... 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 synthesis pathways for ...

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 ...

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 ...

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?? ...

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+ ...

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 ``A`` ...

... concerning A-site ion substitutions for lanthanum ... lanthanum calcium system, the calcium ions prefer ... Yttrium and neodymium could be substituted ...

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 ...

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 ...

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 ...

-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 ...

divalent alkaline earth elements, thereby driving manganese ions into a ... and alkaline earth elements and the amount of alkaline earth substitution. ...

... BiFeO3 films substituted with nonmagnetic perovskites, zinc ferrite, copper ferrite and calcium ferrite. Magnetization and ...

... the program was on the preparation and magnetic characterization of amorphous BiFeO3 films substituted with nonmagnetic perovskites, zinc ferrite ...

The inherent uncertainties in modern first-principles calculations are reviewed using geophysically relevant examples. The elastic constants of perovskite at lower-mantle temperatures and pressures are calculated using ab initio molecular dynamics. These are used in conjunction with seismic tomographic models to estimate that the lateral temperature contrasts in the Earth's ...

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 neutron diffraction ...

Ethane oxidation reactions were studied over pure and Ca-, Mg-, Sr-, La-, Nd-, and Y-substituted BaCeO{sub 3} perovskites under oxygen limited conditions. Several of the materials, notably the Ca- and Y-substituted materials, show activity for complete oxidation of the hydrocarbon to CO{sub 2} at temperatures below 650 C. At higher ...

MgSiO3-rich perovskite is expected to dominate Earth's lower mantle (pressures >25 GPa) with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms: MgA + SiB = MA + MB and SiB = AlB + 0.5 (vacancy)O. Phase synthesis studies show that both substitutions do occur and the ...

As part of its goal to minimize requirements for mineral commodities through conservation and substitution, the Bureau of Mines conducted research to develop molybdenum as a potential substitute for superalloys containing the strategic and critical materi...

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 ...

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' site and ...

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 dependent effective ...

The effects of Ca doping on the Curie temperature, structural, dielectric, and elastic properties of Ba0.4Sr0.6-xCaxTiO3 (0<=x<=0.3) has been studied. Powder x-ray diffraction revealed that the cubic lattice constant a decreases linearly with increasing x from 0 to 0.15, while showing an anomalous expansion between x=0.15 and x=0.18. This, together with the anomalies in the dielectric ...

The interplay between the various patterns of structural instability that are related to the electromechanical coupling in ferroelectric perovskites is discussed using results of density functional based first principles calculations. We focus on two main issues: (1) the competition between tetragonal and rhombohedral ferroelectric states in A-site driven (tolerance factor, ...

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 ...

We use state-of-the-art ab initio calculations based on the generalized gradient approximation of the density functional theory in the planar augmented wavefunction formalism to determine the elastic constants tensor of perovskite and post-perovskite with formulas AlFeO3 and FeAlO3 in which Fe or Al respectively occupy only octahedral sites, for the stable ...

It has been predicted that silicate perovskite in the lower mantle may be a significant reservoir for hydrogen in the Earth's interior, although quantitative analysis of the hydrogen storage capacity has remained elusive. This is primarily due to difficulties in interpreting FTIR spectra of perovskite samples at room pressure [eg. Murakami et al. 2002, ...

We have investigated the effect of Al3+ on the room-temperature compressibility of perovskite for stoichiometric compositions along the MgSiO3-AlO1.5 join with up to 25 mol% AlO1.5. Aluminous Mg-perovskite was synthesized from glass starting materials, and was observed to remain a stable phase in the range of ~30-100 GPa at temperatures of ~2000 to 2600 K. ...

Polycrystalline La1-xAgxMnO3 perovskite compounds (with x=0.10-0.30) have been synthesised by both the conventional solid-state reaction and the sol-gel method. While all samples with Ag concentrations up to 0.20 consist of single-phase perovskites with rhombohedral structure, unreacted Ag was found in the samples with Ag concentrations of 0.22 and higher. ...

In this investigation cubic cm-size crystals of perovskites were grown activated with divalent or tetravalent dopant cations which substitute directly without charge compensation. The fluorescence characteristics of these materials were determined. The pe...

Results of our studies on thin films of amorphous magnetic oxides are summarized in this report. The main emphasis of the program was on the preparation and magnetic characterization of amorphous BiFeO3 films substituted with nonmagnetic perovskites, zinc...

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 recognized only very ...

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 ...

Temperature dependence of the electrical resistivity of La{sub 1{minus}x}Ca{sub x}MnO{sub 3} (x = 0.2, 0.3) samples sintered at two different temperatures are compared to understand the origin of the double-maxima-type resistivity curves of some doped perovskite manganates reported in the literature. It is shown that compositional inhomogeneity is responsible for the anomalous ...

The present invention provides novel compositions that find advantageous use in making electrodes for electrochemical cells. Also provided are electrochemical devices that include active oxygen reduction electrodes, such as solid oxide fuel cells, sensors, pumps and the like. The compositions comprises a copper-substituted ferrite perovskite material. The ...

Aluminum incorporation in the rhombohedrally distorted perovskite lattice of (La0.5Sr0.5)1?xFe1?yAlyO3?? (x=0 0.05, y=0 0.30) decreases the unit cell volume and partial ionic and p-type electronic conductivities, while the oxygen nonstoichiometry and thermal expansion at 900 1200 K increase on doping. The creation of A-site cation vacancies has an opposite effect on the ...

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 ...

(Mg,Fe)SiO3 perovskite is thought to be the most abundant phases in the Earth�s lower mantle. The perovskite phase transforms into a denser phase, the post-perovskite, at the P-T conditions of the D�� layer. Mineral physical studies on these phases are therefore of significant importance in investigating structure and dynamics of ...

DC magnetization measurements have been made on two systems with 30 atomic% and 50 atomic% substitutions of Bi for La in the perovskite LaMn0.8Co0.2O3. At 50 atomic% substitution the system switches over from hexagonal to orthorhombic structure. The two systems are ferromagnetic and the Curie temperature decreasing with increasing ...

LaMnO(3)-based perovskites are used as cathode materials in solid oxide fuel cells (SOFC). A major aspect for their applicability is their chemical inertness in connection with the electrolyte material YSZ (Zr(0.85)Y(0.15)O(1.93)) against zirconate formations. Perovskites with the composition La(y-x)(Sr, Ca)(x)Mn(1-u)Co(u)O(3) (y = 1.0 and 0.95; x = 0- 0.2 ...

It is known that aluminous silicate perovskite, the major mineral of Earth's lower mantle, can accommodate significant amounts of ferric Fe. We have performed multianvil experiments to determine the influence of oxygen fugacity and temperature on ferric iron solubility in aluminous perovskite. High-pressure melting and sub-solidus experiments were ...

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

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 ...

Upconversion photoluminescence (PL) of Er(3+)-doped BaTiO3 (BTO) with perovskite ABO3 structure is studied in terms of Er3+ substitutions for Ba (A-) and Ti (B-site) with different Er3+ doping concentrations. PL quenching with an increase Er3+ doping concentration is investigated based on the structural change and energy transfer of cross-relaxation ...

the substitution of the lower valent copper for titanium was an attempt to increase the copper oxidation state-axis, while a minor decrease in the a-axis is observed. Replacement of barium and titanium by lanthanum for barium, and simultaneous replacement of lanthanum for barium and copper for titanium. However, both

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 natural orthopyroxenes, ...

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 ...

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 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 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 ...

It is suggested that the high-transition temperatures (Tc's) observed in the superconducting oxygen-deficient perovskites may be a consequence of highly anharmonic potentials. Evidence is cited which demonstrates that the harmonic approximation fails badly for Cu2+ ions in a ligand field with octahedral symmetry. Since Barden-Cooper-Schrieffer Theory and its strong-coupling ...

It is suggested that the high-transition temperatures (T/sub c/'s) observed in the superconducting oxygen-deficient perovskites may be a consequence of highly anharmonic potentials. Evidence is cited which demonstrates that the harmonic approximation fails badly for Cu/sup 2+/ ions in a ligand field with octahedral symmetry. Since Barden-Cooper-Schrieffer Theory and ...

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 ...

Perovskites in the system SrO-TiO{sub 2}-Fe{sub 2}O{sub 3} can be good candidates for electrochemical applications, and the properties of sintered, fully dense bodies depend on the Fe to Ti stoichiometry and the prevailing temperature and oxygen partial pressure. Conductivity studies normally require that the oxides with the desired stoichiometry and structure be synthesized. ...

We have determined the partitioning of a wide range of trace elements between silicate melts and CaSiO3 and MgSiO3 perovskites using both laser ablation-ICPMS and ion microprobe techniques. Our results show that, with the exception of Sc, Zr, and Hf, all trace elements we considered are incompatible in MgSiO3 perovskite, from highly incompatible for U, Th, ...

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.

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 ...

Perovskite-structured MgSiO3 dominates the mineralogy of Earth's lower mantle. As a result, the physical properties and phase transitions of this mineral are key to understanding anomalous seismic observations of the mantle's lowermost 150-300 km---the D'' region. Recent literature suggests a post-perovskite phase of MgSiO3, experimentally observed at ...

A series of bulk and Al(2)O(3)-supported perovskite oxides of the type LaMn(1-x-y)Fe(x)Mo(y)O(3) (x = 0.00-0.90 and y = 0.00-0.09) were synthesized by the citric acid complexation-gelation method followed by annealing in air at 800 degrees C. For all samples, the local environment and the chemical state and concentration of surface species were determined. M�ssbauer spectra ...

By means of static ab-initio computations we investigate the influence of Al on the recently discovered perovskite to post-perovskite phase transition in MgSiO3. We examine three substitution mechanisms for Al in the two structures: MgSi -> AlAl; SiSiO -> AlAl? and Si -> AlH. The substitutions introducing ...

Perovskite catalysts in the LaMnO/sub 3/ family have been produced with A site substitutions of Sr, Pb, K and Ce, and with B site substitutions of Ni, Co, Li and Mg from nitrate solutions by freeze drying, spray drying and precipitation. Freeze drying in some cases gave a single phase perovskite at a lower ...

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 ...

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 partial substitution for lanthanum in LaFeO3 perovskite with calcium, a cation with lower oxidation state, causes an electronic unbalance. The X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results suggest that, consequently, the elevation of the iron oxidation state to Fe(IV) occurs. The M�ssbauer spectroscopy studies confirm the ...

Since the discovery of the perovskite to post-perovskite transition in MgSiO3 in a laser-heated DAC, wide attention has been focussed on the post-perovskite phase of MgSiO3. This is because the post-perovskite phase is likely to play a key role in Earth�s lowermost mantle, and because the ...

Cobalt oxide materials have recently shown promise for use in thermoelectric applications due to enhancement of the Seebeck coefficient (S) by the spin and orbital degeneracy of the Co^3+ and Co^4+ ions. We have studied Sr substituted RCoO3 (R = rare earth elements) perovskites that exhibit increased transition temperatures to the low-spin ground state, ...

In the present paper, we study the effect of element substitution for quarter-filled nanoclusters of perovskite manganite by introducing Jahn-Teller type of perturbation interaction to the double-exchange Hamiltonian. Using the unrestricted real-space Hartree-Fock approximation method we find that, the Jahn-Teller electron-phonon interaction plays the ...

The recent discovery that perovskite-type crystal structures composed of La-Cu oxides substituted with small amounts of alkaline earth cations have exceptionally high superconducting critical temperatures has stimulated much interest in these potentially important materials. The most promising material reported thus far in the literature is La/sub ...

The fundamental phenomena underlying the electrical conduction properties of Sr-containing LaAlO3 perovskites are studied through DFT simulations. The most energetically favourable substitution sites for Sr in the LaAlO3 lattice and the energetic barriers for oxygen diffusion were calculated. Ab initio molecular dynamics was used to investigate the onset ...

The fundamental phenomena underlying the electrical conduction properties of Sr-containing LaAlO(3) perovskites are studied through DFT simulations. The most energetically favourable substitution sites for Sr in the LaAlO(3) lattice and the energetic barriers for oxygen diffusion were calculated. Ab initio molecular dynamics was used to investigate the ...

The destruction of the ferromagnetism of alloyed SrRuO(3) can be caused by electron localization at the substitution sites. Among all the non-magnetic cations that enter the B site, Zr(4+) is the least disruptive to conductivity and ferromagnetism. This is because Zr(4+) does not cause any charge disorder, and its empty d electron states which are poorly matched in energy with ...

The destruction of the ferromagnetism of alloyed SrRuO3 can be caused by electron localization at the substitution sites. Among all the non-magnetic cations that enter the B site, Zr4 + is the least disruptive to conductivity and ferromagnetism. This is because Zr4 + does not cause any charge disorder, and its empty d electron states which are poorly matched in energy with ...

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 investigated. The compounds investigated include NaLaMgWO{sub 6}, ...

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 ...

Magnetite single crystals with Al, Ga and Ti substitutions were measured by means of 57Fe nuclear magnetic resonance (NMR) technique. Satellite structure of NMR spectra well above the Verwey temperature was detected and analyzed to obtain information on the distribution of substituting cations on iron sublattices. It was confirmed that Al and Ti enter iron ...

Two polycrystalline-, Fe-bearing MgSiO3 enstatite and perovskite have been probed by x-ray absorption near edge structure (XANES) spectroscopy at the Fe K-edge under ambient conditions. The perovskite sample was synthesized at 260 kbar and 1973 K in a multianvil apparatus. The experimental XANES spectrum has been compared to ab-initio-, x-ray ...

Oxides of the (Ba{sub 1{minus}x}Sr{sub x})NbO{sub 3} system (x = 0, 0.1, 0.4, 0.5, 0.7, and 1.0) have been synthesized by a solid-state reaction technique with zirconium metal. The oxides with x = 0, 0.1, 0.5, 0.7, and 1.0 present a simple cubic perovskite structure while a distorted perovskite is observed in the oxide with x = 0.4. Infrared spectra showed ...

Natural pyroxene and garnet starting material are used to study the effects of joint Fe and Al substitution into MgSiO3 perovskite at approxmiately 50 GPa. Garnet is found to coexist with perovskite in samples containing both Fe and Al to pressures occurring deep into the lower mantel (approximately 1200 km depth). The volume of the ...

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 owing to local structural distortions and ...

The garnet-perovskite transition is studied in this work with magnetic disaccommodation on polycrystalline Nd doped YIG samples Y3-xNdxFe5O12 (0 < x < 2.5). A very different behaviour with the sintering atmosphere is observed. The results of magnetic disaccommodation for samples sintered in air reveal that the low temperature peak of YIG at 120 K disappear and another ...

The structural and electronic properties of both inorganic and hybrid organic-inorganic perovskites based on tin halides are investigated from the first principles. In particular, we contrast the inorganic CsSnCl3 and CsSnI3 to their hybrid counterparts (CH3NH3)SnCl3 , (CH3NH3)SnI3 , and (NH2CH=NH2)SnI3 , which were obtained by substituting the ...

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 ...

A-site isovalent substitutions trigger ferroelectric transitions in Pb0.7(1-x)A0.7xLa0.2TiO3, where A=Ca, Sr, or Ba. The transitions are dependent on the type and amount of substitutions such as Ca2+, Sr2+, and Ba2+. A transition from normal ferroelectric (FE) to relaxor FE (RFE) is induced by Ca2+, Ba2+, and Sr2+ ...

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

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 ...

Atomistic computer simulation techniques based on energy minimization procedures are utilized for the structural investigation of perovskite-type SmCoO(3). A reliable potential model is derived which reproduces both cubic as well as orthorhombic phases of SmCoO(3). We observe a negative chemical pressure induced structural phase transformation from distorted ...

Mixed perovskite-like oxides based on strontium cobaltate exhibit high oxygen conductivity superimposed over the much higher electronic conductivity and are, therefore, promising materials for producing different high-temperature electrochemical devices. The maximum oxygen conductivity was found in SrCo{sub 1-x}Fe{sub x}O{sub 3-{delta}} solid solutions with x = 0.2-0.3. The ...

Polyadenylation of Rous sarcoma virus (RSV) RNA is inefficient, as approximately 15% of RSV RNAs represent read-through transcripts that use a downstream cellular polyadenylation site (poly(A) site). Read-through transcription has implications for the virus and the host since it is associated with oncogene capture and tumor induction. To explore the basis ...

Polyadenylation of Rous sarcoma virus (RSV) RNA is inefficient, as approximately 15% of RSV RNAs represent read-through transcripts that use a downstream cellular polyadenylation site (poly(A) site). Read-through transcription has implications for the virus and the host since it is associated with oncogene capture and tumor induction. To explore the basis ...

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

Nickel and iron substituted LaCoO{sub 3} with rhombohedrally distorted perovskite structure were obtained in the temperature range of 600-900 deg. C by thermal decomposition of freeze-dried citrates and by the Pechini method. The crystal structure, morphology and defective structure of LaCo{sub 1-x}Ni{sub x}O{sub 3} and LaCo{sub 1-x}Fe{sub x}O{sub 3} were ...

New ferroelectric ceramics of ABO3 perovskite type were synthesized in the Ba1-x (Sm0.5Na0.5)x TiO3 system by solid state reaction technique. The effect of the replacement of barium by samarium and sodium in the A cationic site on structural and physical properties was investigated. These compounds crystallize with tetragonal or cubic symmetry. The material is classical ...

We use first-principles density-functional-theory calculations to investigate the ground state structures of Ba(Ti1?xCex)O3 solid solutions containing Pd. Previous studies have shown that the properties of BaTiO3 , a Pb-free ferroelectric ABO3 perovskite, can be tailored via B -site substitution. In the present study, we ...

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 ...

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 displacements Q that ...

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 ...

Thin films of zirconium-substituted barium titanate were deposited by chemical solution deposition on platinum-coated silicon substrates at a temperature of 700 �C. The films showed a polycrystalline perovskite structure. The grain size was found to decrease with increase of Zr substitution. The effect of Zr ...

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 ...

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 ...

Cation-exchangeable d(0) layered perovskites are amenable to intercalation, exfoliation, and a variety of topochemical reactions, but they lack the interesting electronic and magnetic functionalities of mixed-valent perovskites. Conversely, electronically and magnetically interesting layered perovskites lack scope in terms of ...

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 ...

Polycrystalline perovskite cobalt oxides Sr{sub 1-x}R{sub x}CoO{sub 3} (R=Y and Ho; 0=<x=<1) were prepared by high-pressure/high-temperature technique. X-ray powder patterns of the Y-system indicated cubic perovskite form for 0=<x=<0.5, and orthorhombic perovskite form for x=0.8 and 1.0, while coexisting of ...

Redox properties of high-surface-area LaM1-xCuxO3 (M=Mn or Co) perovskites prepared by the citrate method were studied by H2 TPR and O2 TPD techniques. We have found that the reduction of Mn4+ occurs in all La-Mn-Cu perovskites at temperatures lower than that of Co3+ in La-Co-Cu samples. The presence of copper affects the reduction of both Mn4+ and Co3+, ...

Perovskite solid solutions xBiInO3-(1 - x)PbTiO3, (BI-PT), xBiLaO3-(1 - x)PbTiO3 (BL-PT), and complex xBi(B', B")O3-(1 - x)PbTiO3 (where B' and B" refer to 3+ cations) were fabricated using conventional ceramic processing. The extent of Bi(B')/(B'B")O3 substitution in the perovskite system and the corresponding shifts in the ...

We combine the results of magnetic and transport measurements with neutron-diffraction data to construct the structural and magnetic phase diagram of the entire family of SrMn{sub 1-x}Ru{sub x}O{sub 3} (0 {le} x {le} 1) perovskites. We have found antiferromagnetic (AF) ordering of the C type for lightly Ru-substituted materials (0.06 {le} x {le} 0.5) in a ...

We combine the results of magnetic and transport measurements with neutron-diffraction data to construct the structural and magnetic phase diagram of the entire family of SrMn1?xRuxO3 (0?x?1) perovskites. We have found antiferromagnetic (AF) ordering of the C type for lightly Ru-substituted materials (0.06?x?0.5) in a similar manner to RySr1?yMnO3 ...

Structural phase transitions from orthorhombic (O, Pbnm) to tetragonal (T, P4/mbm) to cubic (C, Pm3m) and an increase in unit cell volume are confirmed as potassium is substituted for Na in Neighborite (NaMgF3). Substitution of the 19% larger potassium ion for sodium in the A-site of the perovskite structure decreases tilting of MgF6 ...

Recent experiments indicate that aluminum, which is believed to comprise only a few weight percent of the Earth's mantle, may play an important role in the properties of the most abundant mantle mineral, (Mg,Fe)SiO3 perovskite. In particular, aluminum may aid in the incorporation of ferric iron into perovskite, thus affecting the partitioning of iron among ...

In this work we report the structure and magnetic properties of a series of single-phase indium-substituted yttrium iron garnet (In-YIG) nanoparticles with nominal composition of Y3InxFe5?xO12 (x=0.1, 0.2, 0.3 and 0.4) prepared by conventional mixed oxide route. Based on XRD results, the lattice parameters of the samples increased with increase in In3+ content due to its ...

The incorporation of water into nominally anhydrous silicates is associated with mechanical weakening and lowered melting points such that small amounts of water in mantle minerals can serve to alter planetary dynamics. The effects of minor phases have been largely neglected, yet CaSiO3-perovskite, which may contain a large vacancy population, could serve as a repository for ...

We have studied the effect of Cr substitution for Fe in Sr2Fe1?xCrxMoO6 (x?0.3) double perovskites. X-ray diffraction, neutron powder diffraction (NPD), magnetisation measurements as well as Mossbauer spectroscopy have been used to determine the structural and magnetic properties of these compounds. All these materials were found to crystallise with ...

We use an effective classical spin model, which we have recently derived and validated, to examine the effect of disorder on the magnetic properties of double perovskites like Sr2FeMoO6 (SFMO). We compute the effects of excess Fe, excess Mo, and anti-site disorder on the magnetization M(T) and the ferromagnetic transition temperature Tc, and show that our results are ...

Perovskite-type compounds (ABO3) of (Ca,Sr)TiO3 doped with trivalent europium (Eu3+) were synthesized by sonochemical techniques. Powder X-ray diffraction measurement on (Ca,Sr)TiO3 were used to identify the perovskite crystal structure. The photoluminescence property in (Ca,Sr)TiO3 with europium substitution several atoms in the host ...

Sintering shrinkage curves and phase changes were compared for calcium-substituted lanthanum chromates with either slight Asite enrichment or depletion. Of the former type, La[sub 0.7]Ca[sub 0.31],CrO[sub 3] that was synthesized by the glycine-nitrate method sintered to high density in air at 1250C, exhibiting two rapid-shrinkage events. Weight loss measurements corroborated ...

Sintering shrinkage curves and phase changes were compared for calcium-substituted lanthanum chromates with either slight Asite enrichment or depletion. Of the former type, La{sub 0.7}Ca{sub 0.31},CrO{sub 3} that was synthesized by the glycine-nitrate method sintered to high density in air at 1250C, exhibiting two rapid-shrinkage events. Weight loss measurements corroborated ...

Crystallographic study of compounds with the formula Ba/sub 3/Fe/sub 2 - x/Lu/sub x/UO/sub 9/ (0 less than or equal to x less than or equal to 1.2) shows that they are cubic ordered perovskite-type compounds with probable space group Fm3m. Lutetium is equally distributed between the site of coordination 12 (8c) and the site 4b. On the magnetic point of view, these compounds ...

High-resolution x-ray diffraction data were collected from 10 to 433K on a homogeneous polycrystalline specimen of Mg{sub 0.9}Fe{sub 0.1}SiO{sub 3}-perovskite. Rietveld structural refinement and x-ray absorption fluorescence measurements demonstrate that Fe substitutes for Mg and not Si. The thermal expansion behavior is anisotropic, with the orthorhombic ...

A new perovskite-related compound, Y{sub 2}Ba{sub 3}Cu{sub 3}Co{sub 2}O{sub 12}, has been synthesized by solid state reaction. Its structure is tetragonal with a = 3.878(2) {angstrom} and c = 19.193(8) {angstrom}; XRD and HREM investigations indicate that it consists of a regular intergrowth of YBa{sub 2}(Cu, Co){sub 3}O{sub 7} and YBa(Cu, Co){sub 2}O{sub 5}. Possible ...

... 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 ...

In this work, we studied the effect of heterovalent Ca, Sr, Pb, and Ba substitution on the crystal structure, dielectric, local ferroelectric, and magnetic properties of the BiFeO3 multiferroic perovskite. Ceramic solid solutions with the general formula Bi0.7A0.3FeO3 (A is a doping element) were prepared and characterized by x-ray diffraction, dielectric, ...

Perovskite oxides have attracted considerable attention in the area of thermoelectrics owing to the advantages of their isotropic crystal structure and straightforward control of their electrical properties. Among the many perovskites, different types of polycrystalline Ca1- x R x MnO3 (R: Pr, Nd, Sm) were prepared by solid-state reaction in this study. ...

The high cost and poor thermal durability of current lean nitrogen oxides (NOx) aftertreatment catalysts are two of the major barriers to widespread adoption of highly fuel-efficient diesel engines. We demonstrated the use of strontium-doped perovskite oxides as efficient platinum substitutes in diesel oxidation (DOC) and lean NOx trap (LNT) catalysts. The ...

A new perovskite, Na[Cu(2.5)Ti(0.5)]Ti4O12, has been synthesized using a conventional solid-state technique. Neutron and synchrotron X-ray powder diffraction studies in combination with density measurements and bond-valence calculations have revealed that the material crystallizes in the cubic Im space group (a = 7.38472(2) A, Z = 2) with the square-plane site accommodating ...

Single-phase samples of (Lu1?xCax)MnO3 of the orthorhombic perovskite structure have been realized through solid-state synthesis under high pressures for the Ca contents 0?x?0.3 and at ambient pressure for x=0.5. The samples were characterized for basic structural, magnetic and transport properties with respect to x. With increasing x, Mn is gradually oxidized and the ...

The high ability of the Al-rich CaSiO3 perovskite to contain large amounts of uranium (up to 4 at.% U) has been studied up to 54 GPa and 2400 K, using laser-heated diamond anvil cell (LH-DAC) and up to 18 GPa and 2200 K using a multi-anvil press (MAP). Both latter HP-HT techniques proved to be complementary and gave similar results, in spite of different heating modes (laser ...

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 ...

The Earth's internal activity shows off through, among others, earthquakes, volcanic eruptions and continental drifts. These events are energetically related to the heat flux at the Earth surface (44 TW). About half of this heat flux comes from the radioactive decay of uranium, thorium and potassium, with 9 TW accounting for U alone. Uranium is expected to be mainly present in the mantle and it is ...

A new series of complex perovskite-type compounds La{sub 1{minus}x}Sr{sub x}Cr{sub 1{minus}x}Ti{sub x}O{sub 3} involving substitutions at both A and B sites was prepared by the ceramic technique (final heating at 1350 C). X-ray powder diffraction and profile-refinement study of this series show it to comprise orthorhombic perovskites ...

We carried out the partial substitution of the B-site in BaFeO{sub 3-{delta}}perovskite with divalent cations to develop novel oxygen-permeable materials. We demonstrated that the partial substitution of Cu or Ni by more than 10% resulted in the stabilization of the cubic perovskite structure even at room ...

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 ...

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 ...

The double perovskites Sr2FeMO6 (M=Re,Mo) belong to the important class of half-metallic magnetic materials. In this study we explore the effect of replacing the electronic 5d buffer element Re with variable valency by the main group element Sb with fixed valency. X-ray diffraction reveals Sr2FeRe1?xSbxO6 (0

While commonly accepted mineralogical models of the Earth's lower mantle consist of the three phases: (Mg,Fe)SiO3 perovskite, (Mg,Fe)O (magensiow�stite), and CaSiO3 perovskite, little is known about how the minor and rare gas elements fit in. The role of aluminum in MgSiO3 perovskite has received much notice recently. As a trivalent ...

Two different cobaltites, LaCoO{sub 3} and La{sub 0.5}Sr{sub 0.5}CoO{sub 3-{delta}}, have been prepared and characterized by means of high energy Co K-edge and low energy O K-edge X-ray absorption spectroscopy (XAS). The partial substitution of La(III) by Sr(II) species induces important changes in the reactivity and electronic state of the perovskite, ...

Solid mixed-conducting electrolytes in the series La{sub l-x}A{sub x}Co{sub l-y}Fe{sub y}O{sub 3-{delta}} (A = Sr,Ca,Ba) are potentially useful as passive membranes to separate high purity oxygen from air and as cathodes in fuel cells. All of the compositions studied exhibited very high electrical conductivities. At lower temperatures, conductivities increased with increasing temperature, ...

Solid mixed-conducting electrolytes in the series La(1-x)A(x)Co(1-y)Fe(y)O(3-delta) (A = Sr,Ca,Ba) are potentially useful as passive membranes to separate high purity oxygen from air and as cathodes in fuel cells. All of the compositions studied exhibited very high electrical conductivities. At lower temperatures, conductivities increased with increasing temperature, characterized by activation ...

Perturbed angular correlation (PAC) measurements have been carried out in the antiferromagnetic GdCrO3 perovskite oxide using 111In (111Cd) and 181Hf(181Ta) nuclear probes. The radioactive parent nuclei 111In and 181Hf were introduced in the compound through a chemical process during sample preparation. The PAC measurements were carried out in the temperature range 20-300 K. ...

The dielectric properties of Ba(Zr0.25Ti0.75)O3+xY 2O3 ceramics are investigated. We believe that, integrating with the lattice parameters, there is an alternation of substitution preference of yttrium ions for the host cations in perovskite lattice that is responsible for the Curie point. The Tc rises with the increase of Y 3+ doping when the doping ...

... 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. ...

The effects of Ga substitution on the Co-site on the high-temperature thermoelectric properties and microstructure are investigated for the misfitlayered Ca3Co4O9 and the complex perovskite-related Sr3RECo4O10.5 (RE = rare earth) cobalt-based oxides. For both systems, substitution of Ga for Co results in a simultaneous increase in the ...

We have investigated the substitution effect of pentavalent bismuth ions on the electronic structure and physicochemical properties of barium indium tantalate. X-ray diffraction, X-ray absorption spectroscopic, and energy dispersive spectroscopic microprobe analyses reveal that, under oxygen atmosphere of 1 atm, pentavalent Bi ions are successfully stabilized in the octahedral ...

This paper reviews existing data on the thermal conductivity of high-T, superconductors. Included are discussions of pristine polycrystalline high-Tc ceramics, single crystal specimens, and high-Tc, materials structurally modified by(c) substitution or by radiation damage. The thermal conductivity of high-Tc super-conductors is compared with that of conventional ...

Perovskites are important materials in a number of important technological applications, including solid oxide fuel cells, catalysis, and giant magneto-resistance materials. For many of these purposes, a mixture of B-cations can be used to tune the desired properties, e.g., oxygen reduction, ionic conductivity. For a solid oxide fuel cell, two particular ceramic components are ...

The results suggest that garnet phosphors can be engineered to function thermographically over desired temperature ranges by adjusting gallium content. Substituting gadolinium for the yttrium in the host matrix also has an effect but it is not as large. A silicate phosphor showed the greatest temperature dependence though it could not be excited to fluoresce by a blue LED. All ...

The isomer ratio in the mono-nitration of toluene and catalysis, when - of phenylacetylene, indicate that the rate coefffeient for at the rate of rupture of the carbon tritium bond. (auth) >s)O/sup 3/ were prepared tions the cubic ordered perovskite type. The compounds with manganese and iron are magnetic. Substitution of strontium and ...

Certain ceramic compounds such as rare-earth perovskites and transition-metal diborides that exhibit metallic conductivity are readily available or can be easily synthesized. Some are stable in air firing temperatures typical of hybrid-circuit processing. The work described is part of an exploratory program to determine whether these materials can be used as low-cost ...

Certain ceramic compounds such as rare-earth perovskites and transition-metal diborides that exhibit metallic conductivity are readily available or can be easily synthesized. Some are stable in air firing temperatures typical of hybrid-circuit processing. The work described is part of an exploratory program to determine whether these materials can be used as low-cost ...

First-principles supercell calculations are used to investigate the lattice distortions in BaZrO3 heavily codoped with K and La. We find that nonferroelectric BaZrO3 can be made ferroelectric in this way. The ferroelectricity is the result of La off-centerings and can be understood using ionic size considerations. In particular, size disorder on the perovskite A site ...

(Ca x ,Sr1? x )ZrO3 and Ca(Sn y ,Zr1- y )O3 solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO3 perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that ...

(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 ...

Perovskite oxides with higher phase transition temperature receive much attention as promising candidates which possess excellent and stable dielectric properties over wide temperature range. In the present research, dense ceramics of Ba-based perovskite oxides of Ba(Cu1/3Nb2/3)O3 (BCN) were fabricated by powder sintering. ...

High-pressure melting experiments were performed at ~26 GPa and ~2,200-2,400�C on synthetic peridotite compositions with varying FeO and Al2O3 contents and on a synthetic CI chondrite analogue composition. Peridotite liquids show a crystallisation sequence of ferropericlase (Fp) followed down temperature by Mg-silicate perovskite (MgPv) + Fp, which contrasts a sequence of ...

Two different cobaltites, LaCoO3 and La0.5Sr0.5CoO3??, have been prepared and characterized by means of high energy Co K-edge and low energy O K-edge X-ray absorption spectroscopy (XAS). Even though half of the La(III) is substituted by Sr(II), little or no changes can be detected in the formal oxidation state of cobalt atoms. The presence of strontium cations induces two main ...

The structural and magnetic properties of the complex metal oxides Pb(Mn{sub 1/2}Nb{sub 1/2})O{sub 3} (PMNO) and Pb(Mn{sub 1/4}Fe{sub 1/4}Nb{sub 1/2})O{sub 3} (PMFNO), which belong to a class of disordered perovskites have been studied. The magnetic susceptibilities of PMNO showed hysteresis between field cooled and zero-field cooled conditions below the transition of 15 K, ...

The influence of cation substitution on the magnetic properties of single and polycrystals of FeCr2S4 spinel has been studied. The tetrahedral A-site substitution of the Fe by Cu in Fe1?xCuxCr2S4 was found to increase significantly the value of temperature Tm of the spin-glass like magnetization anomaly, whereas the octahedral B-site ...

The effects of aluminum substitution into the M-type Ba-hexaferrites on the saturation magnetization and Mossbauer spectrum of these ferrites are studied. The saturation magnetization M{sub s} of the BaFe{sub 12{minus}x}Al{sub x}O{sub 12} is seen to decrease linearly with increasing Al substitution. The Mossbauer spectrums for the x = 0.1, 0.2 and 0.6 ...

An investigation of phase transitions in dipole like B-site substituted perovskites is reported. Several doped Barium Titanite materials were examined over a temperature range of 173 k to1200 K. Their structural changes were examined by X-Ray diffraction as a function of temperature. Several phase transitions of the doped Barium Titanate have noted and ...

Bismuth titanates with La-substituted (Bi(3.25)La(0.75)Ti(3)O(12), BLT) nanofibers were synthesized by sol-gel based electrospinning. Pure phase perovskite structure BLT nanofibers could be obtained by annealing at 700 degrees C in air for 1 h. The morphology, crystallized phase and crystal structure were investigated by means of scanning electron ...

The effect of dopants on the superconductivity of YBa2Cu3O7 ceramics was investigated, comparing the effects of SrTiO3 and 17 different oxide dopants (namely, Ca, Sc, La, and Zr with possible substitution in the yttrium sites; K, Sr, and Pb in the barium sites; and Li, Mg, Fe, Co, Ni, Zn, Al, Ti, Nb, and Si in the copper sites). The results showed that these dopants can be ...

We present a computationally efficient semi-empirical method, based on standard first-principles techniques and the so-called virtual crystal approximation, for determining the average atomic structure of crystals with substitutional disorder. We show that, making use of a minimal amount of experimental information, it is possible to define convenient figures of merit that ...

Hyperfine parameters on 57Fe, 119Sn and 111Cd substituted into the Mn sublattice were measured by M�ssbauer and PAC spectroscopies. From these results it is tentatively concluded that C15 and C14 HoMn2 are mixed-phase compounds. In C14 HoMn2 there is no (or small) moment on the 2a site.

Selected perovskite solid electrolytes incorporated into research size fuel cells have shown stability for > 4000 hours at 600(degrees)C. Perovskite lattice requirements which favor low E(sub a) for ionic conduction include (i) that the perovskite lattice...

The thermoelectric properties and crystallographic features of layered perovskite-type Ca-substituted (Sr1-xCax)3(Ti1-yNby)2O7 (y=0-0.2), Ruddlesden-Popper phases were investigated. The influence of crystal structure and carrier concentration on the carrier effective mass for Ti-based metal oxides based on TiO6 octahedra and having a significant Ca ...

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 [A2+2(1+x)/3La (1-2x)/3][Li1/3(Nb,Ta1-xWx)2/3 ...

The thermodynamic mixing functions of MgSiO3-Al2O3 solid solutions in perovskite and ilmenite structures were modeled based on the results of ab initio calculations applied to a set of supercell structures containing 64 and 48 exchangeable sites, respectively. The sampled structures were constructed from the supercells of the end-members MgSiO3 perovskite ...

We report the synthesis of SrMn{sub 1-x}Ga{sub x}O{sub 3-{delta}} perovskite compounds and describe the dependence of their phase stability and structural and physical properties over extended cation and oxygen composition ranges. Using special synthesis techniques derived from thermogravimetric measurements, we have extended the solubility limit of random ...

This goal of this research project was to determine the solid solubility of Pu, U, Gd, and Hf in candidate ceramics for immobilization of high-level nuclear waste. The experimental approach was to saturate each phase by adding more than the solid solubility limit of the given cation, using a nominated substitution scheme, and then analyzing the candidate phase that formed to ...

Structural characterization and electronic properties of the LaNi{sub 0.95}M{sub 0.05}O{sub 3} (M = Mo, W, Sb, Ti, Cu, Zn) perovskite-like system are reported. These compounds can be regarded as being derived from LaNiO{sub 3} by partial substitution of Ni{sup 3+} in this material by M{sup 6+}, M{sup 5+}, M{sup 4+}, or M{sup 2+} formal cations, with a ...

The compression behavior of various (Al,Fe)-MgSiO3 perovskites was investigated by powder X-ray diffraction up to 70 GPa on the ID30 beamline of ESRF (Grenoble). We used diamond anvil cell coupled with CO2 laser-heating, a most powerful technique to relax stresses and perform reliable equation of state up to typical lower mantle pressures. In contrast to Fe which essentially ...

Strategies for the design of an improved oxide -ion electrolyte for medium-temperature fuel cells, sensors, and oxygen pumps are outlined. Anion-deficient oxides with the perovskite structure were chosen for study. Stoichiometric oxides contain a high fraction of vacancies, but vacancy ordering suppresses ionic conductivity. Nevertheless, the brownmillerite rm Ba_2In_2O _5 ...

... Descriptors : *PEROVSKITES, *RADIOACTIVE WASTES, *WASTE DISPOSAL, *CHEMICAL ATTACK(DEGRADATION), *DISSOLVING, SILICON ...

... Descriptors : *PEROVSKITES, *PRECIPITATES, *TITANIUM COMPOUNDS, ATTACK, UNITED KINGDOM, LAYERS, RADIOACTIVE WASTES ...

... Accession Number : AD0846664. Title : Single Crystal Perovskites as Electrooptically Active Materials. Descriptive Note ...

The investigation of the perovskites and the related ilmenites, olivines and ..... is a displacive ferroelectric similar to the perovskites. ...

... 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 ...

... Title : MOSSBAUER STUDIES ON IRON IN THE PEROVSKITES LA1-XSR- XFEO3 (0< OR = X< OR = 1). CONDITION FOR MAXIMUM ...

... These will be accomplished in eight project tasks: fabrication of simple perovskites; fabrication of mixed perovskites; fabrication of duplex structures ...

... Accession Number : ADD116807. Title : Evaluation of Selected Spinels and Perovskites as Candidate High-Temperature Molybdenum Coatings,. ...

... Abstract : The dielectric properties of perovskites have been the subject of many investigations, but a direct correlation between the dielectric ...

"amorphous citrate" process for preparing perovskites and other oxides ... The citrate method was used to prepare these perovskites. Unfortunately ...