal phase is grown by metal flux technique. • Magnetic and XANES measurements exhibit divalent nature of Eu in EuAg{sub 4}In{sub 8}. • Resistivity measurement suggests metallic nature and probable Fermi liquid behavior.« less

Role of multiorbital effects in the magnetic phase diagram of iron pnictides

NASA Astrophysics Data System (ADS)

Christensen, Morten H.; Scherer, Daniel D.; Kotetes, Panagiotis; Andersen, Brian M.

2017-07-01

We elucidate the pivotal role of the band structure's orbital content in deciding the type of commensurate magnetic order stabilized within the itinerant scenario of iron pnictides. Recent experimental findings in the tetragonal magnetic phase attest to the existence of the so-called charge and spin ordered density wave over the spin-vortex crystal phase, the latter of which tends to be favored in simplified band models of itinerant magnetism. Here we show that employing a multiorbital itinerant Landau approach based on realistic band structures can account for the experimentally observed magnetic phase, and thus shed light on the importance of the orbital content in deciding the magnetic order. In addition, we remark that the presence of a hole pocket centered at the Brillouin zone's M point favors a magnetic stripe rather than a tetragonal magnetic phase. For inferring the symmetry properties of the different magnetic phases, we formulate our theory in terms of magnetic order parameters transforming according to irreducible representations of the ensuing D4 h point group. The latter method not only provides transparent understanding of the symmetry-breaking schemes but also reveals that the leading instabilities always belong to the {A1 g,B1 g} subset of irreducible representations, independently of their C2 or C4 nature.

Thermoelastic behaviour of martensitic alloy in the vicinity of critical point in the stress-temperature phase diagram

NASA Astrophysics Data System (ADS)

L'vov, V. A.; Matsishin, N.; Glavatska, N.

2010-04-01

The theoretical phase diagram of the shape memory alloy, which exhibits the first-order martensitic phase transition of the cubic-tetragonal type, has been considered. The thermoelastic behaviour of the ultra-soft Ni-Mn-Ga alloy in the vicinity of the endpoint of the phase transitions line has been modelled. To this end, the strain-temperature and stress-strain dependencies have been computed with the account of the temperature dependence of the elastic modulus of the alloy. Two important features of thermoelastic behaviour of the alloy have been disclosed: (1) even in the case of complete stress-induced martensitic transformation (MT), the MT strain determined from the length of the plateaus at the stress-strain curves is smaller than the 'spontaneous' tetragonal distortion of the crystal lattice, which arises on cooling of the alloy and (2) the stress-strain loops may include the plateau-like segment even at temperatures above the critical temperature, which corresponds to the endpoint of the stress-strain phase diagram. These features render the observation of the endpoint of phase transitions line impossible with the help of the stress-strain tests and make preferable the direct structural studies of MTs in the stressed single-crystalline specimens.

Pseudomorphic to orthomorphic growth of Fe films on Cu3Au(001)

NASA Astrophysics Data System (ADS)

Bruno, F.; Terreni, S.; Floreano, L.; Cossaro, A.; Cvetko, D.; Luches, P.; Mattera, L.; Morgante, A.; Moroni, R.; Repetto, M.; Verdini, A.; Canepa, M.

2002-06-01

The structure of Fe films grown on the (001) surface of a Cu3Au single crystal at room temperature has been investigated by means of grazing incidence x-ray diffraction (GIXRD) and photo/Auger-electron diffraction (ED) as a function of thickness in the (3-36)-Å range. The combination of GIXRD and ED allows one to obtain quantitative information on the in-plane spacing a from the former technique, and the ratio between the vertical spacing c and a, from the latter one. At low coverage the film grows pseudomorphic to the face-centered-cubic substrate. The experimental results obtained on a film of 8 Å thickness clearly indicate the overcoming of the limit for pseudomorphic growth. Above this limit the film is characterized by the coexistence of the pseudomorphic phase with another tetragonally strained phase γ, which falls on the epitaxial line of ferromagnetic face-centered cubic Fe. Finally, the development of a body-centered phase α, whose unit cell is rotated by 45° with respect to the substrate one, has been clearly observed at ~17 Å. α is the dominating phase for film thickness above ~25 Å and its lattice constant evolves towards the orthomorphic phase in strict quantitative agreement with epitaxial curves calculated for body-centered tetragonal iron phases.

Giant piezoelectric property of (110) oriented BaxSr1-xTiO3 films

NASA Astrophysics Data System (ADS)

Chen, Z. H.; Chen, Z.; Qiu, J. H.; Yuan, N. Y.; Ding, J. N.

2017-10-01

A phenomenological Landau-Devonshire theory is applied to investigate the phase diagrams and physical properties of (110) oriented BaxSr1-xTiO3 films. New ferroelectric phases, such as the tetragonal a1 phase and the orthorhombic a2 c phase, appear in the ;misfit strain-temperature; phase diagrams for (110) oriented films compared with that of (001) oriented films. Moreover, the orthorhombic a2 c phase, and the tetragonal c phase and the triclinic γ phase are stable at low temperature for x = 0.5 and x = 0.7 , respectively. The ferroelectric, dielectric, and piezoelectric properties strongly depend on the misfit strain and electric field. (110) oriented Ba0.7Sr0.3TiO3 film has the larger ferroelectric polarization and piezoelectric coefficient than that of Ba0.5Sr0.5TiO3 film. The giant piezoelectric coefficient of 340 pm / V is obtained at the electric field of 50 KV / cm in (110) oriented Ba0.7Sr0.3TiO3 film, which is comparable with the values of Pb (Zr1-xTix)O3 and (1 - x) Pb (Mg1/3Nb2/3)O3 -xPbTiO3 films. It makes (110) oriented BaxSr1-xTiO3 films suitable for applications in electromechanical devices.

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

Effect of particle in-flight behavior on the composition of thermal barrier coatings

NASA Astrophysics Data System (ADS)

Zhao, L.; Bai, Y.; Tang, J. J.; Liu, K.; Ding, C. H.; Yang, J. F.; Han, Z. H.

2013-12-01

In this work, 6 to 11 mol% YO1.5-stabilized zirconia (YSZ) coatings were deposited by supersonic and conventional atmospheric plasma spraying. During spraying, the surface temperature and velocity of in-flight particles were monitored by Spray Watch 2i on-line system. The phase composition of as-sprayed coatings was analyzed by X-ray diffractometry (XRD). Lattice parameters, tetragonality and the content of YO1.5 (mol%) of as-sprayed coatings were calculated according to the position of (0 0 4) and (4 0 0) diffraction peaks. It was found that the as-sprayed coatings were composed of metastable non-transformable tetragonal phase (t‧). However, the amount of YO1.5 (mol%) in the as-sprayed coatings decreased with the increase of melting index of in-flight particles due to the partial evaporation of YO1.5 during spraying.

Effect of the CTAB concentration on the upconversion emission of ZrO 2:Er 3+ nanocrystals

NASA Astrophysics Data System (ADS)

López-Luke, T.; De la Rosa, E.; Sólis, D.; Salas, P.; Angeles-Chavez, C.; Montoya, A.; Díaz-Torres, L. A.; Bribiesca, S.

2006-10-01

Upconversion emission of ZrO 2:Er 3+ (0.2 mol%) nanophosphor were studied as function of surfactant concentration after excitation at 968 nm. The strong green emission was produced by the transition 2H 11/2 + 4S 3/2 → 4I 15/2 and was explained in terms of cooperative energy transfer between neighboring ions. The upconverted signal was enhanced but the fluorescence decay time was reduced as either the surfactant concentration increases or the annealing time reduces. Experimental results show that surfactant concentration controls the particle size and morphology while annealing time control the phase composition and crystallite size. The highest intensity was obtained for a sample composed of a mixture of tetragonal (33 wt.%) and monoclinic (67 wt.%) phase with crystallite size of 31 and 59 nm, respectively. This result suggests that tetragonal crystalline structure and small crystallite size are more favorable for the upconversion emission.

Eco-friendly p-type Cu2SnS3 thermoelectric material: crystal structure and transport properties

PubMed Central

Shen, Yawei; Li, Chao; Huang, Rong; Tian, Ruoming; Ye, Yang; Pan, Lin; Koumoto, Kunihito; Zhang, Ruizhi; Wan, Chunlei; Wang, Yifeng

2016-01-01

As a new eco-friendly thermoelectric material, copper tin sulfide (Cu2SnS3) ceramics were experimentally studied by Zn-doping. Excellent electrical transport properties were obtained by virtue of 3-dimensionally conductive network for holes, which are less affected by the coexistence of cubic and tetragonal phases that formed upon Zn subsitition for Sn; a highest power factors ~0.84 mW m−1 K−2 at 723 K was achieved in the 20% doped sample. Moreover, an ultralow lattice thermal conductivity close to theoretical minimum was observed in these samples, which could be related to the disordering of atoms in the coexisting cubic and tetragonal phases and the interfaces. Thanks to the phonon-glass-electron-crystal features, a maximum ZT ~ 0.58 was obtained at 723 K, which stands among the tops for sulfide thermoelectrics at the same temperature. PMID:27666524

Strain Accommodation By Facile WO6 Octahedral Distortion and Tilting During WO3 Heteroepitaxy on SrTiO3(001)

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

Du, Yingge; Gu, Meng; Varga, Tamas

2014-08-27

In this paper, we show that compared to other BO6 octahedra in ABO3 structured perovskite oxides, the WO6 octahedra in tungsten trioxide (WO3) can withstand a much larger degree of distortion and tilting to accommodate interfacial strain, which in turn strongly impact the nucleation, structure, and defect formation during the epitaxial growth of WO3 on SrTiO3(001). A meta-stable tetragonal phase can be stabilized by epitaxy and a thickness dependent phase transition (tetragonal to monoclinic) is observed. In contrast to misfit dislocations to accommodate the interfacial stain, the facial WO6 octahedral distortion and tilting give rise to three types of planarmore » defects that affect more than 15 monolayers from the interface. These atomically resolved, unusual interfacial defects may significantly alter the electronic, electrochromic, and mechanical properties of the epitaxial films.« less

PAC characterization of Gd and Y doped nanostructured zirconia solid solutions

NASA Astrophysics Data System (ADS)

Caracoche, María C.; Martínez, Jorge A.; Pasquevich, Alberto F.; Rivas, Patricia C.; Djurado, Elizabeth; Boulc'h, Florence

2007-02-01

A perturbed angular correlation (PAC) study as a function of temperature has been carried out on spray pyrolysis-derived powders and compacts of 2.5 mol% Y 2O 3-ZrO 2 and 2 mol% Gd 2O 3-ZrO 2 nanostructured tetragonal zirconias. The powders undergo the ordinary thermal transformation between the two known defective t‧- and regular t-tetragonal forms and also a partial and irreversible change to an ordered cubic configuration. The dynamical nature of the t‧-form leads to an activation energy of about 0.15 eV for the oxygen vacancies movement. The as-obtained compacts do not exhibit any known cubic nanostructure but some additional contributions. In both of them a hyperfine component assigned to the orthorhombic phase is determined. In the smaller cation Y doped ceramic a small amount of monoclinic phase reflects an incomplete stabilization.

Cubic martensite in high carbon steel

NASA Astrophysics Data System (ADS)

Chen, Yulin; Xiao, Wenlong; Jiao, Kun; Ping, Dehai; Xu, Huibin; Zhao, Xinqing; Wang, Yunzhi

2018-05-01

A distinguished structural characteristic of martensite in Fe-C steels is its tetragonality originating from carbon atoms occupying only one set of the three available octahedral interstitial sites in the body-centered-cubic (bcc) Fe lattice. Such a body-centered-tetragonal (bct) structure is believed to be thermodynamically stable because of elastic interactions between the interstitial carbon atoms. For such phase stability, however, there has been a lack of direct experimental evidence despite extensive studies of phase transformations in steels over one century. In this Rapid Communication, we report that the martensite formed in a high carbon Fe-8Ni-1.26C (wt%) steel at room temperature induced by applied stress/strain has actually a bcc rather than a bct crystal structure. This finding not only challenges the existing theories on the stability of bcc vs bct martensite in high carbon steels, but also provides insights into the mechanism for martensitic transformation in ferrous alloys.

Improving Qubit Phase Estimation in Amplitude-damping Channel by Partial-collapse Measurement

NASA Astrophysics Data System (ADS)

Liao, Xiang-Ping; Zhou, Xin; Fang, Mao-Fa

2018-03-01

An efficient method is proposed to improve qubit phase estimation in amplitude-damping channel by partial-collapse measurement in this paper. It is shown that the quantum Fisher information (QFI) can be distinctly enhanced under amplitude-damping decoherence with partial-collapse measurement. Moreover, the optimal QFI is approximately close to the maximum value 1 regardless of the decoherence parameter by choosing the appropriate measurement strengths.

Ab initio study of the structural phase transitions of the double perovskites Sr2MWO6 (M=Zn, Ca, Mg)

NASA Astrophysics Data System (ADS)

Petralanda, U.; Etxebarria, I.

2014-02-01

We study the interplay of structural distortions in double perovskites Sr2MWO6 (M = Zn, Ca, Mg) by means of first-principles calculations and group theoretical analysis. Structure relaxations of the cubic, tetragonal, and monoclinic phases show that the ground states of the three compounds are monoclinic, although the energy difference between the monoclinic and tetragonal structures is very small in the case of Sr2MgWO6. The symmetry analysis of the distortions involved in the experimental and calculated low-temperature structures shows that the amplitude of two primary distortions associated to rigid rotations of the MX6 and WO6 octahedra are dominant, although the amplitude of a third mode related to deformations of the MX6 groups can not be neglected. The energy maps of the space spanned by the three relevant modes are calculated, and the couplings among the modes are evaluated, showing that the role of a hard secondary mode (in the Landau sense) coupled trilinearly to the two primary instabilities is crucial to stabilize the monoclinic ground state. Results suggest that the key role of the trilinear coupling among three modes could be rather common. A phenomenological theory including the effects of the chemical pressure is also developed. We find that the evolution of the stiffness constants in terms of the atomic substitution follows an accurate linear dependence and that the influence of quantum saturation of the order parameters could stabilize the tetragonal phase of Sr2MgWO6.

Microstructural and mechanical properties of Al2O3/ZrO2 nanomultilayer thin films prepared by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Balakrishnan, G.; Sastikumar, D.; Kuppusami, P.; Babu, R. Venkatesh; Song, Jung Il

2018-02-01

Single layer aluminium oxide (Al2O3), zirconium oxide (ZrO2) and Al2O3/ZrO2 nano multilayer films were deposited on Si (100) substrates at room temperature by pulsed laser deposition. The development of Al2O3/ZrO2 nanolayered structure is an important method used to stabilize the high temperature phase (tetragonal and cubic) of ZrO2 at room temperature. In the Al2O3/ZrO2 multilayer structure, the Al2O3 layer was kept constant at 5 nm, while the ZrO2 layer thickness varied from 5 to 20 nm (5/5, 5/10, 5/15 and 5/20 nm) with a total of 40 bilayers. The X-ray diffraction studies of single layer Al2O3 indicated the γ-Al2O3 of cubic structure, while the single layer ZrO2 indicated both monoclinic and tetragonal phases. The 5/5 and 5/10 nm multilayer films showed the nanocrystalline nature of ZrO2 with tetragonal phase. The high resolution transmission electron microscopy studies indicated the formation of well-defined Al2O3 and ZrO2 layers and that they are of uniform thickness. The atomic force microscopy studies revealed the uniform and dense distribution of nanocrystallites. The nanoindentation studies indicated the hardness of 20.8 ± 1.10 and 10 ± 0.60 GPa, for single layer Al2O3 and ZrO2, respectively, and the hardness of multilayer films varied with bilayer thickness.

Collapsing lattice animals and lattice trees in two dimensions

NASA Astrophysics Data System (ADS)

Hsu, Hsiao-Ping; Grassberger, Peter

2005-06-01

We present high statistics simulations of weighted lattice bond animals and lattice trees on the square lattice, with fugacities for each non-bonded contact and for each bond between two neighbouring monomers. The simulations are performed using a newly developed sequential sampling method with resampling, very similar to the pruned-enriched Rosenbluth method (PERM) used for linear chain polymers. We determine with high precision the line of second-order transitions from an extended to a collapsed phase in the resulting two-dimensional phase diagram. This line includes critical bond percolation as a multicritical point, and we verify that this point divides the line into different universality classes. One of them corresponds to the collapse driven by contacts and includes the collapse of (weakly embeddable) trees. There is some evidence that the other is subdivided again into two parts with different universality classes. One of these (at the far side from collapsing trees) is bond driven and is represented by the Derrida-Herrmann model of animals having bonds only (no contacts). Between the critical percolation point and this bond-driven collapse seems to be an intermediate regime, whose other end point is a multicritical point P* where a transition line between two collapsed phases (one bond driven and the other contact driven) sparks off. This point P* seems to be attractive (in the renormalization group sense) from the side of the intermediate regime, so there are four universality classes on the transition line (collapsing trees, critical percolation, intermediate regime, and Derrida-Herrmann). We obtain very precise estimates for all critical exponents for collapsing trees. It is already harder to estimate the critical exponents for the intermediate regime. Finally, it is very difficult to obtain with our method good estimates of the critical parameters of the Derrida-Herrmann universality class. As regards the bond-driven to contact-driven transition in the collapsed phase, we have some evidence for its existence and rough location, but no precise estimates of critical exponents.

Influences of annealing temperature on structural characterization and magnetic properties of Mn-doped BaTiO3 ceramics

NASA Astrophysics Data System (ADS)

Phan, The-Long; Zhang, P.; Grinting, D.; Yu, S. C.; Nghia, N. X.; Dang, N. V.; Lam, V. D.

2012-07-01

Polycrystalline samples of BaTiO3 doped with 2.0 at. % Mn were prepared by solid-state reaction at various temperatures (Tan) ranging from 500 to 1350 °C, used high-pure powders of BaCO3, TiO2, and MnCO3 as precursors. Experimental results obtained from x-ray diffraction patterns and Raman scattering spectra reveal that tetragonal Mn-doped BaTiO3 starts constituting as Tan ≈ 500 °C. The Tan increase leads to the development of this phase. Interestingly, there is the tetragonal-hexagonal transformation in the crystal structure of BaTiO3 as Tan ≈ 1100 °C. Such the variations influence directly magnetic properties of the samples. Besides paramagnetic contributions of Mn2+ centers traced to electron spin resonance, the room-temperature ferromagnetism found in the samples is assigned to exchange interactions taking place between Mn3+ and Mn4+ ions located in tetragonal BaTiO3 crystals.

Substitutional Cd and Cd-Oxygen Vacancy Complexes in ZrO2 and Ce-doped ZrO_2

NASA Astrophysics Data System (ADS)

Zacate, Matthew O.; Karapetrova, E.; Platzer, R.; Gardner, J. A.; Evenson, W. E.; Sommers, J. A.

1996-03-01

We are using Perturbed Angular Correlation Spectroscopy (PAC) to study oxygen vacancy (V_O) dynamics in tetragonal ZrO2 and Ce-doped ZrO_2. PAC requires a radioactive probe atom, Cd in this study, which sits substitutionally for a Zr ion. Cd is doubly-negatively charged relative to the lattice and attracts doubly-positively charged V_Os. Pure tetragonal zirconia exists only above 950 ^circC and in this temperature range, the V_Os are very mobile. Above 950 ^circC we observe V_Os rapidly hopping about the Cd allowing us to determine the VO concentration and the trapping energy. We have been Ce-doping to stabilize the tetragonal phase to lower temperature to determine the electric field gradient the Cd experiences due to a stationary V_O. As a consequence of the Ce-doping, we observe a local lattice distortion about the Cd which increases with Ce-doping.

Low temperature molten-salt synthesis of nanocrystalline cubic Sr{sub 2}SbMnO{sub 6}

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

Baral, Antara; Varma, K.B.R., E-mail: kbrvarma@mrc.iisc.ernet.i

2009-12-15

Sr{sub 2}SbMnO{sub 6} (SSM) powders were successfully synthesized at reasonably low temperatures via molten-salt synthesis (MSS) method using eutectic composition of 0.635 Li{sub 2}SO{sub 4}-0.365 Na{sub 2}SO{sub 4} (flux). High-temperature cubic phase SSM was stabilized at room temperature by calcining the as-synthesized powders at 900 deg. C/10 h. The phase formation and morphology of these powders were characterized via X-ray powder diffraction and scanning electron microscopy, respectively. The SSM phase formation associated with {approx}60 nm sized crystallites was also confirmed by transmission electron microscopy. The activation energy associated with the particle growth was found to be 95+-5 kJ mol{sup -1}.more » The dielectric constant of the tetragonal phase of the ceramic (fabricated using this cubic phase powder) with and without the flux (sulphates) has been monitored as a function of frequency (100 Hz-1 MHz) at room temperature. Internal barrier layer capacitance (IBLC) model was invoked to rationalize the dielectric properties. - Graphical abstract: The as synthesized powders of Sr{sub 2}SbMnO{sub 6} calcined at 900 deg. C/10 h yielded a cubic phase ({approx}60 nm sized crystallites). Centrosymmetric tetragonal (I4/mcm) phase was obtained by increasing the calcination temperature to 1000 deg. C. Display Omitted« less

Giant Polarization and High Temperature Monoclinic Phase in a Lead-Free Perovskite of Bi(Zn 0.5Ti 0.5)O 3-BiFeO 3

DOE PAGES

Pan, Zhao; Chen, Jun; Yu, Runze; ...

2016-09-15

Lead-free piezoelectrics have attracted increasing attention due to the awareness of lead toxicity to the environment. Here, a new Bi-based lead-free perovskite of (1-x)Bi(Zn 0.5Ti 0.5)O 3-xBiFeO 3 has been synthesized via high-pressure and high-temperature method. It exhibits interest-ing properties of giant polarization, morphotropic phase boundary (MPB), and monoclinic phase. In particular, large tetragonality ( c/a = 1.228) and giant spontaneous polariza-tion of 110 μC/cm 2 has been obtained in 0.6Bi(Zn 0.5Ti 0.5)O 3-0.4BiFeO 3, which is much higher than most available lead-free materials and conventional Pb(Zr,Ti)O 3. MPB is clearly identified to be constituted by tetragonal and monoclinic phasesmore » at x = 0.5. Notably, a single monoclinic phase has been observed at x = 0.6, which exhibits an intriguing high temperature property. In conclusion, the present results are helpful to explore new lead-free MPB systems in bismuth-based compounds.« less

Tuning upconversion luminescence of LiYF4:Yb3+,Er3+/Tm3+/Ho3+ microcrystals synthesized through a molten salt process.

PubMed

Niu, Na; He, Fei; Wang, Liuzhen; Wang, Lin; Wang, Yan; Gai, Shili; Yang, Piaoping

2014-05-01

In this paper, well-defined tetragonal-phase LiYF4:Yb3+,Er3+/Tm3+/Ho3+ micro-crystals with octahedral morphology were successfully prepared through a surfactant-free molten salt process for the first time. By gradually increasing the LiF content in the NaNO3-KNO3 reaction medium, the crystal phase transforms from a mixture of YF3 and LiYF4 to pure tetragonal-phase LiYF4. The possible formation process for the phase and morphology evolution is also presented. Moreover, upon 980 nm laser diode (LD) excitation, the lanthanide ions (Yb3+, Er3+/Tm3+/Ho3+) doped LiYF4 crystals exhibit intense upconversion emission lights. By tuning the sensitizer concentrations of Yb3+ ions in LiYF4:Yb3+,Er3+, the relative intensities of green and red emissions can be precisely adjusted under single wavelength excitation. Consequently, multicolor upconversion emissions can be obtained. On the other hand, UC mechanisms were also given based on the emission spectra and the plot of luminescence intensity to pump power.

Oxygen stoichiometry: A key parameter to tune structural phase diagram of La{sub 0.2}Sr{sub 0.8}MnO{sub 3-δ}

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

Shahee, Aga, E-mail: agashahee@gmail.com; Lalla, N. P.

2015-06-24

Low temperature x-ray powder diffraction studies, in conjunction with transmission electron microscopy on stoichiometric (δ = 0.01) and oxygen deficient (δ =0.12) samples of La{sub 0.2}Sr{sub 0.8}MnO{sub 3-δ} manganites have been carried out. These studies revealed that oxygen stoichiometry plays a key role in controlling ground state of electron doped manganites. It is observed that the La{sub 0.2}Sr{sub 0.8}MnO{sub 2.99} undergoes a first order phase transition from cubic (Pm-3m) to JT-distorted twin tetragonal (I4/mcm) phase associated with C-type antiferromagnetic ordering at ∼260K. This JT-distortion induced cubic to tetragonal phase transition get totally suppressed in La{sub 0.2}Sr{sub 0.8}MnO{sub 2.88}. The basicmore » perovskite lattice of the off-stoichiometric La{sub 0.2}Sr{sub 0.8}MnO{sub 2.88} remains cubic down to 80K but undergoes a well-developed charge-ordering transition with 9x9 modulations at ∼260K.« less

Accelerated aging characteristics of three yttria-stabilized tetragonal zirconia polycrystalline dental materials.

PubMed

Flinn, Brian D; deGroot, Dirk A; Mancl, Lloyd A; Raigrodski, Ariel J

2012-10-01

Concerns have been expressed about the effect of aging on the mechanical properties of zirconia. The purpose of this study was to assess the accelerated aging characteristics of 3 commercially available yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) materials by exposing specimens to hydrothermal treatments at 134°C, 0.2 MPa and 180°C, 1.0 MPa in steam. Thin bars of Y-TZP from 3 manufacturers, Lava, Zirkonzahn, and Zirprime, n=30 for each brand (22 × 3 × 0.2 mm), were cut and ground from blocks and sintered according to the manufacturer's specifications. Control specimens (n=10) for each brand were evaluated in the as-received condition. Experimental specimens were artificially aged at standard autoclave sterilization conditions,134°C at 0.2 MPa (n=5 per group at 50, 100, 150, and 200 hours) and standard industrial ceramic aging conditions, 180°C at 1.0 MPa (n=5 per group at 8, 16, 24, 28, and 48 hours). Tetragonal to monoclinic transformation was measured by using X-ray diffraction (XRD) for all groups. Flexural strength was measured in 4-point bending (ASTM1161-B) for all groups. Fracture surfaces were examined by scanning electron microscopy (SEM). Data were analyzed as a function of aging time. The statistical comparisons were based on the log value and 2-way ANOVA with heteroscedasticity-consistent standard errors used to compare mean strength among conditions (α=.05). After 200 hours at 134°C and 0.2 MPa, flexural strength (SD) decreased significantly from 1156 (87.6) MPa to 829.5 (71) MPa for Lava; 1406 (243) MPa to 882.7 (91) MPa for Zirkonzahn; and 1126 (92.4) MPa to 976 (36.4) MPa for Zirprime with P<.001 for all 3 comparisons. After 200 hours at 134°C and 0.2 MPa, some tetragonal crystals transformed to the monoclinic phase. The relative XRD peak intensity of the monoclinic to tetragonal crystal phases increased from 0.07 to 1.82 for Lava, from 0.06 to 2.43 for Zirkonzahn, and from 0.05 to 0.53 for Zirprime. After 28 hours at 180°C and 1.0 MPa, all Lava and Zirkonzahn specimens spontaneously fractured during aging. The Noritake specimens were intact after 48 hours, and the flexural strength showed no significant change, 1156 (87.6) MPa to 1122 (108) MPa. The flexural strength decreased with an increase in the monoclinic phase. SEM micrographs revealed a transformed layer on the fracture surfaces. Hydrothermal aging of Y-TZP can cause significant transformation from tetragonal to monoclinic crystal structure, which results in a statistically significant decrease in the flexural strength of thin bars. Although the strengths of all 3 Y-TZP materials are higher than other materials used for ceramic restorations, there are notable differences among them. Copyright © 2012 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

Preparation and evaluation of thin-film sodium tungsten bronzes

NASA Technical Reports Server (NTRS)

Kautz, H. E.; Fielder, W. L.; Singer, J.; Fordyce, J. S.

1974-01-01

Thin films of sodium tungsten bronze (NaxWO3) were investigated as reversible sodium ion electrodes for solid electrolytes. The films were made by electron beam evaporation of the three phases, W metal, Na2WO4, and WO3, followed by sintering. The substrates were sodium beta alumina disks and glass slides. X-ray diffraction analyses of the films showed that sintering in dry nitrogen with prior exposure to air lead to mixed phases. Sintering in vacuum with no air exposure produced tetragonal I bronze with a nominal composition of Na0.31WO3, single phase within the limits of X-ray diffraction detectability. The films were uniform and adherent on sodium beta alumina substrates. The ac and dc conductivities of the beta alumina were measured with the sodium tungsten bronze films as electrodes. These experiments indicated that the tetragonal I bronze electrodes were not completely reversible. This may have resulted from sodium ion blocking within the bronze film or at the bronze beta alumina interface. Methods for attempting to make more completely reversible electrodes are suggested.

Approaching Piezoelectric Response of Pb-Piezoelectrics in Hydrothermally Synthesized Bi0.5(Na1- xK x)0.5TiO3 Nanotubes.

PubMed

Ghasemian, Mohammad Bagher; Rawal, Aditya; Liu, Yun; Wang, Danyang

2018-06-20

A large piezoelectric coefficient of 76 pm/V along the diameter direction, approaching that of lead-based piezoelectrics, is observed in hydrothermally synthesized Pb-free Bi 0.5 (Na 0.8 K 0.2 ) 0.5 TiO 3 nanotubes. The 30-50 nm diameter nanotubes are formed through a scrolling and wrapping mechanism without the need of a surfactant or template. A molar ratio of KOH/NaOH = 0.5 for the mineralizers yields the Na/K ratio of ∼0.8:0.2, corresponding to an orthorhombic-tetragonal (O-T) phase boundary composition. X-ray diffraction patterns along with transmission electron microscopy analysis ascertain the coexistence of orthorhombic and tetragonal phases with (110) and (001) orientations along the nanotube length direction, respectively. 23 Na NMR spectroscopy confirms the higher degree of disorder in Bi 0.5 (Na 1- x K x ) 0.5 TiO 3 nanotubes with O-T phase coexistence. These findings present a significant advance toward the application of Pb-free piezoelectric materials.

Role of organic cations on hybrid halide perovskite CH3NH3PbI3 surfaces

NASA Astrophysics Data System (ADS)

Teng, Qiang; Shi, Ting-Ting; Tian, Ren-Yu; Yang, Xiao-Bao; Zhao, Yu-Jun

2018-02-01

Organic-inorganic hybrid halide perovskite CH3NH3PbI3 (MAPbI3) has received rapid progress in power conversion efficiency as promising photovoltaic materials, yet the surface structures and the role of MA cations are not well understood. In this work, we investigated the structural stability and electronic properties of (001) surface of cubic, (001) and (110) surfaces of tetragonal and orthorhombic phases of MAPbI3 with considering the orientation of MA cations, by density functional theory calculations. We demonstrate that the orientation of MA cations has profound consequences on the structural stability and the electronic properties of the surfaces, in contrast to the bulk phases. Compared with the MA-I terminated surfaces, the Pb-I2 terminated ones generally have smaller band gaps and the advantage to enable the photo-excited holes to transfer to the hole-transport materials in both tetragonal and orthorhombic phases. Overall, we suggest that the films with Pb-I2 terminated surfaces would prevail in high performance solar energy absorbers.

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.

Variation of oxygen content in selected potassium fluorido-oxido-tantalate phases

NASA Astrophysics Data System (ADS)

Boča, Miroslav; Moncoĺ, Ján; Netriová, Zuzana; Velič, Dušan; Jerigová, Monika; Nunney, Tim S.; Baily, Christopher J.; Kubíková, Blanka; Šimko, František; Janderka, Pavel

2011-12-01

The compound K 3[TaO 4]•K 3[TaF 4O 2] crystallises in a tetragonal system (space group I-4) with cell parameters a = 6.2220(3) Å and c = 8.7625(34) Å, respectively. The crystal structure consists of two anions, [TaO 4] 3- and [TaF 4O 2] 3- and cations K +. The tantalum atoms lie in special positions and serve as centres of both anions, which are substitution disorders. XPS measurements confirmed the existence of different binding energies corresponding to the different bonds of Ta sbnd O and Ta sbnd F. Oxygen is bound more strongly in [TaF 4O 2] 3-. By combination of single crystal analysis, XRD, SIMS and XPS it was suggested that previously reported cubic phase K 3TaOF 6 is in fact K 3TaO 2F 4 and previously reported tetragonal phase K 3TaO 2F 4 is in fact K 3[TaO 4]•K 3[TaF 4O 2].

Role of lattice distortion on diffuse phase transition temperatures in Bi0.5Na0.5TiO3-BaTiO3 [BNBTO] solid solutions

NASA Astrophysics Data System (ADS)

Pradhan, Lagen Kumar; Pandey, Rabichandra; Kumar, Sunil; Supriya, Sweety; Kar, Manoranjan

2018-04-01

Effect of lattice distortion on diffuse phase transition in BNBTO solid solutions near Morphotropic phase boundary (MPB) has been investigated. Solid solutions of (Bi0.5Na0.5)1-xBaxTiO3 (with mole % of x= 0.04, 0.05, 0.06, 0.07 and 0.08) were prepared by the planetary ball mill method in ethanol medium. Rietveld refinement technique with rhombohedral (R3c) and tetragonal (P4bm) crystal symmetry has been employed for structural as well as phase analysis of the solid solutions. Both rhombohedral and tetragonal lattice distortion (c/a) tends toward the pseudo-cubic crystal symmetry with the increase of mole fraction of Ba2+ near MPB (x= 6 mole %). Also, the average crystallite size and grain size decrease with increase of mole fraction of Ba2+ in BNT ceramic are due to larger ionic radius of Ba2+ and grain boundary pinning process in the solid solutions respectively. Additionally, depolarization temperature (Td) and maximum temperature (Tm) reduces due to the lattice distortion of both the phases in BNBTO solid solutions, which is explained extensively. Significant increase of dielectric constant has been observed near MPB composition (x=6%) in BNBTO solid solutions.

Investigations of Ba{sub x}Sr{sub 1−x}TiO{sub 3} ceramics and powders prepared by direct current arc discharge technique

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

Li, Shuangbin; Wang, Xiaohan; University of Chinese Academy of Sciences, Beijing 100049

2014-09-01

Ba{sub x}Sr{sub 1−x}TiO{sub 3} ceramics with x ranging from 0 to 1 were prepared by direct current arc discharge technique and studied by means of x-ray diffraction (XRD) and Raman spectroscopy. The cubic-tetragonal ferroelectric phase transition in Ba{sub x}Sr{sub 1−x}TiO{sub 3} ceramics was found to occur at x ≈ 0.75. XRD investigation of as-grown BaTiO{sub 3} ceramics revealed co-existence of tetragonal and hexagonal modifications with a small amount of impurity phase BaTi{sub 4}O{sub 9}. No evidences of hexagonal phase were observed in Raman spectra of as-grown BaTiO{sub 3} ceramics, while Raman peaks related to hexagonal phase were clearly observed in the spectrummore » of fine-grain powders prepared from the same ceramics. A core-shell model for BaTiO{sub 3} ceramics prepared by direct current arc discharge technique is proposed. Absence of the hexagonal phase in any Ba{sub x}Sr{sub 1−x}TiO{sub 3} solid solution with x < 1 is discussed in the frame of specific atomic arrangement.« less

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe 1 -xCox)2As2

NASA Astrophysics Data System (ADS)

Sapkota, A.; Das, P.; Böhmer, A. E.; Ueland, B. G.; Abernathy, D. L.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.; McQueeney, R. J.

2018-05-01

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe 1 -xCox)2As2,x =0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x =0.026 , similar to the parent CaFe2As2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe 1 -xCox)2As2 , wherein the crossover corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe 1 -xCox)2As2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x =0.030 sample and high-temperature x =0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x =0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. One possible scenario ascribes this loss of moment to a sensitivity to the c -axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.

Unraveling the origins of electromechanical response in mixed-phase Bismuth Ferrite

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

Vasudevan, Rama K; Okatan, M. B.; Liu, Y. Y.

The origin of giant electromechanical response in a mixed-phase rhombohedral-tetragonal BiFeO3 thin film is probed using sub-coercive scanning probe microscopy based multiple-harmonic measurements. Significant contributions to the strain arise from a second-order harmonic response localized at the phase boundaries. Strain and dissipation data, backed by thermodynamic calculations suggest that the source of the enhanced electromechanical response is the motion of phase boundaries. These findings elucidate the key role of labile phase boundaries, both natural and artificial, in achieving thin films with giant electromechanical properties.

Strain-driven phase transitions and associated dielectric/piezoelectric anomalies in BiFeO3 thin films

NASA Astrophysics Data System (ADS)

Huang, C. W.; Chu, Y. H.; Chen, Z. H.; Wang, Junling; Sritharan, T.; He, Q.; Ramesh, R.; Chen, Lang

2010-10-01

Strain-driven phase transitions and related intrinsic polarization, dielectric, and piezoelectric properties for single-domain films were studied for BiFeO3 using phenomenological Landau-Devonshire theory. A stable and mixed structure between tetragonal and rhombohedral-like (monoclinic) phases is predicted at a compressive misfit strain of um=-0.0382 without an energy barrier. For a tensile misfit strain of um=0.0272, another phase transition between the monoclinic and orthorhombic phases was predicted with sharply high dielectric and piezoelectric responses.

Structural stability and electronic properties of β-tetragonal boron: A first-principles study

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

Hayami, Wataru, E-mail: hayami.wataru@nims.go.jp

2015-01-15

It is known that elemental boron has five polymorphs: α- and β-rhombohedral, α- and β-tetragonal, and the high-pressure γ phase. β-tetragonal (β-t) boron was first discovered in 1960, but there have been only a few studies since then. We have thoroughly investigated, using first-principles calculations, the atomic and electronic structures of β-t boron, the details of which were not known previously. The difficulty of calculation arises from the fact that β-t boron has a large unit cell that contains between 184 and 196 atoms, with 12 partially-occupied interstitial sites. This makes the number of configurations of interstitial atoms too greatmore » to calculate them all. By introducing assumptions based on symmetry and preliminary calculations, the number of configurations to calculate can be greatly reduced. It was eventually found that β-t boron has the lowest total energy, with 192 atoms (8 interstitial atoms) in an orthorhombic lattice. The total energy per atom was between those of α- and β-rhombohedral boron. Another tetragonal structure with 192 atoms was found to have a very close energy. The valence bands were fully filled and the gaps were about 1.16 to 1.54 eV, making it comparable to that of β-rhombohedral boron. - Graphical abstract: Electronic density distribution for the lowest-energy configuration (N=192) viewed from the 〈1 0 0〉 direction. Left: isosurface (yellow) at d=0.09 electrons/a.u.{sup 3} Right: isosurface (orange) at d=0.12 electrons/a.u.{sup 3}. - Highlights: • β-tetragonal boron was thoroughly investigated using first-principles calculations. • The lowest energy structure contains 192 atoms in an orthorhombic lattice. • Another tetragonal structure with 192 atoms has a very close energy. • The total energy per atom is between those of α- and β-rhombohedral boron. • The band gap of the lowest energy structure is about 1.16 to 1.54 eV.« less

Non-singular Brans-Dicke collapse in deformed phase space

NASA Astrophysics Data System (ADS)

Rasouli, S. M. M.; Ziaie, A. H.; Jalalzadeh, S.; Moniz, P. V.

2016-12-01

We study the collapse process of a homogeneous perfect fluid (in FLRW background) with a barotropic equation of state in Brans-Dicke (BD) theory in the presence of phase space deformation effects. Such a deformation is introduced as a particular type of non-commutativity between phase space coordinates. For the commutative case, it has been shown in the literature (Scheel, 1995), that the dust collapse in BD theory leads to the formation of a spacetime singularity which is covered by an event horizon. In comparison to general relativity (GR), the authors concluded that the final state of black holes in BD theory is identical to the GR case but differs from GR during the dynamical evolution of the collapse process. However, the presence of non-commutative effects influences the dynamics of the collapse scenario and consequently a non-singular evolution is developed in the sense that a bounce emerges at a minimum radius, after which an expanding phase begins. Such a behavior is observed for positive values of the BD coupling parameter. For large positive values of the BD coupling parameter, when non-commutative effects are present, the dynamics of collapse process differs from the GR case. Finally, we show that for negative values of the BD coupling parameter, the singularity is replaced by an oscillatory bounce occurring at a finite time, with the frequency of oscillation and amplitude being damped at late times.

Insights on the High-Temperature Operational Limits of ZrO2-Y2O3 TBCs Manufactured via Air Plasma Spray

NASA Astrophysics Data System (ADS)

Lima, Rogerio S.; Marple, Basil R.

2017-03-01

The effective high-temperature operation limit of a ZrO2-7-8 wt.%Y2O3 (YSZ) thermal barrier coating (TBC) manufactured via air plasma spray (APS) is considered to be 1300 °C. This is related to the metastable tetragonal t'-phase formed during the rapid quenching of the YSZ particles during spraying. The t'-phase transforms into the equilibrium tetragonal and cubic phases at temperatures ≥ 1300 °C, which can lead to the formation of the monoclinic phase of YSZ upon cooling to room temperature. This formation of the monoclinic phase is accompanied by a volume expansion that leads to TBC failure due to extensive micro-cracking. To further investigate this limitation, an APS YSZ TBC was sprayed on a CMSX-4 substrate. By using a thermal (laser) gradient cyclic testing, a temperature gradient was generated across the TBC/substrate system. The YSZ T- front and substrate backside T- back temperature levels were 1500 and 1000 °C, respectively. In cycle conditions (5-min or 1-h hot and 2-min cool), no TBC failure has been observed. This behavior was partially attributed to the unexpected absence of the monoclinic phase of the YSZ in the cycled coatings. Although preliminary, these results are promising regarding increasing the effective high-temperature operational limits of APS YSZ TBCs.

Reactive sputter deposition of metal oxide nanolaminates

NASA Astrophysics Data System (ADS)

Rubin Aita, Carolyn

2008-07-01

We discuss the reactive sputter deposition of metal oxide nanolaminates on unheated substrates using four archetypical examples: ZrO2 Al2O3, HfO2 Al2O3, ZrO2 Y2O3, and ZrO2 TiO2. The pseudobinary bulk phase diagrams corresponding to these nanolaminates represent three types of interfaces. I. Complete immiscibility (ZrO2 Al2O3 and HfO2 Al2O3). II. Complete miscibility (ZrO2 Y2O3). III. Limited miscibility without a common end-member lattice (ZrO2 TiO2). We found that, although reactive sputter deposition is a far-from-equilibrium process, thermodynamic considerations strongly influence both phase formation within layers and at interfaces. We show that pseudobinary phase diagrams can be used to predict interfacial cation mixing in the nanolaminates. However, size effects must be considered to predict specific structures. In the absence of pseudoepitaxy, size effects play a significant role in determining the nanocrystalline phases that form within a layer (e.g. tetragonal ZrO2, tetragonal HfO2, and orthorhombic HfO2) and at interfaces (e.g. monoclinic (Zr,Ti)O2). These phases are not bulk standard temperature and pressure phases. Their formation is understood in terms of self-assembly into the lowest energy structure in individual critical nuclei.

Strain Phase Diagram of SrTiO3 Thin Films

NASA Astrophysics Data System (ADS)

He, Feizhou; Shapiro, S. M.

2005-03-01

SrTiO3 thin films were used as a model system to study the effects of strain and epitaxial constraint on structural phase transitions of oxide films. The basic phenomena revealed will apply to a variety of important structural transitions including the ferroelectric transition. Highly strained, epitaxial films of SrTiO3 were grown on different substrates. The structural phase transition temperature Tc increases from 105 K in bulk STO to 167 K for films under tensile strain and 330 K for films with compressive strain. The measured temperature-strain phase diagram is qualitatively consistent with theory [1], however the increase in Tc is much larger than predicted in all cases. The symmetry of the phases involved in the transition is different from the corresponding bulk structures largely because of epitaxial constraint, the clamping effect. Thus the shape of the STO unit cell is tetragonal at all temperatures. The possibility exists of a very unique low temperature phase with orthorhombic symmetry (Cmcm) but tetragonal unit cell shape. More generally, we have characterized at least three different manifestations of the clamping effect, showing it is much more subtle than usually recognized. This work is supported through NSF DMR-0239667, DMR-0132918, by the Research Corp, and at BNL by the US DOE DE-AC02-98CH10886. [1] N. A. Pertsev, A. K. Tagantsev and N. Setter, Phys. Rev. B61, R825 (2000).

Thermodynamic Phenomenology for Perovskite Structure Ferroelectric Solid Solutions with Morphotropic Phase Boundaries

DTIC Science & Technology

2005-12-13

American Advanced Study Institute on Science and Technology of Ferroelectric Materials: Rosario Argentina, September 2002. a. Brief History of...zirconium-rich rhombohedral perovskite and the titani - composition. 8,𔄃) um-rich tetragonal perovskite phases. Within recent years, three factors have...of Physics. [DOI: 10.1063/1.1570517] The well-known elastoelectric coupling effects include When reviewing the history of flexoelectric investiga

[In vitro evaluation of low-temperature aging effects of Y2O3 stabilized tetragonal zirconia polycrystals dental ceramics].

PubMed

Yi, Yuan-fu; Liu, Hong-chen; Wang, Chen; Tian, Jie-mo; Wen, Ning

2008-03-01

To investigate the influence of in vitro low-temperature degradation (LTD) treatment on the structural stability of 5 kinds of Y2O3 stabilized tetragonal zirconia polycrystals (Y-TZP) dental ceramics. TZ-3YS powder was compacted at 200 MPa using cold isostatic pressure and pre-sintered at 1050 degrees C for 2 h forming presintered blocks. Specimens were sectioned into 15 mm x 15 mm x 1.5 mm slices from blocks of TZ-3YS, Vita In-Ceram YZ, Ivoclar, Cercon Smart, and Kavo Y-TZP presintered blocks, 18 slices for each brand, and then densely sintered. Specimens were divided into 6 groups and subjected to an accelerated aging test carried out in an autoclave in steam at 134 degrees C, 0.2 MPa, for 0, 1, 2, 3, 4, and 5 h. X-ray diffraction (XRD) was used to identify crystal phases and relative content of monoclinic phase was calculated. Specimens for three-point bending test were fabricated using TZ-3YS ceramics according to the ISO 6872 standard and bending strength was tested before and after aging. The polished and aging specimens of TZ-3YS and Cercon Smart zirconia ceramics were observed by atomic force microscopy (AFM) to evaluate surface microstructure. Tetragonal-to-monoclinic phase transformation was detected for specimens of TZ-3YS, Vita In-Ceram YZ, Ivoclar, and Kavo zirconia ceramics except for Cercon Smart ceramics after aging, and the relative content of monoclinic phase was increasing with the prolonged aging time. TZ-3YS was the most affected material, Kavo took the second, and Vita and Ivoclar were similar. Aging had no significant negative effects on flexural strength of TZ-3YS with average bending strength being over 1100 MPa. The nucleation and growth of monoclinic phase were detected by AFM in surface of Cercon Smart zirconia in which monoclinic phase was not detected by XRD. The results suggest that LTD of dental Y-TZP is time dependent, but the aging test does not reduce the flexural strength of TZ-3YS. The long-term clinical serviceability of dental Y-TZP needs further observation.

Complete titanium substitution by boron in a tetragonal prism: exploring the complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) by experiment and theory.

PubMed

Fokwa, Boniface P T; Hermus, Martin

2011-04-18

Polycrystalline samples and single crystals of four members of the new complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti(3)Co(5)B(2) structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti(3)Ru(2.9)Ir(2.1)B(2)). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti(2)Ru(2.8)Ir(2.2)B(3)). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir-B and Ru/Ir-Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides.

The New Superconductor tP-SrPd2Bi2: Structural Polymorphism and Superconductivity in Intermetallics.

PubMed

Xie, Weiwei; Seibel, Elizabeth M; Cava, Robert J

2016-04-04

We consider a system where structural polymorphism suggests the possible existence of superconductivity through the implied structural instability. SrPd2Bi2 has two polymorphs, which can be controlled by the synthesis temperature: a tetragonal form (CaBe2Ge2-type) and a monoclinic form (BaAu2Sb2-type). Although the crystallographic difference between the two forms may, at first, seem trivial, we show that tetragonal SrPd2Bi2 is superconducting at 2.0 K, whereas monoclinic SrPd2Bi2 is not. We rationalize this finding and place it in context with other 1-2-2 phases.

Temperature and electric-field induced phase transitions, and full tensor properties of [011] C-poled domain-engineered tetragonal 0 .63 Pb (M g1 /3N b2 /3) -0 .37 PbTi O3 single crystals

NASA Astrophysics Data System (ADS)

Zheng, Limei; Jing, Yujia; Lu, Xiaoyan; Wang, Ruixue; Liu, Gang; Lü, Weiming; Zhang, Rui; Cao, Wenwu

2016-03-01

The phase-transition sequence of 0.67 Pb (M g1 /3N b2 /3)- 0.37 PbTi O3 (PMN-0.37PT) single crystals driven by the electric (E ) field and temperature is comprehensively studied. Based on the strain-E field loop, polarization-E field loop, and the evolution of domain configurations, the E field along the [011] C induced phase transitions have been confirmed to be as follows: tetragonal (T ) → monoclinic (MC)→ single domain orthorhombic (O ) phase. As the E field decreases, the induced O phase cannot be maintained and transformed to the MC phase, then to the coexistence state of MC and T phases. In addition, the complete sets of dielectric, piezoelectric, and elastic constants for the [011] C-poled domain-engineered PMN-0.37PT single crystal were measured at room temperature, which show high longitudinal dielectric, piezoelectric, and electromechanical properties (ɛ33T=10 661 ,d33=1052 pC /N , and k33= 0.766 ). Our results revealed that the MC phase plays an important role in the high electromechanical properties of this domain-engineered single crystal. The temperature dependence of the domain configuration revealed that the volume fraction of the MC phase decreases with temperature accompanied by the reduction of ɛ33T,d31, and k31 due to the substantially smaller intrinsic properties of the T phase.

Binary Colloidal Alloy Test-5: Phase Separation

NASA Technical Reports Server (NTRS)

Lynch, Matthew; Weitz, David A.; Lu, Peter J.

2008-01-01

The Binary Colloidal Alloy Test - 5: Phase Separation (BCAT-5-PhaseSep) experiment will photograph initially randomized colloidal samples onboard the ISS to determine their resulting structure over time. This allows the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-PhaseSep studies collapse (phase separation rates that impact product shelf-life); in microgravity the physics of collapse is not masked by being reduced to a simple top and bottom phase as it is on Earth.

Electrocaloric effect in BaTiO3 at all three ferroelectric transitions: Anisotropy and inverse caloric effects

NASA Astrophysics Data System (ADS)

Marathe, Madhura; Renggli, Damian; Sanlialp, Mehmet; Karabasov, Maksim O.; Shvartsman, Vladimir V.; Lupascu, Doru C.; Grünebohm, Anna; Ederer, Claude

2017-07-01

We study the electrocaloric (EC) effect in bulk BaTiO3 (BTO) using molecular dynamics simulations of a first principles-based effective Hamiltonian, combined with direct measurements of the adiabatic EC temperature change in BTO single crystals. We examine in particular the dependence of the EC effect on the direction of the applied electric field at all three ferroelectric transitions, and we show that the EC response is strongly anisotropic. Most strikingly, an inverse caloric effect, i.e., a temperature increase under field removal, can be observed at both ferroelectric-ferroelectric transitions for certain orientations of the applied field. Using the generalized Clausius-Clapeyron equation, we show that the inverse effect occurs exactly for those cases where the field orientation favors the higher temperature/higher entropy phase. Our simulations show that temperature changes of around 1 K can, in principle, be obtained at the tetragonal-orthorhombic transition close to room temperature, even for small applied fields, provided that the applied field is strong enough to drive the system across the first-order transition line. Our direct EC measurements for BTO single crystals at the cubic-tetragonal and at the tetragonal-orthorhombic transitions are in good qualitative agreement with our theoretical predictions, and in particular confirm the occurrence of an inverse EC effect at the tetragonal-orthorhombic transition for electric fields applied along the [001] pseudocubic direction.

First-Principles Study of the Jahn-Teller Distortion in the Ti1-XVXH2 and Zr1-XNbxH2 Alloys

NASA Astrophysics Data System (ADS)

Quijano, Ramiro; de Coss, Romeo; Singh, David

2008-03-01

The transition metal dihydrides TiH2 and ZrH2 present the fluorite structure (CaF2) at high temperature but undergoes a tetragonal distortion with c/a<1 at low temperature. Electronic band structure calculations have shown that TiH2 and ZrH2 in the cubic phase display a very flat band at the Fermi level. Thus the low temperature tetragonal distortion has been associated to a Jahn-Teller effect. In order to understand the role of band filling in controlling the structural instability of the transition metal dihydrides, we have performed a first-principles total energy study of the Ti1-XVxH2 and Zr1-xNbxH2 alloys. The calculations were performed using FP-LAPW method within the (DFT) and we use the GGA for exchange correlation functional energy. The critical concentration for which the Jahn-Teller effect is suppressed, was determined from the evolution of the tetragonal-cubic energy barrier. We discuss the electronic mechanism of the structural-instability, in terms of the band filling. From the obtained results we conclude that the tetragonal distortion in TiH2 and ZrH2 is not produced only by a Jahn-Teller Effect. This research was supported by Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grant No. 43830-F.

Growth of epitaxial orthorhombic YO{sub 1.5}-substituted HfO{sub 2} thin film

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

Shimizu, Takao; Katayama, Kiliha; Kiguchi, Takanori

YO{sub 1.5}-substituted HfO{sub 2} thin films with various substitution amounts were grown on (100) YSZ substrates by the pulsed laser deposition method directly from the vapor phase. The epitaxial growth of film with different YO{sub 1.5} amounts was confirmed by the X-ray diffraction method. Wide-area reciprocal lattice mapping measurements were performed to clarify the crystal symmetry of films. The formed phases changed from low-symmetry monoclinic baddeleyite to high-symmetry tetragonal/cubic fluorite phases through an orthorhombic phase as the YO{sub 1.5} amount increased from 0 to 0.15. The additional annular bright-field scanning transmission electron microscopy indicates that the orthorhombic phase has polarmore » structure. This means that the direct growth by vapor is of polar orthorhombic HfO{sub 2}-based film. Moreover, high-temperature X-ray diffraction measurements showed that the film with a YO{sub 1.5} amount of 0.07 with orthorhombic structure at room temperature only exhibited a structural phase transition to tetragonal phase above 450 °C. This temperature is much higher than the reported maximum temperature of 200 °C to obtain ferroelectricity as well as the expected temperature for real device application. The growth of epitaxial orthorhombic HfO{sub 2}-based film helps clarify the nature of ferroelectricity in HfO{sub 2}-based films (186 words/200 words)« less

Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature

NASA Astrophysics Data System (ADS)

Jiang, Shengli; Huang, Xiao; He, Zhang; Buyers, Andrew

2018-01-01

To examine the effect of doping/co-doping on high-temperature phase compositions of YSZ, stand-alone YSZ and CeO2 and Nb2O5 co-doped YSZ samples were prepared using mechanical alloy and high-temperature sintering. XRD analysis was performed on these samples from room temperature to 1100 °C. The results show that the structure for the co-doped samples tends to be thermally stable when the test temperature is higher than a critical value. Monoclinic phase was dominant in Nb2O5 co-doped YSZ at temperatures lower than 600 °C, while for the YSZ and CeO2 co-doped YSZ, cubic/tetragonal phase was dominant in the whole test temperature range. The lattice parameters for all the samples increase with increasing test temperature generally. The lattice parameters for the two non-trivalent rare earth oxides co-doped YSZ show that the lattice parameter a for the cubic phase of the Ce4+ co-doped YSZ is consistently greater than that of 7YSZ which is related to the presence of larger radius of Ce4+ in the matrix. The lattice parameters a, b, c for the monoclinic phase of Ce4+ co-doped YSZ are much closer to each other than that of the Nb5+ co-doped YSZ, indicating the former has better tendency to form cubic/tetragonal phase, which is desired for vast engineering applications.

Electric-field-induced strain contributions in morphotropic phase boundary composition of (Bi{sub 1/2}Na{sub 1/2})TiO{sub 3}-BaTiO{sub 3} during poling

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

Khansur, Neamul H.; Daniels, John E.; Hinterstein, Manuel

2015-12-14

The microscopic contributions to the electric-field-induced macroscopic strain in a morphotropic 0.93(Bi{sub 1/2}Na{sub 1/2}TiO{sub 3})−0.07(BaTiO{sub 3}) with a mixed rhombohedral and tetragonal structure have been quantified using full pattern Rietveld refinement of in situ high-energy x-ray diffraction data. The analysis methodology allows a quantification of all strain mechanisms for each phase in a morphotropic composition and is applicable to use in a wide variety of piezoelectric compositions. It is shown that during the poling of this material 24%, 44%, and 32% of the total macroscopic strain is generated from lattice strain, domain switching, and phase transformation strains, respectively. The resultsmore » also suggest that the tetragonal phase contributes the most to extrinsic domain switching strain, whereas the lattice strain primarily stems from the rhombohedral phase. The analysis also suggests that almost 32% of the total strain is lost or is a one-time effect due to the irreversible nature of the electric-field-induced phase transformation in the current composition. This information is relevant to on-going compositional development strategies to harness the electric-field-induced phase transformation strain of (Bi{sub 1/2}Na{sub 1/2})TiO{sub 3}-based lead-free piezoelectric materials for actuator applications.« less

Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature

NASA Astrophysics Data System (ADS)

Jiang, Shengli; Huang, Xiao; He, Zhang; Buyers, Andrew

2018-05-01

To examine the effect of doping/co-doping on high-temperature phase compositions of YSZ, stand-alone YSZ and CeO2 and Nb2O5 co-doped YSZ samples were prepared using mechanical alloy and high-temperature sintering. XRD analysis was performed on these samples from room temperature to 1100 °C. The results show that the structure for the co-doped samples tends to be thermally stable when the test temperature is higher than a critical value. Monoclinic phase was dominant in Nb2O5 co-doped YSZ at temperatures lower than 600 °C, while for the YSZ and CeO2 co-doped YSZ, cubic/tetragonal phase was dominant in the whole test temperature range. The lattice parameters for all the samples increase with increasing test temperature generally. The lattice parameters for the two non-trivalent rare earth oxides co-doped YSZ show that the lattice parameter a for the cubic phase of the Ce4+ co-doped YSZ is consistently greater than that of 7YSZ which is related to the presence of larger radius of Ce4+ in the matrix. The lattice parameters a, b, c for the monoclinic phase of Ce4+ co-doped YSZ are much closer to each other than that of the Nb5+ co-doped YSZ, indicating the former has better tendency to form cubic/tetragonal phase, which is desired for vast engineering applications.

Thermotropic phase transitions in Pb{sub 1−x}Sr{sub x}(Al{sub 1/3}Nb{sub 2/3}){sub 0.1}(Zr{sub 0.52}Ti{sub 0.48}){sub 0.9}O{sub 3} ceramics: Temperature dependent dielectric permittivity and Raman scattering

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

Li, C. Q.; Peng, L.; Jiang, K.

2015-06-15

The phase transitions of Pb{sub 1−x}Sr{sub x}(Al{sub 1/3}Nb{sub 2/3}){sub 0.1}(Zr{sub 0.52}Ti{sub 0.48}){sub 0.9}O{sub 3} (Sr-modified PAN-PZT) ceramics with Sr compositions of x = 2%, 5%, 10% and 15% have been investigated using X-ray diffraction (XRD), temperature dependent dielectric permittivity and Raman scattering. The XRD analysis show that the phase transition occurs between Sr composition of 5% and 10%. Based on the broad dielectric peaks at 100 Hz, the diffused phase transition from tetragonal (T) to cubic (C) structure shifts to lower temperature with increasing Sr composition. The dramatic changes of wavenumber and full width at half-maximum (FWHM) for E(TO{sub 4})′more » softing mode can be observed at morphotropic phase boundary (MPB). Moreover, the MPB characteristic shows a wider and lower trend of temperature region with increasing Sr composition. It could be ascribed to the diminishment of the energy barrier and increment of A-cation entropy. Therefore, the Sr-modified PAN-PZT ceramics unambiguously undergo two successive structural transitions (rhombohedral-tetragonal-cubic phase) with temperature from 80 to 750 K. Correspondingly, the phase diagram of Sr-modified PAN-PZT ceramics can be well depicted.« less

Structural and electronic properties of LaPd2As2 superconductor: First-principle calculations

NASA Astrophysics Data System (ADS)

Singh, Birender; Kumar, Pradeep

2017-05-01

In present work we have studied electronic and structural properties of superconducting LaPd2As2 compound having collapsed tetragonal structure using first-principle calculations. The band structure calculations show that the LaPd2As2 is metallic consistent with the reported experimental observation, and the density of states plots clearly shows that at the Fermi level major contribution to density of states arises from Pd 4d and As 4p states, unlike the Fe-based superconductors where major contribution at the Fermi level comes from Fe 3d states. The estimated value of electron-phonon coupling is found to be 0.37, which gives the upper bound of superconducting transition temperature of 5K, suggesting the conventional nature of this superconductor.

Effect of annealing time, weight pressure and cobalt doping on the electrical and magnetic behavior of barium titanate

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

Samuvel, K., E-mail: kssamuvel@gmail.com; Ramachandran, K., E-mail: ramach76@yahoo.com

2016-05-06

BaTi{sub 0.5}CO{sub 0.5}O{sub 3} (BTCO) nanoparticles were prepared by the solid state reaction technique using different starting materials and the microstructure examined by XRD, FESEM, BDS and VSM. X-ray diffraction and electron diffraction patterns showed that the nanoparticles were the tetragonal BTCO phase. The BTCO nanoparticles prepared from the starting materials of as prepared titanium-oxide, Cobalt -oxide and barium carbonate have spherical grain morphology, an average size of 65 nm and a fairly narrow size distribution. The nano-scale presence and the formation of the tetragonal perovskite phase as well as the crystallinity were detected using the mentioned techniques. Dielectric properties ofmore » the samples were measured at different frequencies. Broadband dielectric spectroscopy is applied to investigate the electrical properties of disordered perovskite-like ceramics in a wide temperature range. The doped BTCO samples exhibited low loss factor at 1 kHz and 1 MHz frequencies respectively.« less

Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La 1.875Ba 0.125CuO 4

DOE PAGES

S. -H. Baek; Gu, G. D.; Utz, Y.; ...

2015-10-26

We report 139La nuclear magnetic resonance studies performed on a La 1.875Ba 0.125CuO 4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T –1 1 sharply upturns at the charge-ordering temperature T CO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T –1 1 below the spin-ordering temperature T SO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state formore » H ∥ [001], which are completely suppressed for large fields along the CuO 2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less

Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La 1.875Ba 0.125CuO 4

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

S. -H. Baek; Gu, G. D.; Utz, Y.

We report 139La nuclear magnetic resonance studies performed on a La 1.875Ba 0.125CuO 4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T –1 1 sharply upturns at the charge-ordering temperature T CO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T –1 1 below the spin-ordering temperature T SO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state formore » H ∥ [001], which are completely suppressed for large fields along the CuO 2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less

Crystallization of Chicken Egg White Lysozyme from Sulfate Salts

NASA Technical Reports Server (NTRS)

Forsythe, Elizabeth; Pusey, Marc

1998-01-01

It has been "known" that chicken egg white lysozyme does not crystallize from sulfate, particularly ammonium sulfate, salts, but instead gives amorphous precipitates. This has been the basis of several studies using lysozyme comparing macromolecule crystal nucleation and amorphous precipitation. Recently Ries-Kautt et al (Acta Cryst D50, (1994) 366) have shown that purified isoionic CEWL could be crystallized from low concentrations of sulfate at basic pH, and we subsequently showed that in fact CEWL could be purified in both the tetragonal and orthorhombic forms using ammonium sulfate over the pH range 4.0 to 7.8 (Acta Cryst D53, (1997) 795). We have now extended these observations to include a range of common sulfate salts, specifically sodium, potassium, rubidium, magnesium, and manganese sulfates. In all cases but the manganese sulfates both the familiar tetragonal and orthorhombic forms were obtained, with unit cell dimensions close to those known for the "classic" sodium chloride crystallized forms. Manganese sulfate has only yielded orthorhombic crystals to date. All crystallizations were carried out using low (typically less than or equal to 6 M) salt and high (greater than approximately 90 mg/ml) protein concentrations. As with ammonium sulfate, the tetragonal - orthorhombic phase shift appears to be a function of both the temperature and the protein concentration, with higher temperatures and concentrations favoring the orthorhombic and lower the tetragonal form. The phase change range is somewhat reduced for the sulfate salts, depending upon conditions being typically between approximately 15 - 20 C. Both the magnesium and manganese sulfates gave crystals at salt concentrations over 0.6 M as well, with magnesium sulfate giving a very slowly nucleating and growing hexagonal form. A triclinic crystal form, characterized by aggressively small crystals (typically 0.1 mm in size) has been occasionally obtained from ammonium sulfate. Finally, preliminary spot solubility determinations have suggested that in some cases the solubility increases with increasing salt concentrations.

Chemical vapor deposition of yttria-stabilized zirconia as a thermal barrier coating for gas turbine engines

NASA Astrophysics Data System (ADS)

Varanasi, Venu Gopal

The gas turbine engine uses an yttria-stabilized zirconia (YSZ) coating to provide thermal insulation for its turbine blades. This YSZ coating must be tetragonal in crystal structure, columnar in microstructure, and be 100--250 mum thick to provide for adequate protection for the turbine blades in the severe engine environment. Currently, YSZ coatings are fabricated by electron-beam physical vapor deposition (EB-PVD), but this fabrication method is cost intensive. Chemical vapor deposition (CVD) is a more commercially viable processing method and a possible alternative to EB-PVD. The deposition of tetragonal YSZ from gaseous metal and oxidation sources were studied. A chemical equilibrium analysis modeled the feasibility of depositing tetragonal YSZ for both chloride CVD (Zr-Y-C-O-Cl-H-Inert system) and metal-organic CVD (MOCVD) (Zr-Y-C-O-H system). Pure thermochemical properties and the assessed YSZ phase diagram were used in this analysis. Using the molar input of metals ((nY + nZr) and ( nY/(nY + nZr ) = 0.08)) as bases, equilibrium calculations showed that tetragonal YSZ formation was feasible. Tetragonal YSZ formation was feasible with high oxygen content (nO/(nY + nZr) > 8) and high temperature (T > 100°C) in the case of chloride CVD (Zr-Y-C-O-Cl-H-Inert). Tetragonal YSZ formation was feasible with high oxygen content (nO/( nY + nZr) > 5) and high temperature (T > 950°C) in the case of MOCVD (Zr-Y-C-O-H). Although solid carbon formation did not appear in chloride CVD, additional oxygen (nO/( nY + nZr) > 32) and low hydrogen content relative to carbon (nH/nC < 2) were required to avoid solid carbon formation in MOCVD. Coatings were deposited using a set of base conditions derived from the chemical equilibrium analysis. In chloride CVD, YCl3 was not included because of its low vapor pressure, thus, ZrCl4 was oxidized with the H2-CO2 gas mixture. Monoclinic ZrO2 coatings were deposited at the thermochemically optimized conditions (n O/(nY + nZr) > 8, T > 1004°C) with approximately 5.5 mum h-1 growth rate. In metal-organic CVD (MOCVD), liquid precursor solutions of Y- and Zr-beta-diketonate and Y- and Zr-n-butoxide precursors were used as the metal sources and O2 gas was used as the oxidation source. Using the Y- and Zr-beta-diketonate liquid precursor solution, tetragonal YSZ was deposited with a layered microstructure apparent and a maximum growth rate of approximately 14 mum h-1 (activation energy (E a) of 50.9 +/- 4.3 kJ mol-1). The growth rate (approximately 43 mum h-1 with Ea = 53.8 +/- 7.9 kJ mol-1) was improved using Y- and Zr- n-butoxide liquid precursor solutions, and the microstructure was columnar. Yet, two-phase deposition of monoclinic ZrO2 and tetragonal YSZ occurred. Results of electron-probe micro-analysis showed that the nY/(nY + nZr ) ratio was less than 45% of the nY/( nY + nZr) ratio in the liquid precursor solution.

Non-singular Brans–Dicke collapse in deformed phase space

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

Rasouli, S.M.M., E-mail: mrasouli@ubi.pt; Centro de Matemática e Aplicações; Physics Group, Qazvin Branch, Islamic Azad University, Qazvin

2016-12-15

We study the collapse process of a homogeneous perfect fluid (in FLRW background) with a barotropic equation of state in Brans–Dicke (BD) theory in the presence of phase space deformation effects. Such a deformation is introduced as a particular type of non-commutativity between phase space coordinates. For the commutative case, it has been shown in the literature (Scheel, 1995), that the dust collapse in BD theory leads to the formation of a spacetime singularity which is covered by an event horizon. In comparison to general relativity (GR), the authors concluded that the final state of black holes in BD theorymore » is identical to the GR case but differs from GR during the dynamical evolution of the collapse process. However, the presence of non-commutative effects influences the dynamics of the collapse scenario and consequently a non-singular evolution is developed in the sense that a bounce emerges at a minimum radius, after which an expanding phase begins. Such a behavior is observed for positive values of the BD coupling parameter. For large positive values of the BD coupling parameter, when non-commutative effects are present, the dynamics of collapse process differs from the GR case. Finally, we show that for negative values of the BD coupling parameter, the singularity is replaced by an oscillatory bounce occurring at a finite time, with the frequency of oscillation and amplitude being damped at late times.« less

Spin-orbital model of stoichiometric LaMnO3 with tetragonal distortions

NASA Astrophysics Data System (ADS)

Snamina, Mateusz; Oleś, Andrzej M.

2018-03-01

The spin-orbital superexchange model is derived for the cubic (perovskite) symmetry of LaMnO3, whereas real crystal structure is strongly deformed. We identify and explain three a priori important physical effects arising from tetragonal deformation: (i) the splitting of eg orbitals ∝Ez , (ii) the directional renormalization of d -p hybridization tp d, and (iii) the directional renormalization of charge excitation energies. Using the example of LaMnO3 crystal we evaluate their magnitude. It is found that the major effects of deformation are an enhanced amplitude of x2-y2 orbitals induced in the orbital order by Ez≃300 meV and anisotropic tp d≃2.0 (2.35) eV along the a b (c ) cubic axis, in very good agreement with Harrison's law. We show that the improved tetragonal model analyzed within mean field approximation provides a surprisingly consistent picture of the ground state. Excellent agreement with the experimental data is obtained simultaneously for: (i) eg orbital mixing angle, (ii) spin exchange constants, and (iii) the temperatures of spin and orbital phase transition.

Tetragonal (K, Na)NbO3 based lead-free single crystal: Growth, full tensor properties, and their orientation dependence

NASA Astrophysics Data System (ADS)

Zheng, Limei; Wang, Junjun; Liu, Xuedong; Yang, Liya; Lu, Xiaoyan; Li, Yanran; Huo, Da; Lü, Weiming; Yang, Bin; Cao, Wenwu

2017-10-01

A Li and Ta modified (K, Na)NbO3 lead-free single crystal with a large size (13 × 10 × 20 mm3) has been grown by using the top-seeded solution growth method. The large size allows us to carry out an extensive study on this tetragonal crystal. We have measured a complete set of elastic, dielectric, and piezoelectric constants for the [001]C poled crystal with the single domain state. The crystal exhibits high shear piezoelectricity with d15 = 518 pC/N and k15 = 0.733, showing excellent potential in shear electro-sonic energy transformation devices. It is found that the high shear piezoelectricity originates from the vicinity of orthorhombic-tetragonal phase transition, which favors polarization rotation greatly. The orientation dependence of longitudinal dielectric, piezoelectric, and elastic constants and electromechanical coupling factor in the 3-dimentional space were calculated based on the single domain dataset. We believe that this work is of great importance for both fundamental studies and device designs for lead-free materials.

Growth and study of first order metal insulator transition in VO2 films

NASA Astrophysics Data System (ADS)

Rathore, Ajay K.; Kumar, Satish; Kumar, Dhirendra; Sathe, V. G.

2015-06-01

VO2 films have been grown on Si substrate using pulse laser deposition technique. The as-deposited film prepared by V2O3 target is found to possess signatures of V2O5 phase. Up on annealing at 780°C the film transforms to VO2 phase. The annealed film is found to be highly oriented along (011) and single phase in nature. The high temperature Raman spectroscopic measurements on the annealed film showed first order transition from monoclinic insulating phase to conductive tetragonal rutile phase around 65°C.

Phase analysis of plasma-sprayed zirconia-yttria coatings

NASA Technical Reports Server (NTRS)

Shankar, N. R.; Berndt, C. C.; Herman, H.

1983-01-01

Phase analysis of plasma-sprayed 8 wt pct-yttria-stabilized zirconia (YSZ) thermal barrier coatings and powders was carried out by X-ray diffraction. Step scanning was used for increased peak resolution. Plasma spraying of the YSZ powder into water or onto a steel substrate to form a coating reduced the cubic and monoclinic phases with a simultaneous increase in the tetragonal phase. Heat treatment of the coating at 1150 C for 10 h in an Ar atmosphere increased the amount of cubic and monoclinic phases. The implications of these transformations on coating performance and integrity are discussed.

Metallic behavior of lanthanum disilicide

NASA Technical Reports Server (NTRS)

Long, Robert G.; Bost, M. C.; Mahan, John E.

1988-01-01

Polycrystalline thin films of LaSi2 were prepared by reaction of sputter-deposited lanthanum layers with silicon wafers. Samples of the low-temperature tetragonal and the high-temperature orthorhombic phases were separately obtained. The room-temperature intrinsic resistivities were 24 and 57 microohm cm for the low- and high-temperature structures, respectively. Although lanthanum disilicide had been previously reported to be a semiconductor, classical metallic behavior was found for both phases.

Powder-metallurgy superalloy strengthened by a secondary gamma phase.

NASA Technical Reports Server (NTRS)

Kotval, P. S.

1971-01-01

Description of experiments in which prealloyed powders of superalloy compositions were consolidated by extrusion after the strengthening by precipitation of a body-centered tetragonal gamma secondary Ni3 Ta phase. Thin foil electron microscopy showed that the mechanical properties of the resultant powder-metallurgy product were correlated with its microstructure. The product exhibited high strength at 1200 F without loss of ductility, after thermomechanical treatment and aging.

Relaxor ferroelectricity and electric-field-driven structural transformation in the giant lead-free piezoelectric (Ba ,Ca ) (Ti ,Zr ) O3

NASA Astrophysics Data System (ADS)

Brajesh, Kumar; Tanwar, Khagesh; Abebe, Mulualem; Ranjan, Rajeev

2015-12-01

There is great interest in lead-free (B a0.85C a0.15 ) (T i0.90Z r0.10 ) O3 (15/10BCTZ) because of its exceptionally large piezoelectric response [Liu and Ren, Phys. Rev. Lett. 103, 257602 (2009), 10.1103/PhysRevLett.103.257602]. In this paper, we have analyzed the nature of: (i) crystallographic phase coexistence at room temperature, (ii) temperature- and field-induced phase transformation to throw light on the atomistic mechanisms associated with the large piezoelectric response of this system. A detailed temperature-dependent dielectric and lattice thermal expansion study proved that the system exhibits a weak dielectric relaxation, characteristic of a relaxor ferroelectric material on the verge of exhibiting a normal ferroelectric-paraelectric transformation. Careful structural analysis revealed that a ferroelectric state at room temperature is composed of three phase coexistences, tetragonal (P 4 m m )+ orthorhombic(Amm 2 )+rhombohedral(R 3 m ) . We also demonstrate that the giant piezoresponse is associated with a significant fraction of the tetragonal phase transforming to rhombohedral. It is argued that the polar nanoregions associated with relaxor ferroelectricity amplify the piezoresponse by providing an additional degree of intrinsic structural inhomogeneity to the system.

A two-phase flow model for submarine granular flows: With an application to collapse of deeply-submerged granular columns

NASA Astrophysics Data System (ADS)

Lee, Cheng-Hsien; Huang, Zhenhua

2018-05-01

The collapse process of a submerged granular column is strongly affected by its initial packing. Previous models for particle response time, which is used to quantify the drag force between the solid and liquid phases in rheology-based two-phase flow models, have difficulty in simulating the collapse process of granular columns with different initial concentrations (initial packing conditions). This study introduces a new model for particle response time, which enables us to satisfactorily model the drag force between the two phases for a wide range of volume concentration. The present model can give satisfactory results for both loose and dense packing conditions. The numerical results have shown that (i) the initial packing affects the occurrence of contractancy/diltancy behavior during the collapse process, (ii) the general buoyancy and drag force are strongly affected by the initial packing through contractancy and diltancy, and (iii) the general buoyancy and drag force can destabilize the granular material in loose packing condition but stabilize the granular material in dense packing condition. The results have shown that the collapse process of a densely-packed granular column is more sensitive to particle response time than that of a loosely-packed granular column.

Structure of dental gallium alloys.

PubMed

Herø, H; Simensen, C J; Jørgensen, R B

1996-07-01

The interest in gallium alloys as a replacement for amalgam has increased in recent years due to the risk of environmental pollution from amalgam. Alloy powders with compositions close to those for alloys of amalgam are mixed with a liquid gallium alloy. The mix is condensed into a prepared cavity in much the same way as for amalgam. The aim of the present work was to study the structure of: (1) two commercial alloy powders containing mainly silver, tin and copper, and (2) the phases formed by mixing these powders with a liquid alloy of gallium, indium and tin. One of the alloy powders contained 9 wt% palladium. Cross-sections of cylindrical specimens made by these gallium mixes were investigated by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Discrete grains of the following phases were found to be present in both gallium alloys: hexagonal Ag2Ga, tetragonal Cu(Pd)Ga2, cubic Ag9In4 and tetragonal beta-Sn. Indications of hexagonal or orthorhombic Ag2Sn were found in the remaining, unreacted alloy particles. In the palladium-containing alloy the X-ray reflections indicate a minor fraction of cubic Cu9Ga4 in addition to the Cu(Pd)Ga2 phase. Particles of beta-Sn are probably precipitated because Sn-Ga phases cannot be formed according to the binary phase diagram.

First-principles study of Co- and Cu-doped Ni2MnGa along the tetragonal deformation path

NASA Astrophysics Data System (ADS)

Zelený, M.; Sozinov, A.; Straka, L.; Björkman, T.; Nieminen, R. M.

2014-05-01

The influence of Co and Cu doping on Ni-Mn-Ga Heusler alloy is investigated using the first-principles exact muffin-tin orbital method in combination with the coherent-potential approximation. Single-element doping and simultaneous doping by both elements are investigated in Ni50-xCoxMn25-yGa25-zCuy+z alloys, with dopant concentrations x ,y, and z up to 7.5 at. %. Doping with Co in the Ni sublattice decreases the (c/a)NM ratio of the nonmodulated (NM) martensite, but it simultaneously increases the cubic phase stability with respect to the NM phase. Doping with Cu in the Mn or in Ga sublattices does not change the (c/a)NM ratio significantly and it decreases the cubic phase stability. For simultaneous doping by Co in the Ni sublattice and Cu in the Mn or Ga sublattices, the effects of the individual dopants are independent and about the same as for the single-element doping. Thus, the (c/a)NM ratio can be adjusted by Co doping while the phase stability can be balanced by Cu doping, resulting in stable martensite with a reduced (c/a)NM. The local stability of the cubic phase with respect to the tetragonal deformation can be understood on the basis of a density-of-states analysis.

Anisotropic phonon coupling in the relaxor ferroelectric (Na1/2Bi1/2)TiO3 near its high-temperature phase transition

NASA Astrophysics Data System (ADS)

Cai, Ling; Toulouse, Jean; Luo, Haosu; Tian, Wei

2014-08-01

The lead free relaxor Na1/2Bi1/2TiO3 (NBT) undergoes a structural cubic-to-tetragonal transition near 800 K which is caused by the cooperative rotations of O6 octahedra. These rotations are also accompanied by the displacements of the cations and the formation of the polar nanodomains (PNDs) that are responsible for the characteristic dielectric dispersion of relaxor ferroelectrics. Because of their intrinsic properties, spontaneous polarization, and lack of inversion symmetry, these PNDs are also piezoelectric and can mediate an interaction between polarization and strain or couple the optic and acoustic phonons. Because PNDs introduce a local tetragonal symmetry, the phonon coupling they mediate is found to be anisotropic. In this paper we present inelastic neutron scattering results on coupled transverse acoustic (TA) and transverse optic (TO) phonons in the [110] and [001] directions and across the cubic-tetragonal phase transition at TC˜800 K. The phonon spectra are analyzed using a mode coupling model. In the [110] direction, as in other relaxors and some ferroelectric perovskites, a precipitous drop of the TO phonon into the TA branch or "waterfall" is observed at a certain qwf˜0.14 r.l.u. In the [001] direction, the highly overdamped line shape can be fitted with closely positioned bare mode energies which are largely overlapping along the dispersion curves. Two competing lattice coupling mechanism are proposed to explain these observations.

Symmetry of Epitaxial BiFeO3 Films in the Ultrathin Regime

NASA Astrophysics Data System (ADS)

Yang, Yongsoo; Schlep&üTz, Christian; Adamo, Carolina; Schlom, Darrell; Clarke, Roy

2013-03-01

BiFeO3 (BFO) films grown on SrTiO3 (STO) with a SrRuO3 buffer layer exhibit a monoclinic structure at thicknesses greater than 40 nm, but higher structural symmetry can be observed for thinner films [Phys. Rev. B 81, 144115 (2010)]. We report a structural phase transition from monoclinic to tetragonal in ultra-thin BFO films grown directly on (100)-oriented STO. X-ray diffraction measurements of 3-dimensional reciprocal space maps reveal half-integer order peaks due to oxygen octahedral tilting. When the film thickness is decreased below 20 unit cells, the integer-order Bragg peak splitting associated with the presence of multiple domains of the monoclinic phase disappears. Instead, a single peak that is commensurate with the STO substrate lattice appears. The diffraction pattern has four-fold symmetry, ruling out the presence of a single monoclinic domain in favor of a tetragonal film structure. The evolution of the oxygen octahedra tilt pattern inferred from the intensities of half-order peaks suggests that this transition originates from the corner-connectivity of oxygen atoms at the interface between BFO and STO, and also strongly supports this monoclinic to tetragonal transition. Supported in part by the U.S. Department of Energy (DE-FG02-06ER46273). Measurements performed at Sectors 13-BMC, 33-IDD, 33-BMC of the Advanced Photon Source, Argonne National Laboratory, USA (DOE contract No. DE-AC02-06CH11357).

The structure and optical properties of Sr{sub 1−x}Ca{sub x}MoO{sub 3}

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

Hopper, H.A.; Macphee, D.E.; Mclaughlin, A.C., E-mail: a.c.mclaughlin@abdn.ac.uk

2016-10-15

The solid solution Sr{sub 1−x}Ca{sub x}MoO{sub 3} (x=0.00, 0.05, 0.10, 0.13, 0.15 and 0.17) has successfully been synthesised and X-ray Powder diffraction has revealed the occurrence of structural phase transitions, from cubic Pm−3m to tetragonal I4/mcm, and then to orthorhombic Imma as the value of x increased. Discontinuities were observed in the cell parameters and bond lengths and angles at the transition from tetragonal to orthorhombic symmetry as a result of the switching of the octahedral rotation axis at the tetragonal to orthorhombic transition. The increased octahedral tilting could also be linked to the decrease in the band gap frommore » 2.20 eV to 2.10 eV as x increased from 0 to 0.17. - Graphical abstract: Table of Contents Figure Caption: Ultraviolet-visible absorbance spectra for Sr{sub 1−x}Ca{sub x}MoO{sub 3} showing a reduction in band gap upon increasing x as a result of increased octahedral tilting. - Highlights: • The solid solution Sr{sub 1−x}Ca{sub x}MoO{sub 3} has been synthesised. • Structural phase transitions are observed. • Discontinuities were observed in the cell parameters and bond lengths and angles. • Upon increasing x from 0 to 0.17 the band gap reduces from 2.20 eV to 2.10 eV.« less

NASA Astrophysics Data System (ADS)

Knight, Kevin S.; Marshall, William G.; Hawkins, Philip M.

2014-06-01

The fluoroperovskite phase RbCaF3 has been investigated using high-pressure neutron powder diffraction in the pressure range ~0-7.9 GPa at room temperature. It has been found to undergo a first-order high-pressure structural phase transition at ~2.8 GPa from the cubic aristotype phase to a hettotype phase in the tetragonal space group I4/ mcm. This transition, which also occurs at ~200 K at ambient pressure, is characterised by a linear phase boundary and a Clapeyron slope of 2.96 × 10-5 GPa K-1, which is in excellent agreement with earlier, low-pressure EPR investigations. The bulk modulus of the high-pressure phase (49.1 GPa) is very close to that determined for the low-pressure phase (50.0 GPa), and both are comparable with those determined for the aristotype phases of CsCdF3, TlCdF3, RbCdF3, and KCaF3. The evolution of the order parameter with pressure is consistent with recent modifications to Landau theory and, in conjunction with polynomial approximations to the pressure dependence of the lattice parameters, permits the pressure variation of the bond lengths and angles to be predicted. On entering the high-pressure phase, the Rb-F bond lengths decrease from their extrapolated values based on a third-order Birch-Murnaghan fit to the aristotype equation of state. By contrast, the Ca-F bond lengths behave atypically by exhibiting an increase from their extrapolated magnitudes, resulting in the volume and the effective bulk modulus of the CaF6 octahedron being larger than the cubic phase. The bulk moduli for the two component polyhedra in the tetragonal phase are comparable with those determined for the constituent binary fluorides, RbF and CaF2.

Raman Spectrum of Er-Y-codoped ZrO2 and Fluorescence Properties of Er3+

NASA Astrophysics Data System (ADS)

He, Jun; Luo, Meng-fei; Jin, Ling-yun; He, Mai; Fang, Ping; Xie, Yun-long

2007-02-01

Er-Y-codoped ZrO2 mixed oxides with monoclinic, tetragonal and cubic structures were prepared by a sol-gel method. The crystal structure of ZrO2 matrix and the effect of the ZrO2 phases on the fluorescence properties of Er3+ were studied using Raman spectroscopy. The results indicated that the fluorescence properties of Er3+ depend on its local ZrO2 crystal structures. As ZrO2 matrix transferred from monoclinic to tetragonal and cubic phase, the Raman and fluorescence bands of Er3+ decreased in intensities and tended to form a single peak. With 632.8 nm excitation, the bands between 640 and 680 nm were attributed to the fluorescence of Er3+ in the ZrO2 environment. However, only the fluorescence was observed and no Raman spectra were seen under 514.5 nm excitation, while only Raman spectra were observed under 325 nm excitation. UV Raman spectroscopy was found to be more sensitive in the surface region while the information provided by XRD mainly came from the bulk. The phase with lower symmetry forms more easily on the surface than in the bulk.

Peculiar magnetism of UAu2Si2

NASA Astrophysics Data System (ADS)

Tabata, Chihiro; Miura, Naoyuki; Uhlířová, Klára; Vališka, Michal; Saito, Hiraku; Hidaka, Hiroyuki; Yanagisawa, Tatsuya; Sechovský, Vladimír; Amitsuka, Hiroshi

2016-12-01

Single-crystalline UAu2Si2 has been grown by a floating-zone melting method, and its magnetic, thermal, and transport properties have been investigated through measurements of magnetization, specific heat, and electrical resistivity to reveal its peculiar magnetism. It is shown that UAu2Si2 undergoes a second-order phase transition at Tm = 19 K, which had been believed to be ferromagnetic ordering in the literature, from a paramagnetic phase to an uncompensated antiferromagnetic phase with spontaneous magnetization along the tetragonal c axis (the easy magnetization direction). The magnetic entropy analysis points to the itinerant character of 5 f electrons in the magnetic ordered state of UAu2Si2 with large enhancement of the electronic specific heat coefficient of γ ˜150 mJ/K2mol at 2 K. It also reveals the relatively isotropic crystalline electric field effect of this compound, with contrast to the other relative isostructural compounds. The observed magnetization curves strongly suggest that there is a parasitic ferromagnetic component developing below ˜50 K in high coercivity with the easy axis along the tetragonal c axis. The results are discussed in the context of evolution of magnetism within the entire family of isostructural U T2Si2 compounds.

Structural and low temperature transport properties of Fe2B and FeB systems at high pressure

NASA Astrophysics Data System (ADS)

Kumar, P. Anand; Satya, A. T.; Reddy, P. V. Sreenivasa; Sekar, M.; Kanchana, V.; Vaitheeswaran, G.; Mani, Awadhesh; Kalavathi, S.; Shekar, N. V. Chandra

2017-10-01

The evolution of crystal structure and the ground state properties of Fe2B and FeB have been studied by performing high pressure X-ray diffraction up to a pressure of ∼24 GPa and temperature dependent (4.2-300 K range) high-pressure resistivity measurements up to ∼ 2 GPa. While a pressure induced reversible structural phase transition from tetragonal to orthorhombic structure is observed at ∼6.3 GPa in Fe2B, FeB has been found to be stable in its orthorhombic phase up to the pressure of 24 GPa. In the case of Fe2B, both parent and daughter phases coexist beyond the transition pressure. The bulk modulus of FeB and Fe2B (tetragonal) have been found to be 248 GPa and 235 GPa respectively. First principle electronic structure calculations have been performed using the present experimental inputs and the calculated ground state properties agree quite well with the major findings of the experiments. Debye temperature extracted from the analysis of low temperature resistivity data is observed to decrease with pressure indicating softening of phonons in both the systems.

Synthesis and Phase Stability of Scandia, Gadolinia, and Ytterbia Co-doped Zirconia for Thermal Barrier Coating Application

NASA Astrophysics Data System (ADS)

Li, Qi-Lian; Cui, Xiang-Zhong; Li, Shu-Qing; Yang, Wei-Hua; Wang, Chun; Cao, Qian

2015-01-01

Scandia, gadolinia, and ytterbia co-doped zirconia (SGYZ) ceramic powder was synthesized by chemical co-precipitation and calcination processes for application in thermal barrier coatings to promote the durability of gas turbines. The ceramic powder was agglomerated and sintered at 1150 °C for 2 h, and the powder exhibited good flowability and apparent density to be suitable for plasma spraying process. The microstructure, morphology and phase stability of the powder and plasma-sprayed SGYZ coatings were analyzed by means of scanning electron microscope and x-ray diffraction. Thermal conductivity of plasma-sprayed SGYZ coatings was measured. The results indicated that the SGYZ ceramic powder and the coating exhibit excellent stability to retain single non-transformable tetragonal zirconia even after high temperature (1400 °C) exposure for 500 h and do not undergo a tetragonal-to-monoclinic phase transition upon cooling. Furthermore, the plasma-sprayed SGYZ coating also exhibits lower thermal conductivity than yttria stabilized zirconia coating currently used in gas turbine engine industry. SGYZ can be explored as a candidate material of ultra-high temperature thermal barrier coating for advanced gas turbine engines.

Photo-induced Low Temperature Structural Transition in the "114" YbaFe 4O 7 oxide

DOE PAGES

Duffort, V.; Caignaert, Vincent; Pralong, V.; ...

2013-11-11

Synchrotron irradiation of the oxide YBaFe 4O 7.0 below 190 K converts the low temperature monoclinic structure to a higher symmetry tetragonal form analogous to the room temperature structure. This photo-induced metastable tetragonal form is stable even in the absence of irradiation over the range 4-60 K, however, above 60 K the photo-transition is reversible. These structural phenomena are correlated to the magnetic behaviour of this system, suggesting possible spin-lattice coupling. Lastly, a scenario explaining the low temperature photo-induced transition is proposed, based on the different distributions of the valence electrons in the iron sub-lattice of the monoclinic and tetragonalmore » phases.« less

Nematic fluctuations and phase transitions in LaFeAsO: A Raman scattering study

DOE PAGES

Kaneko, U. F.; Gomes, P. F.; Garcia-Flores, A. F.; ...

2017-07-10

Raman scattering experiments on LaFeAsO with distinct antiferromagnetic ( T AFM=140 K) and tetragonal-orthorhombic ( T S=155 K) transitions show a quasielastic peak (QEP) in B 2g symmetry (2 Fe tetragonal cell) that fades away below ~ T AFM and is ascribed to electronic nematic fluctuations. A scaling of the reported shear modulus with the T dependence of the QEP height rather than the QEP area indicates that magnetic degrees of freedom drive the structural transition. As a result, the large separation between T S and T AFM in LaFeAsO compared to BaFe 2As 2 manifests itself in slower dynamicsmore » of nematic fluctuations in the former.« less

Raman spectra and phase transitions in Rb{sub 2}KInF{sub 6} elpasolite

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

Krylov, A. S.; Krylova, S. N., E-mail: slanky@iph.krasn.ru; Vtyurin, A. N.

2011-01-15

The Raman spectra of Rb{sub 2}KInF{sub 6} elpasolite crystal have been studied in a wide temperature range, including two phase transitions: from the cubic phase to the tetragonal phase and then to the monoclinic phase. Several anomalies of internal modes of InF{sub 6} octahedra and low-frequency lattice vibrations, which are related to the structural changes at the transition points, have been found and quantitatively analyzed. The results of a quantitative analysis of the temperature dependences of the parameters of spectral lines are in good agreement with the thermodynamic data on the phase transitions.

Physical properties of V 1-xTi xO₂ (0 < x < 0.187) single crystals

DOE PAGES

Kong, Tai; Masters, Morgan W.; Bud’ko, Sergey L.; ...

2015-02-13

Free standing, low strain, single crystals of pure and titanium doped VO₂ were grown out of an excess of V ₂O₅ using high temperature solution growth techniques. At T MI ~ 340 K, pure VO₂ exhibits a clear first-order phase transition from a high-temperature paramagnetic tetragonal phase (R) to a low-temperature non-magnetic monoclinic phase (M1). With Ti doping, another monoclinic phase (M2) emerges between the R and M1 phases. The phase transition temperature between R and M2 increases with increasing Ti doping while the transition temperature between M2 and M1 decreases.

Synthesis, Characterization, and Self-Controlled Orthorhombic to Tetragonal Polymorphic Transformation in BaTiO3 Nanoparticles

NASA Astrophysics Data System (ADS)

Ram, S.; Jana, A.; Kundu, T. K.

The phase formation and thermal-induced phase transformation are studied in BaTiO3 nanoparticles. 2 h of heating a polymer precursor at 550°C in air formed a single phase BaTiO3 of 15 nm average crystallite size D. The X-ray diffraction peaks are analyzed assuming a Pnma orthorhombic (o) crystal structure of lattice parameters a = 0.6435 nm, b = 0.5306 nm, and c = 0.8854 nm. The lattice volume V = 0.3023 nm3, with z = 4 formula units, yields a density ρ = 5.124 g/cm3. This is a new polymorph in comparison to well-known Pm3m tetragonal (t) structure, V = 0.0644 nm3 or ρ = 6.016 g/cm3 (z = 1). An o ↦ t transformation appears on heating at temperature as high as 650°C in air. A proposed model explains the transformation above a certain D value in terms of the Gibbs free energy. Unless heating above 750°C, the two phases coexist in a composite structure (D≤27 nm), with as much residual o-phase trace as ~28 vol%. As a function of temperature both the phases decrease in the V values up to 0.2975 and 0.0643 nm3 at 750°C respectively (0.0650 nm3 at 650°C). This is an important parameter for designing useful ferroelectric and other properties in a hybrid composite structure.

Electrical conduction mechanism and phase transition studies using dielectric properties and Raman spectroscopy in ferroelectric Pb0.76Ca0.24TiO3 thin films

NASA Astrophysics Data System (ADS)

Pontes, F. M.; Pontes, D. S. L.; Leite, E. R.; Longo, E.; Chiquito, A. J.; Pizani, P. S.; Varela, J. A.

2003-12-01

We have studied the phase transition behavior of Pb0.76Ca0.24TiO3 thin films using Raman scattering and dielectric measurement techniques. We also have studied the leakage current conduction mechanism as a function of temperature for these thin films on platinized silicon substrates. A Pb0.76Ca0.24TiO3 thin film was prepared using a soft chemical process, called the polymeric precursor method. The results showed that the dependence of the dielectric constant upon the frequency does not reveal any relaxor behavior. However, a diffuse character-type phase transition was observed upon transformation from a cubic paraelectric phase to a tetragonal ferroelectric phase. The temperature dependency of Raman scattering spectra was investigated through the ferroelectric phase transition. The soft mode showed a marked dependence on temperature and its disappearance at about 598 K. On the other hand, Raman modes persist above the tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive above the phase transition temperature. The origin of these modes must be interpreted in terms of a local breakdown of cubic symmetry by some kind of disorder. The lack of a well-defined transition temperature suggested a diffuse-type phase transition. This result corroborate the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in the thin film. The leakage current density of the PCT24 thin film was studied at elevated temperatures, and the data were well fitted by the Schottky emission model. The Schottky barrier height of the PCT24 thin film was estimated to be 1.49 eV.

Anharmonicity and Disorder in the Black Phases of Cesium Lead Iodide Used for Stable Inorganic Perovskite Solar Cells.

PubMed

Marronnier, Arthur; Roma, Guido; Boyer-Richard, Soline; Pedesseau, Laurent; Jancu, Jean-Marc; Bonnassieux, Yvan; Katan, Claudine; Stoumpos, Constantinos C; Kanatzidis, Mercouri G; Even, Jacky

2018-04-24

Hybrid organic-inorganic perovskites emerged as a new generation of absorber materials for high-efficiency low-cost solar cells in 2009. Very recently, fully inorganic perovskite quantum dots also led to promising efficiencies, making them a potentially stable and efficient alternative to their hybrid cousins. Currently, the record efficiency is obtained with CsPbI 3 , whose crystallographical characterization is still limited. Here, we show through high-resolution in situ synchrotron XRD measurements that CsPbI 3 can be undercooled below its transition temperature and temporarily maintained in its perovskite structure down to room temperature, stabilizing a metastable perovskite polytype (black γ-phase) crucial for photovoltaic applications. Our analysis of the structural phase transitions reveals a highly anisotropic evolution of the individual lattice parameters versus temperature. Structural, vibrational, and electronic properties of all the experimentally observed black phases are further inspected based on several theoretical approaches. Whereas the black γ-phase is shown to behave harmonically around equilibrium, for the tetragonal phase, density functional theory reveals the same anharmonic behavior, with a Brillouin zone-centered double-well instability, as for the cubic phase. Using total energy and vibrational entropy calculations, we highlight the competition between all the low-temperature phases of CsPbI 3 (γ, δ, β) and show that avoiding the order-disorder entropy term arising from double-well instabilities is key to preventing the formation of the yellow perovskitoid phase. A symmetry-based tight-binding model, validated by self-consistent GW calculations including spin-orbit coupling, affords further insight into their electronic properties, with evidence of Rashba effect for both cubic and tetragonal phases when using the symmetry-breaking structures obtained through frozen phonon calculations.

Impact of the oxygen defects and the hydrogen concentration on the surface of tetragonal and monoclinic ZrO2 on the reduction rates of stearic acid on Ni/ZrO2

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

Foraita, Sebastian D.; Fulton, John L.; Chase, Zizwe A.

2015-02-02

The effect of the physicochemical properties of ZrO2 phases on the activity of Ni/ZrO2 catalysts for hydrodeoxygenation of stearic acid are described. A synergistic interaction between Ni and ZrO2 support was found. The effect is greatest for the monoclinic phase of ZrO2.

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca ( Fe 1 – x Co x ) 2 As 2

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

Sapkota, A.; Das, P.; Bohmer, A. E.

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe 1–xCo x) 2As 2, x = 0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x = 0.026, similar to the parent CaFe 2As 2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe 1–xCo x) 2As 2, wherein the crossovermore » corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe 1–xCo x) 2As 2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x = 0.030 sample and high-temperature x = 0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x = 0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. In conclusion, one possible scenario ascribes this loss of moment to a sensitivity to the c-axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.« less

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca ( Fe 1 – x Co x ) 2 As 2

DOE PAGES

Sapkota, A.; Das, P.; Bohmer, A. E.; ...

2018-05-29

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe 1–xCo x) 2As 2, x = 0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x = 0.026, similar to the parent CaFe 2As 2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe 1–xCo x) 2As 2, wherein the crossovermore » corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in Ca(Fe 1–xCo x) 2As 2 due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the x = 0.030 sample and high-temperature x = 0.026 sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the x = 0.030 sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. In conclusion, one possible scenario ascribes this loss of moment to a sensitivity to the c-axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.« less

Automatic procedure for stable tetragonal or hexagonal structures: application to tetragonal Y and Cd

NASA Astrophysics Data System (ADS)

Marcus, P. M.; Jona, F.

2005-05-01

A simple effective procedure (MNP) for finding equilibrium tetragonal and hexagonal states under pressure is described and applied. The MNP procedure finds a path to minima of the Gibbs free energy G at T=0 K (G=E+pV, E=energy per atom, p=pressure, V=volume per atom) for tetragonal and hexagonal structures by using the approximate expansion of G in linear and quadratic strains at an arbitrary initial structure to find a change in the strains which moves toward a minimum of G. Iteration automatically proceeds to a minimum within preset convergence criteria on the calculation of the minimum. Comparison is made with experimental results for the ground states of seven metallic elements in hexagonal close-packed (hcp), face- and body-centered cubic structures, and with a previous procedure for finding minima based on tracing G along the epitaxial Bain path (EBP) to a minimum; the MNP is more easily generalized than the EBP procedure to lower symmetry and more atoms in the unit cell. Comparison is also made with a molecular-dynamics program for crystal equilibrium structures under pressure and with CRYSTAL, a program for crystal equilibrium structures at zero pressure. Application of MNP to the elements Y and Cd, which have hcp ground states at zero pressure, finds minima of E at face-centered cubic (fcc) structure for both Y and Cd. Evaluation of all the elastic constants shows that fcc Y is stable, hence a metastable phase, but fcc Cd is unstable.

Phase Behavior of Salt-Free Polyelectrolyte Gel-Surfactant Systems.

PubMed

Andersson, Martin; Hansson, Per

2017-06-22

Ionic surfactants tend to collapse the outer parts of polyelectrolyte gels, forming shells that can be used to encapsulate other species including protein and peptide drugs. In this paper, the aqueous phase behavior of covalently cross-linked polyacrylate networks containing sodium ions and dodecyltrimethylammonium ions as counterions is investigated by means of swelling isotherms, dye staining, small-angle X-ray scattering, and confocal Raman spectroscopy. The equilibrium state is approached by letting the networks absorb pure water. With an increasing fraction of surfactant ions, the state of the water-saturated gels is found to change from being swollen and monophasic, via multiphasic states, to collapsed and monophasic. The multiphasic gels have a swollen, micelle-lean core surrounded by a collapsed, micelle-rich shell, or a collapsed phase forming a spheroidal inner shell separating two micelle-lean parts. It is shown that the transition between monophasic and core-shell states can be induced by variation of the osmotic pressure and variation of the charge of the micelles by forming mixed micelles with the nonionic surfactant octaethyleneglycol monododecylether. The experimental data are compared with theoretical predictions of a model derived earlier. In the calculations, the collapsed shell is assumed to be homogeneous, an approximation introduced here and shown to be excellent for a wide range of compositions. The theoretical results highlight the electrostatic and hydrophobic driving forces behind phase separation.

Composition and annealing effects on superconductivity in sintered and arc-melted Fe1+εTe0.5Se0.5

NASA Astrophysics Data System (ADS)

Foreman, M. M.; Ponti, G.; Mozaffari, S.; Markert, J. T.

2018-03-01

We present the results of x-ray diffraction, electrical resistivity, and ac magnetic susceptibility measurements on specimens of the “11”-structure superconductor Fe1+εTe0.50Se0.50 (0 ≤ ε ≤ 0.15). Samples were initially either sintered in sealed quartz tubes or melted in a zirconium-gettered arc furnace. Sintered samples were fired two to three times at temperatures of 425°C, 600°C, or 675°C, while arc-melted samples were studied both asmelted and after annealing at 650°C. X-ray diffraction data show a predominant PbO-type tetragonal phase, with a secondary hexagonal NiAs-type phase; for sintered specimens annealed at 600°C, the secondary phase decreases as ε increases over the range 0 ≤ ε ≤ 0.10, with the composition Fe1.10Te0.5Se0.5 exhibiting x-ray phase purity. A higher annealing temperature of 675°C provided such tetragonal phase purity at the composition Fe1.05Te0.5Se0.5. The resistive superconducting transition temperature Tc was nearly independent of the iron concentration 1+ε, suggesting a single superconducting phase, while the magnetic screening fraction varied greatly with concentration and conditions, peaking at ɛ = 0.07, indicating that the amount of superconducting phase is strongly dependent on conditions. We propose that the behaviour can also be viewed in terms of an electron-doped, chalcogen-deficient stoichiometry.

Experimental observation of the luminescence flash at the collapse phase of a bubble produced by pulsed discharge in water

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

Huang, Yifan; Zhang, Liancheng; Zhu, Xinlei

2015-11-02

This letter presents an experimental observation of luminescence flash at the collapse phase of an oscillating bubble produced by a pulsed discharge in water. According to the high speed records, the flash lasts around tens of microseconds, which is much longer than the lifetime of laser and ultrasound induced luminescence flashes in nanoseconds and picoseconds, respectively. The pulse width of temperature waveform and minimum radius calculated at the collapse phase also show that the thermodynamic and dynamic signatures of the bubbles in this work are much larger than those of ultrasound and laser induced bubbles both in time and spacemore » scales. However, the peak temperature at the point of collapse is close to the results of ultrasound and laser induced bubbles. This result provides another possibility for accurate emission spectrum measurement other than amplification of the emitted light, such as increasing laser energy or sound energy or substituting water with sulphuric acid.« less

Phase-field model of domain structures in ferroelectric thin films

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

Li, Y. L.; Hu, S. Y.; Liu, Z. K.

A phase-field model for predicting the coherent microstructure evolution in constrained thin films is developed. It employs an analytical elastic solution derived for a constrained film with arbitrary eigenstrain distributions. The domain structure evolution during a cubic{r_arrow}tetragonal proper ferroelectric phase transition is studied. It is shown that the model is able to simultaneously predict the effects of substrate constraint and temperature on the volume fractions of domain variants, domain-wall orientations, domain shapes, and their temporal evolution. {copyright} 2001 American Institute of Physics.

Metastable and equilibrium phase formation in sputter-deposited Ti/Al multilayer thin films

NASA Astrophysics Data System (ADS)

Lucadamo, G.; Barmak, K.; Lavoie, C.; Cabral, C., Jr.; Michaelsen, C.

2002-06-01

The sequence and kinetics of metastable and equilibrium phase formation in sputter deposited multilayer thin films was investigated by combining in situ synchrotron x-ray diffraction (XRD) with ex situ electron diffraction and differential scanning calorimetry (DSC). The sequence included both cubic and tetragonal modifications of the equilibrium TiAl3 crystal structure. Values for the formation activation energies of the various phases in the sequence were determined using the XRD and DSC data obtained here, as well as activation energy data reported in the literature.

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.

Anomalous critical behavior in the polymer collapse transition of three-dimensional lattice trails.

PubMed

Bedini, Andrea; Owczarek, Aleksander L; Prellberg, Thomas

2012-07-01

Trails (bond-avoiding walks) provide an alternative lattice model of polymers to self-avoiding walks, and adding self-interaction at multiply visited sites gives a model of polymer collapse. Recently a two-dimensional model (triangular lattice) where doubly and triply visited sites are given different weights was shown to display a rich phase diagram with first- and second-order collapse separated by a multicritical point. A kinetic growth process of trails (KGTs) was conjectured to map precisely to this multicritical point. Two types of low-temperature phases, a globule phase and a maximally dense phase, were encountered. Here we investigate the collapse properties of a similar extended model of interacting lattice trails on the simple cubic lattice with separate weights for doubly and triply visited sites. Again we find first- and second-order collapse transitions dependent on the relative sizes of the doubly and triply visited energies. However, we find no evidence of a low-temperature maximally dense phase with only the globular phase in existence. Intriguingly, when the ratio of the energies is precisely that which separates the first-order from the second-order regions anomalous finite-size scaling appears. At the finite-size location of the rounded transition clear evidence exists for a first-order transition that persists in the thermodynamic limit. This location moves as the length increases, with its limit apparently at the point that maps to a KGT. However, if one fixes the temperature to sit at exactly this KGT point, then only a critical point can be deduced from the data. The resolution of this apparent contradiction lies in the breaking of crossover scaling and the difference in the shift and transition width (crossover) exponents.

Transformation to Ni5Al3 in a 63.0 at. pct Ni-Al alloy

NASA Technical Reports Server (NTRS)

Khadkikar, P. S.; Locci, I. E.; Vedula, K.; Michal, G. M.

1993-01-01

Microstructures of 63 at. pct P/M Ni-Al alloys with a composition close to the stoichiometry of the Ni5Al3 phase were investigated using homogenized and quenched specimens aged at low temperatures for various times. Results of analyses of XRD data and electron microscopy observations were used for quantitative phase analysis, performed to calculate the (NiAl + Ni5Al3)/Ni5Al3 phase boundary locations. The measured lattice parameters of Ni5Al3 phase formed at 823, 873, and 923 K indicated an increase in tetragonality of the phase with increasing nickel content.

Analytical Study on the Saturated Polarization Under Electric Field and Phase Equilibrium of Three-Phase Polycrystalline Ferroelectrics by Using the Generalized Inverse-Pole-Figure Model

NASA Astrophysics Data System (ADS)

Ju, Kyong-Sik; Ryo, Hyok-Su; Pak, Sung-Nam; Pak, Chang-Su; Ri, Sung-Guk; Ri, Dok-Hwan

2018-07-01

By using the generalized inverse-pole-figure model, the numbers of crystalline particles involved in different domain-switching near the triple tetragonal-rhombohedral-orthorhombic (T-R-O) points of three-phase polycrystalline ferroelectrics have been analytically calculated and domain-switching which can bring out phase transformations has been considered. Through polarization by an electric field, different numbers of crystalline particles can be involved in different phase transformations. According to the phase equilibrium conditions, the phase equilibrium compositions of the three phases coexisting near the T-R-O triple point have been evaluated from the results of the numbers of crystalline particles involved in different phase transformations.

Temperature Dependent Surface Structures and Electronic Properties of Organic-Inorganic Hybrid Perovskite Single Crystals

NASA Astrophysics Data System (ADS)

Jao, M.-H.; Teague, M. L.; Huang, J.-S.; Tseng, W.-S.; Yeh, N.-C.

Organic-inorganic hybrid perovskites, arising from research of low-cost high performance photovoltaics, have become promising materials not only for solar cells but also for various optoelectronic and spintronic applications. An interesting aspect of the hybrid perovskites is that their material properties, such as the band gap, can be easily tuned by varying the composition, temperature, and the crystalline phases. Additionally, the surface structure is critically important for their optoelectronic applications. It is speculated that different crystalline facets could show different trap densities, thus resulting in microscopically inhomogeneous performance. Here we report direct studies of the surface structures and electronic properties of hybrid perovskite CH3NH3PbI3 single crystals by scanning tunneling microscopy and spectroscopy (STM/STS). We found long-range spatially homogeneous tunneling conductance spectra with a well-defined energy gap of (1.55 +/- 0.1) eV at 300 K in the tetragonal phase, suggesting high quality of the single crystals. The energy gap increased to (1.81 +/- 0.1) eV in the orthorhombic phase, below the tetragonal-to-orthorhombic phase transition temperature at 150 K. Detailed studies of the temperature evolution in the spatially resolved surface structures and local density of states will be discussed to elucidate how these properties may influence the optoelectronic performance of the hybrid perovskites. We thank the support from NTU in Taiwan and from NSF in the US.

Photoluminescent emission of Pr 3+ ions in different zirconia crystalline forms

NASA Astrophysics Data System (ADS)

Ramos-Brito, F.; Alejo-Armenta, C.; García-Hipólito, M.; Camarillo, E.; Hernández A, J.; Murrieta S, H.; Falcony, C.

2008-08-01

Polycrystalline praseodymium doped-zirconia powders were synthesized by crystallization of a saturated solution and annealed in air at T a = 950 °C. Monoclinic, tetragonal and cubic crystalline phases of zirconia were obtained. EDS studies showed homogeneous chemical composition over all the powders particles and chemical elemental contents in good agreement with the incorporation of Pr 3+ ion in Zr 4+ sites. XRD patterns showed stabilization of tetragonal and cubic phases at 1.28 and 2.87 at.% of Pr 3+ doping concentrations, respectively. Both unit cells expand when Pr 3+ content increases. All samples showed a crystallite size lower than 27 nm. Diffuse reflectance studies exhibited the presence of the 4f5d absorption band of Pr 3+, and absorption peaks in 440-610 nm region associated with 4f inter-level electronic transitions in Pr 3+ ion. Low temperature (20 K) photo-luminescent spectroscopic measurements over excitation of 488 nm for praseodymium doped zirconia, showed multiple emission peaks in the 520-900 nm range of the electromagnetic spectrum, associated with typical 4f inter-level electronic transition in Pr 3+. Incorporation of Pr 3+ in more than one zirconia crystalline phase and the incorporation in cubic C 2 sites, were observed. Zirconia powders presented significant differences in its emission spectra as a function of the type of crystalline phase compounds.

Structural and optical study of γ –BIMEVOX; ME: Ba{sup 2+} and Sr{sup 2+}

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

Gupta, Sakshi, E-mail: Sakshi.gupta@thapar.edu; Singh, K., E-mail: kusingh@thapar.edu

2015-05-15

Bismuth oxide based compounds, such as Bi{sub 4}V{sub 2}O{sub 11-δ} (BIVOX), exhibit Aurivillus type of interleaving arrangement of (Bi{sub 2}O{sub 2}){sup 2+} and (VO{sub 3}□{sub 0.5}){sup 2-} (□: oxygen vacancies). Bi{sub 4}V{sub 2}O{sub 11-δ,} is known to have three kinds of temperature dependent interconvertible polymorphs α (monoclinic), β (orthorhombic) and γ (tetragonal). Out of all the three phases, the γ – phase is highly disordered and hence, is the most conductive one which can be stabilized by proper lower valence cation (ME) doping at V site. Bi{sub 4}V{sub 1.90}ME{sub 0.20}O{sub 11-δ} (ME: Ba{sup 2+} and Sr{sup 2+}) were prepared viamore » splat quenching technique. The required compositions were melted at 1250 °C in an electric furnace. The as quenched samples were sintered at 800 °C for 12 hours (h). The formed phases were analyzed using X-ray diffraction on quenched and sintered samples, the peak at 32{sup °} is found to be singlet in all the samples which confirms the presence of γ-phase. Hence, the stabilization of γ-phase with tetragonal structure was found to have taken place with doping and quenching. These samples are also studied by FT-IR and UV/vis spectroscopy to investigate the effect of dopants on structure and band gaps respectively.« less

Tuning the metal-insulator transition of VO2 by introducing W dopants via a combinatorial approach

NASA Astrophysics Data System (ADS)

Liang, Yangang; Lee, Seunghun; Zhang, Xiaohang; Takeuchi, Ichiro

We have systematically studied the structural phase transition and the electronic properties of composition spread V1-xWxO2 (0 <= x <= 0.037) thin films fabricated on silicon (001) and c-cut sapphire substrates through combinatorial pulsed laser deposition of a V2O5 target and a WO3 target. Our in-situ temperature-dependent x-ray diffraction measurements reveal a gradual change in the film structure from a monoclinic phase to a tetragonal phase via an intermediate mixture of the two as the concentration of tungsten increases from 0% to 3.7% at 300 K. At 358 K, the film is found to be in a tetragonal phase for the entire composition range we studied. The results also suggest that the volume of the unit cell increases as the concentration of tungsten increases. Electrical transport results further show that both the phase transition temperature and the width of the hysteresis loop decrease with the increasing of the concentration of tungsten. Especially, epitaxial V1-xWxO2 films fabricated on c-cut sapphire substrates show narrower hysteresis loop compared to textured V1-xWxO2 films fabricated on Si (100) substrates. In addition, the Hall effect measurements on the epitaxial V1-xWxO2 thin films at various temperature points provide important information for the change in the electronic structure upon increasing the concentration of tungsten. This work was supported by CNAM.

Review of high pressure phases of calcium by first-principles calculations

NASA Astrophysics Data System (ADS)

Ishikawa, T.; Nagara, H.; Suzuki, N.; Tsuchiya, J.; Tsuchiya, T.

2010-03-01

We review high pressure phases of calcium which have obtained by recent experimental and first-principles studies. In this study, we investigated the face-centered cubic (fcc) structure, the body-centered cubic (bcc) structure, the simple cubic (sc) structure, a tetragonal P43212 [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmca [Ishikawa T et al. 2008 Phys. Rev. B 77 020101(R)], an orthorhombic Cmcm [Teweldeberhan A M and Bonev S A 2008 Phys. Rev. B 78 140101(R)], an orthorhombic Pnma [Yao Y et al. 2008 Phys. Rev. B 78 054506] and a tetragonal I4/mcm(00) [Arapan S et al. 2008 Proc. Natl. Acad. Sci. USA 105 20627]. We compared the enthalpies among the structures up to 200 GPa and theoretically determined the phase diagram of calcium. The sequence of the structural transitions is fcc (0- 3.5 GPa) → bcc (3.5 - 35.7 GPa) → Cmcm (35.7- 52GPa) → P43212 (52-109 GPa) → Cmca (109-117.4GPa) → Pnma (117.4-134.6GPa) → I4/mcm(00) (134.6 GPa -). The sc phase is experimentally observed in the pressure range from 32 to 113 GPa but, in our calculation, there is no pressure region where the sc phase is the most stable. In addition, we found that the enthalpy of the hexagonal close-packed (hcp) structure is lower than that of I4/mcm(00) above 495 GPa.

On the metal-insulator-transition in vanadium dioxide

NASA Astrophysics Data System (ADS)

Jovaini, Azita; Fujita, Shigeji; Godoy, Salvador; Suzuki, Akira

2012-02-01

Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340 K with the structural change from tetragonal to monoclinic crystal. The conductivity σ drops at MIT by four orders of magnitude. The low temperature monoclinic phase is known to have a lower ground-state energy. The existence of the k-vector k is prerequisite for the conduction since the k appears in the semiclassical equation of motion for the conduction electron (wave packet). The tetragonal (VO2)3 unit is periodic along the crystal's x-, y-, and z-axes, and hence there is a three-dimensional k-vector. There is a one-dimensional k for a monoclinic crystal. We believe this difference in the dimensionality of the k-vector is the cause of the conductivity drop.

Influence of samarium substitution on structural, dielectric, and piezoelectric properties of PZT ceramics

NASA Astrophysics Data System (ADS)

Juneja, J. K.; Thakur, O. P.; Prakash, Chandra

2003-10-01

The structural, dielectric and piezoelectric properties have been studied in detail for the samarium modified PZT system. The samples, with chemical formula Pb1-xSmxZr0.52Ti0.48O3 with x varying from 0 to 0.02 in steps of 0.0025, were prepared by standard double sintering ceramic method. XRD analysis showed all the samples to be of single phase with tetragonal structure. Tetragonality (c/a) decreases gradually with samarium concentration (x) and the experimental density increases with x. Dielectric properties were studied as a function of temperature and frequency. All the samples show well-defined ferroelectric behavior. The remanance ratio (Pr/Ps) was found to increase with increasing Sm3+ concentration. Piezoelectric charge coefficient d33 decreases with x.

Effect of off-center ion substitution in morphotropic lead zirconate titanate composition

NASA Astrophysics Data System (ADS)

Bhattarai, Mohan K.; Pavunny, Shojan P.; Instan, Alvaro A.; Scott, James F.; Katiyar, Ram S.

2017-05-01

A detailed study of the effect of off-center donor ion (Sc3+) substitution on structural, microstructural, optical, dielectric, electrical, and ferroelectric properties of morphotropic composition of lead zirconate titanate electroceramics with the stoichiometric formula Pb0.85Sc0.10Zr0.53Ti0.47O3 (PSZT) and synthesized using a high energy solid-state reaction technique was carried out. Powder x-ray diffractometry was used to identify the stabilized tetragonal phase (space group P 4 m m ) with considerably reduced tetragonal strain, c /a = 1.005. An analysis of the thermal dependence of the Raman results indicated a smooth displacive (ferroelectric-paraelectric) phase transition as revealed by the observed disappearance of the soft modes A1 (1TO) and A1 (2TO) above 460 K. The dielectric response of Pt/PSZT/Pt metal-ferroelectric-metal capacitors was probed over a wide range of thermal excursions (85-600 K) and ac signal frequencies (102-106 Hz). Thermally activated dynamic and static conduction processes indicate hopping conduction mechanism ( Ea c t ≤ 0.015 eV) and the formation of small polarons caused by the electron and/or hole-lattice (phonon) interaction ( Ea c t ≥ 0.1 eV) at low (100-300 K) and high temperatures (300-600 K), respectively. The reduction in remnant polarization obtained is in good agreement with the largely reduced tetragonal strain observed in this sample, ( Pr ∝ √{c /a -1 } ). DC conduction is dominated by Poole-Frenkel mechanism that assumes a Coulombic attraction between detrapped electrons and positively charged stationary defect species in the polycrystalline matrix.

Detailed magnetic and structural analysis mapping a robust magnetic C 4 dome in Sr 1 - x Na x Fe 2 As 2

DOE PAGES

Taddei, K. M.; Allred, J. M.; Bugaris, D. E.; ...

2016-04-20

The recently discovered C 4 tetragonal magnetic phase in hole-doped members of the iron-based superconductors provides new insights into the origin of unconventional superconductivity. Previously observed in Ba 1-xNa xFe 2As 2 (with A = K, Na), the C 4 magnetic phase exists within the well studied C 2 spin-density wave (SDW) dome, arising just before the complete suppression of antiferromagnetic (AFM) order but after the onset of superconductivity. Here in this paper, we present detailed x-ray and neutron diffraction studies of Sr 1-xNa xFe 2As 2 (0.10 ≤ x ≤ 0.60) to determine their structural evolution and the extentmore » of the C 4 phase. Spanning Δx ~ 0.14 in composition, the C 4 phase is found to extend over a larger range of compositions, and to exhibit a significantly higher transition temperature, T r ~ 65K, than in either of the other systems in which it has been observed. The onset of this phase is seen near a composition (x~0:30) where the bonding angles of the Fe 2As 2 layers approach the perfect 109.46° tetrahedral angle. We discuss the possible role of this return to a higher symmetry environment for the magnetic iron site in triggering the magnetic reorientation and the coupled re-entrance to the tetragonal structure. Finally, we present a new phase diagram, complete with the C 4 phase, and use its observation in a third hole-doped 122 system to suggest the universality of this phase.« less

Photocatalytic performance of freestanding tetragonal zirconia nanotubes formed in H2O2/NH4F/ethylene glycol electrolyte by anodisation of zirconium

NASA Astrophysics Data System (ADS)

Rozana, Monna; Izza Soaid, Nurul; Kian, Tan Wai; Kawamura, Go; Matsuda, Atsunori; Lockman, Zainovia

2017-04-01

ZrO2 nanotubes (ZrNTs) were produced by anodisation of zirconium foil in H2O2/NH4F/ethylene glycol electrolyte. The as-anodised foils were then soaked in the anodising electrolyte for 12 h. Soaking weakens the adherence of the anodic layer from the substrate resulting in freestanding ZrNTs (FS-ZrNTs). Moreover, the presence of H2O2 in the electrolyte also aids in weakening the adhesion of the film from the foil, as foil anodised in electrolyte without H2O2 has good film adherence. The as-anodised FS-ZrNTs film was amorphous and crystallised to predominantly tetragonal phase upon annealing at >300 °C. Annealing must, however, be done at <500 °C to avoid monoclinic ZrO2 formation and nanotubes disintegration. FS-ZrNTs annealed at 450 °C exhibited the highest photocatalytic ability to degrade methyl orange (MO), whereby 82% MO degradation was observed after 5 h, whereas FS-ZrNTs with a mixture of monoclinic and tetragonal degraded 70% of MO after 5 h.

Gravitational-Wave and Neutrino Signals from Core-Collapse Supernovae with QCD Phase Transition

NASA Astrophysics Data System (ADS)

Zha, Shuai; Leung, Shing Chi; Lin, Lap Ming; Chu, Ming-Chung

Core-collapse supernovae (CCSNe) mark the catastrophic death of massive stars. We simulate CCSNe with a hybrid equations of state (EOS) containing a QCD (quantum chromodynamics) phase transition. The hybrid EOS incorporates the pure hadronic HShen EOS and the MIT Bag Model, with a Gibbs construction. Our two-dimensional hydrodynamics code includes a fifth-order shock capturing scheme WENO and models neutrino transport with the isotropic diffusion source approximation (IDSA). As the proto-neutron-star accretes matter and the core enters the mixed phase, a second collapse takes place due to softening of the EOS. We calculate the gravitational-wave (GW) and neutrino signals for this kind of CCSNe model. Future detection of these signals from CCSNe may help to constrain this scenario and the hybrid EOS.

Ab initio prediction of superdense tetragonal and monoclinic polymorphs of carbon

DOE PAGES

Li, Zhen -Zhen; Wang, Jian -Tao; Xu, Li -Fang; ...

2016-11-02

The design and synthesis of three-dimensional denser carbons are one of the hot issues in condensed matter physics because of their fascinating properties. Here we identify by ab initio calculations several tetragonal and monoclinic polymorphs of carbon that adopt the t32, t32*, m32, and m32* structures in P4¯2 1c, P4 32 12, P2 1/c, and C2 symmetry, respectively. These carbon polymorphs have large 32-atom unit cells in all-sp 3 bonding networks comprising five- and six-membered rings that are dynamically stable, as verified by a phonon mode analysis. Electronic band structure calculations show that they are insulators with band gaps inmore » the range of 5.19–5.41 eV, close to the calculated band gap of 5.34 eV for diamond. Remarkably, these carbon phases possess an extremely high atom number density exceeding that of diamond. Lastly, the present results establish different types of carbon phases and offer insights into their outstanding structural and electronic properties.« less

Thermal annealing and transient electronic excitations induced interfacial and magnetic effects on Pt/Co/Pt trilayer

NASA Astrophysics Data System (ADS)

Sehdev, Neeru; Medwal, Rohit; Malik, Rakesh; Kandasami, Asokan; Kanjilal, Dinakar; Annapoorni, S.

2018-04-01

Present study investigates the importance of thermal annealing and transient electronic excitations (using 100 MeV oxygen ions) in assisting the interfacial atomic diffusion, alloy composition, and magnetic switching field distributions in Pt/Co/Pt stacked trilayer. X-ray diffraction analysis reveals that thermal annealing results in the formation of the face centered tetragonal L1°CoPt phase. The Rutherford back scattering spectra shows a trilayer structure for as-deposited and as-irradiated films. Interlayer mixing on the thermally annealed films further improves by electronic excitations produced by high energy ion irradiation. Magnetically hard face centered tetragonal CoPt alloy retains its hard phase after ion irradiation and reveals an enhancement in the structural ordering and magnetic stability. Enhancement in the homogeneity of alloy composition and its correlation with the magnetic switching field is evident from this study. A detailed investigation of the contributing parameters shows that the magnetic switching behaviour varies with the type of thermal annealing, transient electronic excitations of ion beams and combination of these processes.

Characterization of BaTiO3 nanocubes assembled into highly ordered monolayers using micro- and nano-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Itasaka, Hiroki; Mimura, Ken-ichi; Nishi, Masayuki; Kato, Kazumi

2018-05-01

We investigated the influence of heat treatment on the crystallographic structure and ferroelectric phase transition behavior of barium titanate (BaTiO3, BT) nanocubes assembled into highly ordered monolayers, using tip-enhanced Raman spectroscopy (TERS), temperature-dependent micro-Raman spectroscopy, and scanning transmission electron microscopy (STEM). TER spectra from individual BT nanocubes with the size of about 20 nm were obtained with a side-illumination optical setup, and revealed that heat treatment enhances their tetragonality. The result of temperature-dependent micro-Raman spectroscopy showed that the ferroelectric phase transition behavior of the monolayers becomes similar to that of bulk BT through heat treatment in spite of their thickness. STEM observation for the cross-section of the heated BT nanocube monolayer showed that amorphous layers exist at the interface between BT nanocubes in face-to-face contact. These results indicate that the tetragonal crystal structure of BT nanocubes is stabilized by heat treatment and the formation of the interfacial amorphous layer during heat treatment may be a key to this phenomenon.

Phase study of SiO2-ZrO2 composites prepared from polymorphic combination of starting powders via a ball-milling followed by calcination

NASA Astrophysics Data System (ADS)

Musyarofah; Nurlaila, R.; Muwwaqor, N. F.; Saukani, M.; Kuswoyo, A.; Triwikantoro; Pratapa, S.

2017-04-01

The effects of SiO2-ZrO2 polymorphic combinations as starting powders and calcination temperature on phase composition of the SiO2-ZrO2 composites were studied. Stoichiometric (1:1 mol%) mixtures of the SiO2-ZrO2 composites were mechanically activated using a ball-milling for 5 h followed by calcinations at 1000, 1100 and 1200 °C for 3 h. The composites used in the present study were a-SiO2+ a-ZrO2, a-SiO2+ t-ZrO2, c-SiO2+ a-ZrO2 and c-SiO2+ t-ZrO2 which were symbolized by AA, AT, CA and CT, respectively. Prefixes a, t and c denote amorphous, tetragonal and cristobalite, respectively. The phase composition was determined by Rietveld analysis of X-ray diffraction (XRD) data using Rietica software. The identified phases for all calcined samples were a combination among t-ZrO2, c-SiO2, m-ZrO2 and zircon (ZrSiO4). Amorphous zirconia formed a transient tetragonal zirconia phase during heating, which reacted with silica to form zircon. The zircon phase was not found to form even at 1200 °C in the AT and CT mixtures and at 1100 °C in the CA mixture. The AA mixture in particular crystallized to form zircon at a lower temperature with more composition fraction than the others, ca 82.9 (14) mol%.

Structural and Na-ion conduction characteristics of Na 3PS xSe 4–x

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

Bo, Shou -Hang; Wang, Yan; Ceder, Gerbrand

The recent discovery of the isostructrual cubic Na 3PS 4 and Na 3PSe 4 as fast Na-ion conductors provided a general structural framework for the exploration of new sodium superionic conductors. In this work, we systematically investigated the structures and ionic conduction characteristics of a series of compounds with the general chemical formula of Na 3PS xSe 4–x. Synthesis of Na 3PS 4 under different conditions (e.g., temperature, reaction vessel, mass of the precursors) reveals the reactivity of the precursors with the reaction tubes, producing different polymorphs. X-ray diffraction studies on the solid solution phases Na 3PS xSe 4–x identifiedmore » a tetragonal-to-cubic phase transition with increasing Se concentration. This observation is consistent with the computed stability of the tetragonal and cubic polymorphs, where the energy difference between the two polymorphs becomes very close to zero in Se-rich compositions. Furthermore, ab initio molecular dynamic simulations suggest that the fast Na-ion conduction in Na 3PS xSe 4–x may not be causally related with the symmetry or the composition of these phases. The formation of defects, instead, enables fast Na-ion conduction in this class of materials.« less

Structural and Na-ion conduction characteristics of Na 3 PS x Se 4-x

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

Bo, Shou-Hang; Wang, Yan; Ceder, Gerbrand

The recent discovery of the isostructrual cubic Na 3PS 4 and Na 3PSe 4 as fast Na-ion conductors provided a general structural framework for the exploration of new sodium superionic conductors. In this work, we systematically investigated the structures and ionic conduction characteristics of a series of compounds with the general chemical formula of Na 3PS xSe 4-x. Synthesis of Na 3PS 4 under different conditions (e.g., temperature, reaction vessel, mass of the precursors) reveals the reactivity of the precursors with the reaction tubes, producing different polymorphs. X-ray diffraction studies on the solid solution phases Na 3PS xSe 4-x more » identified a tetragonal-to-cubic phase transition with increasing Se concentration. This observation is consistent with the computed stability of the tetragonal and cubic polymorphs, where the energy difference between the two polymorphs becomes very close to zero in Se-rich compositions. Furthermore, ab initio molecular dynamic simulations suggest that the fast Na-ion conduction in Na 3PS xSe 4-x may not be causally related with the symmetry or the composition of these phases. The formation of defects, instead, enables fast Na-ion conduction in this class of materials.« less

Effect of solutes on the lattice parameters and elastic stiffness coefficients of body-centered tetragonal Fe

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

Fellinger, Michael R.; Hector, Jr., Louis G.; Trinkle, Dallas R.

In this study, we compute changes in the lattice parameters and elastic stiffness coefficients C ij of body-centered tetragonal (bct) Fe due to Al, B, C, Cu, Mn, Si, and N solutes. Solute strain misfit tensors determine changes in the lattice parameters as well as strain contributions to the changes in the C ij. We also compute chemical contributions to the changes in the C ij, and show that the sum of the strain and chemical contributions agree with more computationally expensive direct calculations that simultaneously incorporate both contributions. Octahedral interstitial solutes, with C being the most important addition inmore » steels, must be present to stabilize the bct phase over the body-centered cubic phase. We therefore compute the effects of interactions between interstitial C solutes and substitutional solutes on the bct lattice parameters and C ij for all possible solute configurations in the dilute limit, and thermally average the results to obtain effective changes in properties due to each solute. Finally, the computed data can be used to estimate solute-induced changes in mechanical properties such as strength and ductility, and can be directly incorporated into mesoscale simulations of multiphase steels to model solute effects on the bct martensite phase.« less

Pulsed Laser Deposited Ferromagnetic Chromium Dioxide thin Films for Applications in Spintronics

NASA Astrophysics Data System (ADS)

Dwivedi, S.; Jadhav, J.; Sharma, H.; Biswas, S.

Stable rutile type tetragonal chromium dioxide (CrO2) thin films have been deposited on lattice-matched layers of TiO2 by KrF excimer laser based pulsed laser deposition (PLD) technique using Cr2O3 target. The TiO2 seed layer was deposited on oxidized Si substrates by the same PLD process followed by annealing at 1100 °C for 4 h. The lattice-matched interfacial layer is required for the stabilization of Cr (IV) phase in CrO2, since CrO2 behaves as a metastable compound under ambient conditions and readily converts into its stable phase of Cr (III) oxide, Cr2O3. Analyses with X-ray diffraction (XRD), Glancing-angle XRD (GIXRD), Raman spectroscopy and grazing-angle Fourier transform infra-red (FTIR) spectroscopy confirm the presence of tetragonal CrO2 phase in the as-deposited films. Microstructure and surface morphology in the films were studied with field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). Electrical and magnetic characterizations of the films were performed at room temperature. Such type of stable half-metallic CrO2 thin films with low field magnetoresistive switching behaviour are in demand for applications as diverse as spin-FETs, magnetic sensors, and magneto-optical devices.

Synthesis of nanocrystalline zirconia by amorphous citrate route: structural and thermal (HTXRD) studies

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

Bhagwat, Mahesh; Ramaswamy, Veda

Nanocrystalline zirconia powder with a fairly narrow particle size distribution has been synthesized by the amorphous citrate route. The sample obtained has a high BET surface area of 89 m{sup 2} g{sup -1}. Rietveld refinement of the powder X-ray diffraction (XRD) profile of the zirconia sample confirms stabilization of zirconia in the tetragonal phase with around 8% monoclinic impurity. The data show the presence of both anionic as well as cationic vacancies in the lattice. Crystallite size determined from XRD is 8 nm and is in close agreement with the particle size determined by TEM. The in situ high temperature-X-raymore » diffraction (HTXRD) study revealed high thermal stability of the mixture till around 1023 K after which the transformation of tetragonal phase into the monoclinic phase has been seen as a function of temperature till 1473 K. This transformation is accompanied by an increase in the crystallite size of the sample from 8 to 55 nm. The thermal expansion coefficients are 9.14 x 10{sup -6} K{sup -1} along 'a'- and 15.8 x 10{sup -6} K{sup -1} along 'c'-axis. The lattice thermal expansion coefficient in the temperature range 298-1623 K is 34.6 x 10{sup -6} K{sup -1}.« less

Structural and Na-ion conduction characteristics of Na 3PS xSe 4–x

DOE PAGES

Bo, Shou -Hang; Wang, Yan; Ceder, Gerbrand

2016-05-19

The recent discovery of the isostructrual cubic Na 3PS 4 and Na 3PSe 4 as fast Na-ion conductors provided a general structural framework for the exploration of new sodium superionic conductors. In this work, we systematically investigated the structures and ionic conduction characteristics of a series of compounds with the general chemical formula of Na 3PS xSe 4–x. Synthesis of Na 3PS 4 under different conditions (e.g., temperature, reaction vessel, mass of the precursors) reveals the reactivity of the precursors with the reaction tubes, producing different polymorphs. X-ray diffraction studies on the solid solution phases Na 3PS xSe 4–x identifiedmore » a tetragonal-to-cubic phase transition with increasing Se concentration. This observation is consistent with the computed stability of the tetragonal and cubic polymorphs, where the energy difference between the two polymorphs becomes very close to zero in Se-rich compositions. Furthermore, ab initio molecular dynamic simulations suggest that the fast Na-ion conduction in Na 3PS xSe 4–x may not be causally related with the symmetry or the composition of these phases. The formation of defects, instead, enables fast Na-ion conduction in this class of materials.« less

Temperature-mediated phase transformation, pore geometry and pore hysteresis transformation of borohydride derived in-born porous zirconium hydroxide nanopowders

PubMed Central

Nayak, Nadiya B.; Nayak, Bibhuti B.

2016-01-01

Development of in-born porous nature of zirconium hydroxide nanopowders through a facile hydrogen (H2) gas-bubbles assisted borohydride synthesis route using sodium borohydride (NaBH4) and novel information on the temperature-mediated phase transformation, pore geometry as well as pore hysteresis transformation of in-born porous zirconium hydroxide nanopowders with the help of X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) isotherm and Transmission Electron Microscopy (TEM) images are the main theme of this research work. Without any surfactants or pore forming agents, the borohydride derived amorphous nature of porous powders was stable up to 500 °C and then the seed crystals start to develop within the loose amorphous matrix and trapping the inter-particulate voids, which led to develop the porous nature of tetragonal zirconium oxide at 600 °C and further sustain this porous nature as well as tetragonal phase of zirconium oxide up to 800 °C. The novel hydrogen (H2) gas-bubbles assisted borohydride synthesis route led to develop thermally stable porous zirconium hydroxide/oxide nanopowders with an adequate pore size, pore volume, and surface area and thus these porous materials are further suggested for promising use in different areas of applications. PMID:27198738

Dielectric, Piezoelectric and Variable Range Hopping Conductivity Studies of Bi0.5(Na, K)0.5TiO3 Ceramics

NASA Astrophysics Data System (ADS)

Pattipaka, Srinivas; James, A. R.; Dobbidi, Pamu

2018-04-01

We report a detailed study on the structural, microstructural, piezoelectric, dielectric and AC conductivity of Bi0.5(Na1-x K x )0.5TiO3 (BNKT; x = 0, 0.1, 0.2 and 0.3) ceramics fabricated by a conventional solid-state reaction method. XRD and Raman analysis revealed that Bi0.5(Na0.8K0.2)0.5TiO3 and Bi0.5(Na0.7K0.3)0.5TiO3 ceramics exhibit a mixture of rhombohedral and tetragonal structures. The segregation of K at the grain boundary was confirmed by transmission electron microscopy and is related to typical microstructural local compositional mapping analysis. Two transitions, at ˜ 330°C and 150°C, observed from the ɛ' versus T curve in pure BNT are associated with the ferroelectric tetragonal to paraelectric cubic phase (T C) and ferroelectric rhombohedral to ferroelectric tetragonal phase (T d), respectively. Further, the T C and T d shifted towards the lower temperature with a rise in K concentration. Frequency dispersion of T d and T C suggest that BNKT ceramics exhibit a weak relaxor behavior with diffuse phase transition, which is confirmed by Uchino-Nomura criteria and the Vogel-Fulcher law. The AC resistivity ρ ac(T) follows the Mott variable range hopping conduction mechanism. A significant enhancement of dielectric and piezoelectric properties were observed for x = 0.2 system: dielectric constant (ɛ' = 1273), dielectric loss (tanδ = 0.047) at 1 kHz, electromechanical coupling coefficients (k ij : k 33, k t ˜ 60%, k 31 ˜ 62% and k p ˜ 46%), elastic coupling coefficients ( S_{33}D = 6.40 × 10-13 m2/N and S_{33}E = 10.06 × 10-13 m2/N) and piezoelectric constants (d 33 = 64.23 pC/N and g 33 = 5.69 × 10-3 Vm/N).

Dielectric, Piezoelectric and Variable Range Hopping Conductivity Studies of Bi0.5(Na, K)0.5TiO3 Ceramics

NASA Astrophysics Data System (ADS)

Pattipaka, Srinivas; James, A. R.; Dobbidi, Pamu

2018-07-01

We report a detailed study on the structural, microstructural, piezoelectric, dielectric and AC conductivity of Bi0.5(Na1- x K x )0.5TiO3 (BNKT; x = 0, 0.1, 0.2 and 0.3) ceramics fabricated by a conventional solid-state reaction method. XRD and Raman analysis revealed that Bi0.5(Na0.8K0.2)0.5TiO3 and Bi0.5(Na0.7K0.3)0.5TiO3 ceramics exhibit a mixture of rhombohedral and tetragonal structures. The segregation of K at the grain boundary was confirmed by transmission electron microscopy and is related to typical microstructural local compositional mapping analysis. Two transitions, at ˜ 330°C and 150°C, observed from the ɛ' versus T curve in pure BNT are associated with the ferroelectric tetragonal to paraelectric cubic phase ( T C) and ferroelectric rhombohedral to ferroelectric tetragonal phase ( T d), respectively. Further, the T C and T d shifted towards the lower temperature with a rise in K concentration. Frequency dispersion of T d and T C suggest that BNKT ceramics exhibit a weak relaxor behavior with diffuse phase transition, which is confirmed by Uchino-Nomura criteria and the Vogel-Fulcher law. The AC resistivity ρ ac( T) follows the Mott variable range hopping conduction mechanism. A significant enhancement of dielectric and piezoelectric properties were observed for x = 0.2 system: dielectric constant ( ɛ' = 1273), dielectric loss (tan δ = 0.047) at 1 kHz, electromechanical coupling coefficients ( k ij : k 33, k t ˜ 60%, k 31 ˜ 62% and k p ˜ 46%), elastic coupling coefficients ( S_{33}D = 6.40 × 10-13 m2/N and S_{33}E = 10.06 × 10-13 m2/N) and piezoelectric constants ( d 33 = 64.23 pC/N and g 33 = 5.69 × 10-3 Vm/N).

Does Warming a Lysozyme Solution Cook Ones Data?

NASA Technical Reports Server (NTRS)

Pusey, Marc; Burke, Michael; Judge, Russell

2000-01-01

Chicken egg white lysozyme has a well characterized thermally driven phase transition. Between pH 4.0 and 5.2, the transition temperature, as defined by the point where the tetragonal and orthorhombic solubility are equal, is a function of the pH, salt (precipitant) type and concentration, and most likely of the buffer concentration as well. This phase transition can be carried out with protein solution alone, prior to the initiation of the crystallization process. We have now measured the kinetics of this process and investigated its reversibility. An aliquot of a stock protein solution is held at a given temperature, and at periodic intervals used to set up batch crystallization experiments. The batch solutions were incubated at 20 C until macroscopic crystals were obtained, at which point the number of crystals in each well were counted. The transition effects increased with temperature, slowly falling off at 30 C with a half time (time to approx. 1/2 the t = 0 number of crystals) of approx. 5 hours, and an estimated half time of approx. 0.5 hours at 43 C. Further, the process was not reversible by simple cooling. After holding a lysozyme solution at 37 C (prior to addition of precipitant) for 16 hours, then cooling and holding it at 4 C, no return to the pre-warmed nucleation kinetics are observed after at least 4 weeks. Thus every thermal excursion above the phase transition point results in a further decrease in the nucleation rate of that solution, the extent being a function of the time and temperature. Orthorhombic lysozyme crystals apparently do not undergo the flow-induced growth cessation of tetragonal lysozyme crystals. We have previously shown that putting the protein in the orthorhombic form does not affect the averaged face growth kinetics, only nucleation, for tetragonal crystals. We may be able to use this differential behavior to elucidate how flow affects tile lysozyme crystal growth process.

New insights into organic-inorganic hybrid perovskite CH₃NH₃PbI₃ nanoparticles. An experimental and theoretical study of doping in Pb²⁺ sites with Sn²⁺, Sr²⁺, Cd²⁺ and Ca²⁺.

PubMed

Navas, Javier; Sánchez-Coronilla, Antonio; Gallardo, Juan Jesús; Hernández, Norge Cruz; Piñero, Jose Carlos; Alcántara, Rodrigo; Fernández-Lorenzo, Concha; De los Santos, Desireé M; Aguilar, Teresa; Martín-Calleja, Joaquín

2015-04-14

This paper presents the synthesis of the organic-inorganic hybrid perovskite, CH3NH3PbI3, doped in the Pb(2+) position with Sn(2+), Sr(2+), Cd(2+) and Ca(2+). The incorporation of the dopants into the crystalline structure was analysed, observing how the characteristics of the dopant affected properties such as the crystalline phase, emission and optical properties. XRD showed how doping with Sn(2+), Sr(2+) and Cd(2+) did not modify the normal tetragonal phase. When doping with Ca(2+), the cubic phase was obtained. Moreover, DR-UV-Vis spectroscopy showed how the band gap decreased with the dopants, the values following the trend Sr(2+) < Cd(2+) < Ca(2+) < CH3NH3PbI3 ≈ Sn(2+). The biggest decrease was generated by Sr(2+), which reduced the CH3NH3PbI3 value by 4.5%. In turn, cathodoluminescence (CL) measurements confirmed the band gap obtained. Periodic-DFT calculations were performed to understand the experimental structures. The DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy, with the values calculated following the trend Sn(2+) ≈ Pb(2+) > Cd(2+) > Sr(2+) for the tetragonal structure and Pb(2+) > Ca(2+) for the cubic phase. The electron localization function (ELF) analysis showed similar electron localizations for undoped and Sn(2+)-doped tetragonal structures, which were different from those doped with Sr(2+) and Cd(2+). Furthermore, when Cd(2+) was incorporated, the Cd-I interaction was strengthened. For Ca(2+) doping, the Ca-I interaction had a greater ionic nature than Cd-I. Finally, an analysis based on the non-covalent interaction (NCI) index is presented to determine the weak-type interactions of the CH3NH3 groups with the dopant and I atoms. To our knowledge, this kind of analysis with these hybrid systems has not been performed previously.

Interplay between structural and magnetic-electronic responses of FeA l2O4 to a megabar: Site inversion and spin crossover

NASA Astrophysics Data System (ADS)

Xu, W. M.; Hearne, G. R.; Layek, S.; Levy, D.; Pasternak, M. P.; Rozenberg, G. Kh.; Greenberg, E.

2018-02-01

X-ray diffraction pressure studies at room temperature demonstrate that the spinel FeA l2O4 transforms to a tetragonal phase at ˜18 GPa. This tetragonal phase has a highly irregular unit-cell volume versus pressure dependence up to ˜45 GPa, after which a transformation to a Cmcm postspinel phase is onset. This is attributable to pressure driven Fe↔Al site inversion at room temperature, corroborated by signatures in the 57Fe Mössbauer spectroscopy pressure data. At the tetragonal→postspinel transition, onset in the range 45-50 GPa, there is a concurrent emergence of a nonmagnetic spectral component in the Mössbauer data at variable cryogenic temperatures. This is interpreted as spin crossover at sixfold coordinated Fe locations emanated from site inversion. Spin crossover commences at the end of the pressure range of the tetragonal phase and progresses in the postspinel structure. There is also a much steeper volume change ΔV /V ˜ 10% in the range 45-50 GPa compared to the preceding pressure regime, from the combined effects of the structural transition and spin crossover electronic change. At the highest pressure attained, ˜106 GPa, the Mössbauer data evidence a diamagnetic Fe low-spin abundance of ˜50%. The rest of the high-spin Fe in eightfold coordinated sites continue to experience a relatively small internal magnetic field of ˜33 T. This is indicative of a magnetic ground state associated with strong covalency, as well as substantive disorder from site inversion and the mixed spin-state configuration. Intriguingly, magnetism survives in such a spin-diluted postspinel lattice at high densities. The R (300 K) data decrease by only two orders of magnitude from ambient pressure to the vicinity of ˜100 GPa. Despite a ˜26% unit-cell volume densification from the lattice compressibility, structural transitions, and spin crossover, FeA l2O4 is definitively nonmetallic with an estimated gap of ˜400 meV at ˜100 GPa. At such high densification appreciable bandwidth broadening and gap closure would be anticipated. Reasons for the resilient nonmetallic behavior are briefly discussed.

Microstructure and physical properties of bismuth-lead-tin ternary eutectic alloy

NASA Astrophysics Data System (ADS)

Kamal, M.; Moharram, B. M.; Farag, H.; El-Bediwi, A.; Abosheiasha, H. F.

2006-07-01

Using different experimental techniques, microstructure, electrical resistivity, attenuation coefficient, and mechanical and thermal properties of the quenched Bi-Pb-Sn ternary eutectic alloy have been investigated. From the X-ray analysis, Bi3Pb7 and Bi-Sn meta-stable phases are detected, in addition to rhombohedral bismuth and Sn body-centered tetragonal phases. This study also compared the physical properties of the Bi-Sn-Pb ternary eutectic alloys with the base binary Bi-Sn and Bi-Pb eutectic alloys.

Influence of thermal treatment on the formation of zirconia nanostructured powder by thermal decomposition of different precursors

NASA Astrophysics Data System (ADS)

Stoia, Marcela; Barvinschi, Paul; Barbu-Tudoran, Lucian; Negrea, Adina; Barvinschi, Floricica

2013-10-01

The paper presents some results concerning the preparation of zirconia powders starting from ZrOCl2·8H2O by using two synthesis methods: (a) precipitation with NH3, at 90 °C, and (b) thermal decomposition of carboxylate precursors, obtained in the reaction of zirconium nitrate and two different alcohols, 1,3-propanediol (PD) and poly(vinyl alcohol) (PVA), at 150 °C. The precursors obtained at different temperatures have been characterized by thermal analysis (TG, DTA) and FT-IR spectroscopy. DTA analysis evidenced very clearly the transition temperatures between zirconia crystalline phases. The precursors have been annealed at different temperatures in order to obtain zirconia powders and the as obtained powders have been characterized by means of X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). In case of precipitation method the presence of the tetragonal phase was observed at 400 °C, while the monoclinic phase appears at temperatures higher than 400 °C, becoming major crystalline phase starting with 700 °C. In case of the powders prepared by thermal decomposition of carboxylate precursors, the tetragonal phase was formed at temperatures below 700 °C, when the monoclinic phase begin to crystallize as secondary phase, in a higher proportion for the samples synthesized with 1,3-propanediol. All powders annealed at 1200 °C are pure monoclinic zirconia. SEM images have evidenced for the zirconia powders annealed at 1000 °C particles with diameters up to 150 nm, agglomerated in micrometer-sized aggregates, more individualized and homogenous than that obtained in the case of zirconia powder synthesized with poly(vinyl alcohol).

EVIDENCE FOR COLLAPSING FIELDS IN THE CORONA AND PHOTOSPHERE DURING THE 2011 FEBRUARY 15 X2.2 FLARE: SDO/AIA AND HMI OBSERVATIONS

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

Gosain, S., E-mail: sgosain@nso.edu; Udaipur Solar Observatory, P.O. Box 198, Dewali, Udaipur, Rajasthan 313001

2012-04-10

We use high-resolution Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly observations to study the evolution of the coronal loops in a flaring solar active region, NOAA 11158. We identify three distinct phases of the coronal loop dynamics during this event: (1) slow-rise phase: slow rising motion of the loop-tops prior to the flare in response to the slow rise of the underlying flux rope; (2) collapse phase: sudden contraction of the loop-tops, with the lower loops collapsing earlier than the higher loops; and (3) oscillation phase: the loops exhibit global kink oscillations after the collapse phase at different periods, with themore » period decreasing with the decreasing height of the loops. The period of these loop oscillations is used to estimate the field strength in the coronal loops. Furthermore, we also use SDO/Helioseismic and Magnetic Imager (HMI) observations to study the photospheric changes close to the polarity inversion line (PIL). The longitudinal magnetograms show a stepwise permanent decrease in the magnetic flux after the flare over a coherent patch along the PIL. Furthermore, we examine the HMI Stokes I, Q, U, V profiles over this patch and find that the Stokes-V signal systematically decreases while the Stokes-Q and U signals increase after the flare. These observations suggest that close to the PIL the field configuration became more horizontal after the flare. We also use HMI vector magnetic field observations to quantify the changes in the field inclination angle and find an inward collapse of the field lines toward the PIL by {approx}10 Degree-Sign . These observations are consistent with the 'coronal implosion' scenario and its predictions about flare-related photospheric field changes.« less

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

Zhu, S.; Yang, M.; Song, X.L.

The Laves phase precipitation process was characterised by means of field emission scanning electron microscopy to demonstrate its effect on creep rupture strength of steels with a fully ferritic matrix. To eliminate the effects of carbide and carbonitride precipitations so that the creep rupture data can be analysed exclusively in relation to the Laves phase precipitation process, an alloy Fe–9Cr–3Co–3W (wt.%) without C and N additions was used for the study. Creep rupture strengths were measured and volume fraction and particle size of Laves phase precipitates in the ruptured specimens were analysed. It was found that the creep rupture strengthmore » started to collapse (or decrease more rapidly) long before the Laves phase precipitation reached equilibrium fraction. This was related to the onset of the coarsening of Laves phase particles, which precipitated only on grain boundaries and hence contributed little to precipitation strengthening. Creep deformation had no effect either on the precipitation kinetics or on the growth kinetics of Laves phase particles. - Highlights: • Laves phase precipitation at 650 °C was characterised for Fe–9Cr–3W–3Co alloy. • Laves phase precipitated predominantly on grain boundaries. • Creep deformation had no effect on Laves phase precipitation and growth kinetics. • Creep strength started to collapse long before Laves phase precipitation is ended. • Collapse of creep strength was attributed to the coarsening of Laves phase particles.« less

Study of temperature-dependent Raman spectroscopy and electrical properties in [001]-oriented 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3-Mn single crystals

NASA Astrophysics Data System (ADS)

Liu, Xing; Fang, Bijun; Deng, Ji; Yan, Hong; Deng, Hao; Yue, Qingwen; Ding, Jianning; Zhao, Xiangyong; Luo, Haosu

2016-01-01

In this work, the temperature-dependent Raman spectra and electrical properties of the [001]-oriented 0.5 mol. % Mn-doped 0.35Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.30PbTiO3-Mn (PIMNT-Mn) single crystals were investigated. All the unpoled and poled PIMNT-Mn single crystals experience a ferroelectric tetragonal phase to paraelectric cubic phase transition (FET-PC) around 183 °C (TC), which exhibits a second-order transition behavior. Whereas, the poled PIMNT-Mn single crystals exhibit another two dielectric anomalies around 130 °C (TRM) and 148 °C (TMT), in which the ferroelectric rhombohedral phase to ferroelectric monoclinic phase (FER-FEM) and the ferroelectric monoclinic phase to ferroelectric tetragonal phase (FEM-FET) transitions take place, respectively. Both the two ferroelectric phase transitions exhibit a first-order transition behavior. The discontinuous change of the phase degree (θ) and frequencies (fr and fa) around TRM suggest the occurrence of the FER-FEM phase transition in the poled PIMNT-Mn single crystals. The narrowing of the 510 cm-1 and 582 cm-1 Raman modes around the TRM, TMT, and TC temperatures shown in the temperature-dependent Raman spectra suggests their increased ordering of the local structure. The intensity ratio of I272 cm-1/I801 cm-1 increases obviously around the phase transition temperatures (TRM, TMT, and TC), indicating the reduction of the long-range order. The anomalous broadening of the 272 cm-1 Raman mode around the TRM, TMT, and TC temperatures indicates the occurrence of the successive ferroelectric phase transitions (FER-FEM, FEM-FET, and FET-PC) with increasing temperature in the poled PIMNT-Mn single crystals.

Structural properties of zirconia - in-situ high temperature XRD characterization

NASA Astrophysics Data System (ADS)

Kurpaska, Lukasz

2018-07-01

In this work, the effect of high temperature on structural properties of pure zirconium have been investigated. In-situ X-ray diffraction analysis of the oxide layer formed at temperature window 25-600 °C on pure zirconium were performed. Conducted experiment aimed at investigation of the zirconia phases developed on surface of the metallic substrate. Based on the conducted studies, possible stress state (during heating, continuous oxidation and cooling), cell parameters and HWHM factor were analyzed. A tetragonal and monoclinic phases peak shifts and intensities change were observed, suggesting that different phases react in different way upon temperature effect.

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.

Seamless Collapsible Fuel Tanks. Phase 1

DTIC Science & Technology

1982-03-01

TITLE (and Subtitle) 5. TYrE OF REPORT & PERIOD COVERED Final Report: Phase I Seamless Collapsible Fuel Tanks April 1980 - March 1982 6. PERFORMING...KEY WORDS (Continue on reverse side it neceessery nd identify by block number) tubular weaving, pillow tanks, fuel resistance , water resistance ...ends x 28 picks per inch in a plain or basket weave. The fabric is then coated both sides with an appropriate fuel- resistant compound, usually a nitrile

Variation of transition temperatures and residual resistivity ratio in vapor-grown FeSe

DOE PAGES

Böhmer, A. E.; Taufour, V.; Straszheim, W. E.; ...

2016-07-29

The study of the iron-based superconductor FeSe has blossomed with the availability of high-quality single crystals, obtained through flux/vapor-transport growth techniques below the structural transformation temperature of its tetragonal phase, T≈450°C. Here, we report on the variation of sample morphology and properties due to small modifications in the growth conditions. A considerable variation of the superconducting transition temperature T c, from 8.8 K to 3 K, which cannot be correlated with the sample composition, is observed. Instead, we point out a clear correlation between T c and disorder, as measured by the residual resistivity ratio. Notably, the tetragonal-to-orthorhombic structural transitionmore » is also found to be quite strongly disorder dependent (T s≈72–90K) and linearly correlated with T c.« less

Structure of tetragonal martensite in the In95.42Cd4.58 cast alloy

NASA Astrophysics Data System (ADS)

Khlebnikova, Yu. V.; Egorova, L. Yu.; Rodionov, D. P.; Kazantsev, V. A.

2017-11-01

The structure of martensite in the In95.42Cd4.58 alloy has been studied by metallography, X-ray diffraction, dilatometry, and transmission electron microscopy. It has been shown that a massive structure built of colonies of tetragonal lamellar plates divided by a twin boundary {101}FCT is formed in the alloy under cooling below the martensite FCC → FCT transition temperature. The alloy recrystallizes after a cycle of FCT → FCC → FCT transitions with a decrease in the grain size by several times compared with the initial structure such fashion that the size of massifs and individual martensite lamella in the massif correlates with the change in the size of the alloy grain. Using thermal cycling, it has been revealed that the alloy tends to stabilize the high-temperature phase.

Investigations on composition and morphology of electrochemical alumina and alumina yttria stabilised zirconia deposits

NASA Astrophysics Data System (ADS)

El Hajjaji, S.; Manov, S.; Roy, J.; Aigouy, T.; Ben Bachir, A.; Aries, L.

2001-08-01

Conversion coatings modified by deposits of electrolytic alumina added or not with yttria and/or zirconia, have been studied which are well known for their resistance to chemical attack and high temperature. Conversion coating, characterised by a particular morphology and strong interfacial adhesion with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. Zirconia-alumina coating behaviour at 1000°C is similar to that of alumina coating; from 800°C, the chromium diffuses from the stainless steel through the electrolytic refractory coating up to the external interface, provokes discontinuities and can modify its protective character. Yttrium stabilises the cubic and the tetragonal form of the zirconia; so, during cooling, the phase transformation near 1000°C of tetragonal zirconia to monoclinic form cannot take place.

High pressure spectroscopic studies of phase transition in VO2

NASA Astrophysics Data System (ADS)

Basu, Raktima; Mishra, K. K.; Ravindran, T. R.; Dhara, Sandip

2018-04-01

Vanadium dioxide (VO2) exhibits a reversible first-order metal to insulator transition (MIT) at a technologically important temperature of 340K. A structural phase transition (SPT) from monoclinic M1 to rutile tetragonal R is also reported via another two intermediate phases of monoclinic M2 and triclinic T. Metastable monoclinic M2 phase of VO2 was synthesized by Mg doping in the vapour transport process. Raman spectroscopic measurements were carried out at high pressure on V1-xMgxO2 microrods. Two reversible structural phase transitions from monoclinic M2 to triclinic T at 1.6 GPa and T to monoclinic M1 at 3.2 GPa are observed and are explained by structural relaxation of the strained phases.

Volovik effect and Fermi-liquid behavior in the s -wave superconductor CaPd 2 As 2 :   As 75 NMR-NQR measurements

DOE PAGES

Ding, Q. -P.; Wiecki, P.; Anand, V. K.; ...

2016-04-07

The electronic and magnetic properties of the collapsed-tetragonal CaPd 2As 2 superconductor (SC) with a transition temperature of 1.27 K have been investigated by 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements. The temperature (T) dependence of the nuclear spin lattice relaxation rates (1/T 1) and the Knight shifts indicate the absence of magnetic correlations in the normal state. In the SC state, 1/T 1 measured by 75As NQR shows a clear Hebel-Slichter (HS) peak just below T c and decreases exponentially at lower T, confirming a conventional s-wave SC. Additionally, the Volovik effect, also known asmore » the Doppler shift effect, has been clearly evidenced by the observation of the suppression of the HS peak with applied magnetic field.« less

Volovik effect and Fermi-liquid behavior in the s -wave superconductor CaPd 2 As 2 :   As 75 NMR-NQR measurements

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

Ding, Q. -P.; Wiecki, P.; Anand, V. K.

The electronic and magnetic properties of the collapsed-tetragonal CaPd 2As 2 superconductor (SC) with a transition temperature of 1.27 K have been investigated by 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements. The temperature (T) dependence of the nuclear spin lattice relaxation rates (1/T 1) and the Knight shifts indicate the absence of magnetic correlations in the normal state. In the SC state, 1/T 1 measured by 75As NQR shows a clear Hebel-Slichter (HS) peak just below T c and decreases exponentially at lower T, confirming a conventional s-wave SC. Additionally, the Volovik effect, also known asmore » the Doppler shift effect, has been clearly evidenced by the observation of the suppression of the HS peak with applied magnetic field.« less

Phase collapse and revival of a 1-mode Bose-Einstein condensate induced by an off-resonant optical probe field and superselection rules

NASA Astrophysics Data System (ADS)

Arruda, L. G. E.; Prataviera, G. A.; de Oliveira, M. C.

2018-02-01

Phase collapse and revival for Bose-Einstein condensates are nonlinear phenomena appearing due to atomic collisions. While it has been observed in a general setting involving many modes, for one-mode condensates its occurrence is forbidden by the particle number superselection rule (SSR), which arises because there is no phase reference available. We consider a single mode atomic Bose-Einstein condensate interacting with an off-resonant optical probe field. We show that the condensate phase revival time is dependent on the atom-light interaction, allowing optical control on the atomic collapse and revival dynamics. Incoherent effects over the condensate phase are included by considering a continuous photo-detection over the probe field. We consider conditioned and unconditioned photo-counting events and verify that no extra control upon the condensate is achieved by the probe photo-detection, while further inference of the atomic system statistics is allowed leading to a useful test of the SSR on particle number and its imposition on the kind of physical condensate state.

Al-, Y-, and La-doping effects favoring intrinsic and field induced ferroelectricity in HfO2: A first principles study

NASA Astrophysics Data System (ADS)

Materlik, Robin; Künneth, Christopher; Falkowski, Max; Mikolajick, Thomas; Kersch, Alfred

2018-04-01

III-valent dopants have shown to be most effective in stabilizing the ferroelectric, crystalline phase in atomic layer deposited, polycrystalline HfO2 thin films. On the other hand, such dopants are commonly used for tetragonal and cubic phase stabilization in ceramic HfO2. This difference in the impact has not been elucidated so far. The prospect is a suitable doping to produce ferroelectric HfO2 ceramics with a technological impact. In this paper, we investigate the impact of Al, Y, and La doping, which have experimentally proven to stabilize the ferroelectric Pca21 phase in HfO2, in a comprehensive first-principles study. Density functional theory calculations reveal the structure, formation energy, and total energy of various defects in HfO2. Most relevant are substitutional electronically compensated defects without oxygen vacancy, substitutional mixed compensated defects paired with a vacancy, and ionically compensated defect complexes containing two substitutional dopants paired with a vacancy. The ferroelectric phase is strongly favored with La and Y in the substitutional defect. The mixed compensated defect favors the ferroelectric phase as well, but the strongly favored cubic phase limits the concentration range for ferroelectricity. We conclude that a reduction of oxygen vacancies should significantly enhance this range in Y doped HfO2 thin films. With Al, the substitutional defect hardly favors the ferroelectric phase before the tetragonal phase becomes strongly favored with the increasing concentration. This could explain the observed field induced ferroelectricity in Al-doped HfO2. Further Al defects are investigated, but do not favor the f-phase such that the current explanation remains incomplete for Al doping. According to the simulation, doping alone shows clear trends, but is insufficient to replace the monoclinic phase as the ground state. To explain this fact, some other mechanism is needed.

High-temperature structural phase transitions in neighborite: a high-resolution neutron powder diffraction investigation

NASA Astrophysics Data System (ADS)

Knight, Kevin S.; Price, G. David; Stuart, John A.; Wood, Ian G.

2015-01-01

The nature of the apparently continuous structural phase transition at 1,049 K in the perovskite-structured, MgSiO3 isomorph, neighborite (NaMgF3), from the orthorhombic ( Pbnm) hettotype phase to the cubic () aristotype structure, has been re-investigated using high-resolution, time-of-flight neutron powder diffraction. Using data collected at 1 K intervals close to the nominal phase transition temperature, the temperature dependence of the intensities of superlattice reflections at the M point and the R point of the pseudocubic Brillouin zone indicate the existence of a new intermediate tetragonal phase in space group P4/ mbm, with a narrow phase field extending from ~1,046.5 to ~1,048.5 K, at ambient pressure. Group theoretical analysis shows that the structural transitions identified in this study, Pbnm- P4/ mbm, and P4/ mbm-, are permitted to be second order. The observation of the tetragonal phase resolves the longstanding issue of why the high-temperature phase transition, previously identified as Pbnm-, and which would be expected to be first order under Landau theory, is in fact found to be continuous. Analysis of the pseudocubic shear strain shows it to vary with a critical exponent of 0.5 implying that the phase transition from Pbnm to P4/ mbm is tricritical in character. The large librational modes that exist in the MgF6 octahedron at high temperature, and the use of Gaussian probability density functions to describe atomic displacements, result in apparent bond shortening in the Mg-F distances, making mode amplitude determination an unreliable method for determination of the critical exponent from internal coordinates. Crystal structures are reported for the three phases of NaMgF3 at 1,033 K ( Pbnm), 1,047 K ( P4/ mbm) and 1,049 K ().

Structural and elastic properties of InX (X = P, As, Sb) at pressure and room temperature

NASA Astrophysics Data System (ADS)

Pawar, Pooja; Singh, Sadhna

2018-06-01

We have investigated the pressure-induced phase transition of InX (X = P, As, Sb) from Zinc-Blende (ZB) to NaCl structure by using realistic interaction potential model involving the effect of temperature. This model consists of Coulomb interaction, three-body interaction and short-range overlap repulsive interaction upto the second nearest neighbor involving temperature. Phase-transition pressure is associated with a sudden collapse in volume, showing the incidence of first-order phase transition. The phase-transition pressure is associated with volume collapses, and the elastic constants obtained from the present model indicate good agreement with the available experimental and theoretical data.

Effect of Rubidium Incorporation on the Structural, Electrical, and Photovoltaic Properties of Methylammonium Lead Iodide-Based Perovskite Solar Cells.

PubMed

Park, Ik Jae; Seo, Seongrok; Park, Min Ah; Lee, Sangwook; Kim, Dong Hoe; Zhu, Kai; Shin, Hyunjung; Kim, Jin Young

2017-12-06

We report the electrical properties of rubidium-incorporated methylammonium lead iodide ((Rb x MA 1-x )PbI 3 ) films and the photovoltaic performance of (Rb x MA 1-x )PbI 3 film-based p-i-n-type perovskite solar cells (PSCs). The incorporation of a small amount of Rb + (x = 0.05) increases both the open circuit voltage (V oc ) and the short circuit photocurrent density (J sc ) of the PSCs, leading to an improved power conversion efficiency (PCE). However, a high fraction of Rb + incorporation (x = 0.1 and 0.2) decreases the J sc and thus the PCE, which is attributed to the phase segregation of the single tetragonal perovskite phase to a MA-rich tetragonal perovskite phase and a RbPbI 3 orthorhombic phase at high Rb fractions. Conductive atomic force microscopic and admittance spectroscopic analyses reveal that the single-phase (Rb 0.05 MA 0.95 )PbI 3 film has a high electrical conductivity because of a reduced deep-level trap density. We also found that Rb substitution enhances the diode characteristics of the PSC, as evidenced by the reduced reverse saturation current (J 0 ). The optimized (Rb x MA 1-x )PbI 3 PSCs exhibited a PCE of 18.8% with negligible hysteresis in the photocurrent-voltage curve. The results from this work enhance the understanding of the effect of Rb incorporation into organic-inorganic hybrid halide perovskites and enable the exploration of Rb-incorporated mixed perovskites for various applications, such as solar cells, photodetectors, and light-emitting diodes.

Biaxial stress driven tetragonal symmetry breaking and high-temperature ferromagnetic semiconductor from half-metallic CrO2

NASA Astrophysics Data System (ADS)

Xiao, Xiang-Bo; Liu, Bang-Gui

2018-03-01

It is highly desirable to combine the full spin polarization of carriers with modern semiconductor technology for spintronic applications. For this purpose, one needs good crystalline ferromagnetic (or ferrimagnetic) semiconductors with high Curie temperatures. Rutile CrO2 is a half-metallic spintronic material with Curie temperature 394 K and can have nearly full spin polarization at room temperature. Here, we find through first-principles investigation that when a biaxial compressive stress is applied on rutile CrO2, the density of states at the Fermi level decreases with the in-plane compressive strain, there is a structural phase transition to an orthorhombic phase at the strain of -5.6 % , and then appears an electronic phase transition to a semiconductor phase at -6.1 % . Further analysis shows that this structural transition, accompanying the tetragonal symmetry breaking, is induced by the stress-driven distortion and rotation of the oxygen octahedron of Cr, and the half-metal-semiconductor transition originates from the enhancement of the crystal field splitting due to the structural change. Importantly, our systematic total-energy comparison indicates the ferromagnetic Curie temperature remains almost independent of the strain, near 400 K. This biaxial stress can be realized by applying biaxial pressure or growing the CrO2 epitaxially on appropriate substrates. These results should be useful for realizing full (100%) spin polarization of controllable carriers as one uses in modern semiconductor technology.

Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys

NASA Astrophysics Data System (ADS)

Jin, Y.; Kharel, P.; Lukashev, P.; Valloppilly, S.; Staten, B.; Herran, J.; Tutic, I.; Mitrakumar, M.; Bhusal, B.; O'Connell, A.; Yang, K.; Huh, Y.; Skomski, R.; Sellmyer, D. J.

2016-08-01

The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L21 structure with small disorder. The cubic phase of CoFeCrSi was found to be highly stable against heat treatment, but CoFeCrGe disintegrated into other new compounds when the temperature reached 402 °C (675 K). Although the first-principle calculation predicted the possibility of tetragonal phase in CoFeCrGe, the tetragonal phase could not be stabilized experimentally. Both CoFeCrSi and CoFeCrGe compounds showed ferrimagnetic spin order at room temperature and have Curie temperatures (TC) significantly above room temperature. The measured TC for CoFeCrSi is 790 K but that of CoFeCrGe could not be measured due to its dissociation into new compounds at 675 K. The saturation magnetizations of CoFeCrSi and CoFeCrGe are 2.82 μB/f.u. and 2.78 μB/f.u., respectively, which are close to the theoretically predicted value of 3 μB/f.u. for their half-metallic phases. The calculated band gaps for CoFeCrSi and CoFeCrGe are, respectively, 1 eV and 0.5 eV. These materials have potential for spintronic device applications, as they exhibit half-metallic electronic structures with large band gaps, and Curie temperatures significantly above room temperature.

Geology and evolution of lakes in north-central Florida

USGS Publications Warehouse

Kindinger, J.L.; Davis, J.B.; Flocks, J.G.

1999-01-01

Fluid exchange between surficial waters and groundwater in karst environments, and the processes that control exchange, are of critical concern to water management districts and planners. High-resolution seismic data were collected from 30 lakes of north-central Florida. In each case study, lake structure and geomorphology were controlled by solution and/or mechanical processes. Processes that control lake development are twofold: (1) karstification or dissolution of the underlying limestone, and (2) the collapse, subsidence, or slumping of overburden to form sinkholes. Initial lake formation is directly related to the karst topography of the underlying host limestone. Case studies have shown that lakes can be divided by geomorphic types into progressive developmental phases: (1) active subsidence or collapse phase (young); (2) transitional phase (middle age); (3) baselevel phase (mature); and (4) polje (drowned prairie) - broad flat-bottom that have one or all phases of sinkhole. Using these criteria, Florida lakes can be classified by size, fill, subsurface features, and geomorphology.Fluid exchange between surficial waters and groundwater in karst environments, and the processes that control exchange, are of critical concern to water management districts and planners. High-resolution seismic data were collected from 30 lakes of north-central Florida. In each case study, lake structure and geomorphology were controlled by solution and/or mechanical processes. Processes that control lake development are twofold: (1) karstification or dissolution of the underlying limestone, and (2) the collapse, subsidence, or slumping of overburden to form sinkholes. Initial lake formation is directly related to the karst topography of the underlying host limestone. Case studies have shown that lakes can be divided by geomorphic types into progressive developmental phased: (1) active subsidence or collapse phase (young); (2) transitional phase (middle age); (3) baselevel phase (mature); and (4) polje (drowned prairie) - broad flat-bottom that have one or all phases of sinkhole. Using these criteria, Florida lakes can be classified by size, fill, subsurface features, and geomorphology.

Phase diagram and equation of state of praseodymium at high pressures and temperatures

NASA Astrophysics Data System (ADS)

Baer, Bruce J.; Cynn, Hyunchae; Iota, Valentin; Yoo, Choong-Shik; Shen, Guoyin

2003-04-01

The phase diagram for praseodymium (Pr) has been determined for pressures between 5 and 60 GPa and temperatures between 295 and 830 K using both in situ energy- and angle-dispersive x-ray diffraction with externally heated diamond-anvil cells. Mineral oil and argon were alternatively used as pressure media in order to compare conflicting results in the literature and to ensure the validity of mineral oil as an inert medium. Evidence for the presence of an, as yet, unidentified phase (denoted Pr-VI) above 675 K has been observed, whereas no compelling evidence has been observed for the existence of the recently reported monoclinic phase (Pr-V). The new constraints of the phase diagram, therefore, suggest that the phase transitions occur as Pr-I(dhcp)→Pr-II(fcc)→Pr-VI→Pr-IV(α-U) above approximately 700 K. Additionally, there is a Pr-III(distorted fcc), Pr-VI, and Pr-IV triple point at approximately 675 K and 23.8 GPa. Temperature-dependent equations of state have been determined, allowing the temperature-dependent volume collapse at the transition between Pr-III and Pr-IV to be calculated. We report a linear decrease of the volume collapse along the Pr-III to Pr-IV boundary with temperature, ΔV/V (%)=16.235-0.0156[T(K)]; the extrapolation indicates that the volume collapse should vanish well below the melting point. With the temperature-dependent equation of state data and new phase diagram we demonstrate that the volume collapse can be accounted for by a change in the multiplicity of Pr atoms as the f electrons go from localized to itinerant.

Temperature-induced local and average structural changes in BaTiO3-xBi(Zn1/2Ti1/2)O3 solid solutions: The origin of high temperature dielectric permittivity

NASA Astrophysics Data System (ADS)

Hou, Dong; Usher, Tedi-Marie; Zhou, Hanhan; Raengthon, Natthaphon; Triamnak, Narit; Cann, David P.; Forrester, Jennifer S.; Jones, Jacob L.

2017-08-01

The existence of local tetragonal distortions is evidenced in the BaTiO3-xBi(Zn1/2Ti1/2)O3 (BT-xBZT) relaxor dielectric material system at elevated temperatures. The local and average structures of BT-xBZT with different compositions are characterized using in situ high temperature total scattering techniques. Using the box-car fitting method, it is inferred that there are tetragonal polar clusters embedded in a non-polar pseudocubic matrix for BT-xBZT relaxors. The diameter of these polar clusters is estimated as 2-3 nm at room temperature. Sequential temperature series fitting shows the persistence of the tetragonal distortion on the local scale, while the average structure transforms to a pseudocubic paraelectric phase at high temperatures. The fundamental origin of the temperature stable permittivity of BT-xBZT and the relationship with the unique local scale structures are discussed. This systematic structural study of the BT-xBZT system provides both insight into the nature of lead-free perovskite relaxors, and advances the development of a wide range of electronics with reliable high temperature performance.

Temperature-induced local and average structural changes in BaTiO 3- xBi(Zn 1/2Ti 1/2)O 3 solid solutions: The origin of high temperature dielectric permittivity

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

Hou, Dong; Usher, Tedi -Marie; Zhou, Hanhan

The existence of local tetragonal distortions is evidenced in the BaTiO 3–xBi(Zn 1/2Ti 1/2)O 3 (BT–xBZT) relaxor dielectric material system at elevated temperatures. The local and average structures of BT-xBZT with different compositions are characterized using in situ high temperature total scattering techniques. Using the box-car fitting method, it is inferred that there are tetragonal polar clusters embedded in a non-polar pseudocubic matrix for BT-xBZT relaxors. The diameter of these polar clusters is estimated as 2–3 nm at room temperature. Sequential temperature series fitting shows the persistence of the tetragonal distortion on the local scale, while the average structure transformsmore » to a pseudocubic paraelectric phase at high temperatures. The fundamental origin of the temperature stable permittivity of BT-xBZT and the relationship with the unique local scale structures are discussed. This systematic structural study of the BT-xBZT system provides both insight into the nature of lead-free perovskite relaxors, and advances the development of a wide range of electronics with reliable high temperature performance.« less

Temperature-induced local and average structural changes in BaTiO 3- xBi(Zn 1/2Ti 1/2)O 3 solid solutions: The origin of high temperature dielectric permittivity

DOE PAGES

Hou, Dong; Usher, Tedi -Marie; Zhou, Hanhan; ...

2017-08-11

The existence of local tetragonal distortions is evidenced in the BaTiO 3–xBi(Zn 1/2Ti 1/2)O 3 (BT–xBZT) relaxor dielectric material system at elevated temperatures. The local and average structures of BT-xBZT with different compositions are characterized using in situ high temperature total scattering techniques. Using the box-car fitting method, it is inferred that there are tetragonal polar clusters embedded in a non-polar pseudocubic matrix for BT-xBZT relaxors. The diameter of these polar clusters is estimated as 2–3 nm at room temperature. Sequential temperature series fitting shows the persistence of the tetragonal distortion on the local scale, while the average structure transformsmore » to a pseudocubic paraelectric phase at high temperatures. The fundamental origin of the temperature stable permittivity of BT-xBZT and the relationship with the unique local scale structures are discussed. This systematic structural study of the BT-xBZT system provides both insight into the nature of lead-free perovskite relaxors, and advances the development of a wide range of electronics with reliable high temperature performance.« less

Nonlinear lower hybrid structures in auroral plasmas: comparison of theory with observations

NASA Astrophysics Data System (ADS)

Robinson, P. A.

1999-01-01

Intense, localized lower hybrid wave structures are widely observed in auroral plasmas, often associated with density depletions. Commonly it is concluded without further analysis that these structures are solitons, collapsing wave packets, or other nonlinear entities. Such conclusions are often not justified on theoretical grounds. This review outlines theoretical constraints on field intensity, wave-packet scale length, timescales, and levels of density perturbations that must be met before nonlinear phenomena such as wave collapse and strong turbulence can occur. These criteria are determined within the framework of the modern nucleation scenario for the maintenance of strong turbulence, which involves collapse and dissipation (burnout) of each wave packet, followed by relaxation of its associated density perturbation, then renucleation of further energy into fields trapped in this relaxing perturbation, often leading to further collapse. The criteria are illustrated by applying them to a range of in situ auroral data that have been commonly interpreted in terms of lower hybrid solitons. It will be shown that the data are consistent with some of these criteria, but violate others if packets are all assumed to be observed in the collapse phase. However, theory and observations are consistent within the full nucleation scenario in which packets spend most of their time in the relaxation and renucleation phases, rather than undergoing collapse or burnout.

Phase transformation in multiferroic Bi5Ti3FeO15 ceramics by temperature-dependent ellipsometric and Raman spectra: An interband electronic transition evidence

NASA Astrophysics Data System (ADS)

Jiang, P. P.; Duan, Z. H.; Xu, L. P.; Zhang, X. L.; Li, Y. W.; Hu, Z. G.; Chu, J. H.

2014-02-01

Thermal evolution and an intermediate phase between ferroelectric orthorhombic and paraelectric tetragonal phase of multiferroic Bi5Ti3FeO15 ceramic have been investigated by temperature-dependent spectroscopic ellipsometry and Raman scattering. Dielectric functions and interband transitions extracted from the standard critical-point model show two dramatic anomalies in the temperature range of 200-873 K. It was found that the anomalous temperature dependence of electronic transition energies and Raman mode frequencies around 800 K can be ascribed to intermediate phase transformation. Moreover, the disappearance of electronic transition around 3 eV at 590 K is associated with the conductive property.

PLUTONIUM-URANIUM ALLOY

DOEpatents

Coffinberry, A.S.; Schonfeld, F.W.

1959-09-01

Pu-U-Fe and Pu-U-Co alloys suitable for use as fuel elements tn fast breeder reactors are described. The advantages of these alloys are ease of fabrication without microcracks, good corrosion restatance, and good resistance to radiation damage. These advantages are secured by limitation of the zeta phase of plutonium in favor of a tetragonal crystal structure of the U/sub 6/Mn type.

Synthesis and structural analysis of Fe doped TiO2 nanoparticles using Williamson Hall and Scherer Model

NASA Astrophysics Data System (ADS)

Patle, L. B.; Labhane, P. K.; Huse, V. R.; Gaikwad, K. D.; Chaudhari, A. L.

2018-05-01

The nanoparticles of Pure and doped Ti1-xFexO were synthesized by modified co-precipitation method successfully with nominal composite of x=0.0, 0.01, 0.03 and 0.05 at room temperature. The precursors were further calcined at 500°C for 6hrs in muffle furnace which results in the formation of different TiO2 phase compositions. The structural analysis carried out by XRD (Bruker D8 Cu-Kα1). X-ray peak broadening analysis was used to evaluate the crystalline sizes, the lattice parameters, atomic packing fraction, c/a ratio, X-ray density and Volume of unit cell. The Williamson Hall analysis is used to find grain size and Strain of prepared TiO2 nano particles. Crystalline TiO2 with a Tetragonal Anatase phase is confirmed by XRD results. The grain size of pure and Fe doped samples were found in the range of 10nm to 18nm. All the physical parameters of anatase tetragonal TiO2 nanoparticles were calculated more precisely using modified W-H plot a uniform deformation model (UDM). The results calculated from both the techniques were approximately similar.

Metastable α-AgVO3 microrods as peroxidase mimetics for colorimetric determination of H2O2.

PubMed

Wang, Yi; Zhang, Dun; Wang, Jin

2017-12-01

Single phase metastable α-AgVO 3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion were synthesized by direct coprecipitation at room temperature. They are shown to be viable peroxidase mimics that catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine in the presence of H 2 O 2 . Kinetic analysis indicated typical Michaelis-Menten catalytic behavior. The findings were used to design a colorimetric assay for H 2 O 2 , best measured at 652 nm. The method has a linear response in the 60 to 200 μM H 2 O 2 concentration range, with a 2 μM detection limit. Benefitting from the chemical stability of the microrods, the method is well reproducible. It also is easily performed and highly specific. Graphic abstract Single phase metastable α-AgVO 3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion can efficiently catalyze the oxidation reaction of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H 2 O 2 to produce a blue color change.

Dielectric properties of (K0.5Na0.5)NbO3-(Bi0.5Li0.5)ZrO3 lead-free ceramics as high-temperature ceramic capacitors

NASA Astrophysics Data System (ADS)

Yan, Tianxiang; Han, Feifei; Ren, Shaokai; Ma, Xing; Fang, Liang; Liu, Laijun; Kuang, Xiaojun; Elouadi, Brahim

2018-04-01

(1 - x)K0.5Na0.5NbO3- x(Bi0.5Li0.5)ZrO3 (labeled as (1 - x)KNN- xBLZ) lead-free ceramics were fabricated by a solid-state reaction method. A research was conducted on the effects of BLZ content on structure, dielectric properties and relaxation behavior of KNN ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, an orthorhombic-tetragonal phase coexistence was identified for x = 0.03, a tetragonal phase was determined for x = 0.05, and a single rhombohedral structure occurred at x = 0.08. The 0.92KNN-0.08BLZ ceramic exhibits a high and stable permittivity ( 1317, ± 15% variation) from 55 to 445 °C and low dielectric loss (≤ 6%) from 120 to 400 °C, which is hugely attractive for high-temperature capacitors. Activation energies of both high-temperature dielectric relaxation and dc conductivity first increase and then decline with the increase of BLZ, which might be attributed to the lattice distortion and concentration of oxygen vacancies.

Crystal structures and transition mechanism of VO{sub 2}(A)

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

Oka, Yoshio; Yao, Takeshi; Yamamoto, Naoichi

1998-12-01

Structures of VO{sub 2}(A) have been redetermined by single-crystal diffractometry for low- (LTP) and high-temperature (HTP) phases at 298 and 473 K, respectively. The LTP adopts the tetragonal system P4/ncc with a = 8.4403(9) {angstrom}, c = 7.666(1) {angstrom}, and Z = 16, whereas the HTP adopts the body-centered tetragonal system I4/m with a = 8.476(2) {angstrom}, c = 3.824(2) {angstrom}, and Z = 8. The refinements led to R/R{sub w} = 0.031/0.032 for LTP and 0.012/0.033 for HTP. The structures of both phases consist of edge-sharing VO{sub 6} octahedra and exhibit quite similar oxygen frameworks. Through the transition themore » V{sup 4+}-V{sup 4+} bonding in LTP with a distance of 2.7695(8) {angstrom} is dissociated in HTP to a distance of 3.0794(3) {angstrom}. The transition occurs with cooperative movements of the V atoms, namely, a rotation around the c axis and a shift along the c axis. Strangely, twinning is induced on the LTP to HTP transition but disappears on the reverse transition.« less

The crystal structure and morphology of NiO-YSZ composite that prepared from local zircon concentrate of Bangka Island

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

Rahmawati, F., E-mail: fitria@mipa.uns.ac.id; Apriyani, K.; Heraldy, E.

2016-03-29

In order to increase the economic value of local zircon concentrate from Bangka Island, NiO-YSZ was synthesized from Zirconia, ZrO{sub 2} that was prepared from local zircon concentrate. The NiO-YSZ composite was synthesized by solid state reaction method. XRD analysis equipped with Le Bail refinement was carried out to analyze the crystal structure and cell parameters of the prepared materials. The result showed that zirconia was crystallized in tetragonal structure with a space group of P42/NMC. Yttria-Stabilized-Zirconia (YSZ) was prepared by doping 8% mol yttrium oxide into zirconia and then sintered at 1250°C for 3 hours. Doping of 8% molmore » Yttria allowed phase transformation of zirconia from tetragonal into the cubic structure. Meanwhile, the composite of NiO-YSZ consists of two crystalline phases, i.e. the NiO with cubic structure and the YSZ with cubic structure. SEM analysis of the prepared materials shows that the addition of NiO into YSZ allows the morphology to become more roughness with larger grain size.« less

Study of the transformation sequence on a high temperature martensitic transformation Ni-Mn-Ga-Co shape memory alloy

NASA Astrophysics Data System (ADS)

Recarte, V.; Pérez-Landazábal, J. I.; Sánchez-Alarcos, V.; Rodríguez-Velamazán, J. A.

2014-11-01

Ni-Mn-Ga alloys show the highest magnetic-field-induced strain among ferromagnetic shape memory alloys. A great effort is being done in this alloy system to increase the application temperature range. In this sense, the addition of small amounts of Cobalt to NiMnGa alloys has been proved to increase the MT temperatures through the increase of the electron per atom relation (e/a). In this work, the analysis of the crystal structure of the present phases and the phase transformations has been performed on a Ni-Mn-Ga-Co alloy by neutron diffraction measurements from 10 K to 673 K. The study has been completed by means of calorimetric and magnetic measurements. On cooling the alloy undergoes a martensitic transformation from a face centered cubic structure to a nonmodulated tetragonal martensite. The appearance of intermartensite transformations can be disregarded in the whole temperature range below the martensitic transformation. However, a jump in the unit-cell volume of the tetragonal martensite has been observed at 325 K. Since this temperature is close to the Curie temperature of the alloy both, the structural and magnetic contributions are taken into account to explain the results.

Kinematic fingerprint of core-collapsed globular clusters

NASA Astrophysics Data System (ADS)

Bianchini, P.; Webb, J. J.; Sills, A.; Vesperini, E.

2018-03-01

Dynamical evolution drives globular clusters towards core collapse, which strongly shapes their internal properties. Diagnostics of core collapse have so far been based on photometry only, namely on the study of the concentration of the density profiles. Here, we present a new method to robustly identify core-collapsed clusters based on the study of their stellar kinematics. We introduce the kinematic concentration parameter, ck, the ratio between the global and local degree of energy equipartition reached by a cluster, and show through extensive direct N-body simulations that clusters approaching core collapse and in the post-core collapse phase are strictly characterized by ck > 1. The kinematic concentration provides a suitable diagnostic to identify core-collapsed clusters, independent from any other previous methods based on photometry. We also explore the effects of incomplete radial and stellar mass coverage on the calculation of ck and find that our method can be applied to state-of-art kinematic data sets.

Carbon concentration measurements by atom probe tomography in the ferritic phase of high-silicon steels

DOE PAGES

Rementeria, Rosalia; Poplawsky, Jonathan D.; Aranda, Maria M.; ...

2016-12-19

Current studies using atom probe tomography (APT) show that bainitic ferrite formed at low temperature contains more carbon than what is consistent with the paraequilibrium phase diagram. However, nanocrystalline bainitic ferrite exhibits a non-homogeneous distribution of carbon atoms in arrangements with specific compositions, i.e. Cottrell atmospheres, carbon clusters, and carbides, in most cases with a size of a few nanometers. The ferrite volume within a single platelet that is free of these carbon-enriched regions is extremely small. Proximity histograms can be compromised on the ferrite side, and a great deal of care should be taken to estimate the carbon contentmore » in regions of bainitic ferrite free from carbon agglomeration. For this purpose, APT measurements were first validated for the ferritic phase in a pearlitic sample and further performed for the bainitic ferrite matrix in high-silicon steels isothermally transformed between 200 °C and 350 °C. Additionally, results were compared with the carbon concentration values derived from X-ray diffraction (XRD) analyses considering a tetragonal lattice and previous APT studies. In conclusion, the present results reveal a strong disagreement between the carbon content values in the bainitic ferrite matrix as obtained by APT and those derived from XRD measurements. Those differences have been attributed to the development of carbon-clustered regions with an increased tetragonality in a carbon-depleted matrix.« less

Interdiffusion-driven synthesis of tetragonal chromium (III) oxide on BaTi O3

NASA Astrophysics Data System (ADS)

Asa, M.; Vinai, G.; Hart, J. L.; Autieri, C.; Rinaldi, C.; Torelli, P.; Panaccione, G.; Taheri, M. L.; Picozzi, S.; Cantoni, M.

2018-03-01

Interfaces play a crucial role in the study of novel phenomena emerging at heterostructures comprising metals and functional oxides. For this reason, attention should be paid to the interface chemistry, which can favor the interdiffusion of atomic species and, under certain conditions, lead to the formation of radically different compounds with respect to the original constituents. In this work, we consider Cr/BaTi O3 heterostructures grown on SrTi O3 (100) substrates. Chromium thin films (1-2 nm thickness) are deposited by molecular beam epitaxy on the BaTi O3 layer, and subsequently annealed in vacuum at temperatures ranging from 473 to 773 K. A disordered metallic layer is detected for annealing temperatures up to 573 K, whereas, at higher temperatures, we observe a progressive oxidation of chromium, which we relate to the thermally activated migration of oxygen from the substrate. The chromium oxidation state is +3 and the film shows a defective rocksalt structure, which grows lattice matched on the underlying BaTi O3 layer. One out of every three atoms of chromium is missing, producing an uncommon tetragonal phase with C r2O3 stoichiometry. Despite the structural difference with respect to the ordinary corundum α-C r2O3 phase, we demonstrate both experimentally and theoretically that the electronic properties of the two phases are, to a large extent, equivalent.

High Performance Relaxor-Based Ferroelectric Single Crystals for Ultrasonic Transducer Applications

PubMed Central

Chen, Yan; Lam, Kwok-Ho; Zhou, Dan; Yue, Qingwen; Yu, Yanxiong; Wu, Jinchuan; Qiu, Weibao; Sun, Lei; Zhang, Chao; Luo, Haosu; Chan, Helen L. W.; Dai, Jiyan

2014-01-01

Relaxor-based ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) have drawn much attention in the ferroelectric field because of their excellent piezoelectric properties and high electromechanical coupling coefficients (d33∼2000 pC/N, kt∼60%) near the morphotropic phase boundary (MPB). Ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals also possess outstanding performance comparable with PMN-PT single crystals, but have higher phase transition temperatures (rhombohedral to tetragonal Trt, and tetragonal to cubic Tc) and larger coercive field Ec. Therefore, these relaxor-based single crystals have been extensively employed for ultrasonic transducer applications. In this paper, an overview of our work and perspectives on using PMN-PT and PIN-PMN-PT single crystals for ultrasonic transducer applications is presented. Various types of single-element ultrasonic transducers, including endoscopic transducers, intravascular transducers, high-frequency and high-temperature transducers fabricated using the PMN-PT and PIN-PMN-PT crystals and their 2-2 and 1-3 composites are reported. Besides, the fabrication and characterization of the array transducers, such as phased array, cylindrical shaped linear array, high-temperature linear array, radial endoscopic array, and annular array, are also addressed. PMID:25076222

Strangeness driven phase transitions in compressed baryonic matter and their relevance for neutron stars and core collapsing supernovae

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

Raduta, Ad. R.; Gulminelli, F.; Oertel, M.

2015-02-24

We discuss the thermodynamics of compressed baryonic matter with strangeness within non-relativistic mean-field models with effective interactions. The phase diagram of the full baryonic octet under strangeness equilibrium is built and discussed in connection with its relevance for core-collapse supernovae and neutron stars. A simplified framework corresponding to (n, p, Λ)(+e)-mixtures is employed in order to test the sensitivity of the existence of a phase transition on the (poorely constrained) interaction coupling constants and the compatibility between important hyperonic abundances and 2M{sub ⊙} neutron stars.

Observations of the collapses and rebounds of millimeter-sized lithotripsy bubbles

PubMed Central

Kreider, Wayne; Crum, Lawrence A.; Bailey, Michael R.; Sapozhnikov, Oleg A.

2011-01-01

Bubbles excited by lithotripter shock waves undergo a prolonged growth followed by an inertial collapse and rebounds. In addition to the relevance for clinical lithotripsy treatments, such bubbles can be used to study the mechanics of inertial collapses. In particular, both phase change and diffusion among vapor and noncondensable gas molecules inside the bubble are known to alter the collapse dynamics of individual bubbles. Accordingly, the role of heat and mass transport during inertial collapses is explored by experimentally observing the collapses and rebounds of lithotripsy bubbles for water temperatures ranging from 20 to 60 °C and dissolved gas concentrations from 10 to 85% of saturation. Bubble responses were characterized through high-speed photography and acoustic measurements that identified the timing of individual bubble collapses. Maximum bubble diameters before and after collapse were estimated and the corresponding ratio of volumes was used to estimate the fraction of energy retained by the bubble through collapse. The rebounds demonstrated statistically significant dependencies on both dissolved gas concentration and temperature. In many observations, liquid jets indicating asymmetric bubble collapses were visible. Bubble rebounds were sensitive to these asymmetries primarily for water conditions corresponding to the most dissipative collapses. PMID:22088027

Investigation of phase segregation using Rietveld refinement in Mg doped BaTiO3 solid solutions and their ferroelectric properties

NASA Astrophysics Data System (ADS)

Aanchal, Kaur, Kiranpreet; Singh, Anupinder; Singh, Mandeep

2018-05-01

Ba(1-x) Mgx Ti O3 (BMT) samples were synthesised using solid state reaction route with `x' varying from 0.025 to 0.10. The structural and ferroelectric properties of the bulk samples were investigated. The XRD analysis shows the presence of two phases, the first phase being magnesium doped BT (space group P4mm) and the second phase being Ba2TiO4 (space group Pna21). The tetragonal phase was found to be the major phase in the samples. The double phase Rietveld refinement was done and the weight percentage of orthorhombic phase was found to vary from 3.43% to 6.96% for x varying from 0.025≤x≤0.10. The P - E measurements reveal that all the samples exhibit lossy behaviour.

Influence of surface treatment of yttria-stabilized tetragonal zirconia polycrystal with hot isostatic pressing on cyclic fatigue strength.

PubMed

Iijima, Toshihiko; Homma, Shinya; Sekine, Hideshi; Sasaki, Hodaka; Yajima, Yasutomo; Yoshinari, Masao

2013-01-01

Hot isostatic pressing processed yttria-stabilized tetragonal zirconia polycrystal (HIP Y-TZP) has the potential for application to implants due to its high mechanical performance. The aim of this study was to investigate the influence of surface treatment of HIP Y-TZP on cyclic fatigue strength. HIP Y-TZP specimens were subjected to different surface treatments. Biaxial flexural strength was determined by both static and cyclic fatigue testing. In the cyclic fatigue test, the load was applied at a frequency of 10 Hz for 10(6) cycles in distilled water at 37°C. The surface morphology, roughness, and crystal phase of the surfaces were also evaluated. The cyclic fatigue strength (888 MPa) of HIP Y-TZP with sandblasting and acid-etching was more than twice that of Y-TZP as specified in ISO 13356 for surgical implants (320 MPa), indicating the clinical potential of this material.

Superconductivity in YTE2Ge2 compounds (TE = d-electron transition metal)

NASA Astrophysics Data System (ADS)

Chajewski, G.; Samsel-Czekała, M.; Hackemer, A.; Wiśniewski, P.; Pikul, A. P.; Kaczorowski, D.

2018-05-01

Polycrystalline samples of YTE2Ge2 with TE = Co, Ni, Ru, Rh, Pd and Pt were synthesized and characterized by means of X-ray powder diffraction and low-temperature electrical resistivity and specific heat measurements, supplemented by fully relativistic full-potential local-orbital band structure calculations. We confirm that most of the compounds studied crystallize in a body-centered tetragonal ThCr2S2 -type structure (space group I 4 / mmm) and have three-dimensional Fermi surfaces, while only one of them (YPt2Ge2) forms with a primitive tetragonal CaBe2Ge2 -type unit cell (space group P 4 / nmm) and possesses quasi-two-dimensional Fermi surface sheets with some nesting. Physical properties data show conventional superconductivity in the phases with TE = Co, Pd and Pt, i.e. independently of the structure type (and hence the dimensionality of the Fermi surface).

Microstructure, crystallization and shape memory behavior of titania and yttria co-doped zirconia

DOE PAGES

Zeng, Xiao Mei; Du, Zehui; Schuh, Christopher A.; ...

2015-12-17

Small volume zirconia ceramics with few or no grain boundaries have been demonstrated recently to exhibit the shape memory effect. To explore the shape memory properties of yttria doped zirconia (YDZ), it is desirable to develop large, microscale grains, instead of submicron grains that result from typical processing of YDZ. In this paper, we have successfully produced single crystal micro-pillars from microscale grains encouraged by the addition of titania during processing. Titania has been doped into YDZ ceramics and its effect on the grain growth, crystallization and microscale elemental distribution of the ceramics have been systematically studied. With 5 mol%more » titania doping, the grain size can be increased up to ~4 μm, while retaining a large quantity of the desired tetragonal phase of zirconia. Finally, micro-pillars machined from tetragonal grains exhibit the expected shape memory effects where pillars made from titania-free YDZ would not.« less

Absence of metastable states in strained monoatomic cubic crystals.

NASA Astrophysics Data System (ADS)

Aguayo, Aarón; Mehl, Michael L.; de Coss, Romeo

2005-03-01

The Bain path distortion of a metal with an fcc (bcc) ground state toward the bcc (fcc) structure initially requires an increase in energy, but at some point along the Bain path the energy will again decrease until a local minimum is reached. We have studied the tetragonal distortion (Bain path) of monoatomic cubic crystals, using a combination of parametrized tight-binding and first-principles linearized augmented plane wave calculations. We show that this local minimum is unstable with respect to an elastic distortion, except in the rare case that the minimum is at the bcc (fcc) point on the Bain path. This shows that body-centered-tetragonal phases of these materials, which have been seen in epitaxially grown thin films, must be stabilized by the substrate and cannot be freestanding films. This work was partially supported by Consejo Nacional de Ciencia y Tecnolog'ia (CONACYT, M'exico) under Grant No. 43830-F.

A self-ordered, body-centered tetragonal superlattice of SiGe nanodot growth by reduced pressure CVD

NASA Astrophysics Data System (ADS)

Yamamoto, Yuji; Zaumseil, Peter; Capellini, Giovanni; Schubert, Markus Andreas; Hesse, Anne; Albani, Marco; Bergamaschini, Roberto; Montalenti, Francesco; Schroeder, Thomas; Tillack, Bernd

2017-12-01

Self-ordered three-dimensional body-centered tetragonal (BCT) SiGe nanodot structures are fabricated by depositing SiGe/Si superlattice layer stacks using reduced pressure chemical vapor deposition. For high enough Ge content in the island (>30%) and deposition temperature of the Si spacer layers (T > 700 °C), we observe the formation of an ordered array with islands arranged in staggered position in adjacent layers. The in plane periodicity of the islands can be selected by a suitable choice of the annealing temperature before the Si spacer layer growth and of the SiGe dot volume, while only a weak influence of the Ge concentration is observed. Phase-field simulations are used to clarify the driving force determining the observed BCT ordering, shedding light on the competition between heteroepitaxial strain and surface-energy minimization in the presence of a non-negligible surface roughness.

Low symmetry phase in Pb(Zr0.52Ti0.48)O3 epitaxial thin films with enhanced ferroelectric properties

NASA Astrophysics Data System (ADS)

Yan, Li; Li, Jiefang; Cao, Hu; Viehland, D.

2006-12-01

The authors report the structural and ferroelectric properties of Pb(Zr0.52Ti0.48)O3 (PZT) epitaxial thin films grown on (001), (110), and (111) SrRuO3/SrTiO3 substrates by pulsed laser deposition. A monoclinic C (Mc) phase has been found for (101) films, whereas (001) and (111) ones were tetragonal (T ) and rhombohedral (R), respectively. The authors find that the ferroelectric polarization of the Mc phase is higher than that in either the T or R ones. These results are consistent with predictions (i) of epitaxial phase diagrams and (ii) that the enhanced ferroelectric properties of morphotropic phase boundary PZT are related to a low symmetry monoclinic phase.

The influence of thermal stresses on the phase composition of 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 thick films

NASA Astrophysics Data System (ADS)

Uršič, Hana; Zarnik, Marina Santo; Tellier, Jenny; Hrovat, Marko; Holc, Janez; Kosec, Marija

2011-01-01

The influence of thermal stresses versus the phase composition for 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 (0.65PMN-0.35PT) thick films is being reported. The thermal residual stresses in the films have been calculated using the finite-element method. It has been observed that in 0.65PMN-0.35PT films a compressive stress enhances the thermodynamic stability of the tetragonal phase with the space group P4mm.

In situ Investigation of Magnetism in Metastable Phases of Levitated Fe83 B17 During Solidification

NASA Astrophysics Data System (ADS)

Quirinale, D. G.; Messina, D.; Rustan, G. E.; Kreyssig, A.; Prozorov, R.; Goldman, A. I.

2017-11-01

In situ measurements of structure, density, and magnetization on samples of Fe83 B17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe23 B6 /fcc Fe coherently grown structures and primitive tetragonal Fe3 B metastable phase in addition to characterizing the equilibrium Fe2 B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperature metastable structures.

Solid-solid collapse transition in a two dimensional model molecular system.

PubMed

Singh, Rakesh S; Bagchi, Biman

2013-11-21

Solid-solid collapse transition in open framework structures is ubiquitous in nature. The real difficulty in understanding detailed microscopic aspects of such transitions in molecular systems arises from the interplay between different energy and length scales involved in molecular systems, often mediated through a solvent. In this work we employ Monte-Carlo simulation to study the collapse transition in a model molecular system interacting via both isotropic as well as anisotropic interactions having different length and energy scales. The model we use is known as Mercedes-Benz (MB), which, for a specific set of parameters, sustains two solid phases: honeycomb and oblique. In order to study the temperature induced collapse transition, we start with a metastable honeycomb solid and induce transition by increasing temperature. High density oblique solid so formed has two characteristic length scales corresponding to isotropic and anisotropic parts of interaction potential. Contrary to the common belief and classical nucleation theory, interestingly, we find linear strip-like nucleating clusters having significantly different order and average coordination number than the bulk stable phase. In the early stage of growth, the cluster grows as a linear strip, followed by branched and ring-like strips. The geometry of growing cluster is a consequence of the delicate balance between two types of interactions, which enables the dominance of stabilizing energy over destabilizing surface energy. The nucleus of stable oblique phase is wetted by intermediate order particles, which minimizes the surface free energy. In the case of pressure induced transition at low temperature the collapsed state is a disordered solid. The disordered solid phase has diverse local quasi-stable structures along with oblique-solid like domains.

Solid-solid collapse transition in a two dimensional model molecular system

NASA Astrophysics Data System (ADS)

Singh, Rakesh S.; Bagchi, Biman

2013-11-01

Solid-solid collapse transition in open framework structures is ubiquitous in nature. The real difficulty in understanding detailed microscopic aspects of such transitions in molecular systems arises from the interplay between different energy and length scales involved in molecular systems, often mediated through a solvent. In this work we employ Monte-Carlo simulation to study the collapse transition in a model molecular system interacting via both isotropic as well as anisotropic interactions having different length and energy scales. The model we use is known as Mercedes-Benz (MB), which, for a specific set of parameters, sustains two solid phases: honeycomb and oblique. In order to study the temperature induced collapse transition, we start with a metastable honeycomb solid and induce transition by increasing temperature. High density oblique solid so formed has two characteristic length scales corresponding to isotropic and anisotropic parts of interaction potential. Contrary to the common belief and classical nucleation theory, interestingly, we find linear strip-like nucleating clusters having significantly different order and average coordination number than the bulk stable phase. In the early stage of growth, the cluster grows as a linear strip, followed by branched and ring-like strips. The geometry of growing cluster is a consequence of the delicate balance between two types of interactions, which enables the dominance of stabilizing energy over destabilizing surface energy. The nucleus of stable oblique phase is wetted by intermediate order particles, which minimizes the surface free energy. In the case of pressure induced transition at low temperature the collapsed state is a disordered solid. The disordered solid phase has diverse local quasi-stable structures along with oblique-solid like domains.

The competition of hydrogen-like and isotropic interactions on polymer collapse

NASA Astrophysics Data System (ADS)

Krawczyk, J.; Owczarek, A. L.; Prellberg, T.

2007-09-01

We investigate a lattice model of polymers where the nearest neighbour monomer monomer interaction strengths differ according to whether the local configurations have so-called 'hydrogen-like' formations or not. If the interaction strengths are all the same then the classical θ-point collapse transition occurs on lowering the temperature, and the polymer enters the isotropic liquid drop phase known as the collapsed globule. On the other hand, strongly favouring the hydrogen-like interactions gives rise to an anisotropic folded (solid-like) phase on lowering the temperature. We use Monte Carlo simulations up to a length of 256 to map out the phase diagram in the plane of parameters and determine the order of the associated phase transitions. We discuss the connections to semi-flexible polymers and other polymer models. Importantly, we demonstrate that for a range of energy parameters, two phase transitions occur on lowering the temperature, the second being a transition from the globule state to the crystal state. We argue from our data that this globule-to-crystal transition is continuous in two dimensions in accord with field-theory arguments concerning Hamiltonian walks, but is first order in three dimensions.

Magnetic structures and excitations in CePd2(Al,Ga)2 series: Development of the "vibron" states

NASA Astrophysics Data System (ADS)

Klicpera, M.; Boehm, M.; Doležal, P.; Mutka, H.; Koza, M. M.; Rols, S.; Adroja, D. T.; Puente Orench, I.; Rodríguez-Carvajal, J.; Javorský, P.

2017-02-01

CePd2Al2 -xGax compounds crystallizing in the tetragonal CaBe2Ge2 -type structure (space group P 4 /n m m ) and undergoing a structural phase transition to an orthorhombic structure (C m m e ) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd2Al2 is described by an incommensurate propagation vector k ⃗=(δx,1/2 +δy,0 ) with δx=0.06 and δy=0.04 . The magnetic moments order antiferromagnetically within the a b planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) μB/Ce3 +. CePd2Ga2 reveals a magnetic structure composed of two components: the first is described by the propagation vector k1⃗=(1/2 ,1/2 ,0 ) , and the second one propagates with k2⃗=(0 ,1/2 ,0 ) . The magnetic moments of both components are aligned along the same direction—the orthorhombic [100] direction—and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors k1⃗ and k2⃗ describe also the magnetic structure of substituted CePd2Al2 -xGax compounds, except the one with x =0.1 .CePd2Al1.9Ga0.1 with magnetic structure described by k ⃗ and k1⃗ stays on the border between pure CePd2Al2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd2Al2 , while only two crystal field (CF) excitations are expected from the splitting of ground state J =5/2 of the Ce3 + ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd2Al2 . A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound CePd2Ga2 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the CePd2Al2 -xGax series is discussed and crystal field parameters determined.

Scandia-and-Yttria-Stabilized Zirconia for Thermal Barriers

NASA Technical Reports Server (NTRS)

Mess, Derek

2003-01-01

yttria in suitable proportions has shown promise of being a superior thermal- barrier coating (TBC) material, relative to zirconia stabilized with yttria only. More specifically, a range of compositions in the zirconia/scandia/yttria material system has been found to afford increased resistance to deleterious phase transformations at temperatures high enough to cause deterioration of yttria-stabilized zirconia. Yttria-stabilized zirconia TBCs have been applied to metallic substrates in gas turbine and jet engines to protect the substrates against high operating temperatures. These coatings have porous and microcracked structures, which can accommodate strains induced by thermal-expansion mismatch and thermal shock. The longevity of such a coating depends upon yttria as a stabilizing additive that helps to maintain the zirconia in an yttria-rich, socalled non-transformable tetragonal crystallographic phase, thus preventing transformation to the monoclinic phase with an associated deleterious volume change. However, at a temperature greater than about 1,200 C, there is sufficient atomic mobility that the equilibrium, transformable zirconia phase is formed. Upon subsequent cooling, this phase transforms to the monoclinic phase, with an associated volume change that adversely affects the integrity of the coating. Recently, scandia was identified as a stabilizer that could be used instead of, or in addition to, yttria. Of particular interest are scandia-and-yttria-stabilized zirconia (SYSZ) compositions of about 6 mole percent scandia and 1 mole percent yttria, which have been found to exhibit remarkable phase stability at a temperature of 1,400 C in simple aging tests. Unfortunately, scandia is expensive, so that the problem becomes one of determining whether there are compositions with smaller proportions of scandia that afford the required high-temperature stability. In an attempt to solve this problem, experiments were performed on specimens made with reduced proportions of scandia. The criterion used to judge these specimens was whether they retained the non-transformable tetragonal phase after a severe heat treatment of 140 hours at 1,400 C.

Geologic controls on the formation of lakes in north-central Florida

USGS Publications Warehouse

Kindinger, Jack G.; Davis, Jeffrey B.; Flocks, James G.; Pitman, Janet K.; Carroll, Alan R.

1998-01-01

Fluid exchange between surficial waters and groundwater, as well as the processes that control this exchange, are of critical concern to water management districts and planners. Digital high-resolution seismic systems were used to collect geophysical data from 30 lakes of north-central Florida. Although using seismic profile data in the past has been less than successful, the use of digital technology has increased the potential for success. Seismic profiles collected from the lakes of north-central Florida have shown the potential application of these techniques in understanding the formation of individual lakes. In each case study, lake structure and geomorphology were controlled by solution and/or mechanical processes. Processes that control lake development are twofold: 1) karstification or dissolution of the underlying limestone, and 2) me collapse, subsidence, or slumping of overburden to form sinkholes. Initial lake formation is directly related to the karst topography of the underlying host limestone. Lake size and shape are a factor of the thickness of overburden and size of the collapse or subsidence and/or clustering of depressions allowing for lake development. Lake development is through progressive sequence stages to maturity that can be delineated into geomorphic types. Case studies have shown that lakes can be divided by geomorphic types into progressive developmental phases: (1) active subsidence or collapse phase (young) - the open to partially filled collapse structures typically associated with sink holes; (2) transitional phase (middle age) - the sinkhole is plugged as the voids within the collapse are filled with sediment, periodic reactivation may occur; (3) baselevel phase (mature) - active sinkholes are progressively plugged by the continual erosion of material into the basin, and eventually sediment fills the basins; and (4) polje (drowned prairie) - broad flat-bottom basins located within the epiphreatic zone that are inundated at high stages of the water table and have one or all phases of sinkhole development and many types of karst and karren features. Most lakes in this study have a small diameter (

Direct observation of growth and collapse of a Bose-Einstein condensate with attractive interactions

NASA Astrophysics Data System (ADS)

Gerton, Jordan M.; Strekalov, Dmitry; Prodan, Ionut; Hulet, Randall G.

2000-12-01

Quantum theory predicts that Bose-Einstein condensation of a spatially homogeneous gas with attractive interactions is precluded by a conventional phase transition into either a liquid or solid. When confined to a trap, however, such a condensate can form, provided that its occupation number does not exceed a limiting value. The stability limit is determined by a balance between the self-attractive forces and a repulsion that arises from position-momentum uncertainty under conditions of spatial confinement. Near the stability limit, self-attraction can overwhelm the repulsion, causing the condensate to collapse. Growth of the condensate is therefore punctuated by intermittent collapses that are triggered by either macroscopic quantum tunnelling or thermal fluctuation. Previous observations of growth and collapse dynamics have been hampered by the stochastic nature of these mechanisms. Here we report direct observations of the growth and subsequent collapse of a 7Li condensate with attractive interactions, using phase-contrast imaging. The success of the measurement lies in our ability to reduce the stochasticity in the dynamics by controlling the initial number of condensate atoms using a two-photon transition to a diatomic molecular state.

Identification and characterization of the intermediate phase in hybrid organic-inorganic MAPbI3 perovskite.

PubMed

Guo, Xin; McCleese, Christopher; Kolodziej, Charles; Samia, Anna C S; Zhao, Yixin; Burda, Clemens

2016-03-07

Perovskite films were prepared using single step solution deposition at different annealing temperatures and annealing times. The crystal structure, phases and grain size were investigated with XRD, XPS and SEM/EDX. The prepared films show a typical orientation of tetragonal perovskite phase and a gradual transition at room temperature from the yellow intermediate phase to the black perovskite phase. Films with high purity were obtained by sintering at 100 °C. In addition, the chemical composition and crystal structure of intermediate phase were investigated in detail. FTIR, UV-vis and NMR spectra revealed the occurance of DMF complexes. Interestingly, the intermediate phase could be transformed to the black perovskite phase upon X-ray irradiation. In addition, the recovery of the aged perovskite films from a yellow intermediate phase back to the black perovskite was shown to be viable via heating and X-ray irradiation.

Zirconia changes after grinding and regeneration firing.

PubMed

Hatanaka, Gabriel R; Polli, Gabriela S; Fais, Laiza M G; Reis, José Maurício Dos S N; Pinelli, Lígia A P

2017-07-01

Despite improvements in computer-aided design and computer-aided manufacturing (CAD-CAM) systems, grinding during either laboratory procedures or clinical adjustments is often needed to modify the shape of 3 mol(%) yttria-tetragonal zirconia polycrystal (3Y-TZP) restorations. However, the best way to achieve adjustment is unclear. The purpose of this in vitro study was to evaluate the microstructural and crystallographic phase changes, flexural strength, and Weibull modulus of a 3Y-TZP zirconia after grinding with or without water cooling and regeneration firing. Ninety-six bar-shaped specimens were obtained and divided as follows: as-sintered, control; as-sintered with regeneration firing; grinding without water cooling; grinding and regeneration firing with water cooling; and grinding and regeneration firing. Grinding (0.3 mm) was performed with a 150-μm diamond rotary instrument in a high-speed handpiece. For regeneration firing, the specimens were annealed at 1000°C for 30 minutes. The crystalline phases were evaluated by using x-ray powder diffraction. A 4-point bending test was conducted (10 kN; 0.5 mm/min). The Weibull modulus was used to analyze strength reliability. The microstructure was analyzed by scanning electron microscopy. Data from the flexural strength test were evaluated using the Kruskal-Wallis and Dunn tests (α=.05). Tetragonal-to-monoclinic phase transformation was identified in the ground specimens; R regeneration firing groups showed only the tetragonal phase. The median flexural strength of as-sintered specimens was 642.0; 699.3 MPa for as-sintered specimens with regeneration firing; 770.1 MPa for grinding and water-cooled specimens; 727.3 MPa for specimens produced using water-cooled grinding and regeneration firing; 859.9 MPa for those produced by grinding; and 764.6 for those produced by grinding and regeneration firing; with statistically higher values for the ground groups. The regenerative firing did not affect the flexural strength. Weibull modulus values ranged from 5.3 to 12.4. The SEM images showed semicircular cracks after grinding. Adjustments by grinding in 3Y-TZP frameworks should be performed with water cooling, and regeneration firing should be undertaken to obtain a more reliable material. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Linear electro-optic properties of relaxor-based ferroelectric 0.24Pb(In1/2Nb1/2)O3-(0.76 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

PubMed Central

Wu, Fengmin; Yang, Bin; Sun, Enwei; Liu, Gang; Tian, Hao; Cao, Wenwu

2013-01-01

Linear electro-optic properties of 0.24Pb(In1/2Nb1/2)O3-(0.76 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals, with compositions in the rhombohedral, morphotropic phase boundary (MPB) and tetragonal phases, have been investigated. Very large effective electro-optic coefficient γc (204 pm/V) was observed in a crystal with the MPB composition when it is poled along [001]. The rhombohedral phase (x = 0.27 and 0.30) single crystals poled along [111] direction and tetragonal phase (x = 0.39) single crystal poled along [001] direction are in single domain, and their electro-optic coefficients (γc = 76, 94, and 43 pm/V for the crystals with x = 0.27, 0.30, and 0.39, respectively) were found to be much higher than that of traditional electro-optic single crystal LiNbO3 (γc = 19.9 pm/V). The electro-optic coefficients of the single crystal in the rhombohedral phase have excellent temperature stability in the experimental temperature range of 10–40 °C. The half-wave voltage Vπ was calculated to be much lower (less than 1000 V) than that of LiNbO3 single crystal (2800 V). These superior properties make the ternary relaxor-PT single crystals very promising for electro-optic modulation applications. PMID:23922449

Effect of Rubidium Incorporation on the Structural, Electrical, and Photovoltaic Properties of Methylammonium Lead Iodide-Based Perovskite Solar Cells

DOE PAGES

Park, Ik Jae; Seo, Seongrok; Park, Min Ah; ...

2017-11-10

We report the electrical properties of rubidium-incorporated methylammonium lead iodide ((Rb xMA 1-x)PbI 3) films and the photovoltaic performance of (Rb xMA 1-x)PbI 3 film-based p-i-n-type perovskite solar cells (PSCs). The incorporation of a small amount of Rb + (x = 0.05) increases both the open circuit voltage (V oc) and the short circuit photocurrent density (J sc) of the PSCs, leading to an improved power conversion efficiency (PCE). However, a high fraction of Rb + incorporation (x = 0.1 and 0.2) decreases the J sc and thus the PCE, which is attributed to the phase segregation of the singlemore » tetragonal perovskite phase to a MA-rich tetragonal perovskite phase and a RbPbI 3 orthorhombic phase at high Rb fractions. Conductive atomic force microscopic and admittance spectroscopic analyses reveal that the single-phase (Rb 0.05MA 0.95)PbI 3 film has a high electrical conductivity because of a reduced deep-level trap density. We also found that Rb substitution enhances the diode characteristics of the PSC, as evidenced by the reduced reverse saturation current (J 0). The optimized (Rb xMA 1-x)PbI 3 PSCs exhibited a PCE of 18.8% with negligible hysteresis in the photocurrent-voltage curve. The results from this work enhance the understanding of the effect of Rb incorporation into organic-inorganic hybrid halide perovskites and enable the exploration of Rb-incorporated mixed perovskites for various applications, such as solar cells, photodetectors, and light-emitting diodes.« less

Effect of Rubidium Incorporation on the Structural, Electrical, and Photovoltaic Properties of Methylammonium Lead Iodide-Based Perovskite Solar Cells

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

Park, Ik Jae; Seo, Seongrok; Park, Min Ah

We report the electrical properties of rubidium-incorporated methylammonium lead iodide ((Rb xMA 1-x)PbI 3) films and the photovoltaic performance of (Rb xMA 1-x)PbI 3 film-based p-i-n-type perovskite solar cells (PSCs). The incorporation of a small amount of Rb + (x = 0.05) increases both the open circuit voltage (V oc) and the short circuit photocurrent density (J sc) of the PSCs, leading to an improved power conversion efficiency (PCE). However, a high fraction of Rb + incorporation (x = 0.1 and 0.2) decreases the J sc and thus the PCE, which is attributed to the phase segregation of the singlemore » tetragonal perovskite phase to a MA-rich tetragonal perovskite phase and a RbPbI 3 orthorhombic phase at high Rb fractions. Conductive atomic force microscopic and admittance spectroscopic analyses reveal that the single-phase (Rb 0.05MA 0.95)PbI 3 film has a high electrical conductivity because of a reduced deep-level trap density. We also found that Rb substitution enhances the diode characteristics of the PSC, as evidenced by the reduced reverse saturation current (J 0). The optimized (Rb xMA 1-x)PbI 3 PSCs exhibited a PCE of 18.8% with negligible hysteresis in the photocurrent-voltage curve. The results from this work enhance the understanding of the effect of Rb incorporation into organic-inorganic hybrid halide perovskites and enable the exploration of Rb-incorporated mixed perovskites for various applications, such as solar cells, photodetectors, and light-emitting diodes.« less

Stable Ferroelectric Behavior of Nb-Modified Bi0.5K0.5TiO3-Bi(Mg0.5Ti0.5)O3 Lead-Free Relaxor Ferroelectric Ceramics

NASA Astrophysics Data System (ADS)

Zaman, Arif; Malik, Rizwan Ahmed; Maqbool, Adnan; Hussain, Ali; Ahmed, Tanveer; Song, Tae Kwon; Kim, Won-Jeong; Kim, Myong-Ho

2018-03-01

Crystal structure, dielectric, ferroelectric, piezoelectric, and electric field-induced strain properties of lead-free Nb-modified 0.96Bi0.5K0.5TiO3-0.04Bi(Mg0.5Ti0.5)O3 (BKT-BMT) piezoelectric ceramics were investigated. Crystal structure analysis showed a gradual phase transition from tetragonal to pseudocubic phase with increasing Nb content. The optimal piezoelectric property of small-signal d 33 was enhanced up to ˜ 68 pC/N with a lower coercive field ( E c) of ˜ 22 kV/cm and an improved remnant polarization ( P r) of ˜ 13 μC/cm2 for x = 0.020. A relaxor-like behavior with a frequency-dependent Curie temperature T m was observed, and a high T m around 320°C was obtained in the investigated system. This study suggests that the ferroelectric properties of BKT-BMT was significantly improved by means of Nb substitution. The possible shift of depolarization temperature T d toward high temperature T m may have triggered the spontaneous relaxor to ferroelectric phase transition with long-range ferroelectric order without any traces of a nonergodic relaxor state in contradiction with Bi0.5Na0.5TiO3-based systems. The possible enhancement in ferroelectric and piezoelectric properties near the critical composition x = 0.020 may be attributed to the increased anharmonicity of lattice vibrations which may facilitate the observed phase transition from a low-symmetry tetragonal to a high-symmetry cubic phase with a decrease in the lattice anisotropy of an undoped sample. This highly flexible (at a unit cell level) narrow compositional range triggers the enhancement of d 33 and P r values.

Observation of Superconductivity in Tetragonal FeS.

PubMed

Lai, Xiaofang; Zhang, Hui; Wang, Yingqi; Wang, Xin; Zhang, Xian; Lin, Jianhua; Huang, Fuqiang

2015-08-19

The possibility of superconductivity in tetragonal FeS has attracted considerable interest because of its similarities to the FeSe superconductor. However, all efforts made to pursue superconductivity in tetragonal FeS have failed so far, and it remains controversial whether tetragonal FeS is metallic or semiconducting. Here we report the observation of superconductivity at 5 K in tetragonal FeS that is synthesized by the hydrothermal reaction of iron powder with sulfide solution. The obtained samples are highly crystalline and less air-sensitive, in contrast to those reported in the literature, which are meta-stable and air-sensitive. Magnetic and electrical properties measurements show that the samples behave as a paramagnetic metal in the normal state and exhibit superconductivity below 5 K. The high crystallinity and the stoichiometry of the samples play important roles in the observation of superconductivity. The present results demonstrate that tetragonal FeS is a promising new platform to realize high-temperature superconductors.

Acoustic transient generation in pulsed holmium laser ablation under water

NASA Astrophysics Data System (ADS)

Asshauer, Thomas; Rink, Klaus; Delacretaz, Guy P.; Salathe, Rene-Paul; Gerber, Bruno E.; Frenz, Martin; Pratisto, Hans; Ith, Michael; Romano, Valerio; Weber, Heinz P.

1994-08-01

In this study the role of acoustical transients during pulsed holmium laser ablation is addressed. For this the collapse of cavitation bubbles generated by 2.12 micrometers Cr:Tm:Ho:YAG laser pulses delivered via a fiber in water is investigated. Multiple consecutive collapses of a single bubble generating acoustic transients are documented. Pulse durations are varied from 130 - 230 microsecond(s) and pulse energies from 20 - 800 mJ. Fiber diameters of 400 and 600 micrometers are used. The bubble collapse behavior is observed by time resolved fast flash photography with 1 microsecond(s) strobe lamp or 5 ns 1064 nm Nd:YAG laser illumination. A PVDF needle probe transducer is used to observe acoustic transients and measure their pressure amplitudes. Under certain conditions, at the end of the collapse phase the bubbles emit spherical acoustic transients of up to several hundred bars amplitude. After the first collapse up to two rebounds leading to further acoustic transient emissions are observed. Bubbles generated near a solid surface under water are attracted towards the surface during their development. The final phase of the collapse generating the acoustic transients takes place directly on the surface, exposing it to maximum pressure amplitudes. Our results indicate a possible mechanism of unwanted tissue damage during holmium laser application in a liquid environment as in arthroscopy or angioplasty that may set limits to the choice of laser pulse duration and energies.

Scanning electron microscopy, X-ray diffraction and thermal analysis study of the TiH{sub 2} foaming agent

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

Mandrino, Djordje, E-mail: djordje.mandrino@imt.si; Paulin, Irena; Skapin, Sreco D.

2012-10-15

The decomposition of commercially available TiH{sub 2} was investigated while performing different thermal treatments. TiH{sub 2} powder, which is widely used as a foaming agent, was heat treated at 450 Degree-Sign C for various times, from 15 min to 120 min. Scanning electron microscopy (SEM) images of the surfaces at different magnifications were obtained and interpreted. A Bragg-Brentano X-ray diffractometer was used to measure the X-ray diffraction (XRD) spectra on all five samples. A close examination of the diffraction spectra showed that for an as-received sample and samples undergoing the longest thermal treatment (1 and 2 h) these spectra canmore » be explained as deriving from cubic TiH{sub 1.924}, while for the other two samples they can be explained as deriving from tetragonal TiH{sub 1.924}. A constant-unit-cell-volume phase transition between the cubic and tetragonal phases in TiH{sub 2-y}-type compounds had been described in the literature. The unit-cell parameters obtained from measured spectra confirm that within the measurement uncertainty the unit-cell volume is indeed constant in all five samples. Thermo-gravimetry (TG) and differential thermal analysis (DTA) measurements were performed on all the samples, showing that the intensity of the dehydrogenation depends on the previous treatment of the TiH{sub 2}. After the thermal analysis XRD of the samples was performed again and the material was found to exhibit a Ti-like unit cell, but slightly enlarged due to the unreleased hydrogen. - Highlights: Black-Right-Pointing-Pointer TiH{sub 2} samples were cubic or tetragonal TiH{sub 1.924} Black-Right-Pointing-Pointer Onset of the hydrogen release temperature increases with the pre-treatment time. Black-Right-Pointing-Pointer Thermal dehydrogenation for the as-prepared TiH{sub 2} is a three-step process. Black-Right-Pointing-Pointer After thermal analysis 2 residual hydrogen TiH{sub x} phases, close to {alpha}Ti, appeared.« less

Pasta phases in core-collapse supernova matter

NASA Astrophysics Data System (ADS)

Pais, Helena; Chiacchiera, Silvia; Providência, Constança

2016-04-01

The pasta phase in core-collapse supernova matter (finite temperatures and fixed proton fractions) is studied within relativistic mean field models. Three different calculations are used for comparison, the Thomas-Fermi (TF), the Coexisting Phases (CP) and the Compressible Liquid Drop (CLD) approximations. The effects of including light clusters in nuclear matter and the densities at which the transitions between pasta configurations and to uniform matter occur are also investigated. The free energy and pressure, in the space of particle number densities and temperatures expected to cover the pasta region, are calculated. Finally, a comparison with a finite temperature Skyrme-Hartree-Fock calculation is drawn.

Structure and properties of U alloys with selected d-metals and their hydrides

NASA Astrophysics Data System (ADS)

Sowa, S.; Kim-Ngan, N.-. T. H.; Krupska, M.; Paukov, M.; Buturlim, V.; Havela, L.

2018-05-01

U-Ti and U-Ru alloys with various Ti, Ru concentrations were prepared using an ultrafast-cooling technique (splat cooling). A phase analysis by X-ray diffraction revealed the presence of the bcc γ-U phase developing with increasing concentration of alloying elements, while the concentration of orthorhombic α-U structure decreases. The tetragonally distorted γ° phase, (existing for 8-10 at. % Ru) is followed by pure cubic γ-U phase (for 12, 15% Ru). For Ti, more than 20 at. % is needed to yield pure γ-U phase. The occurrence of superconductivity was investigated by resistivity and specific heat measurements down to 0.4 K in various magnetic fields. All U-T splats studied become superconducting with Tc not exceeding 2.0 K.

Prediction of novel stable Fe-V-Si ternary phase

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

Nguyen, Manh Cuong; Chen, Chong; Zhao, Xin

Genetic algorithm searches based on a cluster expansion model are performed to search for stable phases of Fe-V-Si ternary. Here, we identify a new thermodynamically, dynamically and mechanically stable ternary phase of Fe 5V 2Si with 2 formula units in a tetragonal unit cell. The formation energy of this new ternary phase is -36.9 meV/atom below the current ternary convex hull. The magnetic moment of Fe in the new structure varies from -0.30-2.52 μ B depending strongly on the number of Fe nearest neighbors. The total magnetic moment is 10.44 μ B/unit cell for new Fe 5V 2Si structure andmore » the system is ordinarily metallic.« less

Prediction of novel stable Fe-V-Si ternary phase

DOE PAGES

Nguyen, Manh Cuong; Chen, Chong; Zhao, Xin; ...

2018-10-28

Genetic algorithm searches based on a cluster expansion model are performed to search for stable phases of Fe-V-Si ternary. Here, we identify a new thermodynamically, dynamically and mechanically stable ternary phase of Fe 5V 2Si with 2 formula units in a tetragonal unit cell. The formation energy of this new ternary phase is -36.9 meV/atom below the current ternary convex hull. The magnetic moment of Fe in the new structure varies from -0.30-2.52 μ B depending strongly on the number of Fe nearest neighbors. The total magnetic moment is 10.44 μ B/unit cell for new Fe 5V 2Si structure andmore » the system is ordinarily metallic.« less

High P-T Raman study of transitions in relaxor multiferroic Pb(Fe 0.5Nb 0.5)O 3

DOE PAGES

Wilfong, Brandon; Ahart, Muhtar; Gramsch, Stephen A.; ...

2015-09-02

The vibrational and structural properties of Pb(Fe 0.5Nb 0.5)O 3 have been investigated using Raman spectroscopy up to 40 GPa at 300 K and from 300 to 415 K at selected pressures. The measurements reveal three phase transitions at 5.5, 8.7 and 24 GPa at room temperature. The temperature dependences of the spectra indicated transitions at 1.5 GPa, at 335 and 365 K. The results support the appearance of an intermediate tetragonal P4mm phase between ferroelectric R3m and paraelectric Pm-3m phases. Furthermore, a P-T phase diagram is proposed that allows further insight into the magnetoelectric coupling present in this material.

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

Orientation dependence of phase diagrams and physical properties in epitaxial Ba0.6Sr0.4TiO3 films

NASA Astrophysics Data System (ADS)

Qiu, J. H.; Zhao, T. X.; Chen, Z. H.; Yuan, N. Y.; Ding, J. N.

2018-04-01

Orientation dependence of phase diagrams and physical properties of Ba0.6Sr0.4TiO3 films are investigated by using a phenomenological Landau-Devonshire theory. New ferroelectric phases, such as the tetragonal a1 phase and the orthorhombic a2 c phase in (110) oriented film and the monoclinic MA phase in (111) oriented film, appear in the "misfit strain-temperature" phase diagrams as compared with (001) oriented film. Moreover, the phase diagrams of (110) and (111) oriented films are more complex than that of (001) oriented film due to the nonlinear coupling terms appeared in the thermodynamic potential. The dielectric and piezoelectric properties largely depend on the misfit strain and orientation. (111) oriented film has the better piezoelectric property than (110) oriented film. Furthermore, the compressive misfit strain is prone to induce the larger piezoelectric property than tensile misfit strain.

Effects of phase transformation on the microstructures and magnetostriction of Fe-Ga and Fe-Ga-Zn ferromagnetic shape memory alloys

NASA Astrophysics Data System (ADS)

Lin, Yin-Chih; Lin, Chien-Feng

2015-05-01

The phase transformation and magnetostriction of bulk Fe73Ga27 and Fe73Ga18Zn9 (at. %) ferromagnetic shape memory alloys (FSMs) were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), and a magnetostrictive-meter setup. For the Fe73Ga27 FSM alloy solution treated at 1100 °C for 4 h and quenched in ice brine, the antiphase boundary segments of the D03 domain were observed in the A2 (disordered) matrix, and the Fe73Ga27 FSM alloy had an optimal magnetostriction (λ‖s = 71 × 10-6 and λ⊥s = -31 × 10-6). In Fe73Ga27 FSM alloy as-quenched, aged at 700 °C for 24 h, and furnace cooled, D03 nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., L10-like martensite) via Bain distortion, and finally L12 (Fe3Ga) structures precipitated, as observed by TEM and XRD. The L10-like martensite and L12 phases in the aged Fe73Ga27 FSM alloy drastically decreased the magnetostriction from positive to negative (λ‖s = -20 × 10-6 and λ⊥s = -8 × 10-6). However, in Fe73Ga18Zn9 FSM alloy as-quenched and aged, the phase transformation of D03 to an intermediate tetragonal martensite phase and precipitation of L12 structures were not found. The results indicate that the aged Fe73Ga18Zn9 FSM alloy maintained stable magnetostriction (λ‖s = 36 × 10-6 and λ⊥s = -31 × 10-6). Adding Zn can improve the ferromagnetic shape memory effect of aged Fe73Ga18Zn9 alloy, which may be useful in application of the alloy in high temperature environments.

Domain and phase change contributions to response in high strain piezoelectric actuators

NASA Astrophysics Data System (ADS)

Cross, L. Eric

2000-09-01

Current solid state actuators are briefly compared to traditional actuator technologies to highlight the major need for enhanced strain capability. For the ferroelectric piezoelectric polycrystal ceramics, the balance of evidence suggests a large entrinsic contribution to the field induced strain from ferroelectric-ferroelastic domain wall motion. Here-to-fore the intrinsic single domain contribution has been derived indirectly from phenomenological analysis. Now, new evidence of a stable monoclinic phase at compositions very close to the MPB suggest that the previous assessment will need to be revised. Actuator behavior in the new lead zinc niobate-lead titanate (PZN:PT) single crystal shows most unusual anisotropic behavior. For 111 oriented field poled crystals in the rhombohedral phase normal low induced strain is observed. For 001 field poled crystals however massive (0.6%) quasi-linear anhysteritic strain can be induced. Since the 001 oriented field in the rhombohedral phase can not drive ferroelastic domain walls it is suggested that the strain must be intrinsic. The suggestion is that it is due to an induced monoclinic phase in which the Ps vector tilts under increasing field up to more than 20° from 111, before the vector switches to the tetragonal 001 direction. Such a polarization rotation mechanism has also been suggested by Fu and Cohen. Calculations of induced single domain strain using measured electrostriction constants agree well with observed behavior. Recent measurements by Park et al. and Wada et al. on single crystal BaTiO3 show strongly enhanced piezoelectricity at temperatures near the ferroelectric phase transitions. Of particular relevance is the inverse experiment forcing the tetragonal over to the rhombohedral phase with high 111 oriented field. From this result it is suggested that both cubic and dodecahedral mirrors participate in the reorientation through orthorhombic to the rhombohedral state giving rise to different value of the induced d33 at different field levels.

Thickness-modulated anisotropic ferromagnetism in Fe-doped epitaxial HfO2 thin films

NASA Astrophysics Data System (ADS)

Liu, Wenlong; Liu, Ming; Zhang, Ruyi; Ma, Rong; Wang, Hong

2017-10-01

Epitaxial tetragonal Fe-doped Hf0.95Fe0.05O2 (FHO) thin films with various thicknesses were deposited on (001)-oriented NdCaAlO4 (NCAO) substrates by using a pulsed laser deposition (PLD) system. The crystal structure and epitaxial nature of the FHO thin films were confirmed by typical x-ray diffraction (XRD) θ-2θ scan and reciprocal space mapping (RSM). The results indicate that two sets of lattice sites exist with two different crystal orientations [(001) and (100)] in the thicker FHO thin films. Further, the intensity of the (100) direction increases with the increase in thicknesses, which should have a significant effect on the anisotropic magnetization of the FHO thin films. Meanwhile, all the FHO thin films possess a tetragonal phase structure. An anisotropy behavior in magnetization has been observed in the FHO thin films. The anisotropic magnetization of the FHO thin films is slowly weakened as the thickness increases. Meanwhile, the saturation magnetization (Ms) of both in-plane and out-of-plane decreases with the increase in the thickness. The change in the anisotropic magnetization and Ms is attributed to the crystal lattice and the variation in the valence of Fe ions. These results indicate that the thickness-modulated anisotropic ferromagnetism of the tetragonal FHO epitaxial thin films is of potential use for the integration of metal-oxide semiconductors with spintronics.

Shock wave interaction with laser-generated single bubbles.

PubMed

Sankin, G N; Simmons, W N; Zhu, S L; Zhong, P

2005-07-15

The interaction of a lithotripter shock wave (LSW) with laser-generated single vapor bubbles in water is investigated using high-speed photography and pressure measurement via a fiber-optic probe hydrophone. The interaction leads to nonspherical collapse of the bubble with secondary shock wave emission and microjet formation along the LSW propagation direction. The maximum pressure amplification is produced during the collapse phase of the bubble oscillation when the compressive pulse duration of the LSW matches with the forced collapse time of the bubble.

Investigation of transport properties of FeTe compound

NASA Astrophysics Data System (ADS)

Lodhi, Pavitra Devi; Solanki, Neha; Choudhary, K. K.; Kaurav, Netram

2018-05-01

Transport properties of FeTe parent compound has been investigated by measurements of electrical resistivity, magnetic susceptibility and Seebeck coefficient. The sample was synthesized through a standard solid state reaction route via vacuum encapsulation and characterized by x-ray diffraction, which indicated a tetragonal phase with space group P4/nmm. The parent FeTe compound does not exhibit superconductivity but shows an anomaly in the resistivity measurement at around 67 K, which corresponds to a structural phase transition along with in the vicinity of a magnetic phase transition. In the low temperature regime, Seebeck coefficient, S(T), exhibited an anomalous dip feature and negative throughout the temperature range, indicating electron-like charge carrier conduction mechanism.

In situ Investigation of Magnetism in Metastable Phases of Levitated Fe 83 B 17 During Solidification

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

Quirinale, D. G.; Messina, D.; Rustan, G. E.

In situ measurements of structure, density, and magnetization on samples of Fe 83 B 17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe 23 B 6 / fcc Fe coherently grown structures and primitive tetragonal Fe 3 B metastable phase in addition to characterizing the equilibrium Fe 2 B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperaturemore » metastable structures.« less

Effect of Biaxial Strain on the Phase Transitions of Ca (Fe1 -xCox)2As2

NASA Astrophysics Data System (ADS)

Böhmer, A. E.; Sapkota, A.; Kreyssig, A.; Bud'ko, S. L.; Drachuck, G.; Saunders, S. M.; Goldman, A. I.; Canfield, P. C.

2017-03-01

We study the effect of applied strain as a physical control parameter for the phase transitions of Ca (Fe1 -xCox)2As2 using resistivity, magnetization, x-ray diffraction, and Fe 57 Mössbauer spectroscopy. Biaxial strain, namely, compression of the basal plane of the tetragonal unit cell, is created through firm bonding of samples to a rigid substrate via differential thermal expansion. This strain is shown to induce a magnetostructural phase transition in originally paramagnetic samples, and superconductivity in previously nonsuperconducting ones. The magnetostructural transition is gradual as a consequence of using strain instead of pressure or stress as a tuning parameter.

Ordered structure of FeGe2 formed during solid-phase epitaxy

NASA Astrophysics Data System (ADS)

Jenichen, B.; Hanke, M.; Gaucher, S.; Trampert, A.; Herfort, J.; Kirmse, H.; Haas, B.; Willinger, E.; Huang, X.; Erwin, S. C.

2018-05-01

Fe3Si /Ge (Fe ,Si ) /Fe3Si thin-film stacks were grown by a combination of molecular beam epitaxy and solid-phase epitaxy (Ge on Fe3Si ). The stacks were analyzed using electron microscopy, electron diffraction, and synchrotron x-ray diffraction. The Ge(Fe,Si) films crystallize in the well-oriented, layered tetragonal structure FeGe2 with space group P 4 m m . This kind of structure does not exist as a bulk material and is stabilized by the solid-phase epitaxy of Ge on Fe3Si . We interpret this as an ordering phenomenon induced by minimization of the elastic energy of the epitaxial film.

Effect of biaxial strain on the phase transitions of Ca ( Fe 1 – x Co x ) 2 As 2

DOE PAGES

Bohmer, A. E.; Sapkota, A.; Kreyssig, A.; ...

2017-03-10

We study the effect of applied strain as a physical control parameter for the phase transitions of Ca(Fe 1–xCo x) 2As 2 using resistivity, magnetization, x-ray diffraction, and 57Fe Mossbauer spectroscopy. Biaxial strain, namely, compression of the basal plane of the tetragonal unit cell, is created through firm bonding of samples to a rigid substrate via differential thermal expansion. This strain is shown to induce a magnetostructural phase transition in originally paramagnetic samples, and superconductivity in previously nonsuperconducting ones. Lastly, the magnetostructural transition is gradual as a consequence of using strain instead of pressure or stress as a tuning parameter.

Electric-field-dependent phase volume fractions and enhanced piezoelectricity near the polymorphic phase boundary of (K0.5Na0.5)1-xLixNbO3 textured ceramics

NASA Astrophysics Data System (ADS)

Ge, Wenwei; Li, Jiefang; Viehland, D.; Chang, Yunfei; Messing, Gary L.

2011-06-01

The structure, ferroelectric and piezoelectric properties of <001> textured (K0.5Na0.5)0.98Li0.02NbO3 ceramics were investigated as a function of temperature and dc bias E. X-ray diffraction revealed an orthorhombic (O) → tetragonal (T) polymorphic phase boundary (PPB). Phase coexistence was found near the PPB over a 30 °C temperature range, where the relative phase volume fractions changed with temperature. Furthermore, increasing E applied along the <001> texture direction resulted in a notable increase in the volume fraction of the T phase at the expense of the O phase, effectively shifting the O → T boundary to lower temperature. An enhancement in the piezoelectric properties was found to accompany this increase in the T volume fraction.

Tailoring the Microstructure of Sol–Gel Derived Hydroxyapatite/Zirconia Nanocrystalline Composites

PubMed Central

2011-01-01

In this study, we tailor the microstructure of hydroxyapatite/zirconia nanocrystalline composites by optimizing processing parameters, namely, introducing an atmosphere of water vapor during sintering in order to control the thermal stability of hydroxyapatite, and a modified sol–gel process that yields to an excellent intergranular distribution of zirconia phase dispersed intergranularly within the hydroxyapatite matrix. In terms of mechanical behavior, SEM images of fissure deflection and the presence of monoclinic ZrO2 content on cracked surface indicate that both toughening mechanisms, stress-induced tetragonal to monoclinic phase transformation and deflection, are active for toughness enhancement. PMID:24764458

The Effect of 24c-Site (A) Cation Substitution on the Tetragonal-Cubic Phase Transition in Li7-xLa3-xAxZr2O12 Garnet-Based Ceramic Electrolyte

DTIC Science & Technology

2013-01-01

with Al [16,20]. In KrogereVink notation, the relationships for Ta and Nb substitution for Zr are as follows [20,22,23]: Ta$ Zr ¼ V0Li (3) Nb ...garnet phase. < CeO2 precipitation at grain boundaries increases grain boundary resistance . < Super-valent cation substitution likely stabilizes the...Introduction Li-ion batteries have played a vital role in the development of current generation mobile devices, microelectronics and electric vehicles [1]. Due

MgF2 monolayer as an anti-reflecting material

NASA Astrophysics Data System (ADS)

Mahida, H. R.; Singh, Deobrat; Sonvane, Yogesh; Gupta, Sanjeev K.; Thakor, P. B.

2017-02-01

The single-layer atomic sheet of magnesium fluoride (MgF2) having 1H and 1T phase structure (hexagonal and tetragonal phase) has been calculated by density functional theory (DFT). Further, we have investigated the structural, electronic and optical properties such as frequency dependent dielectric function, absorption spectra, energy loss spectra, reflectivity, refractive index and optical conductivity of monolayer MgF2 for the direction of parallel and perpendicular electric field polarizations. Our results suggest that monolayer MgF2 provides promising applications in anti-reflection coatings, high-reflective systems and in opto-electronic materials.

About properties of ZrO2 thermal protective coatings obtained from spherical powder mixtures

NASA Astrophysics Data System (ADS)

Berdnik, O. B.; Tsareva, I. N.; Tarasenko, Yu P.

2017-05-01

It is developed the technology of high-energy plasma spraying of the zirconium dioxide (ZrO2) thermal protective coating on the basis of ZrO2 tetragonal and cubic phases with the spheroidal grain shape and the columnar substructure, with the total porosity P = 4 %, the hardness HV = 12 GPa, the roughness parameter R a ˜ 6 μm, the thickness 0.3-3 mm. As a sublayer it is used the heat-resistant coating of “Ni-Co-Cr-Al-Y” system with an intermetallic phase composition and the layered microstructure of the grains.

Local geometric and electronic structures and origin of magnetism in Co-doped BaTiO3 multiferroics

NASA Astrophysics Data System (ADS)

Phan, The-Long; Thang, P. D.; Ho, T. A.; Manh, T. V.; Thanh, Tran Dang; Lam, V. D.; Dang, N. T.; Yu, S. C.

2015-05-01

We have prepared polycrystalline samples BaTi1-xCoxO3 (x = 0-0.1) by solid-state reaction. X-ray diffraction and Raman-scattering studies reveal the phase separation in crystal structure as changing Co-doping content (x). The samples with x = 0-0.01 are single phase in a tetragonal structure. At higher doping contents (x > 0.01), there is the formation and development of a secondary hexagonal phase. Magnetization measurements at room temperature indicate a coexistence of paramagnetic and weak-ferromagnetic behaviors in BaTi1-xCoxO3 samples with x > 0, while pure BaTiO3 is diamagnetic. Both these properties increase with increasing x. Analyses of X-ray absorption spectra recorded from BaTi1-xCoxO3 for the Co and Ti K-edges indicate the presence of Co2+ and Co3+ ions. They locate in the Ti4+ site of the tetragonal and hexagonal BaTiO3 structures. Particularly, there is a shift of oxidation state from Co2+ to Co3+ when Co-doping content increases. We believe that the paramagnetic nature in BaTi1-xCoxO3 samples is due to isolated Co2+ and Co3+ centers. The addition of Co3+ ions enhances the paramagnetic behavior. Meanwhile, the origin of ferromagnetism is due to lattice defects, which is less influenced by the changes caused by the variation in concentration of Co2+ and Co3+ ions.

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

Prosviryakov, A.S., E-mail: pro.alex@mail.ru; Shch

Ground chips of as-cast Al-10 wt.% Zr alloy were subjected to mechanical alloying (MA) with 5 vol.% of nanodiamond addition in a high energy planetary ball-mill. The aim of this work was to investigate the microstructure, phase transformation and mechanical properties of the material both after MA and after subsequent annealing. Optical and transmission electron microscopes were used for morphological and microstructural analysis. The effect of milling time on powder microhardness, Al lattice parameter, lattice microstrain and crystallite size was determined. It was shown that mechanical alloying of as-cast Al-10wt.%Zr alloy during 20 h leads to a complete dissolution ofmore » the primary tetragonal Al{sub 3}Zr crystals in aluminum. At the same time, the powder microhardness increases to 370 HV. Metastable cubic Al{sub 3}Zr phase nanoparticles precipitate from the Al solution due to its decomposition after annealing, however, the Al solid solution remains supersaturated and nanocrystalline. Compression tests at room temperature and at 300 °C showed that the strength values of the hot-pressed samples reach 822 MPa and 344 MPa, respectively. - Highlights: •As-cast Al-10 wt.% Zr alloy was mechanically alloyed with 5 vol.% nanodiamond. •The primary tetragonal Al{sub 3}Zr crystals were completely dissolved in Al after 20 h. •Cubic Al{sub 3}Zr phase nanoparticles precipitated from Al solution after aging. •The aged bulk material showed a high strength at room and elevated temperatures.« less

Symmetry of Highly-Strained BiFeO3 Films in the Ultrathin Regime

NASA Astrophysics Data System (ADS)

Yang, Yongsoo; Senabulya, Nancy; Clarke, Roy; Schlepütz, Christian M.; Beekman, Christianne; Siemons, Wolter; Christen, Hans M.

2014-03-01

At room temperature, highly-strained BiFeO3 (BFO) films grown on LaAlO3 substrates exhibit a monoclinic structure with a giant c/a ratio (~1.3) when the films are thicker than 4 nm. Their structural symmetry can be controlled by adjusting the temperature [Appl. Phys. Express 4, 095801 (2011), Adv. Mater. 25, 5561 (2013)], with a high-temperature tetragonal phase being observed. We report that a structural phase transition can also be achieved by controlling the film thickness: synchrotron x-ray diffraction data shows that the Bragg peak splitting associated with the monoclinic phase disappears as the film thickness decreases below 3 nm, indicating a tetragonal symmetry, but still maintaining the giant c/a ratio. Unlike a similar transition reported for moderately strained BFO grown on SrTiO3 [APL Mater. 1, 052102 (2013)], the half-order Bragg peaks indicate that this transition does not involve a significant change in the octahedral tilt pattern of the film. This suggests that the structural evolution of highly-strained BFO films should be understood in terms of the unique (non-octahedral) oxygen coordination of the Fe ion in this highly-strained BFO, not the corner-connectivity of the oxygen octahedra between the film and the substrate. Funding: U.S. Department of Energy, BES-MSED (U. Michigan: DE-FG02-06ER46273, and at ORNL). Measurements: 13-BMC, 33-IDD, 33-BMC of the Advanced Photon Source, ANL (DE-AC02-06CH11357).

Characterization of SnO2 Film with Al-Zn Doping Using Sol-Gel Dip Coating Techniques

NASA Astrophysics Data System (ADS)

Doyan, A.; Susilawati; Ikraman, N.; Taufik, M.

2018-04-01

Sn1-2x AlxZnxO2 film has been developed using sol-gel dip coating technique. The materials SnCl2.2H2O, AlCl3 and ZnCl2 dissolved in water and ethanol with 5:95 volume ratio. Variations dopant concentration x = 0.000, 0.005, 0.0025, and 0.050. The film was grown with sol concentration 0.4 M, the withdrawal speed of 12 cm/min and sintering at 600 °C for 30 minutes. The characteristics Sn1-2x AlxZnxO2 films with various doping concentration phase were characterized by XRD. The morphological characteristics and the composition of the constituent elements of the film were characterized by SEM-EDX. The characteristics of the shape, structure, and size of the particles were characterized by TEM. The XRD results show that all films have a tetragonal SnO2 rutile phase without any secondary phase with an average particle size in the range 5.14 – 2.09 nm. The SEM results show that the film grown has a smooth morphology with a striped texture (x = 0.00), and there is a crack (x = 0.050). The EDX results show that the composition and distribution of the constituent elements of the film are uniformly distributed. TEM results show that the particle films has tetragonal rutile structure, orthorhombic and amorphous with a spherical shape.

Revealing the optoelectronic and thermoelectric properties of the Zintl quaternary arsenides ACdGeAs{sub 2} (A = K, Rb)

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

Azam, Sikander; Khan, Saleem Ayaz; Goumri-Said, Souraya, E-mail: Souraya.Goumri-Said@chemistry.gatech.edu

Highlights: • Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) are chalcopyrite and semiconductors. • Their direct band gap is suitable for PV, optolectronic and thermoelectric applications. • Combination of DFT and Boltzmann transport theory is employed. • The present arsenides are found to be covalent materials. - Abstract: Chalcopyrite semiconductors have attracted much attention due to their potential implications in photovoltaic and thermoelectric applications. First principle calculations were performed to investigate the electronic, optical and thermoelectric properties of the Zintl tetragonal phase ACdGeAs{sub 2} (A = K, Rb) using the full potential linear augmented plane wave method andmore » the Engle–Vosko GGA (EV–GGA) approximation. The present compounds are found semiconductors with direct band gap and covalent bonding character. The optical transitions are investigated via the dielectric function (real and imaginary parts) along with other related optical constants including refractive index, reflectivity and energy-loss spectrum. Combining results from DFT and Boltzmann transport theory, we reported the thermoelectric properties such as the Seebeck’s coefficient, electrical and thermal conductivity, figure of merit and power factor as function of temperatures. The present chalcopyrite Zintl quaternary arsenides deserve to be explored for their potential applications as thermoelectric materials and for photovoltaic devices.« less

Phase transition hysteresis and anomalous Curie-Weiss behavior of ferroelectric tetragonal tungsten bronzes Ba2RETi2Nb3O15:RE=Nd,Sm

NASA Astrophysics Data System (ADS)

Prades, Marta; Beltrán, Héctor; Masó, Nahum; Cordoncillo, Eloisa; West, Anthony R.

2008-11-01

The ferroelectric tetragonal tungsten bronze (TTB) phases, Ba2RETi2Nb3O15:RE=Nd,Sm, were prepared by low temperature solvothermal synthesis. The permittivity versus temperature data of sintered ceramics show two unusual features: first, a hysteresis of 50-100 °C between values of the Curie temperature Tc on heat-cool cycles and second: a huge depression in the Curie-Weiss temperature T0. Both effects are attributed to the complex nature of their TTB-related crystal structures with different superstructures above and below Tc and the difficulty in nucleating ferroelectric domains on cooling through Tc. Several factors may contribute to the latter difficulty: first, the structures contain two sets of crystallographic sites for the "active" Ti, Nb ions; second, the distribution of Ti and Nb over these two sets of sites is not random but partially ordered; and third, below Tc a weak commensurate superstructure perpendicular to the polar c&barbelow; axis is present, but above Tc a weak incommensurate superstructure in a similar orientation is present. Hence the formation of the ferroelectric structure on cooling requires both nucleation of polar domains involving two sets of cation sites and structural change from an incommensurate to a commensurate supercell.

Dielectric, thermal and Raman spectroscopy studies of lead-free (Na0.5Bi0.5)1-xSrxTiO3 (x = 0, 0.04 and 0.06) ceramics

NASA Astrophysics Data System (ADS)

Suchanicz, J.; Bovtun, V.; Dutkiewicz, E. M.; Konieczny, K.; Sitko, D.; Kluczewska, K.; Wajda, A.; Kalvane, A.; Sternberg, A.

2016-08-01

Lead-free (Na0.5Bi0.5)1-xSrxTiO3 (x = 0, 0.04 and 0.06) ceramics with relative densities above 97% were prepared by solid-state synthesis process. Their dielectric, thermal and Raman properties were studied. X-ray diffraction analysis shows perovskite structure with rhombohedral symmetry at room temperature. Sr doping of Na0.5Bi0.5TiO3 (NBT) results in an increase of the dielectric permittivity, diffusing of the permittivity maximum and its shift toward lower temperatures. The temperature of the rhombohedral-tetragonal phase transition indicated by the differential scanning calorimetry (DSC) peak and relaxational dielectric anomaly near the depolarization temperature are also shifted toward lower temperatures. The observed increase and broadening of the permittivity maximum, enhancement of the dielectric relaxation near the depolarization temperature, broadening of the DSC anomaly related to the rhombohedral-tetragonal phase transition and broadening of the Raman bands with increasing Sr content are attributed to the increase of the degree of cationic disorder and evident enhancement of the relaxor-like features in NBT-xST. This enhancement could play a positive role in the improvement of the piezoelectric performance of NBT-based ceramics.

Magnetic ordering induced giant optical property change in tetragonal BiFeO3

NASA Astrophysics Data System (ADS)

Tong, Wen-Yi; Ding, Hang-Chen; Gong, Shi Jing; Wan, Xiangang; Duan, Chun-Gang

2015-12-01

Magnetic ordering could have significant influence on band structures, spin-dependent transport, and other important properties of materials. Its measurement, especially for the case of antiferromagnetic (AFM) ordering, however, is generally difficult to be achieved. Here we demonstrate the feasibility of magnetic ordering detection using a noncontact and nondestructive optical method. Taking the tetragonal BiFeO3 (BFO) as an example and combining density functional theory calculations with tight-binding models, we find that when BFO changes from C1-type to G-type AFM phase, the top of valance band shifts from the Z point to Γ point, which makes the original direct band gap become indirect. This can be explained by Slater-Koster parameters using the Harrison approach. The impact of magnetic ordering on band dispersion dramatically changes the optical properties. For the linear ones, the energy shift of the optical band gap could be as large as 0.4 eV. As for the nonlinear ones, the change is even larger. The second-harmonic generation coefficient d33 of G-AFM becomes more than 13 times smaller than that of C1-AFM case. Finally, we propose a practical way to distinguish the two AFM phases of BFO using the optical method, which is of great importance in next-generation information storage technologies.

Preparation and study of (1 - x)CuFe2O4-xBaTiO3 (x = 0, 0.1 and 1) composite multiferroics

NASA Astrophysics Data System (ADS)

Murtaza, Tahir; Ali, Javid; Khan, M. S.

2018-07-01

The parent and mixed spinel-perovskite composite of (1 - x)CuFe2O4-xBaTiO3 (x = 0, 0.1 and 1) has been prepared by solid-state reaction method and studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, magnetometry and P-E lope tracer. The XRD results showed the formation of single phase tetragonal spinel CuFe2O4 and tetragonal perovskite BaTiO3 at room temperature, further XRD of composite 0.1CuFe2O4-0.9BaTiO3 reflects the two crystallographic phases with 1:9 ratio. The SEM micrographs show the homogeneous and uniform formation of the samples. Through EDAX analysis, the chemical composition of the sample is found to be same as the nominal composition. The high field Mossbauer data of CuFe2O4 sample shows the ferrimagnetic ordering in the sample. The observed M-H and P-E loops of the composite 0.1CuFe2O4-0.9BaTiO3 sample show the presence of spontaneous magnetization and spontaneous electric polarization indicating the multiferroic nature of the sample.

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

Rementeria, Rosalia; Poplawsky, Jonathan D.; Aranda, Maria M.

Current studies using atom probe tomography (APT) show that bainitic ferrite formed at low temperature contains more carbon than what is consistent with the paraequilibrium phase diagram. However, nanocrystalline bainitic ferrite exhibits a non-homogeneous distribution of carbon atoms in arrangements with specific compositions, i.e. Cottrell atmospheres, carbon clusters, and carbides, in most cases with a size of a few nanometers. The ferrite volume within a single platelet that is free of these carbon-enriched regions is extremely small. Proximity histograms can be compromised on the ferrite side, and a great deal of care should be taken to estimate the carbon contentmore » in regions of bainitic ferrite free from carbon agglomeration. For this purpose, APT measurements were first validated for the ferritic phase in a pearlitic sample and further performed for the bainitic ferrite matrix in high-silicon steels isothermally transformed between 200 °C and 350 °C. Additionally, results were compared with the carbon concentration values derived from X-ray diffraction (XRD) analyses considering a tetragonal lattice and previous APT studies. In conclusion, the present results reveal a strong disagreement between the carbon content values in the bainitic ferrite matrix as obtained by APT and those derived from XRD measurements. Those differences have been attributed to the development of carbon-clustered regions with an increased tetragonality in a carbon-depleted matrix.« less

Ab initio DFT+U study of He atom incorporation into UO(2) crystals.

PubMed

Gryaznov, Denis; Heifets, Eugene; Kotomin, Eugene

2009-09-07

We present and discuss results of the density functional theory (DFT) for perfect UO(2) crystals with He atoms in octahedral interstitial positions therein. We have calculated basic bulk crystal properties and He incorporation energies into the low temperature anti-ferromagnetic UO(2) phase using several exchange-correlation functionals within the spin-polarized local density (LDA) and generalized gradient (GGA) approximations. In all DFT calculations we included the on-site correlation corrections using the Hubbard model (DFT+U approach). We analysed a potential crystalline symmetry reduction from tetragonal down to orthorhombic structure and confirmed the presence of the Jahn-Teller effect in a perfect UO(2). We discuss also the problem of a conducting electronic state arising when He is placed into a tetragonal antiferromagnetic phase of UO(2) commonly used in defect modelling. Consequently, we found a specific monoclinic lattice distortion which allowed us to restore the semiconducting state and properly estimate He incorporation energies. Unlike the bulk properties, the He incorporation energy strongly depends on several factors, including the supercell size, the use of spin polarization, the exchange-correlation functionals and on-site correlation corrections. We compare our results for the He incorporation with the previous shell model and ab initio DFT calculations.

Volume collapse phase transitions in cerium-praseodymium alloys under high pressure

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

Perreault, Christopher S.; Velisavljevic, Nenad; Samudrala, Gopi K.

Cerium-12at%Praseodymium(Ce 0.88Pr 0.12) and Ce-50at%Praseodymium(Ce 0.50Pr 0.50) alloy samples that contain a random solid-solution of Ce (4f1 (J=5/2)) and Pr (4f2 (J=4)) localized f-states have been studied by angle dispersive x-ray diffraction in a diamond anvil cell to a pressure of 65 GPa and 150 GPa respectively using a synchrotron source. Ce 0.88Pr 0.12 alloy crystallizes in a face-centered cubic (γ-phase) structure at ambient conditions, while Ce 0.50Pr 0.50 alloy crystallizes in the double hexagonal close packed (dhcp) structure at ambient conditions. Two distinct volume collapse transitions are observed in Ce 0.88Pr 0.12 alloy at 1.5 GPa and 18 GPamore » with volume change of 8.5% and 3% respectively. In contrast, Ce 0.50Pr 0.50 alloy shows only a single volume collapse of 5.6% at 20 GPa on phase transformation to α-Uranium structure under high pressure. Electrical transport measurements under high pressure show anomalies in electrical resistance at phase transitions for both compositions of this alloy.« less

Volume collapse phase transitions in cerium-praseodymium alloys under high pressure

DOE PAGES

Perreault, Christopher S.; Velisavljevic, Nenad; Samudrala, Gopi K.; ...

2018-06-08

Cerium-12at%Praseodymium(Ce 0.88Pr 0.12) and Ce-50at%Praseodymium(Ce 0.50Pr 0.50) alloy samples that contain a random solid-solution of Ce (4f1 (J=5/2)) and Pr (4f2 (J=4)) localized f-states have been studied by angle dispersive x-ray diffraction in a diamond anvil cell to a pressure of 65 GPa and 150 GPa respectively using a synchrotron source. Ce 0.88Pr 0.12 alloy crystallizes in a face-centered cubic (γ-phase) structure at ambient conditions, while Ce 0.50Pr 0.50 alloy crystallizes in the double hexagonal close packed (dhcp) structure at ambient conditions. Two distinct volume collapse transitions are observed in Ce 0.88Pr 0.12 alloy at 1.5 GPa and 18 GPamore » with volume change of 8.5% and 3% respectively. In contrast, Ce 0.50Pr 0.50 alloy shows only a single volume collapse of 5.6% at 20 GPa on phase transformation to α-Uranium structure under high pressure. Electrical transport measurements under high pressure show anomalies in electrical resistance at phase transitions for both compositions of this alloy.« less

Course 6: Star Formation

NASA Astrophysics Data System (ADS)

Natta, A.

Contents 1 Introduction 2 Collapse of molecular cores 2.1 Giant molecular clouds and cores 2.2 Conditions for collapse 2.3 Free-fall collapse 2.4 Collapse of an isothermal sphere of gas 2.5 Collapse of a slowly rotating core 3 Observable properties of protostars 3.1 Evidence of infall from molecular line profiles 3.2 SEDs of protostars 3.3 The line spectrumof a protostar 4 Protostellar and pre-main-sequence evolution 4.1 The protostellar phase 4.2 Pre-main-sequence evolution 4.3 The birthline 5 Circumstellar disks 5.1 Accretion disks 5.2 Properties of steady accretion disks 5.3 Reprocessing disks 5.4 Disk-star interaction 6 SEDs of disks 6.1 Power-law disks 6.2 Long-wavelength flux and disk mass 6.3 Comparison with TTS observations: Heating mechanism 7 Disk properties from observations 7.1 Mass accretion rate 7.2 Inner radius 7.3 Masses 7.4 Sizes 8 Disk lifetimes 8.1 Ground-based near and mid-infrared surveys 8.2 Mid-infrared ISOCAMsurveys 8.3 ISOPHOT 60 microm survey 8.4 Surveys at millimeter wavelengths 9 Disk evolution 9.1 Can we observe the early planet formation phase? 9.2 Evidence for grain growth 9.3 Evidence of planetesimals 9.4 Where is the diskmass? 10 Secondary or debris disks 11 Summary

Characterizing the collapse of a cavitation bubble cloud in a focused ultrasound field

NASA Astrophysics Data System (ADS)

Maeda, Kazuki; Colonius, Tim

2017-11-01

We study the coherent collapse of clouds of cavitation bubbles generated by the passage of a pulse of ultrasound. In order to characterize such collapse, we conduct a parametric study on the dynamics of a spherical bubble cloud with a radius of r = O(1) mm interacting with traveling ultrasound waves with an amplitude of pa = O(102 -106) Pa and a wavelength of λ = O(1 - 10) mm in water. Bubbles with a radius of O(10) um are treated as spherical, radially oscillating cavities dispersed in continuous liquid phase. The volume of Lagrangian point bubbles is mapped with a regularization kernel as void fraction onto Cartesian grids that defines the Eulerian liquid phase. The flow field is solved using a WENO-based compressible flow solver. We identified that coherent collapse occurs when λ >> r , regardless of the value of pa, while it only occurs for sufficiently high pa when λ r . For the long wavelength case, the results agree with the theory on linearized dynamics of d'Agostino and Brennen (1989). We extend the theory to short wave length case. Finally, we analyze the far-field acoustics scattered by individual bubbles and correlate them with the cloud collapse, for applications to acoustic imaging of bubble cloud dynamics. Funding supported by NIH P01-DK043881.

Simulation of the ultrasound-induced growth and collapse of a near-wall bubble

NASA Astrophysics Data System (ADS)

Boyd, Bradley; Becker, Sid

2017-11-01

In this study, we consider the acoustically driven growth and collapse of a cavitation bubble in a fluid medium exposed to an ultrasound field. The bubble dynamics are modelled using a compressible, inviscid, multiphase model. The numerical scheme consists of a conservative interface capturing scheme which uses the fifth-order WENO reconstruction with a maximum-principle-satisfying and positivity-preserving limiter, and the HLLC approximate Riemann flux. To model the ultrasound input, a moving boundary oscillates through a fixed grid of finite-volume cells. The growth phase of the simulation shows the rapid non-spherical growth of the near-wall bubble. Once the bubble reaches its maximum size and the collapse phase begins, the simulation shows the formation of a jet which penetrates the bubble towards the wall at the later stages of the collapse. For a bubble with an initial radius of 50 μ m and an ultrasound pressure amplitude of 200 kPa, the pressure experienced by the wall increased rapidly nearing the end of the collapse, reaching a peak pressure of 13 MPa. This model is an important development in the field as it represents the physics of acoustic cavitation in more detail than before. This work was supported by the Royal Society of New Zealand's Marsden Fund.

Bubble Proliferation in Shock Wave Lithotripsy Occurs during Inertial Collapse

NASA Astrophysics Data System (ADS)

Pishchalnikov, Yuri A.; McAteer, James A.; Pishchalnikova, Irina V.; Williams, James C.; Bailey, Michael R.; Sapozhnikov, Oleg A.

2008-06-01

In shock wave lithotripsy (SWL), firing shock pulses at slow pulse repetition frequency (0.5 Hz) is more effective at breaking kidney stones than firing shock waves (SWs) at fast rate (2 Hz). Since at fast rate the number of cavitation bubbles increases, it appears that bubble proliferation reduces the efficiency of SWL. The goal of this work was to determine the basis for bubble proliferation when SWs are delivered at fast rate. Bubbles were studied using a high-speed camera (Imacon 200). Experiments were conducted in a test tank filled with nondegassed tap water at room temperature. Acoustic pulses were generated with an electromagnetic lithotripter (DoLi-50). In the focus of the lithotripter the pulses consisted of a ˜60 MPa positive-pressure spike followed by up to -8 MPa negative-pressure tail, all with a total duration of about 7 μs. Nonlinear propagation steepened the shock front of the pulses to become sufficiently thin (˜0.03 μm) to impose differential pressure across even microscopic bubbles. High-speed camera movies showed that the SWs forced preexisting microbubbles to collapse, jet, and break up into daughter bubbles, which then grew rapidly under the negative-pressure phase of the pulse, but later coalesced to re-form a single bubble. Subsequent bubble growth was followed by inertial collapse and, usually, rebound. Most, if not all, cavitation bubbles emitted micro-jets during their first inertial collapse and re-growth. After jetting, these rebounding bubbles could regain a spherical shape before undergoing a second inertial collapse. However, either upon this second inertial collapse, or sometimes upon the first inertial collapse, the rebounding bubble emerged from the collapse as a cloud of smaller bubbles rather than a single bubble. These daughter bubbles could continue to rebound and collapse for a few cycles, but did not coalesce. These observations show that the positive-pressure phase of SWs fragments preexisting bubbles but this initial fragmentation does not yield bubble proliferation, as the daughter bubbles coalesce to reform a single bubble. Instead, bubble proliferation is the product of the subsequent inertial collapses.

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

Jansson, Karl Wahlberg; Johansen, Anders; Syed, Mohtashim Bukhari

Some scenarios for planetesimal formation go through a phase of collapse of gravitationally bound clouds of millimeter- to centimeter-size pebbles. Such clouds can form, for example, through the streaming instability in protoplanetary disks. We model the collapse process with a statistical model to obtain the internal structure of planetesimals with solid radii between 10 and 1000 km. During the collapse, pebbles collide, and depending on their relative speeds, collisions have different outcomes. A mixture of particle sizes inside a planetesimal leads to better packing capabilities and higher densities. In this paper we apply results from new laboratory experiments of dustmore » aggregate collisions (presented in a companion paper) to model collision outcomes. We find that the internal structure of a planetesimal is strongly dependent on both its mass and the applied fragmentation model. Low-mass planetesimals have no/few fragmenting pebble collisions in the collapse phase and end up as porous pebble piles. The number of fragmenting collisions increases with increasing cloud mass, resulting in wider particle size distributions and higher density. The collapse is nevertheless “cold” in the sense that collision speeds are damped by the high collision frequency. This ensures that a significant fraction of large pebbles survive the collapse in all but the most massive clouds. Our results are in broad agreement with the observed increase in density of Kuiper Belt objects with increasing size, as exemplified by the recent characterization of the highly porous comet 67P/Churyumov–Gerasimenko.« less

Phase-driven collapse of the Cooper condensate in a nanosized superconductor

NASA Astrophysics Data System (ADS)

Ronzani, Alberto; D'Ambrosio, Sophie; Virtanen, Pauli; Giazotto, Francesco; Altimiras, Carles

2017-12-01

Superconductivity can be understood in terms of a phase transition from an uncorrelated electron gas to a condensate of Cooper pairs in which the relative phases of the constituent electrons are coherent over macroscopic length scales. The degree of correlation is quantified by a complex-valued order parameter, whose amplitude is proportional to the strength of the pairing potential in the condensate. Supercurrent-carrying states are associated with nonzero values of the spatial gradient of the phase. The pairing potential and several physical observables of the Cooper condensate can be manipulated by means of temperature, current bias, dishomogeneities in the chemical composition, or application of a magnetic field. Here we show evidence of complete suppression of the energy gap in the local density of quasiparticle states (DOS) of a superconducting nanowire upon establishing a phase difference equal to π over a length scale comparable to the superconducting coherence length. These observations are consistent with a complete collapse of the pairing potential in the center of the wire, in accordance with theoretical modeling based on the quasiclassical theory of superconductivity in diffusive systems. Our spectroscopic data, fully exploring the phase-biased states of the condensate, highlight the profound effect that extreme phase gradients exert on the amplitude of the pairing potential. Moreover, the sharp magnetic response (up to 27 mV/Φ0) observed near the onset of the superconducting gap collapse regime is exploited to realize magnetic flux detectors with noise-equivalent resolution as low as 260 n Φ0/√{Hz} .

Effects of high shock pressures and pore morphology on hot spot mechanisms in HMX

NASA Astrophysics Data System (ADS)

Springer, H. K.; Tarver, C. M.; Bastea, S.

2017-01-01

The shock initiation and detonation behavior of heterogeneous solid explosives is governed by its microstructure and reactive properties. New additive manufacturing techniques offer unprecedented control of explosive microstructures previously impossible, enabling us to develop novel explosives with tailored shock sensitivity and detonation properties. Since microstructure-performance relationships are not well established for explosives, there is little material design guidance for these manufacturing techniques. In this study, we explore the effects of high shock pressures (15-38 GPa) with long shock durations and different pore morphologies on hot spot mechanisms in HMX. HMX is chosen as the model material because we have experimental data on many of the chemical-thermal-mechanical properties required for pore collapse simulations. Our simulations are performed using the multi-physics arbitrary Lagrangian Eulerian finite element hydrocode, ALE3D, with Cheetah-based models for the unreacted and the product equation-of-states. We use a temperature-dependent specific heat with the unreacted equation-of-state and a temperature-dependent viscosity model to ensure accurate shock temperatures for subsequent chemistry. The Lindemann Law model is used for shock melting in HMX. In contrast to previous pore collapse studies at lower shock pressures (≤10 GPa) in HMX and shorter post-collapse burning times, our calculations show that shock melting occurs above 15 GPa due to higher bulk heating and a prominent elongated ("jet-like") hot spot region forms at later times. The combination of the elongated, post-collapse hot spot region and the higher bulk heating with increasing pressure dramatically increases the growth rate of reaction. Our calculations show that the reaction rate, dF/dt, increases with increasing shock pressure. We decompose the reaction rate into ignition ((dF/dt)ig) and growth ((dF/dt)gr) phases to better analyze our results. We define the ignition phase to primarily include pore collapse and growth phase to primarily include post-collapse grain burning. We are able to track late-time, post-collapse burning due to the unique loading conditions employed in these calculations. We find that (dF/dt)gr > (dF/dt)ig for all pressures considered. (dF/dt)gr changes more significantly from 25 to 38 GPa (from 0.05/µs to >10-100/µs) than from 15 to 25 GPa (from 0.005/µs to 0.05/µs). There is a three order-of-magnitude difference in the reaction from 15 to 38 GPa just after pore collapse. This is qualitatively consistent with fitting the (macroscopic) Ignition and Growth model to high pressure shock initiation data, where much larger reaction fractions are needed to capture the early stages of reaction. Calculated burn rates demonstrate better agreement with data at intermediate times in the growth phase for 15 to 25 GPa and late times for 30 GPa then at any time in the growth phase for 38 GPa. Our calculations are much higher than burn rate data at the earliest times in the growth phase for all pressures, which may reflect the higher localized pressures and temperatures just after pore collapse in the ignition phase. Our calculations with spherical, conical, and elliptical pores show that the influence of morphology on reaction rate is pressure dependent and the most influential pore shapes at lower pressures aren't the same at higher pressures in the regime studied. Altogether these studies provide the basis for developing microstructure-aware models that can be used to design new explosives with optimal performance-safety characteristics. Such models can be used to guide additive manufacturing of explosives and fully exploit their disruptive nature.

The CaGeO3 Ca3Fe2Ge3O12 garnet join: an experimental study

NASA Astrophysics Data System (ADS)

Iezzi, Gianluca; Boffa-Ballaran, Tiziana; McCammon, Catherine; Langenhorst, Falko

2005-06-01

Germanate garnets are often used as isostructural analogues of silicate garnets to provide insight into the crystal chemistry and symmetry of the less accessible natural garnet solid solutions. We synthesised two series of germanate garnets at 3 GPa along the joinVIIICa3VI(CaGe)IVGe3O12 VIIICa3VIFe2IVGe3O12 at 900 °C and 1,100 °C. Samples with compositions close to the CaGeO3 end-member consist of tetragonal garnet with a small amount of triclinic CaGe2O5. Samples with nominal compositions between XFe=0.4 and 1.0 consist of a mixture of tetragonal and cubic garnets; whereas, single-phase cubic garnets were obtained for compositions with XFe>1.2 (XFe gives the iron content expressed in atoms per formula unit, and varies between 0 and 2 along the join). Run products which were primarily single-phase garnet were investigated using Mössbauer spectroscopy. Spectra from samples synthesised at 1,100°C consist of one well-resolved doublet that can be assigned to Fe3+ in the octahedral site of the garnet structure. A second doublet, present primarily in samples synthesised at 900°C, can be assigned to Fe2+ at the octahedral sites of the garnet structure. The relative abundance of Fe2+ decreases with increasing iron content. Transmission electron microscopy analyses confirm this tendency and show that the garnets are essentially defect-free. The unit-cell parameters of tetragonal VIIICa3VI(CaGe)IVGe3O3 garnet decrease with increasing synthesis temperature, and the deviation from cubic symmetry becomes smaller. Cubic garnets show a linear decrease of unit-cell parameter with increasing iron content. The results are discussed in the context of iron incorporation into VIIIMg3VI(MgSi)IVSi3O3 majorite.

Discovery of a Frank-Kasper [sigma] Phase in Sphere-Forming Block Copolymer Melts

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

Lee, Sangwoo; Bluemle, Michael J.; Bates, Frank S.

Sphere-forming block copolymers are known to self-assemble into body-centered cubic crystals near the order-disorder transition temperature. Small-angle x-ray scattering and transmission electron microscopy experiments on diblock and tetrablock copolymer melts have revealed an equilibrium phase characterized by a large tetragonal unit cell containing 30 microphase-separated spheres. This structure, referred to as the sigma ({sigma}) phase by Frank and Kasper more than 50 years ago, nucleates and grows from the body-centered cubic phase similar to its occurrence in metal alloys and is a crystal approximant to dodecagonal quasicrystals. Formation of the {sigma} phase in undiluted linear block copolymers (and certain branchedmore » dendrimers) appears to be mediated by macromolecular packing frustration, an entropic contribution to the interparticle interactions that control the sphere-packing geometry.« less

Reconciliation of local and long-range tilt correlations in underdoped La 2-xBa xCuO 4(0 ≤ x ≤ 0.155)

DOE PAGES

Bozin, Emil S.; Zhong, Ruidan; Knox, Kevin R.; ...

2015-02-26

A long standing puzzle regarding the disparity of local and long range CuO₆ octahedral tilt correlations in the underdoped regime of La₂₋ xBa xCuO₄ is addressed by utilizing complementary neutron powder diffraction and inelastic neutron scattering (INS) approaches. Long-range and static CuO₆ tilt order with orthogonally inequivalent Cu-O bonds in the CuO₂ planes in the low temperature tetragonal (LTT) phase is succeeded on warming through the low-temperature transition by one with orthogonally equivalent bonds in the low temperature orthorhombic (LTO) phase. In contrast, the signatures of LTT-type tilts in the instantaneous local atomic structure persist on heating throughout the LTOmore » crystallographic phase on the nanoscale, although becoming weaker as temperature increases. Analysis of the INS spectra for the x = 1/8 composition reveals the dynamic nature of the LTT-like tilt fluctuations within the LTO phase and their 3D character. The doping dependence of relevant structural parameters indicates that the magnitude of the Cu-O bond anisotropy has a maximum at x = 1/8 doping where bulk superconductivity is most strongly suppressed, suggesting that the structural anisotropy might be influenced by electron-phonon coupling and the particular stability of the stripe-ordered phase at this composition. The bond-length modulation that pins stripe order is found to be remarkably subtle, with no anomalous bond length disorder at low temperature, placing an upper limit on any in-plane Cu-O bondlength anisotropy. The results further reveal that although appreciable octahedral tilts persist through the high-temperature transition and into the high temperature tetragonal (HTT) phase, there is no significant preference between different tilt directions in the HTT regime. As a result, this study also exemplifies the importance of a systematic approach using complementary techniques when investigating systems exhibiting a large degree of complexity and subtle structural responses.« less

Spin-phonon coupling and high-pressure phase transitions of RMnO 3 (R=Ca and Pr): An inelastic neutron scattering and first-principles study

DOE PAGES

Mishra, S. K.; Gupta, M. K.; Mittal, R.; ...

2016-06-22

Here, we report inelastic neutron scattering measurements over 7–1251 K in CaMnO 3 covering various phase transitions, and over 6–150 K in PrMnO 3 covering the magnetic transition. The excitations around 20 meV in CaMnO 3 and at 17 meV in PrMnO 3 at low temperatures are found to be associated with magnetic origin. We observe coherent magnetic neutron scattering in localized regions in reciprocal space and show it to arise from long-range correlated magnetic spin-waves below the magnetic transition temperature (TN) and short-range stochastic spin-spin fluctuations above T N. In spite of the similarity of the structure of themore » two compounds, the neutron inelastic spectrum of PrMnO 3 exhibits broad features at 150 K unlike well-defined peaks in the spectrum of CaMnO 3. This might result from the difference in the nature of interactions in the two compounds (magnetic and Jahn-Teller distortion). Ab initio phonon calculations have been used to interpret the observed phonon spectra. The ab initio calculations at high pressures show that the variations of Mn-O distances are isotropic for CaMnO 3 and highly anisotropic for PrMnO 3. The calculation in PrMnO 3 shows the suppression of Jahn-Teller distortion and simultaneous insulator-to-metal transition. It appears that this transition may not be associated with the occurrence of the tetragonal phase above 20 GPa as reported in the literature, since the tetragonal phase is found to be dynamically unstable, although it is found to be energetically favored over the orthorhombic phase above 20 GPa. CaMnO 3 does not show any phase transition up to 60 GPa.« less

Lateral electric-field control of giant magnetoresistance in Co/Cu/Fe/BaTiO{sub 3} multiferroic heterostructure

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

Savitha Pillai, S.; Kojima, H.; Itoh, M.

2015-08-17

We report lateral electric-field-driven sizable changes in the magnetoresistance of Co/Cu/Fe tri-layered wires on BaTiO{sub 3} single crystal. While the observed change is marginal in the tetragonal phase of BaTiO{sub 3}, it reaches over 40% in the orthorhombic and rhombohedral phases with an electric field of 66 kV/cm. We attribute it to possible electric-field-induced variations of the spin-dependent electronic structures, i.e., spin polarization, of the Fe via interfacial strain transfer from BaTiO{sub 3}. The contrasting results for the different phases of BaTiO{sub 3} are discussed, associated with the distinct aspects of the ferroelectric polarization switching processes in each phase.

Unusual structural phase transition in [N(C2H5)4][N(CH3)4][ZnBr4

NASA Astrophysics Data System (ADS)

Krawczyk, Monika K.; Ingram, Adam; Cach, Ryszard; Czapla, Zbigniew; Czupiński, Olaf; Dacko, Sławomir; Staniorowski, Piotr

2018-04-01

The new hybrid organic-inorganic crystal [N(C2H5)4][N(CH3)4][ZnBr4] was grown and its physical properties and structural phase transition are presented. On the basis of thermal analysis (DSC (differential scanning calorimetry), DTA (differential thermal analysis), DTG), X-ray structural, dilatometric and dielectric studies as well as optical observation, the reversible first-order phase transition at 490/488 K on heating and cooling run, respectively, has been found. An appearance of domain structure of ferroelastic type gives evidence for an untypical lowering of crystal symmetry during the phase transition. At room temperature, the satisfying crystal structure solution was found in the tetragonal system, in the P?21m space group.

The role of microstructure and phase distribution in the failure mechanisms and life prediction model for PSZ coatings

NASA Technical Reports Server (NTRS)

Sisson, R. D., Jr.; Sone, Ichiro; Biederman, R. R.

1985-01-01

Partially Stabilized Zirconia (PSZ) may become widely used for Thermal Barrier Coatings (TBC). Failure of these coatings can occur due to thermal fatigue in oxidizing atmospheres. The failure is due to the strains that develop due to thermal gradients, differences in thermal expansion coefficients, and oxidation of the bond coating. The role of microstructure and the cubic, tetragonal, and monoclinic phase distribution in the strain development and subsequent failure will be discussed. An X-ray diffraction technique for accurate determination of the fraction of each phase in PSZ will be applied to understanding the phase transformations and strain development. These results will be discussed in terms of developing a model for life prediction in PSZ coatings during thermal cycling.

Origin of phase transition in VO2

NASA Astrophysics Data System (ADS)

Basu, Raktima; Sardar, Manas; Dhara, Sandip

2018-04-01

Vanadium dioxide (VO2) exhibits a reversible first-order metal to insulator transition (MIT) along with a structural phase transition (SPT) from monoclinic M1 to rutile tetragonal R via another two intermediate phases of monoclinic M2 and triclinic T at a technologically important temperature of 340K. In the present work, besides synthesizing M1 phase of VO2, we also stabilized M2 and T phases at room temperature by introducing native defects in the system and observed an increase in transition temperature with increase in native defects. Raman spectroscopic measurements were carried out to confirm the pure VO2 phases. Since the MIT is accompanied by SPT in these systems, the origin of the phase transition is still under debate. The controversy between MIT and SPT, whether electron-phonon coupling or strong electron-electron correlation triggers the phase transition in VO2 is also resolved by examining the presence of intermediate phase M2 during phase transition.

Metal Insulator transition in Vanadium Dioxide

NASA Astrophysics Data System (ADS)

Jovaini, Azita; Fujita, Shigeji; Suzuki, Akira; Godoy, Salvador

2012-02-01

MAR12-2011-000262 Abstract Submitted for the MAR12 Meeting of The American Physical Society Sorting Category: 03.9 (T) On the metal-insulator-transition in vanadium dioxide AZITA JOVAINI, SHIGEJI FUJITA, University at Buffalo, SALVADOR GODOY, UNAM, AKIRA SUZUKI, Tokyo University of Science --- Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 340 K with the structural change from tetragonal to monoclinic crystal. The conductivity _/ drops at MIT by four orders of magnitude. The low temperature monoclinic phase is known to have a lower ground-state energy. The existence of the k-vector k is prerequisite for the conduction since the k appears in the semiclassical equation of motion for the conduction electron (wave packet). The tetragonal (VO2)3 unit is periodic along the crystal's x-, y-, and z-axes, and hence there is a three-dimensional k-vector. There is a one-dimensional k for a monoclinic crystal. We believe this difference in the dimensionality of the k-vector is the cause of the conductivity drop. Prefer Oral Session X Prefer .

Synthesis of ZrO 2 thin films by atomic layer deposition: growth kinetics, structural and electrical properties

NASA Astrophysics Data System (ADS)

Cassir, Michel; Goubin, Fabrice; Bernay, Cécile; Vernoux, Philippe; Lincot, Daniel

2002-06-01

Ultra thin films of ZrO 2 were synthesized on soda lime glass and SnO 2-coated glass, using ZrCl 4 and H 2O precursors by atomic layer deposition (ALD), a sequential CVD technique allowing the formation of dense and homogeneous films. The effect of temperature on the film growth kinetics shows a first temperature window for ALD processing between 280 and 350 °C and a second regime or "pseudo-window" between 380 and 400 °C, with a growth speed of about one monolayer per cycle. The structure and morphology of films of less than 1 μm were characterized by XRD and SEM. From 275 °C, the ZrO 2 film is crystallized in a tetragonal form while a mixture of tetragonal and monoclinic phases appears at 375 °C. Impedance spectroscopy measurements confirmed the electrical properties of ZrO 2 and the very low porosity of the deposited layer.

Structural analysis and ferroelectric properties of Fe doped BaTiO{sub 3}

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

Mishra, Ashutosh, E-mail: a.mansuri14@gmail.com, E-mail: amishra1960@yahoo.co.in; Mansuri, Amantulla, E-mail: a.mansuri14@gmail.com, E-mail: amishra1960@yahoo.co.in; Dwivedi, J. P.

2016-05-23

The polycrystalline samples of Fe doped BaTiO{sub 3} (BTO) with compositional formula BaTi{sub 1-x}Fe{sub x}O{sub 3} (x = 0, 0.03, 0.04 and 0.05) were prepared by solid-state reaction route. The influence of the Fe content on the structural, vibrational and electric properties of BaTiO{sub 3} was investigated using X-ray powder diffraction (XRD), Raman spectroscopy and Polarization techniques. XRD analysis indicates the formation of single-phase tetragonal structure for all the prepared samples. Tetragonal cubic structure with space group P4mm of all samples is further approved by Rietveld refinement. Room temperature Raman spectra of pure BaTiO{sub 3} show four active modes ofmore » vibration whose intensity decreases with increasing Fe doping. Small shift in Raman modes and increment in the line width has been observed with the doping ions. The hysteresis loop is very well performed with regular sharp characteristic of ferroelectric materials.« less

Polarized light microscopy study on the reentrant phase transition in a (Ba 1–xK x)Fe 2As 2 single crystal with x = 0.24

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

Liu, Yong; Tanatar, Makariy A.; Timmons, Erik

In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba 1–xK x)Fe 2As 2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba 1–xK x)Fe 2As 2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition T N ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at T N ~more » 80 K, LTO1 to low temperature tetragonal (LTT) structure at T c ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.« less

Polarized light microscopy study on the reentrant phase transition in a (Ba 1–xK x)Fe 2As 2 single crystal with x = 0.24

DOE PAGES

Liu, Yong; Tanatar, Makariy A.; Timmons, Erik; ...

2016-11-09

In this study, a sequence of structural/magnetic transitions on cooling is reported in the literature for hole-doped iron-based superconductor (Ba 1–xK x)Fe 2As 2 with x = 0.24. By using polarized light microscopy, we directly observe the formation of orthorhombic domains in (Ba 1–xK x)Fe 2As 2 (x = 0.24) single crystal below a temperature of simultaneous structural/magnetic transition T N ~ 80 K. The structural domains vanish below ~30 K, but reappear below T = 15 K. Our results are consistent with reentrance transformation sequence from high-temperature tetragonal (HTT) to low temperature orthorhombic (LTO1) structure at T N ~more » 80 K, LTO1 to low temperature tetragonal (LTT) structure at T c ~ 25 K, and LTT to low temperature orthorhombic (LTO2) structure at T ~ 15 K.« less

Optical properties of body-centered tetragonal C4: Insights from many-body perturbation and time-dependent density functional theories

NASA Astrophysics Data System (ADS)

Tarighi Ahmadpour, Mahdi; Rostamnejadi, Ali; Hashemifar, S. Javad

2018-04-01

We study the electronic structure and optical properties of a body-centered tetragonal phase of carbon (bct-C4) within the framework of time-dependent density functional theory and Bethe-Salpeter equation. The results indicate that the optical properties of bct-C4 are strongly affected by the electron-hole interaction. It is demonstrated that the long-range corrected exchange-correlation kernels could fairly reproduce the Bethe-Salpeter equation results. The effective carrier number reveals that at energies above 30 eV, the excitonic effects are not dominant any more and that the optical transitions originate mainly from electronic excitations. The emerged peaks in the calculated electron energy loss spectra are discussed in terms of plasmon excitations and interband transitions. The results of the research indicate that bct-C4 is an indirect wide-band-gap semiconductor, which is transparent in the visible region and opaque in the ultraviolet spectral range.

Strain effect in epitaxial VO2 thin films grown on sapphire substrates using SnO2 buffer layers

NASA Astrophysics Data System (ADS)

Kim, Heungsoo; Bingham, Nicholas S.; Charipar, Nicholas A.; Piqué, Alberto

2017-10-01

Epitaxial VO2/SnO2 thin film heterostructures were deposited on m-cut sapphire substrates via pulsed laser deposition. By adjusting SnO2 (150 nm) growth conditions, we are able to control the interfacial strain between the VO2 film and SnO2 buffer layer such that the semiconductor-to-metal transition temperature (TC) of VO2 films can be tuned without diminishing the magnitude of the transition. It is shown that in-plane tensile strain and out-of-plane compressive strain of the VO2 film leads to a decrease of Tc. Interestingly, VO2 films on SnO2 buffer layers exhibit a structural phase transition from tetragonal-like VO2 to tetragonal-VO2 during the semiconductor-to-metal transition. These results suggest that the strain generated by SnO2 buffer provides an effective way for tuning the TC of VO2 films.

Scaling of the Stress and Temperature Dependence of the Optical Anisotropy in Ba(Fe 1-x Co x ) 2As 2

DOE PAGES

Mirri, C.; Dusza, A.; Bastelberger, S.; ...

2016-09-15

We revisit our recent investigations of the optical properties in the underdoped regime of the title compounds with respect to their anisotropic behavior as a function of both temperature and uniaxial stress across the ferro-elastic tetragonal-to-orthorhombic transition. By exploiting a dedicated pressure device, we can tune and control uniaxial stress in situ thus changing the degree of detwinning of the samples in the orthorhombic SDW state as well as pressure-inducing an orthorhombicity in the paramagnetic tetragonal phase. Here we discover a hysteretic behavior of the optical anisotropy; its stress versus temperature dependence across the structural transition bears testimony to themore » analogy with the magnetic-field versus temperature dependence of the magnetization in a ferromagnet when crossing the Curie temperature. In this context, we find furthermore an intriguing scaling of the stress and temperature dependence of the optical anisotropy in Ba(Fe 1-xCo x) 2As 2.« less

Transferable atomistic model to describe the energetics of zirconia

NASA Astrophysics Data System (ADS)

Wilson, Mark; Schönberger, Uwe; Finnis, Michael W.

1996-10-01

We have investigated the energies of a number of phases of ZrO2 using models of an increasing degree of sophistication: the simple ionic model, the polarizable ion model, the compressible ion model, and finally a model including quadrupole polarizability of the oxygen ions. The three structures which are observed with increasing temperatures are monoclinic, tetragonal, and cubic (fluorite). Besides these we have studied some hypothetical structures which certain potentials erroneously predict or which occur in other oxides with this stoichiometry, e.g., the α-PbO2 structure and rutile. We have also performed ab initio density functional calculations with the full-potential linear combination of muffin-tin orbitals method to investigate the cubic-tetragonal distortion. A detailed comparison is made between the results using classical potentials, the experimental data, and our own and other ab initio results. The factors which stabilize the various structure are analyzed. We find the only genuinely transferable model is the one including compressible ions and anion polarizability to the quadrupole level.

Terminal Transient Phase of Chaotic Transients

NASA Astrophysics Data System (ADS)

Lilienkamp, Thomas; Parlitz, Ulrich

2018-03-01

Transient chaos in spatially extended systems can be characterized by the length of the transient phase, which typically grows quickly with the system size (supertransients). For a large class of these systems, the chaotic phase terminates abruptly, without any obvious precursors in commonly used observables. Here we investigate transient spatiotemporal chaos in two different models of this class. By probing the state space using perturbed trajectories we show the existence of a "terminal transient phase," which occurs prior to the abrupt collapse of chaotic dynamics. During this phase the impact of perturbations is significantly different from the earlier transient and particular patterns of (non)susceptible regions in state space occur close to the chaotic trajectories. We therefore hypothesize that even without perturbations proper precursors for the collapse of chaotic transients exist, which might be highly relevant for coping with spatiotemporal chaos in cardiac arrhythmias or brain functionality, for example.

Quantitative evaluation of the piezoelectric response of unpoled ferroelectric ceramics from elastic and dielectric measurements: Tetragonal BaTiO3

NASA Astrophysics Data System (ADS)

Cordero, F.

2018-03-01

A method is proposed for evaluating the potential piezoelectric response, that a ferroelectric material would exhibit after full poling, from elastic and dielectric measurements of the unpoled ceramic material. The method is based on the observation that the softening in a ferroelectric phase with respect to the paraelectric phase is of piezoelectric origin, and is tested on BaTiO3. The angular averages of the piezoelectric softening in unpoled ceramics are calculated for ferroelectric phases of different symmetries. The expression of the orientational average with the piezoelectric and dielectric constants of single crystal tetragonal BaTiO3 from the literature reproduces well the softening of the Young's modulus of unpoled ceramic BaTiO3, after a correction for the porosity. The agreement is good in the temperature region sufficiently far from the Curie temperature and from the transition to the orthorhombic phase, where the effect of fluctuations should be negligible, but deviations are found outside this region, and possible reasons for this are discussed. This validates the determination of the piezoelectric response by means of purely elastic measurements on unpoled samples. The method is indirect and, for quantitative assessments, requires the knowledge of the dielectric tensor. On the other hand, it does not require poling of the sample, and therefore is insensitive to inaccuracies from incomplete poling, and can even be used with materials that cannot be poled, for example, due to excessive electrical conductivity. While the proposed example of the Young's modulus of a ceramic provides an orientational average of all the single crystal piezoelectric constants, a Resonant Ultrasound Spectroscopy measurement of a single unpoled ceramic sample through the ferroelectric transition can in principle measure all the piezoelectric constants, together with the elastic ones.

Correlation Between the Microstructural Defects and Residual Stress in a Single Crystal Nickel-Based Superalloy During Different Creep Stages

NASA Astrophysics Data System (ADS)

Mo, Fangjie; Wu, Erdong; Zhang, Changsheng; Wang, Hong; Zhong, Zhengye; Zhang, Jian; Chen, Bo; Hofmann, Michael; Gan, Weimin; Sun, Guangai

2018-03-01

The present work attempts to reveal the correlation between the microstructural defects and residual stress in the single crystal nickel-based superalloy, both of which play the significant role on properties and performance. Neutron diffraction was employed to investigate the microstructural defects and residual stresses in a single crystal (SC) nickel-based superalloy, which was subjected to creeping under 220 MPa and 1000 °C for different times. The measured superlattice and fundamental lattice reflections confirm that the mismatch and tetragonal distortions with c/a > 1 exist in the SC superalloy. At the initially unstrained state, there exists the angular distortion between γ and γ' phases with small triaxial compressive stresses, ensuring the structural stability of the superalloy. After creeping, the tetragonal distortion for the γ phase is larger than that for the γ' phase. With increasing the creeping time, the mismatch between γ and γ' phases increases to the maximum, then decreases gradually and finally remains unchanged. The macroscopic residual stress shows a similar behavior with the mismatch, indicating the correlation between them. Based on the model of shear and dislocations, the evolution of microstructural defects and residual stress are reasonably explained. The effect of shear is dominant at the primary creep stage, which greatly enlarges the mismatch and the residual stress. The dislocations weaken the effect of shear for the further creep stage, resulting in the decrease of the mismatch and relaxation of the residual stress. Those findings add some helpful understanding into the microstructure-performance relationship in the SC nickel-based superalloy, which might provide the insight to materials design and applications.