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Sample records for sr ba zn

  1. AC Susceptibilities in Zn Doped (Bi,Pb)(Sr,Ba):2223 Superconductor

    NASA Astrophysics Data System (ADS)

    Pop, V.

    AC susceptibility measurements as a function of temperature and amplitude of alternative magnetic field have been carried out on the samples (Bi,Pb)(Sr,Ba):2223 with Cu substituted by Zn at a concentration of x = 0.00, 0.02 and 0.05. The decrease of intergrain and intragrain critical temperatures with increasing x is in agreement with the increase of the residual resistivity. Using Muller critical state model and the linear dependence of Tp for the maximum of imaginary χ''(T) peak, as a function of AC field amplitude, the intergranular pining force density was obtained. The intergrain properties are more influenced than the intragrain ones.

  2. Very high or close to zero thermal expansion by the variation of the Sr/Ba ratio in Ba(1-x)Sr(x)Zn2Si2O7- solid solutions.

    PubMed

    Thieme, Christian; Rüssel, Christian

    2016-03-21

    The compound BaZn2Si2O7 shows a highly positive coefficient of thermal expansion. At a temperature of 280 °C, it transforms to a high temperature phase, which exhibits a coefficient of thermal expansion near zero. The partial replacement of Ba(2+) against Sr(2+) leads to a decrease of the phase transition temperature. If more than 10% of Ba(2+) are replaced by Sr(2+), the high-temperature phase is completely stable at room temperature and consequently, the thermal expansion is near zero or negative. The effect of the Sr(2+)/Ba(2+)-ratio on the phase transition temperature and the thermal expansion behavior is measured using high-temperature X-ray diffraction up to 1000 °C. The Sr(2+)/Ba(2+)-ratio strongly affects the overall thermal expansion as well as the anisotropy. The latter increases with decreasing Sr-concentration. The strong differences in the thermal expansion behavior between phases with the structure of the low-temperature phase and the high-temperature phase of BaZn2Si2O7 can be explained by a comparison of the ZnO4-chains inside these two crystal structures.

  3. Magnetoelectric memory effect in the Y-type hexaferrite BaSrZnMgFe12O22

    NASA Astrophysics Data System (ADS)

    Wang, Fen; Shen, Shi-Peng; Sun, Young

    2016-08-01

    We report on the magnetic and magnetoelectric properties of the Y-type hexaferrite BaSrZnMgFe12O22, which undergoes transitions from a collinear ferrimagnetic phase to a proper screw phase at 310 K and to a longitudinal conical phase at 45 K. Magnetic and electric measurements revealed that the magnetic structure with spiral spin order can be modified by applying a magnetic field, resulting in magnetically controllable electric polarization.It was observed that BaSrZnMgFe12O22 exhibits an anomalous magnetoelectric memory effect: the ferroelectric state can be partially recovered from the paraelectric phase with collinear spin structure by reducing magnetic field at 20 K. We ascribe this memory effect to the pinning of multiferroic domain walls, where spin chirality and structure are preserved even in the nonpolar collinear spin state. Project supported by the National Natural Science Foundation of China (Grant Nos. 11534015 and 51371193).

  4. High-pressure modifications of CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2}: Implications for Laves phase structural trends

    SciTech Connect

    Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich

    2008-11-15

    High-pressure forms of intermetallic compounds with the composition CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2} were synthesized from CeCu{sub 2}-type precursors (CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}) and Ba{sub 21}Al{sub 40} by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl{sub 2} and BaAl{sub 2}), X-ray single-crystal diffraction (CaZn{sub 2}), and electron microscopy (SrZn{sub 2}). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu{sub 2} (C15) structure, the dizincides adopt the hexagonal MgZn{sub 2} (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu{sub 2}-type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration.

  5. Preparation and magnetic properties of Ba-Co2Z and Sr-Zn2Y ferrites

    NASA Astrophysics Data System (ADS)

    Chen, In-Gann; Hsu, Shu-Hau; Chang, Y. H.

    2000-05-01

    We have prepared Ba-Co2Z and Sr-Zn2Y ferrites by mixing SrCO3 (BaCO3), Co2O3 (ZnO), and Fe2O3 and calcinating in air and O2. The effects of sintering atmosphere (O2 and Ar) and sintering temperatures (1373-1573 K) on the structural, magnetic, and electrical properties have been measured. The Ba-Co2Z sample sintered at 1573 K under a flowing O2 exhibits superior dc electrical resistivity (˜108Ω-cm), high initial permeability (u'˜21), and low loss factor (F˜1.6×10-3) at 20 MHz. The related XRD and SEM/EDS analyses of these samples have also been studied to correlate these properties. These results indicate that significant modification of magnetic properties up to 20 MHz can be achieved with the addition of the quaternary component and proper control of the processing oxygen atmosphere.

  6. A{sub 2}Zn{sub 3}As{sub 2}O{sub 2} (A Ba, Sr): A rare example of square planar zinc

    SciTech Connect

    Brock, S.L.; Kauzlarich, S.M.

    1994-05-25

    The synthesis and structural characterization of Ba{sub 3}Zn{sub 3}As{sub 2}O{sub 2} and Sr{sub 3}Zn{sub 3}As{sub 2}O{sub 2} is reported. These compounds are novel in that they are the first compounds without Mn that crystallize in the ThCr{sub 2}Si{sub 2} structure type. In addition, Zn is in a rare square planar oxygen coordination mode.

  7. Ba(1-x)Sr(x)Zn2Si2O7--A new family of materials with negative and very high thermal expansion.

    PubMed

    Thieme, Christian; Görls, Helmar; Rüssel, Christian

    2015-12-15

    The compound BaZn2Si2O7 shows a high coefficient of thermal expansion up to a temperature of 280 °C, then a transition to a high temperature phase is observed. This high temperature phase exhibits negative thermal expansion. If Ba(2+) is successively replaced by Sr(2+), a new phase with a structure, similar to that of the high temperature phase of BaZn2Si2O7, forms. At the composition Ba0.8Sr0.2Zn2Si2O7, this new phase is completely stabilized. The crystal structure was determined with single crystal X-ray diffraction using the composition Ba0.6Sr0.4Zn2Si2O7, which crystallizes in the orthorhombic space group Cmcm. The negative thermal expansion is a result of motions and distortions inside the crystal lattice, especially inside the chains of ZnO4 tetrahedra. Dilatometry and high temperature X-ray powder diffraction were used to verify the negative thermal expansion. Coefficients of thermal expansion partially smaller than -10·10(-6) K(-1) were measured.

  8. Structural and Optoelectronic Properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds

    NASA Astrophysics Data System (ADS)

    Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.

    2016-06-01

    We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) anti-perovskite compounds using an all-electron full-potential linearized augmented plane-wave method. Optimized structural parameters are found to be in good agreement with the available experimental measurements. The electronic band structure is calculated using different exchange-correlation potentials which reveal that the investigated compounds are narrow direct band gap semiconductors. A direct narrow band gap at the center of the Brillouin zone emphasises the optical activity of these compounds. Prediction of the optical properties, such as the real and imaginary parts of the dielectric function and refractive index along with reflectivity and optical conductivity, reveals the importance of these compounds in the visible and near UV optoelectronic devices industry.

  9. Lattice modulation induced by magnetic order in the magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22

    NASA Astrophysics Data System (ADS)

    Asaka, T.; Yu, X. Z.; Hiraoka, Y.; Kimoto, K.; Hirayama, T.; Kimura, T.; Matsui, Y.

    2011-04-01

    By means of an electron diffraction technique, crystal-lattice modulations were investigated for a hexaferrite, Ba0.5Sr1.5Zn2Fe12O22, showing a helimagnetic order below TN=320 K. We observed a lattice modulation with a wave vector Q=(0,0,3δ) below TN. The value of δ varies between ~0.23 and 0.5 as a function of temperature and corresponds well to that of the magnetic modulation vector. By applying magnetic fields, Ba0.5Sr1.5Zn2Fe12O22 was found to exhibit successive changes in the lattice modulation, accompanied by the modifications of the helical magnetic order. We concluded that the observed lattice modulation is induced by the helical magnetic order via exchange magnetostriction.

  10. Giant magnetoelastic effect in multiferroic Ba0.6Sr1.4Zn2Fe12O22

    NASA Astrophysics Data System (ADS)

    Talbayev, Diyar; Averitt, Richard D.; Taylor, Antoinette J.; Kimura, Tsuyoshi

    2007-03-01

    Dynamical studies of multiferroic materials help unravel the fundamental interactions between various degrees of freedom and answer technological questions such as achievable switching speeds in multiferroic-based memory elements. We report the results of the ultrafast optical study of multiferroic Ba0.6Sr1.4Zn2Fe12O22, which reveals a giant magnetoelastic effect in the material. The compound exhibits a hexagonal crystal structure and a helical magnetic ground state below ˜ 330 K. In applied magnetic field, the hexaferrite undergoes a series of magnetic phase transitions and develops ferroelectric polarization. The magnetoelastic effect is detected via the measurement of the speed of sound in the crystal as a function of magnetic field. The oscillation in the optically induced transient reflectivity resulting from the propagating coherent-phonon strain pulse allows us to measure the field-induced changes in the speed of sound and the corresponding dramatic changes in the elastic stiffness. The dependence of the exchange interaction on the distance between Fe ions gives rise to the observed magnetoelasticity. Our results indicate a route towards the magnetically modulated transducers and piezoelectric devices.

  11. 57Fe NMR study of the magnetoelectric hexaferrite Ba0.5Sr1.5Zn2Fe12O22 and Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22

    NASA Astrophysics Data System (ADS)

    Kwon, Sangil; Yoon, Dong Young; Lee, Soonchil; Chai, Yi Sheng; Chun, Sae Hwan; Kim, Kee Hoon

    2013-08-01

    Magnetoelectric hexaferrite Ba0.5Sr1.5Zn2Fe12O22 (BSZFO) and Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 (BSZFAO) were investigated by 57Fe nuclear magnetic resonance (NMR). The spin-canting angles of all NMR peaks were measured to assign each peak to corresponding Fe3+ sites. It was revealed that the spin-canting angle of Fe3+ ions at off-centered octahedra is fixed and Al3+ ions substitute for Fe3+ ions at those sites. The temperature dependence of the NMR frequency indicates that the low-temperature excitation is spin wave in ferromagnetic phase.

  12. Al doping effect on magnetic phase transitions of magnetoelectric hexaferrite Ba0.7Sr1.3Zn2(Fe1-xAlx)12O22

    NASA Astrophysics Data System (ADS)

    Chang, Hun; Lee, Hak Bong; Song, Young-Sang; Chung, Jae-Ho; Kim, S. A.; Oh, I. H.; Reehuis, M.; Schefer, J.

    2012-02-01

    We investigated the effect of Al doping in magnetic properties of the Y-type hexaferrite Ba0.7Sr1.3Zn2(Fe1-xAlx)12O22 (0≤x≤0.12), which exhibit field-induced magnetoelectric polarization. We find that Al doping increases the pitch of a spin helix and enhances c-axis magnetization, stabilizing longitudinal conical phases. These conical phases eventually collapse at x≥ 0.10. These results suggest that competitions between easy-axis and easy-plane anisotropy fields play a key role in generating stable magnetoelectric polarization in Y-type hexaferrites.

  13. Effect of Mg(2+), Ca(2+), Sr(2+) and Ba(2+) metal ions on the antifungal activity of ZnO nanoparticles tested against Candida albicans.

    PubMed

    Haja Hameed, Abdulrahman Syedahamed; Karthikeyan, Chandrasekaran; Senthil Kumar, Venugopal; Kumaresan, Subramanian; Sasikumar, Seemaisamy

    2015-01-01

    The antifungal ability of pure and alkaline metal ion (Mg(2+), Ca(2+), Sr(2+) and Ba(2+)) doped ZnO nanoparticles (NPs) prepared by the co-precipitation method was tested against the pathogenic yeast, Candida albicans (C. albicans), and the results showed that the Mg-doped ZnO NPs possessed greater effect than the other alkaline metal ion doped ZnO NPs. The impact of the concentration of Mg doped ZnO sample on the growth of C. albicans was also studied. The Minimal Fungicidal Concentration (MFC) of the Mg doped ZnO NPs was found to be 2000 μg/ml for which the growth of C. albicans was completely inhibited. The ZnO:Mg sample (1.5mg/ml) with various concentrations of histidine reduced the fungicidal effect of the nanoparticles against C. albicans, which was deliberately explained by the role of ROS. The ZnO:Mg sample added with 5mM of histidine scavenged the ample amount of generated ROS effectively. The binding of the NPs with fungi was observed by their FESEM images and their electrostatic attraction is confirmed by the zeta potential measurement.

  14. High-resolution of trace elements (Mg, U, Sr, Ba and Zn) in speleothems as Holocene palaeoclimatic proxies: Père Noël cave, Belgium

    NASA Astrophysics Data System (ADS)

    Allan, Mohammed; Verheyden, Sophie; Riotte, Jean; Ghaleb, Bassam; Chmeleff, Jerome; fagel, Nathalie

    2013-04-01

    Speleothems are now regarded as valuable archives of climatic conditions on the continents, offering the advantages of absolute U-series dating relative to other continental climate proxy recorders such as lake sediments and peat cores. High spatial resolution measurements of Mg, U, Sr, Ba and Zn were realized by laser-ablation inductively coupled plasma mass spectrometry in the Belgian Père Noël cave Holocene stalagmite (Verheyden et al., 2000, 2008). The stalagmite of 65 cm long was deposited from ~12000 years to ~2000 years dated by U/Th method. Mg, Sr, Ba, U, and Zn are known as indicators for hydrological conditions (e.g. Ayalon et al., 1999; Fairchild et al., 2000). Mg, Sr, Ba concentrations are positively correlated (r> 0.7) with similar changes in the δ 13C implying similar processes influence their concentration changes. U has an inverse relationship with δ 13C. The study suggests that trace elements in the Père Noël stalagmite have the potential to provide high resolution insights into variability in water recharge during the Holocene. References Ayalon A., Bar-Matthews M. and Kaufman A., 1999. Petrography, strontium, barium and uranium concentrations, and strontium and uranium isotope ratios in speleothems as palaeoclimatic proxies: Soreq cave, Israel. The Holocene 9 (6), 715-722. Fairchild I.J., Borsato A., Tooth A.F.,Frisia S., Hawkesworth C.J., Huang Y., Mcdermott F. and Spiro B., 2000. Controls on trace element (Sr-Mg) compositions of carbonate cave waters: implications for speleothem climatic records. Chemical Geology 166, 255-269. Verheyden S., Keppens E. , Fairchild I.J., Mc Dermott F. and D. Weis, 2000. Sr isotope geochemistry of a Belgian Holocene speleothem: implications for paleoclimate reconstructions. Chemical Geology, 169: 131 144. Verheyden S., Genty D., Deflandre G., Quinif Y. and Keppens E., 2008. Monitoring climatological, hydrological and geochemical parameters in the Père Noël cave (Belgium): Implication for the interpretation

  15. Thermal Expansion of Sintered Glass Ceramics in the System BaO-SrO-ZnO-SiO2 and Its Dependence on Particle Size.

    PubMed

    Thieme, Christian; Schlesier, Martin; Bocker, Christian; Buzatto de Souza, Gabriel; Rüssel, Christian

    2016-08-10

    The thermal expansion behavior of sintered glass-ceramics containing high concentrations of Ba1-xSrxZn2Si2O7, a phase with very low and highly anisotropic thermal expansion behavior, was investigated. The observed phase has the crystal structure of the high-temperature phase of BaZn2Si2O7, which can be stabilized by the introduction of Sr(2+) into this phase. The high anisotropy leads to microcracking within the volume of the samples, which strongly affects the dilatometric thermal expansion. However, these cracks also have an influence on the nominal thermal expansion of the as-mentioned phase, which decreases if the cracks appear. Below a grain size of approximately 80 μm, the sintered glass-ceramics have almost no cracks and show positive thermal expansion. Hence, coefficients of thermal expansion between -5.6 and 6.5 × 10(-6) K(-1) were measured. In addition to dilatometric studies, the effect of the microstructure on the thermal expansion was also measured using in situ X-ray diffraction at temperatures up to 1000 °C.

  16. Commensurate and Incommensurate Phases in the System A4A'Ir 2O 9( A=Sr, Ba; A'=Cu, Zn)

    NASA Astrophysics Data System (ADS)

    Battle, Peter D.; Blake, Graeme R.; Sloan, Jeremy; Vente, Jaap F.

    1998-02-01

    The crystal structure of Sr 4CuIr 2O 9is very sensitive to the conditions of synthesis. Prolonged heating of a commensurate trigonal sample prepared at 1120°C leads to the adoption of an incommensurate structure which can be regarded as a composite of two substructures having common unit cell parameters aand bbut different parameters c1and c2. No detectable change in chemical composition accompanies the structural transition, nor do the magnetic properties of the sample change significantly. The structure of the commensurate form has been determined from neutron powder diffraction data collected at 4.5 K (space group P321, a=9.68540(3) Å, c=8.04726(6) Å). Ir 2O 9octahedral dimers and CuO 6trigonal prisms alternate in chains parallel to z, with the Sr cations located between the chains; the Cu 2+cations are disordered within the prisms. The incommensurate form has been studied by X-ray diffraction and electron microscopy ( a=9.7020(6) Å, c1=4.0069(5) Å, c2=2.6993(4) Å). The relationship between the commensurate and incommensurate unit cells is discussed ( c˜2 c1˜3 c2). No commensurate Ba 4A'Ir 2O 9phases could be prepared, but incommensurate samples having A'=Cu, Zn showed behavior similar to that of Sr 4CuIr 2O 9.

  17. Magnetic comparison of BaCa and BaSr substituted hexaferrite powders

    NASA Astrophysics Data System (ADS)

    González-Angeles, A.; Lipka, J.; Grusková, A.; Sláma, J.; Jančárik, V.; Slugeň, V.

    2010-03-01

    Results on magnetic studies of Ba0.5Sr0.5Fe12-2x(ZnTi)xO19 and Ba0.75Ca0.25Fe12-2x(ZnTi)xO19, where x = 0.2 to 0.6, ferromagnetic powders prepared by mechanical alloying are discussed. The structural and magnetic properties of the resulting powders were analyzed by thermo-magnetic analysis, X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy and magnetic measurements. Curie temperature, Tc decreased dramatically (drop ~ 39%) for BaCa samples, whilst for BaSr samples remained almost without change (diminution ~ 2%) at x <= 0.2. SEM studies showed that all the particles present nearly hexagonal platelet shape.

  18. B-site ordered double perovskite LaBa1-xSrxZnSbO6 (0 ≤ x ≤ 1): Sr(2+)-doping-induced symmetry evolution and structure-luminescence correlations.

    PubMed

    Jiang, Pengfei; Zhou, Zhengyang; Gao, Wenliang; Cong, Rihong; Yang, Tao

    2016-03-07

    The study of perovskites has been active for a long time. Here, we rationally designed and prepared a double perovskite, LaBaZnSbO6, by selecting Zn(2+) and Sb(5+) with large size and charge differences, and, indeed, complete B-site ordering can be achieved. Careful study using powder X-ray diffraction data pinpointed its space group to be I2/m, which has rarely been seen in double perovskites. Thereafter, an interesting observation of Sr(2+)-doping-induced symmetry evolution from I2/m to P21/n was confirmed in the complete solid solutions LaBa1-xSrxZnSbO6, where the tilting system also transferred from a(-)a(-)c(0) to a(-)a(-)c(+). The transition boundary is around x = 0.4. It can also be visualized by the variation of θ (defined as c/[(a + b)/2]), which is associated with the anisotropic shrinkage of the unit cell lattice and indeed shows a minimum at x = 0.4. Such a successive modulation of both the structural symmetry and the average La/Ba/Sr-O bond distances (revealed by Rietveld refinements) motivated us to study the Eu(3+) luminescence in La0.95Eu0.05Ba1-xSrxZnSbO6. Interestingly, the maximum of charge transfer absorption of Eu(3+) shows a precise changing tendency with the A-O bond distances along with the Sr(2+) doping, clearly revealing the structure-luminescence correlations.

  19. Spin-state transition of iron in (Ba0.5Sr0.5)(Fe0.8Zn0.2)O perovskite

    NASA Astrophysics Data System (ADS)

    Feldhoff, Armin; Martynczuk, Julia; Arnold, Mirko; Myndyk, Maxym; Bergmann, Ingo; Šepelák, Vladimir; Gruner, Wolfgang; Vogt, Ulrich; Hähnel, Angelika; Woltersdorf, Jörg

    2009-11-01

    The redox behavior of iron during heating of a high-performance perovskite for ceramic oxygen separation membranes was studied by combined electron energy-loss (EELS, esp. ELNES) and Mössbauer spectroscopical in situ methods. At room temperature, the iron in (Ba0.5Sr0.5)(Fe0.8Zn0.2)O (BSFZ) is in a mixed valence state of 75% Fe in the high-spin state and 25% Fe predominantly in the low-spin state. When heated to 900C, a slight reduction of iron is observed that increases the quantity of Fe species. However, the dominant occurrence is a gradual transition in the spin-state of trivalent iron from a mixed low-spin/high-spin to a pure high-spin configuration. In addition, a remarkable amount of hybridization is found in the Fe-O bonds that are highly polar rather than purely ionic. The coupled valence/spin-state transition correlates with anomalies in thermogravimetry and thermal expansion behavior observed by X-ray diffraction and dilatometry, respectively. Since the effective cationic radii depend not only on the valence but also on the spin-state, both have to be considered when estimating under which conditions a cubic perovskite will tolerate specific cations. It is concluded that an excellent phase stability of perovskite-based membrane materials demands a tailoring, which enables pure high-spin states under operational conditions, even if mixed valence states are present. The low spin-state transition temperature of BSFZ provides that all iron species are in a pure high-spin configuration already above ca. 500C making this ceramic highly attractive for intermediate temperature applications ( 500-800C).

  20. Sub-seasonally resolved δ18O, δ13C, Mg, Sr, Ba, U and Zn records from a Belgian spleothem covering the last 700 years

    NASA Astrophysics Data System (ADS)

    Van Rampelbergh, M.; Verheyden, S.; Cheng, H.; Edwards, R.; Keppens, E.; Claeys, P. F.

    2013-12-01

    Every cave system is unique and every stalagmite has its own behavior. Therefore, when using stalagmites for paleoclimate reconstructions at high-resolution, a good understanding of what the measured proxies are reflecting is required. Generally such information is obtained by cave monitoring and/or by comparing the measured records with other paleoclimate records in the region. A stalagmite from the Han-sur-Lesse cave (Belgium) displays an extremely high growth rate (1mm/y) and annual lamination over the last 700 years allowing the comparison of the measured proxy values with the instrumental record and leading to a robust understanding of their climate transfer functions. The age model is established by layer counting and agrees well with 4 U/Th-ages and one 14C-age, confirming the seasonal character of the layering. A one-year cave monitoring with a two-week cave-visiting frequency monitored the recording of the different proxy signals in the modern calcite and their relationships to the outside cave conditions. Sub-seasonal δ18O and δ13C measurements (3 samples a layer) were carried out on the upper 50 years. The remaining 650 years were sampled for isotopes on a seasonal scale by drilling one sample per layer. LA-ICP-MS measurements for Mg, Sr, Ba, U and Zn concentrations were line tracked on the upper 50 years and are compared with the sub-seasonally resolved isotope records. Cave monitoring results show that the δ18O and δ13C values of fresh glass-slab calcite increase from November to April when the cave temperatures decrease and the drip rate increase. Results from the sub-seasonal isotope sampling show that the δ18O and δ13C values increase within the white more porous layers and decrease in the dark more compact layers. Consequently, white layers are formed during wetter and colder periods while dark layers reflect drier and warmer conditions. Further comparison of the sub-seasonal isotope and trace elemental records with instrumental data will

  1. Electronic structure of Ca, Sr, and Ba under pressure.

    NASA Technical Reports Server (NTRS)

    Animalu, A. O. E.; Heine, V.; Vasvari, B.

    1967-01-01

    Electronic band structure calculations phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure

  2. Effects of Al substitution and thermal annealing on magnetoelectric Ba0.5Sr1.5Zn2Fe12O22 investigated by the enhancement factor of 57Fe nuclear magnetic resonance.

    PubMed

    Kwon, Sangil; Kang, Byeongki; Kim, Changsoo; Jo, Euna; Lee, Soonchil; Chai, Yi Sheng; Chun, Sae Hwan; Kim, Kee Hoon

    2014-04-09

    The magnetoelectric properties of hexaferrite Ba0.5Sr1.5Zn2Fe12O22 are significantly improved by Al substitution and thermal annealing. Measuring the enhancement factor of 57Fe NMR, we found direct microscopic evidence that the magnetic moments of the L and S blocks are rotated by a magnetic field in such a way as to increase the net magnetic moment of a magnetic unit, even after the field is removed. Al substitution makes magnetoelectric property arise easily by suppressing the easy-plane anisotropy. The effect of thermal annealing is to stabilize the multiferroic state by reducing the number of pinning sites and the electron spin fluctuation. The transverse conic structure gradually changes to the alternating longitudinal conic structure where spins fluctuate more severely.

  3. Proton uptake in the H(+)-SOFC cathode material Ba(0.5)Sr(0.5)Fe(0.8)Zn(0.2)O(3-δ): transition from hydration to hydrogenation with increasing oxygen partial pressure.

    PubMed

    Poetzsch, Daniel; Merkle, Rotraut; Maier, Joachim

    2015-01-01

    Thermogravimetric investigations on the perovskite Ba(0.5)Sr(0.5)Fe(0.8)Zn(0.2)O(3-δ) (BSFZ, with mixed hole, oxygen vacancy and proton conductivity) from water vapor can occur by acid-base reaction (hydration) or redox reaction (hydrogen uptake), depending on the oxygen partial pressure, i.e. on the material's defect concentrations. In parallel, the effective diffusion coefficient of the stoichiometry relaxation kinetics also changes. These striking observations can be rationalized in terms of a defect chemical model and transport equations for materials with three mobile carriers. Implications for the search of cathode materials with mixed electronic and protonic conductivity for application on proton conducting oxide electrolytes are discussed.

  4. Magnetic Origin of Giant Magnetoelectricity in Doped Y-type Hexaferrite Ba0.5Sr1.5Zn2(Fe1 -xAlx)12O22

    NASA Astrophysics Data System (ADS)

    Noh, Woo-Suk; Ko, Kyung-Tae; Chun, Sae Hwan; Kim, Kee Hoon; Park, Byeong-Gyu; Kim, Jae-Young; Park, Jae-Hoon

    2015-03-01

    We investigated site-specific magnetic behaviors of multiferroic Ba0.5Sr1.5Zn2(Fe1 -xAlx)12O22 using Fe L2 ,3-edge x-ray magnetic circular dichroism. The Al dopants mostly replace the Fe3 + ions at octahedral (Oh) sites, which contribute unquenched angular momenta through off-centering displacements. This replacement greatly reduces the magnetic anisotropy energy to change the magnetic order from a helical to a heliconical type with enhanced magnetoelectric susceptibility (αME). The tetrahedral (Td) Fe sites exhibit magnetic hysteresis distinguishable from that of the Oh sites, especially at low magnetic fields. These results provide essential clues for the heliconical order with a giant αME and multibit memory effects in the Al-doped Y-type hexaferrite.

  5. Magnetic field reversal of electric polarization and magnetoelectric phase diagram of the hexaferrite Ba1.3Sr0.7Co0.9Zn1.1Fe10.8Al1.2O22

    NASA Astrophysics Data System (ADS)

    Shen, Shipeng; Yan, Liqin; Chai, Yisheng; Cong, Junzhuang; Sun, Young

    2014-01-01

    Low magnetic field reversal of electric polarization has been demonstrated in the multiferroic Y-type hexaferrite Ba1.3Sr0.7Co0.9Zn1.1Fe10.8Al1.2O22 single crystal. The maximum magnetoelectric coefficient at 200 K reaches 1065 ps/m near zero magnetic field. By a systematic investigation of magnetic field dependence of magnetic and dielectric responses at various temperatures, we obtained the magnetoelectric phase diagram describing the detailed evolution of the spin-induced ferroelectric phases with temperature and magnetic field. Below 225 K, the transverse spin cone can be stabilized at zero magnetic field, which is responsible for the reversal behavior of electric polarization. Our study reveals how to eventually achieve magnetic field reversal of electric polarization in hexaferrites at room temperature.

  6. Field-induced incommensurate-to-commensurate phase transition in the magnetoelectric hexaferrite Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22

    NASA Astrophysics Data System (ADS)

    Lee, Hak Bong; Song, Young-Sang; Chung, Jae-Ho; Chun, Sae Hwan; Chai, Yi Sheng; Kim, Kee Hoon; Reehuis, M.; Prokeš, K.; Mat'Aš, S.

    2011-04-01

    Using neutron diffraction, we investigated the spin structures of magnetoelectric hexaferrite, Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 (x=0.08) under a magnetic field (H⊥c). When the crystal was cooled in a zero field, longitudinal spin cones were observed at low temperatures. These incommensurate phases, however, were replaced by the commensurate phase [k1=(0,0,(3)/(2))] when the ferroelectricity was induced by an external field perpendicular to the c axis. Magnetic structure refinement confirms that this commensurate order is compatible with the spin-current polarization. We argue that planar magnetic anisotropy plays an important role in determining the magnetic structure that is responsible for its magnetoelectricity.

  7. The effect of field cooling on a spin-chiral domain structure in a magnetoelectric helimagnet Ba0.5Sr1.5Zn2Fe12O22

    NASA Astrophysics Data System (ADS)

    Hiraoka, Y.; Tanaka, Y.; Oura, M.; Wakabayashi, Y.; Kimura, T.

    2015-06-01

    Spin-chiral domain structures near a cleaved crystal face of a magnetoelectric helimagnet, Ba0.5Sr1.5Zn2Fe12O22, were examined after various magnetic and electric field-cooling procedures by means of the scanning resonant X-ray microdiffraction technique using circularly polarized X-rays. We have found that the application of a magnetic field (1-2 k Oe) during the field-cooling procedure stabilizes one of the handedness among the two spin-chiral states (left- or right-handed screw structure) and makes nearly a single spin-chiral domain in the vicinity of the cleaved crystal face. However, it makes the degree of the spin chirality spatially inhomogeneous even within a domain. We discuss the observed field-cooling effect in terms of possible formation of spin-chiral domains with "stripe-type" domain walls accompanied by randomly-distributed ferromagnetic islands.

  8. Magnetocaloric effect in multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22

    NASA Astrophysics Data System (ADS)

    Xu, Wenfei; Yang, Jing; Shen, Yude; Bai, Wei; Zhang, Yuanyuan; Liu, Jia; Tang, Kai; Wang, Zhi; Duan, Chun-gang; Tang, Xiaodong; Chu, Junhao

    2014-06-01

    Magnetocaloric effect is investigated in multiferroic Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 ceramic with Y-type hexagonal system. Three magnetic transitions, from alternating longitudinal conical to mixed conical at ˜240 K, to ferrimagnetic at ˜297 K, further to paramagnetic at ˜702 K, are unambiguously determined. Furthermore, obvious MCE is shown, and the maximum values of the magnetic entropy change and relative cooling power are evaluated to be 1.53 JKg-1K-1 and 280 JKg-1 for a field change of 7 T, respectively. In addition, inverse MCE is also observed, which might be associated with the first-order magnetic phase transition between two incommensurate longitudinal conical phases.

  9. Magnetic origin of giant magnetoelectricity in doped Y-type hexaferrite Ba(0.5)Sr(1.5)Zn(2)(Fe(1-x)Al(x))(12)O(22).

    PubMed

    Noh, Woo-Suk; Ko, Kyung-Tae; Chun, Sae Hwan; Kim, Kee Hoon; Park, Byeong-Gyu; Kim, Jae-Young; Park, Jae-Hoon

    2015-03-20

    We investigated site-specific magnetic behaviors of multiferroic Ba(0.5)Sr(1.5)Zn(2)(Fe(1-x)Al(x))(12)O(22) using Fe L(2,3)-edge x-ray magnetic circular dichroism. The Al dopants mostly replace the Fe(3+) ions at octahedral (O(h)) sites, which contribute unquenched angular momenta through off-centering displacements. This replacement greatly reduces the magnetic anisotropy energy to change the magnetic order from a helical to a heliconical type with enhanced magnetoelectric susceptibility (α(ME)). The tetrahedral (T(d)) Fe sites exhibit magnetic hysteresis distinguishable from that of the O(h) sites, especially at low magnetic fields. These results provide essential clues for the heliconical order with a giant α(ME) and multibit memory effects in the Al-doped Y-type hexaferrite.

  10. Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22

    NASA Astrophysics Data System (ADS)

    Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.

    2016-10-01

    The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multi-domain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature.

  11. Dielectric, magnetic, and lattice dynamics properties of Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22: Comparison of ceramics and single crystals

    NASA Astrophysics Data System (ADS)

    Kamba, S.; Goian, V.; Savinov, M.; Buixaderas, E.; Nuzhnyy, D.; Maryško, M.; Kempa, M.; Bovtun, V.; Hlinka, J.; Knížek, K.; Vaněk, P.; Novák, P.; Buršík, J.; Hiraoka, Y.; Kimura, T.; Kouřil, K.; Štěpánková, H.

    2010-05-01

    We prepared multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at TC=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near TC. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D3d5 hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T.

  12. Structure refinement and dielectric relaxation of M-type Ba, Sr, Ba-Sr, and Ba-Pb hexaferrites

    NASA Astrophysics Data System (ADS)

    Ashima; Sanghi, Sujata; Agarwal, Ashish; Reetu; Ahlawat, Neetu; Monica

    2012-07-01

    M-type hexaferrites with compositions BaFe12O19 (BFO), SrFe12O19 (SFO), Ba0.5Sr0.5Fe12O19 (BSFO), and Ba0.5Pb0.5Fe12O19 (BPFO) were synthesized by commercial solid state reaction method. The Rietveld refinement of x-ray powder diffraction revealed a single hexagonal phase with space group P63/mmc for BFO, SFO, and BSFO samples, whereas BPFO sample contains hematite (α-Fe2O3) phase with space group R3c along with the M-type main phase. All the samples show dispersion in dielectric constant (ɛ') and dielectric loss (tan δ) values with frequency. The values of ɛ' and tan δ increase with increase in temperature due to increase in the number of charge carriers and their mobilities, which are thermally activated. The reciprocal temperature dependence of conductivity (σac) and the most probable relaxation time (τM″) satisfies the Arrhenius relation. A perfect overlapping of the normalized plots of modulus isotherms on a single "super curve" for all the studied temperatures reveals a temperature independence of dynamic processes involved in conduction and for relaxation. Further, the complex plots of M* (M″ vs M') indicate that dc conductivity dominates in the region below the M″max point. Above M″max, the variations follow Jonscher power law (σ = Aωs) implying that ac conductivity is dominating in this region. Among the prepared samples, SFO hexaferrite has lowest values of σac, ɛ', and tan δ making it suitable for use in microwave devices.

  13. Structure refinement and dielectric relaxation of M-type Ba, Sr, Ba-Sr, and Ba-Pb hexaferrites

    SciTech Connect

    Ashima; Sanghi, Sujata; Agarwal, Ashish; Reetu; Ahlawat, Neetu; Monica

    2012-07-01

    M-type hexaferrites with compositions BaFe{sub 12}O{sub 19} (BFO), SrFe{sub 12}O{sub 19} (SFO), Ba{sub 0.5}Sr{sub 0.5}Fe{sub 12}O{sub 19} (BSFO), and Ba{sub 0.5}Pb{sub 0.5}Fe{sub 12}O{sub 19} (BPFO) were synthesized by commercial solid state reaction method. The Rietveld refinement of x-ray powder diffraction revealed a single hexagonal phase with space group P6{sub 3}/mmc for BFO, SFO, and BSFO samples, whereas BPFO sample contains hematite ({alpha}-Fe{sub 2}O{sub 3}) phase with space group R3c along with the M-type main phase. All the samples show dispersion in dielectric constant ({epsilon} Prime ) and dielectric loss (tan {delta}) values with frequency. The values of {epsilon} Prime and tan {delta} increase with increase in temperature due to increase in the number of charge carriers and their mobilities, which are thermally activated. The reciprocal temperature dependence of conductivity ({sigma}{sub ac}) and the most probable relaxation time ({tau}{sub M Double-Prime }) satisfies the Arrhenius relation. A perfect overlapping of the normalized plots of modulus isotherms on a single 'super curve' for all the studied temperatures reveals a temperature independence of dynamic processes involved in conduction and for relaxation. Further, the complex plots of M{sup *} (M Double-Prime vs M Prime ) indicate that dc conductivity dominates in the region below the M Double-Prime {sub max} point. Above M Double-Prime {sub max}, the variations follow Jonscher power law ({sigma} = A{omega}{sup s}) implying that ac conductivity is dominating in this region. Among the prepared samples, SFO hexaferrite has lowest values of {sigma}{sub ac}, {epsilon} Prime , and tan {delta} making it suitable for use in microwave devices.

  14. Reaction kinetics and magnetic properties of Ba and Sr ferrites

    NASA Astrophysics Data System (ADS)

    Melzer, K.; Martin, A.; Klink, T.; Wartewig, P.

    1992-04-01

    This Mössbauer study is concerned with the formation mechanism of hexaferrites (n=6) and of monoferrites (n=1) in the systems (1) BaCO3+nFe2O3, (2) SrCO3+nFe2O3 and (3) 0.5BaCO3+0.5SrCO3+nFe2O3. With a molar ratio of 1∶1 for the starting materials one gets final reaction products with different crystalline structures. The experimental results indicate that the thermodynamical final state of the hexaferrite formation is reached on different routes. Various reaction models are discussed.

  15. Domain matched epitaxial growth of (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} thin films on (0001) Al{sub 2}O{sub 3} with ZnO buffer layer

    SciTech Connect

    Krishnaprasad, P. S. E-mail: mkj@cusat.ac.in; Jayaraj, M. K. E-mail: mkj@cusat.ac.in; Antony, Aldrin; Rojas, Fredy

    2015-03-28

    Epitaxial (111) Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) thin films have been grown by pulsed laser deposition on (0001) Al{sub 2}O{sub 3} substrate with ZnO as buffer layer. The x-ray ω-2θ, Φ-scan and reciprocal space mapping indicate epitaxial nature of BST thin films. The domain matched epitaxial growth of BST thin films over ZnO buffer layer was confirmed using Fourier filtered high resolution transmission electron microscope images of the film-buffer interface. The incorporation of ZnO buffer layer effectively suppressed the lattice mismatch and promoted domain matched epitaxial growth of BST thin films. Coplanar inter digital capacitors fabricated on epitaxial (111) BST thin films show significantly improved tunable performance over polycrystalline thin films.

  16. White HDPE bottles as source of serious contamination of water samples with Ba and Zn.

    PubMed

    Reimann, Clemens; Grimstvedt, Andreas; Frengstad, Bjørn; Finne, Tor Erik

    2007-03-15

    During a recent study of surface water quality factory new white high-density polyethylene (HDPE) bottles were used for collecting the water samples. According to the established field protocol of the Geological Survey of Norway the bottles were twice carefully rinsed with water in the field prior to sampling. Several blank samples using milli-Q (ELGA) water (>18.2 MOmega) were also prepared. On checking the analytical results the blanks returned values of Ag, Ba, Sr, V, Zn and Zr. For Ba and Zn the values (c. 300 microg/l and 95 microg/l) were about 10 times above the concentrations that can be expected in natural waters. A laboratory test of the bottles demonstrated that the bottles contaminate the samples with significant amounts of Ba and Zn and some Sr. Simple acid washing of the bottles prior to use did not solve the contamination problem for Ba and Zn. The results suggest that there may exist "clean" and "dirty" HDPE bottles depending on manufacturer/production process. When collecting water samples it is mandatory to check bottles regularly as a possible source of contamination.

  17. Magnetic field reversal of electric polarization and magnetoelectric phase diagram of the hexaferrite Ba{sub 1.3}Sr{sub 0.7}Co{sub 0.9}Zn{sub 1.1}Fe{sub 10.8}Al{sub 1.2}O{sub 22}

    SciTech Connect

    Shen, Shipeng; Yan, Liqin; Chai, Yisheng; Cong, Junzhuang; Sun, Young

    2014-01-20

    Low magnetic field reversal of electric polarization has been demonstrated in the multiferroic Y-type hexaferrite Ba{sub 1.3}Sr{sub 0.7}Co{sub 0.9}Zn{sub 1.1}Fe{sub 10.8}Al{sub 1.2}O{sub 22} single crystal. The maximum magnetoelectric coefficient at 200 K reaches 1065 ps/m near zero magnetic field. By a systematic investigation of magnetic field dependence of magnetic and dielectric responses at various temperatures, we obtained the magnetoelectric phase diagram describing the detailed evolution of the spin-induced ferroelectric phases with temperature and magnetic field. Below 225 K, the transverse spin cone can be stabilized at zero magnetic field, which is responsible for the reversal behavior of electric polarization. Our study reveals how to eventually achieve magnetic field reversal of electric polarization in hexaferrites at room temperature.

  18. The Structural Disorder and Lattice Stability of (Ba,Sr)(Co,Fe)O3 Complex Perovskites

    SciTech Connect

    S.N.Rashkeev

    2011-05-01

    The structural disorder and lattice stability of complex perovskite (Ba,Sr)(Co,Fe)O3, a promising cathode material for solid oxide fuel cells and oxygen permeation membranes, is explored by means of first principles DFT calculations. It is predicted that Ba and Sr ions easily exchange their lattice positions (A-cation disorder) similarly to Co and Fe ions (B-cation disorder). The cation antisite defects (exchange of A- and B-type cations) have a relatively high formation energy. The BSCF is predicted to exist in an equilibrium mixture of several phases and can decompose exothermically into the Ba- and Co-rich hexagonal (Ba,Sr)CoO3 and Sr- and Fe-rich cubic (Ba,Sr)FeO3 perovskites.

  19. First principles investigations of structural, elastic, dielectric and piezoelectric properties of { Ba,Sr,Pb } TiO3, { Ba,Sr,Pb } ZrO3 and { Ba,Sr,Pb } { Zr,Ti } O3 ceramics

    NASA Astrophysics Data System (ADS)

    Akgenc, Berna; Tasseven, Cetin; Cagin, Tahir

    2015-03-01

    We use first-principle density-functional study of structural, anisotropic mechanical, dielectric and piezoelectric properties of {Ba,Sr,Pb}TiO3, {Ba,Sr,Pb}ZrO3 and {Ba,Sr,Pb}{Zr,Ti}O3 alloys in cubic perovskite structures at zero temperature. Because there is significant interest in finding new piezoelectrics that do not contain toxic elements such as lead. In this study, we compare piezoelectric response of those alloys to synthesize outstanding piezoelectric materials. In perovskite structures, the spontaneous polarization is due to enormous values of Born effective charges computed by linear response within density functional perturbation theory, which are much larger than predicted nominal charge. We deeply investigated the effects of composition, order and site defects structure on piezoelectric constants.

  20. Syntheses, crystal structures and characterizations of BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}

    SciTech Connect

    Jiang Hailong; Feng Meiling; Mao Jianggao . E-mail: mjg@ms.fjirsm.ac.cn

    2006-06-15

    Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by the solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with three ZnO{sub 3}Cl tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements. -- Graphical abstract: Two new barium zinc selenite and tellurite, namely, BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2}, have been synthesized by solid state reaction. The structure of BaZn(SeO{sub 3}){sub 2} features 1D double chains of [Zn(SeO{sub 3}){sub 2}]{sup 2-} anions composed of four- and eight-member rings which are alternatively along a-axis. The 1D double chains of [Zn{sub 2}(TeO{sub 3}){sub 2}Cl{sub 3}]{sup 3-} anions in BaZn(TeO{sub 3})Cl{sub 2} are formed by Zn{sub 3}Te{sub 3} rings in which each tellurite group connects with one ZnO{sub 3}Cl and two ZnO{sub 2}Cl{sub 2} tetrahedra. BaZn(SeO{sub 3}){sub 2} and BaZn(TeO{sub 3})Cl{sub 2} are wide bandgap semiconductors based on optical diffuse reflectance spectrum measurements.

  1. Crystal chemical and quantum chemical studies of Ba(Sr)-Nb oxide compounds

    NASA Technical Reports Server (NTRS)

    Zubkov, V. G.; Turzhevsky, S. A.; Pereliaev, V. A.; Liechtenstein, A. I.; Gubanov, V. A.

    1990-01-01

    The information available on the BaO(SrO)-NbO-NbO2 system with the niobium atom in the lower oxidation degree is very limited. Very few compounds have been found previously in this system. They are BaNbO3, SrxNbO3(0,7=x=1), Ba2Nb2O9, SrNb8O14; and some suggestions on the BaNb8O14 existence have been made also. At the same time Nb-based oxide compounds could be quite interesting in the search of new noncopper high T(sub c) superconductors Researchers studied Ba(Sr) NbxO2x-2 and Ba2(Sr2)-NbxO2x-1 compositions in the phase diagram of BaO(SrO)-NbO-NbO2 system. The synthesis of the materials was carried out in vacuum at the temperatures of 1000 to 1500 C. Barium carbonate and niobium pentoxide were used as initial components. X-ray analysis was carried out.

  2. Soft-mode spectroscopy in cubic (Ba0.8Sr0.2)Ti0.95(Zn1/3Nb2/3)0.05O3 by hyper-Raman scattering and the mechanism of the phase transition

    NASA Astrophysics Data System (ADS)

    Nabil, Dhifallah; Hehlen, Bernard; El Marssi, Mimoun; Mohamed, Dammak; Khemakhem, Hamadi

    2016-12-01

    This paper presents a survey of soft modes and their relationship to structural phase transitions. After introducing the concept of a soft mode, the origin of softening is considered from a lattice-dynamical point. The Landau theory approach to structural transitions is then discussed, followed by a generalization of the soft-mode concept through the use of the dynamic order-parameter susceptibility. The hyper-Raman spectra in the cubic phase of (Ba0.8Sr0.2)Ti0.95(Zn1/3Nb2/3)0.05O3 are studied with special emphasis on the lowest-frequency phonon mode. The spectral structure is found to change above the Curie temperature (303-873 K). Soft modes were put forward by Cochran and Anderson about 50 years ago as an explanation of structural phase transitions. Extending Landau's theory of phase transitions, their prediction was that the square of the frequency of the soft mode was proportional to ω0 (T) = C √{ T - TC } where Tc is the transition temperature.

  3. Dielectric, magnetic, and lattice dynamics properties of Y-type hexaferrite Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}Fe{sub 12}O{sub 22}: Comparison of ceramics and single crystals

    SciTech Connect

    Kamba, S.; Goian, V.; Savinov, M.; Buixaderas, E.; Nuzhnyy, D.; Marysko, M.; Kempa, M.; Bovtun, V.; Hlinka, J.; Knizek, K.; Vanek, P.; Novak, P.; Bursik, J.; Hiraoka, Y.; Kimura, T.; Kouril, K.; Stepankova, H.

    2010-05-15

    We prepared multiferroic Y-type hexaferrite Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}Fe{sub 12}O{sub 22} ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at T{sub C}=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near T{sub C}. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D{sub 3d}{sup 5} hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T.

  4. Superconductivity in the Sn-Ba-Sr-Y-Cu-O system

    NASA Technical Reports Server (NTRS)

    Aleksandrov, K. S.; Khrustalev, B. P.; Krivomazov, S. N.; Petrov, M. I.; Vasilyev, A. D.; Zwegintsev, S. A.

    1991-01-01

    After the discovery of high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides were synthesized. Here, researchers report the results of the search for superconductivity in the compounds based on tin which has a lone electron pair like Bi, Tl, and Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3O(sub x), Sn1Ba1Ca1Cu3O(sub x), Sn1Ba1Mg1Cu3O(sub x), Sn1Sr1Ca1Cu3O(sub x), Sn1Sr1Mg1Cu3O(sub x), and Sn1Ca1Mg1Cu3O(sub x). The initial components were oxides and carbonates of the appropriate elements. A standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3O(sub x) showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3O(sub x) was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperature undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3O(sub x) ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase, two-valent cations Ba and Sr were partially substituted by univalent (K) and three-valent ones (Y).

  5. Superconductivity in the Sn-Ba-Sr-Y-Cu-O system

    NASA Technical Reports Server (NTRS)

    Aleksandrov, K. S.; Khrustalev, B. P.; Krivomazov, S. N.; Petrov, M. I.; Vasilyev, A. D.; Zwegintsev, S. A.

    1990-01-01

    Since Bednorz and Muller discovered high-T(sub c) superconductivity in the La-Ba-Cu-O compound, several families of superconducting oxides have been synthesized. Here, researchers report the results of search for superconductivity in the compounds based on tin, which has a lone electron pair like Bi, Tl, Pb. The following compounds were synthesized: Sn1Ba1Sr1Cu3Ox, Sn1Ba1Ca1Cu3Ox, Sn1Ba1Mg1Cu3Ox, Sn1Sr1Ca1Cu3Ox, Sn1Sr1Mg1Cu3Ox, Sn1Ca1Mg1Cu3Ox. The initial components were oxides and carbonates of the appropriate elements. Standard firing-grinding procedure was used. Final heating was carried out at 960 C during 12 hours. Then the samples were cooled inside the furnace. All the synthesis cycles were carried out in air atmosphere. Among the synthesized compounds only Sn1Ba1Sr1Cu3Ox showed remarkable conductivity. Other compounds were practically dielectrics. Presence of a possible superconductivity in Sn1Ba1Sr1Cu3Ox was defined by using the Meissner effect. At low temperature a deviation from paramagnetic behavior is observed. The hysteresis loops obtained at lower temperatures undoubtly testify to the presence of a superconductive phase in the sample. However, the part of the superconductive phase in the Sn1Ba1Sr1Cu3Ox ceramic turned out to be small, less than 2 percent, which agrees with the estimation from magnetic data. In order to increase the content of the superconductive phase two-valent cations Ba, Sr were partially substituted by univalent (K) and three-valent ones (Y).

  6. The solubility of (Ba,Sr)SO 4 precipitates: Thermodynamic equilibrium and reaction path analysis

    NASA Astrophysics Data System (ADS)

    Felmy, Andrew R.; Rai, Dhanpat; Moore, Dean A.

    1993-09-01

    The solubility of (Ba,Sr)SO 4 precipitates, varying in SrSO 4 mole fraction from 0.05-0.90, was investigated at room temperature with an equilibration period extending to almost three years. The data show that on or before 315 days of equilibration the precipitates reach a reversible equilibrium with the aqueous solution. The reversibility of this equilibrium was verified both by the attainment of steady-state concentrations with time and by heating the samples to perturb the equilibrium and then observing the slow return to the initial equilibrium state. The dissolution of the (Ba,Sr)SO 4 precipitates does not, in general, follow limiting reaction paths as defined by the Lippmann solutus or stoichiometric dissolution curves. In addition, activity coefficient calculations for the BaSO 4 and SrSO 4 components of the solid phase, using either total bulk analysis or near-surface analysis of the component mole fractions, do not satisfy the Gibbs-Duhem equation, demonstrating that a single solid-solution phase does not control both the aqueous Ba and Sr concentrations. Instead, our long-term equilibration data can be explained by the unavoidable formation of small amounts of barite and substitution of Sr into a solid-solution phase with the BaSO 4 component of the solid-solution phase never reaching thermodynamic equilibrium with the aqueous phase.

  7. Bi3+ Luminescence in ABiO2Cl (A = Sr, Ba) and BaBiO2Br

    SciTech Connect

    Porter-Chapman, Yetta D.; Bourret-Courchesne, Edith E.; Derenzo,Stephen E.

    2007-01-18

    Trivalent bismuth luminescence is reported in three Sillenbismuth oxyhalide phases, SrBiO2Cl, BaBiO2Cl, and BaBiO2Br. Thesecompounds exhibit Bi 6s6->6 s2 emission under UV and X-ray radiation.At room temperature, BaBiO2Cl shows the most intense light emission, withspectral and decay properties similar to those found in Bi4Ge3O12 (BGO).At low temperatures, each phase show an increase in the photoluminescenceintensities and a narrowing of the emission peaks. In contrast to thetemperature dependence of BGO, X-ray excited luminescence intensities ofall three phases remain relatively constant throughout the temperaturerange 10 - 295 K. This result indicates that the Sillen phases undergoless thermal quenching than BGO. The low temperature and room temperatureradio-luminescence decay times were determined from pulsed x-raymeasurements. At room temperature, SrBiO2Cl exhibits faster decays thanBGO, while, BaBiO2Cl and BaBiO2Br have decay times similar toBGO.

  8. Room temperature magnetoelectric coupling in Zn1-xCoxO/BaTiO3 bilayer system

    NASA Astrophysics Data System (ADS)

    Sundararaj, Anuraj; Annal Therese, Helen; Ramaswamy, Shivaraman; Chandrasekaran, Gopalakrishnan; Annamalai, Karthigeyan

    2014-09-01

    We report on room temperature magnetoelectric coupling in Zn1-xCoxO/BaTiO3 (x = 0.02, 0.05, and 0.10) bilayer thinfilm multiferroic system (BLS) grown on SrTiO3 (100) substrate. All the BLSs exhibit room temperature ferroelectric response. The BLS with x = 0.02 is paramagnetic, while the BLS with x = 0.05 and 0.10 is weakly ferromagnetic. Increase in Co concentration of the BLS results in reduction of permittivity and electric polarization along with increase of coercive voltage, coercive field, and magnetic moment. The d33 value change from 23 pm/V to 30 pm/V with increase in external magnetic field from 1500 G to 2500 G for BLS with x = 0.05. This shows that Zn1-xCoxO/BaTiO3 is magnetoelectrically coupled at room temperature.

  9. Effect of local environment on crossluminescence kinetics in SrF2:Ba and CaF2:Ba solid solutions

    NASA Astrophysics Data System (ADS)

    Terekhin, M. A.; Makhov, V. N.; Lebedev, A. I.; Sluchinskaya, I. A.

    2015-10-01

    Spectral and kinetic properties of extrinsic crossluminescence (CL) in SrF2:Ba(1%) and CaF2:Ba(1%) are compared with those of intrinsic CL in BaF2 and are analyzed taking into account EXAFS data obtained at the Ba LIII edge and results of first-principles calculations. The CL decay time was revealed to be longer in SrF2:Ba and CaF2:Ba compared to BaF2. This fact contradicts the expected acceleration of luminescence decay which could result from an increased overlap of wave functions in solid solutions due to shortening of the Ba-F distance obtained in both EXAFS measurements and first-principles calculations. This discrepancy is explained by the effect of migration and subsequent non-radiative decay of the Ba(5p) core holes in BaF2 and by decreasing of the probability of optical transitions between Ba(5p) states and the valence band in SrF2:Ba and CaF2:Ba predicted by first-principles calculations.

  10. Thermoelectric properties of BaSi2, SrSi2, and LaSi

    NASA Astrophysics Data System (ADS)

    Hashimoto, Kohsuke; Kurosaki, Ken; Imamura, Yasushi; Muta, Hiroaki; Yamanaka, Shinsuke

    2007-09-01

    We studied the thermoelectric properties of BaSi2, SrSi2, and LaSi. The polycrystalline samples were prepared by spark plasma sintering (SPS). The electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) were measured above room temperature. The power factor (S2/ρ) is quite low (below 10-5 Wm-1 K-2 over the whole temperature range) for BaSi2 and LaSi, while relatively high (1.19×10-3 Wm-1 K-2 at 331 K) for SrSi2. BaSi2 exhibits quite low κ. The κ values at room temperature are 1.56, 5.25, and 6.71 Wm-1 K-1 for BaSi2, SrSi2, and LaSi, respectively. The maximum values of the dimensionless figure of merit, ZT =S2T/ρ/κ, are 0.01 at 954 K for BaSi2, 0.09 at 417 K for SrSi2, and 0.002 at 957 K for LaSi.

  11. High-pressure densified solid solutions of alkaline earth hexaborides (Ca/Sr, Ca/Ba, Sr/Ba) and their high-temperature thermoelectric properties

    SciTech Connect

    Gürsoy, M.; Takeda, M.; Albert, B.

    2015-01-15

    Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB{sub 6}, SrB{sub 6}, BaB{sub 6} and the ternary hexaborides Ca{sub x}Sr{sub 1−x}B{sub 6}, Ca{sub x}Ba{sub 1−x}B{sub 6}, Sr{sub x}Ba{sub 1−x}B{sub 6} (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB{sub 6} (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process. - Highlights: • Solid solutions of alkaline earth hexaborides were synthesized. • High-temperature thermoelectric properties of mixed calcium borides are excellent. • Spark plasma source densification results in high ZT values. • Borides are rare-earth free and refractory materials.

  12. Hysteretic electrical transport in BaTiO{sub 3}/Ba{sub 1−x}Sr{sub x}TiO{sub 3}/Ge heterostructures

    SciTech Connect

    Ngai, J. H.; Kumah, D. P.; Walker, F. J.; Ahn, C. H.

    2014-02-10

    We present electrical transport measurements of heterostructures comprised of BaTiO{sub 3} and Ba{sub 1−x}Sr{sub x}TiO{sub 3} epitaxially grown on Ge. Sr alloying imparts compressive strain to the BaTiO{sub 3}, which enables the thermal expansion mismatch between BaTiO{sub 3} and Ge to be overcome to achieve c-axis oriented growth. The conduction bands of BaTiO{sub 3} and Ba{sub 1−x}Sr{sub x}TiO{sub 3} are nearly aligned with the conduction band of Ge, which facilitates electron transport. Electrical transport measurements through the dielectric stack exhibit rectifying behavior and hysteresis, where the latter is consistent with ferroelectric switching.

  13. Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH

    SciTech Connect

    Evans, Michael J.; Lee, Myeong H.; Holland, Gregory P.; Daemen, Luke L.; Sankey, Otto F.; Haeussermann, Ulrich

    2009-08-15

    Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH (AeGaTtH) have been investigated by means of inelastic neutron scattering (INS) and first principles calculations. The compounds contain separated Ga-H units being part of a two dimensional polyanionic layer, [TtGaH]{sup 2-} (Tt=Si, Ge, Sn). The INS spectra show internal Ga-H bending and stretching modes at frequencies around 900 and 1200 cm{sup -1}, respectively. While the stretching mode is virtually invariant with respect to the variable chemical environment of the Ga-H unit, the bending mode frequency varies and is highest for BaGaSiH and lowest for BaGaSnH. The stretching mode is a direct measure of the Ga-H bond strength, whereas the bending mode reflects indirectly the strength of alkaline earth metal-hydrogen interaction. Accordingly, the terminal Ga-H bond in solid state AeGaTtH is distinct, but-compared to molecular gallium hydrides-very weak. - Graphical abstract: Vibrational properties of the gallium monohydrides SrGaGeH, BaGaSiH, BaGaGeH, and BaGaSnH have been investigated and revealed Ga-H stretching mode frequencies around 1200 cm{sup -1}. This implies that the terminal Ga-H bond in solid state polyanionic gallium hydrides is very weak compared to molecular gallium hydride species.

  14. The new barium zinc mercurides Ba3ZnHg10 and BaZn0.6Hg3.4 - Synthesis, crystal and electronic structure

    NASA Astrophysics Data System (ADS)

    Schwarz, Michael; Wendorff, Marco; Röhr, Caroline

    2012-12-01

    The title compounds Ba3ZnHg10 and BaZn0.6Hg3.4 were synthesized from stoichiometric ratios of the elements in Ta crucibles. Their crystal structures, which both represent new structure types, have been determined using single crystal X-ray data. The structure of Ba3ZnHg10 (orthorhombic, oP28, space group Pmmn, a=701.2(3), b=1706.9(8), c=627.3(3)pm, Z=2, R1=0.0657) contains folded 44 Hg nets, where the meshes form the bases of flat rectangular pyramids resembling the structure of BaAl4. The flat pyramids are connected via Hg-Zn/Hg bonds, leaving large channels at the folds, in which Ba(1) and Hg(2) atoms alternate. Whereas the remaining Hg/Zn atoms form a covalent 3D network of three- to five-bonded atoms with short M-M distances (273-301 pm; CN 9-11), the Hg(2) atoms in the channels adopt a comparatively large coordination number of 12 and increased distances (317-348 pm) to their Zn/Hg neighbours. In the structure of BaZn0.6Hg3.4 (cubic, cI320, space group I4bar3d, a=2025.50(7) pm, Z=64, R1=0.0440), with a chemical composition not much different from that of Ba3ZnHg10, the Zn/Hg atoms of the mixed positions M(1/2) are arranged in an slightly distorted primitive cubic lattice with a 4×4×4 subcell relation to the unit cell. The 24 of the originating 64 cubes contain planar cis tetramers Hg(5,6)4 with Hg in a nearly trigonal planar or tetrahedral coordination. In another 24 of the small cubes, two opposing faces are decorated by Hg(3,4)2 dumbbells, two by Ba(2) atoms respectively. The third type of small cubes are centered by Ba(1) atoms only. The complex 3D polyanionic Hg/Zn network thus formed is compared with the Hg partial structure in Rb3Hg20 applying a group-subgroup relation. Despite their different overall structures, the connectivity of the negatively charged Hg atoms, the rather metallic Zn bonding characteristic (as obtained from FP-LAPW band structure calculations) and the coordination number of 16 for all Ba cations relate the two title compounds.

  15. Sr/Ca and Ba/Ca variations in environmental and biological sources: A survey of marine and terrestrial systems

    NASA Astrophysics Data System (ADS)

    Peek, Stephanie; Clementz, Mark T.

    2012-10-01

    The relative concentrations of strontium to calcium (Sr/Ca) and barium to calcium (Ba/Ca) in mammalian bioapatite are common biogeochemical indicators for trophic level and/or dietary preferences in terrestrial foodwebs; however, similar research in marine foodwebs is lacking. This study combined environmental and biological Sr/Ca and Ba/Ca data from both terrestrial and marine settings from 62 published books, reports, and studies along with original data collected from 149 marine mammals (30 species) and 83 prey items (18 species) and found that variations in Sr/Ca and Ba/Ca ratios of biological and environmental samples are appreciably different in terrestrial and marine systems. In terrestrial systems, environmental sources account for most of the variations in Sr/Ca and Ba/Ca ratios. In contrast, environmental sources in marine systems (i.e., seawater) are comparatively invariant, meaning most of the variations in Sr/Ca and Ba/Ca ratios originate from biological processes. Marine consumers, particularly non-mammalian and mammalian vertebrates, show evidence of biopurification of Ca relative to Sr and Ba, similar to what is observed in terrestrial systems; however, unlike terrestrial systems, variations in Sr/Ca and Ba/Ca ratios of environmental sources are overprinted by bioaccumulation of Sr and Ba at the base of marine foodwebs. This demonstrates that in marine systems, spatial or temporal differences may have little to no effect on Sr/Ca and Ba/Ca ratios of marine vertebrates, making Sr/Ca, and to a lesser extent Ba/Ca, potentially useful global proxies for trophic level and dietary preferences of marine vertebrates.

  16. Structure and magnetic properties of Zn-Ti-substituted Ba-ferrite particles for magnetic recording

    NASA Astrophysics Data System (ADS)

    Wang, C. S.; Wei, F. L.; Lu, M.; Han, D. H.; Yang, Z.

    1998-03-01

    The formation process of Zn-Ti-doped Ba-ferrite particles was investigated by the X-ray diffraction technique, transmission electron microscope and magnetic measurements. The effects of heating temperature Th and the Zn-Ti substitution x on the microstructure and magnetic properties of BaFe 12-2 xZn xTi x O 19 particles with x=0.10-0.80 were studied. The temperature dependence of magnetic properties of these particles was measured.

  17. Synthesis and Structure Determination of Ferromagnetic Semiconductors LaAMnSnO6 (A = Sr Ba)

    SciTech Connect

    T Yang; T Perkisas; J Hadermann; M Croft; A Ignatov; M Greenblatt

    2011-12-31

    LaAMnSnO{sub 6} (A = Sr, Ba) have been synthesized by high temperature solid-state reactions under dynamic 1% H{sub 2}/Ar flow. Rietveld refinements on room temperature powder X-ray diffraction data indicate that LaSrMnSnO{sub 6} crystallizes in the GdFeO{sub 3}-structure, with space group Pnma and, combined with transmission electron microscopy, LaBaMnSnO{sub 6} in Imma. Both space groups are common in disordered double-perovskites. The Mn{sup 3+} and Sn{sup 4+} ions whose valence states were confirmed by X-ray absorption spectroscopy, are completely disordered over the B-sites and the BO{sub 6} octahedra are slightly distorted. LaAMnSnO{sub 6} are ferromagnetic semiconductors with a T{sub C} = 83 K for the Sr- and 66 K for the Ba-compound. The title compounds, together with the previously reported LaCaMnSnO{sub 6} provide an interesting example of progression from Pnma to Imma as the tolerance factor increases. An analysis of the relationship between space group and tolerance factor for the series LaAMnMO{sub 6} (A = Ca, Sr, Ba; M = Sn, Ru) provides a better understanding of the symmetry determination for double perovskites.

  18. Growth and interface engineering in thin-film Ba0.6Sr0.4TiO3 /SrMoO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Radetinac, Aldin; Ziegler, Jürgen; Vafaee, Mehran; Alff, Lambert; Komissinskiy, Philipp

    2017-04-01

    Epitaxial heterostructures of ferroelectric Ba0.6Sr0.4TiO3 and highly conducting SrMoO3 were grown by pulsed laser deposition on SrTiO3 (0 0 1) substrates. Surface oxidation of the SrMoO3 film is suppressed using a thin cap interlayer of Ba0.6Sr0.4TiO3-δ grown in reduced atmosphere. As shown by X-ray photoelectron spectroscopy, the Mo4+ valence state of the SrMoO3 films is stable upon annealing of the sample in oxygen up to 600 °C. The described oxygen interface engineering enables utilization of the highly conducting material SrMoO3 in multilayer oxide ferroelectric varactors.

  19. Characterization of novel BaZnSnO thin films by solution process and applications in thin film transistors

    SciTech Connect

    Li, Jun; Huang, Chuan-Xin; Zhang, Jian-Hua; Zhu, Wen-Qing; Jiang, Xue-Yin; Zhang, Zhi-Lin

    2015-08-15

    Graphical abstract: This work reports the Ba content on thin film transistor based on a novel BaZnSnO semiconductor using solution process. - Highlights: • No reports about BaZnSnO thin film using solution process. • BaZnSnO thin film transistor (TFT) was firstly fabricated. • BaZnSnO-TFT shows a acceptable performace. • Influence of Ba content on BaZnSnO-TFT. - Abstract: A novel BaZnSnO semiconductor is fabricated using solution process and the influence of Ba addition on the structure, the chemical state of oxygen and electrical performance of BaZnSnO thin films are investigated. A high performance BaZnSnO-based thin film transistor with 15 mol% Ba is obtained, showing a saturation mobility of 1.94 cm{sup 2}/V s, a threshold voltage of 3.6 V, an on/off current ratio of 6.2 × 10{sup 6}, a subthreshold swing of 0.94 V/decade, and a good bias stability. Transistors with solution processed BaZnSnO films are promising candidates for the development of future large-area, low-cost and high-performance electronic devices.

  20. Petrogenesis and Tectonic Implications for High Ba-Sr Porphyries from South Qinling Oroganic Belt, China

    NASA Astrophysics Data System (ADS)

    Zhang, H. F.; Luo, B. J.; Shen, L. M.; Liu, Y.

    2014-12-01

    The Qinling orgenic belt resulted from collision between the North China plate and the Yangtze blocks during Triassic. In the South Qinling orogenic belt, there are lots of small porphyry bodies with area <0.5 km2. These porphyry bodies consist mainly of granodiorite porphyries in petrography. They are closely related to Cu, Mo, Au and Fe mineralization. In this presentation, we carry out an integrated study of LA-ICP-MS zircon U-Pb dating, geochemical and Sr-Nd-Hf isotopic compositions for the porphyry bodies. U-Pb zircon dating shows that they have magma crystallization ages of 145~150 Ma.They are high-potassium calc-alkaline, characterized by high Sr (up to 1300 ppm) and Ba (up to 5000 ppm). Rear earth element data for the porphyries display moderately fractionated REE patterns with (La/Yb)N=9~26 and Eu/Eu*=0.8~1.0. Geochemical characteristics of the granodiorite porphyries are good consistent with high Ba-Sr granitoids [1,2]. These granodiorite porphyries have whole-rock initial 87Sr/86Sr ratios ranging from 0.7046 to 0.7075, ɛNd (t) values ranging from - 4.6 to - 2.5, and zircon ɛHf(t) values ranging from - 2.2 to +0.8. We suggest that their magma was derived from partial melting of enriched mantle sources. The strong enrichment of Sr and Ba imply that the mantle sources could be metasomatized by fluid or melt released from subducting slab (including sediments) due to previous subduction of the Ma-Lue ocean slab at the south of the South Qinling orogenic belt. Lithospheric delamination at ~150 Ma can account for their magma generation for the porphyries. References [1] Fowler M B, Henney P J, Darbyshire D, et al. Petrogenesis of high Ba-Sr granites: the Rogart pluton, Sutherland. Journal of the Geological Society. 2001, 158: 521-534. [2] Choi S G, Rajesh V J, Seo J, et al. Petrology, geochronology and tectonic implications of Mesozoic high Ba-Sr granites in the Haemi area, Hongseong Belt, South Korea. Island Arc. 2009, 18: 266-281.

  1. Ca, Sr and Ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence

    USGS Publications Warehouse

    Bullen, Thomas D.; Chadwick, Oliver A.

    2016-01-01

    Nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus (P) and calcium (Ca) from minerals at depth and concentrate those nutrients at the surface. Here we use soil chemistry and stable isotopes of the alkaline earth elements Ca, strontium (Sr) and barium (Ba) to test the hypothesis that biolifting of P has been an important pedogenic process across a soil climosequence developed on volcanic deposits at Kohala Mountain, Hawaii. The geochemical linkage between these elements is revealed as generally positive site-specific relationships in soil mass gains and losses, particularly for P, Ba and Ca, using the ratio of immobile elements titanium and niobium (Ti/Nb) to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials. At sites where P is enriched in surface soils relative to abundances in deeper soils, the isotope compositions of exchangeable Ca, Sr and Ba in the shallowest soil horizons (< 10 cm depth) are lighter than those of the volcanic parent materials and trend toward those of plants growing on fresh volcanic deposits. In contrast the isotope composition of exchangeable Ba in deeper soil horizons (> 10 cm depth) at those sites is consistently heavier than the volcanic parent materials. The isotope compositions of exchangeable Ca and Sr trend toward heavier compositions with depth more gradually, reflecting increasing leakiness from these soils in the order Ba < Sr < Ca and downward transfer of light biocycled Ca and Sr to deeper exchange sites. Given the long-term stability of ecosystem properties at the sites where P is enriched in surface soils, a simple box model demonstrates that persistence of isotopically light exchangeable Ca, Sr and Ba in the shallowest soil horizons requires that the uptake flux to plants from those near-surface layers is less than the recycling flux returned to the surface as

  2. Clathrate formation in the systems Sr–Cu–Ge and (Ba,Sr)–Cu–Ge

    SciTech Connect

    Zeiringer, I.; Moser, R.; Kneidinger, F.; Podloucky, R.; Royanian, E.; Grytsiv, A.; Bauer, E.; Giester, G.; Falmbigl, M.; Rogl, P.

    2014-09-15

    In the ternary system Sr–Cu–Ge, a novel clathrate type-I phase was detected, Sr{sub 8}Cu{sub x}Ge{sub 46−x} (5.2≤x<5.4), which exists close to the Zintl limit in a small temperature interval. Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} decomposes eutectoidally on cooling at 730±3 °C into (Ge), SrGe{sub 2} and τ{sub 1}-SrCu{sub 2−x}Ge{sub 2+x}. Phase equilibria at 700 °C have been established for the Ge rich part and are characterized by the appearance of only one ternary compound, τ{sub 1}-SrCu{sub 2−x}Ge{sub 2+x}, which crystallizes with the ThCr{sub 2}Si{sub 2} structure type and forms a homogeneity range up to x=0.4 (a=0.42850(4), c=1.0370(1) nm). Additionally, the extent of the clathrate type-I solid solution Ba{sub 8−y}Sr{sub y}Cu{sub x}Ge{sub 46−x} (0≤y≤∼5.6; 5.2≤x≤5.4, from as cast alloys) has been studied at various temperatures. The clathrate type-I crystal structure (space group Pm3{sup ¯}n) has been proven by X-ray single crystal diffraction on two single crystals with the composition (from refinement): Sr{sub 8}Cu{sub 5.36}Ge{sub 40.64} (a=1.06368(2) nm at 300 K) and Ba{sub 4.86}Sr{sub 3.14}Cu{sub 5.36}Ge{sub 40.64} (a=1.06748(2) nm at 300 K) measured at 300, 200 and 100 K. From the temperature dependence of the lattice parameters and the atomic displacement parameters, thermal expansion coefficients, Debye- and Einstein-temperatures and the speed of sound have been determined. From heat capacity measurements of Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} at low temperatures the Sommerfeld coefficient (γ=24 mJ/mol K{sup 2}) and the Debye temperature (Θ{sub D}{sup LT}=273 K) have been extracted. From a detailed analysis of these data at higher temperatures, Einstein branches of the phonon dispersion relation have been derived and compared to those obtained from the atomic displacement parameters. Electrical resistivity measurements of Sr{sub 8}Cu{sub 5.3}Ge{sub 40.7} reveal a rather metallic behavior in the low temperature range (<300 K

  3. Pressure driven ferroelectric to paraelectric transition in Sr doped BaTiO{sub 3}

    SciTech Connect

    Basu, Abhisek Jana, Rajesh; Mandal, Guruprasad; Mukherjee, Goutam Dev; Chandra, Amreesh

    2015-02-07

    High pressure Raman spectroscopy, X-ray diffraction, and dielectric measurements have been carried out in Ba{sub 1−x}Sr{sub x}TiO{sub 3} (x = 0.05 and 0.1). Detailed structural analysis revealed a single phase transition from tetragonal P4mm to cubic Pm3m symmetry. Increase in Sr ion concentration resulted in decrease in the phase transition pressure. The dielectric measurements showed considerable lowering of transition pressure which has been attributed to bulk behaviour of the material.

  4. Zn location in the W-type hexagonal ferrite SrZnCoFe16O27.

    PubMed

    Graetsch, Heribert A

    2002-11-01

    The title compound, SrZnCoFe(16)O(27) (ZnCo-W), strontium zinc cobalt hexadecairon oxide, crystallizes in space group P6(3)/mmc, with the Sr atom at a site with -6 m 2 symmetry and Zn(2+) located at two tetrahedral sites (4e and 4f, each with 3m symmetry) of the spinel blocks. The Zn occupancy is 36% on equipoint 4e and 14% on 4f. The enrichment of diamagnetic ions on one of seven sublattices is thought to be responsible for the high temperature dependence of the saturation magnetization.

  5. Magnetic properties of Ba- and Sr-hexaferrite prepared by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Ding, J.; Street, R.; Nishio, H.

    1996-12-01

    Samples of Ba- and Sr-hexaferrite were prepared by mechanical alloying and subsequent heat treatment were found to consist of single domain particles of the single hexaferrite phase. The particles had a wide distribution of anisotropy fields. Study of irreversible magnetisation suggested, that the demagnetisation process is mainly controlled by the Wohlfarth rotation. It was deduced from the results of measurements of magnetic viscosity, that the activation volume was of same order of magnitude as the cube of the domain wall thickness.

  6. Petrogenesis of Post-collisional high Ba-Sr granitoids: the Solarya Pluton, NW Turkey

    NASA Astrophysics Data System (ADS)

    Unal, Alp; Kamaci, Omer; Altunkaynak, Safak

    2015-04-01

    In NW Turkey, the Late Oligocene-Early Miocene phase of post-collisional magmatism is characterized by widespread granitic pluton emplacements straddling the continental collision zone marked by the Izmir-Ankara suture zone (IASZ). This granitic magmatism produced both low Ba-Sr- and high Ba-Sr granitoids with distinct geochemical properties. One of the major plutons emplaced to the north of İzmir-Ankara suture zone, the Solarya pluton is representative of high Ba-Sr granitoids. We present here whole-rock chemical and Sr-Nd-Pb-O isotopic compositions, as well as 40Ar/39Ar ages of the Solarya pluton to evaluate the timing, nature and genesis of potassic, high Ba-Sr granites. The Solarya pluton consists of three coeval granitic members (K-Feldspar megacrystalline granodiorite, fine grained granodiorite and haplogranite) and associated mafic magmatic enclaves/dykes of gabbroic diorite to dioritic in composition. K-feldspar megacrystalline granodiorite, fine grained granodiorite and haplogranite are high K calc-alkaline in character whereas low silica mafic magmatic enclaves and dykes are mildly alkaline and display shoshonitic affinity. Both granitic members and mafic enclaves/dykes are characterized by high Ba (710-2489 ppm), Sr (305-708ppm), low Y and HREE contents and lack of significant negative Eu anomalies. They are metaluminous and display enrichment in LILE and depletion in P, Ta, Nb and Ti. Sr-Nd-Pb and O isotope compositions of mafic enclaves and dykes are similar to their host granitoids. They have initial 87Sr/86Sr values of 0.70702- 0.70805 and 143Nd/144Nd values of 0.51235-0.51250 and their ɛNd values range between -4,9 and -2,05. 206Pb/204Pb and 207Pb/204 Pb isotopic values vary from 18,75 to 18,88 and 15,68 to 15,73, respectivelly. Whole rock and quartz 18O isotopic ratios range between 8 and 10,6. All these isotopic characteristics and major-trace element compositions of Solarya pluton and associated mafic enclaves/dykes suggest a subcontinental

  7. A first principles study on newly proposed (Ca/Sr/Ba)Fe2Bi2 compounds with their parent compounds

    NASA Astrophysics Data System (ADS)

    Sundareswari, M.; Jayalakshmi, D. S.; Viswanathan, E.

    2016-02-01

    The structural, electronic, bonding and magnetic properties of newly proposed iron-based compounds viz., CaFe2Bi2, SrFe2Bi2, BaFe2Bi2 with their Fermi surface topology are reported here for the first time by means of first principles calculation. All these properties of newly proposed compounds are compared and analysed along with their respective parent compounds namely (Ca,Sr,Ba)Fe2As2.

  8. Mechanochemical synthesis of MgF2 - MF2 composite systems (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Scholz, G.; Breitfeld, S.; Krahl, T.; Düvel, A.; Heitjans, P.; Kemnitz, E.

    2015-12-01

    The capability of mechanochemical synthesis for the formation of MgF2-MF2 (M: Ca, Sr, Ba) composites, solid solutions or well-defined compounds was tested applying a fluorination of different fluorine-free metal sources with NH4F directly at milling. No evidence was found for a substitution of Mg2+ with Ca2+ (Sr2+, Ba2+) ions, or vice versa, in rutile or fluorite structure. However, an equimolar ratio of Mg2+ to the second cation allows the mechanochemical synthesis of tetrafluoromagnesates, MMgF4, which is more and more hampered the smaller the radius of the cation M2+ is. BaMgF4 is formed even phase pure from the acetates, SrMgF4 can only be observed in a mixture accompanied by the binary fluorides. In addition, 19F MAS NMR spectra along with calculations of 19F isotropic chemical shift values according to the superposition model point to the formation of a metastable phase of CaMgF4, which disappears at thermal treatment and decomposes into the binary fluorides CaF2 and MgF2.

  9. Diffusion of Zr, Ru, Ce, Y, La, Sr and Ba fission products in UO2

    NASA Astrophysics Data System (ADS)

    Perriot, R.; Liu, X.-Y.; Stanek, C. R.; Andersson, D. A.

    2015-04-01

    The diffusivity of the solid fission products (FP) Zr (Zr4+), Ru (Ru4+, Ru3+), Ce (Ce4+), Y (Y3+), La (La3+), Sr (Sr2+) and Ba (Ba2+) by a vacancy mechanism has been calculated, using a combination of density functional theory (DFT) and empirical potential (EP) calculations. The activation energies for the solid fission products are compared to the activation energy for Xe fission gas atoms calculated previously. Apart from Ru, the solid fission products all exhibit higher activation energy than Xe. For all solid FPs except Y3+, the migration of the FP has lower barrier than the migration of a neighboring U atom, making the latter the rate limiting step for direct migration. An indirect mechanism, consisting of two successive migrations around the FP, is also investigated. The calculated diffusivities show that most solid fission products diffuse with rates similar to U self-diffusion. However, Ru, Ba and Sr exhibit faster diffusion than the other solid FPs, with Ru3+ and Ru4+ diffusing even faster than Xe for T < 1200 K. The diffusivities correlate with the observed fission product solubility in UO2, and the tendency to form metallic and oxide second phase inclusions.

  10. Molecular Dynamics Simulations of Chemically Disordered Ferroelectric (Ba,Sr)TiO3 with a Semi-Empirical Effective Hamiltonian

    NASA Astrophysics Data System (ADS)

    Nishimatsu, Takeshi; Grünebohm, Anna; Waghmare, Umesh V.; Kubo, Momoji

    2016-11-01

    We present a semi-empirical effective Hamiltonian to capture effects of disorder associated with Ba and Sr cations occupying A sites in (BaxSr1-x)TiO3 on its ferroelectric phase transition. Averaging between the parameters of first-principles effective Hamiltonians of end members BaTiO3 and SrTiO3, we include a term with an empirical parameter to capture the local polarization and strains arising from the difference between ionic radii of Ba and Sr. Using mixed-space molecular dynamics of the effective Hamiltonian, we determine T-dependent ferroelectric phase transitions in (BaxSr1-x)TiO3 which are in good agreement with experiment. Our scheme of determination of semi-empirical parameters in effective Hamiltonian should be applicable to other perovskite-type ferroelectric solid solutions.

  11. Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Punugupati, Sandhyarani; Prater, John T.; Narayan, Jagdish

    2016-04-01

    We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO3 (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba0.4Sr0.6TiO3 (BST). The epitaxial integration of BST (˜800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A1TO3 mode (at 521.27 cm-1) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.

  12. Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.; Drummond, Charles H., III

    1991-01-01

    Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glass transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder X ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structural transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

  13. Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.; Drummond, Charles H., III

    1991-01-01

    Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glasss transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder x ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structure transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

  14. Determination of Sr and Ba partition coefficients between apatite from fish ( Sparus aurata) and seawater: The influence of temperature

    NASA Astrophysics Data System (ADS)

    Balter, Vincent; Lécuyer, Christophe

    2010-06-01

    The Sr/Ca and Ba/Ca ratios in inorganic apatite are strongly dependent on the temperature of the aqueous medium during precipitation. If valid in biogenic apatite, these thermometers would offer the advantage of being more resistant to diagenesis than those calibrated on biogenic calcite and aragonite. We have reared seabreams ( Sparus aurata) in tanks with controlled conditions during experiments lasting for more than 2 years at 13, 17, 23 and 27 °C, in order to determine the variations in Sr and Ba partitioning relative to Ca ( DSr and DBa, respectively) between seawater and fish apatitic hard tissues (i.e. teeth and bones), as a function of temperature. The sensitivity of the Sr and Ba thermometers (i.e. ∂ DSr/∂ T and ∂ DBa/∂ T, respectively), are similar in bone ( ∂Db-wSr/∂ T = 0.0036 ± 0.0003 and ∂Db-wBa/∂ T = 0.0134 ± 0.0026, respectively) and enamel ( ∂De-wSr/∂ T = 0.0037 ± 0.0005 and ∂De-wBa/∂ T = 0.0107 ± 0.0026, respectively). The positive values of ∂ DSr/∂ T and ∂ DBa/∂ T in bone and enamel indicate that DSr and DBa increase with increasing temperature, a pattern opposite to that observed for inorganic apatite. This distinct thermodependent trace element partitioning between inorganic and organic apatite and water highlights the contradictory effects of the crystal-chemical and biological controls on the partitioning of Ca, Sr and Ba in vertebrate organisms. Taking into account the diet Sr/Ca and Ba/Ca values, it is shown that the bone Ba/Ca signature of fish can be explained by Ca-biopurification and inorganic apatite precipitation, whereas both of these processes fail to predict the bone Sr/Ca values. Therefore, the metabolism of Ca as a function of temperature still needs to be fully understood. However, the biogenic Sr thermometer is used to calculate an average seawater temperature of 30.6 °C using the Sr/Ca compositions of fossil shark teeth at the Cretaceous/Tertiary boundary, and a typical seawater Sr

  15. The low Sr/Ba ratio on some extremely metal-poor stars

    NASA Astrophysics Data System (ADS)

    Spite, M.; Spite, F.; Bonifacio, P.; Caffau, E.; François, P.; Sbordone, L.

    2014-11-01

    Context. It has been noted that, in classical extremely metal-poor (EMP) stars, the abundance ratio of two well-observed neutron-capture elements, Sr and Ba, is always higher than [Sr/Ba] = -0.5, which is the value of the solar r-only process; however, a handful of EMP stars have recently been found with a very low Sr/Ba ratio. Aims: We try to understand the origin of this anomaly by comparing the abundance pattern of the elements in these stars and in the classical EMP stars. Methods: For a rigorous comparison with previous data, four stars with very low Sr/Ba ratios were observed and analyzed in the same way as in the First Stars program: analysis within LTE approximation through 1D (hydrostatic) model atmosphere, providing homogeneous abundances of nine neutron-capture elements. Results: In CS 22950-173, the only turnoff star of the sample, the Sr/Ba ratio is, in fact, found to be higher than the r-only solar ratio, so the star is discarded. The remaining stars (CS 29493-090, CS 30322-023, HE 305-4520) are cool evolved giants. They do not present a clear carbon enrichment, but in evolved giants C is partly burned into N, and owing to their high N abundance, they could still have initially been carbon-rich EMP stars (CEMP). The abundances of Na to Mg present similar anomalies to those in CEMP stars. The abundance patterns of the neutron-capture elements in the three stars are strikingly similar to a theoretical s-process pattern. This pattern could at first be attributed to pollution by a nearby AGB, but none of the stars presents a clear variation in the radial velocity indicating the presence of a companion. The stellar parameters seem to exclude any internal pollution in a TP-AGB phase for at least two of these stars. The possibility that the stars are early-AGB stars polluted during the core He flash does not seem compatible with the theory. Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory, Chile (ID 077.D-0299(A) PI

  16. Optical and impedance studies of pure and Ba-doped ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Firdous, Arfat; Baba, M. Aslam; Singh, D.; Bhat, Abdul Hamid

    2015-02-01

    Chemical precipitation method using a high-boiling solvent is used to synthesize ZnS and Ba-doped ZnS quantum dots. The presence of organic ligands in the prepared nanostructures is verified using Fourier transform infra-red spectroscopic studies. The samples have been analysed using X-ray diffraction analysis confirming nanocrystallinity of the as-prepared quantum dots (QD). The mean crystal size obtained by full width half maxima analysis is 3.2 nm for ZnS and 3.9, 4.2 nm for ZnS:Ba (2, 4 mM). TEM micrographs also reveal nanosized particles of ZnS and Ba-doped ZnS. An optical absorption study conducted in UV-Vis range 150-600 nm reveals the transparency of these quantum dots in entire visible range but not in ultraviolet range. The results based on optical analysis yield band gap values as 4.88 eV for ZnS and 4.69, 4.43 eV for ZnS:Ba (2, 4 mM) quantum dots. Impedance analysis of the samples was carried out to reveal the variation of impedance with frequency at room temperature. These results show the capacitive admittance associated with the quantum dots and hence nanostructure ZnS and Ba-doped ZnS can have potential applications in electronics as nano-tuned devices in which resonant frequency can be adjusted by controlling the size and shape of the quantum dots.

  17. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr

    PubMed Central

    Li, H. F.; Xie, X. H.; Zheng, Y. F.; Cong, Y.; Zhou, F. Y.; Qiu, K. J.; Wang, X.; Chen, S. H.; Huang, L.; Tian, L.; Qin, L.

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  18. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

    PubMed

    Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

    2015-05-29

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals.

  19. Thermoelectric Hexagonal A-Mg-Si with A = Sr and Ba Zintl Phases

    NASA Astrophysics Data System (ADS)

    Kajitani, T.; Takahashi, K.; Saito, M.; Suzuki, H.; Kikuchi, S.; Kubouchi, M.; Hayashi, K.

    2016-10-01

    Hexagonal A-Mg-Si with A = Sr and Ba Zintl phases are promising candidates for p-type magnesium silicides usable with n-Mg2Si under 900 K. We synthesized p-type A-Mg-Si Zintl phases by the spark plasma synthesis procedure. Mg2Si and Mg2A powders were mixed at the ratio of 1- x/ x with x = 0.3-0.4. Two-step synthesis was performed at 850 K for 20 min and 1100 K for 20 min under uniaxial pressure at 30 MPa. Sintered pellets exhibited a stable p-type thermoelectric property. These pellets consisted of several unknown phases. We found two semiconductor phases, namely A2Mg4Si3 and A2Mg12Si7. The crystal structures of the 2/4/3- and 2/12/7-phases were Pbar{6}2m (No. 189)- and P63 /m (No. 176)-types, respectively. Sr0.70Mg2Si, Ba3Mg10Si7 and Sr3Mg10Si7 phases are newly found and characterized by a single crystal diffraction study. Previously found Sr2Mg4Si3 single phase polycrystalline 30φ × 10 mm pellets were successfully synthesized. The thermoelectric performance of the Sr2Mg4Si3 single phase sample was tested. The pellets exhibit p-type behavior from room temperature to 700 K. The thermal conductivity, κ, was almost constant at 1.1 W/mK from 350 K to 700 K.

  20. Investigation of structural, mechanical, electronic, optical, and dynamical properties of cubic BaLiF3, BaLiH3, and SrLiH3

    NASA Astrophysics Data System (ADS)

    Yalcin, Battal G.; Salmankurt, Bahadır; Duman, Sıtkı

    2016-03-01

    The structural, mechanical, electronic, optical, and dynamical properties of BaLiF3, BaLiH3, and SrLiH3 cubic perovskite materials are theoretically investigated by using first principles calculations. Obtained results are in reasonable agreement with other available theoretical and experimental studies. The considered materials are found to be mechanically stable in the cubic structure. We found that all materials are brittle. The modified Becke-Johnson (mBJ) exchange potential has been used here to obtain an accurate band order. The calculated band-gap energy value of BaLiF3 (8.26 eV) within the mBJ potential agrees very well with the experimentally reported value of 8.41 eV. In order to have a deeper understanding of the bonding mechanism and the effect of atomic relaxation on the electronic band structure, the total and partial density of states have also been calculated. We have investigated the fundamental optical properties, such as the real ɛ 1(ω) and imaginary ɛ 2(ω) parts of the dielectric function, absorption coefficient α(ω), reflectivity R(ω), and refractive index n(ω) in the energy range from 0 to 40 eV within the mBJ potential. The band-gap energy obtained from the absorption spectrum is around 8.76, 3.99, and 3.31 eV for BaLiF3, BaLiH3, and SrLiH3 crystals, respectively. It should be noted that BaLiF3 could be a strong potential candidate as a laser material for the development of a vacuum-ultraviolet light emitting diode once direct transition is confirmed by experimental studies. Finally, we have calculated the lattice dynamical properties of BaLiF3, BaLiH3, SrLiH3, and SrLiF3 crystals. The full phonon dispersion curves of these materials are reported for the first time. Our results clearly indicate that the materials are dynamically stable, except for SrLiF3, in the cubic structure. The obtained zone-center phonon frequencies of BaLiF3, BaLiH3, and SrLiH3 accord very well with previous experimental measurements.

  1. High temperature crystal structures and superionic properties of SrCl{sub 2}, SrBr{sub 2}, BaCl{sub 2} and BaBr{sub 2}

    SciTech Connect

    Hull, Stephen; Norberg, Stefan T.; Ahmed, Istaq; Eriksson, Sten G.; Mohn, Chris E.

    2011-11-15

    The structural properties of the binary alkaline-earth halides SrCl{sub 2}, SrBr{sub 2}, BaCl{sub 2} and BaBr{sub 2} have been investigated from ambient temperature up to close to their melting points, using the neutron powder diffraction technique. Fluorite-structured SrCl{sub 2} undergoes a gradual transition to a superionic phase at 900-1100 K, characterised by an increasing concentration of anion Frenkel defects. At a temperature of 920(3) K, the tetragonal phase of SrBr{sub 2} undergoes a first-order transition to a cubic fluorite phase. This high temperature phase shows the presence of extensive disorder within the anion sublattice, which differs from that found in superionic SrCl{sub 2}. BaCl{sub 2} and BaBr{sub 2} both adopt the cotunnite crystal structure under ambient conditions. BaCl{sub 2} undergoes a first-order structural transition at 917(5) K to a disordered fluorite-structured phase. The relationship between the (disordered) crystal structures and the ionic conductivity behaviour is discussed and the influence of the size of the mobile anion on the superionic behaviour is explored. - Graphical abstract: Anomalous behaviour of the lattice expansion of SrCl{sub 2} at temperatures of {approx}1000 K is associated with the gradual transition to a superionic phase, whilst SrBr{sub 2} undergoes a first-order structural transition ({beta}{yields}{alpha}) to a fluorite-structured superionic phase at 920(3) K. Highlights: > Anomalous behaviour of the lattice expansion of SrCl{sub 2} occurs at temperatures {approx}1000 K. > Crystal structure of {beta}-SrBr{sub 2} is described in detail. > On heating, SrBr{sub 2} and BaCl{sub 2} transform to a fluorite-structured superionic phase. > Temperature dependence of the BaCl{sub 2} and BaBr{sub 2} structures is presented. > Nature of the superionic phases within the alkaline-earth halides is discussed.

  2. Gulf of Alaska and California bamboo corals: Ba/Ca and Sr/Ca records

    NASA Astrophysics Data System (ADS)

    Sauthoff, W.; LaVigne, M.; Hill, T. M.; Roark, E.; Dunbar, R. B.; Guilderson, T. P.; Spero, H. J.

    2012-12-01

    Deep-sea bamboo coral communities form on seamounts and along continental margins with near global distribution. Bamboo [Isididae] corals record surrounding ocean geochemistry presenting reliable proxy records of changes in seawater conditions, including productivity and nutrient content. Here we investigate bamboo coral specimens from the California margin and Gulf of Alaska (634-1288 m water depth; ~37oN-48oN), to provide insight into latitudinal and temporal differences in eastern Pacific Ocean climate processes. Past oceanic conditions were reconstructed in this investigation by trace element analyses (Ba/Ca, Sr/Ca) using laser ablation ICP-MS, using a 85 μm spot size at 10 μm/s, 4.45 J/cm2 fluence, and 10 Hz repetition rate. Two California specimens show differences in mean Ba/Ca content: 13.73 compared to 18.55 μmol/mol, which we attribute to differences in collection depth (T1104 A10: 833 m and T1100 A04: 1288 m, respectively). Gulf of Alaska corals show a more subdued nutrient signal with lower mean Ba/Ca values of 10.56 and 10.05 μmol/mol across a narrower depth range (ALV3803 #3: 720 m; ALV3803 #5: 634 m, respectively). This trend of increasing Ba/Ca with depth is in consensus with eastern Pacific dissolved barium and California margin bamboo coral depth transects. Sr/Ca content was uniform between four coral specimens with values ranging from 3.01 to 3.06 mmol/mol. Coral chronologies were compared against indices of climate oscillations, including El Niño Southern Oscillation and Pacific Decadal Oscillation, using time series based upon radiocarbon dating. The corals investigated here show a limited connection with El Niño Southern Oscillation; longer-term changes related Pacific Decadal Oscillation may be evidenced in this climate archive.

  3. Structure and physical properties of Y(La)-Ba(Sr)-Cu-O superconducting compounds

    NASA Astrophysics Data System (ADS)

    Verkin, B. I.; Bandurian, B. B.; Baryl'Nik, A. S.; Batrak, A. G.; Bobrov, N. L.

    1987-07-01

    The structure and physical properties of Y(La)-Ba(Sr)-Cu-O superconducting compounds prepared by the cryogenic dispersion of a mixture of oxides and carbonates are investigated experimentally in the temperature range from 21 mK to 300 K. In particular, attention is given to the electrical conductivity and critical current density of the superconductors. Attention is also given to the degradation of the critical parameters of the superconductors with time, their structural characteristics, magnetic suceptibility, specific heat, and acoustic properties; the volt-ampere characteristics of the superconducting compounds are determined.

  4. Competing atomic processes in Ba and Sr injection critical velocity experiments

    NASA Technical Reports Server (NTRS)

    Newell, P. T.; Torbert, R. B.

    1985-01-01

    The critical ionization velocity effect requires a superthermal electron population to ionize through collisional impact. Such superthermal electrons can however lose energy to competing atomic processes, as well as to ionization, thus limiting the efficiency of the effect. Considering Ba and Sr magnetospheric injection experiments designed to test the CIV theory, it is found that in both cases roughly 60 percent of the superthermal electron energy is lost on exciting line radiation. Moreover, energy loss to background neutral oxygen places a strict limit on the injected cloud densities for which critical velocity effects are possible; a finding which explains the consistently negative results in radial injection experiments.

  5. Dielectric properties of (Ba,Sr)TiO{sub 3} films by RF sputtering

    SciTech Connect

    Mikami, N.; Horikawa, T.; Makita, T.; Sato, K.; Kuroiwa, T.; Honda, T.; Watarai, H.

    1994-12-31

    The dielectric properties of (Ba,Sr)TiO{sub 3}(BST) thin films prepared by RF sputtering method, were investigated. Polycrystalline film structure and grain size were estimated by transmission electron microscopy (TEM) and Xray diffraction. The dielectric constant of BST films depends on their grain size rather than thickness of the film. A broad maximum in the temperature dependence of the dielectric constant of the films was observed, and Curie temperature was not clear. No hysteresis was observed in a D-E curve of the film at 77K.

  6. Rare gases and Ca, Sr, and Ba in Apollo 17 drill-core fines

    NASA Technical Reports Server (NTRS)

    Pepin, R. O.; Dragon, J. C.; Johnson, N. L.; Bates, A.; Coscio, M. R., Jr.; Murthy, V. R.

    1975-01-01

    Trapped gas isotopic compositions and spallation gas concentrations as functions of depth in the Apollo 17 drill core were determined from mass spectrometer studies by means of correlation techniques. The distribution of He, Ne, Ar, Kr, and Xe as well as Ca, Sr, and Ba was investigated, and rare-gas spallation and neutron capture profiles are compared with attention to proposed depositional models for the Taurus-Littrow regolith. The data exclude a sedimentation pattern similar to that found at the Apollo 15 site but are possibly compatible with long-term continuous accretion models or models of very recent rapid accumulation of regolith.

  7. Magnetic and magnetocaloric properties of Ba and Ti co-doped SrRuO{sub 3}

    SciTech Connect

    Sarkar, Babusona; Dalal, Biswajit; Dev Ashok, Vishal; De, S. K.

    2014-12-28

    Temperature evolution of magnetic properties in Ba and Ti doped SrRuO{sub 3} has been investigated to observe the effects of larger ionic radius Ba at Sr site and isovalent nonmagnetic impurity Ti at Ru site. Ionic radius mismatch and different electronic configuration in comparison with Ru modify Sr(Ba)-O and Ru(Ti)-O bond lengths and Ru-O-Ru bond angle. The apical and basal Ru-O-Ru bond angles vary significantly with Ti doping. Ferromagnetic Curie temperature decreases from 161 K to 149 K monotonically with Ba (10%) and Ti (10%) substitutions at Sr and Ru sites. The zero field cooled (ZFC) magnetization reveals a prominent peak which shifts towards lower temperature with application of magnetic field. The substitution of tetravalent Ti with localized 3d{sup 0} orbitals for Ru with more delocalized 4d{sup 4} orbitals leads to a broad peak in ZFC magnetization. A spontaneous ZFC magnetization becomes negative below 160 K for all the compositions. The occurrence of both normal and inverse magnetocaloric effects in Ba and Ti co-doped SrRuO{sub 3} makes the system more interesting.

  8. Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films.

    PubMed

    Kang, Seung Beom; Kwak, Min Hwan; Choi, Muhan; Kim, Sungil; Kim, Taeyong; Cha, Eun Jong; Kang, Kwang Yong

    2011-11-01

    Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.

  9. Structure determination and relative properties of novel cubic borates MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba).

    PubMed

    Wu, L; Chen, X L; Li, H; He, M; Xu, Y P; Li, X Z

    2005-09-05

    A series of novel borates, MM'4(BO3)3 (M = Li, M' = Sr; M = Na, M' = Sr, Ba), have been successfully synthesized by standard solid-state reaction. The crystal structures have been determined from powder X-ray diffraction data. They crystallize in the cubic space group Iad with large lattice parameters: a = 14.95066(5) A for LiSr4(BO3)3, a = 15.14629(6) A for NaSr4(BO3)3, and a = 15.80719(8) A for NaBa4(BO3)3. The structure was built up from 64 small cubic grids, in which the M' atoms took up the corner angle and the BO3 triangles or MO6 cubic octahedra filled in the interspaces. The isolated [BO3]3- anionic groups are perpendicular to each other, distributed along three 100 directions. The anisotropic polarizations were counteracting, forming an isotropic crystal. Sr and Ba atoms were found to be completely soluble in the solid solution NaSr(4-)xBax(BO3)3 (0 < or = x < or = 4). The photoluminescence of samples doped with the ions Eu2+ and Eu3+ was studied, and effective yellow and red emission was detected, respectively. The results are consistent with the crystallographic study. The DTA and TGA curves of them show that they are chemically stable and congruent melting compounds.

  10. Metal-semiconductor-transition observed in Bi2Ca(Sr, Ba)2Co2O8+δ single crystals

    NASA Astrophysics Data System (ADS)

    Dong, Song-Tao; Zhang, Bin-Bin; Zhang, Lun-Yong; Chen, Y. B.; Yao, Shu-Hua; Zhou, Jian; Zhang, Shan-Tao; Gu, Zheng-Bin; Chen, Yan-Feng

    2014-07-01

    Electrical property evolution of Bi2AE2Co2O8+δ single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi2Ca2Co2O8+δ and Bi2Sr2Co2O8+δ demonstrates semiconductor-like properties. But Bi2Ba2Co2O8+δ shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi2Ba2Co2O8+δ to semiconductor-like Bi2Sr2Co2O8+δ can be attributed to Anderson localization. However the semiconductor behaviour of Bi2Sr2Co2O8+δ and Bi2Ca2Co2O8+δ is related to electronic correlations effect that is inferred by large negative magnetoresistance (˜70%). The theoretical electronic structures and valence X-ray photoemission spectroscopy substantiate that there is a relative large density of state around Fermi level in Bi2Ba2Co2O8+δ compared with other two compounds. It suggests that Bi2Ba2Co2O8+δ is more apt to be metal in this material system.

  11. ESR Study of (La,Ba)MnO3/ZnO Nanostructure for Resistive Switching Device

    NASA Astrophysics Data System (ADS)

    Polek, Taras; Semen'ko, Mykhaylo; Endo, Tamio; Nakamura, Yoshinobu; Lotey, Gurmeet Singh; Tovstolytkin, Alexandr

    2017-03-01

    Structure, electric, and resonance properties of (La,Ba)MnO3/ZnO nanostructure grown on SrTiO3 (001) substrate have been investigated. It is found that at room temperature and relatively low voltages (| V |< 0.2 V), the structure shows good rectification behavior with rectification factor near 210. Resistive switching properties are detected after application of higher voltages. Temperature evolution of magnetic phase composition of the sample is analyzed in detail, based on results of electron spin resonance measurements. It is shown that magnetic state below 260 K is characterized by coexistence of ferromagnetic and paramagnetic phases, but no evidence of magnetic phase separation is revealed at higher temperatures. Different driving mechanisms for resistive switching, such as magnetic phase separation and/or electric field-induced migration of oxygen vacancies, are discussed in the context of obtained results.

  12. Theoretical investigation of optical and structural properties of Ba-doped ZnO material

    NASA Astrophysics Data System (ADS)

    Lacerda, L. H. S.; de Lazaro, S. R.; Ribeiro, R. A. P.

    2015-11-01

    The doping process is a technique widely used for improving the properties of semiconductors. Through insertion of doping controlled amount is possible change drastically the electronic, optical and structural properties of a material. This work focuses on effects of Ba atoms insertion on wurtzite-ZnO structure at 12.5% amount. The results showed that the presence of Ba in low quantity cause increase in the lattice parameters and decrease in band- gap in relation to the ZnO material. In the percentage of 12.5%, the doping is noted as a potential alternative for application in opt-electronic devices, electronic devices, solar cells and photocatalytic process.

  13. MBiO{sub 2}Cl (M=Sr, Ba) as novel photocatalysts: Synthesis, optical property and photocatalytic activity

    SciTech Connect

    Huang, Hongwei Wang, Shuobo; Zhang, Yihe Han, Xu

    2015-02-15

    Novel quaternary photocatalysts MBiO{sub 2}Cl (M=Sr, Ba) have been successfully developed for efficient photodecomposition of RhB. Their photocatalytic mechanism was also investigated. - Highlights: • Two Bi-based compounds SrBiO{sub 2}Cl and BaBiO{sub 2}Cl were explored as photocatalysts. • They were successfully synthesized by a solid-state reaction. • RhB can be effectively photodecomposed by SrBiO{sub 2}Cl and BaBiO{sub 2}Cl under UV light. • ·OH radicals serving as active species play important roles in degradation process. - Abstract: Two Bi-based compounds SrBiO{sub 2}Cl and BaBiO{sub 2}Cl were successfully synthesized by a solid-state reaction and investigated as new photocatalysts for the first time. Their microstructures and optical properties were characterized by XRD, SEM and DRS. The band gaps of SrBiO{sub 2}Cl and BaBiO{sub 2}Cl were separately determined to be 3.52 and 3.71 eV, and their E{sub CB} and E{sub VB} were also estimated. The photocatalytic activities of the as-prepared samples were evaluated by photodecomposition of rhodamine B (RhB) in aqueous solution. The results revealed that both SrBiO{sub 2}Cl and BaBiO{sub 2}Cl can be used as effective photocatalysts under UV irradiation, and SrBiO{sub 2}Cl exhibits a higher photocatalytic activity than BaBiO{sub 2}Cl, which was also verified by the PL spectra. Terephthalic acid photoluminescence probing technique (TA-PL) demonstrated that ·OH radicals serving as active species play an important role in photooxidative degradation of RhB over SrBiO{sub 2}Cl and BaBiO{sub 2}Cl. Moreover, a larger amount of ·OH radicals generation was observed over SrBiO{sub 2}Cl, which is in agreement with its higher photocatalytic activity.

  14. PIXE, SR-XRD and EXAFS analysis of Cu-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Zhang, B.; Yang, C.; Wang, J. Z.; Shi, L. Q.; Cheng, H. S.

    2014-08-01

    Cu-doped ZnO films were prepared by rf magnetron sputtering on sapphire substrate at different atmosphere. Microstructure of these films and Cu occupation sites were investigated using PIXE, SR-XRD and EXAFS. Only 2.9 at.% Cu, no other magnetic impurities (e.g., Fe, Co and Ni) were detected. The ZnO:Cu films possessed the wurtzite ZnO structures and no precipitates (e.g., CuO and Cu2O or Cu cluster) were found. Cu atoms were incorporated into ZnO crystal lattice by occupying Zn atomic sites.

  15. Crystal structure and polarization hysteresis properties of ferroelectric BaTiO3 thin-film capacitors on (Ba,Sr)TiO3-buffered substrates

    NASA Astrophysics Data System (ADS)

    Maki, Hisashi; Noguchi, Yuji; Kutsuna, Kazutoshi; Matsuo, Hiroki; Kitanaka, Yuuki; Miyayama, Masaru

    2016-10-01

    Ferroelectric BaTiO3 (BT) thin-film capacitors with a buffer layer of (Ba1- x Sr x )TiO3 (BST) have been fabricated on (001) SrTiO3 (STO) single-crystal substrates by a pulsed laser deposition method, and the crystal structure and polarization hysteresis properties have been investigated. X-ray diffraction reciprocal space mapping shows that the BST buffer effectively reduces the misfit strain relaxation of the BT films on SrRuO3 (SRO) electrodes. The BT capacitor with the SRO electrodes on the BST (x = 0.3) buffer exhibits a well-saturated hysteresis loop with a remanent polarization of 29 µC/cm2. The hysteresis loop displays a shift toward a specific field direction, which is suggested to stem from the flexoelectric coupling between the out-of-plane polarization and the strain gradient adjacent to the bottom interface.

  16. Effect of divalent (Sr, Ba) doping on the structural and magnetic properties of BiFeO{sub 3}

    SciTech Connect

    Rangi, Manisha Sanghi, Sujata; Agarwal, Ashish; Jangra, Sandhaya; Singh, Ompal

    2015-06-24

    The effect of divalent substitution on the crystal structure and magnetic properties of BiFeO{sub 3} has been investigated using X-ray diffraction and magnetic measurements technique. Single phase Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A= Sr, Ba) multiferroics have been synthesized by solid state reaction method. Rietveld analysis of the XRD patterns revealed that the prepared ceramics exhibit rhombohedral structure with space group R3c. M–H hysteresis loops were recorded at 5K revealed that Sr and Ba substitution transformed antiferromagnetic BiFeO3 into weak ferromagnetic. The enhanced magnetization with Sr and Ba addition is confirmed by the MT curve recorded at 1T. It is closely related to intrinsic structural distortion and modification of the antiparallel spin structure.

  17. Cs, Sr, and Ba Sorption on Clays and Fe-Oxides

    SciTech Connect

    Anderson, H.L.; Brady, P.V.; Cygan, R.T.; Gruenhagen, S.E.; Nagy, K.L.; Westrich, H.R.

    1999-06-16

    Technical guidance for performance assessment (PA) of low-level radioactive waste (LLRW) sites is currently dependent upon experimental retardation factors (K{sub D}'s) to predict radionuclide transport. Accurate predictions of waste transport or retardation will require mechanistic models of radionuclide sorption so as to be applicable to a wide range of soil/groundwater environments. To that end, we have investigated Cs{sup +}, Sr{sup +}, and Ba{sup 2+} sorption on several clay and Fe-oxide minerals. Relative metal binding strengths for montmorillonite clay decrease from Ba{sup 2+} to Sr{sup +}, which is similar to that sorption trend noticed for kaolinite. Molecular dynamics simulations for kaolinite suggest that Cs{sup +} is sorbed at aluminol (010) edge sites as an inner-sphere complex and weakly sorbed as an outer-sphere complex on (001) basal surfaces. Sorption is thought to occur on similar sites for smectite clays, however, the basal plane residual charge and its increased basal plane exposure should have a greater influence on metal sorption. On the other hand, phase transformation kinetics (e.g., ferrihydrite to goethite) is a very important control of metal sorption and resorption for Fe-oxides/hydroxides. These results provide a basis for understanding and predicting metal sorption on complex soil minerals.

  18. Solid solution partitioning of Sr 2+, Ba 2+, and Cd 2+ to calcite

    NASA Astrophysics Data System (ADS)

    Tesoriero, Anthony J.; Pankow, James F.

    1996-03-01

    Although solid solutions play important roles in controlling the concentrations of minor metal ions in natural waters, uncertainties regarding their compositions, thermodynamics, and kinetics usually prevent them from being considered. A range of precipitation rates was used here to study the nonequilibrium and equilibrium partitioning behaviors of Sr 2+, Ba 2+, and Cd 2+ to calcite (CaCO 3(s)). The distribution coefficient of a divalent metal ion Me 2+ for partitioning from an aqueous solution into calcite is given by DMe = ( XMeCO 3(s)/[Me 2+])/( XCaCO 3(s)/[Ca 2+]). The X values are solid-phase mole fractions; the bracketed values are the aqueous molal concentrations. In agreement with prior work, at intermediate to high precipitation rates R (nmol/mg-min), DSr, DBa, and DCd were found to depend strongly on R. At low R, the values of DSr, DBa, and DCd became constant with R. At 25 °C, the equilibrium values for DSr, DBa, and DCd for dilute solid solutions were estimated to be 0.021 ± 0.003, 0.012 ± 0.005, and 1240 ± 300, respectively. Calculations using these values were made to illustrate the likely importance of partitioning of these ions to calcite in groundwater systems. Due to its large equilibrium DMe value, movement of Cd 2+ will be strongly retarded in aquifers containing calcite; Sr 2+ and Ba 2+ will not be retarded nearly as much.

  19. Nd:SrWO 4 and Nd:BaWO 4 Raman lasers

    NASA Astrophysics Data System (ADS)

    Šulc, J.; Jelínková, H.; Basiev, T. T.; Doroschenko, M. E.; Ivleva, L. I.; Osiko, V. V.; Zverev, P. G.

    2007-09-01

    Properties of the laser operation and simultaneously stimulated Raman scattering in the SRS-active neodymium doped SrWO4 and BaWO4 crystals coherently end-pumped at wavelength 752 nm by pulsed free-running alexandrite laser radiation were investigated. The Nd3+ ion emission at wavelength λNd ˜ 1.06 μm was corresponding to 4F3/2 → 4I11/2 transition. To reach the SRS-self-conversion threshold inside Raman crystal the Nd3+ lasers were operating in a Q-switching regime. For Q-switching LiF:F2- crystal as a saturable absorber was used. Raman self-conversion at wavelength ˜1.17 μm was successfully reached with both tungstate crystals. The shortest generated pulse (1.3 ns FWHM) and highest peak power (615 kW) was obtained with Nd:BaWO4 Raman laser Q-switched by LiF:F2- crystal with initial transmission T0 = 60%. Up to 0.8 mJ was registered at the first Stokes wavelength 1169 nm. Using Q-switched Nd:SrWO4 laser higher energy in Raman emission was obtained (1.23 mJ) but generated pulse was longer (2.9 ns FWHM) resulting in lower peak power (430 kW).

  20. Solid solution partitioning of Sr2+, Ba2+, and Cd2+ to calcite

    USGS Publications Warehouse

    Tesoriero, A.J.; Pankow, J.F.

    1996-01-01

    Although solid solutions play important roles in controlling the concentrations of minor metal ions in natural waters, uncertainties regarding their compositions, thermodynamics, and kinetics usually prevent them from being considered. A range of precipitation rates was used here to study the nonequilibrium and equilibrium partitioning behaviors of Sr2+, Ba2+, and Cd2+ to calcite (CaCO3(s)). The distribution coefficient of a divalent metal ion Me2+ for partitioning from an aqueous solution into calcite is given by DMe = (XMeCO3(s)/[Me2+])/(XCaCO3(s)/[Ca 2+]). The X values are solid-phase mole fractions; the bracketed values are the aqueous molal concentrations. In agreement with prior work, at intermediate to high precipitation rates R (nmol/mg-min), DSr, DBa, and DCd were found to depend strongly on R. At low R, the values of DSr, DBa, and DCd became constant with R. At 25??C, the equilibrium values for DSr, DBa, and DCd for dilute solid solutions were estimated to be 0.021 ?? 0.003, 0.012 ?? 0.005, and 1240 ?? 300, respectively. Calculations using these values were made to illustrate the likely importance of partitioning of these ions to calcite in groundwater systems. Due to its large equilibrium DMe value, movement of Cd2+ will be strongly retarded in aquifers containing calcite; Sr2+ and Ba2+ will not be retarded nearly as much.

  1. Characterization of MeWO 4 (Me = Ba, Sr and Ca) nanocrystallines prepared by sonochemical method

    NASA Astrophysics Data System (ADS)

    Thongtem, Titipun; Phuruangrat, Anukorn; Thongtem, Somchai

    2008-09-01

    Metal tungstates (MeWO 4, Me = Ba, Sr and Ca) were successfully prepared using the corresponding Me(NO 3) 2·2H 2O and Na 2WO 4·2H 2O in ethylene glycol by the 5 h sonochemical process. The tungstate phases with scheelite structure were detected with X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their calculated lattice parameters are in accord with those of the JCPDS cards. Transmission electron microscopy (TEM) revealed the presence of nanoparticles composing the products. Their average sizes are 42.0 ± 10.4, 18.5 ± 5.1 and 13.1 ± 3.3 nm for Me = Ba, Sr and Ca, respectively. Interplanar spaces of the crystals were also characterized with high-resolution TEM (HRTEM). Their crystallographic planes are aligned in systematic array. Six different vibration wavenumbers were detected using Raman spectrometer and are specified as ν1(A g), ν3(B g), ν3(E g), ν4(B g), ν2(A g) and free rotation. Fourier transform infrared (FTIR) spectra provided the evidence of scheelite structure with W-O anti-symmetric stretching vibration of [WO 4] 2- tetrahedrons at 786-883 cm -1. Photoluminescence emission of the products was detected over the range of 384-416 nm.

  2. Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba)

    SciTech Connect

    Josse, M.; El-Ghozzi, M.; Avignant, D.; Andre, G.; Bouree, F.; Isnard, O.

    2012-01-15

    Neutron powder diffraction has been performed on the MTbF{sub 6} fluorides (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba). Four of these fluorides (Cd, Ca, Sr, {beta}-Ba) are built of a (pseudo-) tetragonal packing of [TbF{sub 6}]{sup 2-} chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb{sup 4+}-Tb{sup 4+} magnetic interactions. All the compounds displayed antiferromagnetic order (T{sub N}=2.70 K (Cd), 2.15 K (Ca), 2.60 K (Sr), 2.10 K ({beta}-Ba)), except for the {alpha} form of BaTbF{sub 6}. The crystal structure of this latter fluoroterbate has also been investigated by means of high-resolution neutron powder diffraction. From Neutron Powder Diffraction data, CdTbF{sub 6} and {beta}-BaTbF{sub 6} magnetic structures were determined, together with the metamagnetic behaviour of {beta}-BaTbF{sub 6} as a function of an external magnetic field. A tentative phase diagram is then given for {beta}-BaTbF{sub 6}. Advantage was taken of the polymorphism of the BaTbF{sub 6} fluoroterbate to analyse, on the basis of topological parameters such as bond distances and angles, the magnetic behaviour of its {alpha} and {beta} forms. It was shown that superexchange interactions are present in {beta}-BaTbF{sub 6}, and that these interactions may also rule the magnetic behaviour of the other MTbF{sub 6} (M=Ca, Sr, Cd) tetravalent terbium fluorides. - Graphical abstract: Powder neutron diffraction revealed magnetic order in four of the five investigated fluoroterbates, while crystal chemical analyses of {alpha} and {beta} forms of BaTbF{sub 6} evidenced the existence of superexchange interactions. Highlights: Black-Right-Pointing-Pointer Five fluoroterbates are investigated by Powder Neutron Diffraction (PND). Black-Right-Pointing-Pointer Four of them are antiferromagnetically ordered at 1.4 K. Black-Right-Pointing-Pointer Magnetic structures of {beta}-BaTbF{sub 6} and CdTbF{sub 6} are determined. Black

  3. Goosenest Volcano, southern Oregon: High K[sub 2]O, BA and Sr basaltic andesite extrusives

    SciTech Connect

    Mertzman, S.A. . Dept. of Geosciences)

    1992-01-01

    Goosenest Volcano, a cinder cone with coeval lava flows, is located nearly 5 miles WNW of the south entrance into Crater Lake National Park. A summit crater unmodified by glacial erosion but with a blanket of Mazama pumice, suggests the age of latest activity to be between 20,000 and 6850 B.P. The pyroclastics and lavas from Goosenest are augite olivine basaltic andesites, with a strong tendency for these minerals to form 2--5 mm in diameter glomeroporphyritic clumps [+-] plagioclase. Three samples from the cone (2 bombs and 1 spatter agglutinate) and five from lava flows were analyzed for major and trace elements through XRF and ICP techniques. These extrusive are calc-alkaline medium to high K[sub 2]O basaltic andesites; in particular, SiO[sub 2] ranges from 53 to 54 wt. %, K[sub 2]O from 1.39 to 1.94, MgO from 6.3 to 7.3, Ba from 774 to 1,069 ppm and Sr from 1,463 to 1,951 ppm. With increasing K[sub 2]O: P[sub 2]O[sub 5], Ba, Be, Ce, La, Sr, and Zr increase in concentration while Ni, Cr, and Co decrease. All major elements are virtually constant or scatter randomly; Y,V,Sc, and Yb follow the same pattern. The lower Al[sub 2]O[sub 3] content (16 to 17 wt.%) precludes the addition of a large plagioclase component as an explanation of the high Sr content. Batch partial melting of a mineralogically homogeneous source that has been fluxed by variable amounts of an LILE-rich fluid phase whose ultimate origin is tied to the subduction process, is a likely scheme which explains the unusual chemical composition of the Gossenest extrusive rocks.

  4. New insulating antiferromagnetic quaternary iridates MLa10Ir4O24 (M=Sr, Ba)

    DOE PAGES

    Zhao, Qingbiao; Han, Fei; Stoumpos, Constantinos C.; ...

    2015-07-01

    Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between Jeff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. Inmore » this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa10Ir4O24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO6 octahedra in which the electronic configuration of Ir is d5. As a result, both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa10Ir4O24 is an insulator.« less

  5. New Insulating Antiferromagnetic Quaternary Iridates MLa10Ir4O24 (M = Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Zhao, Qingbiao; Han, Fei; Stoumpos, Constantinos C.; Han, Tian-Heng; Li, Hao; Mitchell, J. F.

    2015-07-01

    Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between Jeff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa10Ir4O24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO6 octahedra in which the electronic configuration of Ir is d5. Both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa10Ir4O24 is an insulator.

  6. New Insulating Antiferromagnetic Quaternary Iridates MLa10Ir4O24 (M = Sr, Ba)

    PubMed Central

    Zhao, Qingbiao; Han, Fei; Stoumpos, Constantinos C.; Han, Tian-Heng; Li, Hao; Mitchell, J. F.

    2015-01-01

    Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between Jeff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa10Ir4O24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO6 octahedra in which the electronic configuration of Ir is d5. Both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa10Ir4O24 is an insulator. PMID:26129886

  7. Superconductivity in SrCuO2-BaCuO2 Superlattices: Formation of Artificially Layered Superconducting Materials.

    PubMed

    Norton, D P; Chakoumakos, B C; Budai, J D; Lowndes, D H; Sales, B C; Thompson, J R; Christen, D K

    1994-09-30

    Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy was used to stabilize SrCuO(2)-BaCuO(2) superlattices in the infinite layer structure. Using this approach, two new structural families, Ba(2)Srn-1,Cun+1 O2n+2+delta and Ba(4)Srn-1 Cun+3O2n+6+delta have been synthesized; these families superconduct at temperatures as high as 70 kelvin.

  8. Dependence of the Sr-to-Ba and Sr-to-Eu Ratio on the Nuclear Equation of State in Metal-poor Halo Stars

    NASA Astrophysics Data System (ADS)

    Famiano, M. A.; Kajino, T.; Aoki, W.; Suda, T.

    2016-10-01

    A model is proposed in which the dependence on the equation of state (EOS) of the scatter of [Sr/Ba] in metal-poor stars is studied. Light r-process element enrichment in these stars has been explained via a truncated r-process, or “tr-process.” The truncation of the r-process from a generic core-collapse event followed by a collapse into an accretion-induced black hole is examined in the framework of a galactic chemical evolution model. The constraints on this model imposed by observations of extremely metal-poor stars are explained, and the upper limits in the [Sr/Ba] distributions are found to be related to the nuclear EOS in a collapse scenario. The scatter in [Sr/Ba] and [Sr/Eu] as a function of metallicity has been found to be consistent with turbulent ejection in core-collapse supernovae. Adaptations of this model are evaluated to account for the scatter in isotopic observables. This is done by assuming mixing in ejecta in a supernova event. Stiff EOS are eliminated by this model.

  9. Electronic Structure of I-M8Ga16Sn30 (M = Ba, Sr, Yb) by First-Principles Calculation

    NASA Astrophysics Data System (ADS)

    Wang, Jin-song; Liu, Hong-xia; Deng, Shuping; Li, De-cong; Shen, Lan-xian; Cheng, Feng; Deng, Shu-kang

    2016-10-01

    Sn-based clathrates possess excellent thermoelectric properties ascribed to their higher Seebeck coefficient and lower thermal conductivity. Guest atoms significantly modulate the thermoelectric properties of Sn-based calculates because of their diverse atomic radius and interactions with framework atoms. Thus, we explored the electronic structure of I-M8Ga16Sn30 (M = Ba, Sr, Yb) by first-principles calculation. Results revealed significant differences between Yb8Ga16Sn30 and M8Ga16Sn30 (M = Ba, Sr,). In particular, the Yb-filled compound substitution possesses lowest formation energy and the off-center distance of the Yb atom is the largest compared with the other structures. I-M8Ga16Sn30 (M = Ba, Sr, Yb) is an indirect band gap semiconductor, and the enhanced hybridization effect between the guest and framework atoms' orbits exists because the Yb f orbit results in a decrease in band gap. Ba- and Sr-filled clathrates have similar valence bands but slightly different conduction bands; however, Yb8Ga16Sn30 possess the spiculate density of states near the Fermi level that reveals excellent thermoelectric properties.

  10. Hydrostatic pressure effect on the superconducting properties of BaBi3 and SrBi3 single crystals

    NASA Astrophysics Data System (ADS)

    Jha, Rajveer; Avila, Marcos A.; Ribeiro, Raquel A.

    2017-02-01

    We demonstrate the superconducting properties of, and hydrostatic pressure effect on, BaBi3 and SrBi3 superconductors. We measure the dc magnetic susceptibility under hydrostatic pressure for both compounds, which shows a positive pressure coefficient of dT c/dP = 1.22 K GPa-1 for BaBi3 and a negative pressure coefficient of dT c/dP = -0.43 K GPa-1 for SrBi3. The normal state electrical resistivity shows that both compounds are highly metallic in nature. The upper critical fields H c2 evaluated by resistivity under magnetic fields ρ(T,H) are 22 kOe for BaBi3 and 2.9 kOe for SrBi3. A specific heat jump of ΔC e/γT c = 1.05 suggests weak coupling superconductivity in BaBi3, whereas ΔC e/γT c = 2.08 for SrBi3 is higher than the Bardeen-Cooper-Schrieffer theory value of 1.43, indicating a strong coupling superconductor.

  11. Measurement of Ca, Zn and Sr in enamel of human teeth by XRF

    SciTech Connect

    Wielopolski, L.; Featherstone, J.D.B.; Cohn, S.H.

    1984-01-01

    Energy dispersive x-ray fluorescence (EDXRF) has been employed to measure Ca, Zn, and Sr in enamel of human teeth. The calibration of the EDXRF system was performed by comparing Sr/Ca ratios with values obtained by atomic absorption analysis of acid etched biopsies of the enamel surface. Two calibration lines were obtained, one line for untreated teeth and the second line for teeth immersed (treated) in solutions containing Sr. A simple analytical model demonstrated that the two calibration lines were the result of the difference in the depth of the enamel sampled by EDXRF and by the acid-etched biopsy. The multi-elemental, non-destructive and quantitative aspects of EDXRF permit the sequential monitoring of the effects of Sr and Zn ions on the mineralization and demineralization processes in human enamel. The portability of the system and adaptability to non-invasive measurements makes it suitable for field studies. 26 references, 4 figures.

  12. (Ba,Sr)TiO3 tunable capacitors with RF commutation quality factors exceeding 6000

    NASA Astrophysics Data System (ADS)

    Meyers, Cedric J. G.; Freeze, Christopher R.; Stemmer, Susanne; York, Robert A.

    2016-09-01

    The fabrication, measurement, and modeling of radio-frequency (RF), tunable interdigital capacitors (IDCs) are described. High quality factors of 200 in the S/L-bands combined with a 47% tunability are achieved by utilizing epitaxial (Ba,Sr)TiO3 films grown by hybrid molecular beam epitaxy on LaAlO3 substrates. The fabricated devices consisted of one-port and two-port IDCs embedded in ground-signal-ground, coplanar waveguide transmission lines to enable RF probing. Wideband RF scattering parameters under bias were measured from 100 MHz to 40 GHz. A commutation quality factor averaging 6000 across the L band is achieved. These are the highest reported values in this band.

  13. Electronic properties of BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF/ZnPc interfaces

    NASA Astrophysics Data System (ADS)

    Zakutayev, Andriy; Tate, Janet; Platt, Heather A. S.; Keszler, Douglas A.; Hein, Corinna; Mayer, Thomas; Klein, Andreas; Jaegermann, Wolfram

    2010-05-01

    BaCuChF (Ch=S,Se,Te) surfaces and BaCuSeF interfaces with zinc phthalocyanine (ZnPc) were studied by photoelectron spectroscopy. BaCuChF compounds oxidize when exposed to ambient atmosphere. Se capping layers were studied as a means to produce representative surfaces for photoelectron spectroscopic measurements. Decapped BaCuSeF surfaces remain O-free and C-free when the Se layer is evaporated but they become F-deficient. The resulting surfaces have work functions of 4.85 eV and Fermi levels located 0.25 eV above the valence band maximum. In situ stepwise deposition of ZnPc on a BaCuSeF film surface produced a chemically inert interface with a hole-injection barrier of 0.11 eV.

  14. Electronic structures of non-half-metallic antiferromagnetic double perovskites ALaVMoO6 (A = Ca, Sr, and Ba)

    NASA Astrophysics Data System (ADS)

    Kim, I. G.; Park, M. S.

    2005-03-01

    Recently, double perovskites ALaVMoO6 (A= Ca and Sr) of the Fm3m space group were proposed experimentally to be half-metallic antiferromagnets.ootnotetextUehara, Yamada, and Kimishima, Solid St. Commun. 129, 385 (2004). The electronic structures and magnetism of the double perovskites ALaVMoO6 (A= Ca, Sr, and Ba) were determined within the generalized gradient approximation to density functional theory using the all-electron full-potential linearized augmented plane wave (FLAPW) method.ootnotetextWimmer, Krakauer, Weinert, and Freeman, PRB 24, 864 (1981). The A= Ca case shows metallic ferrimagnetism as the most stable phase, with magnetic moments of 1.15;μB for V and -0.53;μB for Mo, whereas the Sr and Ba cases are calculated to be almost non-magnetic metals. Comparing the calculated density of states, we find that the heavier A implies stronger hybridization between the divalent atom sp states and the transition metal atom d states. The stronger sp-d hybridization is considered to be responsible for the suppression of magnetism for the Sr and Ba cases. These results, at least for the Fm3m space group, are in contrast with the recent experimental result proposing half-metallic antiferromagnetism for A= Ca and Sr.

  15. Theoretical study of the new zintl phases compounds K2ACdSb2 (A=(Sr, Ba))

    NASA Astrophysics Data System (ADS)

    Azam, Sikander; Reshak, A. H.

    2015-05-01

    The electronic structure and optical properties of K2SrCdSb2 and K2BaCdSb2 compounds are computed using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in WIEN2k code. In this perspective, the local density approximation (LDA), generalized gradient approximation (GGA) and Engel and Vosko approximation (EV-GGA) were used for the exchange correlation potential. The calculated band structure shows a direct band gap of about 0.344/0.20 eV (LDA), 0.463/0.285 eV (GGA) and 0.904/0.707 eV (EV-GGA) for K2SrCdSb2/K2BaCdSb2 compounds. The part of different bands was scrutinized from total and partial density of states curves. There is strong hybridization between Sr-s and Sr-p states and also between Cd-d and Sb-s states in the valence band. The electronic charge density has also been studied in the (200) crystallographic plane. The K, Sr/Ba, Cd and Sb atoms shows ionic bonding. Besides this, the optical properties, including the dielectric function are obtained and analyzed in details.

  16. The systems Sr-Zn-{l_brace}Si,Ge{r_brace}: Phase equilibria and crystal structure of ternary phases

    SciTech Connect

    Romaka, V.V.; Falmbigl, M.; Grytsiv, A.; Rogl, P.

    2012-02-15

    Phase relations have been established by electron probe microanalysis (EPMA) and X-ray powder diffraction (XPD) for the Sr-poor part of the ternary systems Sr-Zn-Si at 800 Degree-Sign C and Sr-Zn-Ge at 700 Degree-Sign C. In the Sr-Zn-Si system one new ternary compound SrZn{sub 2+x}Si{sub 2-x} (0{<=}x{<=}0.45) with CeAl{sub 2}Ga{sub 2} structure and a statistical mixture of Zn/Si in the 4e site was found. Neither a type-I nor a type-IX clathrate phase was encountered. This system is characterized by formation of two further phases, i.e. SrZn{sub 1-x}Si{sub 1+x} with ZrBeSi-type (0.16{<=}x{<=}0.22) and SrZn{sub 1-x}Si{sub 1+x} with AlB{sub 2}-type (0.35{<=}x{<=}0.65) with a random distribution of Zn/Si atoms in the 2c site. For the Sr-Zn-Ge system, the homogeneity regions of the isotypic phases SrZn{sub 1-x}Ge{sub 1+x} with ZrBeSi-type (0{<=}x{<=}0.17) and AlB{sub 2}-type (0.32{<=}x{<=}0.56), respectively, have been determined. Whereas the germanide SrZn{sub 2+x}Ge{sub 2-x} (CeAl{sub 2}Ga{sub 2}-type) is characterized by a homogeneity region (0{<=}x{<=}0.5), the clathrate type-I phase Sr{sub 8}Zn{sub 8}Ge{sub 38} shows a point composition. - Graphical abstract: Phase equilibria of ternary compounds in the Sr-Zn-Si-system at 800 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Phase equilibria in the Sr-Zn-Si-system are established at 800 Degree-Sign C. Black-Right-Pointing-Pointer Phase equilibria in the Sr-Zn-Ge-system are established at 700 Degree-Sign C. Black-Right-Pointing-Pointer Crystal structures of the ternary compounds were confirmed by X-ray powder diffraction. Black-Right-Pointing-Pointer All ternary compounds except the clathrate-I in the Ge-system are characterized by a homogeneity region.

  17. Transparent Conducting Properties of SrSnO3 and ZnSnO3

    DOE PAGES

    Ong, Khuong P.; Fan, Xiaofeng; Subedi, Alaska; ...

    2015-04-29

    We report optical properties of doped n-type SrSnO3 and ZnSnO3 in relation to potential application as transparent conductors. We find that the orthorhombic distortion of the perovskite structure in SrSnO3 leads to absorption in the visible as the doping level is increased. This arises from interband transitions. We find that strain tuning could modify this absorption, but does not eliminate it. On the other hand, we find that ZnSnO3 although also having a non-cubic structure, can retain excellent transparency when doped, making it a good candidate transparent conductor.

  18. Structural and crystallization behavior of (Ba,Sr)TiO3 borosilicate glasses

    NASA Astrophysics Data System (ADS)

    Yadav, Avadhesh Kumar; Gautam, C. R.; Gautam, Arvind; Mishra, Vijay Kumar

    2013-10-01

    Various glass samples were prepared by melt quench technique in the glass system [(Ba1- x Sr x ) TiO3]-[2SiO2-B2O3]-[K2O] doped with 1 mole% of La2O3. Infrared spectra show the number of absorption peaks with different spliting in the wave number range from 450 to 4000 cm-1. Absorption peaks occurs due to asymetric vibrational streching of borate by relaxation of the bond B-O of trigonal BO3. Raman spectra show the Raman bands due to ring-type metaborate anions, symmetric breathing vibrations BO3 triangles replaced by BO4 tetrahedra, and symmetric breathing vibrations of six-member rings. The differential thermal analysis of a glass sample corresponding to composition x = 0.0 shows crystallization temperature at 847°C and glass transition temperature at 688°C. X-ray diffraction (XRD) pattern of glass ceramic samples shows the major crystalline phase of BaTiO3 whereas pyrochlore phases of barium titanium silicate. Scanning electron micrographs confirm the results of XRD as barium titanate is major crystalline phase along with pyrochlore phase of barium titanium silicate.

  19. ABO3 (A = La, Ba, Sr, K; B = Co, Mn, Fe) perovskites for thermochemical energy storage

    NASA Astrophysics Data System (ADS)

    Babiniec, Sean M.; Coker, Eric N.; Ambrosini, Andrea; Miller, James E.

    2016-05-01

    The use of perovskite oxides as a medium for thermochemical energy storage (TCES) in concentrating solar power systems is reported. The known reduction/oxidation (redox) active perovskites LaxSr1-xCoyMn1-yO3 (LSCM) and LaxSr1-xCoyFe1-yO3 (LSCF) were chosen as a starting point for such research. Materials of the LSCM and LSCF family were previously synthesized, their structure characterized, and thermodynamics reported for TCES operation. Building on this foundation, the reduction onset temperatures are examined for LSCM and LSCF compositions. The reduction extents and onset temperatures are tied to the crystallographic phase and reaction enthalpies. The effect of doping with Ba and K is discussed, and the potential shortcomings of this subset of materials families for TCES are described. The potential for long-term stability of the most promising material is examined through thermogravimetric cycling, scanning electron microscopy, and dilatometry. The stability over 100 cycles (450-1050 °C) of an LSCM composition is demonstrated.

  20. Luminescent nitridophosphates CaP2 N4 :Eu(2+) , SrP2 N4 :Eu(2+) , BaP2 N4 :Eu(2+) , and BaSr2 P6 N12 :Eu(2.).

    PubMed

    Pucher, Florian J; Marchuk, Alexey; Schmidt, Peter J; Wiechert, Detlef; Schnick, Wolfgang

    2015-04-20

    Nitridophosphates MP2 N4 :Eu(2+) (M=Ca, Sr, Ba) and BaSr2 P6 N12 :Eu(2+) have been synthesized at elevated pressures and 1100-1300 °C starting from the corresponding azides and P3 N5 with EuCl2 as dopant. Addition of NH4 Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single-crystal X-ray diffraction data (CaP2 N4 :Eu(2+) (P63 , no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) Å(3) , Z=24, 2033 observed reflections, 176 refined parameters, wR2 =0.096). Upon excitation by UV light, luminescence due to parity-allowed 4f(6) ((7) F)5d(1) →4f(7) ((8) S7/2 ) transition was observed in the orange (CaP2 N4 :Eu(2+) , λmax =575 nm), green (SrP2 N4 :Eu(2+) , λmax =529 nm), and blue regions of the visible spectrum (BaSr2 P6 N12 :Eu(2+) and BaP2 N4 :Eu(2+) , λmax =450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline-earth ions. The corresponding full width at half maximum values (2240-2460 cm(-1) ) are comparable to those of other known Eu(2+) -doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba3 P5 N10 Br:Eu(2+) , this investigation represents the first report on the luminescence of Eu(2+) -doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu(2+) -doped nitridophosphates may have the potential to be further developed into efficient light-emitting diode phosphors.

  1. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    DOE PAGES

    Stoyko, Stanislav; Voss, Leonard; He, Hua; ...

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e.,more » P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.« less

  2. Local structure in perovskite (Ba,Sr)TiO3: Reverse Monte Carlo refinements from multiple measurement techniques

    NASA Astrophysics Data System (ADS)

    Levin, Igor; Krayzman, Victor; Woicik, Joseph C.

    2014-01-01

    Local and average structures of ceramic Ba1-xSrxTiO3 solid solutions have been reconciled using Reverse Monte Carlo (RMC) refinements of atomic positions that employ simultaneous fitting of neutron total scattering data, x-ray absorption fine structure, and patterns of diffuse scattering in electron diffraction. These refinements enable explicit reconstruction of three-dimensional atomic configurations without any effective parameters. The results reveal cube- and parallelepiped-shaped probability density distributions for Ti atoms in the cubic and tetragonal phases of BaTiO3, respectively. These distributions are consistent with the split Ti sites (eight for the cubic and four for the tetragonal polymorphs) separated by ≈0.2 Å. The characters of Ti distributions are retained in the solid solutions, but the magnitude of Ti off-centering decreases as x increases. The Ti displacements remain correlated along the octahedral chains, at least up to x = 0.5, as manifested in the sheets of diffuse scattering in electron diffraction patterns; the correlation parameters and lengths have been quantified using RMC analyses. The ion-size difference between Ba and Sr is accommodated through the approximately isotropic relaxation of the oxygen atoms, which shift toward Sr; a similar relaxation is observed for the Ti atoms. Local Ti off-centering diminishes as the number of Sr atoms in the coordination groups [TiOxBa8-nSrn] increases.

  3. New observations on the pressure dependence of luminescence from Eu2+-doped MF2 (M = Ca, Sr, Ba) fluorides.

    PubMed

    Su, Fu Hai; Chen, Wei; Ding, Kun; Li, Guo Hua

    2008-05-29

    The luminescence from Eu(2+) ions in MF2 (M = Ca, Sr, Ba) fluorides has been investigated under the pressure range of 0-8 GPa. The emission band originating from the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) ions in CaF2 and SrF2 shows the red-shift as increasing pressure with pressure coefficients of -17 meV/GPa for CaF2 and -18 meV/GPa for SrF2. At atmospheric pressure, the emission spectrum of BaF2:Eu(2+) comprises two peaks at 2.20 and 2.75 eV from the impurity trapped exciton (ITE) and the self-trapped exciton (STE), respectively. As the pressure is increased, both emission peaks shift to higher energies, and the shifting rate is slowed by the phase transition from the cubic to orthorhombic phase at 4 GPa. Due to the phase transition at 4-5 GPa pressure, the ITE emission disappears gradually, and the STE emission is gradually replaced by the 4f(6)5d(1) --> 4f(7) transition of Eu(2+). Above 5 GPa, the pressure behavior of the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) in BaF2:Eu(2+) is the same as the normal emission of Eu(2+) in CaF2 and SrF2 phosphors.

  4. Halide Free M(BH4)2 (M = Sr, Ba, and Eu) Synthesis, Structure, and Decomposition.

    PubMed

    Sharma, Manish; Didelot, Emilie; Spyratou, Alexandra; Lawson Daku, Latévi Max; Černý, Radovan; Hagemann, Hans

    2016-07-18

    Borohydrides have attained high interest in the past few years due to their high volumetric and gravimetric hydrogen content. Synthesis of di/trimetallic borohydride is a way to alter the thermodynamics of hydrogen release from borohydrides. Previously reported preparations of M(BH4)2 involved chloride containing species such as SrCl2. The presence of residual chloride (or other halide) ions in borohydrides may change their thermodynamic behavior and their decomposition pathway. Pure monometallic borohydrides are needed to study decomposition products without interference from halide impurities. They can also be used as precursors for synthesizing di/trimetallic borohydrides. In this paper we present a way to synthesize halide free alkaline earth metal (Sr, Ba) and europium borohydrides starting with the respective hydrides as precursors. Two novel high temperature polymorphs of Sr and Eu borohydrides and four polymorphs of Ba borohydride have been characterized by synchrotron X-ray powder diffraction, thermal analysis, and Raman and infrared spectroscopy and supported by periodic DFT calculations. The decomposition routes of these borohydrides have also been investigated. In the case of the decomposition of strontium and europium borohydrides, the metal borohydride hydride (M(BH4)H3, M = Sr, Eu) is observed and characterized. Periodic DFT calculations performed on room temperature Ba(BH4)2 revealed the presence of bidentate and tridentate borohydrides.

  5. Superconducting and normal-state properties of APd2As2 (A = Ca, Sr, Ba) single crystals

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Kim, H.; Tanatar, M. A.; Prozorov, R.; Johnston, D. C.

    2013-06-01

    The synthesis and crystallography, magnetic susceptibility χ, magnetization M, specific heat Cp, in-plane electrical resistivity ρ, and in-plane magnetic penetration depth measurements are reported for single crystals of APd2As2 (A = Ca, Sr, Ba) versus temperature T and magnetic field H. The crystals were grown using PdAs self-flux. CaPd2As2 and SrPd2As2 crystallize in a collapsed body-centered tetragonal ThCr2Si2-type structure (I4/mmm), whereas BaPd2As2 crystallizes in the primitive tetragonal CeMg2Si2-type structure (P4/mmm), in agreement with literature data. The ρ(T) data exhibit metallic behavior for all three compounds. Bulk superconductivity is reported for CaPd2As2 and SrPd2As2 below Tc=1.27 and 0.92 K, respectively, whereas only a trace of superconductivity is found in BaPd2As2. No other phase transitions were observed. The χ(T) and M(H) data reveal anisotropic diamagnetism in the normal state, with χc>χab for CaPd2As2 and BaPd2As2, and χc<χab for SrPd2As2. The normal and superconducting state data indicate that CaPd2As2 and SrPd2As2 are conventional type-II nodeless s-wave electron-phonon superconductors. The electronic superconducting state heat capacity data for CaPd2As2, which has an extremely sharp heat capacity jump at Tc, are analyzed using our recent elaboration of the α-model of the BCS theory of superconductivity, which indicates that the s-wave gap in this compound is anisotropic in momentum space.

  6. Ba(Zn1−2xMnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites

    PubMed Central

    Man, Huiyuan; Guo, Shengli; Sui, Yu; Guo, Yang; Chen, Bin; Wang, Hangdong; Ding, Cui; Ning, F.L.

    2015-01-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn1−2xMnxCux)2As2 with the crystal structure identical to that of “122” family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf  ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with and a DC magnetic field dependence of , demonstrating that a spin glass transition takes place at Tf. As large as −53% negative magnetoresistance has been observed in Ba(Zn1−2xMnxCux)2As2, enabling its possible application in memory devices. PMID:26492957

  7. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    PubMed Central

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-01-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis. PMID:26907515

  8. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn.

    PubMed

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-02-24

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis.

  9. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    NASA Astrophysics Data System (ADS)

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-02-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis.

  10. Electrophoretic Deposition of Chitosan/45S5 Bioactive Glass Composite Coatings Doped with Zn and Sr

    PubMed Central

    Miola, Marta; Verné, Enrica; Ciraldo, Francesca Elisa; Cordero-Arias, Luis; Boccaccini, Aldo R.

    2015-01-01

    In this research work, the original 45S5 bioactive glass was modified by introducing zinc and/or strontium oxide (6 mol%) in place of calcium oxide. Sr was added for its ability to stimulate bone formation and Zn for its role in bone metabolism, antibacterial properties, and anti-inflammatory effect. The glasses were produced by means of melting and quenching process. SEM and XRD analyses evidenced that Zr and Sr introduction did not modify the glass structure and morphology while compositional analysis (EDS) demonstrated the effective incorporation of these elements in the glass network. Bioactivity test in simulated body fluid (SBF) up to 1 month evidenced a reduced bioactivity kinetics for Zn-doped glasses. Doped glasses were combined with chitosan to produce organic/inorganic composite coatings on stainless steel AISI 316L by electrophoretic deposition (EPD). Two EPD processes were considered for coating development, namely direct current EPD (DC-EPD) and alternating current EPD (AC-EPD). The stability of the suspension was analyzed and the deposition parameters were optimized. Tape and bending tests demonstrated a good coating-substrate adhesion for coatings containing 45S5-Sr and 45S5-ZnSr glasses, whereas the adhesion to the substrate decreased by using 45S5-Zn glass. FTIR analyses demonstrated the composite nature of coatings and SEM observations indicated that glass particles were well integrated in the polymeric matrix, the coatings were fairly homogeneous and free of cracks; moreover, the AC-EPD technique provided better results than DC-EPD in terms of coating quality. SEM, XRD analyses, and Raman spectroscopy, performed after bioactivity test in SBF solution, confirmed the bioactive behavior of 45S5-Sr-containing coating while coatings containing Zn exhibited no hydroxyapatite formation. PMID:26539431

  11. Electrophoretic Deposition of Chitosan/45S5 Bioactive Glass Composite Coatings Doped with Zn and Sr.

    PubMed

    Miola, Marta; Verné, Enrica; Ciraldo, Francesca Elisa; Cordero-Arias, Luis; Boccaccini, Aldo R

    2015-01-01

    In this research work, the original 45S5 bioactive glass was modified by introducing zinc and/or strontium oxide (6 mol%) in place of calcium oxide. Sr was added for its ability to stimulate bone formation and Zn for its role in bone metabolism, antibacterial properties, and anti-inflammatory effect. The glasses were produced by means of melting and quenching process. SEM and XRD analyses evidenced that Zr and Sr introduction did not modify the glass structure and morphology while compositional analysis (EDS) demonstrated the effective incorporation of these elements in the glass network. Bioactivity test in simulated body fluid (SBF) up to 1 month evidenced a reduced bioactivity kinetics for Zn-doped glasses. Doped glasses were combined with chitosan to produce organic/inorganic composite coatings on stainless steel AISI 316L by electrophoretic deposition (EPD). Two EPD processes were considered for coating development, namely direct current EPD (DC-EPD) and alternating current EPD (AC-EPD). The stability of the suspension was analyzed and the deposition parameters were optimized. Tape and bending tests demonstrated a good coating-substrate adhesion for coatings containing 45S5-Sr and 45S5-ZnSr glasses, whereas the adhesion to the substrate decreased by using 45S5-Zn glass. FTIR analyses demonstrated the composite nature of coatings and SEM observations indicated that glass particles were well integrated in the polymeric matrix, the coatings were fairly homogeneous and free of cracks; moreover, the AC-EPD technique provided better results than DC-EPD in terms of coating quality. SEM, XRD analyses, and Raman spectroscopy, performed after bioactivity test in SBF solution, confirmed the bioactive behavior of 45S5-Sr-containing coating while coatings containing Zn exhibited no hydroxyapatite formation.

  12. Elemental intermixing within an ultrathin SrRuO{sub 3} electrode layer in epitaxial heterostructure BaTiO{sub 3}/SrRuO{sub 3}/SrTiO{sub 3}

    SciTech Connect

    Zhang, H. B.; Qi, R. J.; Ding, N. F.; Sun, L.; Huang, R.; Duan, C. G. Chu, J. H.; Fisher, Craig A. J.; Ikuhara, Y.

    2016-01-15

    Aberration corrected scanning transmission electron microscopy is used to directly observe atom columns in an epitaxial BaTiO{sub 3} thin film deposited on a 3.6 nm-thick SrRuO{sub 3} electrode layer above an SrTiO{sub 3} (001) substrate. Compositional gradients across the heterointerfaces were examined using electron energy-loss spectroscopy techniques. It was found that a small amount of Ba and Ti had diffused into the SrRuO{sub 3} layer, and that this layer contained a non-negligible concentration of oxygen vacancies. Such point defects are expected to degrade the electrode’s electronic conductivity drastically, resulting in a much longer screening length. This may explain the discrepancy between experimental measurements and theoretical estimates of the ferroelectric critical thickness of a BaTiO{sub 3} ferroelectric barrier sandwiched between metallic SrRuO{sub 3} electrodes, since theoretical calculations generally assume ideal (stoichiometric) perovskite SrRuO{sub 3}.

  13. Half-metallicity and stability of the rock salt BaC and SrC (111) surfaces: A density functional study

    SciTech Connect

    Tabatabaeifar, A. H.; Davatolhagh, S. Foroughpour, M.

    2013-12-07

    The electronic structure and magnetic properties of relaxed (111) surfaces of the alkaline-earth monocarbides BaC and SrC in the stable rock salt structure, are calculated on the basis of first principle density functional theory within the framework of self-consistent field plane wave pseudo-potential method, using the generalized gradient approximation for the exchange-correlation functional. The results of this study reveal that the C-terminated (111) surfaces retain the bulk half-metallic property in both BaC and SrC. The half-metallicity of the C-terminated BaC surface is found to be more robust compared to the bulk BaC due to the larger half-metallic energy gap. In contrast, the half-metallic energy gap of the C-terminated SrC surface is found to be smaller than that of the bulk. The Ba-terminated surface of BaC and the Sr-terminated surface of SrC, however, lose their bulk half-metallicity due to the formation of surface states in the majority spin band gap. The calculations also show that the atomic magnetic moments at the half-metallic C-terminated surfaces in both BaC and SrC increase considerably with respect to the corresponding bulk values, which is explained in terms of an increase in the number of unpaired 2p electrons of the carbon atom at the surface. We also discuss the stability of the surfaces via the calculated bulk formation energies. The bulk formation energies for both BaC and SrC in the rock salt structure are found to be positive, which indicate that the surfaces are not stable at normal pressure and temperature conditions, and non-equilibrium growth techniques may be required for the realization of BaC and SrC thin films.

  14. Crystal structures and chemistry of double perovskites Ba{sub 2}M(II)M'(VI)O{sub 6} (M=Ca, Sr, M'=Te, W, U)

    SciTech Connect

    Fu, W.T. Au, Y.S.; Akerboom, S.; IJdo, D.J.W.

    2008-09-15

    Structures of the double perovskites Ba{sub 2}M(II)M '(VI)O{sub 6} (M=Ca, Sr, M'=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2/m (M' =W) and R3-bar (M'=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P2{sub 1}/n (M'=U) or cubic Fm3-bar m (M'=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba{sub 2}SrTeO{sub 6} and Ba{sub 2}CaUO{sub 6}, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba{sub 2}SrWO{sub 6} and Ba{sub 2}CaWO{sub 6} in the temperature range between 80 and 723 K. It was found that the rhombohedral R3-bar structure exists in Ba{sub 2}SrWO{sub 6} above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba{sub 2}CaWO{sub 6} undergoes a structural phase transition at low temperature to the tetragonal I4/m structure. - Graphical abstract: Evolution of structures as function of temperature in Ba{sub 2}SrWO{sub 6} (left) and Ba{sub 2}CaWO{sub 6} (right). The existence of two phase region in Ba{sub 2}SrWO{sub 6} can be clearly seen by the progressive increase of the rhombohedral R3-bar phase marked by asterisk (*)

  15. The in vitro biological properties of Mg-Zn-Sr alloy and superiority for preparation of biodegradable intestinal anastomosis rings

    PubMed Central

    Liu, Ling; Li, Nianfeng; Lei, Ting; Li, Kaimo; Zhang, Yangde

    2014-01-01

    Background Magnesium (Mg) alloy is a metal-based biodegradable material that has received increasing attention in the field of clinical surgery, but it is currently seldom used in intestinal anastomosis. This study was conducted to comprehensively assess a ternary magnesium (Mg)-zinc (Zn)-strontium (Sr) alloy’s biological superiorities as a preparation material for intestinal anastomosis ring. Material/Methods Mouse L-929 fibroblasts were cultured with Mg-Zn-Sr alloy extract and compared with both positive (0.64% phenol) and negative (original broth culture) controls. The cell morphology of different groups was examined using microscopy, and a cytotoxicity assessment was performed. Fresh anticoagulated human blood was mixed with Mg-Zn-Sr alloy extract and compared with both positive (distilled water) and negative (normal saline) controls. The absorbance of each sample at 570 nm was used to calculate the Mg-Zn-Sr alloy hemolysis ratio in order to test the Mg alloy’s blood compatibility. Bacterial cultures of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were added to Mg-Zn-Sr alloy block samples and compared with positive (Ceftazidime), negative (316LSS stainless steel), and blank controls. The broth cultures were sampled to compare their bacterial colony counts so as to evaluate the antibacterial properties of the Mg-Zn-Sr alloy. The Mg-Zn-Sr alloy was surface-coated with a layer of poly(lactic-co-glycolic acid) carrying everolimus. The surface morphology and degradability of the coating were examined so as to demonstrate feasibility of coating, which can release the drug evenly. Results The experiments proved that Mg-Zn-Sr alloy has good biocompatible, antibacterial, and drug-loaded coating performances, which are lacking in existing intestinal anastomosis devices/materials. Conclusions The Mg-Zn-Sr alloy increases biocompatibility, and yields a safer and better therapeutic effect; therefore, it is a novel biomaterial that is feasible for

  16. Half metallic ferromagnetism in alkaline-earth metal nitrides XN (X=Ca, Sr and Ba): A first principles study

    NASA Astrophysics Data System (ADS)

    Palanichamy, R. Rajeswara; Priyanga, G. Sudha; Cinthia, A. Jemmy; Murugan, A.; Meenaatci, A. T. Asvini; Iyakutti, K.

    2013-11-01

    The structural, electronic, mechanical and magnetic properties of 3 alkaline-earth metal nitrides (XN: X=Ca, Sr, and Ba) are investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation code. At ambient pressure all the 3 nitrides are stable in the ferromagnetic state with a cubic NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that these materials are half metallic ferromagnets at normal pressure. A pressure-induced structural phase transition from NaCl (B1) to CsCl (B2) phase is observed in CaN, SrN and BaN. On further increasing the pressure, a half metallic to metallic transition is also observed in these nitrides. Ferromagnetism is quenched in all the 3 nitrides at high pressures.

  17. Pressure-induced superconductivity in Ba0.5Sr0.5Fe2As2.

    PubMed

    Tsoi, Georgiy M; Malone, Walter; Uhoya, Walter; Mitchell, Jonathan E; Vohra, Yogesh K; Wenger, Lowell E; Sefat, Athena S; Weir, S T

    2012-12-12

    High-pressure electrical resistance measurements have been performed on single crystal Ba(0.5)Sr(0.5)Fe(2)As(2) platelets to pressures of 16 GPa and temperatures down to 10 K using designer diamond anvils under quasi-hydrostatic conditions with an insulating steatite pressure medium. The resistance measurements show evidence of pressure-induced superconductivity with an onset transition temperature at ∼31 K and zero resistance at ∼22 K for a pressure of 3.3 GPa. The transition temperature decreases gradually with increasing pressure before completely disappearing for pressures above 12 GPa. The present results provide experimental evidence that a solid solution of two 122-type materials, i.e., Ba(1-x)Sr(x)Fe(2)As(2) (0 < x < 1), can also exhibit superconductivity under high pressure.

  18. Migration behaviour of twaite shad Alosa fallax assessed by otolith Sr:Ca and Ba:Ca profiles.

    PubMed

    Magath, V; Marohn, L; Fietzke, J; Frische, M; Thiel, R; Dierking, J

    2013-06-01

    Individual migration behaviour during the juvenile and adult life phase of the anadromous twaite shad Alosa fallax in the Elbe estuary was examined using otolith Sr:Ca and Ba:Ca profiles. Between hatching and the end of the first year of life, juveniles showed two migration patterns. Pattern one exhibited a single downstream migration from fresh water to the sea with no return into fresh water. In contrast, pattern two showed a first migration into the sea, then a return into fresh water and, finally, a second downstream migration into marine water. This first report of migration plasticity for A. fallax points to different exposure times to estuarine threats depending on the migration strategy. In adults, high Sr:Ca and low Ba:Ca in the majority of individuals confirmed prior reports of a primarily marine habitat use. Patterns reflecting spawning migrations were rarely observed on otoliths, possibly due to the short duration of visits to fresh water.

  19. Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae = Ca, Sr, Ba, as thermoelectric materials.

    PubMed

    Parker, David; Singh, David J

    2013-10-01

    We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2Sn, Sr2Sn and Ba2Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli-roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

  20. Protonic Conduction of BaCe0.85YO. 1503 Doped with SrTiO3

    NASA Technical Reports Server (NTRS)

    Dynys, Frederick W.; Sayir, Ali

    2005-01-01

    Reformers based on ceramic membrane technology potentially offer hydrogen production that is comparable to the cost of fossil fuels. Protonic conducting ceramic with the chemical formula AB03 offers the promise of highly selective hydrogen separation at intermediate temperature (400-800 C). Among different perovskite-type oxides, BaCe03 and SrCe03 based compositions show high protonic conductivities but strong resistance to densification. X-ray diffraction studies on sintered specimens of BaCe0.85Y0.1503-6 show multi-phase formation which was found to show dependence upon powder synthesis method. Doping with SrTiO3 suppresses multi-phase formation and enhances grain growth. Conductivity measurements in temperature range of 200 to 1000 C were performed by ac impedance spectroscopy under dry and wet conditions. Sintering behavior, phase formation and conductivity results will be reported.

  1. Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae=Ca,Sr,Ba, as thermoelectric materials

    SciTech Connect

    Parker, David S; Singh, David J

    2013-01-01

    We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2 Sn, Sr2 Sn and Ba2 Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli - roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

  2. Memristive behaviors in Pt/BaTiO{sub 3}/Nb:SrTiO{sub 3} ferroelectric tunnel junctions

    SciTech Connect

    Wen, Zheng; Wu, Di Li, Aidong

    2014-08-04

    We demonstrate memristive behaviors in Pt/BaTiO{sub 3}/Nb:SrTiO{sub 3} metal/ferroelectric/semiconductor ferroelectric tunnel junctions, in which the semiconductor electrode can be switched between the accumulated and the depleted states by polarization reversal in the BaTiO{sub 3} barrier via the ferroelectric field effect. An extra barrier, against electron tunneling, forms in the depleted region of the Nb:SrTiO{sub 3} electrode surface, which together with the ferroelectric barrier itself modulate the tunneling resistance with the change of effective polarization. Continuous resistance modulation over four orders of magnitude is hence achieved by application of programmed voltage pulses with different polarity, amplitude, and repetition numbers, as a result of the development of the extra barrier.

  3. Variation of Ca, Sr, Ba and Mg in the otolith of mudskipper in west coast of Peninsular Malaysia.

    PubMed

    Sarimin, A S; Ghaffar, M A; Mohamed, C A R

    2009-02-01

    A study on elemental composition in the otolith of giant mudskipper, Periophthalmodon schlosseri, was done from June to October 2003. Specimens were obtained from the mangrove areas of Kuala Selangor, Sepang and Melaka in the west coast of Peninsular Malaysia. A total of 70 sagitta otoliths were analyzed to detect variation of Sr, Ba and Mg, replacing the natural chemical composition of the otolith, which is the calcium carbonate (CaCO3). The average ratio of Sr:Ca was 0.11 x 10(-4), Ba:Ca was 5.7 x 10(-3) and Mg:Ca was 0.2 x 10(-3). Strong correlation (R > 0.8) between fish body size and otolith weight ofmudskipper (p < 0.01) also found during this study.

  4. The new barium zinc mercurides Ba{sub 3}ZnHg{sub 10} and BaZn{sub 0.6}Hg{sub 3.4} - Synthesis, crystal and electronic structure

    SciTech Connect

    Schwarz, Michael; Wendorff, Marco; Roehr, Caroline

    2012-12-15

    The title compounds Ba{sub 3}ZnHg{sub 10} and BaZn{sub 0.6}Hg{sub 3.4} were synthesized from stoichiometric ratios of the elements in Ta crucibles. Their crystal structures, which both represent new structure types, have been determined using single crystal X-ray data. The structure of Ba{sub 3}ZnHg{sub 10} (orthorhombic, oP28, space group Pmmn, a=701.2(3), b=1706.9(8), c=627.3(3)pm, Z=2, R1=0.0657) contains folded 4{sup 4} Hg nets, where the meshes form the bases of flat rectangular pyramids resembling the structure of BaAl{sub 4}. The flat pyramids are connected via Hg-Zn/Hg bonds, leaving large channels at the folds, in which Ba(1) and Hg(2) atoms alternate. Whereas the remaining Hg/Zn atoms form a covalent 3D network of three- to five-bonded atoms with short M-M distances (273-301 pm; CN 9-11), the Hg(2) atoms in the channels adopt a comparatively large coordination number of 12 and increased distances (317-348 pm) to their Zn/Hg neighbours. In the structure of BaZn{sub 0.6}Hg{sub 3.4} (cubic, cI320, space group I4{sup Macron }3d, a=2025.50(7) pm, Z=64, R1=0.0440), with a chemical composition not much different from that of Ba{sub 3}ZnHg{sub 10}, the Zn/Hg atoms of the mixed positions M(1/2) are arranged in an slightly distorted primitive cubic lattice with a 4 Multiplication-Sign 4 Multiplication-Sign 4 subcell relation to the unit cell. The 24 of the originating 64 cubes contain planar cis tetramers Hg(5,6){sub 4} with Hg in a nearly trigonal planar or tetrahedral coordination. In another 24 of the small cubes, two opposing faces are decorated by Hg(3,4){sub 2} dumbbells, two by Ba(2) atoms respectively. The third type of small cubes are centered by Ba(1) atoms only. The complex 3D polyanionic Hg/Zn network thus formed is compared with the Hg partial structure in Rb{sub 3}Hg{sub 20} applying a group-subgroup relation. Despite their different overall structures, the connectivity of the negatively charged Hg atoms, the rather metallic Zn bonding characteristic

  5. Water oxidation catalysis: an amorphous quaternary Ba-Sr-Co-Fe oxide as a promising electrocatalyst for the oxygen-evolution reaction.

    PubMed

    Zhang, Cuijuan; Berlinguette, Curtis P; Trudel, Simon

    2016-01-25

    We present an amorphous quaternary Ba-Sr-Co-Fe oxide (a-BSCF) with a specific stoichiometry, readily fabricated via a photochemical decomposition method. a-BSCF demonstrates high catalytic activity towards the oxygen-evolution reaction (OER).

  6. Solution processed Ni-doped TiO2 p-type channel in field effect transistor assembly with <10 nm thin Ba0.5Sr0.5TiO3 dielectric layer

    NASA Astrophysics Data System (ADS)

    Das, Soumen; Kim, Jin-Hwan; Park, Yong-Kyu; Hahn, Yoon-Bong

    2011-05-01

    Solution processed field effect transistor structures were fabricated by inserting a Ba0.5Sr0.5TiO3 layer to form Ag/ZnO/Ba0.5Sr0.5TiO3/Ni2+:TiO2/n-Si assembly. Such assembly registered an on-to-off current ratio as large as 103 with very low off-state current ˜10-12 A. The low leakage current is attributed to the appreciably higher values of valence/conduction band off-set of Ba0.5Sr0.5TiO3/semiconductor heterojunction. The device response was studied as a function of temperature in the range of 25-175 °C. The hole diffusion coefficient and mobility of p-TiO2 was calculated ˜10-3 cm2/s and ˜0.13-0.15 cm-2 V-1 s-1, respectively.

  7. Redetermination of the structure of ALa₂WO₇ (A=Ba, Sr) with fluorite-like metal ordering

    SciTech Connect

    Fu, W.T.; IJdo, D.J.W.; Bontenbal, A.

    2013-05-01

    The crystal structures of ALa₂WO₇ (A=Ba, and Sr) at room temperature were re-determined by the Rietveld method using the combined X-ray and neutron powder diffraction data. The compounds are confirmed to be isomorphic, crystallizing in the space group P112₁/b. In ALa₂WO₇ the ordering of metal atoms is fluorite-like, but it differs from that of the fluorite-defect compounds of the formula Ln₃MO₇ (Ln=lanthanide or Y, M=pentavalent metal). The structure of ALa₂WO₇ consists of isolated WO₆ octahedra, whereas in the normal Ln₃MO₇ the MO₆ octahedra share corners forming one-dimensional chains. Although ALa₂WO₇ has a centric space group, La ions are not situate at the centre of symmetry, which explains the ⁵D₀→⁷F₂ transition being dominant in emission spectrum of Eu-doped materials. - Graphical abstract: Schematic drawing of the crystal structures of ALa₂WO₇ (A=Ba, Sr) (left) and Ln₃MO₇ (right) showing the different arrangement of metal octahedra. Note that the example of Ln₃MO₇ is the structure of La₃TaO₇ with the space group Cmcm. Highlights: • The structural ambiguity of BaLa₂WO₇ has been resolved. • The details of the crystal structure of SrLa₂WO₇ are reported for the first time. • ALa₂WO₇ (A=Ba, Sr) closely resemble β-La₃RuO₇ and one of the La₃IrO₇ polymorph.

  8. Solid-Phase Equilibria for Metal-Silicon-Oxygen Ternary Systems I: Mg, Ca, Sr and Ba

    DTIC Science & Technology

    1990-07-01

    both Sr and Ba to their respective disilicides . An intermediate situation exists for the Ca oxides and silicates, in which excess Si can react with CaO...Si depends on their structural and electrical properties , and significant amounts of research would be required to grow such films and evaluate their... properties . The phase diagrams in Figs. 2-4 can also be used to estimate whether or not various forms of the new oxide superconductors are compatible

  9. CaF2, BaF2 and SrF2 crystals’ optical anisotropy parameters

    NASA Astrophysics Data System (ADS)

    Snetkov, I. L.; Yakovlev, A. I.; Palashov, O. V.

    2015-09-01

    Using the original method, based on measurements of thermally induced depolarization, the optical anisotropy parameters of CaF2, BaF2 and SrF2 cubic crystals were measured and compared with what is known from the literature. Euler angles of crystallographic axis orientation [C], in which the thermally induced depolarization is minimal, were determined using experimental results for studied fluorides.

  10. Study of non-stoichiometric BaSrTiFeO3 oxide dedicated to semiconductor gas sensors

    NASA Astrophysics Data System (ADS)

    Fasquelle, D.; Verbrugghe, N.; Deputier, S.

    2016-11-01

    Developing instrumentation systems compatible with the European RoHS directive (restriction of hazardous substances) to monitor our environment is of great interest for our society. Our research therefore aims at developing innovating integrated systems of detection dedicated to the characterization of various environmental exposures. These systems, which integrate new gas sensors containing lead-free oxides, are dedicated to the detection of flammable and toxic gases. We have firstly chosen to study semiconductor gas sensors implemented with lead-free oxides in view to develop RoHS devices. Therefore thick films deposited by spin-coating and screen-printing have been chosen for their robustness, ease to realize and ease to finally obtain cost-effective sensors. As crystalline defects and ionic vacancies are of great interest for gas detection, we have decided to study a non-stoichiometric composition of the BaSrTiFeO3 sensible oxide. Nonstoichiometric BaSrTiFeO3 lead-free oxide thick films were deposited by screen-printing on polycrystalline AFO3 substrates covered by a layer of Ag-Pd acting as bottom electrode. The physical characterizations have revealed a crystalline structure mainly composed of BaTiO3 pseudo-cubic phase and Ba4Ti12O27 monoclinic phase for the powder, and a porous microstructure for the thick films. When compared to a BSTF thick film with a stoichiometric composition, a notable increase in the BSTF dielectric constant value was observed when taking into account of a similar microstructure and grain size. The loss tangent mean value varies more softly for the non-stoichiometric BaSrTiFeO3 films than for the perovskite BSTF film as tanδ decreases from 0.45 to 0.04 when the frequency increases from 100 Hz to 1 MHz.

  11. Fine grained Ba(1-x)Sr(x)TiO3 ceramics by spark plasma sintering.

    PubMed

    Tian, Huyong; Chen, Wanpin; Buckley, C E; Chan, H L W

    2008-11-01

    Fine grained Ba(0.75)Sr(0.25)TiO3 (BST) ceramics were prepared via spark plasma sintering technique. BST nano-powders freshly prepared by a low-temperature direct solution synthesis technique were used as starting materials. X-ray diffraction measurements indicated that the ceramics had a pure perovskite phase and the observation under scanning electron microscope revealed that the ceramic had a grain size in the range of 50 to 300 nm. The dielectric properties of the fine-grained BST ceramics were determined at different temperatures and frequencies. At room temperature, the ceramics exhibited a moderate dielectric constant (3962 +/- 10), a good dielectric tunability (53.84% under a dc bias of 19.72 kV/cm). The highest tunability and figure of merit (FOM) values are 83.27% at 50.2 degrees C and 289.28 at 62.3 degrees C, respectively. These results suggested that the BST ceramics are suitable for use in tunable microwave devices.

  12. Interfacial dislocations in (111) oriented (Ba0.7Sr0.3)TiO3 films on SrTiO3 single crystal

    DOE PAGES

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; ...

    2015-10-08

    In this study, we have investigated the interfacial structure of epitaxial (Ba,Sr)TiO3 films grown on (111)-oriented SrTiO3 single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a<110> comprised of a misfit dislocation along <112>, and threading dislocations along <110> or <100>. The misfit dislocation with Burgers vector of a <110> can dissociate into two ½ a <110> partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography, we retrievedmore » the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba0.7Sr0.3)TiO3 films.« less

  13. Inclusion property of Cs, Sr, and Ba impurities in LiCl crystal formed by layer-melt crystallization

    SciTech Connect

    Choi, Jung-Hoon; Cho, Yung-Zun; Lee, Tae-Kyo; Eun, Hee-Chul; Kim, Jun-Hong; Park, Hwan-Seo; Kim, In-Tae; Park, Geun-Il

    2013-07-01

    Pyroprocessing is one of the promising technologies enabling the recycling of spent nuclear fuels from a commercial light water reactor (LWR). In general, pyroprocessing uses dry molten salts as electrolytes. In particular, LiCl waste salt after pyroprocessing contains highly radioactive I/II group fission products mainly composed of Cs, Sr, and Ba impurities. Therefore, it is beneficial to reuse LiCl salt in the pyroprocessing as an electrolyte for economic and environmental issues. Herein, to understand the inclusion property of impurities within LiCl crystal, the physical properties such as lattice parameter change, bulk modulus, and substitution enthalpy of a LiCl crystal having 0-6 at% Cs{sup +} or Ba{sup 2+} impurities under existence of 1 at% Sr{sup 2+} impurity were calculated via the first-principles density functional theory. The substitution enthalpy of LiCl crystals having 1 at% Sr{sup 2+} showed slightly decreased value than those without Sr{sup 2+} impurity. Therefore, through the substitution enthalpy calculation, it is expected that impurities will be incorporated within LiCl crystal as co-existed form rather than as a single component form. (authors)

  14. Epitaxial Stabilization of the Perovskite Phase in (Sr(1-x)Ba(x))MnO3 Thin Films.

    PubMed

    Langenberg, Eric; Guzmán, Roger; Maurel, Laura; Martínez de Baños, Lourdes; Morellón, Luis; Ibarra, M Ricardo; Herrero-Martín, Javier; Blasco, Javier; Magén, César; Algarabel, Pedro A; Pardo, José A

    2015-11-04

    A novel mechanism of ferroelectricity driven by off-centering magnetic Mn(4+) ions was proposed in (Sr1-xBax)MnO3, in its ideal perovskite phase, which yields enormous expectations in the search for strong magnetoelectric materials. Still, the desired perovskite phase has never been stabilized in thin films due to its extremely metastable character. Here, we report on a thorough study of the perovskite phase stabilization of (Sr1-xBax)MnO3 thin films, 0.2 ≤ x ≤ 0.5, grown by pulsed laser deposition onto (001)-oriented perovskite substrates. X-ray diffraction measurements and scanning transmission electron microscopy reveal that, under appropriate deposition conditions, the perovskite phase is fully stabilized over the nonferroelectric hexagonal phase, despite the latter being increasingly favored on increasing Ba-content. Moreover, we have managed to grow epitaxial coherent cube-on-cube (Sr1-xBax)MnO3 films upon strains ranging from 0% to 4%. Our results become a milestone in further studying perovskite (Sr1-xBax)MnO3 thin films and pave the way for tailoring ferroic and magnetoelectric properties either by strain engineering or Ba-doping.

  15. Comparative ab initio calculations of SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) heterostructures

    NASA Astrophysics Data System (ADS)

    Piskunov, Sergei; Eglitis, Roberts I.

    2016-05-01

    Using a B3PW hybrid exchange-correlation functional within the density functional theory (DFT) we calculated from the first principles the electronic structure of BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (0 0 1) interfaces. The optical band gap of both BaTiO3/SrTiO3 and PbZrO3/SrZrO3 (0 0 1) interfaces depends mostly from BaO or TiO2 and SrO or ZrO2 termination of the upper layer, respectively. Based on the results of our calculations we predict increase of the Ti-O and Zr-O chemical bond covalency near the SrTiO3/BaTiO3 and SrZrO3/PbZrO3 (0 0 1) interfaces as compared to the BaTiO3 and PbZrO3 bulk.

  16. Is otolith microchemistry (Sr: Ca and Ba:Ca ratios) useful to identify Mugil curema populations in the southeastern Caribbean Sea?

    PubMed

    Avigliano, E; Callicó-Fortunato, R; Buitrago, J; Volpedo, A V

    2015-11-01

    The aim of the present study was to evaluate the potential use of otolith microchemistry (Sr:Ca and Ba:Ca ratios) to identify silver mullet, Mugil curema, populations in Southeastern Caribbean Sea. Fish samples were collected in 7 areas of Nueva Esparta State (Venezuela). The otolith Sr:Ca and Ba:Ca ratios and water Sr:Ca were determined (by ICP-OES and EDTA volumetric method). Otoliths Sr:Ca and Ba:Ca ratios and Sr:Ca partition coefficient of mullets in Cubagua island (south of the State) were significantly different from ratios in La Guardia (north of the State). A discriminant analysis of otolith Sr:Ca and Ba:Ca ratios separated Cubagua Island from La Guardia values. These results suggest the existence of different mullet groups in the Southeastern Caribbean Sea. For this, the simultaneous use of Sr:Ca and Ba:Ca ratios could be a potential tool to identify populations in the study area.

  17. Ternary fluorides BaMF4 (M = Zn, Mg and Mn) at low temperatures.

    PubMed

    Posse, Jose Maria; Grzechnik, Andrzej; Friese, Karen

    2009-10-01

    Ternary fluorides BaMF4 (M = Zn, Mg, Mn) have been studied in the temperature range from 300 to 10 K using synchrotron and laboratory powder and single-crystal diffraction. The first two compounds are stable down to 10 K, while the third one undergoes a phase transition to an incommensurately modulated structure at approximately 250 K. The modulated phase is stable down to 10 K. The magnetic anomalies at 45 and 27 K observed previously in BaMnF4 are exclusively reflected in the behavior of the gamma component of the q vector, which assumes an irrational value of approximately 0.395 A(-1) at the temperature corresponding to the onset of the magnetic ordering and then stays constant down to 10 K. Mn-Mn distances do not indicate any structural response to the magnetic ordering. The formation of the modulated phase can be explained on the basis of simple geometrical criteria. The incorporation of the large Mn cation in the octahedral sheets implies an increase of the cavity in which the Ba ion is incorporated. This leads to the formation of the modulated structure to adapt the coordination sphere around Ba in such a way that the bond-valence sums can be kept close to the ideal value of two. With further lowering of the temperature, the charge balance around the Ba ion requires an increasingly anharmonic character of the modulation function of Ba, until finally at 10 K a crenel-like shape is assumed for the modulation of this atom.

  18. SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} - two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    SciTech Connect

    Stegmaier, Saskia; Faessler, Thomas F.

    2012-08-15

    SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn{sub 2}Sn{sub 2} comprises (anti-)PbO-like {l_brace}ZnSn{sub 4/4}{r_brace} and {l_brace}SnZn{sub 4/4}{r_brace} layers. Ca{sub 2}Zn{sub 3}Sn{sub 6} shows similar {l_brace}ZnSn{sub 4/4}{r_brace} layers and {l_brace}Sn{sub 4}Zn{r_brace} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn{sub 2}Sn{sub 2} adopts the SrPd{sub 2}Bi{sub 2} structure type, and Ca{sub 2}Zn{sub 3}Sn{sub 6} is isotypic to the R{sub 2}Zn{sub 3}Ge{sub 6} compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {l_brace}Sn{sub 4}Zn{r_brace} layers of Ca{sub 2}Zn{sub 3}Sn{sub 6}. - Graphical abstract: Crystal structures of the new Ae-Zn-Sn polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Highlights: Black-Right-Pointing-Pointer New polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Black-Right-Pointing-Pointer Obtained by high temperature reactions of the elements. Black-Right-Pointing-Pointer Single crystal XRD structure determination and DFT electronic structure calculations. Black-Right-Pointing-Pointer Closely related crystal and electronic structures. Black-Right-Pointing-Pointer Metallic conductivity coexisting with lone pairs and covalent bonding

  19. Trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant photovoltaics.

    PubMed

    Hong, Feng; Lin, Wenjun; Meng, Weiwei; Yan, Yanfa

    2016-02-14

    We propose trigonal Cu2-II-Sn-VI4 (II = Ba, Sr and VI = S, Se) quaternary compounds for earth-abundant solar cell applications. Through density functional theory calculations, we show that these compounds exhibit similar electronic and optical properties to kesterite Cu2ZnSnS4 (CZTS): high optical absorption with band gaps suitable for efficient single-junction solar cell applications. However, the trigonal Cu2-II-Sn-VI4 compounds exhibit defect properties more suitable for photovoltaic applications than those of CZTS. In CZTS, the dominant defects are the deep acceptors, Cu substitutions on Zn sites, which cause non-radiative recombination and limit the open-circuit voltages of CZTS solar cells. On the contrary, the dominant defects in trigonal Cu2-II-Sn-VI4 are the shallow acceptors, Cu vacancies, similar to those in CuInSe2. Our results suggest that the trigonal Cu2-II-Sn-VI4 quaternary compounds could be promising candidates for efficient earth-abundant thin-film solar cell and photoeletrochemical water-splitting applications.

  20. Bioaccessibility of Ba, Cu, Pb, and Zn in urban garden and orchard soils.

    PubMed

    Cai, Meifang; McBride, Murray B; Li, Kaiming

    2016-01-01

    Exposure of young children to toxic metals in urban environments is largely due to soil and dust ingestion. Soil particle size distribution and concentrations of toxic metals in different particle sizes are important risk factors in addition to bioaccessibility of these metals in the particles. Analysis of particle size distribution and metals concentrations for 13 soils, 12 sampled from urban gardens and 1 from orchard found that fine particles (<105 μm) comprised from 22 to 66% by weight of the tested soils, with Ba, Cu, Pb and Zn generally at higher concentrations in the finer particles. However, metal bioaccessibility was generally lower in finer particles, a trend most pronounced for Ba and Pb. Gastric was higher than gastrointestinal bioaccessibility for all metals except Cu. The lower bioaccessibility of Pb in urban garden soils compared to orchard soil is attributable to the higher organic matter content of the garden soils.

  1. New Family of Materials with Negative Coefficients of Thermal Expansion: The Effect of MgO, CoO, MnO, NiO, or CuO on the Phase Stability and Thermal Expansion of Solid Solution Phases Derived from BaZn2Si2O7.

    PubMed

    Thieme, Christian; Waurischk, Tina; Heitmann, Stephan; Rüssel, Christian

    2016-05-02

    Recently, a silicate with the composition SrxBa1-xZn2Si2O7 was reported, which exhibits a negative coefficient of thermal expansion. The compound BaZn2Si2O7 shows a highly positive coefficient of thermal expansion up to a temperature of 280 °C and then transfers to a high temperature phase, which exhibits a coefficient of thermal expansion near zero or negative over a limited temperature range up to around 500 °C. This high temperature modification can be stabilized to room temperature if Ba(2+) is replaced by Sr(2+). In the solid solution SrxBa1-xZn2Si2O7, also Zn(2+) can be replaced in a wide concentration range by other cations with the respective valency. In the present study, Zn was partially or completely replaced by Mg, Co, Mn, Ni, or Cu. If the high temperature phase is stable at room temperature, the thermal expansion is negative, and if the partial substitution exceeds a certain concentration threshold, the low temperature phase with the crystal structure of BaZn2Si2O7 and highly positive thermal expansion is formed. The lowest mean coefficients of thermal expansion were measured for the composition Ba0.5Sr0.5Zn1.4Co0.6Si2O7 with a value of -2.9 × 10(-6) K(-1). In general, a lower Zn-concentration leads to a higher anisotropy and a lower mean coefficient of thermal expansion.

  2. Unexpected ordering at the atomic scale interface of SrRuO3 and BaTiO3

    NASA Astrophysics Data System (ADS)

    Baddorf, Arthur P.

    2011-03-01

    Atomically engineered oxide multilayers and superlattices display unique properties responsive to the electronic and atomic structures of the interfaces. Interfaces can exhibit not only two-dimensional functionality, but have the power to dictate the properties of thin films. A clear example is found in ferroelectric thin films, where the domain size, orientation, and transport properties are controlled by top and buried interfaces. We have explored a prototypical ferroelectric - bottom electrode interface by characterizing BaTi O3 grown on SrRu O3 . Films were grown on SrTi O3 substrates by pulsed laser deposition, monitored by high-pressure reflection high-energy diffraction, exhibited high crystalline quality in electron diffraction and cross-sectional transmission electron microscopy (STEM), and were flat according to atomic force microscopy. Despite multiple indicators commonly accepted to confirm a sharp interface, atomically the structure is more complex. When grown in a typical oxygen pressure, at or below 10 mTorr, in situ scanning tunneling microscopy (STM) revealed the SrRu O3 surface is littered with oxygen vacancies. For growth or post-annealing above ~ 100 mtorr, vacancies were removed, but STM and low energy electron diffraction (LEED) disclosed a surface reconstruction consisting of parallel rows with periodicity doubled in one direction. Density function theory (DFT) suggests these rows are chains of Sr and O raised by excess oxygen. Both LEED and cross-sectional STEM revealed that this reconstruction persists at the buried interface and modifies the structure of subsequent BaTi O3 layers. By four layers, the BaTi O3 surface returns to a bulk-like structure with upward polar distortion. This study emphasizes the importance of atomic scale structural studies of what may otherwise appear as sharp interfaces. Research at ORNL's CNMS was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. DOE.

  3. Impact of Sr on the performance of BaTi0.9Zr0.1O3-BaTiO3 dielectric powders

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Rong, Guijuan; Wang, Tingwei; Yao, Hao

    2014-06-01

    BaTi0.9Zr0.1O3-Ba1-xSrxTiO3 fine-powders are synthesized by two-step liquid phase method. Phase analysis and microstructure evaluation conducted by X-ray diffraction and scanning electron microscopy confirm the perovskite structure of the ceramic grain. Different Sr content is considered to optimize the density and dielectric performance. The dielectric constant increases and dielectric loss decreases with the rising of Sr content until x = 0.05. At the doping content of 5%, the dielectric constant maximum of 42,430 and excellent Y5V dielectric material can be obtained due to composition inhomogeneity and compact properties. Its dielectric properties are as follows: ɛRT = 36,914, tan δ < 0.09, ΔC/C20°C at -30° C and 80°C are -58.98% and 14.94%, respectively, and the breakdown strength Eb ≥ 5.2 kV ṡ mm-1.

  4. Optical properties of A Fe2As2 (A =Ca , Sr, and Ba) single crystals

    NASA Astrophysics Data System (ADS)

    Dai, Y. M.; Akrap, Ana; Bud'ko, S. L.; Canfield, P. C.; Homes, C. C.

    2016-11-01

    The detailed optical properties have been determined for the iron-based materials A Fe2As2 , where A =Ca , Sr, and Ba, for light polarized in the iron-arsenic (a-b) planes over a wide frequency range, above and below the magnetic and structural transitions at TN=138 , 195, and 172 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above TN, the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below TN there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for T ≪TN may be related to the Dirac conelike dispersion of the electronic bands. Below TN new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at Δ1≃45 -80 meV, and Δ2≃110 -210 meV. The reduction in the spectral weight associated with the free carriers is captured by the gap structure; specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.

  5. Optical properties of AFe2As2 ( A=Ca , Sr, and Ba) single crystals

    DOE PAGES

    Dai, Y. M.; Akrap, Ana; Bud'ko, S. L.; ...

    2016-11-23

    The detailed optical properties have been determined for the iron-based materials A Fe2 As2 , where A = Ca , Sr, and Ba, for light polarized in the iron-arsenic (a-b) planes over a wide frequency range, above and below the magnetic and structural transitions at TN = 138 , 195, and 172 K, respectively. The real and imaginary parts of the complex conductivity are fit simultaneously using two Drude terms in combination with a series of oscillators. Above TN, the free-carrier response consists of a weak, narrow Drude term, and a strong, broad Drude term, both of which show only a weak temperature dependence. Below TN there is a slight decrease of the plasma frequency but a dramatic drop in the scattering rate for the narrow Drude term, and for the broad Drude term there is a significant decrease in the plasma frequency, while the decrease in the scattering rate, albeit significant, is not as severe. The small values observed for the scattering rates for the narrow Drude term for Tmore » $$\\ll$$ TN may be related to the Dirac conelike dispersion of the electronic bands. Below TN new features emerge in the optical conductivity that are associated with the reconstruction Fermi surface and the gapping of bands at Δ1 ≃ 45 – 80 meV, and Δ2 ≃ 110 – 210 meV. In conclusion, the reduction in the spectral weight associated with the free carriers is captured by the gap structure; specifically, the spectral weight from the narrow Drude term appears to be transferred into the low-energy gap feature, while the missing weight from the broad term shifts to the high-energy gap.« less

  6. Spin fluctuations in Sr1.6Ba0.4RuO4 : An inelastic neutron scattering study with polarization analysis

    NASA Astrophysics Data System (ADS)

    Li, Z. W.; Guo, H.; Liu, C.-F.; Bourdarot, F.; Schmidt, W.; Skoulatos, M.; Komarek, A. C.

    2017-01-01

    We present inelastic neutron scattering measurements on the ruthenate Sr1.6Ba0.4RuO4 which is on the hitherto almost unknown Ba-substituted side of the doping phase diagram of Sr2 -xAexRuO4 (Ae = Ca, Ba). Unlike the Ca-substituted side of the phase diagram no (quasi)static magnetic peaks can be observed in Sr1.6Ba0.4RuO4 . Instead, incommensurate spin fluctuations can be observed around q0=(±0.3 ,±0.3 ,0 ) . Both the absolute intensity of χ''(Q ,ω ) and its energy and temperature dependence as well as the anisotropy ratio χc''/χa,b '' resemble the ones in Sr2RuO4 . Hence, a random potential implied by the substitution of huge Ba ions as well as the induced increase of interatomic distances has less impact on the magnetic properties than octahedral tilts implied by Ca substitution. Moreover, any ferromagnetic spin fluctuations are either absent in Sr1.6Ba0.4RuO4 or below the detection limit.

  7. Preparation of thermal infrared and microwave absorber using SrTiO3/BaFe12O19/polyaniline nanocomposites

    NASA Astrophysics Data System (ADS)

    Hosseini, Seyed Hossein; Zamani, Parisa

    2016-01-01

    In this research, first, SrTiO3 was synthesized as thermal infrared (TIR) absorbent and core and then BaFe12O19 as microwave absorbent was prepared on SrTiO3 via co-precipitation method as first shell. Second, polyaniline (PANI) was coated on SrTiO3/BaFe12O19 NPs (NPs) via in situ polymerization by multi core-shell structures (SrTiO3/BaFe12O19/PANI). Nanometer size and structures of samples were measured by TEM, XRD and FTIR. Morphology of nanocomposite was showed by SEM images. The magnetic and electric properties were also performed by VSM and four probe methods. The TIR absorption and microwave reflection loss of nanocomposites were investigated at 10-40 μm and 8-12 GHz, TIR and microwave frequencies, respectively. The results showed that the SrTiO3/BaFe12O19/PANI nanocomposites have good compatible electric and magnetic properties and hence the microwave absorbency show wide bandwidth properties. The infrared thermal image testing showed that the ability of infrared thermal imaging was increased by increasing SrTiO3/BaFe12O19 as core and independent to increasing PANI as final shell.

  8. Long-range magnetic interaction and frustration in double perovskites Sr2NiIrO6 and Sr2ZnIrO6

    PubMed Central

    Ou, Xuedong; Li, Zhengwei; Fan, Fengren; Wang, Hongbo; Wu, Hua

    2014-01-01

    One often counts the nearest neighbouring (NN) exchange interactions for understanding of a magnetic insulator. Here we present first-principles calculations for the newly synthesized double perovskites Sr2NiIrO6 and Sr2ZnIrO6, and we find that the 2NN Ir-Ir antiferromagnetic coupling is even stronger than the 1NN Ni-Ir ferromagnetic one. Thus, the leading antiferromagnetic interactions in the fcc Ir sublattice give rise to a magnetic frustration. Sr2NiIrO6 and Sr2ZnIrO6 hence appear very similarly as a distorted low-temperature antiferromagnet (probably, of type III). This work highlights the long-range magnetic interactions of the delocalized 5d electrons, and it also addresses why the spin-orbit coupling is ineffective here. PMID:25519762

  9. Ecotoxicological risks of the abandoned F-Ba-Pb-Zn mining area of Osor (Spain).

    PubMed

    Bori, Jaume; Vallès, Bettina; Navarro, Andrés; Riva, Maria Carme

    2016-06-03

    Due to its potential toxic properties, metal mobilization is of major concern in areas surrounding Pb-Zn mines. In the present study, metal contents and toxicity of soils, aqueous extracts from soils and mine drainage waters from an abandoned F-Ba-Pb-Zn mining area in Osor (Girona, NE Spain) were evaluated through chemical extractions and ecotoxicity bioassays. Toxicity assessment in the terrestrial compartment included lethal and sublethal endpoints on earthworms Eisenia fetida, arthropods Folsomia candida and several plant species, whereas aquatic tests involved bacteria Vibrio fischeri, microalgae Raphidocelis subcapitata and crustaceans Daphnia magna. Total concentrations of Ba (250-5110 mg kg(-1)), Pb (940 to >5000 mg kg(-1)) and Zn (2370-11,300 mg kg(-1)) in soils exceeded intervention values to protect human health. Risks for the aquatic compartment were identified in the release of drainage waters and in the potential leaching and runoff of metals from contaminated soils, with Cd (1.98-9.15 µg L(-1)), Pb (2.11-326 µg L(-1)) and Zn (280-2900 µg L(-1)) concentrations in filtered water samples surpassing US EPA Water Quality Criteria (2016a, b). Terrestrial ecotoxicity tests were in accordance with metal quantifications and identified the most polluted soil as the most toxic. Avoidance and reproduction tests with earthworms showed the highest sensitivity to metal contamination. Aquatic bioassays performed in aqueous extracts from soils confirmed the results from terrestrial tests and also detected toxic effects caused by the mine drainage waters. Algal growth inhibition was the most sensitive aquatic endpoint. In view of the results, the application of a containment or remediative procedure in the area is encouraged.

  10. First-principles study of structural, electronic and magnetic properties of AeX (Ae=Be, Mg, Sr, Ba; X=Si, Ge and Sn) compounds

    NASA Astrophysics Data System (ADS)

    Jaiganesh, G.; Kalpana, G.

    2013-01-01

    The first-principles study of the electronic structure and ferromagnetism of AeX (Ae=Be, Mg, Sr and Ba; X=Si, Ge and Sn) compounds have been performed in the ground-state CrB-type and hypothetical NaCl- and zinc blende-type structures by spin-polarization and non-spin-polarization calculations. The TBLMTO-ASA program was used for the purpose. In the CrB-type structure, all these compounds exhibit non-magnetic and metallic behavior. The calculations show that in the NaCl- and ZB-type structures BeSi, BeGe, BeSn, MgSi, MgGe and MgSn compounds are non-magnets whereas SrSi, SrGe, SrSn, BaSi, BaGe and BaSn compounds are ferromagnetic and metallic. Apart from this the ZB-type SrSi, SrGe, BaSi and BaGe compounds exhibit half-metallicity at their equilibrium volume with a magnetic moment of 2.0 μB per formula unit. However, ZB-type SrSn and BaSn compounds are found to exhibit half-metallic property under expansion of volume. The magnetism arises mainly from the anion p-like states and partial involvement of cation d-like states. The ground state properties like equilibrium lattice parameters, bulk modulus, cohesive energy, magnetic moment, spin-flip-gap and majority spin band gap are calculated and compared with available results. The band structure and density of states are also presented. These materials will be useful for the study of p-electron magnetism and in spintronic devices.

  11. Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

    SciTech Connect

    Stoyko, Stanislav; Voss, Leonard; He, Hua; Bobev, Svilen

    2015-09-24

    New ternary arsenides AE3TrAs3 (AE = Sr, Ba; Tr = Al, Ga) and their phosphide analogs Sr3GaP3 and Ba3AlP3 have been prepared by reactions of the respective elements at high temperatures. Single-crystal X-ray diffraction studies reveal that Sr3AlAs3 and Ba3AlAs3 adopt the Ba3AlSb3-type structure (Pearson symbol oC56, space group Cmce, Z = 8). This structure is also realized for Sr3GaP3 and Ba3AlP3. Likewise, the compounds Sr3GaAs3 and Ba3GaAs3 crystallize with the Ba3GaSb3-type structure (Pearson symbol oP56, space group Pnma, Z = 8). Both structures are made up of isolated pairs of edge-shared AlPn4 and GaPn4 tetrahedra (Pn = pnictogen, i.e., P or As), separated by the alkaline-earth Sr2+ and Ba2+ cations. In both cases, there are no homoatomic bonds, hence, regardless of the slightly different atomic arrangements, both structures can be rationalized as valence-precise [AE2+]3[Tr3+][Pn3-]3, or rather [AE2+]6[Tr2Pn6]12-, i.e., as Zintl phases.

  12. K, Rb, Sr, Ba, U and Th geochemistry of the Lapland Granulites (Fennoscandia). LILE fractionation controlling factors

    NASA Astrophysics Data System (ADS)

    Barbey, P.; Cuney, M.

    1982-12-01

    The LILE geochemical patterns of the three main lithological units (graywacke-shale metasedimentary sequence, tholeiitic metaigneous rocks and migmatitic rocks) of the Lapland Granulite belt are described. K, Ba, Sr and Th concentrations in metasediments are nearly similar to average continental crust, whereas Rb and U are unevenly impoverished. In particular graphitic metashales and calcsilicate rocks are not significantly depleted in uranium. Tholeiitic metaigneous rocks comprises metavolcanics which present K/Rb ratios similar to metasediments, and metaplutonics with LILE abundances close to those of the low-K-tholeiites. Migmatites show wide range in LILE content. Metatexites and diatexites have higher K, Rb, Th and U concentrations and similar K/Rb ratios with respect to equivalent unmobilized rocks. Potassic pegmatoïds are strongly enriched K, Rb, Ba and Th but moderately in Sr and U. Plagioclasic pegmatoids and ferromagnesian restites are rich in Sr and poor in other LIL elements. A comparative review of the LILE geochemistry between Lapland granulites and equivalent lithological units taken from non metamorphosed to high grade terrains suggest that fractionation processes are not systematic but controlled by original lithology and mineralogy, mineral — fluid equilibria during progressive (or retrogressive) metamorphism and mineral-melt-fluid equilibria during anatexis. Moreover, statistical analysis on K-Rb distribution patterns in these various rock types shows that there is no metamorphic trend characteristic of granulite facies terrains as previously suggested.

  13. Low loss NiZn spinel ferrite-W-type hexaferrite composites from BaM addition for antenna applications

    NASA Astrophysics Data System (ADS)

    Zheng, Zongliang; Zhang, Huaiwu; Xiao, John Q.; Yang, Qinghui; Jia, Lijun

    2014-03-01

    A series of NiZn ferrite composites with various BaFe12O19 hexaferrite (BaM) additions (x) were successfully synthesized by the solid-state reaction method for their potential application as magneto-dielectric antenna substrate materials. XRD and energy-dispersive spectrum analyses reveal that a W-type hexagonal phase is formed when the mixture of NiZn ferrite and BaM are sintered at 1200 °C, and diphase composite ferrite that consists of NiZn spinel ferrite and BaW hexaferrite is finally obtained. The composites display much smaller grain size and a refined microstructure. With the increasing x, the initial permeability decreases from ˜84.5 to ˜15.5, while the cut-off frequency is dramatically improved from 75 to 570 MHz. BaM addition significantly inhibits the frequency dispersion of permittivity spectrum and stable permittivity ɛ‧ around 15 is observed for the doped samples from 1 MHz to 1 GHz, which is proved to be closely related to the refined grains according to Koops' theory. Besides, compared with the undoped NiZn ferrite, both the magnetic loss and dielectric loss are found to be reduced in the doped samples. Almost equal values of μ‧ and ɛ‧ is obtained in the sample with x = 30 wt%. Related magnetic and dielectric mechanisms are also discussed.

  14. Structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Cinthia, A. Jemmy; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Iyakutti, K.

    2015-04-01

    The structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba) in the cubic (B1, B2 and B3) phases and in the wurtzite (B4) phase are investigated using density functional theory calculations as implemented in VASP code. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are computed. The calculated lattice parameters are in good agreement with the experimental and the other available theoretical results. Electronic structure reveals that all the five alkaline earth metal oxides exhibit semiconducting behavior at zero pressure. The estimated band gaps for the stable wurtzite phase of BeO is 7.2 eV and for the stable cubic NaCl phases of MgO, CaO, SrO and BaO are 4.436 eV, 4.166 eV, 4.013 eV, and 2.274 eV respectively. A pressure induced structural phase transition occurs from wurtzite (B4) to NaCl (B1) phase in BeO at 112.1 GPa and from NaCl (B1) to CsCl (B2) phase in MgO at 514.9 GPa, in CaO at 61.3 GPa, in SrO at 42 GPa and in BaO at 14.5 GPa. The elastic constants are computed at zero and elevated pressures for the B4 and B1 phases for BeO and for the B1 and B2 phases in the case of the other oxides in order to investigate their mechanical stability, anisotropy and hardness. The sound velocities and the Debye temperatures are calculated for all the oxides using the computed elastic constants.

  15. (Sr,Ba)(Si,Ge){sub 2} for thin-film solar-cell applications: First-principles study

    SciTech Connect

    Kumar, Mukesh E-mail: mkgarg79@gmail.com; Umezawa, Naoto; Imai, Motoharu

    2014-05-28

    In order to meet the increasing demand for electric power generation from solar energy conversion, the development of efficient light absorber materials has been awaited. To this end, the electronic and optical properties of advanced alkaline-earth-metals disilicides and digermanides (SrSi{sub 2}, BaSi{sub 2}, SrGe{sub 2}, and BaGe{sub 2}) are studied by means of the density functional theory using HSE06 exchange-correlation energy functional. Our calculations show that all these orthorhombic structured compounds have fundamental indirect band gaps in the range E{sub g} ≈ 0.89–1.25 eV, which is suitable for solar cell applications. The estimated lattice parameters and band gaps are in good agreement with experiments. Our calculations show that the electronic band structures of all four compounds are very similar except in the vicinity of the Γ-point. The valence band of these compounds is made up by Si(Ge)-p states, whereas the conduction band is composed of Sr(Ba)-d states. Their band alignments are carefully determined by estimating the work function of each compound using slab model. The optical properties are discussed in terms of the complex dielectric function ε(ω) = ε{sub 1}(ω) + iε{sub 2}(ω). The static and high-frequency dielectric constants are calculated, taking into account the ionic contribution. The absorption coefficient α(ω) demonstrates that a low energy dispersion of the conduction band, which results in a flat conduction band minimum, leads to large optical activity in these compounds. Therefore, alkaline-earth-metals disilicides and digermanides possess great potential as light absorbers for applications in thin-film solar cell technologies.

  16. Influence of interfacial coherency on ferroelectric switching of superlattice BaTiO3/SrTiO3

    SciTech Connect

    Wu, Pingping; Ma, Xingqiao; Li, Yulan; Eom, C. B.; Schlom, Darrell G.; Gopalan, Venkatraman; Chen, Long-Qing

    2015-04-11

    Switching behavior of (BaTiO3)8/ (SrTiO3)4 heterostructure superlattice grown on SrTiO3 substrate was studied by employing the phase field method. To investigate the constraint effect of the substrate on switching, three types of superlattice/substrate interface mechanical relaxation conditions were considered, i.e. the fully ommensurate, partially relaxed and fully relaxed. Our simulation results demonstrated that the hysteresis loops under the three types of constraints were very different. The interfacial coherency affects dramatically the coercivity and remanence of the superlattice films. The mechanism of the hysteresis loop varying with interfacial coherency was analyzed by the ferroelectric domain configuration and its evolution during the switching process. The hysteresis loop of fully relaxed superlattice shows application potential on ferroelectric energy storage materials.

  17. Growth of Sr(0.61)Ba(0.39)Nb2O6 fibers - New results regarding orientation

    NASA Technical Reports Server (NTRS)

    Wilde, Jeffrey P.; Jundt, Dieter H.; Galambos, Ludwig; Hesselink, Lambertus

    1991-01-01

    The paper describes stable growth of Sr(0.61)Ba(0.39)Nb2O6 (SBN) single-crystal optical fibers (grown by the laser-heated pedestal growth method) along the 100-line and 110-line crystallographic axes. The orientation of SBN fibers was investigated using transmission holograms recorded by focusing two separate, but mutually coherent, optical wavefronts into one end of the fiber. Results showed that the crystal quality of 100-line and 110-line SBN fibers grown at a given pull velocity strongly depended on the fiber diameter; generally, the quality improves with decreasing diameter.

  18. Correlated nucleosynthetic isotopic variability in Cr, Sr, Ba, Sm, Nd and Hf in Murchison and QUE 97008

    NASA Astrophysics Data System (ADS)

    Qin, Liping; Carlson, Richard W.; Alexander, Conel M. O.'D.

    2011-12-01

    Acid leaching of the primitive C-chondrite Murchison and O-chondrite QUE 97008 reveal nucleosynthetic anomalies in Cr, Sr, Ba, Nd, Sm and Hf. The anomalies in all but Cr and Sm are best explained by variable additions of pure s-process nuclides to a background nebular composition slightly enriched in r-process isotopes compared to average Solar System material. Leaching leaves a residue in Murchison that is strongly enriched in s-process nuclides with depletions of over 0.1% in 135Ba and seven parts in 10,000 in 84Sr. If there are p-process anomalies in these two elements, they are lost in the variability caused by different r-, s-process contributions to the normalizing isotopes. The concentration and isotope systematics are consistent with the Ba and Sr isotopic composition in the Murchison residue being strongly influenced by s-process-rich presolar SiC. In general, the nucleosynthetic isotope anomalies are 2- to 5-fold smaller in QUE 97008 than in Murchison. The different magnitudes of isotope anomalies are similar to the difference in matrix abundance between CM and O chondrites consistent with the suggestion that the carriers of nucleosynthetically anomalous material preferentially reside in the matrix and that some of this material has been distributed throughout the O-chondrite minerals as a result of thermal metamorphism. Neodymium, Sm and Hf display variable s-, r-process nuclide abundances as in Ba and Sr, but the anomalies are much smaller (e.g. ɛ 148Nd, ɛ 148Sm = -5.7, 2.1, respectively, in Murchison and -0.43, 0.16, respectively in QUE 97008 residues). After correcting Nd and Sm for s-, r-process variability, Sm in whole rock chondrites shows variable relative abundances of the p-process isotope 144Sm that correlate weakly with 142Nd suggesting that the direct p-process contribution to 142Nd is small (˜7-9%). Nucleosynthetic variability in Nd explains the range in 142Nd/ 144Nd seen between C and O, E-chondrites, but not the difference between

  19. Magnetism in the magnetoelectric hexaferrite system (Ba1-xSrx)2Zn2Fe12O22

    NASA Astrophysics Data System (ADS)

    Novák, P.; Knížek, K.; Rusz, J.

    2007-07-01

    The hexaferrite system (Ba1-xSrx)2Zn2Fe12O22 possesses a rich magnetic phase diagram and for strontium content x=0.75 exhibits a magnetoelectricity, the existence of which is intimately connected to the noncollinear arrangement of the iron spins. The system comprises seven cation sublattices, two of which have tetrahedral coordination. The tetrahedral sublattices are partly occupied by Fe and partly by Zn. Using ab initio-calculated exchange interactions we show that the magnetism in the (Ba1-xSrx)2Zn2Fe12O22 system is sensitive to the Fe and Zn distributions. The region of existence of the noncollinear spin structure and hence of ferroelectricity is determined and found to be rather narrow. The critical temperature of magnetic ordering is calculated using molecular field and random phase approximations. The results are in good agreement with the experiment.

  20. A study of the pseudogap state in Bi2Sr2CaCu2Ox and Bi2Sr2ZnCu2Oy HTSC materials

    NASA Astrophysics Data System (ADS)

    Aliev, V. M.; Mamedova, A. N.; Raqimov, S. S.; Selim-zade, R. I.; Tairov, B. A.

    2016-10-01

    We examine the effect of replacing calcium by zinc has on the transport properties of the BiSrCaCuO-2221 system. It is shown that the critical temperatures Tc of the Bi2Sr2CaCu2Ox(B1) and Bi2Sr2ZnCu2Oy(B2) samples are close (81 K and 80.72 K). However, the resistivity ρ of the Bi2Sr2ZnCu2Oy sample increases considerably, and the ratio ρB2/ρB1 ≈ 10 at 100 K. We use the local pair model to analyze the mechanism behind the formation of excess conductivity in Bi2Sr2CaCu2Ox and Bi2Sr2ZnCu2Oy(B2), with consideration of the Aslamazov-Larkin theory near Tc. We determined the temperature T0 of the transition from the 2D fluctuation area to the 3D region (i.e., the 2D-3D crossover temperature). We calculated the coherence length of the fluctuation Cooper pairs along the c axis, ξc(0). It is shown that substituting Zn for Ca reduces ξc(0) by almost 1.5 times (4.8 Å and 3.3 Å, respectively), and also leads to a narrowing of both the pseudogap region and the superconducting fluctuation area near Tc. We determined the temperature dependence of the pseudogap Δ * T and Δ * (Tc). The increase of ρ, its specific temperature dependence and the significant decrease of T * in sample B2, all point to the destruction of local pairs at all high temperatures, i.e., to the suppression of the pseudogap by Zn doping.

  1. Tilting structures in inverse perovskites, M3TtO (M = Ca, Sr, Ba, Eu; Tt = Si, Ge, Sn, Pb).

    PubMed

    Nuss, Jürgen; Mühle, Claus; Hayama, Kyouhei; Abdolazimi, Vahideh; Takagi, Hidenori

    2015-06-01

    Single-crystal X-ray diffraction experiments were performed for a series of inverse perovskites, M3TtO (M = Ca, Sr, Ba, Eu; Tt = tetrel element: Si, Ge, Sn, Pb) in the temperature range 500-50 K. For Tt = Sn, Pb, they crystallize as an 'ideal' perovskite-type structure (Pm3m, cP5); however, all of them show distinct anisotropies of the displacement ellipsoids of the M atoms at room temperature. This behavior vanishes on cooling for M = Ca, Sr, Eu, and the structures can be regarded as `ideal' cubic perovskites at 50 K. The anisotropies of the displacement ellipsoids are much more enhanced in the case of the Ba compounds. Finally, their structures undergo a phase transition at ∼ 150 K. They change from cubic to orthorhombic (Ibmm, oI20) upon cooling, with slightly tilted OBa6 octahedra, and bonding angles O-Ba-O ≃ 174° (100 K). For the larger Ba(2+) cations, the structural changes are in agreement with smaller tolerance factors (t) as defined by Goldschmidt. Similar structural behavior is observed for Ca3TtO. Smaller Tt(4-) anions (Si, Ge) introduce reduced tolerance factors. Both compounds Ca3SiO and Ca3GeO with cubic structures at 500 K, change into orthorhombic (Ibmm) at room temperature. Whereby, Ca3SiO is the only representative within the M3TtO family where three polymorphs can be found within the temperature range 500-50 K: Pm3m-Ibmm-Pbnm. They show tiny differences in the tilting of the OCa6 octahedra, expressed by O-Ca-O bond angles of 180° (500 K), ∼ 174° (295 K) and 170° (100 K). For larger M (Sr, Eu, Ba), together with smaller Tt (Si, Ge) atoms, pronounced tilting of the OM6 octahedra, and bonding angles of O-M-O ≃ 160° (295 K) are observed. They crystallize in the anti-GdFeO3 type of structure (Pbnm, oP20), and no phase transitions occur between 500 and 50 K. The observed phase transitions are all accompanied by multiple twinning, in terms of pseudo-merohedry or reticular pseudo-merohedry.

  2. High-mobility two-dimensional electron gas in SrGeO3- and BaSnO3-based perovskite oxide heterostructures: an ab initio study.

    PubMed

    Wang, Yaqin; Tang, Wu; Cheng, Jianli; Nazir, Safdar; Yang, Kesong

    2016-11-23

    We explored the possibility of producing a high-mobility two-dimensional electron gas (2DEG) in the LaAlO3/SrGeO3 and LaGaO3/BaSnO3 heterostructures using first-principles electronic structure calculations. Our results show that the 2DEG occurs at n-type LaAlO3/SrGeO3 and LaGaO3/BaSnO3 interfaces. Compared to the prototype LaAlO3/SrTiO3, LaAlO3/SrGeO3 and LaGaO3/BaSnO3 systems yield comparable total interfacial charge carrier density but much lower electron effective mass (nearly half the value of LaAlO3/SrTiO3), thus resulting in about twice larger electron mobility and enhanced interfacial conductivity. This work demonstrates that SrGeO3 and BaSnO3 can be potential substrate materials to achieve a high-mobility 2DEG in the perovskite-oxide heterostructures.

  3. Elevated silver, barium and strontium in antlers, vegetation and soils sourced from CWD cluster areas: do Ag/Ba/Sr piezoelectric crystals represent the transmissible pathogenic agent in TSEs?

    PubMed

    Purdey, Mark

    2004-01-01

    High levels of Silver (Ag), Barium (Ba) and Strontium (Sr) and low levels of copper (Cu) have been measured in the antlers, soils and pastures of the deer that are thriving in the chronic wasting disease (CWD) cluster zones in North America in relation to the areas where CWD and other transmissible spongiform encephalopathies (TSEs) have not been reported. The elevations of Ag, Ba and Sr were thought to originate from both natural geochemical and artificial pollutant sources--stemming from the common practise of aerial spraying with 'cloud seeding' Ag or Ba crystal nuclei for rain making in these drought prone areas of North America, the atmospheric spraying with Ba based aerosols for enhancing/refracting radar and radio signal communications as well as the spreading of waste Ba drilling mud from the local oil/gas well industry across pastureland. These metals have subsequently bioconcentrated up the foodchain and into the mammals who are dependent upon the local Cu deficient ecosystems. A dual eco-prerequisite theory is proposed on the aetiology of TSEs which is based upon an Ag, Ba, Sr or Mn replacement binding at the vacant Cu/Zn domains on the cellular prion protein (PrP)/sulphated proteoglycan molecules which impairs the capacities of the brain to protect itself against incoming shockbursts of sound and light energy. Ag/Ba/Sr chelation of free sulphur within the biosystem inhibits the viable synthesis of the sulphur dependent proteoglycans, which results in the overall collapse of the Cu mediated conduction of electric signals along the PrP-proteoglycan signalling pathways; ultimately disrupting GABA type inhibitory currents at the synapses/end plates of the auditory/circadian regulated circuitry, as well as disrupting proteoglycan co-regulation of the growth factor signalling systems which maintain the structural integrity of the nervous system. The resulting Ag, Ba, Sr or Mn based compounds seed piezoelectric crystals which incorporate PrP and ferritin into

  4. Surface composition of BaTiO{sub 3}/SrTiO{sub 3}(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

    SciTech Connect

    Barbier, A.; Stanescu, D.; Jegou, P.; Magnan, H.; Mocuta, C.; Jedrecy, N.

    2012-12-01

    We have investigated the growth of BaTiO{sub 3} thin films deposited on pure and 1% Nb-doped SrTiO{sub 3}(001) single crystals using atomic oxygen assisted molecular beam epitaxy and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO{sub 3} layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {approx}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO{sub 3} layers, especially in view of their integration in devices.

  5. M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion

    SciTech Connect

    Popa, Karin; Wallez, Gilles; Bregiroux, Damien; Loiseau, Pascal

    2011-10-15

    Three earth alkali-germanium monophosphates M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO{sub 4}){sub 2} and high-temperature {beta}-SrGe(PO{sub 4}){sub 2} (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO{sub 4}){sub 2} and low-temperature {alpha}-SrGe(PO{sub 4}){sub 2} (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic. - Graphical abstract: The superstructure of SrGe(PO{sub 4}){sub 2} at room temperature ({alpha}) results from the off-centering of cation Sr{sup II}. Highlights: > Crystal structures of yavapaiite-type M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) have been solved. > Distortion and superstructure result from Ca and Sr off-centering. > A global scheme for the polymorphism of yavapaiites is proposed.

  6. Role of film stoichiometry and interface quality in the performance of (Ba,Sr)TiO3 tunable capacitors with high figures of merit

    NASA Astrophysics Data System (ADS)

    Freeze, Christopher R.; Stemmer, Susanne

    2016-11-01

    Parallel plate capacitors with quality factors exceeding 1000 were fabricated using Ba0.3Sr0.7TiO3 (BST) thin films grown by hybrid molecular beam epitaxy on epitaxial Pt bottom electrodes. The influence of film stoichiometry was investigated by varying the (Ba + Sr)/Ti ratio around the stoichiometric composition. The quality factor is highest for stoichiometric films, but (Ba + Sr)-rich films can be biased to higher fields. Furthermore, two different processes were used to deposit the top electrodes of the parallel plate capacitors. While the quality of the top contact/BST interface did not strongly affect the device quality factor, an enhancement in the dielectric tunability was seen for capacitors with top electrodes deposited at high temperatures, which effectively removes interfacial contamination layers.

  7. The influences of mole composition of strontium (x) on properties of barium strontium titanate (Ba{sub 1−x}Sr{sub x}TiO{sub 3}) prepared by solid state reaction method

    SciTech Connect

    Sandi, Dianisa Khoirum; Supriyanto, Agus; Iriani, Yofentina; Jamaluddin, Anif

    2016-02-08

    Barium Strontium Titanate (Ba{sub 1-x}Sr{sub x}TiO{sub 3}) or BST was prepared by solid state reaction method. Raw materials are BaCO{sub 3}, SrCO{sub 3}, and TiO{sub 2}. Those materials are mixed for 8 h, pressed, and sintered at temperature 1200°C for 2 h. Mole composition of Sr (x) was varied to study its influences on structural, morphological, and electrical properties of BST. Variation of (x) are x = 0; x = 0.1; and x = 0.5. XRD patterns showed a single phase of BST, which mean that mixture of raw materials was homogenous. Crystal structure was influenced by x. BaTiO{sub 3} and Ba{sub 0.9}Ti{sub 0.1}TiO{sub 3} have tetragonal crystal structure, while Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} is cubic. The diffraction angle shifted to right side (angle larger) as the increases of x. Crystalline size of BaTiO{sub 3}, Ba{sub 0.9}Sr{sub 0.1}TiO{sub 3}, and Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} are 38.13 nm; 38.62 nm; and 37.13 nm, respectively. SEM images showed that there are still of pores which were influenced by x. Ba{sub 0.9}Sr{sub 0.1}TiO{sub 3} has densest surface (pores are few and small in size). Sawyer Tower circuit showed that BaTiO{sub 3} and Ba{sub 0.9}Sr{sub 0.1} TiO{sub 3} is ferroelectric, while Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} is paraelectric. The dielectric constants of BaTiO{sub 3}, Ba{sub 0.9}Sr{sub 0.1}TiO{sub 3} and Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} at frequency of 1 KHz are 156; 196; and 83, respectively. Ba{sub 0.9}Sr{sub 0.1}TiO{sub 3} has relatively highest dielectric constant. It is considered that Ba{sub 0.9}Sr{sub 0.1}TiO{sub 3} has densest surface.

  8. Crystal and magnetic structures and their temperature dependence of Co2Z-type hexaferrite (Ba,Sr)3Co2Fe24O41 by high-temperature neutron diffraction

    NASA Astrophysics Data System (ADS)

    Takada, Yukio; Nakagawa, Takashi; Tokunaga, Masatoshi; Fukuta, Yasunari; Tanaka, Takayoshi; Yamamoto, Takao A.; Tachibana, Takeshi; Kawano, Shinji; Ishii, Yoshinobu; Igawa, Naoki

    2006-08-01

    We have prepared nonoriented and magnetically oriented specimens of Co2Z-type Ba ferrite Ba3Co2Fe24O41 (Ba3Z) and those with Sr2+ substitution for Ba2+, i.e., Ba1.5Sr1.5Co2Fe24O41 (Ba1.5Sr1.5Z) and Sr3Co2Fe24O41 (Sr3Z) with the conventional solid-state reaction method. Permeability measurements of nonoriented specimens have shown that this substitution improves the frequency characteristic of permeability, though the permeability in Sr3Z significantly decreases. X-ray diffraction (XRD) and magnetization measurements of magnetically oriented specimens have shown that the magnetic moments of iron and cobalt ions in Ba3Z and Ba1.5Sr1.5Z lie in the c plane, but that those in Sr3Z deviate from the c plane. We have studied the substitution effect of Sr2+ for Ba2+ on the crystal structures and the effective sizes and directions of magnetic moments and their temperature dependences with high-temperature neutron diffraction technique. This substitution induces the change in the distribution of cobalt ions and moment directions of magnetic ions. Magnetic moments in Ba3Z and Ba1.5Sr1.5Z turn to the c axis when temperature rises from 523to573K. However, the moments in Sr3Z turn to the c axis at the lower temperature of 50K. These results were consistent with the present measurements on permeability, XRD, and magnetization. The change in moment direction caused by temperature rise must be attributed to the disappearance of effective moments of cobalt ions in these temperature regions.

  9. Current Status of Thin Film (Ba,Sr)TiO3 Tunable Microwave Components for RF Communications

    NASA Technical Reports Server (NTRS)

    VanKeuls, F. W.; Romanofsky, R. R.; Mueller, C. H.; Warner, J. D.; Canedy, C. L.; Ramesh, R.; Miranda, F. A.

    2000-01-01

    The performance of proof-of-concept ferroelectric microwave devices has been moving steadily closer to the level needed for satellite and other rf communications applications. This paper will review recent progress at NASA Glenn in developing thin film Ba(x)Sr(1-x)TiO3 tunable micro-wave components for these applications. Phase shifters for phased array antennas, tunable filters and tunable oscillators employing microstrip and coupled microstrip configurations will be presented. Tunabilities, maximum dielectric constants, and phase shifter parameters will be discussed (e.g., coupled microstrip phase shifters with phase shift over 200 deg at 18 GHz and a figure of merit of 74.3 deg/dB). Issues of post-annealing, Mn-doping and Ba(x)Sr(1-x) TiO3 growth on sapphire and alumina substrates will be covered. The challenges of incorporating these devices into larger systems, such as yield, variability in phase shift and insertion loss, and protective coatings will also be addressed.

  10. Current Status of Thin Film (Ba,Sr) TiO3 Tunable Microwave Components for RF Communications

    NASA Technical Reports Server (NTRS)

    VanKeuls, F. W.; Romananofsky, R. R.; Mueller, C. H.; Warner, J. D.; Canedy, C. L.; Ramesh, R.; Miranda, F. A.

    2000-01-01

    The performance of proof-of-concept ferroelectric microwave devices has been moving steadily closer to the level needed for satellite and other rf communications applications. This paper will review recent progress at NASA Glenn in developing thin film Ba(x)Sr(1-x)TiO3 tunable microwave components for these applications. Phase shifters for phased array antennas, tunable filters and tunable oscillators employing microstrip and coupled microstrip configurations will be presented. Tunabilities, maximum dielectric constants, and phase shifter parameters will be discussed (e.g., coupled microstrip phase shifters with phase shift over 200 deg. at 18 GHz and a figure of merit of 74.3 deg./dB). Issues of postannealing, Mn-doping and Ba(x)Sr(1-x)TiO3 growth on sapphire and alumina substrates will be covered. The challenges of incorporating these devices into larger systems, such as yield, variability in phase shift and insertion loss, and protective coatings will also be addressed.

  11. Thickness Dependence of Characteristics for (Ba, Sr)TiO3 Thin Films Prepared by Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Takeshima, Yutaka; Tanaka, Katsuhiko; Sakabe, Yukio

    2000-09-01

    (Ba0.6, Sr0.4)TiO3 thin films were prepared by metalorganic chemical vapor deposition (MOCVD) using bisdipvaloylmethanatobarium tetraethylenepentamine adduct (Ba(C11H19O2)2(C8H23N5)2), bisdipvaloylmethanatostrontium tetraethylenepentamine adduct (Sr(C11H19O2)2(C8H23N5)2), and titanium isopropoxide (Ti(i-OC3H7)4) as starting materials. The thickness dependence of permittivity and other characteristics were investigated for epitaxially grown barium strontium titanate (BST) thin films on Pt(100)/MgO(100) substrates and nonepitaxially grown BST films on Pt(111)/MgO(100) substrates. The epitaxially grown films had a high relative permittivity (1200) at thicknesses greater than 120 nm. Permittivity decreased with the film thickness when the thickness was less than 120 nm, but remained constant at thicknesses between 50 and 80 nm. The nonepitaxially grown films had a relative permittivity of 600 at a thickness greater than 100 nm and decreased with decreasing film thickness when the thickness was below 100 nm. In this paper, the origin of thickness dependence is discussed in terms of the grain-size effect and the strain effect.

  12. Acoustoelastic effect of textured (Ba,Sr)TiO{sub 3} thin films under an initial mechanical stress

    SciTech Connect

    Kamel, Marwa; Mseddi, Souhir; Njeh, Anouar; Ben Ghozlen, Mohamed Hédi; Donner, Wolfgang

    2015-12-14

    Acoustoelastic (AE) analysis of initial stresses plays an important role as a nondestructive tool in current engineering. Two textured BST (Ba{sub 0.65}Sr{sub 0.35}TiO{sub 3}) thin films, with different substrate to target distance, were grown on Pt(111)/TiO{sub 2}/SiO{sub 2}/Si(001) substrate by rf-magnetron sputtering deposition techniques. A conventional “sin{sup 2} ψ” method to determine residual stress and strain in BST films by X-ray diffraction is applied. A laser acoustic waves (LA-waves) technique is used to generate surface acoustic waves (SAW) propagating in both samples. Young's modulus E and Poisson ratio ν of BST films in different propagation directions are derived from the measured dispersion curves. Estimation of effective second-order elastic constants of BST thin films in stressed states is served in SAW study. This paper presents an original investigation of AE effect in prestressed Ba{sub 0.65}Sr{sub 0.35}TiO{sub 3} films, where the effective elastic constants and the effect of texture on second and third order elastic tensor are considered and used. The propagation behavior of Rayleigh and Love waves in BST thin films under residual stress is explored and discussed. The guiding velocities affected by residual stresses, reveal some shifts which do not exceed four percent mainly in the low frequency range.

  13. Acoustoelastic effect of textured (Ba,Sr)TiO3 thin films under an initial mechanical stress

    NASA Astrophysics Data System (ADS)

    Kamel, Marwa; Mseddi, Souhir; Njeh, Anouar; Donner, Wolfgang; Ben Ghozlen, Mohamed Hédi

    2015-12-01

    Acoustoelastic (AE) analysis of initial stresses plays an important role as a nondestructive tool in current engineering. Two textured BST (Ba0.65Sr0.35TiO3) thin films, with different substrate to target distance, were grown on Pt(111)/TiO2/SiO2/Si(001) substrate by rf-magnetron sputtering deposition techniques. A conventional "sin2 ψ" method to determine residual stress and strain in BST films by X-ray diffraction is applied. A laser acoustic waves (LA-waves) technique is used to generate surface acoustic waves (SAW) propagating in both samples. Young's modulus E and Poisson ratio ν of BST films in different propagation directions are derived from the measured dispersion curves. Estimation of effective second-order elastic constants of BST thin films in stressed states is served in SAW study. This paper presents an original investigation of AE effect in prestressed Ba0.65Sr0.35TiO3 films, where the effective elastic constants and the effect of texture on second and third order elastic tensor are considered and used. The propagation behavior of Rayleigh and Love waves in BST thin films under residual stress is explored and discussed. The guiding velocities affected by residual stresses, reveal some shifts which do not exceed four percent mainly in the low frequency range.

  14. Structure-Property Relationships in W Doped (Ba,Sr)TiO(3) Thin Films Deposited by Pulsed Laser Deposition on (001) MgO

    DTIC Science & Technology

    2003-04-03

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP013347 TITLE: Structure-Property Relationships in W Doped [Ba,Sr]TiO[3... Doped (Ba,Sr)TiO 3 Thin Films Deposited by Pulsed Laser Deposition on (001) MgO N. Navi1’*, J.S. Horwitz, H.-D. Wu2 and S.B. Qadri, Naval Research...oscillators, delay lines and phase shifters [1]. These devices will reduce the size and the operating power of the current semiconducting and ferrite based

  15. Geometry and Vibrational Spectra of the Alkaline Earth Dihalides. III. MgCl2, CaCl2, SrCl2 and BaCl2.

    DTIC Science & Technology

    The infrared spectra of MgCl2 , CaCl2, SrCl2 and BaCl2 trapped in solid krypton matrices at 20K are reported. From precise measurements of changes in...the vibrational modes on isotopic substitution, a linear configuration for MgCl2 and CaCl2 is confirmed and an apex angle of 120 degrees is...established for SrCl. For BaCl2 the bond angle has been estimated at 100 degrees. Using a valence force field a set of force constants has been obtained from

  16. Heterostructures (CaSrBa)F2 on InP for Optoelectronics

    DTIC Science & Technology

    1995-01-01

    and SrF2 layers onto InP(100) have been grown at 350’C under ultra-high vacuum conditions using epitaxial and bulk substrates. MBE and Laser Vacuum... SrF2 /InP diodes prepared by sublimation of the fluoride under vacuum, an important modulation without hysteresis of the surface potential of the...grew the thin films of SrF2 by sublimation under a classical vacuum (10-7 Torr). They showed by Rutherford backscattering and by XPS measurements that

  17. Thermally assisted interlayer magnetic coupling through Ba0.05Sr0.95TiO3 barriers

    NASA Astrophysics Data System (ADS)

    Carreira, Santiago J.; Avilés Félix, Luis; Sirena, Martín; Alejandro, Gabriela; Steren, Laura B.

    2016-08-01

    We report on the interlayer exchange coupling across insulating barriers observed on Ni80Fe20/Ba0.05Sr0.95TiO3/La0.66Sr0.33MnO3 (Py/BST0.05/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO3 (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST0.05. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component.

  18. Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

    PubMed Central

    Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; Van Overmeere, Quentin; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Maran, Ronald; Anazawa, Toshihisa; Valanoor, Nagarajan; Imanaka, Yoshihiko

    2017-01-01

    The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=Ca, Sr, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for SrSnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices. PMID:28195149

  19. Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

    NASA Astrophysics Data System (ADS)

    Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; van Overmeere, Quentin; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Maran, Ronald; Anazawa, Toshihisa; Valanoor, Nagarajan; Imanaka, Yoshihiko

    2017-02-01

    The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=Ca, Sr, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for SrSnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices.

  20. Blue-shift of Eu²⁺ emission in (Ba,Sr)₃Lu(PO₄)₃:Eu²⁺ eulytite solid-solution phosphors resulting from release of neighbouring-cation-induced stress.

    PubMed

    Wang, Ziyuan; Xia, Zhiguo; Molokeev, Maxim S; Atuchin, Victor V; Liu, QuanLin

    2014-11-28

    A series of iso-structural eulytite-type (Ba,Sr)3Lu(PO4)3:Eu(2+) solid-solution phosphors with different Sr/Ba ratios were synthesized by a solid-state reaction. Crystal structures of (Ba,Sr)3Lu(PO4)3:Eu(2+) were resolved by the Rietveld method, which shows an eulytite-type cubic Bi4(SiO4)3 structure with cations disordered in a single C3 site while the oxygen atoms were distributed over two partially occupied sites. The emission peaks of Ba((3-x))Sr(x)Lu(PO4)3:Eu(2+) (0 ≤ x ≤ 3) phosphors were blue-shifted, from 506 to 479 nm, with increasing Sr/Ba ratio upon the same excitation wavelength of 365 nm, and such interesting luminescence behaviours can also be found in other eulytite-type (Ba,Sr)3Ln(PO4)3:Eu(2+) (Ln = Y, Gd) solid-solution phosphors. The blue-shift of the Eu(2+) emission with increasing Sr/Ba ratio was ascribed to the variation of the crystal field strength that the 5d orbital of Eu(2+) ion experiences, and a new model based on the Eu-O bond length and released neighboring-cation stress in disordered Ba(2+)/Sr(2+)/Ln(3+) sites is proposed.

  1. Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices—CCSD(T) calculations and atomic site occupancies

    SciTech Connect

    Davis, Barry M.; McCaffrey, John G.

    2016-01-28

    Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y{sup 1}P←a{sup 1}S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (>5 Å) and shallow bound regions (<130 cm{sup −1}). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing very different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr{sub 2} while this transition is quenched in Ba{sub 2}. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba{sub 2} indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.

  2. Absorption spectroscopy of heavy alkaline earth metals Ba and Sr in rare gas matrices--CCSD(T) calculations and atomic site occupancies.

    PubMed

    Davis, Barry M; McCaffrey, John G

    2016-01-28

    Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y(1)P ← a(1)S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (>5 Å) and shallow bound regions (<130 cm(-1)). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing very different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr2 while this transition is quenched in Ba2. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba2 indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.

  3. Luminescent properties of SrZn2(PO4)2:Tb3+ and its luminescence improvement by incorporating A+ (A=Li, Na, and K)

    NASA Astrophysics Data System (ADS)

    Li, Panlai; Wang, Zhijun; Yang, Zhiping; Guo, Qinglin

    2014-12-01

    A novel green phosphor SrZn2(PO4)2:Tb3+ is synthesized by a high temperature solid-state method, and its luminescent property is investigated. X-ray diffraction patterns of SrZn2(PO4)2:Tb3+ indicate a similarity crystalline phase to SrZn2(PO4)2. SrZn2(PO4)2:Tb3+ shows green emission under 369 nm excitation, and the prominent luminescence in green (544 nm) due to 5D4-7F5 transition of Tb3+. For the 544 nm emission, excitation spectrum has several excitation band from 200 nm to 400 nm. Emission intensity of SrZn2(PO4)2:Tb3+ is influenced by Tb3+ concentration, and concentration quenching effect of Tb3+ in SrZn2(PO4)2 is also observed. With incorporating A+ (A=Li, Na, and K) as compensator charge, the emission intensity of SrZn2(PO4)2:Tb3+ can be obviously enhanced. CIE color coordinates of SrZn2(PO4)2:Tb3+ locate in the green region. The results indicate this phosphor may be a potential application in white LEDs.

  4. Synthesis, crystal structures, and magnetic properties of double perovskites SrLaNiOsO6 and BaLaNiOsO6

    NASA Astrophysics Data System (ADS)

    Feng, Hai L.; Schnelle, Walter; Tjeng, Liu Hao; Jansen, Martin

    2016-10-01

    New double perovskite oxides SrLaNiOsO6 and BaLaNiOsO6 were synthesized by solid state reactions from the respective binary metal oxides, and their crystal structures and magnetic properties were characterized. At room temperature SrLaNiOsO6 and BaLaNiOsO6 crystallize in ordered double perovskite structures with space groups of P21/n (monoclinic) and I4/m (tetragonal), respectively. They are electrically semiconducting with an activation energy of ≈0.35 eV. Specific heat and magnetic measurements indicate that SrLaNiOsO6 shows predominantly antiferromagnetic correlations and displays antiferromagnetic transition around 60 K. However, for the isoelectronic BaLaNiOsO6 ferromagnetic correlations are predominant and there is no clear feature of a magnetic transition detectable. The remarkable change in magnetic properties of ALaNiOsO6 (A = Sr and Ba) can be related to the degree of structure distortions, i.e. the bending of the O-B-O (B = Ni,Os) links.

  5. Blockage of domain growth by nanoscale heterogeneities in a relaxor ferroelectric Sr0.61Ba0.39Nb2O6

    NASA Astrophysics Data System (ADS)

    Pertsev, N. A.; Gainutdinov, R. V.; Bodnarchuk, Ya. V.; Volk, T. R.

    2015-01-01

    The growth of localized subsurface domains in a relaxor ferroelectric Sr0.61Ba0.39Nb2O6 is studied using the technique of piezoresponse force microscopy (PFM). Ferroelectric domains are created by applying moderate voltages of 10-50 V to the conductive tip of a scanning force microscope brought into contact with a nonpolar face of a Sr0.61Ba0.39Nb2O6 crystal. PFM images of written domains are acquired and analyzed quantitatively to determine the domain length along the polar axis and its width in the transverse direction. The dependences of domain sizes on the applied voltage, pulse duration, and the time passed after completion of the voltage pulse are reported and analyzed theoretically. It is shown that the observed kinetics of domain growth can be explained by the creep of domain boundaries occurring in the presence of random electric fields inherent in Sr0.61Ba0.39Nb2O6. The comparison of measured domain sizes with their equilibrium values calculated with the aid of the thermodynamic theory demonstrates that the growth of subsurface domains in Sr0.61Ba0.39Nb2O6 is blocked by nanoscale heterogeneities characteristic of this relaxor ferroelectric. These results may have important implications for the development of nonlinear optical devices based on nanoheterogeneous ferroelectrics.

  6. White-light-emitting diodes based on Ba2+ co-doped Sr3SiO5: Ce3+, Li+ phosphor

    NASA Astrophysics Data System (ADS)

    Shen, Changyu; Li, Ke; Yang, Yi

    2009-11-01

    A yellow-orange-emitting Ba2+ codoped Sr3SiO5: Ce3+, Li+ phosphor was prepared by high-temperature solid-state reaction. Through transitions of 5d-->4f in Ce3+, the phosphor showed a very broad and strong yellow emission under near ultraviolet (UV) or blue light excitation. The shifts of the emission band to longer wavelength (yellow-orange) of the Sr3SiO5: Ce3+, Li+ yellow phosphor under the 450-470 nm excitation range have been achieved by adding the element Ba2+ in the Sr3SiO5 host. White light could be obtained by combining this phosphor with 460nm light-emitting diodes. As the concentrations of the Ba2+, Ce3+ and Li+ ions in the phosphor were 0.35mol, 0.024mol and 0.024mol respectively, the InGaN-based Ba2+ codoped Sr3SiO5: Ce3+, Li+ LED presented intense white emitting and good color rendering of 88.

  7. In vitro synthesis of amorphous Mg-, Ca-, Sr- and Ba-carbonates: What do we learn about intracellular calcification by cyanobacteria?

    NASA Astrophysics Data System (ADS)

    Cam, N.; Georgelin, T.; Jaber, M.; Lambert, J.-F.; Benzerara, K.

    2015-07-01

    Some cyanobacteria, including Candidatus Gloeomargarita lithophora, which was isolated from Lake Alchichica (Mexico), can form intracellular carbonates. This contradicts the common paradigm that cyanobacterial calcification is always extracellular and suggests that calcification might be controlled by these cyanobacterial species. Intracellular carbonates have several peculiar characteristics: they are relatively small (between 60 and 500 nm), they are poorly crystalline, and they have Sr/Ca and Ba/Ca ratios much higher than the solution in which the cells grow. It is therefore crucial to understand whether these unique features may indicate the involvement of specific biological processes. Here, in vitro abiotic syntheses were performed to synthesize Mg-, Ca-, Sr- and Ba-containing carbonates with compositions, crystallinities and sizes close to those observed in intracellularly calcifying cyanobacteria. Precipitates were characterized by scanning and transmission electron microscopies coupled with energy dispersive X-ray spectroscopy, thermogravimetric analysis and X-ray diffraction. The size and the poor crystallinity of cyanobacterial intracellular carbonates could be mimicked under these abiotic conditions. It was shown that similarly to Mg, elements such as Sr and Ba can favor stabilization of poorly crystalline carbonates. In contrast, the differential partitioning of Sr, Ba and Ca between the solution and the solids as observed in cyanobacteria could not be mimicked in vitro. This provides keys to a better understanding of biological processes involved in the formation of intracellular carbonates by some cyanobacteria, including the involvement of membrane transporters.

  8. A New Ba0.6 Sr0.4 TiO3 -Silicon Hybrid Metamaterial Device in Terahertz Regime.

    PubMed

    Wu, Liang; Du, Ting; Xu, Ningning; Ding, Chunfeng; Li, Hui; Sheng, Quan; Liu, Ming; Yao, Jianquan; Wang, Zhiyong; Lou, Xiaojie; Zhang, Weili

    2016-05-01

    Metamaterials, offering unprecedented functionalities to manipulate electromagnetic waves, have become a research hotspot in recent years. Through the incorporation of active media, the exotic electromagnetic behavior of metamaterials can be dramatically empowered by dynamic control. Many ferroelectric materials such as BaSrTiO3 (abbreviated as BST), exhibiting strong response to external electric field, hold great promise in both microwave and terahertz tunable devices. A new active Ba0.6 Sr0.4 TiO3 -silicon hybrid metamaterial device, namely, a SRR (square split-ring resonator)-BaSrTiO3 thin film-silicon three-layer structure is fabricated and intensively studied. The active Ba0.6 Sr0.4 TiO3 thin film hybrid metamaterial, with nanoscale thickness, delivers a transmission contrast up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate. This work has significantly increased the low modulation rate of ferroelectric based devices in terahertz range, a major problem in this field remaining unresolved for many years. The proposed BST metamaterial is promising in developing high-performance real world photonic devices for terahertz technology.

  9. Crystallite size characterization and magnetism properties of composite (BaFe12O19)1-X-(SrTiO3)X

    NASA Astrophysics Data System (ADS)

    Novizal, Manaf, Azwar; Doni, Rahmad

    2013-09-01

    A study conducted on the magnetic properties of composite material made of two materials i.e. BaFe12O19 (Barium Hexaferrite) and SrTiO3 (Strontium Titanate) using mechanical Alloy method. Composition proportion refers to the equation (BaFe12O19)1-X(SrTiO3)X X=20%, 50%,and 80% wt. Each BaFe12O19 material produced from base material of BaCO3 and Fe2O3 powder, SrTiO3 produced from mixture of SrCO3 and TiO2 powder. Each material are milled for 80 hours, of which on interval 20 hours, powder is extracted for particle measurement only for X=20 % wt composition, the X=50% wt and 80 % wt compositions are not measured. Next the material was made into bulk with 70 kN pressure die, and sintered at temperature of 1100°C for 4 hours, characterized with XRD, then magnetic character is measured with fermagraph.

  10. The photo-catalytic activities of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) microparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Shi, Yuanji; Zhao, Zongshan; Song, Weijie; Cheng, Yang

    2014-02-01

    For the good performance of apatite-based materials in the removal of dyes and their environment-friendly advantage, five kinds of apatite microparticles of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) were synthesized by a simple precipitation method and their photo-catalytic properties were invested. Better performance in the decolorization of methyl orange (MO) under the assistance of H2O2 than that of TiO2 were obtained for all the MPs. The photo-catalytic activity was mainly affected by surface area, energy band, impurity, crystallinity and crystal structure. The DFT calculation results demonstrated that the 2p of O and 3p of P in PO43- played the main role in the photo-catalytic process. This work would be helpful to design and synthesize low cost apatite materials with good photo-catalytic performance.

  11. Unconventional Electronic Reconstruction in Undoped (Ba,Sr)Fe2As2 Across the Spin Density Wave Transition

    SciTech Connect

    Yi, M.

    2010-06-02

    Through a systematic high-resolution angle-resolved photoemission study of the iron pnictide compounds (Ba,Sr)Fe{sub 2}As{sub 2}, we show that the electronic structures of these compounds are significantly reconstructed across the spin density wave transition, which cannot be described by a simple folding scenario of conventional density wave ordering. Moreover, we find that LDA calculations with an incorporated suppressed magnetic moment of 0.5{mu}{sub B} can match well the details in the reconstructed electronic structure, suggesting that the nature of magnetism in the pnictides is more itinerant than local, while the origin of suppressed magnetic moment remains an important issue for future investigations.

  12. Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi₃ (A = Sr and Ba).

    PubMed

    Shao, D F; Luo, X; Lu, W J; Hu, L; Zhu, X D; Song, W H; Zhu, X B; Sun, Y P

    2016-02-19

    Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi3 (A = Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi3. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures (Tc), while with SOC the calculated Tc are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi3 is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi3 can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity.

  13. Spin-orbit coupling enhanced superconductivity in Bi-rich compounds ABi3 (A = Sr and Ba)

    NASA Astrophysics Data System (ADS)

    Shao, D. F.; Luo, X.; Lu, W. J.; Hu, L.; Zhu, X. D.; Song, W. H.; Zhu, X. B.; Sun, Y. P.

    2016-02-01

    Recently, Bi-based compounds have attracted attentions because of the strong spin-orbit coupling (SOC). In this work, we figured out the role of SOC in ABi3 (A = Sr and Ba) by theoretical investigation of the band structures, phonon properties, and electron-phonon coupling. Without SOC, strong Fermi surface nesting leads to phonon instabilities in ABi3. SOC suppresses the nesting and stabilizes the structure. Moreover, without SOC the calculation largely underestimates the superconducting transition temperatures (Tc), while with SOC the calculated Tc are very close to those determined by measurements on single crystal samples. The SOC enhanced superconductivity in ABi3 is due to not only the SOC induced phonon softening, but also the SOC related increase of electron-phonon coupling matrix elements. ABi3 can be potential platforms to construct heterostructure of superconductor/topological insulator to realize topological superconductivity.

  14. Optical and spectral studies on pure and europium doped olgite type Na(Sr,Ba)PO4 ceramics.

    PubMed

    Jawaher, K Rackesh; Jagannathan, R; Das, S Jerome; Krishnan, S

    2015-04-05

    Europium ion doped olgite type Na(Sr,Ba)PO4 ceramics, a new generation of light emitting bulb, was prepared by a high temperature solid-state reaction method. The synthesized materials were subjected to various characterizations such as X-ray powder diffraction, Scanning electron microscopy and FT-IR spectra measurements. The EPR spectrum of the sample exhibits a well-resolved hyperfine structure of 151Eu2+ and 153Eu2+ isotopes and the g value has been calculated. Fluorescence spectra revealed that europium ions were present in divalent as well as in the trivalent oxidation states. The critical distance for energy transfer between Eu2+ and Eu2+ ion is calculated as 20Å, which is in good agreement with that of experimental data. The FTIR analysis reveals all the vibrations of PO4(3-) ions.

  15. LETTER TO THE EDITOR: Collective modes of tri-nuclear molecules of the type 96Sr+ 10Be+ 146Ba

    NASA Astrophysics Data System (ADS)

    Hess, P. O.; Scheid, W.; Greiner, W.; Hamilton, J. H.

    1999-12-01

    The collective modes of the tri-nuclear molecule 96Sr+ 10Be+ 146Ba, observed in recent cold fission decay of 252Cf into three clusters, are theoretically investigated. The main excitations are rotations, the butterfly and belly-dancer modes and icons/Journals/Common/beta" ALT="beta" ALIGN="TOP"/>- and icons/Journals/Common/gamma" ALT="gamma" ALIGN="TOP"/>-vibrations. Due to the presence of the Be nucleus, butterfly excitation energies are shifted up to 2 MeV. There are only a few collective states below 1 MeV which are not rotational. The first rotational level of spin 2+ lies at an energy of about 6 keV. Proposals of how these collective modes may be measured are suggested.

  16. Biological responses of human bone marrow mesenchymal stem cells to Sr-M-Si (M = Zn, Mg) silicate bioceramics.

    PubMed

    Zhang, Meili; Wu, Chengtie; Lin, Kaili; Fan, Wei; Chen, Lei; Xiao, Yin; Chang, Jiang

    2012-11-01

    Strontium (Sr), Zinc (Zn), magnesium (Mg), and silicon (Si) are reported to be essential trace elements for the growth and mineralization of bone. We speculated that the combination of these bioactive elements in bioceramics may be effective to regulate the osteogenic property of bone-forming cells. In this study, two Sr-containing silicate bioceramics, Sr(2)ZnSi(2)O(7) (SZS) and Sr(2)MgSi(2)O(7) (SMS), were prepared. The biological response of human bone marrow mesenchymal stem cells (BMSCs) to the two bioceramics (in the forms of powders and dense ceramic bulks) was systematically studied. In powder form, the effect of powder extracts on the viability and alkaline phosphatase (ALP) activity of BMSCs was investigated. In ceramic disc form, both direct and indirect coculture of BMSCs with ceramic discs were used to investigate their biological response, including attachment, proliferation, ALP activity, and bone-related genes expression. Beta-tricalcium phosphate (β-TCP) and akermanite (Ca(2)MgSi(2)O(7), CMS) were used as control materials. The results showed that the Sr, Zn, and Si (or Sr, Mg, and Si)-containing ionic products from SZS and SMS powders enhanced ALP activity of BMSCs, compared to those from β-TCP. Both SZS and SMS ceramic discs supported the growth of BMSCs, and most importantly, significantly enhanced the ALP activity and bone-related genes expression of BMSCs as compared to β-TCP. The results suggest that the specific combination of bioactive ions (Sr, Zn, Si, e.g.) in bioceramics is a viable way to improve the biological performance of biomaterials, and the form of materials and surface properties were nonnegligible factors to influence cell response.

  17. First-Principles Prediction of Two-Dimensional Electron Gas Driven by Polarization Discontinuity in Nonpolar/Nonpolar AHfO3/SrTiO3 (A = Ca, Sr, and Ba) Heterostructures.

    PubMed

    Cheng, Jianli; Nazir, Safdar; Yang, Kesong

    2016-11-23

    By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) in nonpolar/nonpolar AHfO3/SrTiO3 (A = Ca, Sr, and Ba) heterostructures. Two types of nonpolar/nonpolar interfaces, (AO)(0)/(TiO2)(0) and (HfO2)(0)/(SrO)(0), each with AO and HfO2 surface terminations, are modeled, respectively. The polarization domain and resulting interfacial electronic property are found to be more sensitive to the surface termination of the film rather than the interface model. As film thickness increases, an insulator-to-metal transition is found in all the heterostructures with HfO2 surface termination: for (AO)(0)/(TiO2)(0) interfaces, predicted critical film thickness for an insulator-to-metal transition is about 7, 6, and 3 unit cells for CaHfO3/SrTiO3, SrHfO3/SrTiO3, and BaHfO3/SrTiO3, respectively; for (HfO2)(0)/(SrO)(0) interfaces, the critical film thickness is about 7.5, 5.5, and 4.5 unit cells, respectively. In contrast, for the heterostructures with AO surface termination, CaHfO3/SrTiO3 exhibits a much larger critical film thickness about 11-12 unit cells for an insulator-to-metal transition; while SrHfO3/SrTiO3 and BaHfO3/SrTiO3 do not show any polarization behavior even film thickness increases up to 20 unit cells. The strain-induced polarization behavior was well-elucidated from energy versus polarization profile. This work is expected to stimulate further experimental investigation to the interfacial conductivity in the nonpolar/nonpolar AHfO3/SrTiO3 HS.

  18. Microwave loss mechanisms in Ba0.25Sr0.75TiO3 thin film varactors

    NASA Astrophysics Data System (ADS)

    Vorobiev, A.; Rundqvist, P.; Khamchane, K.; Gevorgian, S.

    2004-10-01

    Parallel-plate Au(Pt )/Ba0.25Sr0.75TiO3/(Pt)Au thin film varactors were fabricated on high resistance Si substrates and characterized at dc, rf, and microwave frequencies. In the frequency range 10-45 GHz the varactors show relatively low losses, with loss tangent less than 0.025 at 45 GHz. Due to the thick and highly conductive Pt/Au electrodes the metal losses are less than 10%. However, the loss tangent of the ferroelectric film is still three to five times higher than that in Ba0.27Sr0.73TiO3 single crystal. The analysis of the dc field dependences of loss tangent and permittivity in a wide frequency range shows that these additional losses are mainly due to the charged defects. Extrapolation of measured low frequency (1 MHz) loss tangents to the microwave region using the power law ω1/3 is in good agreement with experiment. The dc current through the varactor is found to be controlled by Schottky emission and Poole-Frenkel mechanisms depending on the polarity. The Poole-Frenkel mode is associated with field enhanced thermal excitation of charge carriers from internal traps. The trap activation energy (about 0.15 eV) determined from the Poole-Frenkel mode agrees well with the energy level of the oxygen vacancy. We assume that the oxygen vacancies within the grain boundaries of the ferroelectric film act as charged defects and cause additional (extrinsic) microwave losses. The possible correlation between the film's internal strains and density of the oxygen vacancies are discussed. The knowledge of the extrinsic loss mechanism and corresponding microstructure defects is useful in optimization of the varactor design, deposition, annealing process, and further improvement of the varactor performance.

  19. SrAgZn and EuAgZn with KHg{sub 2}-type structure—Structure, magnetic properties, and {sup 151}Eu Mössbauer spectroscopy

    SciTech Connect

    Gerke, Birgit; Rodewald, Ute Ch.; Niehaus, Oliver; Pöttgen, Rainer

    2013-07-15

    Samples of SrAgZn and EuAgZn were synthesized by reaction of the elements in sealed tantalum crucibles. Both structures were refined on the basis of single crystal X-ray diffractometer data: KHg{sub 2}-type, Imma, a=476.7(1), b=780.9(2), c=810.1(2) pm, R{sub 1}/wR{sub 2}=0.0189/0.0119, 381 F² values for SrAg{sub 1.12}Zn{sub 0.88} and a=474.43(9), b=760.8(2), c=799.0(2) pm, R{sub 1}/wR{sub 2}=0.0226/0.0483, 370 F² values for EuAg{sub 1.17}Zn{sub 0.83} with 13 variables per refinement. Silver and zinc are randomly distributed on the Hg position and build up three-dimensional networks. EuAgZn shows ferromagnetic ordering at 29(1) K. In the temperature range from 75 to 300 K the sample shows Curie–Weiss behaviour with μ{sub eff}=7.87(1) μ{sub B}/Eu atom and θ{sub P}=37.1(1) K, indicating divalent europium. {sup 151}Eu Mössbauer spectroscopic measurements confirmed the divalent state with an isomer shift of −9.31 mm/s at 78 K. Temperature dependent {sup 151}Eu data show first magnetic hyperfine field splitting at 25 K and a saturated magnetization of 17 T at 5.2 K. The temperature dependence can be described by an S=7/2 Brillouin function. - Graphical abstract: The near neighbor coordination of the strontium and europium atoms in SrAg{sub 1.12}Zn{sub 0.88}, EuAg{sub 1.17}Zn{sub 0.83}, and EuAuZn. - Highlights: • Synthesis of new intermetallic zinc compounds SrAgZn and EuAgZn. • Ferromagnetic ordering of EuAgZn at 29 K. • Magnetic hyperfine field splitting in the {sup 151}Eu Mössbauer spectrum.

  20. Influence of Co-substitution on the structural and magnetic properties of nanocrystalline Ba0.5Sr0.5Fe12O19

    NASA Astrophysics Data System (ADS)

    Ezhil Vizhi, R.; Harikrishnan, V.; Saravanan, P.; Rajan Babu, D.

    2016-10-01

    One-step citrate gel combustion method followed by annealing (800 °C/2 h) was employed to synthesize cobalt substituted barium strontium hexaferrite with a chemical composition of Ba0.5Sr0.5Fe12-xCoxO19 (x=0, 0.5, 0.7, and 0.9). A combination of thermo-gravimetric analysis and differential scanning calorimetry was employed to understand the thermo-chemical behavior of Ba0.5Sr0.5Fe12O19. X-ray diffraction (XRD) was used to evaluate the hexagonal phase evolution for the barium strontium ferrite nanopowders and a formation of secondary phase: α-Fe2O3 is evident for the Ba0.5Sr0.5Fe12O19. Raman spectroscopy confirmed the presence of different sublattices of Fe3+ present in the hexaferrite structure. Fourier transform infrared spectroscopy demonstrated the usual stretching vibrations of tetrahedral and octahedral M-O bands. The morphology and chemical composition of the samples were analyzed by transmission electron microscopy and field emission scanning electron microscopy attached with energy dispersive X-ray analysis, respectively. Selected area electron diffraction studies showed the nanocrystalline nature of the samples. The magnetic parameters such as saturation magnetization MS, coercivity, HC and remanent magnetization, MR were estimated from the hysteresis loops. Maximum value of MS (70.5 emu/g) was obtained for the Ba0.5Sr0.5Fe11.5Co0.5O19 nanoparticles. A possible growth mechanism on the crystallization of Ba0.5Sr0.5Fe12O19 hexagonal platelets during the citrate gel combustion synthesis is highlighted.

  1. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    PubMed Central

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-01-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3. PMID:27185343

  2. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-05-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3.

  3. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19.

    PubMed

    Rowley, S E; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A T; Watts, B E; Scott, J F

    2016-05-17

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T(3), in contrast to the 1/T(2) dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T(3), i.e. with a critical exponent γ = 3. In general γ = (d + z - 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T(3).

  4. Hexamer clusters in MeF2:Yb3+ (Me = Ca,Sr,Ba)

    NASA Astrophysics Data System (ADS)

    Chernyshev, V. A.; Nikiforov, A. E.; Nazemnikh, A. D.

    2011-10-01

    The electronic structure and g factors of simple impurity centers and hexamer ytterbium clusters in fluorites have been calculated in terms of the exchange charge model. Preliminarily, their local crystal structures have been calculated in the framework of the shell model with the inclusion of lattice distortions near the impurity. Crystal structure and g factors have been calculated of linear cluster Yb-F-Yb-F oriented along a trigonal axis in BaF2.

  5. Surface structures of ternary iron arsenides AFe2As2 ( A=Ba , Sr, or Ca)

    NASA Astrophysics Data System (ADS)

    Gao, Miao; Ma, Fengjie; Lu, Zhong-Yi; Xiang, Tao

    2010-05-01

    By the first-principles electronic structure calculations, we find that energetically the most favorable cleaved AFe2As2(001) surface is A -terminated with either 2×2 or 1×2 order. For BaFe2As2 , the surface Ba atoms are predominantly in a 2×2 order. A low-temperature cleaving may generate a metastable As-terminated surface. The As-terminated surface in the antiferromagnetic orthorhombic BaFe2As2 also takes a 2×2 order, resulting from the buckling of the surface As atoms and giving rise to a switchable 2×2 scanning tunneling microscopy (STM) pattern upon varying the applied bias. In a 1×2 -ordered A -terminated surface, the high-density spots in the STM image do not directly correspond to the positions of surface atoms. Our results are consistent with the STM observations and resolve the discrepancy between different experimental groups. The study helps establish a physical picture to understand the cleaved AFe2As2 surfaces.

  6. New Fluoride-arsenide Diluted Magnetic Semiconductor (Ba,K)F(Zn,Mn)As with Independent Spin and Charge Doping

    NASA Astrophysics Data System (ADS)

    Chen, Bijuan; Deng, Zheng; Li, Wenmin; Gao, Moran; Liu, Qingqing; Gu, C. Z.; Hu, F. X.; Shen, B. G.; Frandsen, Benjamin; Cheung, Sky; Lian, Liu; Uemura, Yasutomo J.; Ding, Cui; Guo, Shengli; Ning, Fanlong; Munsie, Timothy J. S.; Wilson, Murray Neff; Cai, Yipeng; Luke, Graeme; Guguchia, Zurab; Yonezawa, Shingo; Li, Zhi; Jin, Changqing

    2016-11-01

    We report the discovery of a new fluoride-arsenide bulk diluted magnetic semiconductor (Ba,K)F(Zn,Mn)As with the tetragonal ZrCuSiAs-type structure which is identical to that of the “1111” iron-based superconductors. The joint hole doping via (Ba,K) substitution & spin doping via (Zn,Mn) substitution results in ferromagnetic order with Curie temperature up to 30 K and demonstrates that the ferromagnetic interactions between the localized spins are mediated by the carriers. Muon spin relaxation measurements confirm the intrinsic nature of the long range magnetic order in the entire volume in the ferromagnetic phase. This is the first time that a diluted magnetic semiconductor with decoupled spin and charge doping is achieved in a fluoride compound. Comparing to the isostructure oxide counterpart of LaOZnSb, the fluoride DMS (Ba,K)F(Zn,Mn)As shows much improved semiconductive behavior that would be benefit for further application developments.

  7. New Fluoride-arsenide Diluted Magnetic Semiconductor (Ba,K)F(Zn,Mn)As with Independent Spin and Charge Doping

    PubMed Central

    Chen, Bijuan; Deng, Zheng; Li, Wenmin; Gao, Moran; Liu, Qingqing; Gu, C. Z.; Hu, F. X.; Shen, B. G.; Frandsen, Benjamin; Cheung, Sky; Lian, Liu; Uemura, Yasutomo J.; Ding, Cui; Guo, Shengli; Ning, Fanlong; Munsie, Timothy J. S.; Wilson, Murray Neff; Cai, Yipeng; Luke, Graeme; Guguchia, Zurab; Yonezawa, Shingo; Li, Zhi; Jin, Changqing

    2016-01-01

    We report the discovery of a new fluoride-arsenide bulk diluted magnetic semiconductor (Ba,K)F(Zn,Mn)As with the tetragonal ZrCuSiAs-type structure which is identical to that of the “1111” iron-based superconductors. The joint hole doping via (Ba,K) substitution & spin doping via (Zn,Mn) substitution results in ferromagnetic order with Curie temperature up to 30 K and demonstrates that the ferromagnetic interactions between the localized spins are mediated by the carriers. Muon spin relaxation measurements confirm the intrinsic nature of the long range magnetic order in the entire volume in the ferromagnetic phase. This is the first time that a diluted magnetic semiconductor with decoupled spin and charge doping is achieved in a fluoride compound. Comparing to the isostructure oxide counterpart of LaOZnSb, the fluoride DMS (Ba,K)F(Zn,Mn)As shows much improved semiconductive behavior that would be benefit for further application developments. PMID:27874044

  8. Synthesis of nanostructured framework of novel ZnBaO2 nanopowder via wet chemical approach and hepatocytotoxicity response

    NASA Astrophysics Data System (ADS)

    Athar, Taimur; Vishwakarma, Sandeep Kumar; Alabass, Razzaq; Alqaralosy, Ahmed; Khan, Aleem Ahmed

    2016-08-01

    Wet synthetic process is an effective and facile method at low cost, environmentally benign process for easy scaling-up and then used for fabrication of multi-utility devices. Self-assembling of nanobrick leads to architecture framework with new functional properties which help to make its vast applications as nanodevices with their intrinsic shape, size and functional properties. The bimetallic oxide nanostructure with phase structure was characterized by FTIR, UV-visible electronic absorption, XRD, thermal studies, SEM, TEM, DLS and fluorescence. Nanocrystalline ZnBaO2 powder can be used due to its chemical stability and excellent transmission in the visible region. It was observed that the annealing rate plays an important role to redefine the structural and other physicochemical properties which finally help to change gel into crystalline functional properties with porosity. Wet chemical approach can be used for the synthesis of other metal oxide nanopowders which can be easily scale up for production level. Along with synthesis and characterization, we also assessed biological responses of human hepatocytes exposed to ZnBaO2 nanopowder. Cell membrane permeability and ammonia detoxification were investigated against various concentrations of nanoparticles on in vitro cultured hepatocytes. Our results suggest that low concentrations (<40 μg/ml) of ZnBaO2 nanopowder have no cytotoxic effect on hepatocytes viability, proliferation and detoxification, whereas concentrations above 40 μg/ml depict significant toxicity on cells.

  9. New Fluoride-arsenide Diluted Magnetic Semiconductor (Ba,K)F(Zn,Mn)As with Independent Spin and Charge Doping.

    PubMed

    Chen, Bijuan; Deng, Zheng; Li, Wenmin; Gao, Moran; Liu, Qingqing; Gu, C Z; Hu, F X; Shen, B G; Frandsen, Benjamin; Cheung, Sky; Lian, Liu; Uemura, Yasutomo J; Ding, Cui; Guo, Shengli; Ning, Fanlong; Munsie, Timothy J S; Wilson, Murray Neff; Cai, Yipeng; Luke, Graeme; Guguchia, Zurab; Yonezawa, Shingo; Li, Zhi; Jin, Changqing

    2016-11-22

    We report the discovery of a new fluoride-arsenide bulk diluted magnetic semiconductor (Ba,K)F(Zn,Mn)As with the tetragonal ZrCuSiAs-type structure which is identical to that of the "1111" iron-based superconductors. The joint hole doping via (Ba,K) substitution &spin doping via (Zn,Mn) substitution results in ferromagnetic order with Curie temperature up to 30 K and demonstrates that the ferromagnetic interactions between the localized spins are mediated by the carriers. Muon spin relaxation measurements confirm the intrinsic nature of the long range magnetic order in the entire volume in the ferromagnetic phase. This is the first time that a diluted magnetic semiconductor with decoupled spin and charge doping is achieved in a fluoride compound. Comparing to the isostructure oxide counterpart of LaOZnSb, the fluoride DMS (Ba,K)F(Zn,Mn)As shows much improved semiconductive behavior that would be benefit for further application developments.

  10. High ferroelectric polarization in c-oriented BaTiO3 epitaxial thin films on SrTiO3/Si(001)

    SciTech Connect

    Scigaj, M.; Chao, C. H.; Gázquez, J.; Fina, I.; Moalla, R.; Saint-Girons, G.; Chisholm, M. F.; Herranz, G.; Fontcuberta, J.; Bachelet, R.; Sánchez, F.

    2016-09-21

    The integration of epitaxial BaTiO3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3/LaNiO3/SrTiO3 heterostructure is grown monolithically on Si(001). The BaTiO3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. Lastly, this result paves the way towards the fabrication of lead-free BaTiO3 ferroelectric memories on silicon platforms.

  11. High ferroelectric polarization in c-oriented BaTiO3 epitaxial thin films on SrTiO3/Si(001)

    DOE PAGES

    Scigaj, M.; Chao, C. H.; Gázquez, J.; ...

    2016-09-21

    The integration of epitaxial BaTiO3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3/LaNiO3/SrTiO3 heterostructure is grown monolithically on Si(001). The BaTiO3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. Lastly, this result paves the way towards the fabrication of lead-free BaTiO3 ferroelectric memories on silicon platforms.

  12. High ferroelectric polarization in c-oriented BaTiO3 epitaxial thin films on SrTiO3/Si(001)

    NASA Astrophysics Data System (ADS)

    Scigaj, M.; Chao, C. H.; Gázquez, J.; Fina, I.; Moalla, R.; Saint-Girons, G.; Chisholm, M. F.; Herranz, G.; Fontcuberta, J.; Bachelet, R.; Sánchez, F.

    2016-09-01

    The integration of epitaxial BaTiO3 films on silicon, combining c-orientation, surface flatness, and high ferroelectric polarization is of main interest towards its use in memory devices. This combination of properties has been only achieved so far by using yttria-stabilized zirconia buffer layers. Here, the all-perovskite BaTiO3/LaNiO3/SrTiO3 heterostructure is grown monolithically on Si(001). The BaTiO3 films are epitaxial and c-oriented and present low surface roughness and high remnant ferroelectric polarization around 6 μC/cm2. This result paves the way towards the fabrication of lead-free BaTiO3 ferroelectric memories on silicon platforms.

  13. Large-scale synthesis of Ba{sub x}Sr{sub 1−x}TiO{sub 3} nanowires with controlled stoichiometry

    SciTech Connect

    Tang, Haixiong E-mail: hsodano@ufl.edu; Zhou, Zhi; Sodano, Henry A. E-mail: hsodano@ufl.edu

    2014-04-07

    This study demonstrates a highly efficient method for large-scale synthesis BaTiO{sub 3} nanowires (NWs) using a two-step hydrothermal reaction. This synthesis process provides a facile approach to the growth of BaTiO{sub 3} NWs with high yield and control over the stoichiometry of the Ba{sub x}Sr{sub 1−x}TiO{sub 3} solid solution. The ferroelectricity of the BaTiO{sub 3} NWs is directly characterized using atomic force microscopy with the piezoelectric strain coupling coefficient (d{sub 33}) reaching 31.1 pm/V. This work provide an avenue for high volume manufacturing of ferroelectric NWs, allowing both fundamental investigation of nanoscale ferroelectricity as well as their future application in the electrical devices.

  14. Visible to near-infrared luminescence properties of Nd{sup 3+}-doped La{sub 2}BaZnO{sub 5} phosphor

    SciTech Connect

    Cao, Renping Cao, Chunyan; Yu, Xiaoguang; Sun, Xinyuan; Tang, Pengjie; Ao, Hui

    2014-07-01

    La{sub 2}BaZnO{sub 5}:Nd{sup 3+} phosphors are synthesized by a conventional high temperature solid state reaction method, and its crystal structure and luminescence properties are investigated. Photoluminescence bands peaking at ∼496, 540, 630, 670, 905, 1070, and 1350 nm of La{sub 2}BaZnO{sub 5}:Nd{sup 3+} phosphors are observed at room temperature due to f–f transition of Nd{sup 3+} ion. The optimum Nd{sup 3+} doped concentration is ∼0.03. Lifetimes of La{sub 1.97}BaZnO{sub 5}:0.03Nd{sup 3+} phosphor with 496 and 1070 nm monitoring wavelengths are ∼280 and 250 µs, respectively. The luminescence mechanism is explained by using simplified energy lever diagram of Nd{sup 3+} ion. La{sub 2}BaZnO{sub 5}:Nd{sup 3+} material can be applied to powerful solid-state lasers as high efficient light sources. - Graphical abstract: PL spectra of La{sub 2}BaZnO{sub 5}:Nd{sup 3+} phosphor in the visible and near-infrared regions and their corresponding to PLE at room temperature. - Highlights: • La{sub 2}BaZnO{sub 5}:Nd{sup 3+} phosphor is synthesized. • PL spectrum is observed in the visible region. • PL spectrum is observed in the near-infrared region.

  15. Theoretical survey on M@C80 (M = Ca, Sr, and Ba): Behavior of different alkaline earth metal impacting the chemical stability and electronic properties

    NASA Astrophysics Data System (ADS)

    Cui, Jin-Bo; Guo, Yi-Jun; Li, Qiao-Zhi; Zhao, Pei; Zhao, Xiang

    2016-08-01

    Structures of mono-metallofullerenes M@C80 (M = Ca, Sr, and Ba) that separated in early experiment are determined owning the C2v(31920)-C80 cage. The change rule of properties for M@C80 (M = Ca, Sr, and Ba) influenced by different inner metal are discussed. As the trapped metal changes from calcium to barium, performance of thermodynamic stabilities for M@C2v(31920)-C80, M@C2v(31922)-C80, and M@D5h(31923)-C80 are significantly different. Orbital analysis suggests that the lowest unoccupied molecular orbitals (LUMOs) of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 are mostly located on the trapped metal, whereas reduction reactions of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 occur on the fullerene cage. Natural electron configuration analyses demonstrates that the decentralized electron back-donation of Ba@C2v(31920)-C80 would take responsible for the instability of itself. Electronic properties such as electron affinities and ionization potentials are significantly affected by encapsulated metal are also found. Computational UV-visible-NIR spectra for M@C2v(31920)-C80 (M = Ca, Sr, Ba) are in perfect accord with the spectra obtained experimentally.

  16. Mechanochemical synthesis, structure, and properties of solid solutions of alkaline earth metal fluorides: Ma1-xMbxF2 (M: Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Heise, M.; Scholz, G.; Düvel, A.; Heitjans, P.; Kemnitz, E.

    2016-10-01

    The capability of mechanochemical synthesis for the formation of solid solutions of alkaline earth metal fluorides Ma1-xMbxF2 (M: Ca, Sr, Ba) was tested by fluorination of metal acetates and metal hydroxides with ammonium fluoride directly at milling. Evidence was found for a mutual substitution of cations on their lattice positions in Ca1-xSrxF2 and Ba1-xSrxF2 samples. For the Ba/Ca-system this synthesis route is only partially successful. X-ray diffraction and 19F MAS NMR spectroscopy were used to characterize all samples concerning their crystal structure and local fluorine coordination. Calculations of 19F chemical shifts with the superposition model along with probability calculations for the intensity of the individual 19F lines, performed in dependence on the molar composition of the samples, perfectly agree with the experimental findings. The fluoride ion conductivity of as-prepared samples, determined by temperature dependent DC conductivity measurements, is significantly higher than those of crystalline binary fluorides. Moreover, a higher F- ion conductivity is observed for samples with higher mixing grade in the Ca/Sr-and the Ba/Sr-systems.

  17. Les Néandertaliens étaient-ils essentiellement carnivores ? Résultats préliminaires sur les teneurs en Sr et en Ba de la paléobiocénose mammalienne de Saint-CésaireWere Neandertalians essentially carnivores? Sr and Ba preliminary results of the mammalian palaeobiocoenosis of Saint-Césaire

    NASA Astrophysics Data System (ADS)

    Balter, Vincent; Person, Alain; Labourdette, Nathalie; Drucker, Dorothée; Renard, Maurice; Vandermeersch, Bernard

    2001-01-01

    Strontium-calcium (Sr/Ca) and barium-calcium (Ba/Ca) ratios are reduced constantly between diet and bioapatite in mammal organisms. This phenomenon leads to a reduction in the Sr/Ca and Ba/Ca ratios at higher trophic level in predator-prey mammalian communities, and is applied here to the reconstruction of a castelperronian food web, which includes a Neanderthal specimen. Adapted chemical pretreatment allows to isolate bioapatite from diagenetic compounds for analysis of Ca, Sr and Ba. Sr/Ca and Ba/Ca results of the fauna are consistent with trophic predictions. Initial results for the Neandertal suggest that he was mostly carnivorous. Distribution of Ba/Ca values of bones of herbivorous taxa reveals that ruminant animals can be distinguished from non-ruminants. The biosegregation model predicts that the diet of the Neandertal was composed by about 97 % in weight of meat with a weak contribution of vegetable or fish, and that the association of fish and plant is excluded in any proportion.

  18. Effect of Sr doping on the electrochemical properties of bi-functional oxygen electrode PrBa1-xSrxCo2O5+δ

    NASA Astrophysics Data System (ADS)

    Wu, Zhouling; Sun, Li-Ping; Xia, Tian; Huo, Li-Hua; Zhao, Hui; Rougier, Aline; Grenier, Jean-Claude

    2016-12-01

    Sr-doped double perovskite oxides PrBa1-xSrxCo2O5+δ (x = 0.0-1.0) are prepared and characterized by X-ray diffraction, X-ray photoelectron spectra, cyclic voltammetry and linear sweep voltammetry, respectively. Sr2+ doping is found to promote the electrocatalytic activity towards both oxygen evolution reduction and oxygen reduction reaction, due to the concentration enhancement of Co4+ (eg = 1) on the oxide surface. The PrBa0.25Sr0.75Co2O5.95 catalyst, with the highest concentration of Co4+, exhibits the superior electrocatalytic activity. The onset potential, Tafel slope and the overpotential at given current density of 10.0 mA·cmgeom-2 for the OER are 1.52 V, 75.8 mV·dec-1 and 0.42 V, respectively, comparable to the currently reported high performance OER catalysts. At the same time, the onset potential, Tafel slope, limiting current density and electron transfer number of PrBa0.25Sr0.75Co2O5.95 for ORR are 0.753 V, 58.3 mV·dec-1, 4.081 mA·cmgeom-2 and n = 3.92, respectively, implying much improved ORR activity.

  19. On the characterization of Bi MO 2NO 3 ( M=Pb, Ca, Sr, Ba) materials related with the Sillén X 1 structure

    NASA Astrophysics Data System (ADS)

    Ziegler, Peter; Grigoraviciute, Inga; Gibson, Katharina; Glaser, Jochen; Kareiva, Aivaras; Meyer, H.-Jürgen

    2004-10-01

    The compounds BiMO2NO3, with M=Pb, Ca, Sr, and Ba, were obtained as single-phase products from solid-state reactions in an atmosphere of nitrous gases. The oxide nitrates with Pb and Ca crystallize in the tetragonal space group I4/mmm with two formula units per unit cell; the oxide nitrates with Sr and Ba crystallize in the orthorhombic space group Cmmm with four formula units per unit cell. Lattice parameters at room temperature are a=397.199(4), c=1482.57(2) pm for M=Pb; a=396.337(5), c=1412.83(3) pm for M=Ca; a=1448.76(3), b=567.62(1), c=582.40(1) pm for M=Sr and a=1536.50(8), b=571.67(3), c=597.55(3) pm for M=Ba. The structures, which were refined by powder X-ray diffraction, consist of alternating [BiMO2]+ and [NO3]- layers stacked along the direction of the long axis. IR and thermogravimetric data are also given. The various M2+ cations in BiMO2NO3 are compatible with each other; therefore and because of their layer-type structure, these compounds are interesting precursors for oxide materials, e.g., the HTSC compounds (Bi,Pb)2Sr2Can-1CunOx.

  20. Pressure-Induced Structural and Electronic Transition in Sr2ZnWO6 Double Perovskite.

    PubMed

    Li, Nana; Manoun, Bouchaib; Tang, Lingyun; Ke, Feng; Liu, Fengliang; Dong, Haini; Lazor, Peter; Yang, Wenge

    2016-07-05

    High-pressure structural and electrical properties of Sr2ZnWO6 double perovskite were investigated using in situ angle-dispersive synchrotron X-ray diffraction (XRD), Raman, and alternating current (AC) impedance spectroscopy. A structural transition from monoclinic (P21/n) to triclinic (P1̅) phase around 9 GPa was observed due to the pressure-induced distortion of (W, Zn)O6 octahedron. In situ high-pressure Raman spectroscopy showed the increasing interaction among O-W-O in WO6 octahedron with pressure and a transition pressure consistent with the XRD results. From the AC impedance spectroscopy measurements, the resistivity increased steeply by ∼1 order of magnitude around 11 GPa, indicating an electronic transition accompanying the symmetry change. The increase in the interaction among O-W-O enhances the attraction of O(2-) electrons toward W(6+), thus increasing the covalence, which in turn lowers the charge transfer energy between O(2-) and W(6+) and induces the resistivity increase under high pressure.

  1. Preferential Eu Site Occupation and Its Consequences in the Ternary Luminescent HalidesAB2I5:Eu2+(A=Li–Cs;B=Sr, Ba)

    DOE PAGES

    Fang, C.  M.; Biswas, Koushik

    2015-07-22

    Several rare-earth-doped, heavy-metal halides have recently been identified as potential next-generation luminescent materials with high efficiency at low cost. AB2I5:Eu2+ (A=Li–Cs; B=Sr, Ba) is one such family of halides. Its members, such as CsBa2I5:Eu2+ and KSr2I5:Eu2+, are currently being investigated as high-performance scintillators with improved sensitivity, light yield, and energy resolution less than 3% at 662 keV. Within the AB2I5 family, our first-principles-based calculations reveal two remarkably different trends in Eu site occupation. The substitutional Eu ions occupy both eightfold-coordinated B1(VIII) and the sevenfold-coordinated B2(VII) sites in the Sr-containing compounds. However, in the Ba-containing crystals, Eu ions strongly prefer themore » B2(VII)sites. This random versus preferential distribution of Eu affects their electronic properties. The calculations also suggest that in the Ba-containing compounds one can expect the formation of Eu-rich domains. These results provide atomistic insight into recent experimental observations about the concentration and temperature effects in Eu-doped CsBa2I5. We discuss the implications of our results with respect to luminescent properties and applications. We also hypothesize Sr, Ba-mixed quaternary iodides ABaVIIISrVIII5:Eu as scintillators having enhanced homogeneity and electronic properties.« less

  2. Site-related near-infrared luminescence in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):Fe{sup 3+} phosphors

    SciTech Connect

    Li, Y.J.; Ma, Y.Y.; Ye, S.; Hu, G.P.; Zhang, Q.Y.

    2014-03-01

    Graphical abstract: - Highlights: • Intense 700–850 nm NIR emissions in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):1%Fe{sup 3+} has been obtained. • The NIR emissions can be ascribed to the octahedral Fe{sup 3+} sites. • The site symmetry of Fe{sup 3+} in CA{sub 6} and SA{sub 6} may be lower than that in BA{sub 6}. • The phosphors may be potentially applied in the high-resolution bioimaging. - Abstract: Intense and broad near-infrared (NIR) photoluminescence (PL) peaks locating at 777, 808 and 810 nm is observed for BaAl{sub 12}O{sub 19} (BA{sub 6}):1%Fe{sup 3+}, CaAl{sub 12}O{sub 19} (CA{sub 6}):1%Fe{sup 3+} and SrAl{sub 12}O{sub 19} (SA{sub 6}):1%Fe{sup 3+}, respectively. Electron paramagnetic resonance (EPR) spectra show that Fe{sup 3+} ions substitute for the different types of Al{sup 3+} sites simultaneously. Meanwhile, the luminescence of Fe{sup 3+} in MAl{sub 12}O{sub 19} (M = Ca, Sr and Ba) are ascribed to octahedral Fe{sup 3+}. In addition, the site symmetry of Fe{sup 3+} in CA{sub 6}/SA{sub 6} is lower compared with BA{sub 6}, deduced from the photoluminescence excitation (PLE), EPR and Fourier-transform infrared (FT-IR) spectra. These phosphors can be considered as good candidates for the applications in the field of high-resolution bioimaging.

  3. Explaining the Ba, Y, Sr, and Eu abundance scatter in metal-poor halo stars: constraints to the r-process

    NASA Astrophysics Data System (ADS)

    Cescutti, G.; Chiappini, C.

    2014-05-01

    Context. Thanks to the heroic observational campaigns carried out in recent years we now have large samples of metal-poor stars for which measurements of detailed abundances exist. In particular, large samples of stars with metallicities -5 < [Fe/H] <-1 and measured abundances of Sr, Ba, Y, and Eu are now available. These data hold important clues on the nature of the contribution of the first stellar generations to the enrichment of our Galaxy. Aims: We aim to explain the scatter in Sr, Ba, Y, and Eu abundance ratio diagrams unveiled by the metal-poor halo stars. Methods: We computed inhomogeneous chemical evolution models for the Galactic halo assuming different scenarios for the r-process site: the electron-capture (EC) supernovae and the magnetorotationally driven (MRD) supernovae scenarios. We also considered models with and without the contribution of fast-rotating massive stars (spinstars) to an early enrichment by the s-process. A detailed comparison with the now large sample of stars with measured abundances of Sr, Ba, Y, Eu, and Fe is provided (both in terms of scatter plots and number distributions for several abundance ratios). Results: The scatter observed in these abundance ratios of the very metal-poor stars (with [Fe/H] <-2.5) can be explained by combining the s-process production in spinstars, and the r-process contribution coming from massive stars. For the r-process we have developed models for both the EC and the MRD scenarios that match the observations. Conclusions: With the present observational and theoretical constraints we cannot distinguish between the EC and the MRD scenarios in the Galactic halo. Independently of the r-process scenarios adopted, the production of elements by an s-process in spinstars is needed to reproduce the spread in abundances of the light neutron capture elements (Sr and Y) over heavy neutron capture elements (Ba and Eu). We provide a way to test our suggestions by means of the distribution of the Ba isotopic

  4. In vitro and in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass.

    PubMed

    Li, H F; Xie, X H; Zhao, K; Wang, Y B; Zheng, Y F; Wang, W H; Qin, L

    2013-11-01

    In order to enhance the corrosion resistance of the Ca65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass because of the unique properties of high-entropy alloys. Our results showed that the mechanical properties and corrosion behavior were enhanced. The in vitro tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass did not show any obvious degradation after 4 weeks of implantation, and they can promote osteogenesis and new bone formation after 2 weeks of implantation. The improved mechanical properties and corrosion behavior can be attributed to the different chemical composition as well as the formation of a unique high-entropy atomic structure with a maximum degree of disorder.

  5. Sintering of BaCe(0.85)Y(0.15)O3-(Beta) With/Without SrTiO Dopant

    NASA Technical Reports Server (NTRS)

    Dynys, Fred; Sayir, Ali; Heimann, Paula J.

    2004-01-01

    The sintering behavior of BaCe(0.85)Y(0.15)O3-(Beta) doped with SrTiO is described. Complete reaction and crystallization of perovskite phase by solid state was achieved by calcining at 1200 degrees C for 24 hours.Smaples were sintered at 1450 degrees C, 1550 degrees C, and 1650 degrees C. SrTiOsub3 enhanced sintering, while optimal dopant level was different for powders synthesized by solid state and co-precipitation. Both powders exhibit similar grain growth behavior.

  6. Luna 16 - Some Li, K, Rb, Sr, Ba, rare-earth, Zr, and Hf concentrations.

    NASA Technical Reports Server (NTRS)

    Philpotts, J. A.; Schnetzler, C. C.; Schuhmann, S.; Thomas , H. H.; Bottino, M. L.

    1972-01-01

    Concentrations of Li, K, Rb, Sr, Na, rare-earths, Zr and Hf have been determined for some Luna 16 core materials by mass-spectrometric isotope-dilution. Two regolith fines samples from different depths in the core, and four rock-chips, including both igneous rocks and breccias, have similar trace-element concentrations. The Luna 16 materials have general lunar trace-element characteristics but differ from other returned lunar samples in a manner that suggests the presence of excess feldspar. Unless the Luna 16 igneous rocks are fused soils, they appear to represent either partial plagioclase cumulates or the least differentiated igneous material yet returned from the moon. The similarity in trace-element concentrations of the igneous rocks and the fines would then suggest largely local derivation of the Luna 16 regolith.

  7. Enhance D. C. resistivity of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} ceramic by acceptor (Mn) doping

    SciTech Connect

    Sharma, Hakikat Arya, G. S.; Pramar, Kusum; Negi, N. S.

    2015-05-15

    In the present work, we prepared Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} and Mn (2 and 3 at % on Ti site) doped Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} ceramic by sol- gel method. The samples were characterized by X-ray diffraction (XRD). The XRD patterns reveled that Mn ions did not change the perovskite structure of BST (70/30). The dielectric measurements proved that dielectric constant decreased with Mn doping. The dc resistivity was studied by using I-V measurements. The dc resistivity of the BST increased with Mn doping, which suppressed the leakage current.

  8. Structural and complex AC impedance spectroscopic studies of A 2CoNbO 6 (A = Sr, Ba) ordered double perovskites

    NASA Astrophysics Data System (ADS)

    Bashir, J.; Shaheen, R.

    2011-05-01

    Powder X-ray diffraction has been employed to study the crystal structures of Sr 2CoNbO 6 ( SCNO) and Ba 2CoNbO 6 ( BCNO) double perovskites. Rietveld fit to the X-ray diffraction data showed that Ba 2CoNbO 6 perovskites was monoclinic with space group P2 1/ n whereas Sr 2CoNbO 6 was found to be tetragonal with space group I4/ m. Like other cobalt based perovskites, both materials exhibit high values of dielectric constant at room temperature and low frequencies. Room temperature impedance and modulus spectra, measured over the 1 Hz to 10 MHz, reveal two relaxation processes with different relaxation times which were attributed to the grain and grain boundaries.

  9. Precise lattice parameter measurements of Sr0.72Ba0.25Nb2O5.97 single crystals

    NASA Astrophysics Data System (ADS)

    Paszkowski, R.; Wokulska, K. B.; Dec, J.; Łukasiewicz, T.

    2014-09-01

    Pure and undoped strontium-barium niobate Sr0.72Ba0.25Nb2O5.97 single crystals grown by the Czochralski method were investigated. Using X-ray Bond's method lattice parameters of this crystals are determined with high accuracy in the order of Δd/d=10-5. Based on the lattice parameter data measured at 298 K it was ascertained that the Sr0.72Ba0.25Nb2O5.97 single crystals belong to the tetragonal system. The additional analysis of the diffraction patterns performed by the Laue method confirmed the occurrence of a four-fold axis of symmetry.

  10. Structural, elastic and electronic properties of C14-type Al2M (M=Mg, Ca, Sr and Ba) Laves phases

    NASA Astrophysics Data System (ADS)

    Lishi, Ma; Yonghua, Duan; Runyue, Li

    2017-02-01

    The structural and mechanical properties, Debye temperatures and anisotropic sound velocities of the Laves phases Al2M (M=Mg, Ca, Sr and Ba) with C14-type structure were investigated using the first-principles corresponding calculations. The corresponding calculated structural parameters and formation enthalpies are in good agreement with the available theoretical values, and Al2Ca has the best phase stability. The mechanical properties, including elastic constants, bulk modulus B, shear modulus G, Young's modulus E, and Poisson ratio ν, were deduced within the Voigt-Reuss-Hill approximation. The brittleness and ductility were estimated by the values of Poisson ratio, B/G and Cauchy pressure. Moreover, the elastic anisotropy was investigated by calculating and discussing several anisotropy indexes. Finally, the electronic structures were used to illustrate the bonding characteristics of C14-Al2M (M=Mg, Ca, Sr and Ba) phases.

  11. Abnormal thermal conductivity in tetragonal tungsten bronze Ba{sub 6−x}Sr{sub x}Nb{sub 10}O{sub 30}

    SciTech Connect

    Kolodiazhnyi, T. Sakurai, H.; Vasylkiv, O.; Borodianska, H.; Mozharivskyj, Y.

    2014-03-17

    Ba{sub 6−x}Sr{sub x}Nb{sub 10}O{sub 30} solid solution with 0 ≤ x ≤ 6 crystallizes in centrosymmetric tetragonal “tungsten bronze” structure (space group P4/mbm). We report on the x dependence of thermal conductivity of polycrystalline samples measured in the 2–400 K temperature interval. Substitution of Sr for Ba brings about a significant decrease in thermal conductivity at x ≥ 3 accompanied by development of a low-temperature (T ≈ 10–30 K) “plateau” region reminiscent of a glass-like compounds. We explain this behaviour based on a size-driven site occupancy and atomic displacement parameters associated with an alkaline earth atomic positions in the title compounds.

  12. A comparative study on the magnetic and electrical properties of MFe12O19 (M=Ba and Sr)/BiFeO3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Ahmed, M. A.; Mansour, S. F.; Ismael, H.

    2015-03-01

    M-type hexaferrite (MFe12O19), M=Ba or Sr nanoparticles with hexagonal crystal structure have been successfully synthesized by a citrate auto-combustion method. BiFeO3 (BFO) was prepared by the flash auto-combustion technique. Different nanocomposites were prepared according to the formula [(1-X) MFe12O19+XBiFeO3; M=Ba or Sr, X=0.3, 0.4, 0.5 and 0.6]. The structure and morphology of the obtained nanocomposites have been determined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). From the results, it is observed that the value of saturation magnetization decreases with increasing BFO content, which was mainly due to the contribution of the volume of the weak-magnetic BFO to the total sample volume.

  13. Studies of EPR spectra and defect structure for Er3+ ions in BaF2 and SrF2 crystals

    NASA Astrophysics Data System (ADS)

    Li, Hui; Kuang, Xiao-Yu; Mao, Ai-Jie; Li, Cheng-Gang

    2013-02-01

    The local lattice structure and electron paramagnetic resonance (EPR) spectra have been studied systematically by diagonalizing 364 × 364 complete energy matrices for a f11 ion in a trigonal ligand-field. By simulating the calculated Stark levels and EPR parameters to the experimental results, the shift parameters are determined for Er3+ ions in BaF2 and SrF2. The results show that the trigonal center is attributed to an interstitial F- ion located at the [1 1 1] axis of the cube, and the nearest ligand close to the charge compensator has a displacement towards central ion by 0.042 Å for L center in BaF2:Er3+ and 0.026 Å for J center in SrF2:Er3+, respectively. Moreover, the relationships between g-factors and shift parameter ΔZ as well as orbit reduction factor k' are discussed.

  14. Microwave Dielectric Properties for Ba(Mg1/3Ta2/3)O3 A(Mg1/2W1/2)O3 (A=Ba, Sr, and Ca) Ceramics

    NASA Astrophysics Data System (ADS)

    Furuya, Mitsuru; Ochi, Atsushi

    1994-09-01

    For a high-Q dielectric resonator at microwave frequencies, complex perovskite-structured Ba(Mg1/3Ta2/3)O3 A(Mg1/2W1/2)O3 (A=Ba, Sr, and Ca) ceramics have been developed. A(Mg1/2W1/2)O3 effects on the crystal structure, microstructure, and microwave characteristic of Ba(Mg1/3Ta2/3)O3 (BMT) were investigated. Ba(Mg1/2W1/2)O3 (BMW) decreased the temperature coefficient of resonant frequency ( TCF) for BMT. Sr(Mg1/2W1/2)O3 (SMW) and Ca(Mg1/2W1/2)O3 (CMW) increased it. Zero TCF was obtained for the BMT/BMW=95/5 composition. With 0.5 mol% BMW content, dielectric loss quality, Q d, reached a maximum (40000 at 10 GHz).

  15. Ferroelectric domain wall relaxation in Ba0.25Sr0.75TiO3 films displaying Curie-Weiss behavior

    NASA Astrophysics Data System (ADS)

    Boikov, Yu. A.; Khamchane, K.; Claeson, T.

    2004-10-01

    Ferroelectric films may be used in integrated circuits for high frequency and memory applications. Losses and interfaces between films and electrodes are problematic. This work concerns the temperature and electric field response of the complex dielectric permittivity and the relaxation of domain walls in a ferroelectric layer that is of sufficient quality to show a Curie-Weiss behavior. Laser ablation was used to deposit 1200 nm thick Ba0.25Sr0.75TiO3 layers between metallic oxide, (100 nm) SrRuO3 and (120 nm) La0.67Ca0.33MnO3, films in epitaxial heterostructures. The electric field response (E ⩽80kV/cm) of the real ε' and imaginary ε″ parts of the complex permittivity of the intermediate Ba0.25Sr0.75TiO3 layer in these parallel plane film capacitors was studied at temperatures above and below the phase transition point TCurie. The latter was determined from the temperature dependence of the inverse dielectric permittivity and its value, TCurie=145K, agrees well with that of bulk single crystal. ε' of the Ba0.25Sr0.75TiO3 layer could be suppressed about 80% by a field E =80kV/cm at temperatures close to TCurieε'(T,E) and ε″(T,E) curves were used to gain insight into the relaxation dynamics of ferroelectric domain walls (DW) in the Ba0.25Sr0.75TiO3 layer. Their influence on ε' was noticed up to T =230K, well above TCurie. The most probable relaxation time τ of the DW in Ba0.25Sr0.75TiO3 follows a relation τ =τ0exp[(ϕ-β√E )/kT], where τ0=1.2×10-10sϕ=75-105meV, and β =4.7×10-24Jm1/2V-1/2.

  16. Structural and electronic properties of Sr{sub x}Ba{sub 1-x}SnO{sub 3} from first principles calculations

    SciTech Connect

    Moreira, E.; Henriques, J.M.; Azevedo, D.L.; Caetano, E.W.S.; Freire, V.N.; Albuquerque, E.L.

    2012-03-15

    Neutron diffraction data for Sr{sub x}Ba{sub 1-x}SnO{sub 3} (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) solid solutions were used as inputs to obtain optimized geometries and electronic properties using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. The crystal structures and SnO{sub 6} octahedra tilting angles found after total energy minimization agree well with experiment, specially for the GGA data. Elastic constants were also obtained and compared with theoretical and experimental results for cubic BaSnO{sub 3}. While the alloys with cubic unit cell have an indirect band gap, tetragonal and orthorhombic alloys exhibit direct band gaps (exception made to x=1.0). The Kohn-Sham minimum electronic band gap oscillates from 1.52 eV (cubic x=0.0, LDA) to 2.61 eV (orthorhombic x=1.0, LDA), and from 0.74 eV (cubic BaSnO{sub 3}, GGA) to 1.97 eV (orthorhombic SrSnO{sub 3}, GGA). Parabolic interpolation of bands has allowed us to estimate the effective masses for charge carriers, which are shown to be anisotropic and larger for holes. - Graphical Abstract: Highlights: Black-Right-Pointing-Pointer DFT calculations were performed on Sr{sub x}Ba{sub 1-x}SnO{sub 3} solid solutions. Black-Right-Pointing-Pointer Calculated crystal structures agree well with experiment. Black-Right-Pointing-Pointer Alloys have direct or indirect gaps depending on the Sr molar fraction. Black-Right-Pointing-Pointer The Kohn-Sham gap variation from x=0.0 to x=1.0 is close to the experimental value. Black-Right-Pointing-Pointer Carrier effective masses are very anisotropic, specially for holes.

  17. Comparative studies of dipole polarizabilities in Sr{sup +}, Ba{sup +}, and Ra{sup +} and their applications to optical clocks

    SciTech Connect

    Sahoo, B. K.; Timmermans, R. G. E.; Das, B. P.; Mukherjee, D.

    2009-12-15

    Static dipole polarizabilities are calculated in the ground and metastable states of Sr{sup +}, Ba{sup +} and Ra{sup +} using the relativistic coupled-cluster method. Trends of the electron correlation effects are investigated in these atomic ions. We also estimate the Stark and black-body radiation shifts from these results for these systems for the transitions proposed for the optical frequency standards and compare them with available experimental data.

  18. Syntheses and characterization of energetic compounds constructed from alkaline earth metal cations (Sr and Ba) and 1,2-bis(tetrazol-5-yl)ethane

    SciTech Connect

    Xia Zhengqiang; Chen Sanping; Wei Qing; Qiao Chengfang

    2011-07-15

    Two new energetic compounds, [M(BTE)(H{sub 2}O){sub 5}]{sub n} (M=Sr(1), Ba(2)) [H{sub 2}BTE=1,2-bis(tetrazol-5-yl)ethane], have been hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction analyses reveal that they are isomorphous and exhibit 2D (4,4) net framework, generated by 4-connected Sr{sub 2}(H{sub 2}O){sub 10}/Ba{sub 2}(H{sub 2}O){sub 10} SBUs linked up by two independent binding modes of H{sub 2}BTE, and the resulting 2D structure is interconnected by hydrogen-bond and strong face to face {pi}-{pi} stacking interactions between two tetrazole rings to lead to a 3D supramolecular architecture. DSC measurements show that they have significant catalytic effects on thermal decomposition of ammonium perchlorate. Moreover, the photoluminescence properties, thermogravimetric analyses, and flame colors of the as-prepared compounds are also investigated in this paper. - Graphical abstract: Two novel 2D isomorphous alkaline earth metal complexes were assembled by 4-connected Sr{sub 2}(H{sub 2}O){sub 10}/Ba{sub 2}(H{sub 2}O){sub 10} SBUs and two independent binding modes of H{sub 2}BTE ligands, and the catalytic performances toward thermal decomposition of ammonium perchlorate and photoluminescent properties of them were investigated. Highlights: > Two novel alkaline earth energetic coordination polymers have been prepared.{yields} Both structures are layered based on 4-connected Sr{sub 2}(H{sub 2}O){sub 10}/Ba{sub 2}(H{sub 2}O){sub 10} SBUs and two distinct H{sub 2}BTE coordination modes.{yields} The dehydrated products of the compounds possess good thermostability and significant catalytic effects on thermal decomposition of AP.

  19. Spontaneous orientation-tuning driven by the strain variation in self-assembled ZnO-SrRuO{sub 3} heteroepitaxy

    SciTech Connect

    Zhu, Yuanmin; Liu, Ruirui; Zhan, Qian; Chang, Wei Sea; Yu, Rong; Wei, Tzu-Chiao; He, Jr-Hau; Chu, Ying-Hao

    2015-11-09

    Heteroepitaxial ZnO and SrRuO{sub 3} were grown on SrTiO{sub 3} (111) substrates and formed a self-assembled wurtzite-perovskite nanostructure. Spontaneous orientation-tuning of the SrRuO{sub 3} pillars was observed, with the growth direction changing from [111]{sub SRO} to [011]{sub SRO} as the film thickness increased, which is attributed to a misfit strain transition from the biaxial strain imposed by the SrTiO{sub 3} substrate to the vertical strain provided by the ZnO matrix. The [011]-SrRuO{sub 3} and [0001]-ZnO combination presents a favorable matching in the nanocomposite films, resulting in higher charge carrier mobility. This vertically integrated configuration and regulation on the crystallographic orientations are expected to be employed in designing multi-functional nanocomposite systems for applications in electronic devices.

  20. Strain induced enhancement of magnetization in Ba2FeMoO6 based heterostructure with (BaxSr1-x)TiO3

    NASA Astrophysics Data System (ADS)

    Kim, Kyeong-Won; Ghosh, Siddhartha; Buvaev, Sanal; Hebard, Arthur F.; Norton, David P.

    2016-05-01

    High quality epitaxial Ba2FeMoO6 thin films and Ba2FeMoO6-(BaxSr1-x)TiO3 bi-layer (BL) and superlattice (SL) structures were grown via pulsed laser deposition under low oxygen pressure, and their structural, magnetic, and magneto-transport properties were examined. Superlattice and bi-layer structures were confirmed by X-ray diffraction patterns. Low temperature magnetic measurement shows that the saturation magnetization (MS) is significantly higher for SLs and almost similar or lower for BLs, when compared to phase pure Ba2FeMoO6 thin films. The variation of the coercive field (HC) follows exact opposite trend, where BL samples have higher HC and SL samples have lower HC than pure Ba2FeMoO6 thin films. Also, a significant decrease of the Curie temperature is found in both BL and SL structures compared to pure Ba2FeMoO6 thin films. Negative magneto-resistance is seen in all the BL and SL structures as well as in pure Ba2FeMoO6 thin films. In contrast to the magnetic properties, the magneto-transport properties do not show much variation with induced strain.

  1. Crystal structures of the double perovskites Ba{sub 2}Sr{sub 1-} {sub x} Ca {sub x} WO{sub 6}

    SciTech Connect

    Fu, W.T. Akerboom, S.; IJdo, D.J.W.

    2007-05-15

    Structures of the double perovskites Ba{sub 2}Sr{sub 1-} {sub x} Ca {sub x} WO{sub 6} have been studied by the profile analysis of X-ray diffraction data. The end members, Ba{sub 2}SrWO{sub 6} and Ba{sub 2}CaWO{sub 6}, have the space group I2/m (tilt system a {sup 0} b {sup -} b {sup -}) and Fm3-barm (tilt system a {sup 0} a {sup 0} a {sup 0}), respectively. By increasing the Ca concentration, the monoclinic structure transforms to the cubic one via the rhombohedral R3-bar phase (tilt system a {sup -} a {sup -} a {sup -}) instead of the tetragonal I4/m phase (tilt system a {sup 0} a {sup 0} c {sup -}). This observation supports the idea that the rhombohedral structure is favoured by increasing the covalency of the octahedral cations in Ba{sub 2} MM'O{sub 6}-type double perovskites, and disagrees with a recent proposal that the formation of the {pi}-bonding, e.g., d {sup 0}-ion, determines the tetragonal symmetry in preference to the rhombohedral one. - Graphical abstract: Enlarged sections showing the evolution of the basic (222) and (400) reflections in Ba{sub 2}Sr{sub 1-} {sub x} Ca {sub x} WO{sub 6}. Tick marks below are the positions of Bragg's reflections calculated using the space groups I2/m (x=0), R3-bar (x=0.25, 0.5 and 0.75) and Fm3-barm (x=1), respectively.

  2. Effect of manganese doping of BaSrTiO{sub 3} on diffusion and domain wall pinning

    SciTech Connect

    Nadaud, Kevin Borderon, Caroline Renoud, Raphaël; Gundel, Hartmut W.

    2015-02-28

    In the present paper, the influence of manganese doping on the dielectric properties of BaSrTiO{sub 3} thin films is presented. The real and imaginary parts of the material's permittivity have been measured in a large frequency range (100 Hz–1 MHz) and as a function of the electric field. The tunability and the figure of merit of the material have been obtained from the measurement of the permittivity under an applied DC bias electric field. For the undoped material, the dielectric losses become important for a large DC bias which leads to breakdown. At a suitable dopant rate, this effect disappears. In order to better understand the origin of the related phenomena, we measure the permittivity as a function of the AC excitation amplitude and we decompose the obtained permittivity with the hyperbolic law. This enables to extract the different contributions of the bulk (low frequency diffusion and high frequency lattice relaxation) and of the domain wall motions (vibration and pinning/unpinning) to the material's dielectric permittivity and to understand the effect of manganese doping on each contribution. Knowledge of the related mechanisms allows us to establish the optimum dopant rate (mainly conditioned by the lattice contribution) and to reduce the domain wall motion, which finally is beneficial for the desired properties of the ferroelectric thin film. A particular attention is paid to low frequency diffusion, an especially harmful effect when a DC biasing is mandatory (tunable electronic component in mobile telecommunication devices for example)

  3. [Spectroscopic properties of Er3+ : Ba0.65Sr0.35TiO nanopowders].

    PubMed

    Wu, Ji-qing; Zhang, Tian-jin; Wang, Jing-yang; Yu, Lin; Pan, Rui-kun

    2010-11-01

    Ba0.65Sr0.35TiO2 (BST) nanopowders doped with Er3+ were prepared by sol-gel method. The absorption spectrum and photoluminescence (PL) spectrum of Er3+ : BST nanopowders was measured at room temperature. Based on the Judd-Ofelt theory, the intensity parameters of Er3+ in BST nanopowders were determined, omega2 = 0.993 x 10(-20) cm2, omega4 = 1.665 x 10(-20) cm2 and omega = 0.540 x 10(-20) cm2, and then the values of the line strengths, radiative transition probabilities and branching ratios of Er3+ were calculated. According to the PL spectrum, the emission bands centered at about 522, 545, 654 and 851 nm corresponding to 2H(11/2)-->4S(3/2-->4I(15/2), 4F(9/2)-->4I(15/2), and 4S(3/2-->4I(13/2) transition were observed, and the emission properties were also discussed. The results show that the Er3+ : BST nanomaterials are prospective candidates for applications in new photoelectric devices.

  4. Redetermination of the structure of ALa2WO7 (A=Ba, Sr) with fluorite-like metal ordering

    NASA Astrophysics Data System (ADS)

    Fu, W. T.; IJdo, D. J. W.; Bontenbal, A.

    2013-05-01

    The crystal structures of ALa2WO7 (A=Ba, and Sr) at room temperature were re-determined by the Rietveld method using the combined X-ray and neutron powder diffraction data. The compounds are confirmed to be isomorphic, crystallizing in the space group P1121/b. In ALa2WO7 the ordering of metal atoms is fluorite-like, but it differs from that of the fluorite-defect compounds of the formula Ln3MO7 (Ln=lanthanide or Y, M=pentavalent metal). The structure of ALa2WO7 consists of isolated WO6 octahedra, whereas in the normal Ln3MO7 the MO6 octahedra share corners forming one-dimensional chains. Although ALa2WO7 has a centric space group, La ions are not situate at the centre of symmetry, which explains the 5D0→7F2 transition being dominant in emission spectrum of Eu-doped materials.

  5. Effect of manganese doping of BaSrTiO3 on diffusion and domain wall pinning

    NASA Astrophysics Data System (ADS)

    Nadaud, Kevin; Borderon, Caroline; Renoud, Raphaël; Gundel, Hartmut W.

    2015-02-01

    In the present paper, the influence of manganese doping on the dielectric properties of BaSrTiO3 thin films is presented. The real and imaginary parts of the material's permittivity have been measured in a large frequency range (100 Hz-1 MHz) and as a function of the electric field. The tunability and the figure of merit of the material have been obtained from the measurement of the permittivity under an applied DC bias electric field. For the undoped material, the dielectric losses become important for a large DC bias which leads to breakdown. At a suitable dopant rate, this effect disappears. In order to better understand the origin of the related phenomena, we measure the permittivity as a function of the AC excitation amplitude and we decompose the obtained permittivity with the hyperbolic law. This enables to extract the different contributions of the bulk (low frequency diffusion and high frequency lattice relaxation) and of the domain wall motions (vibration and pinning/unpinning) to the material's dielectric permittivity and to understand the effect of manganese doping on each contribution. Knowledge of the related mechanisms allows us to establish the optimum dopant rate (mainly conditioned by the lattice contribution) and to reduce the domain wall motion, which finally is beneficial for the desired properties of the ferroelectric thin film. A particular attention is paid to low frequency diffusion, an especially harmful effect when a DC biasing is mandatory (tunable electronic component in mobile telecommunication devices for example).

  6. Effect of cations on methane adsorption by NaY, MgY, CaY, SrY, and BaY zeolites

    SciTech Connect

    Talu, O.; Zhang, S.Y.; Hayhurst, D.T. )

    1993-12-09

    Methane isotherms on NaY, MgY, CaY, SrY, and BaY zeolites are measured between 25 and 70[degree]C and upto 6760 kPa. All isotherms are of type I. The initial heat of adsorption for divalent cationic forms decreased with decreasing charge density (CaY > MgY > SrY > BaY) except for MgY. Similar anamoly was observed for methane adsorption on MgX (Zhang, S. Y.; Talu, O.; Hayhurst, D. T. J. Phys. Chem. 1991, 95, 1722) and it is attributed to incomplete dehydration (activation) at normal activation temperatures. The cation type significantly affected adsorption properties even at loadings as high as 7.5 molecules/cavity. CaY has the largest capacity per weight, but the methane pore density decreased in order of decreasing cationic size (BaY > SrY > CaY > MgY > NaY) at 25[degrees]C and 5200 kPa fugacity. This unexpected result is attributed to possible differences in molecular packing around the cations at high loadings. The data were satisfactorily correlated by the virial isotherm model. 29 refs., 6 figs., 3 tabs.

  7. Characteristics of quenched Y-Ba-Cu-O thin films on SrTiO/sub 3/ (100),(110) grown by organometallic chemical vapor deposition

    SciTech Connect

    Tsuruoka, T.; Takahashi, H.; Kawasaki, R.; Kanamori, T.

    1989-05-01

    A thin Y-Ba-Cu-O film was formed by the organometallic chemical vapor deposition (OMCVD) method. The substrates used were (100) and (110) SrTiO/sub 3/. After forming Y-Ba-Cu-O at 800 /sup 0/C, it was cooled at a rate of 100 /sup 0/C/min in O/sub 2/ under 1 atm. This film was c-axis oriented, with its (001) surface grown in parallel to the (100) surface of SrTiO/sub 3/ and T/sub c/ = 88 K. The (110) surface of Y-Ba-Cu-O was grown in parallel to the substrate crystal and T/sub c/ = 84 K on the (110) surface of SrTiO/sub 3/. After forming, these films were quenched in air from 800 /sup 0/C to room temperature. The change in resistance of the quenched sample with temperature was metallic, T/sub onset/ = 75 K, and T/sub c/ = 60 K.

  8. Band-gap tuning and magnetic properties of heterovalent ions (Ba, Sr and Ca) substituted BiFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Chauhan, Sunil; Kumar, Manoj; Katyal, S. C.

    2016-05-01

    A Comparative study of heterovalent Ba, Sr and Ca ions substitution on the structural, vibrational, optical and magnetic properties of BiFeO3 nanoparticles was carried out. The distorted rhombohedral structure was confirmed from both X-ray diffraction and Raman spectroscopy techniques in pure BiFeO3 and Bi0.85A0.15FeO3 (A= Ba, Sr and Ca) samples. UV-Visible spectroscopy results show that the band-gap of BiFeO3 nanoparticles can be tuned by heterovalent ions substitution from 2.12 eV for BiFeO3 to 2.10, 2.06 and 2.03 eV for Ca, Sr and Ba substituted BiFeO3 nanoparticles respectively. The magnetic measurements indicate enhancement in magnetization for heterovalent A2+ substituted BiFeO3 samples and the magnetization increases with increase of ionic radius of the substituted ions.

  9. Self-consistent (DFT + U) study of electronic, structural and magnetic properties in A2NiMoO6 (A = Ba, Sr) compounds

    NASA Astrophysics Data System (ADS)

    Aharbil, Y.; Labrim, H.; Benmokhtar, S.; Ait Haddouch, M.; Bahmad, L.; Laanab, L.

    2016-08-01

    This work aims to study the double perovskites A2NiMoO6 (A = Ba, Sr) by using the first principle calculation, within the framework of the self-consistent Hubbard correction. The value of this correction, for Ni and Mo depends strongly on the type of the studied compounds. Such values are determinate as 7.35 eV for Ni and 5.42 eV for Mo in the compound Ba2NiMoO6, whereas in the case of Sr2NiMoO6 the calculated values are 8.71 eV and 5.48 eV for Ni and Mo compound respectively. Based on the densities of state calculation we show that both the compounds are semiconductors with gap energies of 2.20 eV and 2.10 eV for Ba2NiMoO6 for Sr2NiMoO6, respectively. The total energies comparison shows clearly that the ground state is G-type anti-ferromagnetic order in agreement with experimental results, the magnetic interactions are due to the super-exchange mechanism acting in long range via hybridization throw Ni-O-Mo-O-Ni path.

  10. Synthesis of MSnO{sub 3} (M = Ba, Sr) nanoparticles by reverse micelle method and particle size distribution analysis by whole powder pattern modeling

    SciTech Connect

    Ahmed, Jahangeer; Blakely, Colin K.; Bruno, Shaun R.; Poltavets, Viktor V.

    2012-09-15

    Highlights: ► BaSnO{sub 3} and SrSnO{sub 3} nanoparticles synthesized using the reverse micelle method. ► Particle size and size distribution studied by whole powder pattern modeling. ► Nanoparticles are of optimal size for investigation in dye-sensitized solar cells. -- Abstract: Light-to-electricity conversion efficiency in dye-sensitized solar cells critically depends not only on the dye molecule, semiconducting material and redox shuttle selection but also on the particle size and particle size distribution of the semiconducting photoanode. In this study, nanocrystalline BaSnO{sub 3} and SrSnO{sub 3} particles have been synthesized using the microemulsion method. Particle size distribution was studied by whole powder pattern modeling which confirmed narrow particle size distribution with an average size of 18.4 ± 8.3 nm for SrSnO{sub 3} and 15.8 ± 4.2 nm for BaSnO{sub 3}. These values are in close agreement with results of transmission electron microscopy. The prepared materials have optimal microstructure for successive investigation in dye-sensitized solar cells.

  11. Influence of MO/MF2 modifiers (M = Ca, Sr, Ba) on spectroscopic properties of Eu3+ ions in germanate and borate glasses

    NASA Astrophysics Data System (ADS)

    Zur, Lidia; Janek, Joanna; Pietrasik, Ewa; Sołtys, Marta; Pisarska, Joanna; Pisarski, Wojciech A.

    2016-11-01

    Series of Eu3+-doped lead-free germanate and borate glasses were synthesized. The MO glass modifiers (M = Ca, Sr or Ba) were partially or totally substituted by MF2 in chemical composition. In contrast to samples modified by CaO/CaF2 or SrO/SrF2, the germanate glass samples containing BaO and/or BaF2 are fully amorphous, while the lead-free borate glasses are fully amorphous, independently from glass modifiers. Effect of glass modifiers on spectroscopic properties of Eu3+ were systematically investigated. For that reason, excitation and emission spectra of Eu3+ ions in examined systems were registered. Based on the emission spectra, ratio of integrated luminescence intensity of the 5D0 → 7F2 transition to that of the 5D0 → 7F1 transition (R factor) was calculated. Moreover, the luminescence decay curves were collected and the luminescence lifetimes of the 5D0 excited state of Eu3+ ions were determined in function of MF2 concentration.

  12. Transparent Conducting Properties of SrSnO3 and ZnSnO3

    SciTech Connect

    Ong, Khuong P.; Fan, Xiaofeng; Subedi, Alaska; Sullivan, Michael B.; Singh, David J.

    2015-04-29

    We report optical properties of doped n-type SrSnO3 and ZnSnO3 in relation to potential application as transparent conductors. We find that the orthorhombic distortion of the perovskite structure in SrSnO3 leads to absorption in the visible as the doping level is increased. This arises from interband transitions. We find that strain tuning could modify this absorption, but does not eliminate it. On the other hand, we find that ZnSnO3 although also having a non-cubic structure, can retain excellent transparency when doped, making it a good candidate transparent conductor.

  13. Structural dependence of the photocatalytic properties of double perovskite compounds A2InTaO6 (A = Sr or Ba) doped with nickel.

    PubMed

    Lv, Meilin; Wang, Yawei; Lu, Lingwei; Wang, Ruinan; Ni, Shuang; Liu, Gang; Xu, Xiaoxiang

    2016-08-03

    The crystal structure of photocatalysts generally plays a pivotal role in controlling their electronic structure as well as catalytic performance. In this work, a series of double perovskite compounds A2InTaO6 (A = Sr or Ba) and their Ni doped counterparts were investigated with the aim of understanding how doping and structural modification will affect their photocatalytic activity. Our results show that Ni doping is effective in improving the optical absorption of these wide band gap semiconductors and accommodating the Sr cation in the A sites leads to severe structural distortion, i.e. the In(Ni)-O-Ta bond angle deviates largely from 180°. A better photocatalytic performance was observed for samples with Ni doping and Ba in the A sites. The best photocatalytic hydrogen production rate recorded was ∼293.6 μmol h(-1) for Ba2In0.9Ni0.1TaO6 under full range irradiation, corresponding to an apparent quantum efficiency of 2.75%. DFT calculations reveal the role of Ni doping by forming additional spin-polarized bands inside the intrinsic band gap of the native perovskite. The better photocatalytic activity of Ba2In0.9Ni0.1TaO6 can then be understood as a result of a reduced band gap as well as a linear In(Ni)-O-Ta bond arrangement that is favorable for the strong metal-oxygen-metal interactions.

  14. Surface organization of a DPPC monolayer on concentrated SrCl2 and ZnCl2 solutions.

    PubMed

    Adams, Ellen M; Verreault, Dominique; Jayarathne, Thilina; Cochran, Richard E; Stone, Elizabeth A; Allen, Heather C

    2016-11-30

    Transition metals are known to be enriched in organic-coated marine aerosols, but the impact these cations have on their surface properties is not well understood. Here the effect of Zn(2+) enrichment on the surface properties of a dipalmitoylphosphatidylcholine (DPPC) monolayer was investigated and compared to that of the alkaline earth metal Sr(2+), an ion not enriched in aerosols. Phase behavior of the DPPC film on concentrated aqueous solutions was probed with surface pressure-area isotherms while domain morphology was monitored with Brewster angle microscopy (BAM). Infrared reflection-absorption spectroscopy (IRRAS) and vibrational sum frequency generation (VSFG) spectroscopy were used to assess the impact of cations on the conformation and orientation of alkyl chains as well as the hydration state of the carbonyl and phosphatidylcholine (PC) moieties. Results of compression isotherms and BAM show that Zn(2+) strongly interacts with DPPC molecules, and induces condensation of the monolayer while Sr(2+) only weakly interacts with the monolayer in expanded phases. Conformational order and orientation of alkyl chains in the condensed phase are not significantly altered by either cation. IRRAS indicates that Sr(2+) has weak interactions with the PC headgroup. Zn(2+) ions cause dehydration of carbonyl groups and binds to the phosphate group in a 2 : 1 bridging complex. Findings here suggest that Sr(2+) is not enriched in aerosols because it behaves similar to a monovalent ion and only weakly interacts with the monolayer, while enrichment of Zn(2+) is due to strong binding to the lipid film.

  15. Eu(2+)-Activated Alkaline-Earth Halophosphates, M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) for NUV-LEDs: Site-Selective Crystal Field Effect.

    PubMed

    Kim, Donghyeon; Kim, Sung-Chul; Bae, Jong-Seong; Kim, Sungyun; Kim, Seung-Joo; Park, Jung-Chul

    2016-09-06

    Eu(2+)-activated M5(PO4)3X (M = Ca, Sr, Ba; X = F, Cl, Br) compounds providing different alkaline-earth metal and halide ions were successfully synthesized and characterized. The emission peak maxima of the M5(PO4)3Cl:Eu(2+) (M = Ca, Sr, Ba) compounds were blue-shifted from Ca to Ba (454 nm for Ca, 444 nm for Sr, and 434 nm for Ba), and those of the Sr5(PO4)3X:Eu(2+) (X = F, Cl, Br) compounds were red-shifted along the series of halides, F → Cl → Br (437 nm for F, 444 nm for Cl, and 448 nm for Br). The site selectivity and occupancy of the activator ions (Eu(2+)) in the M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) crystal lattices were estimated based on theoretical calculation of the 5d → 4f transition energies of Eu(2+) using LCAO. In combination with the photoluminescence measurements and theoretical calculation, it was elucidated that the Eu(2+) ions preferably enter the fully oxygen-coordinated sites in the M5(PO4)3X:Eu(2+) (M = Ca, Sr, Ba; X = F, Cl, Br) compounds. This trend can be well explained by "Pauling's rules". These compounds may provide a platform for modeling a new phosphor and application in the solid-state lighting field.

  16. Low temperature preparation of nanocrystalline Sr{sub 0.5}Ba{sub 0.5}Nb{sub 2}O{sub 6} powders using an aqueous organic gel route

    SciTech Connect

    Li Yao; Zhao Jiupeng; Wang Biao

    2004-03-01

    Nano-sized Sr{sub 0.5}Ba{sub 0.5}Nb{sub 2}O{sub 6} (SBN50) ceramic powders have been synthesized by an aqueous organic gel route. Homogeneous Sr-Ba-Nb precursor gels are prepared with Ba-EDTA, Sr-EDTA, and Nb-citrate complex as source of Sr, Ba, and Nb, respectively. Citric acid and ethylenediaminetetraacetic acid (EDTA) were used as the chelating agents. The structural variation of the SBN powder with annealing temperature was studied by TG-DTA, FT-IR and XRD. The precursor gel on calcination at 800 deg. C for 2 h produces a pure tungsten bronze SBN phase and the corresponding average particle size is 30-50 nm. The influences of the pH and the molar ratio of citric acid:Nb cation on the formation of homogeneous Sr-Ba-Nb precursor gels were also studied. The results show that a homogeneous Sr-Ba-Nb precursor gel with no precipitate is formed at pH 8 and the optimum molar ratio of citric acid and the metal cations is 3:1.

  17. Design of a new family of inorganic compounds Ae2F2SnX3 (Ae = Sr, Ba; X = S, Se) using rock salt and fluorite 2D building blocks.

    PubMed

    Kabbour, Houria; Cario, Laurent; Danot, Michel; Meerschaut, Alain

    2006-01-23

    We could predict the structure of a new family of compounds Ae(2)F(2)SnX(3) (Ae = Sr, Ba; X = S, Se) from the stacking of known 2D building blocks of the rock salt and fluorite types. With a high-temperature ceramic method we have then succeeded to synthesize the four compounds Ba(2)F(2)SnS(3), Ba(2)F(2)SnSe(3), Sr(2)F(2)SnS(3), and Sr(2)F(2)SnSe(3). The structure refinements from X-ray powder diffraction patterns have confirmed the structure predictions and showed their good accuracy. The structure of the four compounds results from the alternated stacking of fluorite [Ae(2)F(2)] (Ae = Sr, Ba) and distorted rock salt [SnX(3)] (X = S, Se) 2D building blocks. As shown by band structure calculations, these blocks behave as a charge reservoir and a charge acceptor, respectively. Sr(2)F(2)SnS(3) and Ba(2)F(2)SnS(3) are transparent with optical gaps of 3.06 and 3.21 eV, respectively. However, an attempt to obtain a transparent conductor by substituting Ba per La in Ba(2)F(2)SnS(3) was unsuccessful.

  18. Microstructural and dielectric properties of Ba0.6Sr0.4Ti1-xZrxO3 based combinatorial thin film capacitors library

    NASA Astrophysics Data System (ADS)

    Liu, Guozhen; Wolfman, Jérôme; Autret-Lambert, Cécile; Sakai, Joe; Roger, Sylvain; Gervais, Monique; Gervais, François

    2010-12-01

    Epitaxial growth of Ba0.6Sr0.4Ti1-xZrxO3 (0≤x≤0.3) composition spread thin film library on SrRuO3/SrTiO3 layer by combinatorial pulsed laser deposition (PLD) is reported. X-ray diffraction and energy dispersive x-ray spectroscopy studies showed an accurate control of the film phase and composition by combinatorial PLD. A complex evolution of the microstructure and morphology with composition of the library is described, resulting from the interplay between epitaxial stress, increased chemical pressure, and reduced elastic energy upon Zr doping. Statistical and temperature-related capacitive measurements across the library showed unexpected variations in the dielectric properties. Doping windows with enhanced permittivity and tunability are identified, and correlated to microstructural properties.

  19. Noncollinear magnetic order in the S=(1)/(2) magnet Sr3ZnRhO6

    NASA Astrophysics Data System (ADS)

    Hillier, A. D.; Adroja, D. T.; Kockelmann, W.; Chapon, L. C.; Rayaprol, S.; Manuel, P.; Michor, H.; Sampathkumaran, E. V.

    2011-01-01

    The compound Sr3ZnRhO6 with S=1/2 belongs to a family of pseudo-one-dimensional (1D) spin-chain systems with general formula A3A'BO6. The nature of the ground state of Sr3ZnRhO6 is investigated using microscopic techniques such as muon spin relaxation (μSR) and powder neutron diffraction in addition to bulk characterization using magnetization, ac-susceptibility, and heat capacity. Our μSR study clearly reveals the presence of three frequencies, below 16 K, whose temperature dependence follow a mean-field order parameter indicating long-range magnetic ordering of the Rh4+ moment. Powder neutron diffraction reveals the presence of four weak magnetic Bragg peaks below 16 K, indexed by the propagation vector k=(0,(1)/(2),1) in the hexagonal setting of the space group R3̲c. Analysis of the magnetic diffraction pattern constrained to symmetry-adapted magnetic modes reveals a noncollinear magnetic structure with an ordered magnetic moment of Rh4+=0.7(1) μB. This is the first compound in this spin chain family which exhibits noncollinear magnetic order with the moment tilting away from the c axis, highlighting the important role of interchain and intrachain interactions.

  20. Preparation and electromagnetic properties of Polyaniline(polypyrrole)-BaFe12O19/Ni0.8Zn0.2Fe2O4 ferrite nanocomposites

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Huang, Ying; Wang, Qiufen; He, Qian; Chen, Lin

    2012-10-01

    The nanocomposite of hard (BaFe12O19)/soft ferrite (Ni0.8Zn0.2 Fe2O4) was prepared by the sol-gel process, and then the polyaniline(PANI)/polypyrrole(PPY)-BaFe12O19/Ni0.8Zn0.2Fe2O4 was produced by in situ polymerization method. The structures, morphology and electromagnetic properties of the samples were characterized by various instruments. XRD, TEM, and FTIR analysis indicated that BaFe12O19/Ni0.8Zn0.2Fe2O4 ferrite were homogenously enwrapped by PANI(PPY) coating. The VSM and SDY-4 measurement show that the magnetic properties of the composites decreased with the increase in PANI(PPY) amount, However, the electrical conductivity is on the contrary. The electromagnetic properties of the composites were much better than BaFe12O19/Ni0.8Zn0.2Fe2O4 in the frequency range of 2-15 GHz, which mainly depends on the dielectric loss of PANI(PPY). A minimum reflection loss of the PANI(PPY)-BaFe12O19/Ni0.8Zn0.2Fe2O4 ferrite nanocomposite is -19.7 dB(-21.5 dB) at the frequency of 7.3 GHz (10.7 GHz).

  1. First-Principles Study of the Structural, Optical, Dynamical and Thermodynamic Properties of BaZnO2 Under Pressure

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Xian; Hu, Cui-E.; Chen, Yang-Mei; Cheng, Yan; Ji, Guang-Fu

    2016-11-01

    The structural, optical, dynamical, and thermodynamic properties of BaZnO2 under pressure are studied based on the density functional theory. The calculated structural parameters are consistent with the available experimental data. In the ground state, the electronic band structure and density of states indicate that BaZnO2 is an insulator with a direct gap of 2.2 eV. The Mulliken charges are also analyzed to characterize the bonding property. After the structural relaxation, the optical properties are studied. It is found that the dielectric function of E Vert x and EVert y are isotropic, whereas the EVert x and EVert z are anisotropic. The effect of pressure on the energy-loss function in the ultraviolet region becomes more obvious as the pressure increases. Furthermore, the dynamical properties under different pressures are investigated using the finite displacement method. We find that the P3121 phase of BaZnO2 is dynamically stable under the pressure ranging from 0 GPa to 30 GPa. The phonon dispersion curves, phonon density of states, vibrational modes and atoms that contribute to these vibrations at {{\\varvec{Γ }}} point under different pressures are also reported in this work. Finally, by employing the quasi-harmonic approximation, the thermodynamic properties such as the temperature dependence of the thermal expansion coefficient, specific heat, entropy and Gibbs free energy under different pressures are investigated. It is found that the influences of the temperature on the heat capacity are much more significant than that of the pressure on it.

  2. Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: a combined light scattering and ASAXS study.

    PubMed

    Schweins, R; Goerigk, G; Huber, K

    2006-10-01

    Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations Ca(2+), Sr(2+) and Ba(2+). Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl(2)]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca(2+), Sr(2+) and Ba(2+). Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The Sr(2+) scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [ SrCl(2)]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.

  3. Comparative Investigation on the Photocatalytic Degradation of 2,4,6-Trichlorophenol Using Pure and M-Doped (M = Ba, Ce, Mg) ZnO Spherical Nanoparticles.

    PubMed

    Selvam, N Clament Sagaya; Jesudoss, S K; Rajan, P Iyyappa; Kennedy, L John; Vijaya, J Judith

    2015-08-01

    Pure and M-doped (Ba, Ce, Mg) ZnO spherical nanoparticles are synthesized by a simple low temperature co-precipitation method, and were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), and high resolution transmission electron microscopy (HR-TEM). The XRD results showed the formation of single phase ZnO with wurtzite crystal structure and the electron microscopic studies supported the validity for the formation of pure and M-doped (Ba, Ce, Mg) ZnO spherical nanoparticles. Photocatalytic degradation (PCD) of 2,4,6-trichlorophenol, a potent endocrine disrupting chemical in aqueous medium was investigated by both pure and M-doped (Ba, Ce, Mg) ZnO spherical nanoparticles under UV-light irradiation. The influence of the metal dopants on the structure and photocatalytic (PC) activity of ZnO was investigated systematically. Furthermore, the effect of different parameters such as 2,4,6-trichlorophenol concentration, photocatalyst amount, pH and dopant wt% on the resulting PC activity was investigated. The kinetics of the photocatalytic degradation of 2,4,6-trichlorophenol was found to follow the pseudo-first order reaction, and it was established that Ba-doped ZnO is photocatalytically more active than the other photocatalysts.

  4. Cytocompatibility and early inflammatory response of human endothelial cells in direct culture with Mg-Zn-Sr alloys.

    PubMed

    Cipriano, Aaron F; Sallee, Amy; Tayoba, Myla; Cortez Alcaraz, Mayra C; Lin, Alan; Guan, Ren-Guo; Zhao, Zhan-Yong; Liu, Huinan

    2017-01-15

    Crystalline Mg-Zinc (Zn)-Strontium (Sr) ternary alloys consist of elements naturally present in the human body and provide attractive mechanical and biodegradable properties for a variety of biomedical applications. The first objective of this study was to investigate the degradation and cytocompatibility of four Mg-4Zn-xSr alloys (x=0.15, 0.5, 1.0, 1.5wt%; designated as ZSr41A, B, C, and D respectively) in the direct culture with human umbilical vein endothelial cells (HUVEC) in vitro. The second objective was to investigate, for the first time, the early-stage inflammatory response in cultured HUVECs as indicated by the induction of vascular cellular adhesion molecule-1 (VCAM-1). The results showed that the 24-h in vitro degradation of the ZSr41 alloys containing a β-phase with a Zn/Sr at% ratio ∼1.5 was significantly faster than the ZSr41 alloys with Zn/Sr at% ∼1. Additionally, the adhesion density of HUVECs in the direct culture but not in direct contact with the ZSr41 alloys for up to 24h was not adversely affected by the degradation of the alloys. Importantly, neither culture media supplemented with up to 27.6mM Mg(2+) ions nor media intentionally adjusted up to alkaline pH 9 induced any detectable adverse effects on HUVEC responses. In contrast, the significantly higher, yet non-cytotoxic, Zn(2+) ion concentration from the degradation of ZSr41D alloy was likely the cause for the initially higher VCAM-1 expression on cultured HUVECs. Lastly, analysis of the HUVEC-ZSr41 interface showed near-complete absence of cell adhesion directly on the sample surface, most likely caused by either a high local alkalinity, change in surface topography, and/or surface composition. The direct culture method used in this study was proposed as a valuable tool for studying the design aspects of Zn-containing Mg-based biomaterials in vitro, in order to engineer solutions to address current shortcomings of Mg alloys for vascular device applications.

  5. One-dimensional SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers and enhancement magnetic property.

    PubMed

    Song, Fuzhan; Shen, Xiangqian; Liu, Mingquan; Xiang, Jun

    2011-08-01

    SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers of diameters about 100 nm with mass ratio 1:1 have been prepared by the electrospinning and calcination process. The SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrites are formed after calcined at 700 degrees C for 2 hours. The composite ferrite nanofibers are fabricated from nanosized Ni(0.5)Zn(0.5)Fe2O4 and SrFe12O19 ferrite grains with a uniform phase distribution. The ferrite grain size increases from about 11 to 36 nm for Ni(0.5)Zn(0.5)Fe12O4 and 24 to 56 nm for SrFe12O19 with the calcination temperature increasing from 700 to 1100 degrees C. With the ferrite grain size increasing, the coercivity (Hc) and remanence (Mr) for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers initially increase, reaching a maximum value of 118.4 kA/m and 31.5 Am2/kg at the grain size about 40 nm (SrFe12O19) and 24 nm (Ni(0.5)Zn(0.5)Fe2O4) respectively, and then show a reduction tendency with a further increase of the ferrite grain size. The specific saturation magnetization (Msh) of 63.2 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers obtained at 900 degrees C for 2 hours locates between that for the single SrFe12O19 ferrite (48.5 Am2/kg) and the single Ni(0.5)Zn(0.5)Fe2O4 ferrite (69.3 Am2/kg). In particular, the Mr value 31.5 Am2/kg for the SrFe12O19/Ni(0.5)Zn(0.5)Fe2O4 composite ferrite nanofibers is much higher than that for the individual SrFe12O19 (25.9 Am2/kg) and Ni(0.5)Zn(0.5)Fe2O4 ferrite (11.2 Am2/kg). These enhanced magnetic properties for the composite ferrite nanofibers can be attributed to the exchange-coupling interaction in the composite.

  6. Structural and optical study of γ –BIMEVOX; ME: Ba{sup 2+} and Sr{sup 2+}

    SciTech Connect

    Gupta, Sakshi Singh, K.

    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 via 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.

  7. Dual ferroic properties of hexagonal ferrite ceramics BaFe12O19 and SrFe12O19

    NASA Astrophysics Data System (ADS)

    Kostishyn, V. G.; Panina, L. V.; Timofeev, A. V.; Kozhitov, L. V.; Kovalev, A. N.; Zyuzin, A. K.

    2016-02-01

    Dual ferroic properties of a strong magnetism and large ferroelectricity have been observed in barium BaFe12O19 and strontium SrFe12O19 hexaferrite ceramics. The samples were fabricated by a modified ceramic technique from highly purified raw materials with addition of boron oxide allowing the control of grain size and enhancement of bulk resistivity. Whereas the samples of PbFe12O19 fabricated by the same technological method did not have sufficient electric resistivity to support an electric field and did not exhibit the ferroelectric properties. The structure of the samples examined by X-ray diffraction is consistent with a single hexagonal phase. The grains are randomly oriented with the average grain size of 300-400 nm coated with boron oxide. The magnetic properties are characterised by standard ferrimagnetic behavior with the Neel temperature of about 450 °C. Large spontaneous polarization was observed with the maximal values of 45-50 μC/cm2 under an applied electric field of 100-300 kV/m. A strong coupling between magnetic and electric ordering was confirmed by measuring the magnetoelectric (ME) parameter and magnetodielectric ratio. These ME characteristics are more advanced than those for well-known room temperature multiferroic BiFeO3. Furthermore, by applying an electric field, the manipulation of magnetization in the range of up to 9% was observed, which is even greater than in some substituted hexaferrites with a non-collinear magnetic structure. The obtained results on electrical polarization are similar to the values reported for the corresponding hexaferrites sintered by polymer precursor technique. This suggests a promising potential of M-type hexaferrite ceramics in devices utilizing magnetoelectric coupling.

  8. The temperature dependence of magnetic properties of Zn-Ti substituted Ba-ferrite particles for magnetic recording

    NASA Astrophysics Data System (ADS)

    Wei, Fulin; Lu, Mai; Yang, Zheng

    1999-01-01

    It was shown that the morphological and magnetic properties of Zn-Ti doped Ba-ferrite particles are suitable for magnetic recording. In order to clarify the temperature dependence of the magnetic properties of these particles, BaFe 10.8-2 xZn xTi xO 19 particles with the nominal composition x=0.0-0.50 were prepared by synthesis from salt melts. The saturation magnetization Ms, magnetic anisotropy field HA and magnetocrystalline anisotropy constant K1 of the above-mentioned particle assemblies were estimated by using the law of approach to saturation of polycrystalline ferrite, and the Curie temperature Tc was determined by the thermodynamic relation. With an increasing x, the Tc decreased, while the lattice parameters a, c and M s have an unnoticeable maximum at x=0.20. The Hc( T) curves of samples with different x show that all particles have positive temperature coefficient in the vicinity of room temperature, which decreases with increasing x. The Ms( T), H A(T) and K 1(T) were determined and discussed.

  9. Internal electrical and strain fields influence on the electrical tunability of epitaxial Ba0.7Sr0.3TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Bagdzevicius, S.; Mackeviciute, R.; Ivanov, M.; Fraygola, B.; Sandu, C. S.; Setter, N.; Banys, J.

    2016-03-01

    Perpetual demand for higher transfer speed and ever increasing miniaturization of radio and microwave telecommunication devices demands new materials with high electrical tunability. We have investigated built in electrical and strain fields' influence on the electrical tunability in Ba0.7Sr0.3TiO3 thin film hetero-system grown by pulsed laser deposition technique. We observed the built in electrical field by local piezo-force microscopy (as deflected hysteresis loops) and macroscopic impedance analysis (as asymmetric tunability curves), with the calculated 88 kV/cm built in field at room temperature. Negative -1.4% misfit strain (due to clamping by the substrate) enhanced ferroelectric phase transition temperature in Ba0.7Sr0.3TiO3 thin film by more than 300 K. Built in fields do not deteriorate functional film properties—dielectric permittivity and tunability are comparable to the best to date values observed in Ba1-xSrxTiO3 thin films.

  10. Synthesis of high intensity green emitting (Ba,Sr)SiO4:Eu2+ phosphors through cellulose assisted liquid phase precursor process

    NASA Astrophysics Data System (ADS)

    Humayoun, Usama Bin; Song, Young-Hyun; Lee, MinJi; Masato, Kakihana; Abe, Hiroshi; Toda, Kenji; Sato, Yasushi; Masaki, Takaki; Yoon, Dae-Ho

    2016-01-01

    Green emitting phosphor (Ba1-x,Sr1-x)SiO4:2xEu2+, x = 0.03, 0.05, 0.1, and 0.15 were synthesized through a Liquid Phase Precursor Process (LPP). Liquid phase precursor method is reported to result in phosphors with markedly increased emission intensities compared to other synthesis methods. Here microcrystalline cellulose (MCC) and hydroxypropyl cellulose (HPC) templates were studied to achieve high efficiency green phosphors. The phase formation was investigated by XRD analysis which showed the conformation of the Ba2SiO4 (JCPDS card number 761631) phase. The obtained samples exhibited broad excitation spectra with maximum at 430 nm and a green emission centered around 520 nm. An optimized dopant concentration was selected and the effect of two different types of cellulose, i.e. MCC and HPC templates on the emission properties was considered. It was found that the samples synthesized using HPC and fired at 1050 °C under a reducing atmosphere, showed a high intensity of almost 2 times that of the MCC sample. Further experiments were conducted by varying viscosity, particle weight, and molecular weight of the HPC template. It was found that the green emission from the (Ba,Sr)SiO4:Eu2+ increased with the increase in viscosity and molecular weight of the template.

  11. Interfacial dislocations in (111) oriented (Ba0.7Sr0.3)TiO3 films on SrTiO3 single crystal

    SciTech Connect

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; Kamo, Takafumi; Funakubo, Hiroshi; Wu, Di; Xin, Huolin L.; Su, Dong

    2015-10-08

    In this study, we have investigated the interfacial structure of epitaxial (Ba,Sr)TiO3 films grown on (111)-oriented SrTiO3 single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a<110> comprised of a misfit dislocation along <112>, and threading dislocations along <110> or <100>. The misfit dislocation with Burgers vector of a <110> can dissociate into two ½ a <110> partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography, we retrieved the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba0.7Sr0.3)TiO3 films.

  12. Influences of alkaline earth metal substitution on the crystal structure and physical properties of magnetic RuSr1.9A0.1GdCu2O8 (A = Ca, Sr, and Ba) superconductors.

    PubMed

    Hur, Su Gil; Park, Dae Hoon; Hwang, Seong-Ju; Kim, Seung Joo; Lee, J H; Lee, Sang Young

    2005-11-24

    We have investigated the effect of alkaline earth metal substitution on the crystal structure and physical properties of magnetic superconductors RuSr(1.9)A(0.1)GdCu(2)O(8) (A = Ca, Sr, and Ba) in order to probe an interaction between the magnetic coupling of the RuO(2) layer and the superconductivity of the CuO(2) layer. X-ray diffraction and X-ray absorption spectroscopic analyses demonstrate that the isovalent substitution of Sr ions with Ca or Ba ions makes it possible to tune the interlayer distance between the CuO(2) and the RuO(2) layers. From the measurements of electrical resistance and magnetic susceptibility, it was found that, in contrast to negligible change of magnetization, both of the alkaline earth metal substitutions lead to a notable depression of zero-resistance temperature T(c) (DeltaT(c) approximately 17-19 K). On the basis of the absence of a systematic correlation between the T(c) and the interlayer distance/magnetization, we have concluded that the internal magnetic field of the RuO(2) layer has insignificant influence on the superconducting property of the CuO(2) layer in the ruthenocuprate.

  13. The structural and in-plane dielectric/ferroelectric properties of the epitaxial (Ba, Sr)(Zr, Ti)O{sub 3} thin films

    SciTech Connect

    Chan, N. Y. Wang, Y.; Chan, H. L. W.; Wang, D. Y.; Dai, J. Y.

    2014-06-21

    Epitaxial (Ba{sub 1-x}Sr{sub x})(Zr{sub 0.1}Ti{sub 0.9})O{sub 3} (BSZT, x = 0 – 0.45) thin films were deposited on (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.35} (LSAT) substrates by pulsed laser deposition. The experimental results demonstrate that the structural, dielectric, and ferroelectric properties of the BSZT thin films were greatly dependent on the strontium content. The BSZT thin films transformed from tetragonal to cubic phase when x ≥ 0.35 at room temperature. The Curie temperature and room-temperature remnant polarization decrease with increasing strontium concentration. The optimal dielectric properties were found in (Ba{sub 0.55}Sr{sub 0.45})(Zr{sub 0.1}Ti{sub 0.9})O{sub 3} thin films which is in paraelectric state, having tunability of 47% and loss tangent of 0.0338 under an electric field of 20 MV/m at 1 MHz. This suggests that BSZT thin film is a promising candidate for tunable microwave device applications.

  14. Syntheses, crystal structure and physical properties of new Zintl phases Ba{sub 3}T{sub 2}As{sub 4} (T=Zn, Cd)

    SciTech Connect

    Wang, Jian; Xia, Sheng-Qing; Tao, Xu-Tang

    2013-02-15

    Through high temperature Pb-flux reactions, two new arsenide Zintl compounds, Ba{sub 3}Zn{sub 2}As{sub 4} and Ba{sub 3}Cd{sub 2}As{sub 4}, were successfully obtained and their structures were accurately determined with Single-Crystal X-ray Diffraction. Both compounds are isotypic to Ba{sub 3}Cd{sub 2}Sb{sub 4} and crystallize in the monoclinic space group C2/m (No=12) with cell parameters of a=16.916(4)/17.089(3) A, b=4.497(1)/4.6076(7) A, c=7.225(2)/7.304(1) A and {beta}=113.147(2)/112.312(1) Degree-Sign for Ba{sub 3}Zn{sub 2}As{sub 4} and Ba{sub 3}Cd{sub 2}As{sub 4}, respectively. Electrical resistivity measurement on Ba{sub 3}Cd{sub 2}As{sub 4} reveals semiconducting behavior between 10 and 100 K, which results in a very small band gap of 0.01 eV. According to TG/DSC analyses, Ba{sub 3}Cd{sub 2}As{sub 4} exhibits good thermal stability and does not decompose below 950 K. - Graphic abstract: A polyhedral view of the crystal structure for Ba{sub 3}T{sub 2}As{sub 4} (T=Zn or Cd) in which Ba and As atoms are plotted as purple and red spheres, respectively. Highlights: Black-Right-Pointing-Pointer Two new ternary Zintl compounds, Ba{sub 3}Zn{sub 2}As4 and Ba{sub 3}Cd{sub 2}As{sub 4}, have been synthesized. Black-Right-Pointing-Pointer Their structure features polyanionic layers constructed through [MAs{sub 4}] tetrahedra. Black-Right-Pointing-Pointer Ba{sub 3}Cd{sub 2}As{sub 4} has a very narrow band gap of 0.01 eV and are thermally stable up to 950 K.

  15. Investigation of Carbon ion-implanted waveguides in tungsten bronze (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 single crystal

    NASA Astrophysics Data System (ADS)

    Jiao, Yang; Wang, Chuan-Kui; Li, Zong-Liang; Ren, Ying-Ying

    2014-09-01

    Planar optical waveguides were fabricated in (Ca0.28Ba0.72)0.25(Sr0.6Ba0.4)0.75Nb2O6 (CSBN25) crystal by 6.0-MeV C+ ion implantation with fluences of 2, 4 and 6 × 1014 ions/cm2 at room temperature. The mode parameters, refractive indices profiles are measured and the refractive indices behavior in the waveguide region is discussed. The shape of nuclear energy loss distribution of the C+ implantation was similar to those of the waveguide refractive index profiles, which means an inherent relationship between the waveguide formation and the energetic energy deposition. The extraordinary refractive index has a small positive change in the surface region after the implantation.

  16. Microwave Dielectric Properties of ZnNb2O6-SrTiO3 Stacked Resonators

    NASA Astrophysics Data System (ADS)

    Liou, Yi-Cheng; Wu, Yi-Cheng

    2017-04-01

    Microwave dielectric properties of ZnNb2O6-SrTiO3 (ZN/ST) stacked resonators were investigated. ZN/ST stacked resonators with a zero τ f have been obtained by adjusting the volume percentage of ST. Resonant frequency decreased from 9.27 GHz for 8.57% ST to 4.94 GHz for 27.27% ST. ɛ r increased from 24.6 for 8.57% ST to 66.2 for 27.27% ST. Q × f rapidly decreased from 48,230 GHz for 8.57% ST to 7798 GHz for 15.79% ST and then 962 GHz for 27.27% ST. A temperature-stable ZN/ST stacked resonator with τ f = 0 ppm/°C was obtained for 8.57% ST. τ f increased to 678 ppm/°C for 27.27% ST. Dielectric properties: ɛ r = 24.6, Q × f = 48,230 GHz and τ f = 0 ppm/°C are obtained for a ZN/ST stacked resonator with 8.57% ST.

  17. Sr0.95Zn0.05Se:Eu2+ and CdSe/ZnS nanocrystals hybrid phosphors for enhancing color rendering index of white light emitting diode.

    PubMed

    Chung, Wonkeun; Jung, Hyunchul; Lee, Chang Hun; Kim, Sung Hyun

    2012-07-01

    In this study, the yellow emitting cubic structure of Sr0.95Zn0.05Se:Eu2+ phosphors were prepared by high temperature solid state reaction. The Sr0.95Zn0.05Se:Eu2+ phosphors exhibited strong excitation intensity under 400-460 nm region, and broad band emission appeared at around 545-600 nm due to the d-f transition of Eu2+. To enhance the red emission, HDA/TOP/TOPO capped CdSe/ZnS NCs were synthesized via fast nucleation and slow growth method. The narrow emission peak was located at 615 nm with 69% of high quantum yield. Bright white emission was generated by combining a 460 nm InGaN LED chip with CdSe/ZnS NCs and Sr0.95Zn0.05Se:Eu2+ hybrid phosphors. The fabricated white LEDs showed warm white light with acceptable CIE chromaticity coordinate variation from (0.343, 0.255) at 20 mA to (0.335, 0.250) at 50 mA. The addition of CdSe/ZnS NCs contributed to the extension of white light spectrum by supplement of the red region. The color rendering index was largely enhanced from 41.7 to 79.7 compared to the Sr0.95Zn0.05Se:Eu2+ based phosphors white LED.

  18. Extraordinary role of Ce-Ni elements on the electrical and magnetic properties of Sr-Ba M-type hexaferrites

    SciTech Connect

    Iqbal, Muhammad Javed; Farooq, Saima

    2009-11-15

    The structural, electrical and magnetic behavior of Sr{sub 0.5}Ba{sub 0.5-x}Ce{sub x}Fe{sub 12-y}Ni{sub y}O{sub 19} (where x = 0.00-0.10; y = 0.00-1.00) hexaferrite nanomaterials are reported in this paper. The structural analysis indicates that the Ce-Ni doped Sr-Ba M-type hexaferrite samples synthesized by the co-precipitation method are stoichiometric, single magnetoplumbite phase with crystallite sizes in the range of 35-48 nm. The dc-electrical resistivity of the pure Sr-Ba hexaferrite is enhanced to almost 10{sup 2} times by doping with Ce-Ni contents of x = 0.06; y = 0.60. The dielectric constant and dielectric loss tangent decrease to values {approx}14 and <0.2, respectively, by increasing the frequency up to 1 MHz. Small relaxation peaks at frequencies >10{sup 5} Hz are observed for the samples with Ce content of x > 0.06. The values of saturation magnetization increase from 66.32 to 84.33 emu/g and remanance magnetization from 42.64 to 56.01 emu/g but coercivity decreases from 2.85 to 1.59 kOe by substitution of Ce-Ni. Sharp ferri-paramagnetic transition is observed in the samples, which is confirmed by DSC results. Ce-Ni substitution acts to reduce the electron-hopping between Fe{sup 2+}/Fe{sup 3+} ions and also improves the magnetic properties. These characteristics are desirable for their possible use in microwave and chip devices.

  19. Polarization-Mediated Modulation of Electronic and Transport Properties of Hybrid MoS2-BaTiO3-SrRuO3 Tunnel Junctions.

    PubMed

    Li, Tao; Sharma, Pankaj; Lipatov, Alexey; Lee, Hyungwoo; Lee, Jung-Woo; Zhuravlev, Mikhail Y; Paudel, Tula R; Genenko, Yuri A; Eom, Chang-Beom; Tsymbal, Evgeny Y; Sinitskii, Alexander; Gruverman, Alexei

    2017-02-08

    Hybrid structures composed of ferroelectric thin films and functional two-dimensional (2D) materials may exhibit unique characteristics and reveal new phenomena due to the cross-interface coupling between their intrinsic properties. In this report, we demonstrate a symbiotic interplay between spontaneous polarization of the ultrathin BaTiO3 ferroelectric film and conductivity of the adjacent molybdenum disulfide (MoS2) layer, a 2D narrow-bandgap semiconductor. Polarization-induced modulation of the electronic properties of MoS2 results in a giant tunneling electroresistance effect in the hybrid MoS2-BaTiO3-SrRuO3 ferroelectric tunnel junctions (FTJs) with an OFF-to-ON resistance ratio as high as 10(4), a 50-fold increase in comparison with the same type of FTJs with metal electrodes. The effect stems from the reversible accumulation-depletion of the majority carriers in the MoS2 electrode in response to ferroelectric switching, which alters the barrier at the MoS2-BaTiO3 interface. Continuous tunability of resistive states realized via stable sequential domain structures in BaTiO3 adds memristive functionality to the hybrid FTJs. The use of narrow band 2D semiconductors in conjunction with ferroelectric films provides a novel pathway for development of the electronic devices with enhanced performance.

  20. An investigation of the optical properties and water splitting potential of the coloured metallic perovskites Sr{sub 1−x}Ba{sub x}MoO{sub 3}

    SciTech Connect

    Hopper, H.A.; Le, J.; Cheng, J.; Weller, T.; Marschall, R.; Bloh, J.Z.; Macphee, D.E.; Folli, A.; Mclaughlin, A.C.

    2016-02-15

    The solid solution Sr{sub 1−x}Ba{sub x}MoO{sub 3} (x=0.00, 0.025, 0.050, 0.075, 0.100 and 1.00) has been synthesised. Rietveld refinement of X-ray diffraction data shows that all materials crystallise with cubic (Pm-3m) symmetry and that a miscibility gap exists from x=0.1–1.0. The optical properties of the metallic perovskites Sr{sub 1−x}Ba{sub x}MoO{sub 3} have been investigated by a combination of UV–vis spectroscopy and density functional theory (DFT). Upon increasing x from 0 to 1 in Sr{sub 1−x}Ba{sub x}MoO{sub 3} there is a reduction in the measured band gap from 2.20 eV to 2.07 eV. The measured band gap is attributed to the electronic transition from the Mo 4d t{sub 2g} band to the e{sub g} band. The potential of SrMoO{sub 3} and BaMoO{sub 3} as water-splitting photocatalysts was explored but there was no evidence of hydrogen or oxygen evolution, even with the presence of a Pt co-catalyst. - Graphical abstract: Ultraviolet–visible absorbance spectra (converted from diffuse reflectance spectra) for SrMoO{sub 3} and BaMoO{sub 3}. - Highlights: • The solid solution Sr{sub 1-x}Ba{sub x}MoO{sub 3} has been synthesised. • A miscibility gap exists from x=0.1–1.0 in Sr{sub 1−x}Ba{sub x}MoO{sub 3.} • Upon increasing x from 0 to 1 in Sr{sub 1−x}Ba{sub x}MoO{sub 3} there is a reduction in the measured band gap from 2.20 eV to 2.07 eV. • The potential of SrMoO{sub 3} and BaMoO{sub 3} as water-splitting photocatalysts was explored but there was no evidence of hydrogen or oxygen evolution, even with the presence of a Pt co-catalyst.

  1. Interfacial charge-mediated non-volatile magnetoelectric coupling in Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 multiferroic heterostructures

    PubMed Central

    Zhou, Ziyao; Howe, Brandon M.; Liu, Ming; Nan, Tianxiang; Chen, Xing; Mahalingam, Krishnamurthy; Sun, Nian X.; Brown, Gail J.

    2015-01-01

    The central challenge in realizing non-volatile, E-field manipulation of magnetism lies in finding an energy efficient means to switch between the distinct magnetic states in a stable and reversible manner. In this work, we demonstrate using electrical polarization-induced charge screening to change the ground state of magnetic ordering in order to non-volatilely tune magnetic properties in ultra-thin Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 (001) multiferroic heterostructures. A robust, voltage-induced, non-volatile manipulation of out-of-plane magnetic anisotropy up to 40 Oe is demonstrated and confirmed by ferromagnetic resonance measurements. This discovery provides a framework for realizing charge-sensitive order parameter tuning in ultra-thin multiferroic heterostructures, demonstrating great potential for delivering compact, lightweight, reconfigurable, and energy-efficient electronic devices. PMID:25582090

  2. Sputter deposition of ZnS:Mn/SrS:Ce multilayer stacks for use as white phosphor thin film electroluminscent panels

    SciTech Connect

    Ruffner, J.A.; Tuenge, R.T.; Sun, Sey-Shing

    1995-07-01

    Sputter deposition of ZnS:Mn/SrS:Ce multilayered broad-band ``white`` emission thin film electroluminescent (TFEL) stacks has been investigated. To date, deposition of these multilayers has been limited to vacuum evaporation techniques and atomic layer epitaxy, both of which require two different substrate temperatures for growth of high quality ZnS and SrS. This repeated thermal cycling during multilayer deposition can induce stress, defects, and interdiffusion with adversely affect EL performance. Sputter deposition of ZnS and SrS produces high quality TFELs for a wider range of substrate temperatures. Both materials can be sputter deposited at a common temperature (300-350{degrees}C) which eliminates the need for thermal cycling and increases manufacturability. Luminance outputs from sputter deposited ZnS and SrS thin films are comparable to those from evaporated films, making sputtering an attractive alternative deposition technique for these materials. We report on the effects of sputter deposition parameters including chamber pressure, substrate temperature, and H2S process gas partial pressure on the resultant composition and morphology of ZnS:Mn and SrS:Ce thin films and multilayers. Their EL performance was evaluated and correlated to composition and morphology.

  3. Epitaxial Ba{sub 2}IrO{sub 4} thin-films grown on SrTiO{sub 3} substrates by pulsed laser deposition

    SciTech Connect

    Nichols, J. Korneta, O. B.; Terzic, J.; Cao, G.; Brill, J. W.; Seo, S. S. A.

    2014-03-24

    We have synthesized epitaxial Ba{sub 2}IrO{sub 4} (BIO) thin-films on SrTiO{sub 3} (001) substrates by pulsed laser deposition and studied their electronic structure by dc-transport and optical spectroscopic experiments. We have observed that BIO thin-films are insulating but close to the metal-insulator transition boundary with significantly smaller transport and optical gap energies than its sister compound, Sr{sub 2}IrO{sub 4}. Moreover, BIO thin-films have both an enhanced electronic bandwidth and electronic-correlation energy. Our results suggest that BIO thin-films have great potential for realizing the interesting physical properties predicted in layered iridates.

  4. Significant enhancement in energy density of polymer composites induced by dopamine-modified Ba0.6Sr0.4TiO3 nanofibers

    NASA Astrophysics Data System (ADS)

    Song, Yu; Shen, Yang; Hu, Penghao; Lin, Yuanhua; Li, Ming; Nan, C. W.

    2012-10-01

    Ba0.6Sr0.4TiO3 (BST) nanofibers prepared via electrospinning and modified by dopamine are used as dielectric fillers in polyvinylidene fluoride (PVDF)-based composites. With 4.4 vol. % of BST nanofibers, the extractable energy density of the BST/PVDF composites is more than doubled as compared with pure PVDF matrix. Such significant enhancement is attributed to the combined effect of both surface modification by dopamine and large aspect ratio of the BST nanofibers. Paraelectric or anti-ferroelectric fillers of large aspect ratio may serve as a general strategy for enhanced electric energy density in polymer composites.

  5. Molecular dynamics and reverse Monte Carlo modeling of scheelite-type AWO4 (A = Ca, Sr, Ba) W L 3-edge EXAFS spectra

    NASA Astrophysics Data System (ADS)

    Kalinko, Aleksandr; Bauer, Matthias; Timoshenko, Janis; Kuzmin, Alexei

    2016-11-01

    Classical molecular dynamics (MD) and reverse Monte Carlo methods coupled with ab initio multiple-scattering extended x-ray absorption fine structure (EXAFS) calculations were used for modeling of scheelite-type AWO4 (A = Ca, Sr, Ba) W L 3-edge EXAFS spectra. The two theoretical approaches are complementary and allowed us to perform analysis of full EXAFS spectra. Both methods reproduce well the structure and dynamics of tungstates in the outer coordination shells, however the classical MD simulations underestimate the W-O bond MSRD due to a neglect of quantum zero-point-motion. The thermal vibration amplitudes, correlation effects and anisotropy of the tungstate structure were also estimated.

  6. Dipole spring ferroelectrics in superlattice SrTiO3/BaTiO3 thin films exhibiting constricted hysteresis loops

    SciTech Connect

    Wu, Pingping; Ma, Xingqiao; Li, Yulan; Gopalan, Venkatraman; Chen , L.Q.

    2012-03-01

    Ferroelectric superlattice heterostructures have recently been explored for potential applications in electronic devices. In this letter we employed the phase-field approach to simulate the domain structure and switching of a (BaTiO3)8/(SrTiO3)3 superlattice film constrained by a GdScO3 substrate. A constricted ferroelectric hysteresis loop was observed with a high saturation polarization but a small coercive field. The shape of the hysteresis loop is understood by analyzing the ferroelectric polarization distributions during switching. It is demonstrated that the constricted loop show a similar mechanism to the exchange coupling effect in magnetic multilayers.

  7. The crystal chemistry of the alkaline-earth apatites A(10)(PO(4))(6)Cu(x)O(y)(H)(z) (A = Ca, Sr and Ba).

    PubMed

    Baikie, Tom; Ng, George M H; Madhavi, S; Pramana, Stevin S; Blake, Kevin; Elcombe, Margaret; White, T J

    2009-09-14

    The crystal chemistry of the cuprate apatites A(I)(4)A(II)(6)(PO(4))(6)Cu(x)O(y)(H)(z) (A = Ca, Sr and Ba) was investigated by powder X-ray (PXRD) and neutron diffraction (PND) and X-ray photoelectron spectroscopy (XPS). The refined crystal structures confirmed earlier X-ray diffraction studies that showed copper resides in the apatite channels and additionally, located hydrogen. For all materials copper is primarily divalent (Cu(2+)) but in the calcium and strontium analogues co-exists with minor Cu(3+). This is in contrast with a previous work where Cu(1+) and Cu(2+) were reported.

  8. Optical properties of Ag nanoparticles embedded Ba0.5Sr0.5TiO3 films prepared by alternating pulsed laser deposition.

    PubMed

    Kim, Ji-Suk; Lee, Kyeong-Seok; Kim, Sang Sub

    2006-11-01

    Nanocomposite thin films consisting of nanometer-sized Ag particles embedded in amorphous Ba0.5Sr0.5TiO3 matrix were prepared on fused silica substrates by an alternating pulsed laser deposition method. Their optical nonlinearities have been studied using the Z-scan method. The surface plasmon resonance (SPR) peak shifts to red and increases with the increasing the volume fraction of Ag in the nanocomposite films. The magnitude of the third-order nonlinear susceptibility of the nanocomposite with an Ag volume fraction of 3.3% was calculated to be approximately 2 x 10(-8) esu at the SPR wavelength.

  9. Influences of Orientation on Magnetoelectric Coupling at La1-x Sr x MnO3/BaTiO3 Interface from Ab Initio Calculations

    NASA Astrophysics Data System (ADS)

    Nguyen, Thuy Trang; Yamauchi, Kunihiko; Oguchi, Tamio; Hoang, Nam Nhat

    2017-01-01

    An ab initio study on the magnetoelectric coupling at interfaces of ferromagnetic perovskite Sr-doped LaMnO3 (LSMO) and ferroelectric perovskite BaTiO3 (BTO) with (001) and (111) perovskite orientations is presented. It was found that the interfaces with both orientations exhibit significant magnetoelectric couplings. The effects of the orientation on the magnetoelectric coupling are discussed on the basis of the electronic structure, suggesting that the enhancement of electrostatic-screening-induced magnetoelectric coupling at the (111) interface in comparison with the (001) interface is mainly due to strengthened interfacial coupling.

  10. Effect of local A-site strain on dipole stability in A6GaNb9O30 (A = Ba, Sr, Ca) tetragonal tungsten bronze relaxor dielectrics.

    PubMed

    Miller, Andrew J; Rotaru, Andrei; Arnold, Donna C; Morrison, Finlay D

    2015-06-21

    A series of isovalently A-site substituted relaxor dielectric tetragonal tungsten bronzes of general formula Ba(6-x-y)Sr(x)Ca(y)GaNb(9)O(30) were investigated. The long-range (average) crystal structure as determined by conventional diffraction techniques varies monotonically according to Vegard's law. The dielectric properties, however, do not display a similar, simple "average size" dependence and instead show a dependence on the statistical size variance, i.e. size mismatch, of the A-cation. The difficulties in Vogel-Fulcher analysis of relative permittivity and the complementary approach of using dielectric loss data fitted to Jonscher's empirical universal dielectric relaxation model is discussed.

  11. Characterization of (Ba(0.5)Sr(0.5)) TiO3 Thin Films for Ku-Band Phase Shifters

    NASA Technical Reports Server (NTRS)

    Mueller, Carl H.; VanKeuls, Fredrick W.; Romanofsky, Robert R.; Miranda, Felix A.; Warner, Joseph D.; Canedy, Chadwick L.; Ramesh, Rammamoorthy

    1999-01-01

    The microstructural properties of (Ba(0.5)Sr(0.5)TiO3) (BSTO) thin films (300, 700, and 1400 nm thick) deposited on LaAlO3 (LAO) substrates were characterized using high-resolution x-ray diffractometry. Film crystallinity was the parameter that most directly influenced tunability, and we observed that a) the crystalline quality was highest in the thinnest film and progressively degraded with increasing film thickness; and b) strain at the film/substrate interface was completely relieved via dislocation formation. Paraelectric films such as BSTO offer an attractive means of incorporating low-cost phase shifter circuitry into beam-steerable reflectarray antennas.

  12. Method of forming a dielectric thin film having low loss composition of Ba.sub.x Sr.sub.y Ca.sub.1-x-y TiO.sub.3 : Ba.sub.0.12-0.25 Sr.sub.0.35-0.47 Ca.sub.0.32-0.53 TiO.sub.3

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    2000-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  13. Structure refinement of Ba0.5Sr0.5Co0.8Fe0.2O3-d as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFC)

    NASA Astrophysics Data System (ADS)

    Zakaria, Nurhamidah; Osman, Rozana A. M.; Idris, Mohd Sobri

    2016-07-01

    Ba0.5Sr0.5Co0.8Fe0.2O3-δ was successfully prepared using modified solid-state synthesis routes. The lowest temperature to obtained single phase of Ba0.5Sr0.5Co0.8Fe0.2O3-δ is about 900°C for 15 hours. Longer period of time are required compared to only 5 hours at 950°C as established in literatures. The X-ray Diffraction (XRD) data confirmed that Ba0.5Sr0.5Co0.8Fe0.2O3-δ is formed a cubic perovskite with the space group of Pm-3m. The lattice parameters of Ba0.5Sr0.5Co0.8Fe0.2O3-δ are a = 3.990 (1) Å and unit cell volume is V = 63.5 (1) Å3. The Rietveld refinement of XRD data revealed that the crystal structure of Ba0.5Sr0.5Co0.8Fe0.2O3-δ slightly changes as a function of temperature.

  14. Correlation between upconversion photoluminescence and dielectric response in Ba-substituted (Sr{sub 1−x}Ba{sub x}){sub 4}(La{sub 0.85}Ho{sub 0.025}Yb{sub 0.125}){sub 2}Ti{sub 4}Nb{sub 6}O{sub 30}

    SciTech Connect

    Wei, T.; Wang, X. D.; Zhao, C. Z.; Liu, M. F.; Liu, J. M.

    2014-06-30

    The filled tetragonal tungsten bronze (Sr{sub 1−x}Ba{sub x}){sub 4}(La{sub 0.85}Ho{sub 0.025}Yb{sub 0.125}){sub 2}Ti{sub 4}Nb{sub 6}O{sub 30} (SBLTNx: Ho-Yb) ceramics with different Ba substitution levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The substitution of Sr{sup 2+} ions at the A{sub 2}-sites by larger Ba{sup 2+} ions results in substantial variation of the UC-PL intensity as a function of substitution level x. Furthermore, the dielectric response to the substitution of Sr{sup 2+} by Ba{sup 2+} suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.

  15. The effect of composition on ion release from Ca-Sr-Na-Zn-Si glass bone grafts.

    PubMed

    Murphy, S; Boyd, D; Moane, S; Bennett, M

    2009-11-01

    Controlled delivery of active ions from biomaterials has become critical in bone regeneration. Some silica-based materials, in particular bioactive glasses, have received much attention due to the ability of their dissolution products to promote cell proliferation, cell differentiation and activate gene expression. However, many of these materials offer little therapeutic potential for diseased tissue. Incorporating trace elements, such as zinc and strontium, known to have beneficial and therapeutic effects on bone may provide a more viable bone graft option for those suffering from metabolic bone diseases such as osteoporosis. Rational compositional design may also allow for controlled release of these active ions at desirable dose levels in order to enhance therapeutic efficacy. In this study, six differing compositions of calcium-strontium-sodium-zinc-silicate (Ca-Sr-Na-Zn-Si) glass bone grafts were immersed in pH 7.4 and pH 3 solutions to study the effect of glass composition on zinc and strontium release in a normal and extreme physiological environment. The zinc release levels over 30 days for all zinc-containing glasses in the pH 7.4 solution were 3.0-7.65 ppm. In the more acidic pH 3 environment, the zinc levels were higher (89-750 ppm) than those reported to be beneficial and may produce cytotoxic or negative effects on bone tissue. Strontium levels released from all examined glasses in both pH environments similarly fell within apparent beneficial ranges--7.5-3500 ppm. Glass compositions with identical SrO content but lower ZnO:Na(2)O ratios, showed higher levels of Sr(2+) release. Whereas, zinc release from zinc-containing glasses appeared related to ZnO compositional content. Sustainable strontium and zinc release was seen in the pH 7.4 environment up to day 7. These results indicate that the examined Ca-Sr-Na-Zn-Si glass compositions show good potential as therapeutic bone grafts, and that the graft composition can be tailored to allow therapeutic

  16. Crossover from dilute to majority spin freezing in two leg ladder system Sr(Cu,Zn)2O3

    PubMed

    Larkin; Fudamoto; Gat; Kinkhabwala; Kojima; Luke; Merrin; Nachumi; Uemura; Azuma; Saito; Takano

    2000-08-28

    Muon spin relaxation has been measured in Sr(Cu1-xZnx)2O3. The results for low Zn concentration xZn, having approximately 0.5&mgr;(B) frozen moment. A sharp increase of the relaxation rate at T-->0 occurred with increasing x around x approximately 0.8%, accompanied by a change of line shape to that expected in a concentrated magnetic environment. Analyses of the results for x>/=0.8% suggest that the majority of Cu moments participate in spin freezing, yet with a significantly reduced and spatially inhomogeneous moment size having a 1D correlation length xi approximately 6 lattice units, or a 2D correlation area involving approximately 19 Cu spins.

  17. Gold-hosting high Ba-Sr granitoids in the Xincheng gold deposit, Jiaodong Peninsula, East China: Petrogenesis and tectonic setting

    NASA Astrophysics Data System (ADS)

    Wang, Zhong-Liang; Yang, Li-Qiang; Deng, Jun; Santosh, M.; Zhang, Hua-Feng; Liu, Yue; Li, Rui-Hong; Huang, Tao; Zheng, Xiao-Li; Zhao, Hai

    2014-12-01

    The Xincheng deposit is the only large gold deposit with a proven reserve of >200 t gold hosted by the Early Cretaceous granitoids in northwest Jiaodong Peninsula, East China. The granitoids hosting this ore deposit comprise an inner medium- to fine-grained quartz monzonite and an outer medium- to coarse-grained monzogranite with distinctive K-feldspar megacrysts. LA-ICP-MS zircon dating yields U-Pb ages of 128 ± 1 to 132 ± 1 Ma and 127 ± 2 to 129 ± 1 Ma, for the quartz monzonite and the monzogranite, respectively. The Early Cretaceous ages obtained in our study are comparable with the 126-130 Ma age range reported for the Guojialing granitic suite. The monzogranites, typical high Ba-Sr granites, possess high SiO2 (70.89-73.35%), K2O (3.85-4.32%), total alkalis (K2O + Na2O = 8.08-8.68%), Sr (634-888 ppm), Ba (1395-2111 ppm) and LREE (59.43-145.88), with low HREE and HFSE contents and insignificant Eu anomalies. The rocks display markedly high Sr/Y (114-297) and (La/Yb)N (20-79) ratios. They have low MgO (0.23-0.62%), Cr (0.4-8.33 ppm) and Ni (0.47-2.92 ppm) contents. The typical high Ba-Sr signatures of the outer acidic monzogranites are also shared by the inner intermediate-acidic quartz monzonites, with a relatively higher abundance of these elements. The plagioclases in the quartz monzonites and monzogranites are oligoclase-andesine with An contents of 11.7-44.5%, and oligoclase with An contents of 12.9-29.3%, respectively, which both show the reverse zoning texture. The quartz monzonites have zircon εHf(t) values of -21.3 to -13.9 (average -18.7), which are less negative and show larger variations than those of the monzogranites (εHf(t) = -24.7 to -18.1, average -19.5). Detailed elemental, mineralogical and isotopic data suggest that the high Ba-Sr quartz monzonites and monzogranites were most likely generated by partial melting of the basement rocks of the Jiaobei terrane accompanied by crustal assimilation, with minor addition of the intermediate magma

  18. Sol–gel synthesis, structure and luminescence properties of Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors

    SciTech Connect

    Li, Yuntong; Liu, Xiaohua

    2015-04-15

    Graphical abstract: The phosphor powders of Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} were prepared by sol–gel method. The dependence of luminescence intensity on the Eu{sup 3+} concentration was investigated. - Highlights: • We synthesize Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors by the sol–gel method. • The effect of temperature on the crystallinity and morphology is investigated. • The phosphor presents an intense CT band in near UV range (370–410 nm). • The concentration quenching mechanism is the exchange interaction. - Abstract: Double-perovskite Ba{sub 2}Zn{sub 1−x}MoO{sub 6}:xEu{sup 3+} (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) orange–red emitting phosphors were synthesized by using the sol–gel method. The crystalline structure and photoluminescence properties of the phosphors were investigated. The X-ray diffraction (XRD) patterns indicate that the structure of matrix Ba{sub 2}ZnMoO{sub 6} is cubic double-perovskite with space group Fm-3m. The Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors present an intense broad charge transfer (CT) band absorption in near UV range (370–410 nm), which attributes to the charge transfer state of MoO{sub 6}, and performs orange–red emission of Eu{sup 3+} ({sup 5}D{sub 0} → {sup 7}F{sub 1} transition) at around 596 nm. A low concentration quenching occurs in Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} and the optimal doping concentration is about 6 mol%. The Ba{sub 2}ZnMoO{sub 6}:Eu{sup 3+} phosphors are considered to be a promising orange–red emitting phosphor for near ultraviolet GaN-based white light emitting diode.

  19. Anisotropic Exchange within Decoupled Tetrahedra in the Quantum Breathing Pyrochlore Ba3Yb2Zn5O11

    NASA Astrophysics Data System (ADS)

    Rau, J. G.; Wu, L. S.; May, A. F.; Poudel, L.; Winn, B.; Garlea, V. O.; Huq, A.; Whitfield, P.; Taylor, A. E.; Lumsden, M. D.; Gingras, M. J. P.; Christianson, A. D.

    2016-06-01

    The low energy spin excitation spectrum of the breathing pyrochlore Ba3Yb2Zn5O11 has been investigated with inelastic neutron scattering. Several nearly resolution limited modes with no observable dispersion are observed at 250 mK while, at elevated temperatures, transitions between excited levels become visible. To gain deeper insight, a theoretical model of isolated Yb3 + tetrahedra parametrized by four anisotropic exchange constants is constructed. The model reproduces the inelastic neutron scattering data, specific heat, and magnetic susceptibility with high fidelity. The fitted exchange parameters reveal a Heisenberg antiferromagnet with a very large Dzyaloshinskii-Moriya interaction. Using this model, we predict the appearance of an unusual octupolar paramagnet at low temperatures and speculate on the development of intertetrahedron correlations.

  20. Anisotropic Exchange within Decoupled Tetrahedra in the Quantum Breathing Pyrochlore Ba_{3}Yb_{2}Zn_{5}O_{11}.

    PubMed

    Rau, J G; Wu, L S; May, A F; Poudel, L; Winn, B; Garlea, V O; Huq, A; Whitfield, P; Taylor, A E; Lumsden, M D; Gingras, M J P; Christianson, A D

    2016-06-24

    The low energy spin excitation spectrum of the breathing pyrochlore Ba_{3}Yb_{2}Zn_{5}O_{11} has been investigated with inelastic neutron scattering. Several nearly resolution limited modes with no observable dispersion are observed at 250 mK while, at elevated temperatures, transitions between excited levels become visible. To gain deeper insight, a theoretical model of isolated Yb^{3+} tetrahedra parametrized by four anisotropic exchange constants is constructed. The model reproduces the inelastic neutron scattering data, specific heat, and magnetic susceptibility with high fidelity. The fitted exchange parameters reveal a Heisenberg antiferromagnet with a very large Dzyaloshinskii-Moriya interaction. Using this model, we predict the appearance of an unusual octupolar paramagnet at low temperatures and speculate on the development of intertetrahedron correlations.

  1. Anisotropic Exchange within Decoupled Tetrahedra in the Quantum Breathing Pyrochlore Ba3Yb2Zn5O11

    DOE PAGES

    Rau, J. G.; Wu, L. S.; May, A. F.; ...

    2016-06-24

    Tmore » he low energy spin excitation spectrum of the breathing pyrochlore Ba3Yb2Zn5O11 has been investigated with inelastic neutron scattering. Several nearly resolution limited modes with no observable dispersion are observed at 250 mK while, at elevated temperatures, transitions between excited levels become visible. o gain deeper insight, a theoretical model of isolated Yb3+ tetrahedra parametrized by four anisotropic exchange constants is constructed. he model reproduces the inelastic neutron scattering data, specific heat, and magnetic susceptibility with high fidelity. he fitted exchange parameters reveal a Heisenberg antiferromagnet with a very large Dzyaloshinskii-Moriya interaction. Ultimately, using this model, we predict the appearance of an unusual octupolar paramagnet at low temperatures and speculate on the development of inter-tetrahedron correlations.« less

  2. Local atomic and magnetic structure of dilute magnetic semiconductor (Ba,K)(Zn,Mn)2As2

    DOE PAGES

    Frandsen, Benjamin A.; Gong, Zizhou; Terban, Maxwell W.; ...

    2016-09-06

    We studied the atomic and magnetic structure of the dilute ferromagnetic semiconductor system (Ba,K)(Zn,Mn)2As2 through atomic and magnetic pair distribution function analysis of temperature-dependent x-ray and neutron total scattering data. Furthermore, we detected a change in curvature of the temperature-dependent unit cell volume of the average tetragonal crystallographic structure at a temperature coinciding with the onset of ferromagnetic order. We also observed the existence of a well-defined local orthorhombic structure on a short length scale of ≲5Å, resulting in a rather asymmetrical local environment of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic alignment of Mn spinsmore » along the crystallographic c axis, with robust nearest-neighbor ferromagnetic correlations that exist even above the ferromagnetic ordering temperature. Finally, we discuss these results in the context of other experiments and theoretical studies on this system.« less

  3. (Y0.5In0.5)Ba(Co,Zn)4O7 cathodes with superior high-temperature phase stability for solid oxide fuel cells

    SciTech Connect

    Young Nam, Kim; Kim, Jung-Hyun; Paranthaman, Mariappan Parans; Manthiram, Arumugam; Huq, Ashfia

    2012-01-01

    (Y0.5In0.5)BaCo4-xZnxO7 (1.0 x 2.0) oxides crystallizing in a trigonal P31c structure have been synthesized and explored as cathode materials for solid oxide fuel cells (SOFC). At a given Zn content, the (Y0.5In0.5)BaCo4-xZnxO7 sample with 50 % Y and 50 % In exhibits much improved phase stability at intermediate temperatures (600 - 800 oC) compared to the samples with 100 % Y or In. However, the substitution of Zn for Co in (Y0.5In0.5)Ba(Co4-xZnx)O7 (1.0 x 2.0) decreases the amount of oxygen loss on heating, total electrical conductivity, and cathode performance in SOFC while providing good long-term phase stability at high temperatures. Among the various chemical compositions investigated in the (Y0.5In0.5)Ba(Co4-xZnx)O7 system, the (Y0.5In0.5)BaCo3ZnO7 sample offers a combination of good electrochemical performance and low thermal expansion coefficient (TEC) while maintaining superior phase stability at 600 800 oC for 100 h. Fuel cell performances of the (Y0.5In0.5)Ba(Co3Zn)O7 + Ce0.8Gd0.2O1.9 (GDC) (50 : 50 wt. %) composite cathodes collected with anode-supported single cell reveal a maximum power density value of 521 mW cm-2 at 700 oC.

  4. Preparation of barium strontium titanate Ba(1-x)Sr(x)TiO(3) (0

    PubMed

    Jiang, Wanquan; Gong, Xiuqing; Chen, Zuyao; Hu, Yuan; Zhang, Xianzhou; Gong, Xinglong

    2007-02-01

    An ultrasonic irradiation method was applied to the sol/gel synthesis of the single-crystal cubic barium strontium titanate Ba(1-x)Sr(x)TiO(3) (0Ba(0.8)Sr(0.2)TiO(3) are in the range of 70-100 nm and 650-1000 nm, respectively. In addition, the stoichiometric sonogel formation and its heat-treatment process, the relationship between x of Ba(1-x)Sr(x)TiO (3) and the crystal structure, the relationship between synthesis condition of sonogel and morphology have been discussed.

  5. Correlation between upconversion photoluminescence and dielectric response in Ba-substituted (Sr1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30

    NASA Astrophysics Data System (ADS)

    Wei, T.; Wang, X. D.; Zhao, C. Z.; Liu, M. F.; Liu, J. M.

    2014-06-01

    The filled tetragonal tungsten bronze (Sr1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30 (SBLTNx: Ho-Yb) ceramics with different Ba substitution levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The substitution of Sr2+ ions at the A2-sites by larger Ba2+ ions results in substantial variation of the UC-PL intensity as a function of substitution level x. Furthermore, the dielectric response to the substitution of Sr2+ by Ba2+ suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.

  6. Grain growth behavior of Ba1.5Sr1.5Co2Fe24O41 flakes in molten salt synthesis and the magnetic properties of flake/polymer composites

    NASA Astrophysics Data System (ADS)

    Moon, Kyoung-Seok; Kang, Young-Min; Han, InTaek; Lee, Sang-Eui

    2016-11-01

    Single-phase Ba1.5Sr1.5Co2Fe24O41 (Ba1.5Sr1.5Z) hexaferrite flakes were synthesized using a two-step grain growth process, involving a calcination process and molten salt synthesis. Geometric parameters such as aspect ratio and the degree of agglomeration can be controlled by tuning this calcination-molten salt method. The morphological evolution of the flakes was explained using the concept of mixed-control grain growth, i.e., a combination of diffusion for growth and interface reactions, which is a growth mechanism for a faceted interface. The single-phase Ba1.5Sr1.5Z flake particle with high aspect ratio turned out to be a good candidate of soft magnetic inclusion, through an investigation of the correlation between material composition, magnetic behavior, and particle morphology.

  7. Strikingly dissimilar effect of Mn and Zn dopants imposed on local structural distortion of Ba0.5K0.5Fe2As2 superconductor.

    PubMed

    Cheng, Jie; Dong, Peng; Chu, Wangsheng; Xu, Wei; Wen, Haihu; Marcelli, Augusto; Wu, Ziyu

    2013-05-01

    To clarify the contrasting impurity effects of Mn and Zn dopants on the critical temperature of optimally doped Ba0.5K0.5Fe2As2 superconductors, extended X-ray absorption fine-structure spectroscopy was implemented at the Fe and As K-edge. In Mn-doped compounds a gradual deviation of the symmetric FeAs4 tetrahedron and weakening of the Fe-As bond was observed. Conversely, in Zn-doped compounds the perfect FeAs4 tetrahedron is maintained and the Fe-As bond is rigid. The local structural details are consistent with the development of superconductivity in these two systems, suggesting a significant role played by the topology of the FeAs4 tetrahedron and rigidness of the Fe-As bond in Mn/Zn-doped Ba0.5K0.5Fe2As2 superconductors.

  8. Octonary resistance states in La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions

    DOE PAGES

    Yue -Wei Yin; Tao, Jing; Huang, Wei -Chuan; ...

    2015-10-06

    General drawbacks of current electronic/spintronic devices are high power consumption and low density storage. A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents four resistance states in a single device and therefore provides an alternative way to achieve high density memories. Here, an MFTJ device with eight nonvolatile resistance states by further integrating the design of noncollinear magnetization alignments between the ferromagnetic layers is demonstrated. Through the angle-resolved tunneling magnetoresistance investigations on La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 junctions, it is found that, besides collinear parallel/antiparallel magnetic configurations, the MFTJ shows at least two other stable noncollinear (45°more » and 90°) magnetic configurations. As a result, combining the tunneling electroresistance effect caused by the ferroelectricity reversal of the BaTiO3 barrier, an octonary memory device is obtained, representing potential applications in high density nonvolatile storage in the future.« less

  9. Transformation of AeIn4 Indides (Ae = Ba, Sr) into an AeAu2In2 Structure Type Through Gold Substitution

    SciTech Connect

    Dai, Jing-Cao; Corbett, John D.

    2007-04-17

    The title compounds were prepared from the elements by high-temperature solid-state synthesis techniques. X-ray structural analyses shows that BaAu{sub 2}In{sub 2} (1) and SrAu{sub 2}In{sub 2} (2) crystallize in a new orthorhombic structure, Pnma, Z = 4 (a = 8.755(2), 8.530(2) {angstrom}; b = 4.712(1), 4.598(1) {angstrom}; c = 12.368(3), 12.283(4) {angstrom}, respectively). Gold substitutes for 50% of the indium atoms in the tetragonal BaIn{sub 4} and monoclinic SrIn{sub 4} parents to give this new and more flexible orthorhombic structure. The Ae atoms in this structure are contained within chains of hexagonal prisms built of alternating In and Au that have additional augmenting atoms around their waists from further condensation of parallel displaced chains. The driving forces for these structural changes are in part the shorter Au-In distances (2.72 and 2.69 {angstrom}) relative to d(In-In) in the parents, presumably because of relativistic contractions with Au. Generalities about such centered prismatic building blocks and their condensation modes in these and related phases are described. Band structure calculations (EHTB) demonstrate that the two compounds are metallic, which is confirmed by measurements of the resistivity of 1 and the magnetic susceptibilities of both.

  10. Epitaxial Ferroelectric Ba(0.5)Sr(0.5)TiO3 Thin Films for Room-Temperature High-Frequency Tunable Element Applications

    NASA Technical Reports Server (NTRS)

    Chen, C. L.; Feng, H. H.; Zhang, Z.; Brazdeikis, A.; Miranda, F. A.; VanKeuls, F. W.; Romanofsky, R. R.; Huang, Z. J.; Liou, Y.; Chu, W. K.; Chu, C. W.

    1999-01-01

    Perovskite Ba(0.5)SR(0.5)TiO3 thin films have been synthesized on (001) LaAl03 substrates by pulsed laser ablation. Extensive X-ray diffraction, rocking curve, and pole-figure studies suggest that the films are c-axis oriented and exhibit good in-plane relationship of <100>(sub BSTO)//<100>(sub LAO). Rutherford Backscattering Spectrometry studies indicate that the epitaxial films have excellent crystalline quality with an ion beam minimum yield chi(sub min) Of only 2.6 %. The dielectric property measurements by the interdigital technique at 1 MHz show room temperature values of the relative dielectric constant, epsilon(sub r), and loss tangent, tan(sub delta), of 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively. The obtained data suggest that the as-grown Ba(0.5)SR(0.5)TiO3 films can be used for development of room-temperature high-frequency tunable elements.

  11. Preparation of Ba0.09Sr0.91TiO3/YBa2Cu3O7-x bilayers and investigation of their dielectric properties

    NASA Astrophysics Data System (ADS)

    Jia, Jiqiang; Zhao, Gaoyang; Shi, Xiaoxue; Lei, Li

    2016-08-01

    YBa2Cu3O7-x (YBCO) films of 110 nm thickness were prepared on LaAlO3 (LAO) substrates via the sol-gel method. Subsequently, about 400 nm thick Ba0.09Sr0.91TiO3 (BST) films were epitaxially grown on the YBCO and LNO films surface; the BST films exhibited a strong c-axis orientation. The dielectric adjustability and relative dielectric constant was investigated in the range of 300-83 K. Results indicate that the tunability of the Ba0.09Sr0.91TiO3/YBa2Cu3O7-x (BST/YBCO) displayed an increase relative to c-axis-oriented BST on LaNiO3 (LNO). The tunability was further enhanced as the operating temperature decreased, yet the loss tangent (tanδ) decreased. The tunability and the tanδ at 100 kHz and 83 K were 58% and 0.029, respectively.

  12. Electrical Characteristics and Preparation of (Ba0.5Sr0.5)TiO3 Films by Spray Pyrolysis and Rapid Thermal Annealing

    NASA Astrophysics Data System (ADS)

    Koo, Horng-Show; Chen, Mi; Ku, Hong-Kou; Kawai, Tomoji

    2007-04-01

    Functional films of (Ba0.5Sr0.5)TiO3 on Pt (1000 Å)/Ti (100 Å)/SiO2 (2000 Å)/Si substrates are prepared by spray pyrolysis and subsequently rapid thermal annealing. Barium nitrate, strontium nitrate and titanium isopropoxide are used as starting materials with ethylene glycol as solvent. For (Ba0.5Sr0.5)TiO3 functional thin film, thermal characteristics of the precursor powder scratched from as-sprayed films show a remarkable peak around 300-400 °C and 57.7% weight loss up to 1000 °C. The as-sprayed precursor film with coffee-like color and amorphous-like phase is transformed into the resultant film with white, crystalline perovskite phase and characteristic peaks (110) and (100). The resultant films show correspondent increases of dielectric constant, leakage current and dissipation factor with increasing annealing temperatures. The dielectric constant is 264 and tangent loss is 0.21 in the resultant films annealed at 750 °C for 5 min while leakage current density is 1.5× 10-6 A/cm2 in the film annealed at 550 °C for 5 min.

  13. Strain evolution of each type of grains in poly-crystalline (Ba,Sr)TiO3 thin films grown by sputtering

    PubMed Central

    Park, Woo Young; Park, Min Hyuk; Lee, Jong Ho; Yoon, Jung Ho; Han, Jeong Hwan; Choi, Jung-Hae; Hwang, Cheol Seong

    2012-01-01

    The strain states of [111]-, [110]-, and [002]-oriented grains in poly-crystalline sputtered (Ba,Sr)TiO3 thin films on highly [111]-oriented Pt electrode/Si substrates were carefully examined by X-ray diffraction techniques. Remarkably, [002]-oriented grains respond more while [110]- and [111]-oriented grains do less than the theoretically estimated responses, which is understandable from the arrangement of the TiO6 octahedra with respect to the stress direction. Furthermore, such mechanical responses are completely independent of the degree of crystallization and film thickness. The transition growth temperature between the positive and negative strains was also different depending on the grain orientation. The unstrained lattice parameter for each type of grain was different suggesting that the oxygen vacancy concentration for each type of grain is different, too. The results reveal that polycrystalline (Ba,Sr)TiO3 thin films are not an aggregation of differently oriented grains which simply follow the mechanical behavior of single crystal with different orientations. PMID:23230505

  14. Structural and magnetic properties of the new cobaltate series (BaSr)4-xLa2xCo4O15

    SciTech Connect

    Garlea, Elena; Garlea, Vasile O; Ehlers, Georg; Mamontov, Eugene; Custelcean, Radu; Jin, R.

    2012-01-01

    We report the structural and magnetic properties of a new class of cobaltates with the chemical formula (BaSr)4-xLa2xCo4O15 (x = 0, 0.5 and 1). These compounds crystallize in a hexagonal structure in which cobalt ions are distributed among two distinct crystallographic sites with dierent oxygen coordination. Three Co{O tetrahedra and one octahedron are linked by shared oxygen atoms to form Co4O15 clusters, which are packed together into a honeycomb-like network. Partial substitution of Sr and/or Ba atoms by La allows one to adjust the degree of Co valence mixing, but all compositions remain subject to a random distribution of charge. Magnetic susceptibility together with neutron scattering measurements reveal that all studied specimens are characterized by competing ferro- and antiferro-magnetic exchange interactions that give rise to a three dimensional Heisenberg spin-glass state. Neutron spectroscopy shows a clear trend of slowing down of spindynamics upon increasing La concentration, suggesting a reduction in charge randomness in the doped samples.

  15. Average and local structure of the Pb-free ferroelectric perovskites (Sr,Sn)TiO3 and (Ba,Ca,Sn)TiO3

    DOE PAGES

    Laurita, Geneva; Page, Katharine; Suzuki, Shoichiro; ...

    2015-12-16

    The characteristic structural off -centering of Pb2+ in oxides, associated with its 6s2 lone pair, allows it to play a dominant role in polar materials, and makes it a somewhat ubiquitous component of ferroelectrics. In this work, we examine the compounds Sr0.9Sn0.1TiO3 and Ba0.79Ca0.16Sn0.05TiO3 using neutron total scattering techniques with data acquired at di erent temperatures. In these compounds, previously reported as ferroelectrics, Sn2+ appears to display some of the characteristics of Pb2+. We compare the local and long-range structures of the Sn2+-substituted compositions to the unsubstituted parent compounds SrTiO3 and BaTiO3. Lastly, we find that even at these smallmore » substitution levels, the Sn2+ lone pairs drive the local ordering behavior, with the local structure of both compounds more similar to the structure of PbTiO3 rather than the parent compounds.« less

  16. Dielectric relaxation and electrical conduction mechanism in A2HoSbO6 (A=Ba, Sr, Ca) Double Perovskite Ceramics: An impedance spectroscopic analysis

    NASA Astrophysics Data System (ADS)

    Halder, Saswata; Dutta, Alo; Sinha, T. P.

    2017-03-01

    The AC electrical properties of polycrystalline double perovskite oxides A2HoSbO6 (A=Ba, Sr, Ca; AHS) synthesized by solid state reaction technique has been explored by using impedance spectroscopic studies. The Rietveld refinement of the room temperature X-ray diffraction data show that Ba2HoSbO6 (BHS) has cubic phase and Sr2HoSbO6 (SHS) and Ca2HoSbO6 (CHS) crystallize in monoclinic phase. The samples show significant frequency dispersion in their dielectric properties. The polydispersive nature of the relaxation mechanism is explained by the modified Cole-Cole model. The scaling behavior of dielectric loss indicate the temperature independence of the relaxation mechanism. The magnitude of the activation energy indicates that the hopping mechanism is responsible for carrier transport in AHS. The frequency dependent conductivity spectra follow the double power law. Impedance spectroscopic data presented in the Nyquist plot (Z" versus Z‧) are used to identify an equivalent circuit along with to know the grain, grain boundary and interface contributions. The constant phase element (CPE) is used to analyze the experimental response of BHS, SHS and CHS comprehending the contribution of different microstructural features to the conduction process. The temperature dependent electrical conductivity shows a semiconducting behavior.

  17. The first-principle study of the electronic, optical and thermoelectric properties of XTiO3 (X = Ca, Sr and Ba) compounds

    NASA Astrophysics Data System (ADS)

    Mubarak, A. A.

    2016-07-01

    The FP-LAPW method is utilized to investigate the elastic, optoelectronic and thermoelectric properties of XTiO3 (X = Ca, Sr and Ba) within the GGA. The calculated lattice constants and bulk modulus are found in agreement with previous studies. The present oxide-perovskite compounds are characterized as elastically stable and anisotropic. CaTiO3 and SrTiO3 are categorized as ductile compounds, whereas the BaTiO3 compound is in the critical region between ductile and brittle. The DOS and the band structure calculations reveal indirect (M-Γ) energy bandgap for the present compounds. The hydrostatic pressure increases the energy bandgap and the width of the valence band. The character of the band structure does not change due to this pressure. The optical parameters are calculated in different radiation regions. Beneficial optics applications are predicted as revealed from the optical spectra. The transport properties are applied as a function of the variable temperatures or carrier concentration. It is found that the compounds under study are classified as a p-type semiconductor. The majority charge carriers responsible for conduction in these calculated compounds are holes rather than electrons.

  18. On synthesis of BaFe12O19, SrFe12O19, and PbFe12O19 hexagonal ferrite ceramics with multiferroid properties

    NASA Astrophysics Data System (ADS)

    Kostishin, V. G.; Panina, L. V.; Kozhitov, L. V.; Timofeev, A. V.; Zyuzin, A. K.; Kovalev, A. N.

    2015-08-01

    We analyze the possibility of obtaining M-type hexagonal ferrites of barium, strontium, and lead with multiferroid properties with the help of ceramic technology. Using the modified ceramic technology (especially pure initial raw materials, admixture of B2O3, and sintering in the oxygen atmosphere), we obtained for the first time the BaFe12O19 and SrFe12O19 samples with intense multiferroid properties at room temperature. At the same time, the employed technology does not make it possible to obtain PbFe12O19 samples exhibiting ferroelectricity. The multiferroid characteristics of experimental samples are compared with the characteristics of classical high-temperature multiferroic BiFeO3 and with the characteristics of BaFe12O19, SrFe12O19, and PbFe12O19 ferrite ceramics obtained in accordance with polymer precursor technology. We propose a mechanism explaining multiferroid properties of the hexagonal ferrite ceramic samples and note the importance of our results for applications.

  19. High-performance tellurium-free thermoelectrics: all-scale hierarchical structuring of p-type PbSe-MSe systems (M = Ca, Sr, Ba).

    PubMed

    Lee, Yeseul; Lo, Shih-Han; Androulakis, John; Wu, Chun-I; Zhao, Li-Dong; Chung, Duck-Young; Hogan, Timothy P; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2013-04-03

    We present a systematic study of the characterization and thermoelectric properties of nanostructured Na-doped PbSe embedded with 1-4% MSe (M = Ca, Sr, Ba) phases as endotaxial inclusions. The samples were powder-processed by the spark plasma sintering technique, which introduces mesoscale-structured grains. The hierarchical architectures on the atomic scale (Na and M solid solution), nanoscale (MSe nanoprecipitates), and mesoscale (grains) were confirmed by transmission electron microscopy. These structures produce a great reduction in the lattice thermal conductivity relative to pristine PbSe without appreciably affecting the power factor. The lattice thermal conductivity can be reduced by up to ∼29% when the second phase is added. The highest ZT value achieved was ∼1.3 at 923 K for both 2% SrSe-and 3% BaSe-containing samples, while the sample containing 4% CaSe showed a ZT value of ∼1.2 at 923 K. The optimal samples have hole carrier concentration of 1-2 × 10(20) cm(-3). We attribute the high ZT values to the combination of broad-based phonon scattering on multiple length scales and favorable charge transport through coherent interfaces between the PbSe matrix and MSe.

  20. Field emission of silicon emitter arrays coated with sol-gel (Ba0.65Sr0.35)1-xLaxTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Lu, H.; Pan, J. S.; Chen, X. F.; Zhu, W. G.

    2007-07-01

    (Ba0.65Sr0.35)1-xLaxTiO3 (BSLT) thin films with different La concentrations have been deposited on Si field emitter arrays (FEAs) using sol-gel technology for field electron emission applications. The films exhibit the perovskite structure at low La substitution level (x ≤0.5) and the pyrochlore phase at high La concentration (x ≥0.75). The 30-nm-thick BSLT (x =0.25) thin film has higher crystallinity of perovskite structure in the surface region. An x-ray photoelectron spectroscopy study indicates that the oxygen vacancy concentration decreases with La substitution. With respect to the undoped Ba0.65Sr0.35TiO3 thin film, the Fermi level shifts down for the BSLT sample with x =0.1 ascribed to the decreasing oxygen vacancy concentration, and then shifts up for the BSLT sample with x =0.25 attributed to the increasing La substitution level. In highly doped films with an x value over 0.5, it shifts down again associated with the second pyrochlore phase formation. The best enhancement in field emission is found for the BSLT-coated (x =0.25) Si FEAs due to the improved perovskite structure in the surface region and up-moved Fermi level of the coating.

  1. Foliar contamination of Phaseolus vulgaris with aerosols of 137Cs, 85Sr, 133Ba and 123mTe: influence of plant development stage upon contamination and rain.

    PubMed

    Madoz-Escande, C; Henner, P; Bonhomme, T

    2004-01-01

    As part of a requirement to improve the assessment of the impact of radioactive fallout on consumed agricultural products, bean plants at four development stages (seedlings, preflowering, late flowering and mature plants) were contaminated by dry deposition of (137)Cs, (85)Sr, (133)Ba and (123m)Te aerosols. The influence of two rain scenarios and of the development stage upon contamination on interception, retention, and translocation to pods was studied. Interception of the four radionuclides was almost identical and varied from 30 to 60% with increasing development stage. The most important rain parameter was the time which elapsed between contamination and the first rain. Whatever the development stage, rain washed off more cesium from the leaves when it occurred 2 days after the deposit (37% at the seedling stage, for example) rather than later on (6 days, 27%), due to rapid migration of Cs in the plant. The first rain washed off nearly 40% of Ba whatever the scenario. For later stages, Sr and Ba were more washed off by heavy weekly rains than by weak twice-a-week rains, perhaps because of the Sr/Ba-contaminated material loss associated with wash off (desquamation of cuticles). Te showed little wash off (less than 5%). Wash off decreased with an older development stage for a weak rain intensity, due to the superimposition of leaves. Heavy rains removed this shelter effect. At harvest, rain effect was no longer detectable as foliar activity was similar for both rain scenarios. Translocation factors (TF) for strontium and barium increased from 6 x 10(-3) to 1 x 10(-1) with the plant development stage upon contamination, whereas those for cesium remained almost unchanged between 2 x 10(-1) and 4 x 10(-1). Flowering is the most critical stage towards residual contamination in pods at harvest, with the exception of direct deposit on pods at the mature stage (TF values are one order of magnitude higher). TF value for Te was 6.5 x 10(-2) and was due to direct deposit

  2. Electronic structure and x-ray magnetic circular dichroism in A2FeReO6 (A =Ca ,Sr ,andBa ) oxides

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.; Bekenov, L. V.; Ernst, A.

    2016-07-01

    A systematic electronic structure study of A2FeReO6 (A =Ba ,Sr ,andCa ) has been performed by employing the local-spin-density approximation (LSDA) and LSDA +U methods using the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. We investigated the effects of the subtle interplay between spin-orbit coupling, electron correlations, and lattice distortion on the electronic structure of double perovskites. Ca2FeReO6 has a large distortion in the Fe-O-Re bond, and the electronic structure is mainly determined by electron correlations and lattice distortion. In the Ba -Sr -Ca row, the correlation effects at the Fe site are increased. The correlations at the Re site are small in the Ba- and Sr-based compounds but significant in Ca2FeReO6 . Ca2FeReO6 behaves like an insulator only if considered with a relatively large value of Coulomb repulsion Ueff=2.3 eV at the Re site in addition to Ueff=3.1 eV at the Fe site. Ca2FeReO6 possesses a phase transition at 140 K where the metal-insulator transition (MIT) occurs between metallic high-temperature and insulating low-temperature phases. The spin and orbital magnetic moments are linear functions of temperature before and after the MIT but change abruptly at the point of the phase transition. From theoretically calculated magnetocrystalline anisotropy energy (MAE), we found that the easy axis of magnetization for the low-temperature phase is along the b direction, in agreement with experimental data. We found that the major contribution to the MAE is due to the orbital magnetic anisotropy at the Re site. X-ray-absorption spectra and x-ray magnetic circular dichroism at the Re, Fe, and Ba L2 ,3 and Fe, Ca, and O K edges were investigated theoretically in the frame of the LSDA +U method. A qualitative explanation of the x-ray magnetic circular dichroism spectra shape is provided by an analysis of the corresponding selection rules, orbital character, and occupation numbers of individual orbitals

  3. Electric-field control of ferromagnetic resonance in monolithic BaFe12O19-Ba0.5Sr0.5TiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Das, Jaydip; Song, Young-Yeal; Wu, Mingzhong

    2010-08-01

    This paper demonstrates an electric-field tuning of the ferromagnetic resonance (FMR) responses at millimeter wave frequencies for a monolithic magneto-electric heterostructure. The layered stack is comprised of c-axis oriented and low loss barium hexaferrite (BaM) and (111) oriented ferroelectric barium strontium titanate (BSTO) layers along with embedded platinum electrode layers, all fabricated by pulsed laser deposition technique. A tunability of the FMR frequency as large as 3.5 MHz/V has been observed at 60 GHz due to application of bias voltages in the range of several volts. The realization of such a large tunability relies on the quasi-lattice-to-lattice contact between the BaM and BSTO layers as well as the high quality of those layers.

  4. Unraveling the resistive switching effect in ZnO/0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Silva, J. P. B.; Vorokhta, M.; Dvořák, F.; Sekhar, K. C.; Matolín, V.; Moreira, J. Agostinho; Pereira, M.; Gomes, M. J. M.

    2017-04-01

    This work reports the effect of partial oxygen pressure, used in the deposition of the ZnO layer, on the band alignment at ZnO - 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (0.5BZT-0.5BCT) interface and on the resistive switching (RS) behavior of pulsed laser deposited ZnO/0.5BZT-0.5BCT heterostructures. X-ray photoelectron spectroscopy (XPS) has been employed to measure the valence band offset and the conduction band offset of the ZnO/0.5BZT-0.5BCT heterojunctions. The valence and conduction band offsets of the ZnO/0.5BZT-0.5BCT heterostucture with ZnO deposited at 10-2 mbar of partial oxygen pressure were found to be 0.27 and 0.80 eV, respectively. The RS effect in heterostructures is explained on the base of the charge coupling between the switchable polarization of ferroelectric layer and the non-switchable polarization of semiconductor layer. The heterostructure with ZnO deposited at 10-2 mbar of partial oxygen pressure displays optimum RS characteristics, with a switching ratio ≥ 104 and excellent retention and endurance characteristics. The optimum RS characteristics are attributed to a good interface quality with enough carrier concentration in ZnO, as evidenced by XPS.

  5. Formation of multinary intermetallics from reduction of perovskites by aluminum flux: M(3)Au(6+)(x)()Al(26)Ti (M = Ca, Sr, Yb), a stuffed variant of the BaHg(11) type.

    PubMed

    Latturner, Susan E; Kanatzidis, Mercouri G

    2004-01-12

    New intermetallic phases were synthesized by reacting oxidic perovskites and gold metal in aluminum flux. The combination of MTiO(3) (M = Ca, Sr, Ba) and Au metal in excess molten aluminum produces quaternary compounds M(3)Au(6+)(x)()Al(26)Ti with a stuffed BaHg(11) structure type. An analogue with M = Yb was also synthesized; it shows mixed valent behavior.

  6. Normal state transport properties of Y 1- xPr xSrBaCu 3O 7 and Y 1- xPr xSr 2Cu 2.8Re 0.2O 7

    NASA Astrophysics Data System (ADS)

    Das, A.; Zelenay, I.; Suryanarayanan, R.

    1998-01-01

    In order to examine the effect of crystal chemistry on the Tc suppression behaviour of Pr in Y 1- xPr xBa 2Cu 3O 7, we have investigated in detail the normal state transport properties - resistivity ( ρ) and thermo-electric power (TEP) - of two systems, (A) Y 1- xPr xSrBaCu 3O 7 and (B) Y 1- xPr xSr 2Cu 2.8Re 0.2O 7. In case of the compound A, two kinds of samples were prepared - annealed in oxygen [O] and heated in argon followed by oxygen annealing [AO]. As a result of the [AO] treatment, Tc could be increased by 5-14 K and superconductivity was induced in the sample x=0.7. The [AO] treatment further reduced the ρrt and ρ0 pointing to a substantial reduction in scattering by defects (oxygen disorder). The room temperature value of the TEP ( Srt) revealed that the [AO] treatment increased the hole concentration in the CuO 2 planes. In case of compound B, for x=0, the value of Srt indicated that it was underdoped. In spite of this, the effect of Pr was much less drastic as shown by a smaller slope d Tc/d x. Our Srt data as a function of Pr concentration indicated that the hole depletion was retarded considerably due to Sr substitution. To understand this slow charge transfer of holes and the effect of [AO] treatment, one has to take into account of the role played by Cu-O chains and oxygen defects in the basal plane. Our data support the model suggested by Fehrenbacher and Rice [Phys. Rev. Lett. 70 (1993) 3471]. Further detailed microscopic experiments and annealing procedures are needed to determine the role of the chains and how they affect the Pr(f) hybridization in the CuO 2 planes.

  7. Rapid Gel Cast Prototyping of Complex Paraelectric (Ba,Sr)TiO(3)/MgO Composites

    DTIC Science & Technology

    2003-04-03

    40 wt% BaO. 55Sro.45TiO 3 / 60 wt% MgO (see ref. 1) MgCO 3 (Alfa Aesar, MA) + 3 wt% oxalic acid (Fisher Scientific, NY) MgO (Alfa Aesar, MA...the particles with oxalic acid to produce a thin surface layer of magnesium oxalate (cf. Figure 3b). Figure 3. Green body interior a) 40wt% Ba

  8. Direct observation of oxygen-vacancy-enhanced polarization in a SrTiO3-buffered ferroelectric BaTiO3 film on GaAs

    DOE PAGES

    Qiao, Q.; Zhang, Y.; Contreras-Guerrero, Rocio; ...

    2015-11-16

    The integration of functional oxide thin-films on compound semiconductors can lead to a class of reconfigurable spin-based optoelectronic devices if defect-free, fully reversible active layers are stabilized. However, previous first-principles calculations predicted that SrTiO3 thin filmsgrown on Si exhibit pinned ferroelectric behavior that is not switchable, due to the presence of interfacial vacancies. Meanwhile, piezoresponse force microscopy measurements have demonstrated ferroelectricity in BaTiO3 grown on semiconductor substrates. The presence of interfacial oxygen vacancies in such complex-oxide/semiconductor systems remains unexplored, and their effect on ferroelectricity is controversial. We also use a combination of aberration-corrected scanning transmission electron microscopy and first-principles densitymore » functional theory modeling to examine the role of interfacial oxygen vacancies on the ferroelectricpolarization of a BaTiO3 thin filmgrown on GaAs. Moreover, we demonstrate that interfacial oxygen vacancies enhance the polar discontinuity (and thus the single domain, out-of-plane polarization pinning in BaTiO3), and propose that the presence of surface charge screening allows the formation of switchable domains.« less

  9. Films minces ferroélectriques Ba{2/3}Sr{1/3}TiO3 par ablation laser pour applications hyperfréquences

    NASA Astrophysics Data System (ADS)

    Delage, T.; Champeaux, C.; Catherinot, A.; Seaux, J. F.; Madrangeas, V.; Cros, D.

    2003-06-01

    Les matériaux oxydes ferroélectriques semblent des candidats potentiels intéressants pour les composants d'application dans le domaine des télécommunications. Parmi les matériaux ferroélectriques, le Titanate de Baryum Strontium BaxSr(1-x)TiO3 a l'avantage d'avoir une température de transition qui varie suivant son taux x de substitution en baryum. Les films de Ba{2/3}Sr{1/3}TiO3 sont élaborés sur substrats monocristallins MgO par ablation laser pulsée avec un laser KrF (248 nm, durée d'impulsion 14 ns), à un taux de répétition de 10 Hz avec une fluence de 3 J/cm^2 sur la surface de la cible et sous une atmosphère d'oxygène de 3.10^{-1} mbar. Les échantillons réalisés ont été étudiés en diffraction des rayons X en configuration 0-20 afin de déterminer l'orientation des films déposés. Les échantillons sont ensuite caractérisés dans une cavité résonante en hyperfréquence (12,5 GHz) afin de déterminer leur permittivité diélectrique. L'introduction d'une sous-couche de Ba{2/3}Sr{1/3}TiO3 déficitaire en oxygène permet d'obtenir des filnis d'épaisseur micronique possédant de bonnes caractéristiques cristallines et diélectriques.

  10. New insulating antiferromagnetic quaternary iridates MLa10Ir4O24 (M=Sr, Ba)

    SciTech Connect

    Zhao, Qingbiao; Han, Fei; Stoumpos, Constantinos C.; Han, Tian -Heng; Li, Hao; Mitchell, J. F.

    2015-07-01

    Recently, oxides of Ir4+ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, Jeff = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr2IrO4, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between Jeff = ½ and the S = ½ state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa10Ir4O24 (M = Sr, Ba). The crystal structure of both compounds features isolated IrO6 octahedra in which the electronic configuration of Ir is d5. As a result, both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa10Ir4O24 is an insulator.

  11. Temperature-controlled down-conversion luminescence behavior of Eu(3)(+) -doped transparent MF2 (M = Ba, Ca, Sr) glass ceramics.

    PubMed

    Zhou, B; E, C Q; Bu, Y Y; Meng, L; Yan, X H; Wang, X F

    2017-03-01

    Eu(3)(+) -doped transparent glass ceramics containing MF2 (M = Ba, Ca, Sr) nanocrystals were fabricated using a melt-quenching method, and the resulting structures were studied using X-ray diffraction. Levels (5) D1 and (5) D0 of Eu(3)(+) ions were verified as thermally coupled levels using the fluorescence intensity ratio method. The fluorescence intensity ratios, optical temperature sensitivity and thermal quenching ratios of the transparent glass ceramics were studied as a function of temperature. With an increase in temperature, the relative sensitivity (SR ) decreased sharply at first, then slowly increased, before finally decreasing. The minimum SR values of GCBaF2 (GCB), GCCaF2 (GCC) and GCSrF2 (GCS) were 2.8 × 10(-4) , 0.8 × 10(-4) and 1.9 × 10(-)(4)  K(-1) at 360, 269 and 319 K, respectively. Glass ceramics with an intense emission intensity can be used to convert the measured spectrum into temperature and may have an important role in temperature detectors.

  12. Synthesis and luminescence characterization of Y2 BaZnO5 :RE (RE = Eu(3)(+) , Tb(3)(+) , Pr(3)(+) and Sm(3)(+) ) phosphors.

    PubMed

    Taikar, D R; Joshi, C P; Moharil, S V

    2016-12-02

    Modified synthesis and luminescence of Y2 BaZnO5 phosphors activated with the rare earths (RE) Eu(3)(+) , Tb(3)(+) , Pr(3)(+) and Sm(3)(+) are reported. RE2 BaZnO5 phosphors have attracted attention because of their interesting magnetic and optical properties; and are usually prepared using a two-step solid-state reaction. In the first step, carbonates or similar precursors are thoroughly mixed and heated at 900°C to decompose them to oxides. To eliminate the unwanted phases like BaRE2 O4 , the resulting powders are reheated at 1100°C for a long time. We prepared Y2 BaZnO5 phosphors activated with various activators by replacing the first step with combustion synthesis. The photoluminescence results are presented. The photoluminescence results for Eu(3)(+) , Tb(3)(+) and Pr(3)(+) are in good agreement with the literature. However, photoluminescence emission from Sm(3)(+) has not been documented previously. The excitation spectrum of Eu(3)(+) is dominated by a charge transfer band around 261 nm, and an additional band around 238 nm is always present, irrespective of the type of activator. The presence of this band for all these different types of activators was interpreted as host absorption.

  13. Growth and Characterization of High-Quality Single Crystals of Ni- and Zn-Doped Bi2Sr2Ca(Cu2-xMx)O8+δ (M = Ni or Zn) High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Liu, Shan-Yu; Zhang, Wen-Tao; Zhao, Lin; Liu, Hai-Yun; Wu, Yue; Liu, Guo-Dong; Dong, Xiao-Li; Zhou, Xing-Jiang

    2012-08-01

    High-quality large single crystals of Ni- and Zn-doped Bi2Sr2Ca(Cu2-xMx)O8+δ (M = Ni or Zn) have been successfully grown by the traveling solvent floating zone technique. The single crystals are characterized by compositional and structural analyses and their physical properties are investigated by magnetic susceptibility and resistivity measurements. A record high critical temperature with a Tc = 97.5 K has been achieved in the annealed pristine Bi2212 single crystal. Substitution of Cu by Ni or Zn reduces the superconducting transition temperature when compared with pristine Bi2Sr2CaCu2O8+δ (Bi2212) grown under similar conditions. The successful growth of such pristine Ni- and Zn-doped Bi2212 single crystals will facilitate studies of the relationship between the magnetism and superconductivity in high-temperature cuprate superconductors.

  14. The direct growth of SrTiO 3 (100) layers on silicon (100) substrates; application as a buffer layer for the growth of DyBa 2Cu 3O 7- δ thin films

    NASA Astrophysics Data System (ADS)

    Méchin, L.; Gerritsma, G. J.; Garcia Lopez, J.

    1999-10-01

    Highly (100)-oriented SrTiO 3 thin films were sputtered on Si (100) substrates. After the optimization of the deposition conditions, the fraction of (110)-oriented material in the SrTiO 3 films was about 3%, but the rocking curve of the SrTiO 3 (200) peak was quite large (full width at half maximum (FWHM) ∼2.3°). Indeed grain boundaries crossing the whole SrTiO 3 film and an amorphous layer between Si and SrTiO 3 could be observed by transmission electron microscopy. DyBa 2Cu 3O 7- δ (DBCO) films were successively sputtered on the polycrystalline SrTiO 3 layers on Si. An Auger analysis revealed the presence of barium at the Si/SrTiO 3 interface that presumably diffused along the grain boundaries through SrTiO 3 to form barium silicates. By reducing both the DBCO deposition temperature and the SrTiO 3 thickness, we could prevent this diffusion and improve the electrical properties ( R300/ R100∼1 and Tc ( R=0) in the 40-60 K range). The specific problems for the growth of DBCO thin film on SrTiO 3-buffered silicon substrates by sputter deposition are finally pointed out.

  15. Interfacial dominated ferromagnetism in nanograined ZnO: a μSR and DFT study

    PubMed Central

    Tietze, Thomas; Audehm, Patrick; Chen, Yu–Chun; Schütz, Gisela; Straumal, Boris B.; Protasova, Svetlana G.; Mazilkin, Andrey A.; Straumal, Petr B.; Prokscha, Thomas; Luetkens, Hubertus; Salman, Zaher; Suter, Andreas; Baretzky, Brigitte; Fink, Karin; Wenzel, Wolfgang; Danilov, Denis; Goering, Eberhard

    2015-01-01

    Diamagnetic oxides can, under certain conditions, become ferromagnetic at room temperature and therefore are promising candidates for future material in spintronic devices. Contrary to early predictions, doping ZnO with uniformly distributed magnetic ions is not essential to obtain ferromagnetic samples. Instead, the nanostructure seems to play the key role, as room temperature ferromagnetism was also found in nanograined, undoped ZnO. However, the origin of room temperature ferromagnetism in primarily non–magnetic oxides like ZnO is still unexplained and a controversial subject within the scientific community. Using low energy muon spin relaxation in combination with SQUID and TEM techniques, we demonstrate that the magnetic volume fraction is strongly related to the sample volume fraction occupied by grain boundaries. With molecular dynamics and density functional theory we find ferromagnetic coupled electron states in ZnO grain boundaries. Our results provide evidence and a microscopic model for room temperature ferromagnetism in oxides. PMID:25747456

  16. Line patterning of (Sr,Ba)Nb{sub 2}O{sub 6} crystals in borate glasses by transition metal atom heat processing

    SciTech Connect

    Sato, M.; Honma, T.; Benino, Y.; Komatsu, T.

    2007-09-15

    Some NiO-doped Bi{sub 2}O{sub 3},La{sub 2}O{sub 3}-SrO-BaO-Nb{sub 2}O{sub 5}-B{sub 2}O{sub 3} glasses giving the formation of strontium barium niobate Sr{sub 0.5}Ba{sub 0.5}Nb{sub 2}O{sub 6} (SBN) crystals with a tetragonal tungsten-bronze structure through conventional crystallization in an electric furnace have been developed, and SBN crystal lines have been patterned on the glass surface by heat-assisted (250-300 deg. C) laser irradiation and scanning of continuous-wave Nd:YAG laser (wavelength: 1064 nm). The surface morphology and the quality of SBN crystal lines are examined from measurements of confocal scanning laser micrographs and polarized micro-Raman scattering spectra. The surface morphology of SBN crystal lines changes from periodic bump structures to homogeneous structures, depending on laser scanning conditions. It is suggested that the line patterned at the laser irradiation condition of laser power P=1 W and of laser scanning speed S=1 {mu}m/s in 2NiO-4La{sub 2}O{sub 3}-16SrO-16BaO-32Nb{sub 2}O{sub 5}-30B{sub 2}O{sub 3} glass has a possibility of the orientation of SBN crystals along the laser scanning direction. The present study demonstrates that the transition metal atom heat processing (i.e., a combination of cw Nd:YAG laser and Ni{sup 2+} ions) is a novel technique for spatially selected crystallization of SBN crystals in glass. - Graphical abstract: This figure shows the polarization optical (a) and confocal scanning laser (b) micrographs for the sample obtained by heat-assisted (300 deg. C) Nd:YAG laser irradiation with a laser power of P=1 W and laser scanning speed of S=1 {mu}m/s in Glass C. The figure demonstrates that the transition metal atom heat processing (i.e., a combination of cw Nd:YAG laser and Ni{sup 2+} ions) is a novel technique for spatially selected crystallization of SBN crystals in glass.

  17. Experimental study of REE, Ba, Sr, Mo and W partitioning between carbonatitic melt and aqueous fluid with implications for rare metal mineralization

    NASA Astrophysics Data System (ADS)

    Song, WenLei; Xu, Cheng; Veksler, Ilya V.; Kynicky, Jindrich

    2016-01-01

    Carbonatites host some unique ore deposits, especially rare earth elements (REE). Hydrothermal fluids have been proposed to play a significant role in the concentration and transport of REE and other rare metals in carbonatites, but experimental constraints on fluid-melt equilibria in carbonatitic systems are sparse. Here we present an experimental study of trace element (REE, Ba, Sr, Mo and W) partitioning between hydrous fluids and carbonatitic melts, bearing on potential hydrothermal activity associated with carbonatite ore-forming systems. The experiments were performed on mixtures of synthetic carbonate melts and aqueous fluids at 700-800 °C and 100-200 MPa using rapid-quench cold-seal pressure vessels and double-capsule assemblages with diamond traps for analyzing fluid precipitates in the outer capsule. Starting mixtures were composed of Ca, Mg and Na carbonates spiked with trace elements. Small amounts of F or Cl were added to some of the mixtures to study the effects of halogens on the element distribution. The results show that REE, Ba, Sr, Mo and W all preferentially partition into carbonatite melt and have fluid-melt distribution coefficients ( D f/m) below unity. The REE partitioning is slightly dependent on the major element (Ca, Mg and Na) composition of the starting mixtures, and it is influenced by temperature, pressure, and the presence of halogens. The fluid-melt D values of individual REE vary from 0.02 to 0.15 with D_{Lu}^{f} / {fm}{m} being larger than D_{La}^{f} / {fm}{m} by a factor of 1.1-2. The halogens F and Cl have strong and opposite effects on the REE partitioning. Fluid-melt D REE are about three times higher in F-bearing compositions and ten times lower in Cl-bearing compositions than in halogen-free systems. D_{W}^{f} / {fm}{m} and D_{Mo}^{f} / {fm}{m} are the highest among the studied elements and vary between 0.6 and 0.7; D_{Ba}^{f} / {fm}{m} is between 0.05 and 0.09, whereas D_{Sr}^{f} / {fm}{m} is at about 0.01-0.02. The

  18. Infrared study of the vibrational behavior of CrO 42- guest ions matrix-isolated in metal (II) sulfates (Me=Ca, Sr, Ba, Pb)

    NASA Astrophysics Data System (ADS)

    Stoilova, D.; Georgiev, M.; Marinova, D.

    2005-03-01

    Infrared spectra of matrix-isolated CrO 42- guest ions in host sulfate matrices - CaSO 4·2H 2O, SrSO 4, BaSO 4 and PbSO 4 are reported and discussed with respect to the Cr-O stretching and O-Cr-O bending modes. An adequate measure for the CrO 42- guest ion distortion is the site group splitting Δ νas and Δ νmax (the difference between the highest and the lowest wavenumbered components of the stretching and bending modes). When the smaller SO 42- ions are replaced by the larger CrO 42- ions the mean frequencies of the asymmetric stretching and bending modes ( ν and ν) as well as the frequencies of ν1 of the CrO 42- guest ions are shifted to higher wavenumbers as compared to those in the respective neat chromates due to the larger repulsion potential at the host lattice sites (smaller values of the unit-cell volumes of the neat sulfates than those of the neat chromates). The CrO 42- guest ions exhibit three bands corresponding to the ν3 modes as deduced from the site group analysis ( C2 site symmetry in CaSO 4·2H 2O and Cs site symmetry in SrSO 4, BaSO 4 and PbSO 4). However, the bending modes ν4 and ν2 of the CrO 42- guest ions in SrSO 4, BaSO 4 and PbSO 4 show an effectively higher local symmetry than the 'rigorous' crystallographic one (two bands for ν4 and one band for ν2 instead of a triplet and a doublet expected, respectively). Such different apparent site symmetries observed in various spectral regions may be attributed to the different influence of energetic and geometrical distortions of the polyatomic entities at particular site on various modes.

  19. Micro-Structural Properties of YBa2Cu3O(7-x)/ZnO Nanorods on SrTiO3.

    PubMed

    Jin, Zhenlan; Park, Changin; Song, Kyu Jeong; Kang, Sukil; Ko, Kyeong-Eun; Park, Chan; Ko, Rock Kil; Han, S W

    2015-01-01

    We examined the local structural and the interfacial properties of YBa2Cu3O(7-x) (YBCO)/ZnO nanorods on SrTiO3 (STO) substrates using various measurements. Vertically aligned ZnO nanorods were synthesized on STO substrates using a catalyst-free metal-organic chemical vapor deposition. YBCO films were deposited ex-situ on the ZnO nanorods/STO templates using a DC magnetron sputtering deposition. X-ray diffraction revealed that the YBCO films were crystallized along their c-axes on the ZnO nanorods/STO templates. Transmission electron microscopy measurements demonstrated that YBCO filled the space between ZnO nanorods and that both interfaces of YBCO/ZnO nanorods and ZnO nanorods/STO were quite clean with no disorder. Polarization-dependent extended X-ray absorption fine structure measurements at the Cu K edge showed extra disorder in the CuO2 planes of YBCO/ZnO nanorods/STO, compared with that of YBCO/STO. The superconductivity transition temperature (T(c)) of YBCO/ZnO nanorods/STO was approximately 50 K whereas that of YBCO/STO was 93 K. The decrease of T(c) of YBCO/ZnO nanorods/STO was ascribed to the structural disorder of CuO2 planes as well as grain boundaries in the YBCO films.

  20. A promising novel orange-red emitting SrZnV2O7:Sm3+ nanophosphor for phosphor-converted white LEDs with near-ultraviolet excitation

    NASA Astrophysics Data System (ADS)

    Dalal, Mandeep; Taxak, V. B.; Chahar, Sangeeta; Khatkar, Avni; Khatkar, S. P.

    2016-02-01

    A novel trivalent samarium doped SrZnV2O7 nanophosphors was developed via urea assisted solution combustion method using metal nitrates as initial raw materials. The qualitative and quantitative phase analysis was carried out using Rietveld refinement technique. It was found to crystallize in monoclinic lattice with the P121/n1 (14) space group. The photoluminescent spectral study of SrZnV2O7:Sm3+ revealed that the excitation of 405 nm yields the characteristic emission peaks at 569, 599, 640 and 702 nm due to 4G5/2→6H5/2, 4G5/2→6H7/2, 4G5/2→6H9/2 and 4G5/2→6H11/2 respectively. The optimum concentration of Sm3+ ion in SrZnV2O7 for best luminescence was found to be 2 mol%. The luminescence intensity was further enhanced by incorporating compensator charge R+ (R=Li, Na, and K) into the SrZnV2O7:0.02Sm3+ nanophosphor. The critical distance for non-radiative energy transfer was calculated to be 26.64 Å. Dipole-dipole (d-d) interactions were ascribed as the major factor responsible for concentration quenching arising from the over-doping of the activator ions. The results indicate that these nanophosphors are suitable candidate for PC-WLEDs using near UV excitation.

  1. First-principles study of the electronic structure, charge density, Fermi surface and optical properties of zintl phases compounds Sr2ZnA2 (A=P, As and Sb)

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Azam, Sikander

    2013-11-01

    We present first-principles calculations of the electronic structure, Fermi surface, electronic charge density and optical properties of Sr2ZnA2 (A=P, As and Sb) based on density-functional theory using the local density approximation (LDA), generalized-gradient approximation (GGA) and the Engel-Vosko GGA formalism (EV-GGA). Additionally, modified Becke-Johnson (mBJ) is also used to improve the band splitting results. The calculated band structure and density of states show that Sr2ZnA2 compounds are metallic. The total DOS at Fermi level N(EF) is 72.92, 73.06 and 33.47 states/eV and the bare electronic specific heat coefficient (γ) is 12.64, 5.805 and 12.67 mJ/mol-K2 for Sr2ZnP2, Sr2ZnAs2 and Sr2ZnSb2, respectively. The Fermi surface of Sr2ZnA2 compounds is composed of two bands crossing along the Γ-A direction of Brillouin zone. There exists a strong hybridization between Zn-p/s and Sb-d, Sb-p and Sr-d and also between Sr-s and Sr-p states. The bonding features are analyzed by using the electronic charge density contour in the (101) crystallographic plane. We found that Sr forms an ionic bond with Zn, whereas Zn forms a strong covalent interaction with P/As/Sb atoms. For further insight information about the electronic structure, the optical properties are derived and analyzed.

  2. Preparation and Comparison of the Photoelectronic Properties of Sr2Nb207 and Ba0.5Sr0.5Nb2O6.

    DTIC Science & Technology

    1979-08-20

    eV, but a flat-band potential of 0.1 V vs SCE at a pH of 13.3. Hence, the gain of utilizing a larger portion of the solar spectrum obtained from the...as a tetragonally distorted perovskite , ( 3) whereas Sr2Nb2O7 was reported to be orthorhombic (4). - 1...glass cell with a quartz window, and a current amplifier as nreviously described (8). The electrolyte, 0.2 M sodium acetate (pH 8.3), was purged of

  3. Novel lead-free ferroelectric film by ultra-small Ba0.8Sr0.2TiO3 nanocubes assembled for a large electrocaloric effect.

    PubMed

    Su, Ran; Zhang, Dawei; Liu, Yang; Lu, Jiangbo; Wang, Zhipeng; Li, Linglong; Bian, Jihong; Wu, Ming; Lou, Xiaojie; Yang, Yaodong

    2016-10-26

    A giant electrocaloric effect (ECE) can be achieved in ferroelectric thin films, which demonstrates the applications of thin films in alternative cooling. However, electrocaloric thin films fabricated by conventional techniques, such as the pulsed laser deposition or sol-gel methods, may be limited by high costs, low yield and their dependence on substrates. In this study, we present a new bottom-up strategy to construct electrocaloric Ba0.8Sr0.2TiO3 thin films by assembling precisely designed building blocks of ferroelectric nanocubes, which is supported by detailed structural characterization. Moreover, it is found that our assembled Ba0.8Sr0.2TiO3 films differ remarkably from both individual Ba0.8Sr0.2TiO3 NPs and bulk Ba0.8Sr0.2TiO3 ceramics in terms of new collective ferroelectric properties, including superior and diffused permittivity constants and polarization-electric field loops. Benefiting from these unique ferroelectric properties, a giant ECE (9.1 K) over a broad temperature range (20 °C to 60 °C) is achieved, which is very large in the lead-free oxide film. Clearly, this bottom-up strategy provides a promising pathway for developing high electrocaloric effect devices.

  4. Effet du traitement thermique sur la structure cristalline, la température critique et la ligne d'irréversibilité de Lm(SrBa)Cu 3O 6+ z (Lm=Sm, Nd)

    NASA Astrophysics Data System (ADS)

    Bellioua, Mohammed; Nafidi, Abdelhakim; El Kaaouachi, Abdelhamid; Nafidi, Ahmed

    2004-03-01

    We have studied the structural and superconducting properties of Lm(SrBa)Cu 3O 6+ z (Lm=Sm, Nd). Each of the two samples was submitted to two types of heat treatment: an annealing in oxygen [O] and a heated in argon followed by oxygen annealing [A, O]. Our iodometry measurements indicate the same total oxygen constant 6+ z, which was around 6.95±0.04 in each sample. In the case of SmSrBaCu 3O 6+ z, the treatment [A, O] increased the orthorhombicity ɛ= b- a/( b+ a) from 0 to 5.34×10 -3, indicating a tetragonal to orthorhombic structural phase transition, accompanied by an increase of 6 K in critical temperature Tc to Tc[A, O]=85 K. While in the case of NdSrBaCu 3O 6+ z, ɛ[O]= ɛ[A, O]=0 but the Tc[O]=68 K increase by 10 K. Further, there was an enhancement of the irreversibility Tp/ Tc line whatever Lm. A combination of several factors such as the change of the ionic size of the rare earth Lm, its disorder on the (Sr, Ba) site, chain oxygen ordering and increase in phase purity for the [A, O] samples may qualitatively account for the observed data. To cite this article: M. Bellioua et al., C. R. Physique 5 (2004).

  5. Fluorescence and phosphorescence properties of the low temperature forms of the MAl{sub 2}Si{sub 2}O{sub 8}:Eu{sup 2+} (M=Ca, Sr, Ba) compounds

    SciTech Connect

    Clabau, Frederic; Garcia, Alain; Bonville, Pierre; Gonbeau, Danielle; Le Mercier, Thierry; Deniard, Philippe; Jobic, Stephane

    2008-06-15

    The fluorescence and phosphorescence properties of Europium-doped MAl{sub 2}Si{sub 2}O{sub 8} (M=Ca, Sr, Ba) are reinvestigated and discussed on the basis of the propensity of an activator to agglomerate with an oxygen vacancy. Due to a stronger attraction of the anion vacancy towards Eu{sup 2+} cations going from BaAl{sub 2}Si{sub 2}O{sub 8} to SrAl{sub 2}Si{sub 2}O{sub 8} and CaAl{sub 2}Si{sub 2}O{sub 8} host lattices, the interpretation of the fluorescence spectra turns out to be less trivial in the Ca and Sr host lattices than in the Ba one and requests the account for Eu{sup 2+} cations lying at alkaline-earth sites with or without vacancy in their neighborhood. Phosphorescence in these compounds is highlighted. - Graphical abstract: The Eu{sup 2+}-doped MAl{sub 2}Si{sub 2}O{sub 8} (M=Ca, Sr, and Ba) aluminosilicates exhibit a bluish white luminescence, which can last several minutes after the removal of the excitation. The account for Eu{sup 2+} cations coupled with defects is required to explain fluorescence spectra.

  6. The influence of the concentration of Sr ions on the crystal and magnetic structures of Ba2 - x Sr x FeMoO6 double perovskites ( x = 0-1.6)

    NASA Astrophysics Data System (ADS)

    Turchenko, V. A.; Kalanda, N. A.; Kovalev, L. V.; Simkin, V. G.; Balagurov, A. M.

    2017-01-01

    The crystal and magnetic structures of a solid solution of double perovskite Ba2 - x Sr x FeMoO6 ( x = 0-1.6) have been investigated by neutron diffraction. The high-resolution diffraction patterns have provided precise information about the changes in the crystal and magnetic structures with an increase in the strontium content and data on the behavior of the sample microstructure. Replacement of barium with strontium leads to a change in the lattice symmetry from cubic ( x = 0, sp. gr. Fm3¯ m)) to tetragonal ( x = 0.4, sp. gr. I4/ m). At x = 1.0, the symmetry is either tetragonal (sp. gr. I4/ m) or orthorhombic (sp. gr. Fmmm), and at x = 1.6 the symmetry becomes again tetragonal (sp. gr. I4/ m). The values of the Curie temperature and microstrain increase with an increase in the strontium content.

  7. Formation and structural characterization of 1:1 ordered perovskites in the Ba(Zn{sub 1/3}Ta{sub 2/3})O{sub 3}-BaZrO{sub 3} system

    SciTech Connect

    Chai, L.; Davies, P.K.

    1997-12-01

    The phase stabilities in the (1{minus}x)Ba(Zn{sub 1/3}Ta{sub 2/3})O{sub 3} (BZT)-xBaZrO{sub 3} (BZ) system have been investigated using samples prepared by the mixed-oxide method. The substitution of Zr{sup 4+} destabilizes the 1:2 cation ordering in BZT and promotes the formation of a cubic, 1:1 ordered structure with a doubled perovskite repeat. The homogeneity range of the 1:1 phase extends from x = 0.04 to approximately x = 0.25; substitutions beyond this range stabilize a disordered perovskite. The limits of stability of the 1:1 ordering coincide with compositions previously found to exhibit anomalies in their dielectric loss. The range of homogeneity is consistent with a random layer model for the 1:1 ordered Ba{l_brace}{beta}{prime}{sub 1/2}{beta}{double_prime}{sub 1/2}{r_brace}O{sub 3} structure. In this model the {beta}{double_prime} positions are assumed to be occupied exclusively by Ta{sup 5+}, and the {beta}{prime} sites by a random distribution of Zn{sup 2+}, Zr{sup 4+}, and the remaining Ta{sup 5+} cations. The validity of the model, where the ordered solid solutions can be represented by Ba{l_brace}[Zn{sub (2{minus}y)/3}Ta{sub (1{minus}2y)/3}Zr{sub y}]{sub 1/2}[Ta]{sub 1/2}{r_brace}O{sub 3} (y = 2x) was confirmed by Rietveld refinements conducted using data collected with a synchrotron X-ray source.

  8. Structural and dielectric properties of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} thin films grown by PLD

    SciTech Connect

    James, K. K.; Satish, B.; Jayaraj, M. K.

    2014-01-28

    Ferroelectric thin films of Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} (BST) were deposited on Si/SiO{sub 2}/TiO{sub 2}/Pt (PtSi) substrate by pulsed laser deposition (PLD). Crystalline films with perovskite structure were obtained without post-deposition annealing. Phase purity of the deposited films was confirmed by x-ray diffraction. The lowest value of FWHM obtained for the film deposited at oxygen pressure 5.4×10{sup −4} mbar and substrate temperature 600°C, indicates the high crystallinity of the film. The room temperature dielectric constant at 100 kHz was 85. Butterfly loop, which is the characteristic of ferroelectric materials, was obtained in the regime of −4 to +4V. The leakage current density was nearly 9×10{sup −13} Acm{sup −2}.

  9. REDUCED LEAKAGE CURRENT AND ENHANCED MAGNETIC PROPERTIES OF (Bi,Nd)FeO3 THIN FILMS GROWN ON (Ba,Sr)TiO3 BOTTOM LAYER

    NASA Astrophysics Data System (ADS)

    Ma, C. B.; Tang, X. G.; Chen, D. G.; Liu, Q. X.; Jiang, Y. P.; Xiong, D. P.; Zhou, Y. C.

    2012-09-01

    A multiferroic heterostructure composed of (Bi0.875Nd0.125)FeO3 (BNF) are grown on (Ba0.65Sr0.35)TiO3(BST) buffered Pt/Ti/SiO2/Si(100) substrate by rf-magnetron sputtering. The heterostructure BNF/BST exhibits a quite low leakage current (3.7 × 10-7 A/cm2 at 300 kV/cm) and dielectric loss (0.0036 at 100 kHz) at room temperature. The saturated magnetization and the coercive field of the BST/BNF heterostructure are 37.7 emu/cm3 and 357.6 Oe, respectively. The low leakage current owed to the action of BST in the charge transfer between BNF and the bottom electrode, the coupling reaction between BST and BNF films. And the better crystallization in BNF/BST heterostructure thin film lead to the ferromagnetic properties enhanced.

  10. Synthesis and magnetic susceptibility of M /SUB x/ V/sub 2/O/sub 3//sup +/y solid solutions (M = Ca, Sr, Ba)

    SciTech Connect

    Volkov, V.L.; Milova, G.D.; Perelyaev, V.A.

    1985-12-01

    The authors synthesize and study the magnetic susceptibility of solid solutions of alkaline-earth metal oxides in V/sub 2/O/sub 3/. As the initial substances ultrapure V/sub 2/O/sub 5/, CaCo/sub 3/, BaCO/sub 3/, and SrCO/sub 3/ and chemically pure metavanadates and orthovanadates of alkaline-earth metals were used. The x-ray analysis was carried out on a DRON-2.5 diffractometer with ionization detection of Cu Ka radiation. The magnetic susceptibility was measured by the Faraday method. The authors establish the existence of solid solutions of composition MxV/sub 2/O/sub 3//sup +/y, determine their crystallographic parameters, and study the magnetic susceptibility. The transition temperature of the specimens decreases as the radius of the M/sup 2 +/ ions and the unit-cell parameter c of the crystal decrease.

  11. Induced Ti magnetization at La0.7Sr0.3MnO3 and BaTiO3 interfaces

    DOE PAGES

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; ...

    2016-04-01

    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric BaTiO3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. Moreover, the Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. But, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.

  12. Trace element geochemistry (Li, Ba, Sr, and Rb) using Curiosity's ChemCam: early results for Gale crater from Bradbury Landing Site to Rocknest

    USGS Publications Warehouse

    Ollila, Ann M.; Newsom, Horton E.; Clark, Benton; Wiens, Roger C.; Cousin, Agnes; Blank, Jen G.; Mangold, Nicolas; Sautter, Violaine; Maurice, Sylvestre; Clegg, Samuel M.; Gasnault, Olivier; Forni, Olivier; Tokar, Robert; Lewin, Eric; Dyar, M. Darby; Lasue, Jeremie; Anderson, Ryan; McLennan, Scott M.; Bridges, John; Vaniman, Dave; Lanza, Nina; Fabre, Cecile; Melikechi, Noureddine; Perett, Glynis M.; Campbell, John L.; King, Penelope L.; Barraclough, Bruce; Delapp, Dorothea; Johnstone, Stephen; Meslin, Pierre-Yves; Rosen-Gooding, Anya; Williams, Josh

    2013-01-01

    The ChemCam instrument package on the Mars rover, Curiosity, provides new capabilities to probe the abundances of certain trace elements in the rocks and soils on Mars using the laser-induced breakdown spectroscopy technique. We focus on detecting and quantifying Li, Ba, Rb, and Sr in targets analyzed during the first 100 sols, from Bradbury Landing Site to Rocknest. Univariate peak area models and multivariate partial least squares models are presented. Li, detected for the first time directly on Mars, is generally low (100 ppm and >1000 ppm, respectively. These analysis locations tend to have high Si and alkali abundances, consistent with a feldspar composition. Together, these trace element observations provide possible evidence of magma differentiation and aqueous alteration.

  13. Dipole spring ferroelectrics in superlattice SrTiO3/BaTiO3 thin films exhibiting constricted hysteresis loops

    SciTech Connect

    Wu, Pingping; Ma, Xingqiao; Li, Yulan; Gopalan, Venkatraman; Chen , L.Q.

    2012-03-01

    Ferroelectric superlattice heterostructures have recently been explored for potential applications in electronic devices. In this letter we employed the phase-field approach to simulate the domain structure and switching of a (BaTiO3)8/(SrTiO3)3 superlattice film constrained by a GdScO3 substrate. A constricted ferroelectric hysteresis loop was observed with a high saturation polarization but a small coercive field. The shape of the hysteresis loop is understood by analyzing the ferroelectric polarization distributions during switching. It is demonstrated that the multilayers stack behave as dipole spring ferroelectric, named in analogy to exchange spring magnets in magnetic multilayers that show similar loops.

  14. Synthesis and Characterization of Alkaline-Earth Metal (Ca, Sr, and Ba) Doped Nanodimensional LaMnO3 Rare-Earth Manganites

    NASA Astrophysics Data System (ADS)

    Asma, Khalid; Saadat, Anwar Siddiqi; Affia, Aslam

    2013-07-01

    The substitution of divalent cations of alkaline-earth elements in nanodimensional structures of rare-earth manganites produces advanced materials with potential electrical and magnetic functionalities. A systematic investigation of La0.65A0.35MnO3 (A = Ca, Sr, Ba) materials synthesized with a modified citrate route adopting ethanol dehydration has been undertaken. The structural and morphological analyses are carried out by using x-ray diffraction and scanning electron microscopy, respectively. Resistivity measurements are performed in variation with temperature to study the electrical transport properties which are found to vary with the size of the A-site cationic radius. Room temperature magnetic measurements are carried out to investigate the type of magnetic phase present in materials. The stability of the magnetic phase and coercivity are found to be dependent on the size of nanocrystallites.

  15. Thin Film Ba(x)Sr(1-x)TiO3 Ku- and K-Band Phase Shifters Grown on MgO Substrates

    NASA Technical Reports Server (NTRS)

    VanKeuls, F. W.; Mueller, C. H.; Miranda, F. A.; Romanofsky, R. R.; Horwitz, J. S.; Chang, W.; Kim, W. J.

    1999-01-01

    We report measurements of gold circuits fabricated on four Ba(x)Sr(1-x)TiO3 films doped with 1% Mn grown on MgO substrates by laser ablation. Low frequency measurements of epsilon(sub r) and tan(delta) on interdigital capacitors are compared with high frequency measurements of phase shift and insertion loss on coupled microstrip phase shifters done on the same films. The variation in temperature of both high and low frequency device parameters is compared. Annealed and unannealed films are compared. Room temperature figures of merit of phase shift per insertion loss of up to 58.4 C/dB at 18 GHz and 400 V dc bias were measured.

  16. Improvement of critical current density in thallium-based (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) superconductors

    NASA Technical Reports Server (NTRS)

    Ren, Z. F.; Wang, C. A.; Wang, J. H.; Miller, D. J.; Goretta, K. C.

    1995-01-01

    Epitaxial (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) ((Tl,Bi)-1223) thin films on (100) single crystal LaAlO3 substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field cooled magnetization, and transport critical current density (J(sub c)) were measured. The zero-resistance temperature was 105-111 K. J(sub c) at 77 K and zero field was greater than 2 x 10(exp 6) A/sq cm. The films exhibited good flux pinning properties.

  17. Influence of strain on an epitaxial ferroelectric (Ba0.50Sr0.50)TiO3 nanodot under different electrical boundary conditions

    NASA Astrophysics Data System (ADS)

    Bin-Omran, S.

    2017-02-01

    A first-principles-derived effective Hamiltonian approach is used to reveal the temperature-versus-misfit strain phase diagram of an epitaxial (Ba0.50Sr0.50)TiO3 dot under different electrical boundary conditions. The results indicate that the electrical polarization and toroidal moment are highly sensitive to the applied strain and/or electrical boundary conditions, resulting in a wide variety of phases that are not found in a free-standing BST dot and in bulk. The calculations indicate that within a narrow range of surface charge screening an intermediate phase in which the polarization and toroidal moment coexist. The dependences of the electrical polarization, toroidal moment and dielectric permittivity on the misfit strain and electrical boundary conditions at room temperature are also investigated and compared with the available theoretical predictions and experimental measurements.

  18. The coordination complex structures and hydrogen bonding in the three-dimensional alkaline earth metal salts (Mg, Ca, Sr and Ba) of (4-aminophenyl)arsonic acid.

    PubMed

    Smith, Graham; Wermuth, Urs D

    2017-01-01

    (4-Aminophenyl)arsonic acid (p-arsanilic acid) is used as an antihelminth in veterinary applications and was earlier used in the monosodium salt dihydrate form as the antisyphilitic drug atoxyl. Examples of complexes with this acid are rare. The structures of the alkaline earth metal (Mg, Ca, Sr and Ba) complexes with (4-aminophenyl)arsonic acid (p-arsanilic acid) have been determined, viz. hexaaquamagnesium bis[hydrogen (4-aminophenyl)arsonate] tetrahydrate, [Mg(H2O)6](C6H7AsNO3)·4H2O, (I), catena-poly[[[diaquacalcium]-bis[μ2-hydrogen (4-aminophenyl)arsonato-κ(2)O:O']-[diaquacalcium]-bis[μ2-hydrogen (4-aminophenyl)arsonato-κ(2)O:O

  19. Close correlation between magnetic properties and the soft phonon mode of the structural transition in BaFe2As2 and SrFe2As2

    DOE PAGES

    Parshall, D.; Pintschovius, L.; Niedziela, Jennifer L.; ...

    2015-04-27

    Pmore » arent compounds of Fe-based superconductors undergo a structural phase transition from a tetragonal to an orthorhombic structure. We investigated the temperature dependence of the frequencies of TA phonons that extrapolate to the shear vibrational mode at the zone center, which corresponds to the orthorhombic deformation of the crystal structure at low temperatures in BaFe2As2 and SrFe2As2. We found that acoustic phonons at small wave vectors soften gradually towards the transition from high temperatures, tracking the increase of the size of slowly fluctuating magnetic domains. On cooling below the transition to base temperature the phonons harden, following the square of the magnetic moment (which we find is proportional to the anisotropy gap). Finally, our results provide evidence for close correlation between magnetic and phonon properties in Fe-based superconductors.« less

  20. Thickness and temperature dependent electrical characteristics of crystalline Ba{sub x}Sr{sub 1-x}TiO{sub 3} thin films

    SciTech Connect

    Panda, B.; Roy, A.; Dhar, A.; Ray, S. K.

    2007-03-15

    Polycrystalline Ba{sub 1-x}Sr{sub x}TiO{sub 3} (BST) thin films with three different compositions have been deposited by radio-frequency magnetron sputtering technique on platinum coated silicon substrates. Samples with buffer and barrier layers for different film thicknesses and processing temperatures have been studied. Crystallite size of BST films has been found to increase with increasing substrate temperature. Thickness dependent dielectric constant has been studied and discussed in the light of an interfacial dead layer and the finite screening length of the electrode. Ferroelectric properties of the films have also been studied for various deposition conditions. The electrical resistivity of the films measured at different temperatures shows a positive temperature coefficient of resistance under a constant bias voltage.

  1. Rare-Earths Centers (Sm{sup 3+}, Eu{sup 3+}, Yb{sup 3+}) in MeF{sub 2}(Me = Ca, Sr, Ba, Cd) Crystals

    SciTech Connect

    Nikiforov, A. E.; Chernyshev, V. A.; Volodin, V. P.; Avram, N. M.; Avram, C. N.; Vaida, M.

    2010-08-04

    Rare-earth elements RE{sup 3+}(RE = Sm, Eu, Yb) form impurity centers in fluorite-like crystals MeF{sub 2}(Me = Ca, Sr, Ba, Cd). The crystal structure of cubic, trigonal and tetragonal centers in MeF{sub 2} has been investigated in the framework of shell model and pair potential approximation. The crystal field parameters were calculated with the exchange charges model, using the optimized geometry of the doped host matrix. With these parameters we have been calculated the optical spectra and spin-Hamiltonian (g-factors) of RE{sup 3+} in MeF{sub 2}, for some combination of R{sup 3+} and MeF{sup 2}. The obtained results were discussed and comparison with experimental data was made. A good agreement confirms the method and model of calculations.

  2. Flexoelectric Induced Caloric Effect in Truncated Pyramid Shaped Ba0.67Sr0.33TiO3 Ferroelectric Material

    NASA Astrophysics Data System (ADS)

    Patel, Satyanarayan; Chauhan, Aditya; Madhar, Niyaz Ahamad; Ilahi, Bouraoui; Vaish, Rahul

    2017-02-01

    Solid state refrigeration based on ferroelectric materials can potentially be competing in not-in-kind refrigeration technology. However, their functionality is currently limited to Curie temperatures. Through this article, authors have attempted to describe an unexplored component of the stress-driven caloric effect, obtainable beyond the Curie point. The phenomenon, termed as the flexocaloric effect (FCE), relies on inhomogeneous straining of the crystal lattice to induce polarization in centrosymmetric crystals (flexoelectricity). For this study, a truncated pyramid geometry was selected, and the dependence of sample height on caloric capacity was studied. A peak temperature change of 1.75 K (313 K) was estimated for Ba0.67Sr0.33TiO3 (BST) ceramics employing a truncated pyramid configuration.

  3. Neutron scattering studies of the ferroelectric distortion and spin dynamics in the type-1 multiferroic perovskite Sr0.56Ba0.44MnO3

    NASA Astrophysics Data System (ADS)

    Pratt, Daniel K.; Lynn, Jeffrey W.; Mais, James; Chmaissem, Omar; Brown, Dennis E.; Kolesnik, Stanislaw; Dabrowski, Bogdan

    2014-10-01

    The magnetic order, spin dynamics, and crystal structure of the multiferroic Sr0.56Ba0.44MnO3 have been investigated using neutron and x-ray scattering. Ferroelectricity develops at TC=305 K with a polarization of 4.2 µC /cm2 associated with the displacements of the Mn ions, while the Mn4+ spins order below TN≈200 K into a simple G-type commensurate magnetic structure. Below TN the ferroelectric order decreases dramatically, demonstrating that the two order parameters are strongly coupled. The ground state spin dynamics is characterized by a spin gap of 4.6(5) meV and the magnon density of states peaking at 43 meV. Detailed spin wave simulations with a gap and isotropic exchange of J =4.8(2) meV describe the excitation spectrum well. Above TN strong spin correlations coexist with robust ferroelectric order.

  4. A comparative study based on the first principles calculations of ATiO3 ( A = Ba, Ca, Pb and Sr) perovskite structure

    NASA Astrophysics Data System (ADS)

    Kamruzzaman, M.; Helal, M. A.; Ara, I. E.; Farid Ul Islam, A. K. M.; Rahaman, M. M.

    2016-10-01

    Structural, electronic, elastic, thermodynamic, vibrational and optical properties of the cubic phase of ATiO3 ( A = Ba, Ca, Pb and Sr) crystals have been carried out based on the density functional theory (DFT). The calculated equilibrium lattice parameters, band structures, elastic constants and the elastic moduli of ATiO3 are in good agreement with the theoretical and experimental results. The ferroelectric phenomenon of the crystals has been analyzed based on the nature of their phonon spectra. The phonon frequencies and the Born effective charges have been calculated to elucidate the ferroelectric instability of the cubic phase of ATiO3 by calculating the interatomic forces for several small displacements consistent with the symmetry of modes.

  5. Magnetic field controllable electric polarization in Y-type hexaferrite Ba0.5Sr1.5Co2Fe12O22

    NASA Astrophysics Data System (ADS)

    Wang, Guohua; Cao, Shixun; Cao, Yiming; Hu, Shunbo; Wang, Xinyan; Feng, Zhenjie; Kang, Baojuan; Chai, Yisheng; Zhang, Jincang; Ren, Wei

    2015-09-01

    We report the magnetic properties and the magnetoelectric effect in Y-type hexaferrite polycrystalline sample of Ba0.5Sr1.5Co2Fe12O22 (BSCFO). The magnetic critical temperature of BSCFO is 620 K, and the low-temperature helical magnetic order can hold up to 255 K. The isothermal magnetization curves sustain ferromagnetic hysteresis from 10 K to 300 K. Under external magnetic fields, the magnetic field induced electric polarization is observed up to 150 K. The magnitude and the sign of the electric polarization can be controlled by the applied magnetic field. These magnetic and magnetoelectric results provide the promise of the studied new hexaferrite as a potential multiferroic material.

  6. Giant elastocaloric effect in ferroelectric Ba0.5Sr0.5TiO3 alloys from first-principles

    NASA Astrophysics Data System (ADS)

    Lisenkov, S.; Ponomareva, I.

    2012-09-01

    As the need for efficient energy converting devices has been rapidly increasing, the materials that exhibit large or even giant caloric responses have emerged as promising candidates for solid-state refrigeration, which is an energy-efficient and environmentally friendly alternative to the conventional refrigeration technology. However, despite recent ground breaking discoveries of giant caloric responses in some materials, they appear to remain one of nature's rarities. Here we predict the existence of giant elastocaloric effect in ferroelectric Ba0.5Sr0.5TiO3 alloys, which adds one more member to this exclusive collection. Moreover, this computational finding reveals the multicaloric nature of such alloys, which could lead to new paradigms for cooling devices.

  7. Absolute refractive indices and thermal coefficients of CaF2, SrF2, BaF2, and LiF near 157 nm.

    PubMed

    Burnett, John H; Gupta, Rajeev; Griesmann, Ulf

    2002-05-01

    We present high-accuracy measurements for wavelengths near 157 nm of the absolute index of refraction, the index dispersion, and the temperature dependence of the index for the ultraviolet optical materials with cubic symmetry: CaF2, SrF2, BaF2, and LiF. Accurate values of these quantities for these materials are needed for designs of the lens systems for F2 excimer-laser-based exposure tools for 157-nm photolithography. These tools are expected to use CaF2 as the primary optical material and possibly one of the others to correct for chromatic aberrations. These optical properties were measured by the minimum deviation method. Absolute refractive indices were obtained with an absolute accuracy of 5 x 10(-6) to 6 x 10(-6).

  8. Microwave dielectric and optical properties of amorphous and crystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Goud, J. Pundareekam; Joseph, Andrews; Ramakanth, S.; Naidu, Kuna Lakshun; Raju, K. C. James

    2016-05-01

    The thin films of composition Ba0.5Sr0.5TiO3 (BST5) were deposited by Pulsed Laser Deposition technique on amorphous fused silica substrates at room temperature (RT) and at 700°C. The film deposited at RT is amorphous while the other crystallized in cubic structure. The refractive index (n) and optical band gap (Eg) extracted from transmission spectra in the 190 -2500 nm range. Microwave dielectric properties were investigated using the Split Post Dielectric Resonators (SPDR) technique at spot frequencies of 10GHz and 20GHz. The experimental results show that thin films deposited at high temperature (700°C) shows very high dielectric constant for both 10GHz and 20 GHz. These high dielectric constant films can be used in a wide range of applications such as capacitors, non-volatile high speed random access memories, and electro-optic devices.

  9. The features of structural transformations in lanthanum manganites La{sub 1−x}A{sub x}MnO{sub 3+δ} (A = Ca, Sr, Ba)

    SciTech Connect

    Sedykh, Vera D.

    2014-10-27

    In this work, the effect of the ionic radius and concentration of a doping element on the features of the structural transformations in polycrystalline lanthanum manganites, La{sub 1−x}A{sub x}MnO{sub 3+δ} (A = Ca, Sr, Ba), has been studied by Mössbauer spectroscopy and X-ray diffraction analysis. For Mössbauer investigations, a small amount of {sup 57}Fe (2 at%) Mössbauer isotope was introduced into the samples. It follows from the analysis of the obtained data that both common features of the structural transformations and differences between them exist in lanthanum manganites depending on ionic radius and concentration of a doping element.

  10. Structural and Optical properties of poly-crystalline BaTiO3 and SrTiO3 prepared via solid state route

    NASA Astrophysics Data System (ADS)

    Jarabana, Kanaka M.; Mishra, Ashutosh; Bisen, Supriya

    2016-10-01

    Polycrystalline BaTiO3 (BTO) and SrTiO3 (STO) were synthesized by solid state route method and properties of made polycrystalline were characterized by X-Ray diffraction (XRD), Raman Spectroscopy & FTIR Spectroscopy. XRD analysis shows that samples are crystalline in nature. In Raman Spectroscopy measurement, the experiment has been done with the help of JOBIN-YOVN HORIBA LABRAM HR800 single monochromator, which is coupled with a “peltier cooled” charge coupled device (CCD). Raman Spectroscopy at low temperature measurement shows the phase transition above & below the curie temperature in samples. Fourier transform Infrared spectroscopy was used to determine the Ti-O bond length position.

  11. Photoluminescence Properties of Na+(Ba2+) and Nb5+(P5+)-Doped Sr2.4Y0.2Eu0.2V2O8 Phosphors

    NASA Astrophysics Data System (ADS)

    Mu, Jing Jing; Zheng, Gan Hong; Dai, Zhen Xiang; Zhang, Lin Yun; Zhu, Ya Nan

    2016-07-01

    A series of Sr2.4Y0.2Eu0.2V2O8: xNa+( yBa2+) and Sr2.4Y0.2Eu0.2V2O8: zNb5+(mP5+) phosphors are synthesized by solid-state reaction method and the photoluminescence (PL) properties are investigated. All phosphors exhibit bright red emission centered at ˜619 nm. Na+ and Ba2+, as the sensitizers for the luminescence of Eu3+, are found to improve significantly the PL intensity of these phosphors. For the Sr2.4Y0.2Eu0.2V2O8: xNa+( yBa2+) samples, the emission intensity increases with Na+(Ba2+) doping, and the strongest intensity is achieved in the case when x is 0.09 and y is 0.15. The introduction of Nb(P)O4 3- reduces the non-radiative energy transfer between neighboring VO4 3- and results in the energy transfer between VO4 3- and Eu3+, and eventually leads to the enhancement of Eu3+ emission. Comparing the doping effect of between Na and Ba, and the effect between Nb and P, respectively, it is found that both Na and P doping largely tend to improve the emission intensity. The relevant mechanisms have been discussed.

  12. Photoluminescence and cathodoluminescence properties of Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors

    SciTech Connect

    Du, Peng; Yu, Jae Su

    2015-10-15

    Highlights: • Under 393 nm excitation, strong red emission located at 615 nm was observed in all the samples. • The Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest PL properties. • The CIE chromaticity coordinate of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was (0.647,0.352). • The color purity of Eu{sup 3+}-activated CaMoO{sub 4} phosphor was 92.8%. • Strong CL properties were observed in the Eu{sup 3+}-activated CaMoO{sub 4} phosphor. - Abstract: Eu{sup 3+}-activated AMoO{sub 4} (A = Mg, Ca, Sr, Ba) phosphors were synthesized by a solid-state reaction method. Photoluminescence and cathodoluminescence (CL) spectra as well as X-ray diffraction patterns were measured to characterize the fabricated samples. Under 393 nm excitation, strong red emissions located at ∼615 nm corresponding to the {sup 5}D{sub 0} → {sup 7}F{sub 2} transition of Eu{sup 3+} ions were observed in all the samples. Compared with other Eu{sup 3+} ions activated AMoO{sub 4} (A = Mg, Sr, Ba) phosphors, Eu{sup 3+}-activated CaMoO{sub 4} phosphor exhibited the strongest red emission intensity with better Commission Internationale de L’Eclairage chromaticity coordinate and higher color purity. Furthermore, the CL results indicated that the Eu{sup 3+}-activated CaMoO{sub 4} phosphor had excellent luminescence properties.

  13. Effect of A-site cations on the broadband-sensitive upconversion of AZrO3:Er3+,Ni2+ (A = Ca, Sr, Ba) phosphors

    NASA Astrophysics Data System (ADS)

    Luitel, Hom Nath; Mizuno, Shintaro; Tani, Toshihiko; Takeda, Yasuhiko

    2017-02-01

    We investigated broadband-sensitive upconversion processes in a series of AZrO3 type perovskites codoped with Ni2+ and Er3+, especially giving focus on the effect of the A-site host cations viz. Ca, Sr, Ba. Absorption and Stokes emission of the Ni2+ changed remarkably according to the A-site cations making difference in the Ni2+ to Er3+ energy transfer efficiency. The energy transfer extent from the Ni2+ sensitizers to the Er3+ emitters and the back transfer from the Er3+ to the Ni2+ were studied to clarify the guide for efficient broadband-sensitive upconversion. The Ni2+ to Er3+ energy transfer efficiency and hence the Er3+ upconversion emission intensity was dependent on the extent of overlap between the Er3+ absorption and the Ni2+ emission bands. Larger the overlap, faster was the energy transfer from the Ni2+ to the Er3+, leading to more intense Er3+ upconversion emission. However, back energy transfer from the Er3+ to the Ni2+ due to significant overlap of the Er3+ emission band with the Ni2+ absorption band reduced the upconversion emission intensity. Another important factor is the upconversion efficiency of the Er3+ emitters themselves after the energy transfer from the Ni2+ sensitizers, which was significantly improved when the symmetry around the Er3+ was lowered. As a result of these combined effects, the CaZrO3 host exhibited the most intense Ni2+-sensitized upconversion emission compared to the Sr and Ba analogues. Thus, for the efficient broadband-sensitive upconversion to be realized, a low symmetry host to manifest efficient upconversion of the Er3+ emitters and controlled Ni2+ absorption and emission bands to suppress the back energy transfer while maintaining efficient energy transfer in the forward direction are essential.

  14. Remarkable influence of heat treatment on the structural and superconducting properties of (Y1-x Prx )(BaSr)Cu3O6+z

    NASA Astrophysics Data System (ADS)

    Bouallal, B.; Nafidi, A.; El Abidi, A.; El Kaaouachi, A.

    2006-09-01

    We report here on the preparation, X-ray diffraction (XRD), Seebeck effect, AC magnetic susceptibility, resistivity measurements and effect of heat treatments in the high Tc superconductor (Y1-x Prx)(BaSr)Cu3O6+z . Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. When x increase, the oxygen content (6+z) of the samples decrease slightly from 6.9 to 6.8 as determined by our iodometry measurements. The orthorhombicity = (b -a)/(b +a) decreases to zero at xt [O] = 0.6 and xt [AO] = 0.75. These indicate a structural phase transition from orthorhombic to tetragonal at xt. Whereas, Tc decrease to zero at xc [O] = 0.7 and xc [A,O] = 0.75. Therefore the [A,O] heat treatment increase xc. Note that decrease with Tc as foreseen. However, for a given x the [AO] heat treatment makes increase (Tc). Independently of heat treatment, a increase with x, whereas b decreased to its minimum at xt. For a given x < xt, the heat treatment [AO] makes decrease a and increase. A remarkable correlations were observed between Tc (x) and (x); and between the variation δTc (x) = Tc [AO]-Tc [O] and δ (x). A combination of several factors such as decrease in the Cu (1)-apical oxygen distance; cationic order of Prx on the (Sr,Ba) site along c axis, chain oxygen ordering on (O4,O5) sites; increase in p and in-phase purity for the [AO] samples may qualitatively account for the observed data.

  15. Alkaline Earth Metal Zirconate Perovskites MZrO3 (M=Ba(2+), Sr(2+), Ca(2+)) Derived from Molecular Precursors and Doped with Eu(3+) Ions.

    PubMed

    Drąg-Jarząbek, Anna; John, Łukasz; Petrus, Rafał; Kosińska-Klähn, Magdalena; Sobota, Piotr

    2016-03-24

    The effect of alkaline earth metal alkoxides on the protonation of zirconocene dichloride was investigated. This approach enabled the design of compounds with preset molecular structures for generating high-purity binary metal oxide perovskites MZrO3 (M=Ba(2+), Sr(2+), Ca(2+)). Single-source molecular precursors [Ba4 Zr2 (μ6 -O)(μ3 ,η(2)-OR)8 (OR)2(η(2) -HOR)2 (HOR)2 Cl4], [Sr4 Zr2 (μ6 -O)(μ3 ,η(2)-OR)8 (OR)2 (HOR)4 Cl4], [Ca4 Zr2 (μ6-O)(μ3 ,η(2)-OR)8 (OR)2 Cl4], and [Ca6 Zr2 (μ2 ,η(2)-OR)12 (μ-Cl)2 (η(2) -HOR)4 Cl6 ]⋅8 CH2 Cl2 were prepared via elimination of the cyclopentadienyl ring from Cp2 ZrCl2 as CpH in the presence of M(OR)2 and alcohol ROH (ROH=CH3OCH2 CH2OH) as a source of protons. The resulting complexes were characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction. The compounds were then thermally decomposed to MCl2 /MZrO3 mixtures. Leaching of MCl2 from the raw powder with deionized water produced highly pure perovskite-like oxide particles of 40-80 nm in size. Luminescence studies on Eu(3+)-doped MZrO3 revealed that the perovskites are attractive host lattices for potential applications in display technology.

  16. Preparation and magnetic properties of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Huang, Ying; Wang, Qiufen

    2012-09-01

    Nanocomposite of hard (BaFe12O19)/soft ferrite (Ni0.8Zn0.2Fe2O4) have been prepared by the sol-gel process. The nanocomposite ferrite are formed when the calcining temperature is above 800 °C. It is found that the magnetic properties strongly depend on the presintering treatment and calcining temperature. The “bee waist” type hysteresis loops for samples disappear when the presintering temperature is 400 °C and the calcination temperature reaches 1100 °C owing to the exchange-coupling interaction. The remanence of BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite with the mass ratio of 5:1 is higher than a single phase ferrite. The specific saturation magnetization, remanence magnetization and coercivity are 63 emu/g, 36 emu/g and 2750 G, respectively. The exchange-coupling interaction in the BaFe12O19/Ni0.8Zn0.2Fe2O4 nanocomposite ferrite is discussed.

  17. Co-existence of diamagnetism and ferromagnetism and possible superconductivity in Y{sub 8}Ba{sub 5}Zn{sub 4}O{sub 21}

    SciTech Connect

    Topal, Ugur

    2011-02-15

    In the present study, we investigate structural and magnetic properties of the Y{sub 8}Ba{sub 5}Zn{sub 4}O{sub 21} structure, which was recently included in the catalog of the International Centre for Diffraction Data (ICDD) as a prototype structure. It was found that the Y{sub 8}Ba{sub 5}Zn{sub 4}O{sub 21} bulk sample seems to be electrically insulating at temperatures of liquid nitrogen and the room temperature. On the other hand, it has quite interesting magnetic properties. Diamagnetic phase transition was observed at {approx} 90 K, which resembles that of the superconducting materials. The studied composition repels permanent magnets at the liquid nitrogen temperature. Ferromagnetism also co-exists with diamagnetism in the temperature range between 50 K and 90 K. Possible reasons for these behaviors are discussed. - Research Highlights: {yields}Y{sub 8}Ba{sub 5}Zn{sub 4}O{sub 21} possesses both ferromagnetic and diamagnetic properties. {yields}A superconducting-like diamagnetic transition takes place at {approx} 90 K. {yields}Ferromagnetism and diamagnetism coexist between temperatures of 50 K and 90 K. {yields}At 10 K, only ferromagnetism exists and no traces of diamagnetism are detected. {yields}The studied samples repel permanent magnets in liquid nitrogen.

  18. Superconductivity in Zn-doped tetragonal LaBaCaCu{sub 3}O{sub 7{minus}{delta}} systems

    SciTech Connect

    Singh, R.; Lal, R.; Upreti, U.C.; Suri, D.K.; Narlikar, A.V.; Awana, V.P.; Albino Aguiar, J.; Shahabuddin, M.

    1997-01-01

    Resistivity and ac susceptibility of Zn-doped samples of the LaBaCaCu{sub 3}O{sub 7{minus}{delta}} (LBCCO) system have been measured for Zn content of 0.5{percent}, 1.0{percent}, 1.5{percent}, 2.0{percent}, 2.5{percent}, and 3.0{percent} at.wt. X-ray diffraction has been used to find the lattice parameters of the samples. The samples remain tetragonal for all the considered concentrations of Zn. Idometry and thermogravimetric analyses have been done to estimate the oxygen content of different samples. Analyzing the resistivity and ac susceptibility data, the following conclusions are drawn about the role of Zn in the LBCCO samples. (1) The conduction mechanism of electrons appears to follow a crossover from the purely metallic regime to the localization regime due to either weak localization or electron-electron interaction effects after about 1.5{percent} Zn. (2) The superconducting transition as revealed by the resistivity vs temperature curves or susceptibility vs temperature curves becomes sharper with Zn increasing content of Zn up to 1.0{percent}. After 1.5{percent} the resistive and ac susceptibility transitions become broader with increasing Zn. (3) T{sub c} depression up to Zn content of 1.0{percent} seems due to direct suppression of the effective pairing interaction, while at and above 2.5{percent} Zn T{sub c} depression is expected to be due to disorder effects such as reduction of density of states at the Fermi energy. {copyright} {ital 1997} {ital The American Physical Society}

  19. From one to three dimensions: corrugated ∞(1)[NiGe] ribbons as a building block in alkaline earth metal Ae/Ni/Ge phases with crystal structure and chemical bonding in AeNiGe (Ae = Mg, Sr, Ba).

    PubMed

    Hlukhyy, Viktor; Siggelkow, Lisa; Fässler, Thomas F

    2013-06-17

    The new equiatomic nickel germanides MgNiGe, SrNiGe, and BaNiGe have been synthesized from the elements in sealed tantalum tubes using a high-frequency furnace. The compounds were investigated by X-ray diffraction both on powders and single crystals. MgNiGe crystallizes with TiNiSi-type structure, space group Pnma, Z = 4, a = 6.4742(2) Å, b = 4.0716(1) Å, c = 6.9426(2) Å, wR2 = 0.033, 305 F(2) values, 20 variable parameters. SrNiGe and BaNiGe are isotypic and crystallize with anti-SnFCl-type structure (Z = 4, Pnma) with a = 5.727(1) Å, b = 4.174(1) Å, c = 11.400(3) Å, wR2 = 0.078, 354 F(2) values, 20 variable parameters for SrNiGe, and a = 5.969(4) Å, b = 4.195(1) Å, c = 11.993(5) Å, wR2 = 0.048, 393 F(2) values, 20 variable parameters for BaNiGe. The increase of the cation size leads to a reduction of the dimensionality of the [NiGe] polyanions. In the MgNiGe structure the nickel and germanium atoms build a ∞(3)[NiGe] network with magnesium atoms in the channels. In SrNiGe and BaNiGe the ∞(1)[NiGe] ribbons are separated by strontium/barium atoms, whereas in the known CaNiGe structure the ribbons are fused to two-dimmensional atom slabs. The crystal chemistry and chemical bonding in AeNiGe (Ae = Mg, Ca, Sr, Ba) are discussed. The experimental results are reconciled with electronic structure calculations performed using the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method.

  20. Crystal structures of the four new quaternary copper(I)-selenides A0.5CuZrSe3 and ACuYSe3(A=Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Maier, Stefan; Prakash, Jai; Berthebaud, David; Perez, Olivier; Bobev, Svilen; Gascoin, Franck

    2016-10-01

    The four new quaternary copper(I)-selenides, Sr0.5CuZrSe3 (a=3.8386(7), b=14.197(2), c=10.1577(17) Å), Ba0.5CuZrSe3 (a=3.8386(7), b=14.196(2), c=10.1577(17) Å), SrCuYSe3 (a=10.620(2), b=4.1000(8), c=13.540(3) Å) and BaCuYSe3 (a=4.1800(7), b=13.940(2), c=10.6200(17) Å) were synthesized by high-temperature solid state reactions and their crystal structures were determined using single-crystal X-ray diffraction. A0.5CuZrSe3 (A= Sr, Ba) and BaCuYSe3 crystallize in the KCuZrS3 structure type (Cmcm), while SrCuYSe3 is isostructural to Eu2CuS3 (Pnma). All compounds form layered structures in which the charge of the - ∞ 2[CuZrSe3 and 2 - ∞ 2[CuYSe3 ] layers as well as the site occupancy of the A cations depend on the transition metal. Combining the alkaline earth metals Sr and Ba with tetravalent Zr leads to the formation of cation vacancies between the - ∞ 2[CuZrSe3 ] layers and structure type as well as symmetry are determined by the ratio between the cation and transition metal ionic radii r(A2+)/r(M3+/4+).

  1. Magnetic and electrical properties on possible room temperature hybrid multiferroic BaTiO3/La2/3Sr1/3MnO3

    NASA Astrophysics Data System (ADS)

    Ordoñez, John Edward; Gómez, María Elena; Lopera Muñoz, Wilson; Prieto, Pedro Antonio; Thin Film Group Team; Center of Excellence on Novel Materials-CENM, Cali, Colombia Team

    2015-03-01

    We addressed to deposit the ferromagnetic phase of the La1-xSrxMnO3 and the ferroelectric BaTiO3 for possible hybrid multiferroic heterostructure. We have optimized the growth parameters for depositing BaTiO3(BTO) / La2/3Ca1/3MnO3(LCMO) / (001) SrTiO3 by sputtering RF and DC, respectively, in pure oxygen atmosphere and a substrate temperature of 830°C. Keeping fixed the magnetic layer thickness (tLSMO = 40 nm) and varying the thickness of the ferroelectric layer (tBTO = 20, 40, 80, 100 nm). We want to point out the influence of the thicknesses ratio (tBTO/tLSMO) on electrical and magnetic properties. From x-ray diffraction (XRD) analysis, we found the bragg peaks for LSMO maintain its position but BTO peak shift to lower Bragg angle indicating a strained BTO film. Magnetization and polarization measurements indicate a possible multiferroic behavior in the bilayers. Hysteresis loop measurements of bilayers show ferromagnetic behavior. Authors thank Instituto de Nanociencia de Aragón, Zaragoza, Spain. Work partially supported by COLCIENCIAS-UNIVALLE Project 110656933104 Contract No. 2013-0002, CI 7917 and CI 7978.

  2. Polarization-based perturbations to thermopower and electronic conductivity in highly conductive tungsten bronze structured (Sr,Ba)Nb2O6: Relaxors vs normal ferroelectrics

    NASA Astrophysics Data System (ADS)

    Bock, Jonathan A.; Trolier-McKinstry, Susan; Mahan, Gerald D.; Randall, Clive A.

    2014-09-01

    Electrical conductivity, thermopower, and lattice strain were investigated in the tetragonal tungsten bronze structured (Srx,Ba1-x)Nb2O6-δ system for 0.7>x>0.4 with large values of δ. These materials show attractive thermoelectric characteristics, especially in single-crystal form. Here, the Sr/Ba ratio was changed in order to vary the material between a normal ferroelectric with long-range polarization to relaxor behavior with short-range order and dynamic polarization. The influence of this on the electrical conduction mechanisms was then investigated. The temperature dependence of both the thermopower and differential activation energy for conduction suggests that the electronic conduction is controlled by an impurity band with a mobility edge separating localized and delocalized states. Conduction is controlled via hopping at low temperatures, and as temperature rises electrons are activated above the mobility edge, resulting in a large increase in electrical conductivity. For relaxor ferroelectric-based compositions, when dynamic short-range order polarization is present in the system, trends in the differential activation energy and thermopower show deviations from this conduction mechanism. The results are consistent with the polarization acting as a source of disorder that affects the location of the mobility edge and, therefore, the activation energy for conduction.

  3. Up-converted ultraviolet luminescence of Er3+:BaGd2ZnO5 phosphors for healthy illumination

    NASA Astrophysics Data System (ADS)

    Zhang, Ya; Cui, Qingzhi; Wang, Zhanyong; Liu, Gan; Tian, Tian; Xu, Jiayue

    2016-09-01

    Moderate level of exposure to the solar irradiation containing UV component is essential for health care. To incorporate the UV-emitting phosphors into the commercial YAG-based white light-emitting diode introduces the possibilities of healthy illumination to individuals' daily lives. 1 mol.% Er3+-doped BaGd2ZnO5 (BGZ) particles were synthesized via sol-gel method and efficient up-converted luminescence peaked at 380 nm was detected under 480 nm excitation. The mixed phosphors with varied mass ratio of Er3+:BGZ and Ce3+:YAG particles were encapsulated to form LEDs. The study of the LEDs indicated that the introduction of BGZ component favored the enhancement of color-rendering index and the neutralization of the white light emitting. The WLED with the BGZ/YAG ratio of 8:2 was recommendable for its excellent overall white light luminous performances and UV intensity of 84.55 mW/cm2. The UV illumination dose of the WLEDs with mixed YAG and BGZ was controllable by adjusting the ratio, the illumination distance and the illumination time. Er3+:BGZ phosphors are promising UVemitting phosphors for healthy indoor illumination.

  4. Molecular quantum magnetism with strong spin-orbit coupling in inorganic solid Ba3Yb2Zn5O11

    NASA Astrophysics Data System (ADS)

    Park, Sang-Youn; Ji, Sungdae; Park, Jae-Hoon; Do, Seunghwan; Choi, Kwang-Yong; Jang, Dongjin; Schmidt, Burkhard; Brando, Manuel; Butch, Nicholas

    The molecular magnet, assembly of finite number of spins which are isolated from environment, is a model system to study the quantum information process such as the qubit or spintronic devices. In past decades, the molecular magnet has been mostly realized in organic material, however, it has difficulty synthesizing materials or controlling their properties, meanwhile tremendous endeavors to search inorganic molecular magnet are continuing. Here, we propose Ba3Yb2Zn5O11 as a candidate of inorganic molecular magnet. This material consists of an alternating 3D-array of small and large tetrahedron containing antiferromagnetically coupled four pseudospin-1/2 Yb ions, and magnetic properties are described by an isolated tetrahedron without long-range magnetic ordering. Inelastic neutron scattering measurement with external magnetic field reveals that extraordinarily huge Dzyaloshinsky-Moriya (DM) interaction originating from strong spin-orbit coupling in Yb isospin is the key to explain energy level of tetrahedron in addition to Heisenberg exchange interaction and Zeeman effect. Magnetization measurement shows the Landau-Zener transition between avoided crossing levels caused by DM interaction.

  5. Interfacial charge-mediated non-volatile magnetoelectric coupling in Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 multiferroic heterostructures

    DOE PAGES

    Zhou, Ziyao; Howe, Brandon M.; Liu, Ming; ...

    2015-01-13

    The central challenge in realizing non-volatile, E-field manipulation of magnetism lies in finding an energy efficient means to switch between the distinct magnetic states in a stable and reversible manner. In this work, we demonstrate using electrical polarization-induced charge screening to change the ground state of magnetic ordering in order to non-volatilely tune magnetic properties in ultra-thin Co0.3Fe0.7/Ba0.6Sr0.4TiO3/Nb:SrTiO3 (001) multiferroic heterostructures. A robust, voltage-induced, non-volatile manipulation of out-of-plane magnetic anisotropy up to 40 Oe is demonstrated and confirmed by ferromagnetic resonance measurements. This discovery provides a framework for realizing charge-sensitive order parameter tuning in ultra-thin multiferroic heterostructures, demonstrating great potentialmore » for delivering compact, lightweight, reconfigurable, and energy-efficient electronic devices.« less

  6. Transport properties and photo electrochemical characterization of oxygen-deficient ASnO 3- δ (A=Ca, Sr and Ba)

    NASA Astrophysics Data System (ADS)

    Zidi, N.; Omeiri, S.; Hadjarab, B.; Bouguelia, A.; Akroun, A.; Trari, M.

    2010-08-01

    The deficient stannate BaSnO 3- δ, prepared at 980 °C in sealed tube, crystallizes in an ideal perovskite structure. The oxide exhibits a blue color, the bandgap is found to be 2.65 eV and the transition is directly allowed. The non-stoichiometry could not be measured, indicating no appreciable oxygen deficiency. Nevertheless, the transport properties were found to change markedly with the heat treatment. BaSnO 3- δ behaves as degenerate SC with a conductivity σ300 K (=1.63 Ω -1 cm -1) and where the level Ef drops above mobility edge to delocalized states. The electric balance leads to a simultaneous reduction of Sn 4+ inducing n-type behavior. The thermal variation of the thermopower indicates an electron mobility μ300 K (=0.013 cm 2 V -1 s -1) thermally activated. The metal-insulating transition is considered of Anderson type due to the random potential to oxygen vacancies. A predominant variable range hopping is predicted from the non-linearity of Ln σ versus T-1 plot. The capacitance measurement ( C-2- V), measured in KOH media, shows a linear behavior from which a flat band potential Vfb (=-0.67 VSCE) and a density ND (=7.59×10 20 cm -3) are determined. The deficient stannates CaSnO 3 and SrSnO 3 are reported for a comparative purpose. The decrease of Eg is ascribed to the increase of the conduction band width when going from Ba to Ca.

  7. Synergetic pinning centres in BaZrO3-doped YBa2Cu3O7-x films induced by SrTiO3 nano-layers

    NASA Astrophysics Data System (ADS)

    Crisan, A.; Dang, V. S.; Mikheenko, P.; Ionescu, A. M.; Ivan, I.; Miu, L.

    2017-04-01

    We report on the enhancement of critical current density (J c) and the unusual behaviour of its dependence on field orientation in YBa2Cu3O7‑x (YBCO) nanostructured films by a combination of substrate decoration with Ag nano-dots, of the incorporation of BaZrO3 (BZO) nano-particles and nano-rods, and of multilayer architecture (a thin SrTiO3 layer separating two 1.5 μm-thick YBCO layers). SrTiO3 insulating layers were 15, 30 or 45 nm thick. The highest improvement of J c in applied magnetic fields along the c-axis and smaller than 1 T occurs in the bi-layer with 30 nm-thick STO, but the influence of STO thickness is small. Our thick nanostructured films show significant improvement of J c in the magnetic field along the ab-plane direction. The presence of BZO nano-rods, ab-plane defects and nano particles of BZO and Y2O3 was observed in transmission electron microscopy (TEM) images of the film. The peculiarities of artificial pinning centres revealed in the TEM images of the nanostructured films are used to explain an unusual split of the peak in the J c dependence on the magnetic field along the ab-plane of YBCO. Effective pinning potentials in high magnetic fields have rather high values for such thick films.

  8. Ferroelectric Properties of BaZrO3 Doped Sr0.8Bi2.2Ta2O9 Thin Films

    NASA Astrophysics Data System (ADS)

    Bozgeyik, Mehmet S.; Cross, Jeffrey S.; Ishiwara, Hiroshi; Shinozaki, Kazuo

    2009-06-01

    Novel sol-gel derived Sr0.8Bi2.2Ta2O9 (SBT) doped with 5 and 7% molar ratio BaZrO3 (BZ) thin films were fabricated, characterized, and electrical properties were evaluated with Pt electrodes. X-ray diffraction (XRD) analysis showed all the characteristic peaks of the layered perovskite structure with (115) orientation and slight peak broadening by BZ doping. X-ray photoelectron spectra (XPS) showed a small shift in the Sr 3d peak with BZ substitution. Scanning electron microscopy (SEM) cross-sectional photographs of the films show smaller grain size and greater porosity with BZ addition. The remanent polarization (2Pr) was significantly reduced from ˜16.4 µC/cm2 for SBT to ˜2.3 µC/cm2 for SBT with 7% BZ. Capacitance-voltage measurements performed at a frequency of 1 MHz showed butterfly type hysteresis loops, which is further evidence of ferroelectricity of the modified SBT, and dielectric constant of 135 for SBT with 7% BZ. Leakage current measurements showed one order of magnitude higher leakage current for SBT with 5% BZ compared to SBT. Lower film dielectric constant leads to higher leakage current in BZ doped SBT. Although leakage mechanisms predict this general trend, it runs counter to the objective of preparing ferroelectric films with low leakage and low dielectric constants for ferroelectric gate field-effect transistor (FeFET) type memory.

  9. Interlayer states arising from anionic electrons in the honeycomb-lattice-based compounds A e AlSi (A e =Ca , Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Lu, Yangfan; Tada, Tomofumi; Toda, Yoshitake; Ueda, Shigenori; Wu, Jiazhen; Li, Jiang; Horiba, Koji; Kumigashira, Hiroshi; Zhang, Yaoqing; Hosono, Hideo

    2017-03-01

    We report that the interlayer states common to the compounds A e AlSi (A e =Ca , Sr, Ba) arise from F-center-like electrons arrayed in periodic cavities. The SrPtSb-type intermetallic phases exhibit electrons localized to columns of the trigonal bipyramidal A e3A l2 cages running perpendicular to the honeycomb layers. Ab initio calculations in combination with hard/soft x-ray photoemission spectroscopic measurements reveal that these features correspond to the anionic electrons that hybridize with apical Al 3 pz orbitals from the honeycomb layers above and below. Extra bands with a significant dispersion along the kz direction therefore contribute to the Fermi level in contrast to the apparent two-dimensional connectivity of the bonding in the compounds, and completely account for the presence of interlayer states. Our study demonstrates how the cage centers may serve as electronically important crystallographic sites, and extend the anionic electron concept into honeycomb lattice compounds.

  10. Petrogenesis of late Eocene high Ba-Sr potassic rocks from western Yangtze Block, SE Tibet: A magmatic response to the Indo-Asian collision

    NASA Astrophysics Data System (ADS)

    Liu, Zheng; Liao, Shi-Yong; Wang, Jin-Rong; Ma, Zhen; Liu, Yi-Xin; Wang, Dong-Bing; Tang, Yuan; Yang, Jing

    2017-03-01

    The Indo-Asian collision resulted in extrusion of the Indochina Block along the Ailao Shan-Red River (ASRR) shear zone in the Cenozoic, with the emplacement of widespread potassic magmatic rocks. In this contribution, we investigated five potassic felsic intrusions exposed in the western Yangtze Block adjacent to the ASRR shear zone, including the Xiaoqiaotou, Jianchuan, Yuzhaokuai, Laojunshan and South Taohuacun intrusions. New LA-ICP-MS zircon U-Pb results in combination with previous data indicate that these felsic rocks have identical crystallization ages of ∼36-35 Ma. They are characterized by high Ba (mostly >1500 ppm) and Sr (mostly >1000 ppm) abundances, with high K2O contents and K2O/Na2O ratios. They exhibit similar Sr-Nd isotopic components as the coeval shoshonitic mafic rocks exposed in the studied area. Elemental and isotopic data suggest that the five intrusions were likely derived from fractional crystallization of shoshonitic mafic magmas originating from an enriched lithospheric mantle. On the basis of previously published data and results in this paper, we considered that the lithospheric mantle underneath the western Yangtze might have undergone enrichment events twice at least, including the Neoproterozoic oceanic subduction and the Neo-Tethyan oceanic subduction.

  11. Luminescent properties of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} and its luminescence improvement by incorporating A{sup +} (A=Li, Na, and K)

    SciTech Connect

    Li, Panlai Wang, Zhijun Yang, Zhiping; Guo, Qinglin

    2014-12-15

    A novel green phosphor SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} is synthesized by a high temperature solid-state method, and its luminescent property is investigated. X-ray diffraction patterns of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} indicate a similarity crystalline phase to SrZn{sub 2}(PO{sub 4}){sub 2}. SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} shows green emission under 369 nm excitation, and the prominent luminescence in green (544 nm) due to {sup 5}D{sub 4}–{sup 7}F{sub 5} transition of Tb{sup 3+}. For the 544 nm emission, excitation spectrum has several excitation band from 200 nm to 400 nm. Emission intensity of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} is influenced by Tb{sup 3+} concentration, and concentration quenching effect of Tb{sup 3+} in SrZn{sub 2}(PO{sub 4}){sub 2} is also observed. With incorporating A{sup +} (A=Li, Na, and K) as compensator charge, the emission intensity of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can be obviously enhanced. CIE color coordinates of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} locate in the green region. The results indicate this phosphor may be a potential application in white LEDs. - Graphical abstract: SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can produce green emission under near-UV excitation, and its luminescent properties can be improved by incorporating A{sup +} (A=Li, Na, and K). - Highlights: • SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can produce green emission under near-UV excitation. • Concentration quenching effect of Tb{sup 3+} in SrZn{sub 2}(PO{sub 4}){sub 2} is observed. • Emission intensities of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} are enhanced by codoped A{sup +} (A=Li, Na, K)

  12. Structure, spin-stripe order, and superconductivity in La1.905 Ba 0.095 CuO 4 with and without 1% Zn substitution of Cu

    NASA Astrophysics Data System (ADS)

    Wen, Jinsheng; Xu, Z.; Xu, G.; Jie, Q.; Hucker, M.; Zheludev, A.; Tian, W.; Winn, B.; Zarestky, J.; Singh, D.; Hong, T.; Li, Q.; Gu, G.; Tranquada, J.

    2011-03-01

    We have performed susceptibility, thermal transport, and neutron scattering measurements to study the effect of Zn and magnetic field on the structure, spin-stripe order and superconductivity, and the interplay between them in La 1.905 Ba 0.095 Cu O4 with and without 1% Zn. It is shown that the bulk superconductivity is depressed by either the Zn doping or the magnetic field, spin stripe order is enhanced, and the structure is unaffected. For a range of magnetic field, the spin stripe order appears to stabilize a quasi-two-dimensional vortex glass phase. Supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.

  13. The crystal structure and magnetic properties of Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22}

    SciTech Connect

    Cho, Kwang Lae; Rhee, Chan Hyuk; Kim, Chul Sung

    2014-05-07

    We have synthesized the Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22} samples (x = 0.1, 0.2, 0.3, 0.4, 0.5) by the solid-state reaction method and investigated their crystalline and magnetic properties by X-ray diffractometer (XRD), Mössbauer spectrometer, vibrating sample magnetometer, and network analyzer. XRD patterns show that all samples are rhombohedral with space group R-3m. The lattice constants a{sub 0} and c{sub 0} decrease with Sr substitution due to smaller ion radius of Sr{sup 2+} (1.27 Å) than that of Ba{sup 2+} (1.43 Å). The Mössbauer spectroscopy measurements show that the relative area ratios of Fe ion were maintained constant regardless of the Sr concentration. However, average magnetic hyperfine field slightly increased with the Sr concentration. This observation agrees with the fact that the saturation magnetization (M{sub s}) linearly increases due to the increasing super-exchange interaction, originated from the difference in the ionic radius between Ba{sup 2+} and Sr{sup 2+}. To investigate its properties at high frequency range, all samples were sintered at 1100 °C, and complex permeability and permittivity were measured by network analyzer between 100 MHz and 4 GHz. For x below 0.3, the initial permeability at 100 MHz increases, at higher values of x, its value decreases. Our study shows that magnetic properties of Sr{sup 2+} substitution for Ba{sup 2+} in Y-type hexaferrite as well as low magnetic loss less than 0.1 in 1 GHz band, indicating the potential application of Ba{sub 2−x}Sr{sub x}Co{sub 2}Fe{sub 12}O{sub 22} samples for RF and antenna devices in ultra high frequency band.

  14. A salt diapir-related Mississippi Valley-type deposit: the Bou Jaber Pb-Zn-Ba-F deposit, Tunisia: fluid inclusion and isotope study

    NASA Astrophysics Data System (ADS)

    Bouhlel, Salah; Leach, David L.; Johnson, Craig A.; Marsh, Erin; Salmi-Laouar, Sihem; Banks, David A.

    2016-08-01

    The Bou Jaber Ba-F-Pb-Zn deposit is located at the edge of the Bou Jaber Triassic salt diapir in the Tunisia Salt Diapir Province. The ores are unconformity and fault-controlled and occur as subvertical column-shaped bodies developed in dissolution-collapse breccias and in cavities within the Late Aptian platform carbonate rocks, which are covered unconformably by impermeable shales and marls of the Fahdene Formation (Late Albian-Cenomanian age). The host rock is hydrothermally altered to ankerite proximal to and within the ore bodies. Quartz, as fine-grained bipyramidal crystals, formed during hydrothermal alteration of the host rocks. The ore mineral assemblage is composed of barite, fluorite, sphalerite, and galena in decreasing abundance. The ore zones outline distinct depositional events: sphalerite-galena, barite-ankerite, and fluorite. Fluid inclusions, commonly oil-rich, have distinct fluid salinities and homogenization temperatures for each of these events: sphalerite-galena (17 to 24 wt% NaCl eq., and Th from 112 to 136 °C); ankerite-barite (11 to 17 wt% NaCl eq., and Th from 100 to 130 °C); fluorite (19 to 21 wt% NaCl eq., Th from 140 to 165 °C). The mean temperature of the ore fluids decreased from sphalerite (125 °C) to barite (115 °C) and increased during fluorite deposition (152 °C); then decreased to ˜110 °C during late calcite precipitation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in fluorite are metal rich (hundreds to thousands ppm Pb, Zn, Cu, Fe) but the inclusions in barite are deficient in Pb, Zn, Cu, Fe. Inclusions in fluorite have Cl/Br and Na/Br ratios of several thousand, consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a Br-enriched brine derived from evaporation plus a component of halite dissolution. The salinity of the barite-hosted fluid inclusions is less than obtained simply by the

  15. Accuracy and precision of 88Sr/86Sr and 87Sr/86Sr measurements by MC-ICPMS compromised by high barium concentrations

    NASA Astrophysics Data System (ADS)

    Scher, Howie D.; Griffith, Elizabeth M.; Buckley, Wayne P.

    2014-02-01

    (BaSO4) is a widely distributed mineral that incorporates strontium (Sr) during formation. Mass-dependent fractionation of Sr isotopes occurs during abiotic precipitation of barite and formation of barite associated with biological processes (e.g., bacterial sulfide oxidation). Sr isotopes in barite can provide provenance information as well as potentially reconstruct sample formation conditions (e.g., saturation state, temperature, biotic versus abiotic). Incomplete separation of Ba from Sr has complicated measurements of Sr isotopes by MC-ICPMS. In this study, we tested the effects of Ba in Sr sample solutions and modified extraction chromatography of Sr using Eichrom Sr Spec (Eichrom Technologies LLC, USA) resin to enable rapid, accurate, and precise measurements of 88Sr/86Sr and 87Sr/86Sr ratios from Ba-rich matrices. Sr isotope ratios of sample solutions doped with Ba were statistically indistinguishable from Ba-free sample solutions below 1 ppm Ba. Deviations in both 87Sr/86Sr and δ88/86Sr occurred above 1 ppm Ba. An updated extraction chromatography method tested with barite and Ba-doped seawater produces Sr sample solutions containing 10-100 ppb levels of Ba. The practice of Zr spiking for external mass-discrimination correction of 88Sr/86Sr ratios was also evaluated, and it was confirmed that variable Zr levels do not have adverse effects on the accuracy and precision of 87Sr/86Sr ratios in the Zr concentration range required to produce accurate δ88/86Sr values.

  16. Ae2Sb2X4F2 (Ae = Sr, Ba): new members of the homologous series Ae2M(1+n)X(3+n)F2 designed from rock salt and fluorite 2D building blocks.

    PubMed

    Kabbour, Houria; Cario, Laurent

    2006-03-20

    We have designed new compounds within the homologous series Ae2F2M(1+n)X(3+n) (Ae = Sr, Ba; M = main group metal; n = integer) built up from the stacking of 2D building blocks of rock salt and fluorite types. By incrementally increasing the size of the rock salt 2D building blocks, we have obtained two new n = 1 members of this homologous series, namely, Sr2F2Sb2Se4 and Ba2F2Sb2Se4. We then succeeded in synthesizing these compounds using a high-temperature ceramic method. The structure refinements from the powder or single-crystal X-ray diffraction data confirmed presence of the expected alternating stacking of fluorite [Ae2F2] (Ae = Sr, Ba) and rock salt [Sb2Se4] 2D building blocks. However the Ba derivative shows a strong distortion of the [Sb2Se4] block and a concomitant change of the Sb atom coordination likely related to the lone-pair activity.

  17. On the photo-luminescence properties of sol–gel derived undoped and Dy{sup 3+} ion doped nanocrystalline Scheelite type AMoO{sub 4} (A = Ca, Sr and Ba)

    SciTech Connect

    Jena, Paramananda; Gupta, Santosh K.; Natarajan, V.; Padmaraj, O.; Satyanarayana, N.; Venkateswarlu, M.

    2015-04-15

    Nanocrystalline Scheelite type Dy doped AMoO{sub 4} [where A = Ba, Sr and Ca] samples were prepared by acrylamide assisted sol–gel process and characterized by XRD, FT-Raman, FTIR, SEM and photoluminescence (PL). PL of undoped sample shows blue/green emission in CaMoO{sub 4} and SrMoO{sub 4} but multicolour visible emission leading to near white light in BaMoO{sub 4} nanoparticles; the origin of which is explained. It was observed that on doping 0.5 mol% of Dy{sup 3+} in molybdate samples complete energy transfer takes place in case of SrMoO{sub 4} and BaMoO{sub 4}, but host contributed substantially in Dy doped BaMoO{sub 4} sample, resulting in biexponential decay. It was also observed that symmetry around Dy{sup 3+} decreases as the size of alkaline earth ion increases. Due to combined blue, yellow and red colour emission in dysprosium doped sample; all samples showed near white light emission under UV and near UV excitation.

  18. Structure, infrared and Raman spectroscopic studies of newly synthetic AII(SbV0.50FeIII0.50)(PO4)2 (Adbnd Ba, Sr, Pb) phosphates with yavapaiite structure

    NASA Astrophysics Data System (ADS)

    Aatiq, Abderrahim; Tigha, My Rachid; Fakhreddine, Rachid; Bregiroux, Damien; Wallez, Gilles

    2016-08-01

    The synthesis and structural study of three new AII(SbV0.5FeIII0.5)(PO4)2 (Adbnd Ba, Sr, Pb) phosphates belonging to the Asbnd Sbsbnd Fesbnd Psbnd O system were reported here for the first time. Structures of [Ba], [Sr] and [Pb] compounds, obtained by solid state reaction in air atmosphere, were determined at room temperature from X-ray powder diffraction using the Rietveld method. BaII(SbV0.5FeIII0.5)(PO4)2 features the yavapaiite-type structure, with space group C2/m, Z = 2 and a = 8.1568(4) Å; b = 5.1996(3) Å c = 7.8290(4) Å; β = 94.53(1)°. AII(SbV0.5FeIII0.5)(PO4)2 (Adbnd Sr, Pb) compounds have a distorted yavapaiite structure with space group C2/c, Z = 4 and a = 16.5215(2) Å; b = 5.1891(1) Å c = 8.0489(1) Å; β = 115.70(1)° for [Sr]; a = 16.6925(2) Å; b = 5.1832(1) Å c = 8.1215(1) Å; β = 115.03(1)° for [Pb]. Raman and Infrared spectroscopic study was used to obtain further structural information about the nature of bonding in selected compositions.

  19. The role of Al, Ba, and Cd dopant elements in tailoring the properties of c-axis oriented ZnO thin films

    NASA Astrophysics Data System (ADS)

    Ali, Dilawar; Butt, M. Z.; Arif, Bilal; Al-Ghamdi, Ahmed A.; Yakuphanoglu, Fahrettin

    2017-02-01

    Highly c-axis oriented un-doped ZnO and Al-, Ba-, and Cd-doped ZnO thin films were successfully deposited on glass substrate employing sol-gel spin coating method. XRD analysis showed that all thin films possess hexagonal wurtzite structure with preferred orientation along c-axis. Field emission scanning electron microscope (FESEM) was used to study the morphology of thin films. The morphology consists of spherical and non-spherical shape grains. EDX analysis confirms the presence of O, Zn, Al, Ba, and Cd in the relevant thin films. The optical properties of thin films were studied using UV-Vis spectrometer. All thin films possess more than 85% optical transmittance in the visible region. Blue shift in optical band gap Eg has been observed on doping with Al, whereas doping with Ba and Cd resulted in red shift of Eg. Urbach energy Eu of all doped ZnO thin films was found to have excellent correlation with their band gap energy Eg. Moreover, Eg increases while Eu decreases on the increase in crystallite size D. Optical parameters Eg and Eu as well as structural parameters lattice strain and stacking fault probability also show excellent correlation with the B-factor or the mean-square amplitude of atomic vibrations of the dopant elements. Electrical conductivity measurement of the thin films was carried out using two-point probe method. The electrical conductivity was found to increase with the increase in crystallite orientation along c-axis.

  20. Comparison of stripe modulations in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Wilkins, S. B.; Dean, M. P. M.; Fink, Jörg; Hücker, Markus; Geck, J.; Soltwisch, V.; Schierle, E.; Weschke, E.; Gu, G.; Uchida, S.; Ichikawa, N.; Tranquada, J. M.; Hill, J. P.

    2011-11-01

    We report combined soft and hard x-ray scattering studies of the electronic and lattice modulations associated with stripe order in La1.875Ba0.125CuO4 and La1.48Nd0.4Sr0.12CuO4. We find that the amplitude of both the electronic modulation of the hole density and the strain modulation of the lattice is significantly larger in La1.875Ba0.125CuO4 than in La1.48Nd0.4Sr0.12CuO4 and is also better correlated. The in-plane correlation lengths are isotropic in each case; for La1.875Ba0.125CuO4, ξhole=255±5 Å, whereas for La1.48Nd0.4Sr0.12CuO4, ξhole=111±7 Å. We find that the modulations are temperature independent in La1.875Ba0.125CuO4 in the low temperature tetragonal phase. In contrast, in La1.48Nd0.4Sr0.12CuO4, the amplitude grows smoothly from zero, beginning 13 K below the LTT phase transition. We speculate that the reduced average tilt angle in La1.875Ba0.125CuO4 results in reduced charge localization and incoherent pinning, leading to the longer correlation length and enhanced periodic modulation amplitude.

  1. Stripe order, depinning, and fluctuations in La1.875 Ba0.125 CuO4 and La1.875 Ba0.075 Sr0.050 CuO4

    NASA Astrophysics Data System (ADS)

    Fujita, M.; Goka, H.; Yamada, K.; Tranquada, J. M.; Regnault, L. P.

    2004-09-01

    We present a neutron scattering study of stripe correlations measured on a single crystal of La1.875Ba0.125CuO4 . Within the low-temperature-tetragonal (LTT) phase, superlattice peaks indicative of spin and charge stripe order are observed below 50K . For excitation energies ℏω⩽12meV , we have characterized the magnetic excitations that emerge from the incommensurate magnetic superlattice peaks. In the ordered state, these excitations are similar to spin waves. Following these excitations as a function of temperature, we find that there is relatively little change in the Q -integrated dynamical spin susceptibility for ℏω˜10meV as stripe order disappears and then as the structure transforms from LTT to the low-temperature-orthorhombic phase. The Q -integrated signal at lower energies changes more dramatically through these transitions, as it must in a transformation from an ordered to a disordered state. We argue that the continuous evolution through the transitions provides direct evidence that the incommensurate spin excitations in the disordered state are an indicator of dynamical charge stripes. An interesting feature of the thermal evolution is a variation in the incommensurability of the magnetic scattering. Similar behavior is observed in measurements on a single crystal of La1.875Ba0.075Sr0.050CuO4 ; maps of the scattered intensity in a region centered on the antiferromagnetic wave vector and measured at ℏω=4meV are well reproduced by a model of disordered stripes with a temperature-dependent mixture of stripe spacings. We discuss the relevance of our results to understanding the magnetic excitations in cuprate superconductors.

  2. Temperature-dependent phonon Raman scattering and spectroscopic ellipsometry of pure and Ca-doped Sr x Ba1-x Nb2O6 ferroelectric ceramics across the phase transition region

    NASA Astrophysics Data System (ADS)

    Peng, Liang; Jiang, Kai; Zhang, Jinzhong; Hu, Zhigao; Wang, Genshui; Dong, Xianlin; Chu, Junhao

    2016-01-01

    Optical phonons and the phase transition of relaxor ferroelectric ceramics Sr x Ba1-x Nb2O6 (SBN) and Ca y (Sr0.5Ba0.5)1-y Nb2O6 (CSBN) with different composition (0.3≤slant x≤slant 0.5 , 0.1≤slant y≤slant 0.2 ) have been investigated by variable-temperature Raman scattering and spectroscopic ellipsometry. The anomalous temperature dependence of Tauc gap energy (E t ) is used to fit the phonon energy dependence of the permittivity, and the Raman intensity of some interesting optical phonons can be ascribed to the phase transition from a ferroelectric to a paraelectric structure. The Curie temperature of SBN decreases from 556 to 359 K with increasing Sr composition, which can be attributed to the substitution of smaller Sr2+ for Ba2+. On increasing the Ca composition, however, the phase transition temperature of CSBN remains nearly unchanged at about 350 K. This could be due to the fact that most doped Ca2+ ions move into the oxygen ion site and exhibit no obvious effect on the vibrational properties. Therefore, the general disorder which results from Sr2+ substituting Ba2+ , dominates the phase transition process for SBN-based ferroelectric oxides. Meanwhile, the dielectric functions from 200 to 600 K have been evaluated with the aid of the Tauc-Lorentz model. The electronic transition is located at about 5 eV and decreases with increasing temperature for all the samples. Moreover, the phase transition temperature range derived from the spectroscopic ellipsometry agrees well with that from the Raman scattering. It reveals that the variation of the fundamental energy gap may be associated with the phase transition of SBN ceramics. Both Raman scattering and spectroscopic ellipsometry are proven to be a effective method of exploring the phase transition of ferroelectric oxides.

  3. Electronic, optical properties and chemical bonding in six novel 1111-like chalcogenide fluorides AMChF (A=Sr, Ba; M=Cu, Ag; and Ch=S, Se, Te) from first principles calculations

    SciTech Connect

    Bannikov, V.V.; Shein, I.R.; Ivanovskii, A.L.

    2012-12-15

    Employing first-principles band structure calculations, we have examined the electronic, optical properties and the peculiarities of the chemical bonding for six newly synthesized layered quaternary 1111-like chalcogenide fluorides SrAgSF, SrAgSeF, SrAgTeF, BaAgSF, BaAgSeF, and SrCuTeF, which are discussed in comparison with some isostructural 1111-like chalcogenide oxides. We found that all of the studied phases AMChF (A=Sr, Ba; M=Cu, Ag; and Ch=S, Se, Te) are semiconductors for which the fitted 'experimental' gaps lie in the interval from 2.23 eV (for SrAgSeF) to 3.07 eV (for SrCuTeF). The near-Fermi states of AMChF are formed exclusively by the valence orbitals of the atoms from the blocks (MCh); thus, these phases belong to the layered materials with 'natural multiple quantum wells'. The bonding in these new AMChF phases is described as a high-anisotropic mixture of ionic and covalent contributions, where ionic M-Ch bonds together with covalent M-Ch and Ch-Ch bonds take place inside blocks (MCh), while inside blocks (AF) and between the adjacent blocks (MCh)/(AF) mainly ionic bonds emerge. - Graphical Abstract: Isoelectronic surface for SrAgSeF and atomic-resolved densities of states for SrAgTeF, and SrCuTeF. Highlights: Black-Right-Pointing-Pointer Very recently six new layered 1111-like chalcogenide fluorides AMChF were synthesized. Black-Right-Pointing-Pointer Electronic, optical properties for AMChF phases were examined from first principles. Black-Right-Pointing-Pointer All these materials are characterized as non-magnetic semiconductors. Black-Right-Pointing-Pointer Bonding is highly anisotropic and includes ionic and covalent contributions. Black-Right-Pointing-Pointer Introduction of magnetic ions in AMChF is proposed for search of novel magnetic materials.

  4. Data on metals (Zn, Al, Sr, and Co) and metalloid (As) concentration levels of ballast water in commercial ships entering Bushehr port, along the Persian Gulf.

    PubMed

    Soleimani, Farshid; Dobaradaran, Sina; Hayati, Abdolreza; Khorsand, Maryam; Keshtkar, Mozhgan

    2016-12-01

    In this article, we determined the concentration levels of metals including Zn, Al, Sr, and Co and metalloid of As of ballast water in commercial ships entering Bushehr port, along the Persian Gulf. Ballast water samples were taken from commercial ships entering Bushehr port from 34 ports around the world during 15 February and 25 August 2016. The concentration levels of metals and metalloid were determined by using a graphite furnace absorption spectrometer (AAS).

  5. Zn2+ and Sr2+ Adsorption at the TiO2 (110)-Electrolyte Interface: Influence of Ionic Strength, Coverage, and Anions

    SciTech Connect

    Zhang,Z.; Fenter, P.; Cheng, L.; Sturchio, N.; Bedzyk, M.; Machesky, M.; Anovitz, L.; Wesolowski, D.

    2006-01-01

    The X-ray standing wave technique was used to probe the sensitivity of Zn{sup 2+} and Sr{sup 2+} ion adsorption to changes in both the adsorbed ion coverage and the background electrolyte species and concentrations at the rutile ({alpha}-TiO{sub 2}) (110)-aqueous interface. Measurements were made with various background electrolytes (NaCl, NaTr, RbCl, NaBr) at concentrations as high as 1 m. The results demonstrate that Zn{sub 2+} and Sr{sub 2+} reside primarily in the condensed layer and that the ion heights above the Ti-O surface plane are insensitive to ionic strength and the choice of background electrolyte (with <0.1 Angstroms changes over the full compositional range). The lack of any specific anion coadsorption upon probing with Br{sup -}, coupled with the insensitivity of Zn{sup 2+} and Sr{sup 2+} cation heights to changes in the background electrolyte, implies that anions do not play a significant role in the adsorption of these divalent metal ions to the rutile (110) surface. Absolute ion coverage measurements for Zn{sup 2+} and Sr{sup 2+} show a maximum Stern-layer coverage of {approx}0.5 monolayer, with no significant variation in height as a function of Stern-layer coverage. These observations are discussed in the context of Gouy-Chapman-Stern models of the electrical double layer developed from macroscopic sorption and pH-titration studies of rutile powder suspensions. Direct comparison between these experimental observations and the MUltiSIte Complexation (MUSIC) model predictions of cation surface coverage as a function of ionic strength revealed good agreement between measured and predicted surface coverages with no adjustable parameters.

  6. Origin and evolution of the Nakhla meteorite inferred from the Sm-Nd and U-Pb systematics and REE, Ba, Sr, Rb and K abundances

    USGS Publications Warehouse

    Nakamura, N.; Unruh, D.M.; Tatsumoto, M.; Hutchison, R.

    1982-01-01

    Analyses of Sm-Nd and U-Th-Pb systematics, REE, Ba, Sr, Rb and K concentrations were carried out for whole rock and mineral separates from the Nakhla meteorite. The 1.26 ??.07 b.y. Sm-Nd age obtained in this work is in good agreement with those previously obtained by the Rb-Sr and Ar-Ar methods. The high initial ??{lunate}Nd value of +16 suggests that Nakhla was derived from a light REE-depleted, old planetary mantle source. U-Th-Pb data, after correction for pre-analytical terrestrial Pb contamination assuming an age of 1.26 b.y., suggest that the age of the Nakhla source is ???4.33 b.y. The agreement in the age determined by three independent radiometric methods and the high initial ??{lunate}Nd value strongly suggest that the 1.3 b.y. age dates one thorough igneous event in the parent body which not only reset these isotopic systems but also established the chemical and petrologic characteristics observed for the Nakhla meteorite. Using a three-stage Sm-Nd evolution model in combination with LIL element data and estimated partition coefficients, we have tested partial melting and fractional crystallization models to estimate LIL element abundances in a possible Nakhla source. Our model calculations suggest that partial melting of the light REE-depleted source followed by extensive fractional crystallization (???50%) of the partial melt could account for the REE abundances in the Nakhla constituent minerals. The estimated source is depleted in the light REE, Ba, Rb and K and therefore may resemble the MORB source in the earth's upper mantle or the upper 60-300 km of the moon. The significantly younger age of Nakhla than the youngest lunar rock; the young differentiation age inferred from the U-Th-Pb data, and the estimated LIL element abundances (including those of K, U and Th) in the source suggest that the Nakhla meteorite may have been derived from a relatively large, well-differentiated planetary body such as Mars. ?? 1982.

  7. Structural and dielectric properties of A(Fe{sub 1/2}Ta{sub 1/2})O{sub 3} [A = Ba, Sr, Ca

    SciTech Connect

    Dutta, Alo

    2011-04-15

    Graphical abstract: FTIR spectra of BFT, SFT and CFT at room temperature. Research highlights: {yields} The structural and dielectric properties of BaFe{sub 1/2}Ta{sub 1/2}O{sub 3}, SrFe{sub 1/2}Ta{sub 1/2}O{sub 3} and CaFe{sub 1/2}Ta{sub 1/2}O{sub 3}. {yields} Fourier transform infrared spectra show two primary phonon modes of the samples at around 450 cm{sup -1} and 620 cm{sup -1}. {yields} The compounds show significant frequency dispersion in its dielectric properties. {yields} The relaxation mechanism of the samples is modelled by Cole-Cole equation. -- Abstract: The complex perovskite oxide barium iron tantalate (BFT), BaFe{sub 1/2}Ta{sub 1/2}O{sub 3}, strontium iron tantalate (SFT), SrFe{sub 1/2}Ta{sub 1/2}O{sub 3} and calcium iron tantalate (CFT), CaFe{sub 1/2}Ta{sub 1/2}O{sub 3} are synthesized by a solid-state reaction technique. Rietveld refinement of the X-ray diffraction data of the samples shows that BFT and SFT crystallize in cubic structure, with lattice parameter a = 4.06 A for BFT and 3.959 A for SFT, whereas CFT crystallizes in orthorhombic structure having lattice parameters a = 5.443 A, b = 5.542 A and c = 7.757 A. Fourier transform infrared spectra show two primary phonon modes of the samples at around 450 cm{sup -1} and 620 cm{sup -1}. The compounds show significant frequency dispersion in its dielectric properties. The complex impedance plane plots of the samples show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The relaxation mechanism of the samples is modelled by Cole-Cole equation. The frequency dependent conductivity spectra are found to follow the power law.

  8. Influence of surface symmetry breaking on the magnetism, collapsing, and three-dimensional dispersion of the Co pnictides A Co2As2 (A =Ba , Sr, Ca)

    NASA Astrophysics Data System (ADS)

    Mansart, Joseph; Le Fèvre, Patrick; Bertran, François; Forget, Anne; Colson, Dorothée; Brouet, Véronique

    2016-12-01

    We use angle-resolved photoemission (ARPES) to study the three-dimensional (3D) electronic structure of Co pnictides A Co2As2 with A =Ba , Sr, Ca or a mixture of Sr and Ca. These compounds are isostructural to Fe based superconductors but have one more electron in the Co 3 d orbitals. Going from Ba to Ca, they become more and more 3D, eventually forming a "collapsed" tetragonal phase, where the distance between CoAs layers is markedly reduced. We observe with ARPES the periodicity of the electronic structure as a function of kz (i.e., perpendicularly to CoAs layers) and find that it matches in each case that expected from the distance between the planes in the bulk. However, the electronic structure is better fitted by a calculation corresponding to a slab with two CoAs layers than to the bulk structure. We attribute this to subtle modifications of the 2D electronic structure induced by the truncation of the 3D dispersion at the surface in the ARPES measurement. We further study how this affects the electronic properties. We show that, despite this distortion, the electronic structure of CaCo2As2 is essentially that expected for a collapsed phase. Electronic correlations produce a renormalization of the electronic structure by a factor 1.4, which is not affected by the transition to the collapsed state. On the other hand, a small shift of the Fermi level reduces the density of states in the eg bands and suppresses the magnetic transition expected in CaCo2As2 . Our study evidences that observing the 3D bulk periodicity is not sufficient to ensure bulk sensitivity. It further gives direct information on the role of 3D interactions, mostly governed by Co-As hybridization, among eg and t2 g orbitals. It is also useful to better understand the electronic structure of Fe superconductors and the range of validity of ARPES measurements.

  9. La(0.4)Ba(0.6)Fe(0.8)Zn(0.2)O(3-delta) as cathode in solid oxide fuel cells for simultaneous NO reduction and electricity generation.

    PubMed

    Zhou, Renjie; Bu, Yunfei; Xu, Dandan; Zhong, Qin

    2014-01-01

    A perovskite-type oxide La(0.4)Ba(0.6)Fe(0.8)Zn(0.2)O(3-delta) (LBFZ) was investigated as the cathode material for simultaneous NO reduction and electricity generation in solid oxide fuel cells (SOFCs). The microstructure of LBFZ was demonstrated by X-ray diffraction and scanning electron microscopy. The results showed that a single cubic perovskite LBFZ was formed after calcined at 1100 degrees C. Meanwhile, the solid-state reaction between LBFZ and Ce(0.8)Sm(0.2)O(1.9) (SDC) at 900 degrees C was negligible. To measure the electrochemical properties, SOFC units were constructed with Sm(0.9)Sr(0.1)Cr(0.5)Fe(0.5)O3 as the anode, SDC as the electrolyte and LBFZ as the cathode. The maximum power density increased with the increasing NO concentration and temperature. The cell resistance is mainly due to the cathodic polarization resistance.

  10. A salt diapir-related Mississippi Valley-type deposit: The Bou Jaber Pb-Zn-Ba-F deposit, Tunisia: Fluid inclusion and isotope study

    USGS Publications Warehouse

    Bouhlel, Salah; Leach, David; Johnson, Craig A.; Marsh, Erin; Salmi-Laouar, Sihem; Banks, David A.

    2016-01-01

    The Bou Jaber Ba-F-Pb-Zn deposit is located at the edge of the Bou Jaber Triassic salt diapir in the Tunisia Salt Diapir Province. The ores are unconformity and fault-controlled and occur as subvertical column-shaped bodies developed in dissolution-collapse breccias and in cavities within the Late Aptian platform carbonate rocks, which are covered unconformably by impermeable shales and marls of the Fahdene Formation (Late Albian–Cenomanian age). The host rock is hydrothermally altered to ankerite proximal to and within the ore bodies. Quartz, as fine-grained bipyramidal crystals, formed during hydrothermal alteration of the host rocks. The ore mineral assemblage is composed of barite, fluorite, sphalerite, and galena in decreasing abundance. The ore zones outline distinct depositional events: sphalerite-galena, barite-ankerite, and fluorite. Fluid inclusions, commonly oil-rich, have distinct fluid salinities and homogenization temperatures for each of these events: sphalerite-galena (17 to 24 wt% NaCl eq., and Th from 112 to 136 °C); ankerite-barite (11 to 17 wt% NaCl eq., and Th from 100 to 130 °C); fluorite (19 to 21 wt% NaCl eq., Th from 140 to 165 °C). The mean temperature of the ore fluids decreased from sphalerite (125 °C) to barite (115 °C) and increased during fluorite deposition (152 °C); then decreased to ∼110 °C during late calcite precipitation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in fluorite are metal rich (hundreds to thousands ppm Pb, Zn, Cu, Fe) but the inclusions in barite are deficient in Pb, Zn, Cu, Fe. Inclusions in fluorite have Cl/Br and Na/Br ratios of several thousand, consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a Br-enriched brine derived from evaporation plus a component of halite dissolution. The salinity of the barite-hosted fluid inclusions is less than obtained

  11. Synthesis and magnetic properties of hard/soft SrFe12O19/Ni0.7Zn0.3Fe2O4 nanocomposite magnets

    NASA Astrophysics Data System (ADS)

    Radmanesh, M. A.; Seyyed Ebrahimi, S. A.

    2012-09-01

    Magnetic nanocomposite SrFe12O19/Ni0.7Zn0.3Fe2O4 powders with different weight fractions of the Ni0.7Zn0.3Fe2O4 soft ferrite were synthesized by a combination of the sol-gel self-propagation and glyoxilate precursor methods. The results of magnetic measurements revealed the higher Mr/Ms ratio for the nanocomposites than that for the single phase SrFe12O19 which proves the existence of the intergrain exchange coupling between hard and soft magnetic phases with the exchange spring behavior. The highest Mr/Ms ratio of 0.63 was obtained in the composite consisting of 80 wt% of SrFe12O19 and 20 wt% Ni0.7Zn0.3Fe2O4. The microstructural studies of this sample exhibited the average dimensions of hard and soft phases about 20 nm and 15 nm, respectively which are small enough for strong exchange coupling according to the theoretical studies. The variations of the reduced remanence (Mr/Ms) with increasing the weight fraction of the soft phase could be also explained by the role of the exchange and dipolar interactions in tuning the magnetic properties of the nanocomposites.

  12. [Synthesis and fluorescence properties of SrZn(WO4)2:Tb3+, Ce3+ phosphors].

    PubMed

    Wu, Wen; Yin, Jiang-Long; Xuan, Ya-Wen; Zhang, Xin-Lei; Liu, Chun-Xia; Wang, Zhen-Ling

    2014-01-01

    SrZn(1-x) (WO4)2:xTb3+, yCe3+ green fluorescent phosphors for near ultraviolet excitation were prepared using chemical co-precipitation. The phases of different doping ratio samples were characterized by the X-ray diffraction (XRD). The emission spectrum and excitation spectrum of samples were characterized by fluorescence spectroscopy (PL). The luminescence properties of the rare-earth Tb3+ ion doped and Ce3+ and Tb3+ ion codoped samples were discussed. XRD analysis shows that the main diffraction peaks of samples were consistent with the standard card (JCPDS 08-0490 and the JCPDS 15-0774) of the diffraction peak data. This showed that the doping rare earth ions did not change matrix lattice structure. The excitation spectrum showed that the excitation spectrum peaks at 223 nm which is assigned to the 7F-7D absorption transitions of Tb3+. The emission spectrum excited by 223 nm exhibits sharp lines peaking at 543 nm which was assigned to the 5D4-7F5 transitions of the Tb3+ ions. With Tb3+ and Ce3+ co-doping, the spectrum didn't change much. The intensity of fluorescence reached the strongest when the concentration of Tb3+:Ce3+ arrived at 0.06:0.02 which may means that there was energy transfer between the ions of Ce3+ and Tb3+.

  13. Synthesis and luminescence properties of double perovskite Sr2ZnMoO6:Mn4+ deep red phosphor

    NASA Astrophysics Data System (ADS)

    Cao, Renping; Ceng, Xiangfeng; Huang, Jijun; Ao, Hui; Zheng, Guotai; Yu, Xiaoguang; Zhang, Xinqin

    2016-12-01

    A double perovskite Sr2ZnMoO6:Mn4+ (SZM:Mn4+) phosphor is synthesized by high-temperature solid-state reaction method in air. Emission band peaking at ∼705 nm of SZM:Mn4+ phosphor in the range of 650-790 nm is attributed to the 2E → 4A2 transition of Mn4+ ion with activated different lattice vibration modes. Three excitation bands in the range of 210-610 nm are assigned to the O2- → Mn4+ charge transfer and the 4A2 → (4T1, 2T2, and 4T2) transition of Mn4+ ion. The optimal Mn4+ ion concentration is ∼0.8 mol% in SZM:Mn4+ phosphor. Fluorescence lifetime of SZM:Mn4+ phosphor decreases from ∼132 μs to 108 μs with increasing Mn4+ ion concentration in the range of 0.2-1.0 mol%. Time-resolved spectra and fluorescence lifetime data indicate that luminescent center is caused by Mn4+ ion. The luminous mechanism of SZM:Mn4+ phosphor is explained by Tanabe-Sugano energy level diagram of Mn4+ ion. The results are useful to understand the influences of the neighboring coordination environment around Mn4+ and host crystal structure to the luminescence properties of Mn4+ ion and develop other novel Mn4+-doped materials.

  14. Epitaxial growth of dielectric Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} thin film on MgO for room temperature microwave phase shifters

    SciTech Connect

    Chen, C. L.; Shen, J.; Chen, S. Y.; Luo, G. P.; Chu, C. W.; Miranda, F. A.; Van Keuls, F. W.; Jiang, J. C.; Meletis, E. I.; Chang, H. Y.

    2001-01-29

    Dielectric Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} thin films were epitaxially grown on (001) MgO by using pulsed laser ablation. Microstructure studies from x-ray diffraction and electron microscopy suggest that the as-grown films are c-axis oriented with an interface relationship of <100>BSTO//<100>MgO. A room temperature coupled microwave phase shifter has been developed with a phase shift near 250{sup o} at 23.675 GHz under an electrical field of 40 V/{mu}m and a figure of merit of {approx}53{sup o}/dB. The performance of the microwave phase shifter based on the epitaxial Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} thin films on (001) MgO is close to that needed for practical applications in wireless communications.

  15. Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains on MgO, SrTiO3, and LaAlO3 substrates

    NASA Technical Reports Server (NTRS)

    Liou, S. H.; Wu, C. Y.

    1992-01-01

    Crystalline orientations of Tl2Ba2Ca2Cu3O(x) grains in magnetron sputtered films on MgO (001), SrTiO3 (001), and LaAlO3 (001) substrates were investigated by scanning electron microscopy. In contrast to the nearly single crystalline films on the lattice matched substrates SrTiO3 and LaAlO3, films on the MgO (001) substrate, being polycrystalline in nature, exhibit several preferred in-plane grain orientations. These orientations agree well with a simplified theory of near-coincidence site lattices between Tl2Ba2Ca2Cu3O(x) and MgO.

  16. Structural, thermal and optical properties of TeO2-ZnO-CdO-BaO glasses doped with VO2+

    NASA Astrophysics Data System (ADS)

    Sreenivasulu, V.; Upender, G.; Chandra Mouli, V.; Prasad, M.

    2015-09-01

    The glasses with composition 64TeO2-15ZnO-(20-x)CdO-xBaO-1V2O5 (0 ⩽ x ⩽ 20 mol%) were prepared by conventional melt quenching technique. X-ray diffraction analysis was used to confirm the amorphous nature of the glasses. The optical absorption studies revealed that the cut-off wavelength (λα) decreases while optical band gap energy (Eopt) and Urbach energy (ΔE) values increase with an increase of BaO content. Refractive index (n) evaluated from Eopt was found to decrease with an increase of BaO content. The physical parameters such as density (ρ), molar volume (Vm), oxygen packing density (OPD), optical basicity (Λ), molar refraction (Rm), and metallization criterion (M) evaluated and discussed. FTIR and Raman spectroscopic studies showed that the glass network consists of TeO4, TeO3+1/TeO3 and ZnO4 units as basic structural units. The glass transition temperature (Tg) of glass sample, onset crystallization temperature (To) and thermal stability ΔT were determined from Differential Scanning Calorimetry (DSC). Using electron paramagnetic resonance (EPR) spectra of vanadium glasses the spin Hamiltonian parameters and dipolar hyperfine coupling parameters of VO2+ ions were calculated. It was found that V4+ ions in these glasses exist as VO2+ in octahedral coordination with a tetragonal distortion and have C4V symmetry with ground state dxy. Tetragonality (Δg∥ / Δg⊥) of vanadium ion sites exhibited non-linear variation with BaO content.

  17. Electronic structure and properties of isoelectronically substituted compounds Y{sub 1}Ba{sub 2-m}M{sub m}Cu{sub 3}O{sub 7} and Y{sub 1}Ba{sub 2-m}M{sub m}Cu{sub 4}O{sub 8} (M = Be, Mg, Ca, Sr, Ba, Ra)

    SciTech Connect

    Ermakov, A.I.; Zharikova, E.A.; Markushin, N.A.

    1994-09-01

    According to cluster calculations, the electronic structures of compounds based on Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} and Y{sub 1}Ba{sub 2}Cu{sub 4}O{sub 8} with isoelectronically substituted barium have some qualitative distinctions. These compounds behave differently upon barium substitution by other elements due to differences in the character of their highest occupied and lowest unoccupied molecular orbitals. Substitution of barium by radium is expected to lead to an increase in oxygen stability without a significant decrease in the critical temperature of superconduction transition T{sub s}. In order to raise T{sub s}, it is of interest to study the systems YBa{sub 2-m}(Be or Mg){sub m}Cu{sub 3}O{sub x} and YBa{sub 2-m}(Ca, Sr){sub m}Cu{sub 3}O{sub x}. On partial substitution of barium by calcium in YBa{sub 2}Cu{sub 4}O{sub 8}, the mechanism of T{sub s} elevation may involve contraction of the forbidden band due to oxygen sublattice distortions in the vicinity of Ba centers.

  18. Experimental and computational investigation of the group 11-group 2 diatomic molecules: first determination of the AuSr and AuBa bond energies and thermodynamic stability of the copper- and silver-alkaline earth species.

    PubMed

    Ciccioli, A; Gigli, G; Lauricella, M

    2012-05-14

    The dissociation energies of the intermetallic molecules AuSr and AuBa were for the first time determined by the Knudsen effusion mass spectrometry method. The two species were produced in the vapor phase equilibrated with apt mixtures of the constituent elements, and the dissociation equilibria were monitored mass-spectrometrically in the temperature range 1406-1971 K (AuSr) and 1505-1971 K (AuBa). The third-law analysis of the equilibrium data gives the following dissociation energies (D(0)°, in kJ/mol): 244.4 ± 4.8 (AuSr) and 273.3 ± 6.3 (AuBa), so completing the series of D(0)°s for the AuAE (AE = group 2 element) diatomics. The AuAE species were also studied computationally at the coupled cluster including single, double and perturbative triple excitation [CCSD(T)] level with basis sets of increasing zeta quality, and various complete basis set limit extrapolations were performed to calculate the dissociation energies. Furthermore, the entire series of the heteronuclear diatomic species formed from one group 11 (Cu, Ag) and one group 2 (Be, Mg, Ca, Sr, Ba) metal was studied by DFT with the hybrid meta-GGA TPSSh functional and the def2-QZVPP basis set, selected after screening a number of functional-basis set combinations using the AuAE species as benchmark. Dissociation energies, internuclear distances, vibrational frequencies, and anharmonic constants were determined for the CuAE and AgAE species and their thermal functions evaluated therefrom. On this basis, a thermodynamic evaluation of the formation of these species was carried out under various conditions.

  19. Low loss composition of BaxSryCa1-x-yTiO3: Ba0.12-0.25Sr0.35-0.47Ca0.32-0.53TiO3

    DOEpatents

    Xiang, Xiao-Dong; Chang, Hauyee; Takeuchi, Ichiro

    2001-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  20. Effect of high-energy electron irradiation in an electron microscope column on fluorides of alkaline earth elements (CaF2, SrF2, and BaF2)

    NASA Astrophysics Data System (ADS)

    Nikolaichik, V. I.; Sobolev, B. P.; Zaporozhets, M. A.; Avilov, A. S.

    2012-03-01

    The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline earth elements CaF2, SrF2, and BaF2 is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes chemical changes in MF2 crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ˜2 × 103 pA/cm2). In BaF2 samples, the transformation of BaO into Ba(OH)2 was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)2 into BaO. In the initial stage of irradiation of all MF2 compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF2 matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of MF2 destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ˜20 nm in the sample.

  1. Impact of hydrogen forming gas annealing on microwave properties of Ba(Zn1/3Ta2/3)O3 dielectric ceramics

    NASA Astrophysics Data System (ADS)

    Sezer, N.; Saka, E.

    2016-03-01

    The effect of H2 forming gas annealing on the microwave properties of Ba(Zn1/3Ta2/3)O3 (BZT) dielectric ceramics has been studied. The structural, microwave, DC electrical and optical properties were analyzed by experiment results. With elevated temperature annealing, the microwave loss of BZT was increased. This trend correlated with high DC conductivity of annealed samples, as well as dampened phonons found in Raman spectra. These evidences, together, prove that the enhancement of oxygen vacancy defects induced by oxygen deficient sintering environment is one of the main extrinsic root causes for the high microwave loss in practical ceramic materials.

  2. Magnetic structure, magnetization, and magnetotransport properties of (Ba,Sr)M2±xT4∓xO11 ( M=Fe,Co ; T=Ru,Ti )

    NASA Astrophysics Data System (ADS)

    Shlyk, L.; Ueland, B. G.; Lynn, J. W.; Huang, Q.; de Long, L. E.; Parkin, S.

    2010-05-01

    Hexagonal R -type ferrites (Ba,Sr)M2±xT4∓xO11 ( M=Fe,Co ; T=Ru,Ti ) were studied via neutron and x-ray diffraction, magnetization, and electrical transport measurements. Magnetization data for single-crystal BaFe3.26Ti2.74O11 reveal two magnetic transitions at T1=250K and T2=84K , which indicates complex magnetic order driven by competing interactions on a frustrated lattice with a noncentrosymmetric structure. Magnetization data for single-crystal BaCo1.85Ru4.15O11 reveal soft ferromagnetic order at TC=105K with an easy direction perpendicular to the c axis. Neutron diffraction data for polycrystalline BaCo1.68Ru4.32O11 indicate a nearly compensated arrangement of spins lying within the a-b plane with a possible canting out of the plane that yields nonzero scalar spin chirality. The transverse magnetoresistivity ρxy of single-crystal BaCo1.85Ru4.15O11 for current J∥H⊥c axis is typical of an anomalous Hall effect observed in ferromagnets, whereas for J⊥H∥c axis, ρxy is a nonmonotonic function of the magnetic field, consistent with a topological Hall effect that depends upon scalar spin chirality. Neutron diffraction reveals transitions to ferrimagnetic order at TC=262(1)K for single-crystal SrFe2.6Ru3.4O11 , and at TC=403K for polycrystalline SrFe2.96Ru3.04O11 (refined as a collinear structure at T=5K ).

  3. Temperature Dependence of the Surface Energy of the Low-index Planes of CaF2, BaF2 and SrF2

    NASA Astrophysics Data System (ADS)

    Bebelis, S.; Nikolopoulos, P.

    2017-02-01

    The temperature dependence of the surface energy γ of the low-index (111), (110) and (100) planes of CaF2, BaF2 and SrF2 was evaluated for the first time, using a simple method which is based on physical and thermodynamic quantities and considerations. The extrapolated to 0 K surface energy values agree well with the available theoretical data reported in the literature for the (111) plane and are close to those for the (110) plane, whereas they are significantly lower than those for the (100) plane. The calculated γ111 values for 298 K agree well with the corresponding experimentally determined literature values. The calculated γ100/γ111 ratio revealed formation of crystals with truncated octahedron structure in thermodynamic equilibrium. This structure remains practically constant with temperature. The surface energy values of fluoride melts formed by melting of octahedron structures, calculated via extrapolation of the surface energy of the solids to the melting points, were compared with experimentally determined literature values for melts resulting from single or polycrystalline materials.

  4. Magnetic structures and excitations in a multiferroic Y-type hexaferrite BaSrCo2Fe11AlO22

    DOE PAGES

    Nakajima, Taro; Tokunaga, Yusuke; Matsuda, Masaaki; ...

    2016-11-30

    Here, we have investigated magnetic orders and excitations in a Y-type hexaferrite BaSrCo2Fe11AlO22 (BSCoFAO), which was reported to exhibit spin-driven ferroelectricity at room temperature. By means of magnetization, electric polarization, and neutron-diffraction measurements using single-crystal samples, we establish a H-T magnetic phase diagram for magnetic field perpendicular to the c axis (H⟂c). This system exhibits an alternating longitudinal conical (ALC) magnetic structure in the ground state, and it turns into a non-co-planar commensurate magnetic order with spin-driven ferroelectricity under H⟂c. The field-induced ferroelectric phase remains as a metastable state after removing magnetic field below 250 K. This metastability is themore » key to understanding of magnetic field reversal of the spin-driven electric polarization in this system. Inelastic polarized neutron-scattering measurements in the ALC phase reveal a magnetic excitation at around 7.5 meV, which is attributed to spin components oscillating in a plane perpendicular to the cone axis. This phasonlike excitation is expected to be an electric-field active magnon, i.e., electromagnon excitation, in terms of the magnetostriction mechanism.« less

  5. Temperature Dependence of the Surface Energy of the Low-index Planes of CaF2, BaF2 and SrF2

    NASA Astrophysics Data System (ADS)

    Bebelis, S.; Nikolopoulos, P.

    2017-03-01

    The temperature dependence of the surface energy γ of the low-index (111), (110) and (100) planes of CaF2, BaF2 and SrF2 was evaluated for the first time, using a simple method which is based on physical and thermodynamic quantities and considerations. The extrapolated to 0 K surface energy values agree well with the available theoretical data reported in the literature for the (111) plane and are close to those for the (110) plane, whereas they are significantly lower than those for the (100) plane. The calculated γ111 values for 298 K agree well with the corresponding experimentally determined literature values. The calculated γ100/γ111 ratio revealed formation of crystals with truncated octahedron structure in thermodynamic equilibrium. This structure remains practically constant with temperature. The surface energy values of fluoride melts formed by melting of octahedron structures, calculated via extrapolation of the surface energy of the solids to the melting points, were compared with experimentally determined literature values for melts resulting from single or polycrystalline materials.

  6. Ab initio study of the electronic, optical and thermodynamic properties of the ternary phosphides Li AeP ( Ae = Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Benahmed, A.; Bouhemadou, A.; Khenata, R.; Bin-Omran, S.

    2017-02-01

    We report the results of an ab initio study of the electronic, optical and thermodynamic properties of the LiBaP and LiSrP compounds using the pseudopotential plane-wave method within the framework of the density functional theory with the GGA-PBEsol. The calculated equilibrium structural parameters are in good agreement with the available experimental data. The energy band dispersions along the high symmetry directions in the k-space and the density of states diagrams are computed and analyzed. The obtained energy bands show that both examined crystals are indirect band gap semiconductors. The chemical bonding character is examined via electron density map plots. The optical properties are predicted for an incident radiation in an energy range up to 15 eV, and the origins of the main peaks in the optical spectra are discussed in terms of the calculated electronic band structure. We have also predicted the temperature and pressure dependencies of the unit-cell volume, thermal expansion coefficient, heat capacity, Debye temperature and Grüneisen parameter.

  7. Influence of annealing temperature on the dielectric properties of BaSrTiO3 thin films deposited on various substrates

    NASA Astrophysics Data System (ADS)

    Lee, Chil-Hyoung; Oh, Young-Jei; Lee, Deuk Yong; Choi, Doo-Jin

    2016-11-01

    (Ba0.5Sr0.5)TiO3 (BST) thin films were deposited on various substrates, such as LaAlO3(100), MgO(100), R-plane sapphire[1012], and polycrystalline sapphire, by using RF magnetron sputtering to investigate the influence of annealing temperature on the dielectric properties and the tunability of the films. The BST thin films deposited on LaAlO3(100) exhibited a high tunability of 42 % and a low dielectric loss of 0.004 due to the small differences in the lattice parameters and the thermal expansion coefficients between the BST films and the substrates. In contrast, the BST films deposited on a polycrystalline sapphire, exhibiting a relatively high mismatch factor, showed the tunability of 24 % and a dielectric loss of 0.007. The BST thin films on LaAlO3(100), MgO(100), R-plane sapphire[1012], and polycrystalline sapphire were annealed. The optimized annealing temperatures were found to be 950 °C, 1050 °C, 1100 °C, and 1150 °C, respectively. The difference in annealing temperature is likely due to the differences in the lattice parameters and the thermal expansion coefficients between the films and the substrates.

  8. Phase stability, elastic anisotropy and electronic structure of cubic MAl2 (M = Mg, Ca, Sr and Ba) Laves phases from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Kong, Yuanyuan; Duan, Yonghua; Ma, Lishi; Li, Runyue

    2016-10-01

    By performing first-principles calculations within the generalized gradient approximation, the phase stability, elastic constant and anisotropy, and density of states of cubic C15-type MAl2 (M = Mg, Ca, Sr and Ba) Laves phases have been investigated. Optimized equilibrium lattice parameters and formation enthalpies agree well with the available experimental data. Elastic constants C ij have been evaluated, and these C15-type MAl2 Laves phases are mechanically stable due to the meeting of C ij to the mechanical stability criteria. Polycrystalline elastic moduli have been deduced from elastic constants by Voigt-Reuss-Hill approximation. Plastic properties were characterized via values of B/G, Poisson’s ratio ν and Cauchy pressure (C 12-C 44). The elastic anisotropy has been considered by several anisotropy indexes (A U , A Z , A shear and A comp), anisotropy of shear modulus, and 3D surface constructions of bulk and Young’s moduli. Additionally, the sound velocity anisotropy and Debye temperature were predicted. Finally, electronic structures were carried out to reveal the underlying phase stability mechanism of these Laves phases.

  9. Magnetic structures and excitations in a multiferroic Y-type hexaferrite BaSrCo2Fe11AlO22

    NASA Astrophysics Data System (ADS)

    Nakajima, Taro; Tokunaga, Yusuke; Matsuda, Masaaki; Dissanayake, Sachith; Fernandez-Baca, Jaime; Kakurai, Kazuhisa; Taguchi, Yasujiro; Tokura, Yoshinori; Arima, Taka-hisa

    2016-11-01

    We have investigated magnetic orders and excitations in a Y-type hexaferrite BaSrCo2Fe11AlO22 (BSCoFAO), which was reported to exhibit spin-driven ferroelectricity at room temperature [S. Hirose, K. Haruki, A. Ando, and T. Kimura, Appl. Phys. Lett. 104, 022907 (2014), 10.1063/1.4862432]. By means of magnetization, electric polarization, and neutron-diffraction measurements using single-crystal samples, we establish a H -T magnetic phase diagram for magnetic field perpendicular to the c axis (H⊥c). This system exhibits an alternating longitudinal conical (ALC) magnetic structure in the ground state, and it turns into a non-co-planar commensurate magnetic order with spin-driven ferroelectricity under H⊥c. The field-induced ferroelectric phase remains as a metastable state after removing magnetic field below ˜250 K. This metastability is the key to understanding of magnetic field reversal of the spin-driven electric polarization in this system. Inelastic polarized neutron-scattering measurements in the ALC phase reveal a magnetic excitation at around 7.5 meV, which is attributed to spin components oscillating in a plane perpendicular to the cone axis. This phasonlike excitation is expected to be an electric-field active magnon, i.e., electromagnon excitation, in terms of the magnetostriction mechanism.

  10. Improved Dielectric Properties of Heterostructured Ba2.5Sr0.5TiO3 Thin Film Composites for Microwave Dielectric Devices

    NASA Technical Reports Server (NTRS)

    Jain, M.; Majumder, S. B.; Katiyar, R. S.; Bhalla, A. S.; Agrawal, D. C.; Kulkarni, V. N.; VanKeuls, F. W.; Miranda, F. A.; Romanofsky, R. R.; Mueller, C. H.; Fernandez, F.

    2002-01-01

    In the present work we have deposited MgO and Ba(sub 0.5)Sr(sub 0.5)TiO(sub 3)(BST50) thin layers in different sequences to make MgO:BST50 hetero-structured thin films. These films were characterized by X-ray diffraction and Rutherford backscattering technique and found to be highly (100) textured. The figure of merit {(C(sub0)-C(sub v)/(C(sub0-tandelta)} of the hetero-structured films was found to be higher as compared to pure BST50 films measured at 1 MHz frequency with electric field of 25.3 kV/cm. These films were used to make eight element coupled micro-strip phase shifter and characterized in a frequency range of 13-15 GHz. The high frequency figure of merit (kappa factor, defined as the ratio of degree of phase shift per dB loss) measured at around 14 GHz with electric field of 333 kV/cm has been markedly improved (around 64.28 deg/dB for hetero-structured film as compared to 24.65 deg /dB for pure film). Improvement in dielectric properties in a wide frequency range in the MgO:BST are believed to be due to the higher densification of the hetero-structured films.

  11. One step synthesis of Bi(Pb)-2223 phase in Bi(Pb)-Sr(Ba)-Ca-Cu nitrate freeze dried powder

    NASA Astrophysics Data System (ADS)

    Badica, P.; Aldica, G.; Mandache, S.

    1999-03-01

    One step synthesis of the superconducting Bi(Pb)-2223 phase during heat treatment for non-equilibrium decomposition of the freeze dried Bi:Pb:Sr:Ba:Ca:0953-2048/12/3/010/img1:0.4:1.8:0.2:2.2:3.0 nitrate powder has been studied. The heating rate was 0953-2048/12/3/010/img2 and samples were maintained in air at 0953-2048/12/3/010/img3C for 0, 5, 10, 20, 30, 60, 90, 240 and 1080 min. Each batch was investigated by x-ray diffraction analysis and ac magnetic susceptibility 0953-2048/12/3/010/img4. Evolution of phases and kinetics of phase formation-decomposition processes were discussed. 0953-2048/12/3/010/img5% of Bi(Pb)-2223 has formed indicating the possibility of lowering the processing time of the freeze dried precursor powders by one order of magnitude comparative to the multistep synthesis route (from hundreds to tens of hours). A 30 min heat treatment step at 0953-2048/12/3/010/img6C performed on the way up to the synthesis temperature is a forthcoming operation in order to block the formation of secondary undesired phases (e.g. 0953-2048/12/3/010/img7.

  12. Dielectric constant dispersion of yttrium-doped (Ba,Sr)TiO3 films in the high-frequency (10 kHz-67 GHz) domain

    NASA Astrophysics Data System (ADS)

    Jeong, Doo Seok; Hwang, Cheol Seong; Baniecki, J. D.; Shioga, T.; Kurihara, K.; Kamehara, N.; Ishii, M.

    2005-12-01

    The frequency dispersion of the dielectric constant of yttrium (Y)-doped (Ba,Sr)TiO3 thin films (Y-BST) in the high-frequency domain (10kHz-67GHz) was investigated. In order to remove the substantial parasitic capacitances, inductances, and resistances from the measured impedance data, test samples, short-circuit standard, and open-circuit standard structures were fabricated and their frequency response was measured. Before removing parasitic components, the measured dielectric response showed a rolloff at approximately 4GHz. However, after circuit calibration, the dielectric constant was almost constant up to 40GHz where another rolloff was observed. However, this rolloff was due to the uncompensated small parasitic components. Therefore, the dielectric constant of the Y-BST films (170 with a film thickness of 30nm) showed small frequency dispersion corresponding to the Curie-von Schweidler dispersion, of which the exponent is -0.0131, up to 40GHz. Furthermore, the decrease of the capacitance was 17% in the frequency range from 10kHzto40GHz.

  13. Legitional behavior of 5,5-diethylbarbituric acid sodium salt (HL) towards Mg, Ca, Sr, Ba(II), spectral, thermal and biological studies

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; El-Metwaly, Nashwa M.

    2011-03-01

    A new series of sodium barbital complexes with Alkaline earth metals (Mg2+, Ca2+, Sr2+ and Ba2+ ions) was prepared. The molecular formulas for the isolated complexes were suggested basically on the elemental analysis data. The binuclear central were proposed for all investigated complexes. The geometry suggested based on knowing the coordination sits for each complex was built on concerning with the shift observed in IR spectra surround the coordinating groups. The shifts in charge transfer bands appeared in the electronic spectra of the complexes supports the coordination process. The presence of solvent molecules coordinately attached with central metal atoms as well as the conjugated anions was supported based on thermogravimetric analysis. The kinetic parameters were calculated for each complex. The theoretical calculations for the molecular modeling structures reflect an insight about their stability in comparing with the free ligand. The XRD studies were performed and concluding the nanocrystalline feature for all complexes. The biochemical effect of all investigated compounds was performed towards Gram-negative and Gram-positive bacteria as well as their degradation effect on calf Thymus DNA. The biological performance is the major goal in this study especially with such essential metal ions.

  14. Downscaling at submicrometer scale of the gap width of interdigitated Ba0.5Sr0.5TiO3 capacitors.

    PubMed

    Khalfallaoui, Abderrazek; Burgnies, Ludovic; Blary, Karine; Velu, Gabriel; Lippens, Didier; Carru, Jean-Claude

    2015-02-01

    The goal of this work was to study the influence of shrinking the gap width between the fingers of interdigitated tunable capacitors (IDCs). Voltage control of the capacitance was achieved with a 500-nm-thick Ba0.5Sr0.5TiO3 film which is in paraelectric state at room temperature. Eight devices with finger spacing ranging from 3 μm down to 0.25 μm were fabricated by the sol-gel deposition technique, electron beam patterning, and gold evaporation. The equivalent capacitance, quality factor, and tunability of the devices were measured subsequently by vector network analysis from 40 MHz to 40 GHz and for a dc bias voltage varying from -30 V to +30 V. This experimental study mainly shows that a decrease of the gap below 1 μm 1) introduces a frequency dependence of the capacitance caused by resonance effects with the finger inductance; 2) degrades the quality factor above 20 GHz, and 3) optimizes the tunability of the devices by enhancing the local electric field values. As a consequence, some trade-offs are pointed out related to the goal of ultra-thin ferroelectric film which can be voltage controlled by means of finger-shaped electrodes with deep submicrometer spacing.

  15. Decomposition of the different contributions to permittivity, losses, and tunability in BaSrTiO3 thin films using the hyperbolic law

    NASA Astrophysics Data System (ADS)

    Nadaud, Kevin; Borderon, Caroline; Renoud, Raphaël; Gundel, Hartmut W.

    2016-03-01

    In this paper, the different contributions to the permittivity of a 1% manganese-doped BaSrTiO3 thin film are presented as a function of the applied DC field. The hyperbolic law has been used to discern the lattice, domain wall vibration, and pinning/unpinning contributions. This decomposition permits us to study the weight of the respective contribution in the total permittivity, the losses, and the tunability. By determining the figure of merit (FoM) of each contribution, the ratio between tunability and losses, it is possible to identify the phenomenon which should be limited or enhanced in order to optimize the material's dielectric properties. It is shown that the tunability of the domain wall contribution (approximately 80%) is very important compared to the lattice contribution (41%), the associated dissipation factor, however, is also much larger (0.2 instead of 0.014). Even if the domain wall contribution has been shown to be weak in the investigated thin film (less than 3% in permittivity and tunability), the weight of the losses is not negligible (around 18%). Hence, the domain contribution has to be limited in order to conserve a high FoM for the material. Moreover, it is shown that the AC field used for the material's characterization is important because it governs the weight of the domain wall losses and thus the FoM.

  16. A Comparison of MOCLD With PLD Ba(x)Sr(1-x)TiO3 Thin Films on LaAlO3 for Tunable Microwave Applications

    NASA Technical Reports Server (NTRS)

    VanKeuls, F. W.; Mueller, C. H.; Romanofsky, R. R.; Warner, J. D.; Miranda, F. A.; Jiang, H.

    2002-01-01

    Historically, tunable dielectric devices using thin crystalline Ba(x)Sr(1-x)TiO3 (BST) films deposited on lattice-matched substrates, such as LaAlO3, have generally been grown using pulsed laser deposition (PLD). Highly oriented BST films can be grown by PLD but large projects are hampered by constraints of deposition area, deposition time and expense. The Metal-Organic Chemical Liquid Deposition (MOCLD) process allows for larger areas, faster turnover and lower cost. Several BST films deposited on LaAlO3 by MOCLD have been tested in 16 GHz coupled microstrip phase shifters. They can be compared with many PLD BST films tested in the same circuit design. The MOCLD phase shifter performance of 293 deg. phase shift with 53 V/micron dc bias and a figure of merit of 47 deg./dB is comparable to the most highly oriented PLD BST films. The PLD BST films used here have measured XRD full-width-at-half-maxima (FWHM) as low as 0.047 deg.. The best FWHM of these MOCLD BST films has been measured to be 0.058 deg.

  17. Effects of oxygen partial pressure on the ferroelectric properties of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Silva, J. P. B.; Sekhar, K. C.; Almeida, A.; Agostinho Moreira, J.; Pereira, M.; Gomes, M. J. M.

    2013-11-01

    The Ba0.8Sr0.2TiO3 thin films were grown on the Pt-Si substrate at 700 °C by using a pulsed laser deposition technique at different oxygen partial pressure (PO2) in the range of 1-20 Pa and their properties were investigated. It is observed that the PO2 during the deposition plays an important role on the tetragonal distortion ratio, surface morphology, dielectric permittivity, ferroelectric polarization, switching response, and leakage currents of the films. With an increase in PO2, the in-plane strain for the BST films changes from tensile to compressive. The films grown at 7.5 Pa show the optimum dielectric and ferroelectric properties and also exhibit the good polarization stability. It is assumed that a reasonable compressive strain, increasing the ionic displacement, and thus promotes the in-plane polarization in the field direction, could improve the dielectric permittivity. The butterfly features of the capacitance-voltage ( C- V) characteristics and the bell shape curve in polarization current were attributed to the domain reversal process. The effect of pulse amplitude on the polarization reversal behavior of the BST films grown at PO2 of 7.5 Pa was studied. The peak value of the polarization current shows exponential dependence on the electric field.

  18. Phase transition in ABi4Ti4O15 (A=Ca,Sr,Ba) Aurivillius oxides prepared through a soft chemical route

    NASA Astrophysics Data System (ADS)

    Rout, S. K.; Sinha, E.; Hussian, A.; Lee, J. S.; Ahn, C. W.; Kim, I. W.; Woo, S. I.

    2009-01-01

    A series of compounds, CaBi4Ti4O15 (CBT), SrBi4Ti4O15 (SBT), and BaBi4Ti4O15 (BBT), belonging to the Aurivillus-type structure (four layers) has been prepared by a modified chemical route. Different oxalates were precipitated from their respective nitrate solution onto the surface of TiO2 powders. The room temperature x-ray diffraction study reveled that the compounds were having orthorhombic symmetry. Considering the tolerance factor, a significant deformation of the perovskite block is observed and that decreases with increase in ionic radius of A site atom. Temperature dependent dielectric study showed normal ferroelectric to paraelectric transition well above the room temperature except for BBT. The BBT ceramic showed a relaxorlike behavior near phase transition. The quantitative characterization and comparison of relaxor behavior were based on empirical parameters γ and ΔTres. The dielectric relaxation rate follows the Vogel-Fulcher relation with activation energy=0.02 eV and freezing temperature=362 °C. All these measurements confirmed its relaxorlike phase transition.

  19. Increased saturation field as the origin of the giant electrocaloric effect in Ba0.8Sr0.2TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Park, Y. A.; Sung, K. D.; Jung, J. H.; Hur, N.; Cheong, S. W.

    2015-08-01

    We investigated the electrocaloric (EC) effects in epitaxial Ba0.8Sr0.2TiO3 (BSTO) thin films grown on LaAlO3 and MgO substrates and in BSTO sol-gel thin films grown on Si substrates. We compared the EC effects in two forms of BSTO to confirm whether the giant EC effect recently observed in the polycrystalline thin film is an intrinsic effect or an extrinsic effect exclusively occurring in polycrystalline thin films with nano-sized grains. The EC effect in our BSTO single crystals exhibited a moderate EC temperature change over a broad temperature range. On the other hand, the EC effect in the BSTO sol-gel film was observed over a narrow temperature range with a giant Δ T of about 14 °C. We claim that this giant EC effect is due to the increased saturation field related to the small grain size in the sol-gel thin film.

  20. Enhanced dielectric constant and relaxor behavior realized by dual stage sintering of Sr0.5Ba0.5Nb2O6

    NASA Astrophysics Data System (ADS)

    Rathore, Satyapal S.; Vitta, Satish

    2014-04-01

    The relaxor ferroelectric compound, Sr0.5Ba0.5Nb2O6 (SBN50) was synthesized by solid state reaction followed by sintering under two different conditions: single and dual stage sintering. The impact of sintering process on structural and dielectric properties has been studied in detail using X-ray diffraction, scanning electron microscopy and broadband dielectric spectroscopy. The crystal structure determined by performing Rietveld refinement of X-ray diffractogram was found to be identical in both cases. SBN50 crystallizes in the ferroelectric tetragonal tungsten bronze, P4bm structure. It was observed that uniform grain growth can be controlled by dual stage sintering and relatively narrow distribution of grains can be achieved with an average grain size of ˜15 μm. The dielectric studies show that SBN50 exhibits a relaxor ferroelectric behavior with the transformation taking place at ˜ 380 K due to formation of polar nano regions. Although both single and dual stage sintered SBN50 exhibits relaxor behaviour, the maximum dielectric constant of dual stage sintered SBN50 is found to be 1550 compare to 1440 for single stage sintering.

  1. Polar phase transitions and physical properties in fresnoite A2TiSi2O8 (A= Ba, Sr) by first principles calculations

    NASA Astrophysics Data System (ADS)

    Song, Nayoung; Momida, Hiroyoshi; Oguchi, Tamio; Kim, Bog G.

    2016-10-01

    Polar phase transitions of fresnoites, Ba2TiSi2O8 (BTS) and Sr2TiSi2O8 (STS) have been comparatively analyzed by the first principles calculations. We show that both BTS and STS have a polar structure with the space group P4bm as a ground state, and there is a fictitious phase transition in the tetragonal space group from the nonpolar P4/mbm meta-stable phase to the polar P4bm phase. From the analyses of the two atomic structures, we find that a noticeable issue in the phase transition is bond length changes of Si-O and Ti-O which break the inversion symmetry, resulting that one of vertices in the edge-shared Si-O and Ti-O polyhedron is detached in the polar phase. The structural phase transition between the polar and the nonpolar states are discussed in terms of electronic structures and structural symmetry mode analyses. We evaluate the size of spontaneous polarizations of BTS and STS in the polar P4bm phases, and the correlation analysis shows significant contributions of the detached polyhedrons to the strong polar property. We also show second harmonic generation susceptibilities of BTS and STS as a candidate for second-order nonlinear optics materials. Our quantitative studies can provide full understandings of atomic and electronic mechanisms of their polar phase and nonlinear optical properties.

  2. Direct correlation and strong reduction of native point defects and microwave dielectric loss in air-annealed (Ba,Sr)TiO{sub 3}

    SciTech Connect

    Zeng, Z. Q.; Podpirka, A.; Kirchoefer, S. W.; Asel, T. J.; Brillson, L. J.

    2015-05-04

    We report on the native defect and microwave properties of 1 μm thick Ba{sub 0.50}Sr{sub 0.50}TiO{sub 3} (BST) films grown on MgO (100) substrates by molecular beam epitaxy (MBE). Depth-resolved cathodoluminescence spectroscopy (DRCLS) showed high densities of native point defects in as-deposited BST films, causing strong subgap emission between 2.0 eV and 3.0 eV due to mixed cation V{sub C} and oxygen Vo vacancies. Post growth air anneals reduce these defects with 2.2, 2.65, and 3.0 eV V{sub O} and 2.4 eV V{sub C} intensities decreasing with increasing anneal temperature and by nearly two orders of magnitude after 950 °C annealing. These low-defect annealed BST films exhibited high quality microwave properties, including room temperature interdigitated capacitor tunability of 13% under an electric bias of 40 V and tan δ of 0.002 at 10 GHz and 40 V bias. The results provide a feasible route to grow high quality BST films by MBE through post-air annealing guided by DRCLS.

  3. Electrical transport properties and modelling of electrostrictive resonance phenomena in Ba2/3Sr1/3TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Ghalem, A.; Huitema, L.; Crunteanu, A.; Rammal, M.; Trupina, L.; Nedelcu, L.; Banciu, M. G.; Dutheil, P.; Constantinescu, C.; Marchet, P.; Dumas-Bouchiat, F.; Champeaux, C.

    2016-11-01

    We present the conduction mechanisms of Ba2/3Sr1/3TiO3 thin films integrated in metal-insulator-metal (MIM) capacitors and the modelling of the frequency-dependent electrostrictive resonances (in the 100 MHz-10 GHz domain) induced in the devices upon applying different voltage biases. Au/BST/Ir MIM structures on MgO substrates have been fabricated and, depending on their specific polarization, we highlighted different conduction mechanisms in the devices. Depending on the dc bias polarity, the conduction current across the material shows a space-charge-limited-current behavior under negative polarization, whereas under positive bias, the conduction obeys an electrode-limited Schottky-type law at the Au/BST interface. The application of an electric field on the device induces the onset of acoustic resonances related to electrostrictive phenomena in the ferroelectric material. We modeled these acoustic resonances over a wide frequency range, by using a modified Lakin model, which takes into account the dispersions of acoustic properties near the lower electrode/thin film interface.

  4. Morphological and optical properties of sol-gel derived 6SrO·6BaO·7Al 2O 3 thin films

    NASA Astrophysics Data System (ADS)

    Chavhan, P. M.; Sharma, Anubha; Sharma, R. K.; Kaushik, N. K.

    2010-01-01

    A novel 6SrO·6BaO·7Al 2O 3 (S6B6A7) thin film deposited onto soda lime float glass via sol-gel dip coating technique is reported. The morphological and compositional properties of the S6B6A7 thin films have been investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) revealing that the films were composed of S6B6A7 nanoparticles. The optical properties of the S6B6A7 films are affected by sol concentration, film thickness and annealing temperature as revealed by UV-vis transmittance. The transparency of S6B6A7 films improved on increasing annealing temperature up to 450 °C in air. The S6B6A7 films prepared using 2, 5, and 8 (wt.%) sols and annealed at 450 °C exhibit an average transmittance of over ˜91% in wide visible range.

  5. Congruent Sr0.61Ba0.39Nb2O6 doubly doped with Ce and Cr: Photo- and thermoluminescence investigations

    NASA Astrophysics Data System (ADS)

    Kislova, I. L.; Gao, M.; Kapphan, S. E.; Pankrath, R.; Kutsenko, A. B.; Vikhnin, V. S.

    Congruent Sr-x Ba1-xNb2O6 (SBN, x=0.61) doped with Ce or Cr ions exhibits enhanced photorefractive properties and new spectral features like increased red sensitivity. Here special emphasis is placed on the luminescence features of doubly doped Ce+Cr SBN crystals. The luminescence excitation and emission spectra combined with the absorption of the impurities allow to draw conclusions about the origin of the charge carriers und their recombination. The well separated thermo-luminescence peaks detected and their spectral line shape in emission point to specific recombination processes following the thermal liberation of light-induced electron trapping centers: Nb4+ polarons and VIS-centers created at low temperature under light irradiation. The thermal activation energy for the hopping motion of Nb4+ polarons and of VIS-centers are estimated to be 0.18+/-0.02 eV and 0.30+/-0.05 eV respectively. Possible excitation and recombination mechanisms in SBN:Ce+Cr are discussed.

  6. Life Cycle Testing of Ba(x)Sr(1-x)TiO3 Ferroelectric Thin Films in a Tunable Microwave Device

    NASA Technical Reports Server (NTRS)

    Miranda, Felix A.; VanKeuls, Fred W.; Romanofsky, Robert R.; Mueller, Carl H.; Warner, Joseph D.

    2000-01-01

    Thin film ferroelectrics are being studied as candidates for novel tunable microwave components such as tunable filters, tunable oscillators, and phase shifters for applications in phased array antennas. Much work has been done optimizing the ferroelectric material and in producing proof-of-concepts of these components. However, little attention has been given to their reliability. In this study we present our results on the reliability of high quality K-band phase shifters made of Ba(sub x)Sr(sub 1-x)TiO3 (BSTO) ferroelectric thin films (0.5 to 0.75 micrometers thick) on MgO and LAO. The phase shift and insertion loss were measured at 300 K over 104 operation cycles within a 0 to 400 V dc bias range (0 to 40 V/micrometer) at 15, 18, and 22 GHz. Results for these phase shifters indicate that in general there were no appreciable changes in phase shift after 4x10(exp 4) cycles, suggesting that these phase shifters are robust enough to sustain optimal performance under the operating mode typical of fast tracking phased arrays.

  7. Ultra high energy density nanocomposite capacitors with fast discharge using Ba0.2Sr0.8TiO3 nanowires.

    PubMed

    Tang, Haixiong; Sodano, Henry A

    2013-04-10

    Nanocomposites combining a high breakdown strength polymer and high dielectric permittivity ceramic filler have shown great potential for pulsed power applications. However, while current nanocomposites improve the dielectric permittivity of the capacitor, the gains come at the expense of the breakdown strength, which limits the ultimate performance of the capacitor. Here, we develop a new synthesis method for the growth of barium strontium titanate nanowires and demonstrate their use in ultra high energy density nanocomposites. This new synthesis process provides a facile approach to the growth of high aspect ratio nanowires with high yield and control over the stoichiometry of the solid solution. The nanowires are grown in the cubic phase with a Ba0.2Sr0.8TiO3 composition and have not been demonstrated prior to this report. The poly(vinylidene fluoride) nanocomposites resulting from this approach have high breakdown strength and high dielectric permittivity which results from the use of high aspect ratio fillers rather than equiaxial particles. The nanocomposites are shown to have an ultra high energy density of 14.86 J/cc at 450 MV/m and provide microsecond discharge time quicker than commercial biaxial oriented polypropylene capacitors. The energy density of our nanocomposites exceeds those reported in the literature for ceramic/polymer composites and is 1138% greater than the reported commercial capacitor with energy density of 1.2 J/cc at 640 MV/m for the current state of the art biaxial oriented polypropylene.

  8. Order-disorder in In{sup 3+} perovskites: The example of A(In{sub 2/3}B''{sub 1/3})O{sub 3} (A=Ba, Sr; B''=W, U)

    SciTech Connect

    Larregola, S.A. Alonso, J.A.; Pinacca, R.M.; Viola, M.C.; Pedregosa, J.C.

    2008-10-15

    We describe the preparation and structural characterization of four In-containing perovskites from neutron powder diffraction (NPD) and X-ray powder diffraction (XRPD) data. Sr{sub 3}In{sub 2}B''O{sub 9} and Ba(In{sub 2/3}B''{sub 1/3})O{sub 3} (B''=W, U) were synthesized by standard ceramic procedures. The crystal structure of the W-containing perovskites and Ba(In{sub 2/3}U{sub 1/3})O{sub 3} have been revisited based on our high-resolution NPD and XRPD data, while for the new U-containing perovskite Sr{sub 3}In{sub 2}UO{sub 9} the structural refinement was carried out from high-resolution XRPD data. At room temperature, the crystal structure for the two Sr phases is monoclinic, space group P2{sub 1}/n, where the In atoms occupy two different sites Sr{sub 2}[In]{sub 2d}[In{sub 1/3}B''{sub 2/3}]{sub 2c}O{sub 6}, with a=5.7548(2) A, b=5.7706(2) A, c=8.1432(3) A, {beta}=90.01(1){sup o} for B''=W and a=5.861(1) A, b=5.908(1) A, c=8.315(2) A, {beta}=89.98(1){sup o} for B''=U. The two phases with A=Ba should be described in a simple cubic perovskite unit cell (S.G. Pm3-bar m) with In and B'' distributed at random at the octahedral sites, with a=4.16111(1) A and 4.24941(1) A for W and U compounds, respectively. - Graphical abstract: The structure of the new uranium-based double perovskite Sr{sub 3}In{sub 2}UO{sub 9} is described and the true symmetry of the other title compounds are revisited. The presence of long-range ordering in the Sr samples, by contrast with the Ba perovskites, is related with the smaller unit cell and B-B distances in the Sr oxides, promoting the electrostatic repulsions between highly charged W{sup 6+} and U{sup 6+} cations as driving force for the long-range B-site ordering.

  9. Preparation of nanofiber polythiophene layered on Ba x Sr1- x Fe12O19/Fe3O4/polyacrylic acid core-shell structure and its microwave absorption investigation

    NASA Astrophysics Data System (ADS)

    Hosseini, Seyed Hossein; Moloudi, Maryam

    2015-09-01

    Ba x Sr1- x Fe12O19/Fe3O4/polyacrylic acid/polythiophene (Ba x Sr1- x Fe12O19/Fe3O4/PAA/PTh) nanocomposites with multi-core-shell structure were successfully synthesized by four steps. The samples were characterized by FTIR, X-ray diffraction (XRD), transmission electron microscope (TEM), vibrating sample magnetometer, and radar absorbing material reflectivity far-field radar cross-section method, respectively. XRD and TEM results indicated that the obtained nanoparticles have multi-core-shell morphology. The magnetic properties and microwave absorption analyses reveal that there are interphase interactions at the interface of Ba x Sr1- x Fe12O19, Fe3O4, PAA, and PTh, which can affect the magnetic properties and microwave absorption properties of the samples. The microwave-absorbing properties of nanocomposites were investigated at 8-14 GHz. A typical layer absorber exhibited an excellent microwave absorption with a -26 dB maximum absorption at 14 GHz. Compared with core material, the coercivity and saturation magnetization of multi-core-shell nanocomposites decrease obviously, but the microwave absorption properties of nanocomposites are improved greatly. The results show that these composite could be used as advancing absorption and shielding materials due to their favorable microwave-absorbing properties.

  10. Modification of energy band alignment and electric properties of Pt/Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}/Pt thin-film ferroelectric varactors by Ag impurities at interfaces

    SciTech Connect

    Hirsch, S.; Komissinskiy, P. Flege, S.; Li, S.; Rachut, K.; Klein, A.; Alff, L.

    2014-06-28

    We report on the effects of Ag impurities at interfaces of parallel-plate Pt/Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}/Pt thin film ferroelectric varactors. Ag impurities occur at the interfaces due to diffusion of Ag from colloidal silver paint used to attach the varactor samples with their back side to the plate heated at 600–750 °C during deposition of Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}. X-ray photoelectron spectroscopy and secondary ion mass spectrometry suggest that amount and distribution of Ag adsorbed at the interfaces depend strongly on the adsorbent surface layer. In particular, Ag preferentially accumulates on top of the Pt bottom electrode. The presence of Ag significantly reduces the barrier height between Pt and Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} leading to an increased leakage current density and, thus, to a severe degradation of the varactor performance.

  11. Heat capacities and thermodynamic functions of new nanosized ferro-chromo-manganites LaM0.5 IIFeCrMnO6.5 (MII-Mg, Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Kasenov, B. K.; Kasenova, Sh. B.; Sagintaeva, Zh. I.; Turtubaeva, M. O.; Kakenov, K. S.; Esenbaeva, G. A.

    2017-03-01

    The heat capacities of nanosized ferro-chromo-manganites LaM0.5 IIFeCrMnO6.5 (MII-Mg, Ca, Sr, Ba) are measured via dynamic calorimetry in the temperature range of 298.15-673 K using an IT-S-400 instrument. It is established that the C°p f( T) function of LaM0.5 IIFeCrMnO6.5 (MII-Mg, Ca, Sr, Ba) has λ-type effects, due probably to phase transitions of the second order. Considering the temperatures of the phase transitions, equations of the heat capacity of ferro-chromo-manganites LaM0.5 IIFeCrMnO6.5 (MII-Mg, Ca, Sr, Ba) as a function of temperature are derived on the basis of experimental data. Thermodynamic functions H°( T)- H°(298.15), S°( T), and V xx( T) are calculated in the temperature range of 298.15-675 K.

  12. Dielectric properties of xNa0.5Bi0.5TiO3-(1 ‑ x)Ba0.66Mg0.04Sr0.3TiO3 composite ceramics

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Cheng, Haiyan; Gao, Lan; Wang, Xianling; Duan, Ruijie; Li, Jiali

    2017-02-01

    The ceramics with the composition of xNa0.5Bi0.5TiO3-(1 ‑ x)Ba0.66Mg0.04Sr0.3TiO3 (NBT-BMST) in which x = 0.2, 0.3, 0.4 and 0.5 were prepared successfully by the solid-state reaction method. The effects of NBT-doping on phase structure, morphology, temperature stability and dielectric properties had been investigated in detail. The XRD results show that the composites are composed of tetragonal perovskite. The phase structure of NBT-BMST is observed by scanning electron microscopy. The dielectric constant of 0.3Na0.5Bi0.5TiO3-0.7Ba0.66Mg0.04Sr0.3TiO3 ceramic is ˜4100, the temperature coefficients of capacitance are ‑15%, 15% and 22% at ‑55∘C, 60∘C and 200∘C, respectively. And the dielectric loss is less than 0.13, which is obviously superior to other compositions. The results of this work showed that the component of 0.3Na0.5Bi0.5TiO3-0.7Ba0.66Mg0.04Sr0.3TiO3 is a promising candidate to high-temperature stable materials.

  13. Absence of Magnetic Long Range Order in Ba3ZnRu2O9: A Spin-Liquid Candidate in the S = 3/2 Dimer Lattice

    NASA Astrophysics Data System (ADS)

    Terasaki, Ichiro; Igarashi, Taichi; Nagai, Takayuki; Tanabe, Kenji; Taniguchi, Hiroki; Matsushita, Taku; Wada, Nobuo; Takata, Atsushi; Kida, Takanori; Hagiwara, Masayuki; Kobayashi, Kensuke; Sagayama, Hajime; Kumai, Reiji; Nakao, Hironori; Murakami, Youichi

    2017-03-01

    We have discovered a novel candidate for a spin liquid state in a ruthenium oxide composed of dimers of S = 3/2 spins of Ru5+, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000-times lower than the magnetic interaction scale of around 200 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a spin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance of inter- and intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.

  14. Paleontological, mineralogical and chemical studies of syngenetic and epigenetic Pb-Zn-Ba-P mineralizations at the stratotype of the K/P boundary (El Kef area, Tunisia)

    NASA Astrophysics Data System (ADS)

    Dill, H. G.; Weiss, W.; Botz, R.; Dohrmann, R.

    2011-06-01

    The El Kef area, Tunisia, is host of the official stratotype of the K/P boundary and of a complex metallic and non-metallic mineralization at Djebel Sekarna, encompassing syn(dia)genetic shale- and carbonate-hosted Zn-P and epigenetic Pb-Zn-Ba ore mineralizations. Micropaleontological, geological, mineralogical, and chemical studies (major and minor elements, C- and O-isotopes) of Upper Santonian to Lower Eocene calcareous-siliciclastic sediments resulted in a subdivision of this mineralization into eight mineralizing stages. Stages 1 and 2 (late Cretaceous-early Paleogene) are representative of syn(diagenetic) shale- and carbonate-hosted sulfidic and siliceous (Fe)-Zn-P mineralization deposited in shallow marine to slightly brackish sediments. Stages 3-5 (early Eocene respectively—pre- and post- Nummulites involutus-exilis zones) are representatives of epigenetic sulfidic and sulfatic (Fe)-Zn-Pb-Ba mineralizations at temperatures as high as 170/200°C and stages 6 and 7 (early Eocene respectively—post- Alveolina oblonga zone) cover the non-sulfidic Zn-(Pb) mineralization at temperatures as high as 60°C which is transitional from hypogene into supergene mineralization ("epithermal calamine deposits"). Stage 8 represents alteration of the pre-existing mineral assemblages in course of the Holocene weathering. The Cretaceous through Paleogene aquatic system is characterized by a poisoning of the sea with base metals, mainly Zn, and the atmosphere was chocked with clouds of fine-grained volcanic ejecta. Both processes contributed to the build-up of Zn-(Pb) deposits and vast, but uneconomic bentonitic clay deposits around the K/P boundary. Ore mineralization in the El Kef area is a multiple-phase process which reached its climax during the early Eocene as indicated by the large foram zones. These inorganic concentration processes resulting in the formation of mineral deposits had obviously also a negative effect on the long-term course of regional Earth

  15. Novel and easy access to highly luminescent Eu and Tb doped ultra-small CaF2, SrF2 and BaF2 nanoparticles - structure and luminescence.

    PubMed

    Ritter, Benjamin; Haida, Philipp; Fink, Friedrich; Krahl, Thoralf; Gawlitza, Kornelia; Rurack, Knut; Scholz, Gudrun; Kemnitz, Erhard

    2017-02-28

    A universal fast and easy access at room temperature to transparent sols of nanoscopic Eu(3+) and Tb(3+) doped CaF2, SrF2 and BaF2 particles via the fluorolytic sol-gel synthesis route is presented. Monodisperse quasi-spherical nanoparticles with sizes of 3-20 nm are obtained with up to 40% rare earth doping showing red or green luminescence. In the beginning luminescence quenching effects are only observed for the highest content, which demonstrates the unique and outstanding properties of these materials. From CaF2:Eu10 via SrF2:Eu10 to BaF2:Eu10 a steady increase of the luminescence intensity and lifetime occurs by a factor of ≈2; the photoluminescence quantum yield increases by 29 to 35% due to the lower phonon energy of the matrix. The fast formation process of the particles within fractions of seconds is clearly visualized by exploiting appropriate luminescence processes during the synthesis. Multiply doped particles are also available by this method. Fine tuning of the luminescence properties is achieved by variation of the Ca-to-Sr ratio. Co-doping with Ce(3+) and Tb(3+) results in a huge increase (>50 times) of the green luminescence intensity due to energy transfer Ce(3+) → Tb(3+). In this case, the luminescence intensity is higher for CaF2 than for SrF2, due to a lower spatial distance of the rare earth ions.

  16. Dielectric properties of BaMg1/3Nb2/3O3 doped Ba0.45Sr0.55Tio3 thin films for tunable microwave applications

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Pokhodnya, Konstantin

    2015-11-01

    Ba(Mg1/3Nb2/3)O3 (BMN) doped and undoped Ba0.45Sr0.55TiO3 (BST) thin films were deposited via radio frequency magnetron sputtering on Pt/TiO2/SiO2/Al2O3 substrates. The surface morphology and chemical state analyses of the films have shown that the BMN doped BST film has a smoother surface with reduced oxygen vacancy, resulting in an improved insulating properties of the BST film. Dielectric tunability, loss, and leakage current (LC) of the undoped and BMN doped BST thin films were studied. The BMN dopant has remarkably reduced the dielectric loss (˜38%) with no significant effect on the tunability of the BST film, leading to an increase in figure of merit (FOM). This is attributed to the opposing behavior of large Mg2+ whose detrimental effect on tunability is partially compensated by small Nb5+ as the two substitute Ti4+ in the BST. The coupling between MgTi″ and VO•• charged defects suppresses the dielectric loss in the film by cutting electrons from hopping between Ti ions. The LC of the films was investigated in the temperature range of 300-450K. A reduced LC measured for the BMN doped BST film was correlated to the formation of defect dipoles from MgTi″, VO•• and NbTi• charged defects. The carrier transport properties of the films were analyzed in light of Schottky thermionic emission (SE) and Poole-Frenkel (PF) emission mechanisms. The result indicated that while the carrier transport mechanism in the undoped film is interface limited (SE), the conduction in the BMN doped film was dominated by bulk processes (PF). The change of the conduction mechanism from SE to PF as a result of BMN doping is attributed to the presence of uncoupled NbTi• sitting as a positive trap center at the shallow donor level of the BST.

  17. Crystal structure, characterization and thermoelectric properties of the type-I clathrate Ba{sub 8-y}Sr{sub y}Al{sub 14}Si{sub 32} (0.6{<=}y{<=}1.3) prepared by aluminum flux

    SciTech Connect

    Roudebush, John H.; Toberer, Eric S.; Hope, Hakon; Jeffrey Snyder, G.; Kauzlarich, Susan M.

    2011-05-15

    The title compound was prepared as single crystals using an aluminum flux technique. Single crystal and powder X-ray diffraction indicate that this composition crystallizes in the clathrate type-I structure, space group Pm3-bar n. Electron microprobe characterization indicates the composition to be Ba{sub 8-y}Sr{sub y}Al{sub 14.2(2)}Si{sub 31.8(2)} (0.77Ba. The Sr atom preferentially occupies the 2a position; mixed Al/Si occupancy was found on all framework sites. These refinements are consistent with a fully occupied framework and nearly fully occupied cation guest sites as found by microprobe analysis. Temperature dependent electrical resistivity and thermal conductivity have been measured from room temperature to 1200 K on a hot-pressed pellet. Electrical resistivity reveals metallic behavior. The negative Seebeck coefficient indicates transport processes dominated by electrons as carriers. Thermal conductivity is between 22 and 25 mW/cm K. The sample shows n-type conductivity with a maximum figure of merit, zT of 0.3 at 1200 K. A single parabolic band model predicts a five-fold increase in zT at 800 K if carrier concentration is lowered. -- Graphical abstract: The inorganic type-I clathrate phase with nominal composition Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} has been prepared by Al flux. Single crystal diffraction at 90 and 12 K reveal that the framework is fully occupied with the cation sites nearly fully occupied. The lattice thermal conductivity is low thereby suggesting further optimization of the carrier concentration will lead to a high zT. Display Omitted Highlights: {yields} Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} is a light element phase ideal for thermoelectric power generation. {yields} Ba{sub 7}Sr{sub 1}Al{sub 14}Si{sub 32} is a high melting point cubic

  18. Ultraviolet C upconversion fluorescence of trivalent erbium in BaGd2ZnO5 phosphor excited by a visible commercial light-emitting diode.

    PubMed

    Yang, Yanmin; Mi, Chao; Su, Xianyuan; Jiao, Fuyun; Liu, Linlin; Zhang, Jiao; Yu, Fang; Li, Xiaodong; Liu, Yanzhou; Mai, Yaohua

    2014-04-01

    Multiple ultraviolet (UV) emission bands have been obtained in Er3+ doped BaGd2ZnO5 phosphor under the excitation of a 532 nm solid-state laser, and the emission peaks at 217, 254, 278, 296, 314, 348, 374 and 394 nm were determined to stem from the high-energy states 4D(1/2), 4D(7/2), 2H(9/2), 2P(1/2), 2P(3/2), 4G(7/2), 4G(11/2), 4H(9/2) of trivalent erbium, respectively. Some UV emission bands in the UVC region can be observed when the sample was excited by commercial green (529 nm) and blue (460 nm) LED. In view of the small size, low-drive voltage and price of LED, UVC upconversion phosphor BaGd2ZnO5:Er3+ excited by visible LED has potential application in environmental sciences.

  19. Effect of doping on the surface modification of nebulizer sprayed Ba x Zn1‑x O nanocrystalline thin films

    NASA Astrophysics Data System (ADS)

    Gopala Krishnan, V.; Elango, P.; Ragavendar, M.; Sathish, P.; Gowrisankar, G.

    2017-03-01

    The influence of Ba doped zinc oxide films were investigated by nebulizer spray pyrolysis technique at 673 K. X-ray diffraction reveals the polycrystalline hexagonal (wurtzite) crystal structure with (0 0 2) preferential orientation. Energy dispersive spectroscopy confirms the presence of Ba, Zn and O elements in the films. Field emission scanning electron microscopy shows that the surface morphology of the nanocrystalline films were changed from spherical shape structure to flake net-like shape and sprout like spherical structure with average grain size is ~100 nm due to the critical doping concentration. PL spectra prominent peaks corresponding to near band edge UV emission and intrinsic defect of the visible blue light region and defect related deep level green emission regions were discussed. The films are highly transparent in the visible region with a transmittance higher than 74%, and have an optical band gap energy values are increased from 3.22 eV to 4.02 eV depending on the Ba doping concentration. Interparticle like grains, grain boundary effect of deposited films is studied by complex impedance spectroscopy.

  20. Synthesis, Structure and Properties of Tetragonal Sr2M3As2O2 (M3 = Mn3, Mn2Cu and MnZn2) Compounds Containing Alternating CuO2-Type and FeAs-Type Layers

    SciTech Connect

    Nath, R; Garlea, Vasile O; Goldman, Alan; Johnston, david C

    2010-01-01

    Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were synthesized. Their temperature- and applied magnetic field-dependent structural, transport, thermal, and magnetic properties were characterized by means of x-ray and neutron diffraction, electrical resistivity , heat capacity, magnetization and magnetic susceptibility measurements. These compounds have a body-centered-tetragonal crystal structure (space group I 4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the CuO2 layers in high superconducting transition temperature Tc cuprate superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the FeAs layers in high-Tc pnictides. These two types of layers alternate along the crystallographic c-axis and are separated by Sr atoms. The site occupancies of Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron powder diffraction data. The temperature dependences of suggest metallic character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each layer are ferromagnetically aligned, but are antiferromagnetically aligned between layers.

  1. Origin of attendant phenomena of bipolar resistive switching and negative differential resistance in SrTiO{sub 3}:Nb/ZnO heterojunctions

    SciTech Connect

    Jia, C. H.; Sun, X. W.; Li, G. Q.; Zhang, W. F. E-mail: wfzhang6@163.com; Chen, Y. H.

    2014-01-27

    Epitaxial ZnO thin films were grown on SrTiO{sub 3}:Nb (NSTO) substrates by pulsed laser deposition. The NSTO/ZnO heterojunctions exhibit a typical rectification characteristic under a small voltage, while two attendant behaviors of bipolar resistive switching and negative differential resistance appear under a large voltage. The NSTO/ZnO heterojunctions show extremely weak resistance switching hysteresis without applying a forward bias. However, when the forward bias increases to some extent, the hysteresis becomes more and more prominent and negative differential resistance gradually appears. Furthermore, the high resistance state is obtained when sweeping from negative to positive voltage bias, and vice versa. We propose a model for these behaviors at NSTO/ZnO interface, in which the space charge region in ZnO is wide in high resistance state when the interface state is unoccupied, while the space charge region becomes narrower in low resistance state due to Fermi pinning when the interface state is completely occupied, and the low resistance state is remained until electrons are detrapped from the interface state.

  2. Effects of La3+-Zn2+ doping on the structure, magnetic, electrical, and dielectric properties of low temperature sintered Sr-hexaferrites

    NASA Astrophysics Data System (ADS)

    Peng, Long; Li, Lezhong; Zhong, Xiaoxi; Hu, Yuebin; Chen, Sanming

    2017-04-01

    The Sr1-xLaxFe12-xZnxO19 (x=0-0.3) hexaferrites with Bi2O3 additive were prepared by microwave sintering method at low sintering temperatures, and their crystal structure, microstructure, magnetic, electrical, and dielectric properties were studied. The results show that the pure M-type phase is obtained for the ferrites with x≤0.2. With x further increasing to 0.3, the multiphase structure is inevitably formed, where the LaFeO3 phase coexists with the M-type phase. In the single phase region, the varied magnetic, electrical, and dielectric properties with La3+-Zn2+ doping amount are well explained by the occupancy effects of La3+ and Zn2+ in magnetoplumbite structure. It is suggested that the Zn2+ ions replace the Fe3+ ions at 4f1 site with x≤0.15, but the substitution of Zn2+ for Fe3+ occurs at 2b site preferentially when the La3+-Zn2+ doping amount exceeds 0.15.

  3. Transmission Electron Microscopy and Atomic Force Microscopy Observation of Air-Processed GdBa2Cu3O7-δ Superconductors Doped with Metal Oxide Nanoparticles (Metal = Zr, Zn, and Sn)

    NASA Astrophysics Data System (ADS)

    Xu, Caixuan; Hu, Anming; Ichihara, Masaki; Izumi, Mitsuru; Xu, Yan; Sakai, Naomichi; Hirabayashi, Izumi

    2009-02-01

    Single-domain, c-axis-oriented 30-mm-diameter GdBa2Cu3O7-δ (Gd123) melt-textured bulk superconductors have been successfully grown by the top-seeded melt growth method from precursors of Gd123, Gd2BaCuO5, and Ag2O in air with doping of nanosized ZrO2, ZnO, or SnO2. Transmission electron microscopy (TEM) unveils a large amount of BaZrO3 or BaSnO3 particles with an average diameter of approximately 50 nm respectively embedded in ZrO2 or SnO2 doped samples, while no Zn-rich nanoparticles are observed in the ZnO-doped samples. The critical temperature Tc is almost unchanged up to a doping amount of 10 mol % for ZrO2- or SnO2-doped Gd123 melt-textured bulks, while ZnO-doped Gd123 becomes non-superconductive at this doping level. By atomic force microscopy (AFM), nanostripes with a wavelength of 15 nm are observed in the ZnO-doped Gd123 sample. Nanoscale particles in the grown Gd123 single domain, together with the micro-defects induced by nanoparticle doping, can account for the enhanced superconducting properties.

  4. Temperature-composition phase diagrams for Ba1-xSrxFe2As2 (0 ≤x≤ 1) and superconducting Ba0.5Sr0.5(Fe1-yCoy)2As2 (0 ≤y≤ 0.141)

    NASA Astrophysics Data System (ADS)

    Mitchell, Jonathan E.; Saparov, Bayrammurad; Lin, Wenzhi; Calder, Stuart; Li, Qing; Kalinin, Sergei V.; Pan, Minghu; Christianson, Andrew D.; Sefat, Athena S.

    2012-11-01

    Single crystals of mixed alkaline earth metal iron arsenide materials, Ba1-xSrxFe2As2 with 0.185 ≤ x ≤ 0.762 and Ba0.5Sr0.5(Fe1-yCoy)2As2 with 0.028 ≤ y ≤ 0.141, are synthesized via the self-flux method. Ba1-xSrxFe2As2 display spin-density wave features (TN) at temperatures intermediate to the parent materials, x = 0 and 1, with TN(x) following an approximately linear trend. Cobalt doping of the 1:1 Ba:Sr mixture, Ba0.5Sr0.5(Fe1-yCoy)2As2, results in a superconducting dome with maximum transition temperature of TC = 19 K at y = 0.092, close to the maximum transition temperatures observed in unmixed A(Fe1-yCoy)2As2; however, an annealed crystal with y = 0.141 showed a TC increase from 11 to 16 K with a decrease in Sommerfeld coefficient γ from 2.58(2) to 0.63(2) mJ/(K2 mol atom). For the underdoped y = 0.053, neutron diffraction results give evidence that TN and structural transition (TO) are linked at 78 K, with anomalies observed in magnetization, resistivity, and heat capacity data, while a superconducting transition at TC ≈ 6 K is seen in resistivity and heat capacity data. Scanning tunneling microscopy measurements for y = 0.073 give Dynes broadening factor Γ = 1.15 and a superconducting gap Δ = 2.37 meV with evidence of surface inhomogeneity.

  5. Preparation and optical properties of TeO2-BaO-ZnO-ZnF2 fluoro-tellurite glass for mid-infrared fiber Raman laser applications

    NASA Astrophysics Data System (ADS)

    Li, Jie; Xiao, Xusheng; Gu, Shaoxuan; Xu, Yantao; Zhou, Zhiguang; Guo, Haitao

    2017-04-01

    A serial of novel fluoro-tellurite glasses with compositions of 60TeO2-20BaO-(20-x)ZnO-xZnF2 (x = 0, 2, 4, 5 and 6 mol%) were prepared. The compositional dependences of glass structural evaluation, Raman gain coefficient, UV-Vis transmission spectrum, IR transmission spectrum, linear refractive index and third-order nonlinearity were analyzed. The results showed that the addition of 6 mol% ZnF2 can further improve the Raman gain coefficient to as well as 52 × 10-11 cm/W and effectively decrease around 73% and 57% absorption coefficients respectively caused by free Osbnd H groups (@3.3 μm) and hydrogen-bonded Osbnd H groups (@4.5 μm) in glass. Addition of ZnF2 does not change the UV-Vis absorption edge, optical band gap energy and infrared region cut-off edge almost, while the linear refraction index and ultrafast third-nonlinearity show unmonotonic changes. These novel fluoro-tellurite glasses may be suitable candidates for using in mid-infrared Raman fiber laser and/or amplifier.

  6. Sintering of BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) with/without SrTiO3 Dopant

    NASA Technical Reports Server (NTRS)

    Dynys, F.; Sayir, A.; Heimann, P. J.

    2004-01-01

    The perovskite composition, BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta), displays excellent protonic conduction at high temperatures making it a desirable candidate for hydrogen separation membranes. This paper reports on the sintering behavior of BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) powders doped with SrTiO3. Two methods were used to synthesize BaCe(sub 0.85)Y(sub 0.15)O(sub 3-delta) powders: (1) solid state reaction and (2) wet chemical co-precipitation. Co-precipitated powder crystallized into the perovskite phase at 1000 C for 4 hrs. Complete reaction and crystallization of the perovskite phase by solid state was achieved by calcining at 1200 C for 24 hrs. Solid state synthesis produced a coarser powder with an average particle size of 1.3 microns and surface area of 0.74 sq m/g. Co-precipitation produced a finer powder with a average particle size of 65 nm and surface area of 14.9 sq m/g. Powders were doped with 1, 2, 5, and 10 mole % SrTiO3. Samples were sintered at 1450 C, 1550 C and 1650 C. SrTiO3 enhances sintering, optimal dopant level is different for powders synthesized by solid state and co-precipitation. Both powders exhibit similar grain growth behavior. Dopant levels of 5 and 10 mole % SrTiO3 significantly enhances the grain size.

  7. Large dielectric tuning and microwave phase shift at low electric field in epitaxial Ba0.5Sr0.5TiO3 on SrTiO3

    NASA Astrophysics Data System (ADS)

    Leach, J. H.; Liu, H.; Avrutin, V.; Xiao, B.; Özgür, Ü.; Morkoç, H.; Das, J.; Song, Y. Y.; Patton, C. E.

    2010-04-01

    Dielectric properties of annealed and as-grown ferroelectric Ba0.5Sr0.5TiO3 (BST) grown by pulsed laser deposition on sputtered BST seed layers on strontium titanate (STO) substrates were investigated at microwave frequencies in the realm of tunability of its dielectric constant as well as phase shifters based on this material. The as-grown layers were nearly fully relaxed with measured lattice parameters nearly identical to those of bulk BST. The tuning of the relative dielectric constant (˜1750 at zero bias at 10 GHz) of the annealed BST was found to be as high as 59% and 56% at 10 and 19 GHz, respectively. The analysis of the loss in the BST results in a measured tan δ of 0.02 for the annealed as well as the unannealed films at a frequency of 18 GHz. Phase shifters also exhibited high tuning with differential phase shift figures of merit of 35 and 55°/dB at a field of 60 kV/cm at 10 and 19 GHz, respectively. Serendipitously, most of the tuning occurs at low fields, and thus we propose a new figure of merit, taking into account the amplitude of applied electric field in order to achieve the phase shift. In this new realm we achieved the values of this overall figure of merit of 1.2 and 1.8° cm/dB kV at 10 and 19 GHz, respectively, using an applied electric field of only 10 kV/cm.

  8. Preparation Process and Dielectric Properties of Ba(0.5)Sr(0.5)TiO3-P(VDF-CTFE) Nanocomposites

    NASA Technical Reports Server (NTRS)

    Zhang, Lin; Wu, Peixuang; Li, Yongtang; Cheng, Z. -Y.; Brewer, Jeffrey C.

    2014-01-01

    Ceramic-polymer 0-3 nanocomposites, in which nanosized Ba(0.5)Sr(0.5)TiO3 (BST) powders were used as ceramic filler and P(VDF-CTFE) 88/12 mol% [poly(vinylidene fluoridechlorotrifluoroethylene)] copolymer was used as matrix, were studied over a concentration range from 0 to 50 vol.% of BST powders. It is found that the solution cast composites are porous and a hot-press process can eliminate the porosity, which results in a dense composite film. Two different configurations used in the hot-press process are studied. Although there is no clear difference in the uniformity and microstructure of the composites prepared using these two configurations, the composite prepared using one configuration exhibit a higher dielectric constant with a lower loss. For the composite with 40 vol. BST, a dielectric constant of 70 with a loss of 0.07 at 1 kHz is obtained at room temperature. The composites exhibit a lower dielectric loss than the polymer matrix at high frequency. However, at low frequency, the composites exhibit a higher loss than the polymer matrix due to a low frequency relaxation process that appears in the composites. It is believed that this relaxation process is related to the interfacial layer formed between BST particle and the polymer matrix. The temperature dependence of the dielectric property of the composites was studied. It is found that the dielectric constant of these composites is almost independent of the temperature over a temperature range from 20 to 120 C. Key words: A. Polymer-matrix composites (PMCs); B. Electrical Properties; E. Casting; E. Heat treatment; Dielectric properties.

  9. Formation of solar cells based on Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) ferroelectric thick film

    SciTech Connect

    Irzaman, Syafutra, H. Arif, A. Alatas, H.; Hilaluddin, M. N.; Kurniawan, A.; Iskandar, J.; Dahrul, M.; Ismangil, A.; Yosman, D.; Aminullah; Prasetyo, L. B.; Yusuf, A.; Kadri, T. M.

    2014-02-24

    Growth of Ba{sub 0.5}Sr{sub 0.5}TiO{sub 3} (BST) 1 M thick films are conducted with variation of annealing hold time of 8 hours, 15 hours, 22 hours, and 29 hours at a constant temperature of 850 °C on p-type Si (100) substrate using sol-gel method then followed by spin coating process at 3000 rpm for 30 seconds. The BST thick film electrical conductivity is obtained to be 10{sup −5} to 10{sup −4} S/cm indicate that the BST thick film is classified as semiconductor material. The semiconductor energy band gap value of BST thick film based on annealing hold time of 8 hours, 15 hours, 22 hours, and 29 hours are 2.58 eV, 3.15 eV, 3.2 eV and 2.62 eV, respectively. The I-V photovoltaic characterization shows that the BST thick film is potentially solar cell device, and in accordance to annealing hold time of 8 hours, 15 hours, 22 hours and 29 hours have respective solar cell energy conversion efficiencies of 0.343%, 0.399%, 0.469% and 0.374%, respectively. Optical spectroscopy shows that BST thick film solar cells with annealing hold time of 8 hours, 15 hours, and 22 hours absorb effectively light energy at wavelength of ≥ 700 nm. BST film samples with annealing hold time of 29 hours absorb effectively light energy at wavelength of ≤ 700 nm. The BST thick film refraction index is between 1.1 to 1.8 at light wavelength between ±370 to 870 nm.

  10. Optical and scintillation properties of Ce:(Gd8AE2)(SiO4)6O2 (AE = Mg, Ca, Sr and Ba) crystals

    NASA Astrophysics Data System (ADS)

    Igashira, Takuya; Mori, Masaki; Okada, Go; Kawaguchi, Noriaki; Yanagida, Takayuki

    2017-02-01

    1% Ce-doped and non-doped (Gd8AE2)(SiO4)6O2 (AE = Mg, Ca, Sr and Ba) (denoted as GMS, GCS, GSrS and GBS, respectively) single crystals were grown by the Floating Zone (FZ) method to evaluate their optical and scintillation properties. The Ce:GCS and Ce:GSrS samples exhibited scintillation and photoluminescence (PL) around 400 nm due to the 5d-4f transitions of Ce3+. On the other hand, Ce:GMS and Ce:GBS showed much weaker emissions in the wavelength range of 500-650 nm, in which the origin was associated with the host matrices. The PL decay curves were approximated by a double exponential decay function for all the Ce-doped samples. The decay times ranged around 10-30 and 40-90 ns, and faster components coincided with those of the non-doped samples. The scintillation decay curves of Ce-doped samples, on the other hand, were approximated by single exponential functions with slower decay constants than those of PL decay. These constants were very similar to those of non-doped samples. In the X-ray induced afterglow measurements, Ce:GCS exhibited the lowest afterglow level. The pulse height spectrum of these samples showed a full-energy peak under 241Am 5.5 MeV α-ray irradiation. Among these samples, Ce:GSrS exhibited the highest light yield which was around 600 ph/5.5 MeV-α.

  11. Single Variable and Multivariate Analysis of Remote Laser-Induced Breakdown Spectra for Prediction of Rb, Sr, Cr, Ba, and V in Igneous Rocks

    SciTech Connect

    Clegg, Samuel M; Wiens, Roger C.; Speicher, Elly A; Dyar, Melinda D; Carmosino, Marco L

    2010-12-23

    Laser-induced breakdown spectroscopy (LIBS) will be employed by the ChemCam instrument on the Mars Science Laboratory rover Curiosity to obtain UV, VIS, and VNIR atomic emission spectra of surface rocks and soils. LIBS quantitative analysis is complicated by chemical matrix effects related to abundances of neutral and ionized species in the resultant plasma, collisional interactions within plasma, laser-to-sample coupling efficiency, and self-absorption. Atmospheric composition and pressure also influence the intensity of LIBS plasma. These chemical matrix effects influence the ratio of intensity or area of a given emission line to the abundance of the element producing that line. To compensate for these complications, multivariate techniques, specifically partial least-squares regression (PLS), have been utilized to predict major element compositions (>1 wt.% oxide) of rocks, PLS methods regress one or multiple response variables (elemental concentrations) against multiple explanatory variables (intensity at each pixel of the spectrometers). Because PLS utilizes all available explanatory variable and eliminates multicollinearity, it generally performs better than univariate methods for prediction of major elements. However, peaks arising from emissions from trace elements may be masked by peaks of higher intensities from major elements. Thus in PLS regression, wherein a correlation coefficient is determined for each elemental concentration at each spectrometer pixel, trace elements may show high correlation with more intense lines resulting from optical emissions of other elements. This could result in error in predictions of trace element concentrations. Here, results of simple linear regression (SLR) and multivariate PLS-2 regression for determination of trace Rb, Sr, Cr, Ba, and V in igneous rock samples are compared. This study focuses on comparisons using only line intensities rather than peak areas to highlight differences between SLR and PLS.

  12. Unimolecular and hydrolysis channels for the detachment of water from microsolvated alkaline earth dication (Mg2+, Ca2+, Sr2+, Ba2+) clusters

    SciTech Connect

    Miliordos, Evangelos; Xantheas, Sotiris S.

    2014-02-07

    We examine theoretically the three channels that are associated with the detachment of a single water molecule from the aqueous clusters of the alkaline earth dications, [M(H2O)n]2+, M = Mg, Ca, Sr, Ba, n ≤ 6. These are the unimolecular water loss (M2+(H2O)n-1 + H2O) and the two hydrolysis channels resulting to the loss of hydronium ([MOH(H2O)n-2]+ + H3O+) and Zundel ([MOH(H2O)n-3]+ + H3O+(H2O)) cations. The Potential Energy Curves (PECs) corresponding to those three channels were constructed at the Møller-Plesset second order perturbation (MP2) level of theory with basis sets of double- and triple-ζ quality. We furthermore investigated the water and hydronium loss channels from the mono-hydroxide water clusters with up to four water molecules, [MOH(H2O)n]+, 1 ≤ n ≤ 4. Our results indicate the preference of the hydronium loss and possibly the Zundel cation loss channels for the smallest size clusters, whereas the unimolecular water loss channel is preferred for the larger ones as well as the mono-hydroxide clusters. Although the charge separation (hydronium and Zundel cation loss) channels produce more stable products when compared to the ones for the unimolecular water loss, they also require the surmounting of high energy barriers, a fact that makes the experimental observation of fragments related to these hydrolysis channels difficult.

  13. First-Principles Investigation of the Epitaxial Stabilization of Oxide Polymorphs: TiO2 on (Sr,Ba)TiO3.

    PubMed

    Xu, Zhongnan; Salvador, Paul; Kitchin, John R

    2017-02-01

    Metastable polymorphs, many of which have never been fabricated, have been predicted to exhibit interesting and technologically relevant properties. Epitaxial synthesis is a powerful structure-directing method that can produce metastable polymorphs but is typically done in a trial and error fashion. Unfortunately, the relevant thermodynamic terms governing epitaxial synthesis of new materials are unknown. Accurate calculation of the relevant thermodynamic terms and their incorporation into predictive models would accelerate the synthesis of metastable polymorphs by identifying thermodynamically favorable paths. Using density functional theory with three different functionals, we computed several relevant terms for TiO2 anatase (A) and rutile (R) film growth on low-index surfaces of SrTiO3 (STO) and BaTiO3 (BTO) cubic perovskites. After identifying potential coherent epitaxial interfaces based on experimental observations, the volumetric formation, volumetric strain, and areal substrate-film interface energies were calculated for (001)A∥(001)(S/B)TO, (102)A∥(011)(S/B)TO, (100)R∥(111)(S/B)TO, and (112)A∥(111)(S/B)TO coherent interfaces. These terms were integrated into a standard model of epitaxial nucleation, and the results yielded reasonable agreement between experimental observations and DFT predictions of the preferred epitaxial polymorph. Predicted trends in epitaxial stability were essentially independent of the three functionals used in the calculations. These results are discussed in light of their promise that DFT-informed epitaxial film growth can accelerate fabrication of new polymorphs. These results also validate the recently proposed 20 kJ/mol stability window for predicting which polymorphs could be epitaxially stabilized.

  14. Up-conversion luminescence properties and energy transfer of Tm{sup 3+}/Yb{sup 3+} co-doped BaLa{sub 2}ZnO{sub 5}

    SciTech Connect

    Xie, Jing; Mei, Lefu Deng, Junru; Liu, Haikun; Ma, Bin; Guan, Ming; Liao, Libing Lv, Guocheng

    2015-11-15

    Tm{sup 3+}/Yb{sup 3+} co-doped BaLa{sub 2}ZnO{sub 5} up-conversion (UC) phosphors were successfully synthesized by high temperature solid-state reaction method. The X-ray diffraction (XRD) results show that synthesized phosphor co-doped with 0.75% Tm/10% Yb has the optimum pure phase of BaLa{sub 2}ZnO{sub 5} among different co-doping concentrations. The structure of BaLa{sub 2}ZnO{sub 5}:0.75% Tm/10% Yb phosphor was refined by the Rietveld method and results show the decreased unit cell parameters and cell volume after doping Tm{sup 3+}/Yb{sup 3+}, indicating that Tm{sup 3+}/Yb{sup 3+} have successfully replaced La{sup 3+}. Under excitation at 980 nm, Tm{sup 3+}/Yb{sup 3+} co-doped BaLa{sub 2}ZnO{sub 5} phosphors present bright blue emission near 478 nm generated by the {sup 1}G{sub 4}→{sup 3}H{sub 6} transition and weak red emissions around 653 nm and 692 nm generated by the {sup 1}G{sub 4}→{sup 3}F{sub 4} and {sup 3}F{sub 3}→{sup 3}H{sub 6} transitions of Tm{sup 3+}, respectively. The UC luminescence properties of BaLa{sub 2}ZnO{sub 5} phosphors co-doped with different Tm{sup 3+}/Yb{sup 3+} concentrations were investigated, and the related UC mechanisms of Tm{sup 3+}/Yb{sup 3+} co-doped BaLa{sub 2}ZnO{sub 5} depending on pump power were studied in detail. - Graphical abstract: Up-conversion luminescence of BaLa{sub 2}ZnO{sub 5}:Tm{sup 3+}/Yb{sup 3+} and its crystal structure and up-conversion mechanisms. - Highlights: • Up-conversion phosphors BaLa{sub 2}ZnO{sub 5} co-doped with Tm{sup 3+}/Yb{sup 3+} were synthesized by high temperature solid-state reaction method. • The crystal structure of BaLa{sub 2}ZnO{sub 5} and the changes of cell parameters and volume of BaLa{sub 2}ZnO{sub 5} after doping Tm{sup 3+} and Yb{sup 3+} have been discussed. • Up-conversion luminescence properties and energy transfer between Tm{sup 3+} and Yb{sup 3+} in BaLa{sub 2}ZnO{sub 5} have been discussed in detail.

  15. Validity and limitations of the superexchange model for the magnetic properties of Sr2IrO4 and Ba2IrO4 mediated by the strong spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Solovyev, I. V.; Mazurenko, V. V.; Katanin, A. A.

    2015-12-01

    Layered perovskites Sr2IrO4 and Ba2IrO4 are regarded as the key materials for understanding the properties of magnetic relativistic insulators, mediated by the strong spin-orbit (SO) coupling. One of the most fundamental issues is to which extent these properties can be described by the superexchange (SE) model, formulated in the limit of the large Coulomb repulsion for some appropriately selected pseudospin states, and whether these materials themselves can be classified as Mott insulators. In this work, we address these issues by deriving the relevant models and extracting parameters of these models from the electronic-structure calculations with the SO coupling, based on the density functional theory. First, we construct the effective Hubbard-type model for the magnetically active t2 g bands, by recasting the problem in the language of localized Wannier orbitals. Then, we map the obtained electron model onto the pseudospin model by applying the theory of SE interactions, which is based on the second-order perturbation theory with respect to the transfer integrals. We discuss the microscopic origin of anisotropic SE interactions, inherent to the compass Heisenberg model, and the appearance of the antisymmetric Dzyaloshinskii-Moriya term, associated with the additional rotation of the IrO6 octahedra in Sr2IrO4 . In order to solve the pseudospin Hamiltonian problem and evaluate the Néel temperature (TN), we employ the nonlinear sigma model. We have found that, while for Sr2IrO4 our value of TN agrees with the experimental data, for Ba2IrO4 it is overestimated by a factor of 2. We argue that this discrepancy is related to limitations of the SE model: while for more localized t2 g states in Sr2IrO4 it works reasonably well, the higher-order terms in the perturbation theory expansion play a more important role in the more "itinerant" Ba2IrO4 , giving rise to the new type of isotropic and anisotropic exchange interactions, which are not captured by the SE model. This

  16. Synthesis, persistent luminescence, and thermoluminescence properties of yellow Sr3SiO5:Eu2+,RE3+ (RE=Ce, Nd, Dy, Ho, Er, Tm, Yb) and orange-red Sr(3-x)Ba(x)SiO5:Eu2+, Dy3+ phosphor.

    PubMed

    Li, Ye; Li, Baohong; Ni, Chenchen; Yuan, Shuxia; Wang, Jing; Tang, Qiang; Su, Qiang

    2014-02-01

    Sunlight-excitable orange or red persistent oxide phosphors with excellent performance are still in great need. Herein, an intense orange-red Sr3-xBaxSiO5:Eu(2+),Dy(3+) persistent luminescence phosphor was successfully developed by a two-step design strategy. The XRD patterns, photoluminescence excitation and emission spectra, and the thermoluminescence spectra were investigated in detail. By adding non-equivalent trivalent rare earth co-dopants to introduce foreign trapping centers, the persistent luminescence performance of Eu(2+) in Sr3SiO5 was significantly modified. The yellow persistent emission intensity of Eu(2+) was greatly enhanced by a factor of 4.5 in Sr3SiO5:Eu(2+),Nd(3+) compared with the previously reported Sr3SiO5:Eu(2+), Dy(3+). Furthermore, Sr ions were replaced with equivalent Ba to give Sr3-xBaxSiO5 :Eu(2+),Dy(3+) phosphor, which shows yellow-to-orange-red tunable persistent emissions from λ=570 to 591 nm as x is increased from 0 to 0.6. Additionally, the persistent emission intensity of Eu(2+) is significantly improved by a factor of 2.7 in Sr3-xBaxSiO5 :Eu(2+),Dy(3+) (x=0.2) compared with Sr3SiO5 :Eu(2+),Dy(3+). A possible mechanism for enhanced and tunable persistent luminescence behavior of Eu(2+) in Sr3-xBaxSiO5:Eu(2+),RE(3+) (RE=rare earth) is also proposed and discussed.

  17. Material properties and structural characterization of M3Si6O12N2:Eu2+ (M = Ba, Sr)--a comprehensive study on a promising green phosphor for pc-LEDs.

    PubMed

    Braun, Cordula; Seibald, Markus; Börger, Saskia L; Oeckler, Oliver; Boyko, Teak D; Moewes, Alexander; Miehe, Gerhard; Tücks, Andreas; Schnick, Wolfgang

    2010-08-16

    The efficient green phosphor Ba(3)Si(6)O(12)N(2):Eu(2+) and its solid-solution series Ba(3-x)Sr(x)Si(6)O(12)N(2) (with x approximately = 0.4 and 1) were synthesized in a radio-frequency furnace under nitrogen atmosphere at temperatures up to 1425 degrees C. The crystal structure (Ba(3)Si(6)O(12)N(2), space group P3 (no. 147), a = 7.5218(1), c = 6.4684(1) A, wR2 = 0.048, Z = 1) has been solved and refined on the basis of both single-crystal and powder X-ray diffraction data. Ba(3)Si(6)O(12)N(2):Eu(2+) is a layer-like oxonitridosilicate and consists of vertex-sharing SiO(3)N-tetrahedra forming 6er- and 4er-rings as fundamental building units (FBU). The nitrogen atoms are connected to three silicon atoms (N3), while the oxygen atoms are either terminally bound (O1) or bridge two silicon atoms (O2) (numbers in superscripted square brackets after atoms indicate the coordination number of the atom in question). Two crystallographically independent Ba(2+) sites are situated between the silicate layers. Luminescence investigations have shown that Ba(3)Si(6)O(12)N(2):Eu(2+) exhibits excellent luminescence properties (emission maximum at approximately 527 nm, full width at half maximum (FWHM) of approximately 65 nm, low thermal quenching), which provides potential for industrial application in phosphor-converted light-emitting diodes (pc-LEDs). In-situ high-pressure and high-temperature investigations with synchrotron X-ray diffraction indicate decomposition of Ba(3)Si(6)O(12)N(2) under these conditions. The band gap of Ba(3)Si(6)O(12)N(2):Eu(2+) was measured to be 7.05+/-0.25 eV by means of X-ray emission spectroscopy (XES) and X-ray absorption near edge spectroscopy (XANES). This agrees well with calculated band gap of 6.93 eV using the mBJ-GGA potential. Bonding to the Ba atoms is highly ionic with only the 4p(3/2) orbitals participating in covalent bonds. The valence band consists primarily of N and O p states and the conduction band contains primarily Ba d and f states

  18. How does the spin-state of Co ions affect the insulator-metal transition in Bi2A2Co2O8 (A = Ca, Sr, Ba)?

    PubMed

    Huang, Xiaokun; Zhang, Weiyi

    2016-11-30

    The misfit layered Bi2A2Co2O8 (A = Ca, Sr, Ba) compounds experience an insulator to metal transition as A's ionic radius increases. This feature is contradictory to the conventional wisdom that larger lattice constant favors insulating rather than metallic state, and is also difficult to be reconciled using the Anderson weak localization theory. In this paper, we show from the first-principles calculation that an insulator-metal transition takes place from a nonmagnetic low-spin state of Co(3+) ions to a hexagonally arranged intermediate-spin low-spin mixed-state in CoO2 plane when ionic radius increases from Ca to Ba. The predicted low-spin state of Bi2Ca2Co2O8 and Bi2Sr2Co2O8 and intermediate-spin low-spin mixed-state of Bi2Ba2Co2O8 are consistent not only with their measured transport properties, but also with the magnetic-field suppressed specific-heat peak observed at the transition temperature. In agreement with experiments, strong electronic correlation is required to stabilize the low-spin insulator and intermediate-spin low-spin metal.

  19. How does the spin-state of Co ions affect the insulator-metal transition in Bi2A2Co2O8 (A = Ca, Sr, Ba)?

    PubMed Central

    Huang, Xiaokun; Zhang, Weiyi

    2016-01-01

    The misfit layered Bi2A2Co2O8 (A = Ca, Sr, Ba) compounds experience an insulator to metal transition as A’s ionic radius increases. This feature is contradictory to the conventional wisdom that larger lattice constant favors insulating rather than metallic state, and is also difficult to be reconciled using the Anderson weak localization theory. In this paper, we show from the first-principles calculation that an insulator-metal transition takes place from a nonmagnetic low-spin state of Co3+ ions to a hexagonally arranged intermediate-spin low-spin mixed-state in CoO2 plane when ionic radius increases from Ca to Ba. The predicted low-spin state of Bi2Ca2Co2O8 and Bi2Sr2Co2O8 and intermediate-spin low-spin mixed-state of Bi2Ba2Co2O8 are consistent not only with their measured transport properties, but also with the magnetic-field suppressed specific-heat peak observed at the transition temperature. In agreement with experiments, strong electronic correlation is required to stabilize the low-spin insulator and intermediate-spin low-spin metal. PMID:27901119

  20. How does the spin-state of Co ions affect the insulator-metal transition in Bi2A2Co2O8 (A = Ca, Sr, Ba)?

    NASA Astrophysics Data System (ADS)

    Huang, Xiaokun; Zhang, Weiyi

    2016-11-01

    The misfit layered Bi2A2Co2O8 (A = Ca, Sr, Ba) compounds experience an insulator to metal transition as A’s ionic radius increases. This feature is contradictory to the conventional wisdom that larger lattice constant favors insulating rather than metallic state, and is also difficult to be reconciled using the Anderson weak localization theory. In this paper, we show from the first-principles calculation that an insulator-metal transition takes place from a nonmagnetic low-spin state of Co3+ ions to a hexagonally arranged intermediate-spin low-spin mixed-state in CoO2 plane when ionic radius increases from Ca to Ba. The predicted low-spin state of Bi2Ca2Co2O8 and Bi2Sr2Co2O8 and intermediate-spin low-spin mixed-state of Bi2Ba2Co2O8 are consistent not only with their measured transport properties, but also with the magnetic-field suppressed specific-heat peak observed at the transition temperature. In agreement with experiments, strong electronic correlation is required to stabilize the low-spin insulator and intermediate-spin low-spin metal.