... Abstract : Microstructure of ordered A-site perovskites has been studied by transmission electron microscopy and electron diffraction. ...

... ABSTRACT (Maximum 200wcrs) Microstructure of ordered A-site perovskites has been studied by transmission electron microscopy and electron ...

The brownmillerite-type A 2B 2O 5 structure is considered as a parent one, giving rise to different derivatives: layered double perovskites, A-site and anion-vacancy-ordered perovskites, and the perovskite-like compounds with crystallographic shear planes. The structural relationships and ...

Transitions from chain silicates to garnet, ilmenite, and perovskite structures are important in deep earth geophysics and solid-state chemistry. Titanates and other oxides also show polymorphism among ilmenite, lithium niobate (metastable), and perovskite structures. This review brings together the evidence from the recent mineralogical and materials ...

We introduce an electrostatic model including charge transfer, which is shown to account for the observed B-site ordering in Pb-based perovskite alloys. The model allows charge transfer between A sites and is a generalization of Bellaiche and Vanderbilt's purely electrostatic model. The large covalency of Pb2- compared to Ba2+ results in an environment ...

The A-site-ordered perovskite YMn(3)Al(4)O(12) was prepared by high-pressure synthesis. Structural analysis with synchrotron powder X-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the compound has a chemical composition Y(3+)Mn(3+)(3)Al(3+)(4)O(2-)(12) with magnetic Mn(3+) at the A' ...

The structure of La(1/3)NbO3 is that of a perovskite with La3+ cations ordered into alternate layers of perovskite A-sites. This is the description of a tetragonal structure and yet the room-temperature structure shows an orthorhombic distortion. The structure of La(2/3)TiO3 shows similar features. It has been ...

A-site-ordered perovskites LaMn(3)Cr(4)O(12) and LaMn(3)Ti(4)O(12) were synthesized under high-pressure and high-temperature conditions. The charge formula of LaMn(3)Cr(4)O(12) was found to be LaMn(3+)(3)Cr(3+)(4)O(12) with Mn(3+) at the square-coordinated A site. The valence of the A-site Mn ions in LaMn(3)Ti(4)O(12) appeared to be less than +2, and the ...

... For the perovskite Lead Magnesium Niobate which is the prototype for many other relaxor perovskites, the self limiting nonstoichiometric ordering of ...

... For the perovskite Lead Magnesium Niobate which is the prototype for many other relaxor perovskites, the self limiting nonstoichiometric ordering of ...

We elucidate a mechanism for obtaining polar behavior in magnetic perovskites based on A-site disorder and demonstrate this mechanism by density functional calculations for the double perovskite (La,Lu)MnNiO{sub 6} with Lu concentrations at and below 50%. We show that this material combines polar behavior and ferromagnetism. The mechanism is quite general ...

Unlike ordering of the octahedral B-site cations, ordering of the larger A-site cations in stoichiometric perovskites is rare. Herein the A- and B-site ordering characteristics of several double perovskites with AA'BB'O{sub 6} stoichiometry have been ...

... Descriptors : *FERROELECTRIC CRYSTALS, PHASE STUDIES, TRANSITION TEMPERATURE, PEROVSKITES, HYDROGEN COMPOUNDS ...

The decomposition of the cubic perovskite-type oxide Ba(x)Sr(1-x)Co(0.8)Fe(0.2)O(3-delta) (BSCF) into hexagonal and cubic perovskite-type phases has been examined by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED) and X-Ray Diffraction (XRD). SEM and TEM measurements reveal that ...

A-site-ordered perovskites CaCu3Ge4O12 and CaCu3Sn4O12, both isostructural to antiferromagnetic CaCu3Ti4O12, were found to be ferromagnets, which are very rare in cuprates. All of these materials may be called ``A-site magnets'', since they contain magnetic species only at the A-site of the perovskite ABO3 ...

The crystal structure of new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite was investigated by neutron, X-ray and electron diffraction. Neutron and X-ray powder diffraction spectra were refined in the monoclinic I2/m space group, with the parameters of the unit cell a=5.6304(2)A, b=5.6226(2)A, c=7.9434(2)A and {beta}=90.04(1){sup o}. This structural ...

The crystal structure of new A-site deficient La5/3MgTaO6 perovskite was investigated by neutron, X-ray and electron diffraction. Neutron and X-ray powder diffraction spectra were refined in the monoclinic I2/m space group, with the parameters of the unit cell a=5.6304(2) �, b=5.6226(2) �, c=7.9434(2) � and ?=90.04(1)�. This structural model ...

The pressure effect on synthesis of oxides with perovskite ABO3 and perovskite-related structures has become more clear in recent years. The geometric tolerance factor t ? (A-O)/2(B-O) measures the structural stability. High-pressure synthesis enlarges the range of the t factor where the perovskite structure can be stabilized. For the ...

... films, there are potential mechanisms by which the perovskite structure can incorporate excess B-site ... perovskite (in a complicated ordered pattern). ...

Accurate oxygen-content analysis by means of a coulometric redox titration method specially devised for the purpose shows that as-synthesized (in 5% H2/Ar) samples of the recently reported novel solid oxide fuel cells anode material Sr2MgMoO6?? contain oxygen vacancies with a concentration of ??0.05. Oxygen contents and the resultant Mo-valence values are also analyzed for various A2MgMoO6?? ...

The lithium-rich limit of the electrolyte stability window of the fast-ion-conducting defect perovskite Li{sub 0.29}La{sub 0.57}TiO{sub 3} was found to be about 1.7 V vs. Li at 24 C. The coulometric titration curve was determined, indicating that reversible insertion/extraction of 0.14 additional Li, corresponding to the complete occupation of the vacant ...

Large disorder effects due to size differences between A-site R3+ (R=La,Pr,Nd,Sm) and M2+ (M=Ca,Sr,Ba) cations have been found in magnetoresistive (R0.7M0.3)MnO3 perovskites. The ferromagnetic-metal-paramagnetic-insulator transition temperature Tm varies as Tm=Tm(0)-pQ2 due to strain fields resulting from ordered or disordered oxygen ...

An air electrode composition for a solid oxide fuel cell is disclosed. The air electrode material is based on lanthanum manganite having a perovskite-like crystal structure ABO{sub 3}. The A-site of the air electrode composition comprises a mixed lanthanide in combination with rare earth and alkaline earth dopants. The B-site of the composition comprises Mn in combination with ...

An air electrode composition for a solid oxide fuel cell is disclosed. The air electrode material is based on lanthanum manganite having a perovskite-like crystal structure ABO.sub.3. The A-site of the air electrode composition comprises a mixed lanthanide in combination with rare earth and alkaline earth dopants. The B-site of the composition comprises Mn in combination with ...

A Walker-type multianvil high-pressure facility is capable of high-pressure syntheses and measurements beyond 10 GPa and has been utilized in my research to synthesize the 4d Ruthenium and Rhodium and the 5d Iridium oxides with the perovskite-related structures. Under high-pressure and high-temperature conditions, these families of oxides can be enlarged to a great extent so ...

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite

A modified PbZrTiO.sub.3 perovskite crystal material thin film, wherein the PbZrTiO.sub.3 perovskite

Density functional calculations are used to investigate the trends in the lattice instabilities of the perovskites, BaTiO{sub 3}, PbTiO{sub 3}, BaZrO{sub 3}, and PbZrO{sub 3} with volume. A simple scheme for classifying perovskites in terms of A-site and B-site activities is discussed in relation to competition between rhombohedral and tetragonal ground ...

The authors found dynamic ferromagnetic correlations at the room temperature in perovskite manganites which have an antiferromagnetic insulating ground state. They are replaced by antiferromagnetic correlations when the electrons order. The results indicate that the double exchange mechanism is turned off by electron localization at low temperatures.

Solid-state inorganic chemistry is dominated by high-temperature syntheses. As chemists seek to synthesize new materials with superior properties, subtle structural features become increasingly difficult to control thermodynamically. This thesis presents alternative low-temperature strategies for synthesizing inorganic solids and thin films. Layered perovskite tantalates that ...

... Mechanisms relating the bonding nature and the order disorder in complex perovskite niobates and tantalates that governing the characteristics of ...

Magnetic superexchange interactions in single-valent perovskites (R,A)MO3 (R,A = Rare and Alkaline Earth's, M = transition metal) are known to dependent on the M-O-M bond angle ? and the interatomic distances through the band-width relation W ~ cos?/n (n ~ 3.5). It was observed previously that TN ~ W2 ~ for RMO3 with M = Cr3+ (t3), Fe3+ ...

Changes in the charge/orbital ordering (CO/OO) structure with the bandwidth of the e(g) band and quenched disorder were investigated in doped manganites RE(0.5)(Ca(1-y)Sr(y))(1.5)MnO(4)(RE = Pr,Eu) with a single-layer perovskite structure. A systematic study of the modulation structure associated with the CO/OO phase demonstrated that the long-range ...

We have employed aliovalent A-site cation substitution, La{sup III}-for-Sr{sup II}, to dope the Sr(Fe{sub 0.5}Ta{sub 0.5})O{sub 3} perovskite oxide with electrons. Essentially single-phase samples of (Sr{sub 1-} {sub x} La {sub x} )(Fe{sub 0.5}Ta{sub 0.5})O{sub 3} were successfully synthesized up to x{approx}0.3 in a vacuum furnace at 1400 deg. C. The ...

The Czochralski growth of KTN was continued in order to determine reproducibility. In addition, a new growth technique was tested. Thirteen perovskite compounds were selected from the computer output data for melt studies on the strip heater. Twelve of th...

A low temperature method is described for the preparation of the new garnet compounds YCaLnGa{sub 5}O{sub l2} (Ln=Ce, Pr, Th). In this set of compounds (Ca{sup 2+} + Ln{sup 4+}) replaces 2 Y{sup 3+} in the parent gallium based garnet Y{sub 3}Ga{sub 5}O{sub l2} in order to stabilize as effectively as possible the Ln{sup 4+} species in the eight-coordinate ...

Accurate oxygen-content analysis by means of a coulometric redox titration method specially devised for the purpose shows that as-synthesized (in 5% H{sub 2}/Ar) samples of the recently reported novel solid oxide fuel cells anode material Sr{sub 2}MgMoO{sub 6-{delta}} contain oxygen vacancies with a concentration of {delta}{approx}0.05. Oxygen contents and the resultant Mo-valence values are also ...

We have synthesized and characterized new layered perovskites Ag2[A1.5M3O10] (A = Ca, M = Nb, Ta), from their lithium analogues, by soft-chemical ion exchange. These oxides show topotactic irreversible thermally induced A'-A site exchange, resulting in Ag1.1Ca0.9[Ca0.6Ag0.9M3O10], conferred from our high-temperature X-ray and ionic ...

Post-perovskite MgSiO(3) is believed to be present in the D'' region of the Earth's lowermost mantle. Its existence has been used to explain a number of seismic observations, such as the D'' reflector and the high degree of seismic anisotropy within the D'' layer. Ionic diffusion in post-perovskite controls its viscosity, which in turn controls the thermal ...

Perovskite oxides and heterojunctions have attracted much attention due to their multifunctional properties of electricity and optics and magnetic as well as the very good chemical and thermal stability. In this brief review, we describe the novel progress of researches in the optical characteristic, including ultrafast photoelectric effects of picosecond ...

are eliminated (by recent synthesis of Pb-based relaxor perovskites with long-range B-cation ordering}@sas.upenn.edu and yhshin@postech.ac.kr 1. Introduction Perovskite oxides of formula ABO3 have a wide range of structural, ultrasound machines and communication devices. Perovskite solid solutions with high ...

Large disorder effects due to size differences between {ital A}-site {ital R}{sup 3+} ({ital R}=La,Pr,Nd,Sm) and {ital M}{sup 2+} ({ital M}=Ca,Sr,Ba) cations have been found in magnetoresistive ({ital R}{sub 0.7}{ital M}{sub 0.3})MnO{sub 3} perovskites. The ferromagnetic-metal{endash}paramagnetic-insulator transition temperature {ital T}{sub {ital m}} ...

We report a solution-based fabrication of perovskite multilayers and superlattices using perovskite nanosheets. Perovskite nanosheets (LaNb2O7, Ca2Nb3O10, and Sr2Nb3O10) were prepared by delaminating layered perovskites. A layer-by-layer approach using Langmuir--Blodgett deposition was effective for fabricating ...

A combination of electron, synchrotron X-ray and neutron powder diffraction reveals a new orthorhombic structure type within the Sr-doped rare earth perovskite cobaltates Ln{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (Ln=Y{sup 3+}, Dy{sup 3+}, Ho{sup 3+}, Er{sup 3+}, Tm{sup 3+}and Yb{sup 3+}). Electron diffraction shows a C-centred cell based on a 2{radical}2a{sub p}x4a{sub ...

... of the oxides and carbonates. The compounds are ordered perovskites except for Ba2InSbO6. All compounds are cubic ...

Oxygen-deficient perovskites NdCuO{sub 3-{delta}} (0 {le} {delta} {le} 0.5) were prepared for the first time at high pressures in a multianvil apparatus and characterized by X-ray and electron diffraction and by electron microprobe. Several new oxygen vacancy-order phases could be stabilized depending upon {delta} and synthetic conditions. The crystal ...

The authors results indicate that tolerance factor t determines the possibility of the existence of split-minimum ionic potentials and the type of structural phase transition occurring in perovskites. Data on the entropy of phase transitions in PbZrO{sub 3}, PbHfO{sub 3}, and NaNbO{sub 3} can be accounted for in terms of ion ordering. The largest values of ...

Structural, magnetic, and transport properties of (La1-xNdx)0.8Na0.2MnO3(0<=x<=1) are studied. The system exhibits a rhombohedrally distorted perovskite structure for x<=0.2 and it converts to an orthorhombic structure for x>=0.4. Re-entrant ferromagnetic-type charge ordering transitions are observed in the narrow bandwidth samples (x>=0.8). ...

Sodium iridium (V) oxide, NaIrO3, was synthesized by a high pressure solid state method and recovered to ambient conditions. It is found to be isostructural with CaIrO3, the much-studied structural analog of the high-pressure post-perovskite phase of MgSiO3. Among the oxide post-perovskites, NaIrO3 is the first example with a pentavalent cation. The ...

The efficacy of the oxidation systems: O3, UV radiation, O3/UV radiation, O3/perovskite, UV radiation/perovskite, O3/UV radiation/perovskite, H2O2/UV radiation, H2O2/UV radiation/perovskite, has been investigated by using pyruvic acid as probe compound. Under the operating conditions used, the combination of UV ...

We perform Monte-Carlo simulations of a realistic model of the perovskite multiferroic manganites RMnO3 (R = Gd, Tb, Dy) in order to obtain the ground state phase diagram. It is shown that the dynamic Dzyaloshinskii-Moriya interaction plays a crucial role in stabilizing the state with coexisting incommensurate magnetic and ferroelectric ...

We show that the symmetry of the spin zigzag chain E phase of the orthorhombic perovskite manganites and nickelates allows for the existence of a finite ferroelectric polarization. The proposed microscopic mechanism is independent of spin-orbit coupling. We predict that the polarization induced by the E-type magnetic order can potentially be enhanced by up ...

In this work the authors present a systematic study of the crystallographic structure and the magnetic ordering of LaMnO{sub 3{+-}{delta}} perovskites. Changing the oxygen composition within the range 2.995 3 + {delta}{sub 1}) the samples are ferromagnetic. The transition from one region to the other is associated with a change in volume of around 1%.

Structures and magnetic properties of double perovskite-type oxides Eu2LnTaO6 (Ln=Eu, Dy-Lu) were investigated. These compounds adopt a distorted double perovskite structure with space group P21/n. Magnetic susceptibility, specific heat, and 151Eu M�ssbauer spectrum measurements show that the Eu2+ ions at the 12-coordinate sites of the ...

Through the utilization of element-resolved polarized x-ray probes, the electronic and magnetic state of an artificial La2FeCrO6 double perovskite were explored. Applying unit-cell level control of thin film growth on SrTiO3(111), the rock salt double perovskite structure can be created for this system, which does not have an ordered ...

We synthesized a novel perovskite-type oxyfluoride, PbScO{sub 2}F, and investigated its crystal structure, thermal stability and dielectric properties. PbScO{sub 2}F has a cubic perovskite-type structure with Pb ions displaced from the ideal A-site positions along the <110> direction. By thermal gravity and differential ...

SrMnO3 is the end member of a widely explored family of colossal magnetoresistive manganites RxSr1-xMnO3 (R=rare earth elements). Low-level R^3+ substitutions change the antiferromagnetic order from G-type in cubic SrMnO3 to C-type in tetragonal RxSr1-xMnO3 through first-order resistive and structural transitions. From the magnetization, transport, and ...

The effects of A-site ion-size on the crystal structures, transport and magnetic properties of the perovskite manganese oxide Pr0.3Ce0.2CaxSr0.5-xMnO (0 <= x <= 0.25) have been investigated. In those compounds, when 0<=x<=0.125, the temperatures (Tmax) of the resistivity maximums below Curie Temperature TC are correlated with the Kondo-like scattering of ...

The authors carry out thermographic studies, using a derivatograph, in order to understand the nature of the processes taking place during the synthesis of solid solutions of perovskites. Based on the detailed studies on the phase transformations occurring in the charges of the PSN-PMN solid solutions and on the selection of the optimum conditions for ...

The structures of tilted perovskites in each of the 15 tilt systems have been decomposed into the amplitudes of symmetry-adapted modes in order to provide a clear and unambiguous definition of the tilt angles. A full expression in terms of the mode amplitudes for the ratio of the volumes of the two polyhedra within the perovskite ...

The layered compound consists of bilayers of metallic MnO2 sheets separated by insulating material. The compound exhibits markedly anisotropic magnetoresistance at temperatures well below the three-dimensional magnetic ordering temperature Tc=90 K in addi...

Page 1. SINGLE CRYSTAL PEROVSKITES AS ELECTROOPTICALLY ACTIVE MATERIALS ... Computer Study of Complex Perovskites ...

Among perovskite-type compounds exhibiting one or another of the types of dipole ordering, considerable attention is given to mixed niobates and tantalates, AB{sub 1/2}{sup 3+} Nb{sub 1/2}O{sub 3} and AB{sub 1/2}{sup 3+} Ta{sub 1/2}O{sub 3}, containing Ba{sup 2+} ions on the A site. Barium-containing perovskites with complex ...

It was proved earlier that ferroelastic phase transition takes place in the metastable perovskite Pb(Al, Nb)/sub 0.5/O/sub 3/ at approx. 170K. The goal of this work was to study the kinetics of isothermal polymorphic perovskite-pyrochlore transition in this compound. In order to determine the ratio of the pyrochlore and ...

A high-quality polycrystalline sample of the correlated 4d post-perovskite CaRhO(3) (Rh(4+): 4d(5), S(el) = 1/2) was attained under a moderate pressure of 6 GPa. Since the post-perovskite is quenchable at ambient pressure/temperature, it can be a valuable analogue of the post-perovskite MgSiO(3) (stable higher than 120 GPa and unstable ...

Synthesis of the Ruddlesden-Popper phase, LaCa{sub 2}Mn{sub 2}O{sub 7} is presented. The difficulty in obtaining a single-phase material, free from a perovskite impurity, is highlighted. Powder X-ray diffraction indicates an orthorhombic symmetry. Powder neutron diffraction reveals a subtle rotation of the MnO{sub 6} octahedra and reduction of symmetry to a C-centered ...

We have measured the oxygen positions in LaNiO3 films to elucidate the coupling between epitaxial strain and oxygen octahedral rotations. The oxygen positions are determined by comparing the measured and calculated intensities of half-order Bragg peaks, arising from the octahedral rotations. Combining ab initio density-functional calculations with these experimental results, ...

An analysis of the effect that chemical and hydrostatic pressures have on the thermodynamic properties of perovskite-like fluorine-oxygen compounds A 2 A' MeO x F6 - x has revealed that materials under-going order-disorder transitions and having significant external-pressure compliance have the highest caloric efficiency. Some of the fluorides and ...

-perovskite (PPv), the major mineral of the Earth's D layer, is not fully known. In this paper, large-scale ab (GGA) have been carried out in order to investigate the substitution mechanism of Al3+ into PPv at high pressures. We have examined three types of Al substitution in PPv: 6.25 mol% Al substitution via a charge

This paper describes how the luminescence properties of the octahedral uranate group in compounds with ordered perovskite structure are influenced by the chemical constitution of its surroundings. The quenching temperature of the emission is more strongly influenced by the neighboring cations in the (100) direction than by those in the (111) direction. ...

A laser is described that employs solid-state crystalline materials in which the active ion is not a dopant but an integral part of the compound of the crystal. A suitable kind of ordering of ions occurs in halide crystals of the perovskite type. The resulting high concentrations permissible have yielded surprisingly small lasers. Drawings of a preferred ...

Transition-metal oxynitrides with perovskite-type structures are an emerging class of materials with optical, photocatalytic, dielectric and magnetoresistive properties that may be sensitive to oxide-nitride order, but the anion-ordering principles were unclear. Here we report an investigation of the representative compounds SrMO(2)N ...

Transition-metal oxynitrides with perovskite-type structures are an emerging class of materials with optical, photocatalytic, dielectric and magnetoresistive properties that may be sensitive to oxide�nitride order, but the anion-ordering principles were unclear. Here we report an investigation of the representative compounds SrMO2N ...

Iron-bearing magnesium silicate perovskite, the most abundant mineral in the Earth, contains both ferrous and ferric iron. In contrast to ferrous iron, most likely occupying the 8-12 coordinate site (A site), ferric iron also occupies the octahedral site (B site). The spin-state crossover of the ferric iron, which may affect the ...

High-temperature behavior of the fast ionic conductor Li{sub 0.2}Na{sub 0.3}La{sub 0.5}TiO{sub 3} has been investigated by neutron powder diffraction between 300 and 1073K. The Rietveld analysis of diffraction patterns showed around 1000K a change from rhombohedral (R3-bar c) to cubic (Pm3m) symmetry. During the heating, the tilting of octahedra along the [111] direction of the cubic ...

The evolution of the structural properties of A1-xA'xMnO3 was determined as a function of temperature, average A-site radius , and applied pressure for the ``optimal'' doping range x=0.25, 0.30, by using high-resolution neutron powder diffraction. The metal-insulator transition, which can be induced both as a function of temperature and of , was found to be ...

The structural evolution and microwave dielectric properties of (1-x)Ca0.8Sr0.2TiO3-xLi0.5Sm0.5TiO3 (x=0--1.0) solid solutions were investigated. Most samples exhibit the single orthorhombic perovskite structure and a homogeneous microstructure with high density except for the composition with x=0.5 which included a small amount of the TiO2 phase. Increasing Li0.5Sm0.5TiO3 ...

The crystal structure of the RTiGe3 compounds (R=La, Ce and Pr) has been studied by X-ray powder diffraction methods; Rietveld refinement has been carried out on the La homologue. These compounds crystallise in the BaNiO3 prototype structure, hP10-P63/mmc, also called the hexagonal perovskite (a=6.300(1), c=5.915(1) � for LaTiGe3). This seems to be the first example in which ...

The magnetic properties of RE0.7Ca0.3Mn0.95Fe0.05O3 perovskite with rare-earth cations (RE=Sm and Gd) were investigated by means of X-ray diffraction, M�ssbauer spectroscopy, and low temperature (4.2-266 K) magnetization measurements. Structural characterization of these compounds shows that they both have orthorhombic (Pbnm) structure. The M�ssbauer spectra show clear ...

It is shown that 21 ABX(3) perovskites with tilted BX(6) octahedra and layered ordering of A cations can be generated on the basis of group-subgroup relations. These structures (with 16 different space groups) are classified into ten diffraction types in terms of the conditions for superstructure reflections caused by the ordering of A ...

We have investigated the effects of growth interval in pulsed laser deposition on structural, magnetic, and electrical transport properties of (111)-oriented Sr2CrReO6 double perovskite films. It was found that the degree of B-site ordering varied in a wide range by just changing the growth interval. Magnetization under 1 T and metallicity (the ratio of ...

The catalytic activities of cobalt perovskites and various cobalt oxides for the reduction of nitric oxide with carbon monoxide were studied under plug flow reactor conditions. Cobalt tetroxide showed the greatest catalytic activity after pretreatment with CO, and lanthanum strontium cobalt trioxide showed the least catalytic activity. The perovskite ...

We report on the atomic ordering of B-site transition metals and magnetic properties of epitaxial La2CrFeO6 double-perovskite films grown by pulsed-laser deposition under various conditions. The highest-ordered sample exhibited a fraction of antisite disorder of only 0.05 and a saturation magnetization of �2 ?B per formula unit at 5 ...

Magnesium silicate perovskite is thought to be the major constituent of the lower mantle. Consequently, knowledge of the deformation behavior of MgSiO3 perovskite is important for understanding the geodynamic behavior in the deep Earth as well as interpreting observed seismic anisotropy. One mechanism that can generate anisotropy is dislocation glide ...

Perovskite-structured silicate phases are thought to make up ~ 80% of the mantle by volume and likely control many of its mechanical properties. It is therefore crucial to our understanding of earth�s interior to determine the behavior of common cations within the perovskite structure. Recent work on the behavior of iron-bearing silicate ...

The last decade has seen significant advances in the seismological observation of the lowermost mantle, with our understanding of the D' region significantly increasing in complexity. At the same time mineral physics constraints on this region have vastly improved: (1) increases in computing power allow us to simulate the elastic, chemical and transport properties of geologically reasonable ...

Fe-enrichment in the deep lower mantle has been proposed as an explanation for seismic anomalies such as large low shear velocity provinces (LLSVPs) and ultralow velocity zones (ULVZs). In order to resolve the effect of Fe on the stability and equation of state of the lower mantle�s dominant constituent, (Mg,Fe)SiO3 perovskite, we have studied Fe-rich ...

Low-crystal-field octahedral complexes of Chromium (3+) in solids exhibit broad-band fluorescence, useful in tunable laser applications, rather than the narrow-band phosphorescence of high-field complexes such as ruby. Photoluminescence spectra and lifeti...

The intrinsic activity of a series of lanthanum perovskite catalysts for catalytic methane oxidation was determined by temperature programmed reaction and stationary-state order of reaction experiments. The catalysts were prepared by conventional precipit...

It is widely recognised that the electronic properties of the magnetoresistive manganate perovskites can be controlled by substitution at the A cation site (to determine the 3d band filling and overlap integrals) and by manipulating the dimensionality of the arrays of corner sharing manganese oxide octahedra. We have recently been studying in detail the effect of directly ...

Three tetragonal ordered oxygen deficient perovskites (La,Sr){sub 8}Cu{sub 8-x}Fe{sub x}O{sub 20} were studied by powder neutron diffraction. It is found that substitution of iron for copper in the perovskite La{sub 6.4}Sr{sub 1.6}Cu{sub 8}O{sub 20} does not influence oxygen stoichiometry. 11 refs., 2 figs., 2 tabs.

Oxygen vacancies are known to dominate the overall electrical behavior of perovskite oxides, which are used in many applications. Although theories have been developed to explain the effect of these vacancies and the defect chemistry of perovskites, there has yet to be incontrovertible evidence of the fundamental origins of the structure-property ...

The hydrogenation of ethylene over lanthanum transition metal perovskites was studied by characterizing the perovskites by X-ray diffraction, magnetic susceptibility measurements, and scanning electron microscopy; determining the catalytic activity by using a plug-flow microreactor; and determining the surface properties (i.e., work function) by ESCA. The ...

The ordered perovskite Sr(2)YTaO(6), distrontium yttrium tantalum hexaoxide, has been reported as showing an unusual triclinic structure, at odds with the results from a recent group-theoretical analysis. A new investigation establishes that Sr(2)YTaO(6) and the isostructural Sr(2)YNbO(6), distrontium yttrium niobium hexaoxide, in fact both adopt the ...

We propose a general model, based on Anderson superexchange and the pseudo Jahn-Teller effect, to explain why ferroelectric and octahedral tilting distortions are favored by ferromagnetic ordering when compared to antiferromagnetic tilting distortions in ABX3 (A = alkali, alkaline-earth ion, f-filling rare earth; B = magnetic transition-metal ion; X = O2-, F-) ...

A theory of doped perovskite vanadates with spin and orbital orders is presented. Mobile holes are strongly renormalized by spin excitations (magnons) in the spin G-type and orbital C-type (SG-OC) order, and orbital excitations (orbitons) in the spin C-type and orbital G-type (SC-OG) one. Hole dynamics in a staggered t2g orbital array ...

The lattice thermal conductivity of silicate perovskite, the most abundant mineral in the Earth's lower mantle, is calculated by combining the first-principles electronic structure theory and Peierls-Boltzmann transport theory. The phonon scattering rate due to lattice anharmonicity and Mg/Fe mass disorder is evaluated for each mode at the extreme P-T conditions of the lower ...

Recently multiferroic materials have attracted great interest. However, relatively a few pure multiferroic compounds are currently known. Here we show the exploration of design of multiferroic properties in double perovskites by combining the ferrolectrisity driven by the Bi lone pairs and selectively choosing the 3d transition metals following Goodenough-Kanamori's rules to ...

High level waste (HLW) partitioning concept includes separation of a long-lived fraction following by its immobilization in ceramics. Improved process flow sheet suggested for implementation at PA ''Mayak'' implies production of a long-lived HLW fraction with rare earth elements (REE) as major components, Am and Cm as minor constituents, and only traces of U, ...

An investigation has been made on the chemical stability of the cathode-interconnect interface in solid oxide fuel cells. Lanthanum calcium chromite and lanthanum strontium manganite (a dense 10% A-site deficient manganite, a porous 10% A-site deficient one or a dense 1% A-site deficient one) were placed between air and fuel ...

New Bi (V) containing perovskites oxides of the type, BaLaMBiO{sub 6} (M = Mg, Ca, Sr) have been synthesized under high oxygen pressure conditions using the thermal decomposition of peroxides in a tetrahedral anvil apparatus. These compounds have been characterized by X-ray powder diffraction and iodometric titration. All the BaLaMBiO{sub 6} (M + Mg, Ca, Sr) compounds show 1:1 ...

Double perovskites Ba{sub 2}MUO{sub 6} (M=Co, Ni) were prepared by the solid-state reaction. X-ray diffraction measurements show that both cobalt (nickel) and uranium ions are ordered in the NaCl type over the six-coordinate B sites of the perovskite ABO{sub 3}. Detailed magnetic susceptibility and specific heat measurements show that ...

Single phase orthorhombic perovskite Ho1?xLaxMnO3 (x = 0.1, 0.15) compounds are successfully synthesized by using a sol-gel method. We find that the orthorhombic perovskite structure of HoMoO3 compound can be stabilized by partial substitution of smaller Ho ion by larger La ion. The magnetic properties of orthorhombic perovskite ...

Synchrotron X-ray and neutron powder diffraction were used to investigate the formation, structure and bonding in the double perovskite Ba{sub 2-x}Sr{sub x}TbIrO{sub 6} solid solutions. The results showed that these oxides all exhibit ordering of the Tb and Ir cations in a double perovskite-type structure. Three distinct structural ...

Among hexagonal perovskites, the B-cation deficient perovskite-related compounds AnBn-1O3n present two kinds of structural types depending on the stacking sequences of their AO3 layers. All these structures derive from the perovskite, which is periodically disturbed by planar defects. The structures with (hhc...c)-type sequences, ...

... perovskites (that are not too distorted) are included. ... Slist to 1125 compounds which are either confirmed perovskites or compounds which ...

The crystal structure of the Ruddlesden-Popper layered perovskite Li2SrTa2O7 has been characterized at various temperatures between ?185 and 300 �C by several techniques: X-ray and neutron powder diffraction, single crystal diffraction, transmission electron microscopy and Raman spectroscopy. The low temperature structure has been confirmed to be orthorhombic Cmcm with a ...

The structure of the double perovskite Ba{sub 2}PrIrO{sub 6} has been re-examined by profile analysis of X-ray diffraction data. It has been shown that neither the monoclinic P2{sub 1}/n nor the tetragonal P4/mnc space group correctly describes its structure. Ba{sub 2}PrIrO{sub 6} has cubic symmetry, space group Fm3-bar m, cell parameter a=8.40135(6)A. In agreement with ...

Data is presented for a complex structural and compositional modulation in the perovskite (NaNd)(MgW)O{sub 6}. This modulation creates a large 14a{sub p} x 14a{sub p} x 2a{sub p} supercell (a{sub p} {approx} 3.9 {angstrom} is the lattice parameter of the cubic perovskite aristotype) containing ordered regions with doubled (110) ...

Data is presented for a complex structural and compositional modulation in the perovskite (NaNd)(MgW)O6. This modulation creates a large 14ap�14ap�2ap supercell (ap~3.9 A? is the lattice parameter of the cubic perovskite aristotype) containing ordered regions with doubled (110) d-spacings in the a-b plane separated by ...

We report a ferroelectric transition driven by the off-centering of magnetic Mn4+ ions in antiferromagnetic Mott insulators Sr1-xBaxMnO3 with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ...

Recent first principle calculations make it possible to infer rheological properties such as activation energy and volume in deep mantle phases, including perovskite [Ammann et al., 2008] and post-perovskite, which is expected to have a much lower viscosity than perovskite [J. Brodholt, personal communication] as well as other mineral ...

We report measurements on thermal expansion of CaSiO3 perovskite within the stability field and its room temperature volume-pressure behavior, as well as in situ determination of the perovskite stability field. The phase boundary between CaSiO3 perovskite and the lower-pressure phase assemblage Ca2SiO4 + CaSi2O5 was determined at ...

A newly substituted series of perovskites, Bi{sub x}La{sub 2-x}MnMO{sub 6} with M = Ni, Co and x = 0.25, 0.50, were synthesized using a citrate sol-gel technique. The crystal structure, established from neutron diffraction, is a distorted double perovskite with partial transition metal B-site ordering. These ...

A magnetic, electronic and structural study of the double perovskites Ba2REMoO6 (RE=Sm, Eu, Gd, Dy) has been performed. All materials crystallise in the cubic Fm3�m symmetry space group and the cell volume decreases as RE varies from Sm to Dy in accordance with Vegard's law. An antiferromagnetic transition is observed below TN=130 and 112 K for RE=Sm and Eu, respectively. ...

The remarkable properties of manganese oxides AMnO3 with perovskite structure, such as the colossal magnetoresistance and the multiferroicity, arise from peculiar charge, spin and orbital orderings of the Mn eg electrons driven by cooperative Jahn-Teller distortions of the MnO6 octahedra. Mastering these orderings remains a challenge ...

complex perovskites, modified perovskites, and other structure families. New substrate ... on the complex oxide perovskites and related solid solutions. ...

Electrical conductivity measurements of Perovskite and a Perovskite-dominated assemblage synthesized

Quadruple perovskites Ba{sub 4}LnRu{sub 3}O{sub 12} (Ln=La, Nd, Sm-Gd, Dy-Lu) were prepared and their magnetic properties were investigated. They adopt the 12L-perovskite-type structure consisting of Ru{sub 3}O{sub 12} trimers and LnO{sub 6} octahedra. All of these compounds show an antiferromagnetic transition at 2.5-30 K. For Ba{sub 4}NdRu{sub 3}O{sub ...

Group-theoretical methods are used to enumerate the structures of ordered double perovskites, A(2)BB'X(6), in which the ordering of cations B and B' into alternate octahedra is considered in combination with the ubiquitous BX(6) (or B'X(6)) octahedral tilting. The cation ordering on the B-cation site is described ...

The degree of B/B;{'} alternate cation order is known to heavily influence the magnetic properties of A_{2}BB;{'}O_{6} double perovskites although the nature of such disorder has never been critically studied. Our detailed x-ray absorption fine structure studies in conjunction with synchrotron radiation x-ray diffraction experiments on polycrystalline ...

The perovskite-type layer compounds (Csub(n)Hsub(2n+1)NH sub 3 ) sub 2 MeCl sub 4 show a variety of different structural modifications. They differ from one another by the order and dynamical behaviour of the CH sub 3 -CH sub 2 -...-CH sub 2 -NH sub 3 cha...

We have measured the oxygen positions in LaNiO{sub 3} films to elucidate the coupling between epitaxial strain and oxygen octahedral rotations. The oxygen positions are determined by comparing the measured and calculated intensities of half-order Bragg peaks, arising from the octahedral rotations. Combining ab initio density-functional calculations with these experimental ...

The temperature-pressure phase diagram for both the crystal and magnetic structures of LaCrO(3) perovskite has been mapped out by in situ neutron-diffraction experiments under pressure. The system offers the opportunity to study the evolution of magnetic order, spin direction, and magnetic moment on crossing the orthorhombic-rhombohedral phase boundary. ...

We investigated the magnetic phase of the perovskite CaCrO3 by using the muon-spin relaxation technique accompanied by susceptibility measurements. A thermal hysteresis loop is identified with a width of about 1 K at the transition temperature. Within the time scale of the muon lifetime, a static antiferromagnetic order is revealed with distinct multiple ...

High-resolution neutron powder diffraction has been applied to determine the structural evolution in the orthorhombic perovskite RCrO3 family. The structural distortions observed have been found to be closely related to the dramatic variation in the magnetic ordering temperature TN . In addition to the reduction in the orbital overlap integral that can ...

We have investigated the structural and magnetic properties of antiferroelectric A2CoTeO6 perovskites with A=Cd, Ca, Sr, Pb, and Ba. All compounds are antiferromagnetic at low temperatures, with the antiferromagnetic transition temperature slightly decreasing with decreasing ionic size of the A cation. Such a decrease in antiferromagnetic interaction is not observed in ...

The resistivity and magnetization of layered perovskite La{sub 2{minus}2x}Ca{sub 1+2x}Mn{sub 2}O{sub 7} have been studied systematically using bulk samples with a wide doping concentration range 0{le}x{le}0.5 and epitaxial thin film samples with x=0.3. The system becomes a metallic ferromagnet for doping concentrations 0.22{le}x{le}0.5. In this doping region, results for bulk ...

The temperature variation of the dielectric permittivity and loss of the solid solutions (1-x)La(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-xBi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3} [(1-x)LMT-xBMT] (0{<=}x{<=}0.3) measured at radio, microwave, and far infrared frequency ranges has been analyzed in comparison with that observed in other bismuth-containing and bismuth-free ...

The evolution of the structural properties of A{sub 1{minus}x}A{sub x}{sup {prime}}MnO{sub 3} was determined as a function of temperature, average A-site radius {l_angle}r{sub A}{r_angle}, and applied pressure for the {open_quotes}optimal{close_quotes} doping range x=0.25, 0.30, by using high-resolution neutron powder diffraction. The metal-insulator transition, which can be ...

We present transport and neutron-diffraction data establishing a clear link between static and dynamic distortions of the MnO6 octahedra and charge mobility in A1-xA'x MnO3 (A=La or Pr; A'=Ca or Sr). Systematic analysis of the Mn-O bond lengths versus average A-site ionic radius indicates that increasing static coherent MnO6 distortion is associated with increasing insulating ...

The oxygen stoichiometry variation in the BaRE(Cu{sub 0.5}Fe{sub 0.5}){sub 2}O{sub 5+{delta}} series is established with rare earth elements having ionic radii (CN = 8) in the range of 0.977--1.160{angstrom}(Lu-La). The double-perovskite structure is stable with RE = Lu-Pr, while La prefers the simple-perovskite structure. In the ...

The effect of rare-earth ions (La, Pr, Nd, and Gd) in ACoO[sub 3] perovskites on the thermal behavior and on the catalytic activity for methane oxidation has been studied. The thermal reduction, as investigated by oxygen desorption analysis, revealed for all perovskites one evolution step occurring above 1100 K. Transmission electron micrographs at the ...

This dissertation describes the preparation, structure, and dielectric properties of several new families of nonstoichiometric ordered niobate perovskites. First examples of non-stoichiomeeryryc 1:2 ordered perovskites were discovered in the (1-x)A2+(Li1/4Nb,Ta3/4)O 3-xA2+(Li2/5W3/5)O3 (A2+=Ba, Sr and Ca) and ...

Phase-pure, fully epitaxial Sr2FeMoO6 films with a high degree of Fe/Mo ordering have been fabricated using ultrahigh vacuum sputtering and verified by a variety of techniques. Through identifying and controlling critical factors, such as stoichiometry, phase purity, and double-perovskite ordering, that complicate the growth of ...

Computer-based group-theoretical methods are used to enumerate structures arising in A(2)BB'X(6) perovskites, with either rock-salt or checkerboard ordering of the B and B' cations, under the additional assumption that one of these two cations is Jahn-Teller active and thereby induces a distortion of the BX(6) (or B'X(6)) octahedron. The requirement to ...

The double perovskite Sr2FeMoO6 has been prepared in polycrystalline form by high-pressure methods, starting from a precursor developed via a citrate technique, containing an elevated degree of anti-site disordering. The application of high external pressure (2 GPa) to Sr2FeMoO6 promotes the long distance Fe/Mo cationic order, due to the smaller lattice ...

Charge-lattice fluctuations are observed in the layered perovskite manganite LaSr{sub 2}Mn{sub 2}O{sub 7} by Raman spectroscopy at temperatures as high as 340 K, and with decreasing temperature they become static, forming a charge-ordered (CO) phase below T{sub CO}=210 K. In the static regime, superlattice reflections are observed by neutron and x-ray ...

The geometrically frustrated, B-site ordered, S = 1/2, double perovskites Sr2CaReO6 and Sr2MgReO6, which show spin frozen magnetic ground states, have been investigated using neutron powder diffraction (ND) and neutron pair distribution function (NPDF) analysis in a search for evidence for atomic positional disorder. For both materials, data were taken ...

Photo-irradiation effects on the charge and spin ordered manganites at quarter filling are investigated. Time dependence of spin and charge states after irradiation is calculated by utilizing the time-dependent unrestricted Hartree Fock method in a finite size cluster. It is shown, by analyzing charge distribution, energy gap and magnetization, that the transition from the ...

Hyper-Raman scattering is used to investigate the vibrations in two prototypical relaxors, PbMg1/3Nb2/3O3 and PbMg1/3Ta2/3O3 (PMT). First-order scattering from polar modes is clearly observed. Most of the triply-degenerate cubic vibrations are split into doublets and their frequencies compare very well to that of PbTiO3 in its tetragonal phase. Their shape and scattering ...

The A-site-ordered perovskite CaCu3Ge4O12 synthesized under high pressure undergoes ferromagnetic spin ordering below Tc ? 12 K. The critical exponents have been determined from isotherms of magnetization across Tc via an iteration process and the Kouvel-Fisher method as well as from specific heat. Based on fitting parameters of Tc, ?, ...

The real-space recursion method and unrestricted Hartree-Fock approximation have been applied to calculate the density of states of various Co perovskite, CeCoO3, SrCoO3 and Sr1?xCexCoO3. We have studied the magnetically ordered states of these Co perovskites in an enlarged double cell, and find its various magnetic structures due to ...

The authors report differential scanning calorimetric analyses of several reactions leading to the formation of the mixed perovskite La[sub 2]CuTiO[sub 6]. The synthesis of this oxide was carried out following three different strategies: (1) classical ceramic methods, (2) use of a layered oxide precursor (La[sub 2]CuO[sub 4]), and (3) sol-gel method. Electron diffraction and ...

The double perovskite Sr(Ni{sub 1/2}Mo{sub 1/2})O{sub 3} has been prepared with solid-state reaction and was characterized by x-ray diffraction technique. It has been indicated that the single phase is formed at 1300 deg. C in air. The compound undergoes a phase transition at 280 deg. C, where the structure of the ordered perovskite ...

Large intragrain magnetoresistance (MR) in the ordered double perovskite, Ba{sub 2}FeMo{sub 6}, is shown for the first time. The latter appears near {Tc} (340 K), i.e., above room temperature. This effect originates from a double-exchange-like mechanism, based on antiferromagnetic coupling of localized high spin 3d{sup 5}Fe{sup 3+}, and itinerant 4d{sup 1} ...

Single-crystal and powder samples of a new calcium iron (II) titanate, CaFeTi{sub 2}O{sub 6}, have been synthesized at 12-15 GPa and 1200-1400{degrees}C, and studied by X-ray diffraction. This compound is a variant of the perovskite structure and crystallizes in the tetragonal space group P4{sub 2}/nmc, a = 7.5157(2) {angstrom}, c = 7.5548(2) {angstrom}, and z = 4. Calcium and ...

A comparative study of the electronic structures of BaTiO3, SrTiO3, and PbTiO3 perovskite oxides is performed in order to identify the atomistic factors governing the occurrence of a ferroelectric or antiferrodistortive (rotating-type) phase transition in ATiO3 perovskite oxides. The discrete variational-X? molecular orbital method is ...

The defect chemistry of LaMo{sub 3{minus}{delta}} (M = Mn, Fe, Co) perovskite-type oxides has been studied in order to describe the composition versus oxygen partial pressure phase diagrams in these systems. It is proposed that these systems can be described with extended defects. Literature data on LaMnO{sub 3{minus}{delta}} and LaCoO{sub 3{minus}{delta}} ...

We describe in this work the synthesis by the Pechini method of five Mo(VI)- and W(VI)-containing complex perovskites and their structural characterisation by HREM and XRD. The compounds studied, Ba(B2/3'B1/3'')O3 (B'=In and Y; B''=W and Mo) and Sr(In2/3W1/3)O3, were obtained after firing the precursor powders for 8h at 1200�C. Thermal analysis showed that the formation ...

A novel ScVO(3) perovskite phase has been synthesized at 8 GPa and 1073 K from the cation-disordered bixbyite-type ScVO(3). The new perovskite has orthorhombic symmetry at room temperature, space group Pnma, and lattice parameters a = 5.4006(2) �, b = 7.5011(2) �, and c = 5.0706(1) � with Sc(3+) and V(3+) ions fully ordered on ...

We present a theory of the doped perovskite vanadates with spin and orbital orders [1]. Two kinds of spin-orbital orders are found in the ground state: the G-type (three-dimensional (3D) staggered) spin order (SO) with the C-type (rod type) orbital order (OO) (the alternative ...

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

... Accession Number : AD0253293. Title : SOME PROPERTIES OF BISMUTH PEROVSKITES. Corporate Author : MASSACHUSETTS ...

... Accession Number : AD0828049. Title : SINGLE CRYSTAL PEROVSKITES AS ELECTROOPTICALLY ACTIVE MATERIALS. ...

... Accession Number : AD0658461. Title : SINGLE CRYSTAL PEROVSKITES AS ELECTROOPTICALLY ACTIVE MATERIALS. ...

... Accession Number : AD0650411. Title : SINGLE CRYSTAL PEROVSKITES AS ELECTROOPTICALLY ACTIVE MATERIALS. ...

... Accession Number : ADD255364. Title : Kinetics of the Hydrothermal Crystallization of the Perovskite Lead Titanate. Descriptive ...

... Accession Number : AD0447460. Title : INFRARED STUDIES OF PEROVSKITE TITANATES,. Corporate Author : MASSACHUSETTS ...

The relative abundance of noble gases on Earth is very different from the solar abundance pattern. All noble gases are strongly depleted mostly due to loss to space. However, xenon appears to be particularly depleted on Earth. This cannot be explained simply by hydrodynamic escape. Moreover, the amount of radiogenic 40Ar that should have been produced over Earth�s history is twice larger than ...

Our recent work (Catalli et al., 2009) has shown that systems with realistic Fe2+ and Al contents for pyrolite increase the thickness of the post-perovskite boundary to 400-600 km in the binary and ternary systems, which is significantly larger than the thickness of the D� discontinuity, challenging the isochemical phase transition model for the D� discontinuity. More ...

Potentiometric internal reference oxygen sensors were created by embedding a metal/metal oxide mixture within an yttria-stabilized zirconia oxygen-conducting ceramic superstructure. A static internal reference oxygen pressure was produced inside the reference chamber of the sensor at the target application temperature. The metal/metal oxide-containing reference chamber was sealed within the ...

We have studied the Sr(2-x)La(x)Fe(1+x/2)Re(1-x/2)O(6) series in order to check how the increase in the number of Fe-O-Fe superexchange interactions affects the magnetic properties of this family of double perovskites. In these compounds the addition of La(3+) can be compensated by an increase of the Fe(3+) ratio leading to a non-electron-doped system. The ...

Substitution of La(3+) by Sr(2+) in the double perovskite La(2)CoTiO(6) yields materials of the La(2-x)Sr(x)CoTiO(6) series showing a significant amount of trivalent cobalt ions when prepared at ambient atmosphere. The as-prepared compounds can be reduced in severe conditions retaining the perovskite structure while inducing the formation of a large amount ...

Anelastic loss mechanisms associated with phase transitions in BaCeO3 have been investigated at relatively high frequency �1MHz and low stress by resonant ultrasound spectroscopy (RUS), and at relatively low frequency �1Hz and high stress by dynamic mechanical analysis (DMA). Changes in the elastic moduli and dissipation behavior clearly indicate phase transitions due to octahedral ...

Recently, much attention has been paid to the A-site-order perovskites AA'3B4O12 due to the observation of a large variety of intriguing physical properties. We have prepared an A-site-ordered perovskites CaCu3Ir4O12 under 9 GPa and 1250 C with a Walker-type Multianvil module. Rietveld refinements to the ...

Bacterial reaction centers (RCs) catalyze a series of electron-transfer reactions reducing a neutral quinone to a bound, anionic semiquinone. The dissociation constants and association rates of 13 tailless neutral and anionic benzo- and naphthoquinones for the Q(A) site were measured and compared. The K(d) values for these quinones range from 0.08 to 90 ...

We formulate and study an effective Hamiltonian for low-energy Kramers doublets of d;{1} ions on a square lattice. We find that the system exhibits a magnetically hidden order in which the expectation values of the local spin and orbital moments both vanish. The order parameter responsible for a time-reversal symmetry breaking has a composite nature and is ...

Reconciling the apparently contradictory results of NMR and x-ray absorption fine structure measurements on the ferroelectric perovskite BaTiO3 gives insight into the character of the displacive and order-disorder components of the phase transitions of this material. The order-disorder component in the transition consists of local ...

The post-perovskite (pPv) is the high-pressure phase of some highly distorted perovskites. The pPv phase of MgSiO{sub 3} stabilized under 125 GPa and 2000 K cannot be quenched to ambient pressure. In contrast, the pPv CaIrO{sub 3} can be synthesized under a modest pressure or even at ambient pressure. However, the pPv CaIrO{sub 3} has not been fully ...

The post-perovskite (pPv) is the high-pressure phase of some highly distorted perovskites. The pPv phase of MgSiO3 stabilized under 125 GPa and 2000 K cannot be quenched to ambient pressure. In contrast, the pPv CaIrO3 can be synthesized under a modest pressure or even at ambient pressure. However, the pPv CaIrO3 has not been fully characterized. We report ...

Stoichiometric RMnO{sub 3} perovskites have been prepared in the widest range of R{sup 3+} ionic sizes, from PrMnO{sub 3} to ErMnO{sub 3}. Soft-chemistry procedures have been employed; inert-atmosphere annealings were required to synthesize the materials with more basic R cations (R = Pr, Nd), in order to minimize the unwanted presence of Mn{sup 4+}. On ...

Ab initio molecular dynamic (AIMD) simulations were performed to calculate the equation of state (EOS) of CaSiO3 perovskite at mantle pressure temperature conditions. At temperatures above 2000 K, even though the hydrostatic crystal structure is metrically tetragonal in the pressure range of 13 123 GPa, the symmetry of the elastic moduli is consistent with cubic symmetry. Our ...

We report on the unconventional magnetism in the cubic B-site ordered double perovskite Ba2YMoO6, using ac and dc magnetic susceptibility, heat capacity and muon spin rotation. No magnetic order is observed down to 2 K while the Weiss temperature is approximately -160 K. This is ascribed to the geometric frustration in the lattice of ...

A series of osmium double perovskite oxides, Ln2LiOsO6 (Ln=La, Pr, Nd, Sm), has been prepared as single crystals from acidic molten hydroxide. All four oxides crystallize in the monoclinic space group P21/n (Glazer tilt system #10, a?a?b+), forming a 1:1 ordered rock salt lattice of Li+ and Os5+ cations. Magnetic susceptibility measurements show that these ...

A highly oxygen deficient perovskite, BaBio.28Coo.n02.2, was synthesized by solid state reaction. The crystal structure was determined by neutron and x-ray powder diffraction. The material exhlbits semiconducting behavior with an energy gap of 1.8 eV. Magnetic susceptibility studies reveal spin-glass ordering, which may have its origin in the frustration ...

Measurements of thermal conductivity versus temperature and magnetic field are reported for perovskite manganites that exhibit ferromagnetic (FM), charge-ordering (CO), antiferromagnetic, and/or structural phase transitions. The data reveal a dominant lattice contribution to the heat conductivity with {kappa}{approximately}1{minus}2 W/mK near room ...

Magnetoresistance and magnetocaloric effect of a double perovskite oxide PrSrMnCoO6 (cubic, Fm3m) has been studied in fields up to 7 T. This compound is semiconductor-like and its electrical resistivity increases by 5 orders while going from 300 to 50 K. Giant magnetoresistance of ~40% is observed at 200 K in 7 T field. PrSrMnCoO6 ...

Soft x-ray magnetic dichroism, magnetization, and magnetotransport measurements demonstrate that the competition between different magnetic interactions (exchange coupling, electronic reconstruction, and long-range interactions) in La{sub 0.7}Sr{sub 0.3}FeO{sub 3}(LSFO)/La{sub 0.7}Sr{sub 0.3}MnO{sub 3}(LSMO) perovskite oxide superlattices leads to unexpected functional ...

This work focuses on the characterization of the expansion of Landau's main equation for Pm3�m structures, which are transformed with symmetry subgroups, associated with M+3 and R+4 special points of the Brillouin zone, under hydrostatic pressure. This solution has been adapted to include the general influence of hydrostatic pressure and the evolution of the order parameter. ...

Three two-parameter models, one describing an A-body system (the atomic nucleus) and two describing many-body systems (the van der Waals gas and the ferroelectric (perovskite) system) are compared within the framework of catastrophe theory. It is shown that each has a critical point (second-order phase transition) when the two counteracting forces ...

The ternary stoichiometric perovskite compounds, Na{sub 0.75}Ln{sub 0.25}Ti{sub 0.5}Nb{sub 0.5}O{sub 3} (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm) are intermediate members of the NaNbO{sub 3}-Na{sub 0.5}Ln{sub 0.5}TiO{sub 3} solid solution series. The compounds were synthesized by standard ceramic methods at 1300 deg. C followed by annealing at 800 deg. C and quenching to ...

The distribution of radioactive isotopes in the Earth's deep interior is of fundamental interest to geophysics, geochemistry and geodynamics as this could potentially influence the distribution of radiogenic heat production and hence the thermal evolution and dynamics of the Earth. 40K is the most abundant long- lived radiogenic isotope in the Earth and as such, where potassium resides in the ...

Perovskite-type oxides (ABO3) find a great variety of applications in solid oxide fuel cells (SOFCs), including solid electrolytes, cathodes and interconnects, which are closely related to the defect chemistry involved. Thermodynamic studies are needed to systematically understand the nature of the structure-property relations and provide guidance to predict and/or select ...

A study of the crystallographic and magnetic structure of the double perovskite Sr{sub 2}CoMoO{sub 6} (SCMO) has been carried out on a polycrystalline sample using neutron powder diffraction (NPD) data between 10 and 700 K. An analysis of the NPD patterns at room temperature has shown that this compound crystallises in the tetragonal space group I4/m with a = 5.5616(1) A and c ...

Strongly correlated electron systems, especially perovskite type of manganites, in which the electronic transport properties of transition metal oxides strongly interact with the magnetic properties and with the crystal lattice, are of great interest not only due to their application in technology but also to the need of fundamental research in understanding the origin of the ...

Substitution of divalent Sr by trivalent La is found to affect the valence states of both of the two B-site cations, Fe and Ta, in the double perovskite oxide (Sr{sub 1-} {sub x} La {sub x} ){sub 2}FeTaO{sub 6}. Moreover, it improves the degree of order of these cations. From {sup 57}Fe Moessbauer spectra the average Fe valence was found to decrease with ...

The ordered cubic perovskite La/sub 2/LiVO/sub 6/ has been prepared under 60 kbar oxygen pressure at 900/sup 0/C. The double perovskite unit cell has a parameter of 7.746 +/- 0.003 A. An ionic radius of pentavalent vanadium has been estimated for CN6. The assignment of the IR absorption and Raman scattering bands seems to confirm the ...

The evolution of the magnetic ordering temperature of the 4d3 perovskites RTcO3 (R=Ca, Sr, Ba) and its relation with its electronic and structural properties has been studied by means of hybrid density functional theory and Monte Carlo simulations. When compared to the most widely studied 3d perovskites the large spatial extent of the ...

The program POTATO, which was developed to model distorted perovskite structures, has been used to assess the stability of hypothetical compositions and guide the synthesis of new materials at high pressures and high temperatures. The initial result of this effort is the synthesis of two new perovskites, Ca{sub 2}NdAgTi{sub 4}O{sub 12} and NdAgTi{sub ...

We report the results of density functional theory ab-initio calculations and monochromatic synchrotron X-ray diffraction study carried out for orthorhombic NaZnF{sub 3} in the pressure range 0-40 GPa. Perovskite-to-postperovskite phase transition was anticipated by first-principles computations and then observed in high-pressure diamond anvil cell synchrotron diffraction ...

The molar volumes and bulk moduli of CaSiO3 perovskite are calculated in the temperature range from 300 to 2,800 K and the pressure range from 0 to 143 GPa using molecular dynamics simulations that employ the breathing shell model for oxygen and the quantum correction in addition to the conventional pairwise interatomic potential models. The performance of five equations of ...

The synthesis, crystal structure, and dielectric properties of the novel double perovskite Pb(2)TmSbO(6) are described. The room-temperature crystal structure was determined by ab initio procedures from neutron powder diffraction (NPD) and synchrotron X-ray powder diffraction (SXRPD) data in the monoclinic C2/c (No. 15) space group. This double perovskite ...

Group-theoretical methods are used to enumerate the structures of ordered perovskites, in which 1:2 and 1:3 ordering of B and B' cations is considered in combination with the ubiquitous BX6 (or B'X6) octahedral tilting. The cation ordering on the B-cation site is described by irreducible representations of the Pm3 ...

The ordered double perovskites ALaMgTaO6 (A=Ba, Sr, Ca) and La2Mg(Mg1/3Ta2/3)O6 have been prepared and characterized. Synchrotron X-ray powder diffraction analyses show that all four compounds exhibit a rock-salt type ordering of the B-site cations (Mg2+/Ta5+) and a random distribution of A-site cations (A2+/La3+). The space group ...

The ordered double perovskites ALaMgTaO{sub 6} (A=Ba, Sr, Ca) and La{sub 2}Mg(Mg{sub 1/3}Ta{sub 2/3})O{sub 6} have been prepared and characterized. Synchrotron X-ray powder diffraction analyses show that all four compounds exhibit a rock-salt type ordering of the B-site cations (Mg{sup 2+}/Ta{sup 5+}) and a random distribution of ...

A series of perovskite-type manganites, LnMnO{sub 3} (Ln = lanthanoids or Y), were examined for their electrode-catalytic activities to reduce oxygen in alkaline solution. Polarization experiments using gas diffusion-type electrodes revealed that the catalytic activity differed significantly with a change in Ln, being in the order of La > Pr > Nd ...

... Structural distortions of cubic perovskites of the formula ABX3 , where the ... The number of anti-perovskites ABM 3 , where the positions of anion and ...

... Title : Single Crystals of Yttrium and Rare Earth Gallium Perovskites for Use as Substrates for Bubble Domain Iron Perovskites. ...

Magnetic ground states in solids often arise as a result of a delicate balance between competing factors. One currently active area of research in magnetic materials involves compounds in which long-range magnetic ordering at low temperatures is frustrated by the geometry of the crystalline lattice, a situation known as geometrical magnetic frustration. The number of ...