Showing papers on "Perovskite (structure) published in 1997"
TL;DR: The use of chemical solution deposition for the fabrication of perovskite thin films is reviewed in this paper, where a variety of approaches including sol−gel, chelate, and metalloorganic decomposition have all been employed with success in the preparation of these materials.
Abstract: The use of chemical solution deposition for the fabrication of perovskite thin films is reviewed. A variety of approaches including sol−gel, chelate, and metalloorganic decomposition have all been employed with success in the preparation of these materials. For a number of perovskite compounds, thin-film properties that equal those of the bulk materials have been obtained. Various aspects of the solution chemistries for the three different routes are discussed, and the effects of solution precursor properties on the conversion of the as-deposited film to the desired perovskite phase are discussed. The roles that thermodynamic and kinetic factors have on this transformation process are also reviewed. Finally, some of the applications for solution-derived thin films currently under development are reviewed, and the inherent limitations of the deposition technique for device manufacture are considered.
499 citations
TL;DR: In this article, an insulator-to-metal transition triggered by the photocarrier injection into the charge-ordered (CO) state of a perovskite manganite crystal was observed.
Abstract: We have observed an insulator-to-metal (I-M) transition triggered by the photocarrier injection into the charge-ordered (CO) state of a perovskite manganite crystal, ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$. The photocurrent is a highly nonlinear function of applied electric field and of light intensity; both show a threshold behavior for the I-M transition. The dependence of the anomalous photocurrent on the excitation photon energy and the temperature excludes the laser heating as the cause of the effect, suggesting the photocarrier-mediated collapse of the CO state.
433 citations
TL;DR: In this paper, Bismuth sodium titanate (Bi 0.5Na0.5TiO3, BNT) with 0.6 at.% lanthanum was prepared by the conventional mixed oxide method.
Abstract: Bismuth sodium titanate (Bi0.5Na0.5TiO3, BNT) with 0–6 at.% lanthanum was prepared by the conventional mixed oxide method. Each composition was calcined at 800–900°C for 2–5 h to form a pure perovskite phase. Green pellets were sintered at 1050–1150°C for 1–4 h to obtain dense ceramics with at least 95% of theoretical density. X–ray diffraction (XRD) showed phase distortion as lanthanum was added to this system. Meanwhile, a small amount of La was found to affect the grain size and had an influence on the poling conditions and electrical properties. The BNT–based composition with 1 at.% La doping provided a dielectric constant (K) of 560, a piezoelectric charge constant (d33) of 92 pC/N, and a hydrostatic piezoelectric coefficient (dh) of 72 pC/N.
405 citations
TL;DR: In this article, the double exchange mechanism was applied to manganite perovskites to obtain the colossal magnetoresistance (CMR) effect in the vicinity of the transition temperature, where charge transport is enhanced by the magnetic alignment of neighbouring Mn ions of different valence configuration.
Abstract: Manganese oxides with a perovskite structure1 exhibit a transition between a paramagnetic insulating phase and a ferromagnetic metal phase. Associated with this transition is an effect known as colossal magnetoresistance2–5 (CMR)—in the vicinity of the transition temperature, the materials exhibit a large change in resistance in response to an applied magnetic field. Such an effect, if optimized, might find potential application in magnetic devices. But the criteria for achieving (and hence optimizing) CMR are not clear, presenting a challenge for materials scientists. The accepted description of CMR in the manganite perovskites invokes the 'double-exchange' mechanism, whereby charge transport is enhanced by the magnetic alignment of neighbouring Mn ions of different valence configuration (Mn3+ and Mn4+), and inhibited by the formation of charge-induced localized lattice distortions6,7. Here we report the existence of a large magnetoresistive effect in a class of materials—Cr-based chalcogenide spinels—that do not possess heterovalency, distortion-inducing ions, manganese, oxygen or a perovskite structure. The realization of CMR in compounds having a spinel structure should open up a vast range of materials for the further exploration and exploitation of this effect.
381 citations
TL;DR: The low-field magnetoresistance properties of polycrystalline La0.67Sr0.33MnO3 and La 0.67CaO33MnsO3 thin films with different grain sizes have been investigated and compared with epitaxial films as discussed by the authors.
Abstract: The low-field magnetoresistance (MR) properties of polycrystalline La0.67Sr0.33MnO3 and La0.67CaO33MnO3 thin films with different grain sizes have been investigated and compared with epitaxial films. MR as high as 15% has been observed in the polycrystalline films at a field of 1500 Oe at low temperatures, whereas the MR of the epitaxial films is less than 0.3% in the same field range. Based on the magnetization dependence of the MR, the current-voltage characteristics, and the temperature dependence of the resistivity, we attribute the low-field MR to spin-dependent scattering of polarized electrons at the grain boundaries which serve as pinning centers for the magnetic domain walls.
354 citations
TL;DR: In this paper, the grain-size-dependent transport properties in granular perovskite have been investigated and a resistivity formula originating from interfacial tunneling is obtained and the theoretical calculation is found to be in good agreement with the experimental results.
Abstract: The grain-size-dependent transport properties in the granular perovskite ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{MnO}}_{3}$ have been investigated. A giant magnetoresistance (GMR) effect, similar to that observed in granular transition metals, and a crystal intrinsic colossal magnetoresistance (CMR) have been simultaneously observed. With grain growth, the GMR effect gradually weakens and the intrinsic CMR effect becomes prominent in the present granular system. A resistivity formula originating from interfacial tunneling is obtained and the theoretical calculation is found to be in good agreement with our experimental results.
327 citations
TL;DR: In this paper, a series of ion exchangeable layered perovskite type oxides, A2-xLa2Ti3-xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0), were found to be highly efficient photocatalysts for overall water splitting when a small amount of Ni was loaded.
Abstract: A series of ion-exchangeable layered perovskite type oxides, A2-xLa2Ti3-xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0), were found to be highly efficient photocatalysts for overall water splitting when a small amount of Ni was loaded. These compounds are spontaneously hydrated even in an aqueous alkaline solution and decompose intercalated H2O molecules into H2 and O2 under the bandgap irradiation.
327 citations
TL;DR: The electrical properties and defect structure of selected compositions in the SrTi1−xFexO3−y system (x = 0-0.8) have been studied using van der Pauw 4-point conductivity measurements and electron energy loss spectroscopy (EELS) as mentioned in this paper.
309 citations
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TL;DR: In this article, a two-phase region separating an O'-orthorhombic phase stable over 0 ≤ δ ≤ 0.06 and a rhombohedral phase, stable in the range 0.10 − 0.13 − δ ≥ 0.18, is revealed.
290 citations
TL;DR: In this paper, it was shown that the doping of perovskite manganites with either chromium or cobalt induces an insulator to metal transition, which is exceptional since such a transition has not been observed to date in charge ordered manganite Ln 0.5 Ca 0.3 with an A-site cation of such a small size.
269 citations
TL;DR: In this article, a mixed-conducting perovskite dense membrane reactor at 850°C was used for the partial oxidation of methane to synthesis gas (syngas, CO + H2).
Abstract: The partial oxidation of methane to synthesis gas (syngas, CO + H2) was performed in a mixed-conducting perovskite dense membrane reactor at 850°C, in which oxygen was separated from air and simultaneously fed into the methane stream. Steady-state oxygen permeation rates for La1-xA′xFe0.8 Co0.2O3-δ perovskite membranes in nonreacting air/helium experiments were in the order of A′x = Ba0.8 > Ba0.6 > Ca0.6 > Sr0.6. Deep oxidation products were obtained from a La0.2 Ba0.8 Fe0.8 Co0.2 O3–δ disk-shaped membrane reactor without catalyst, with a 4.6% CH4 inlet stream. These products were further reformed to syngas when a downstream catalytic bed was added. Packing the 5% Ni/Al2O3 catalyst directly on the membrane reaction-side surface resulted in a slow fivefold increase in O2 permeation, and a fourfold increase in CH4 conversion. XRD, EDS, and SEM analyses revealed structure and composition changes on the membrane surfaces. Oxygen continuously transported from the air side appeared to stabilize the membrane interior, and the reactor was operated for up to 850 h.
TL;DR: In this paper, the authors studied the properties of perovskite manganese oxides for bolometric applications, and discussed issues related to the choice of material, the influence of deposition parameters, and postdeposition heat treatments on the relevant characteristics such as the resistivity-peak temperature (Tp) and the temperature coefficient of resistance (TCR).
Abstract: We are optimizing thin films of perovskite manganese oxides for bolometric applications. We have studied the relevant material characteristics of several members of this family namely, La0.7Ba0.3MnO3, La0.7Sr0.3MnO3, La0.7Ca0.3MnO3, and Nd0.7Sr0.3MnO3. Here, we discuss issues related to the choice of material, the influence of deposition parameters, and postdeposition heat treatments on the relevant characteristics such as the resistivity-peak temperature (Tp) and the temperature coefficient of resistance (TCR). For a given material, a higher peak temperature implies a larger temperature coefficient of resistance. In contrast, on comparing different material systems, the TCR tends to decrease as Tp increases.
TL;DR: The microwave dielectric properties of MNb2O6 compounds have been investigated as a function of M ions in this paper, and the temperature coefficient of the resonant frequency was found to correlate strongly with the M ions.
TL;DR: In this article, a photocatalyst, K2La2Ti3O10, a layered perovskite-type compound with a hydrated interlayer space, exhibited a high activity for overall water splitting with Ni-loading.
Abstract: Photocatalytic decomposition of H2O into H2 and O2 over a novel photocatalyst, K2La2Ti3O10, was accomplished. K2La2Ti3O10, a layered perovskite-type compound with a hydrated interlayer space, exhibited a high activity for overall water splitting with Ni-loading. The highest activity was obtained over Ni(3.0 wt%)–K2La2Ti3O10 when the reaction was carried out in aqueous KOH solution (0.1 M, pH=12.8). By comparison with other Ni-loaded photocatalysts reported previously, the reaction mechanism of Ni–K2La2Ti3O10 was discussed. © 1997 Elsevier Science S.A.
TL;DR: In this article, perovskite-type oxides were synthesized in the series of Ln 1− x Sr x CoO 3 (Ln = Sm, Dy) and the electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C.
TL;DR: Transport and magnetic studies indicate the following evolution of electronic properties with increasingδ, which creates small-polaron holes that become increasingly trapped at cation vacancies with decreasing temperature in the paramagnetic domain.
TL;DR: In this paper, the authors showed that both phases of Ca 2 RuO 4 are Mott-Hubbard-type gap and showed that the decrease of the 4 d band width in comparison with that of Sr 2RuO 4, caused by distortions in the RuO 2 planes, leads to a MottHubbard type gap.
Abstract: Noncuprate layered perovskite Sr 2 RuO 4 is a highly correlated metal and exhibits superconductivity below T c ≈1.35 K. We have newly synthesized related layered ruthenates Ca 2 RuO 4 in two distinct structural phases with substantially different aspect ratios c / a . Electrical and magnetic measurements show that the two phases are insulating antiferromagnets. We argue that both phases of Ca 2 RuO 4 are Mott insulators. The decrease of the 4 d band width in comparison with that of Sr 2 RuO 4 , caused by distortions in the RuO 2 planes, leads to a Mott-Hubbard-type gap.
TL;DR: In this article, the double exchange mechanism was used to obtain ferromagnetic insulator BiMnO3, which was synthesized under high pressure, and showed that the highly polarizable Bi3+ion with 6s2lone pair would cause local distortion of the perovskite lattice, which presumably reduces the mobility of carriers.
TL;DR: A structural evolution analysis of the long-range and local order and disorder of lead scandium niobate (PSN) down to 10 K, using a combination of neutron and x-ray diffraction on powder and single crystals, is reported in this paper.
Abstract: We report a structural evolution analysis of the long-range and local order and disorder of lead scandium niobate (PSN) down to 10 K, using a combination of neutron and x-ray diffraction on powder and single crystals. The structure of PSN is discussed and compared with those of simple perovskite compounds and . In PSN the existence of a long-range but still disordered ferroelectric phase, different from those of simple perovskites, is evidenced. The disorder of lead and scandium/niobium atoms on short-, medium- and long-range scales is discussed in connection with the dielectric properties of these materials.
Journal Article•
TL;DR: In this article, a systematic study of the magnetic properties of the manganites Ln0.5A 0.5MnO3 (A,A′)0.
Abstract: A systematic study of the magnetic properties of the manganites Ln0.5(A,A′)0.5MnO3 (A,A′=Ba, Ca, Sr) has been carried out. The variations of TC and TN vs two parameters, the average size of the interpolated cations 〈rA〉 and the mismatch effect represented by the variance σ2, have been studied for the series of manganites La0.5(A,A′)0.5MnO3, Pr0.5(A,A′)0.5MnO3, Nd0.5(A,A′)0.5MnO3 and Sm0.5(A,A′)0.5MnO3 (A,A′=Ba, Ca, Sr), involving at most three different cations on the perovskite A site. The results obtained for other (Ln, Ln′)0.5Sr0.5MnO3(Ln, Ln′=Gd, Sm Y, Pr) have been taken into consideration. A σ2−〈rA〉 diagram has been established, which displays the different types of magnetic behaviors that can be exhibited by Ln0.5A0.5MnO3 manganites, i.e., when the temperature is decreasing, either a paramagnetic (PM) to ferromagnetic (FM) transition, or PM to FM followed by FM to antiferromagnetic transitions, or a PM to weak ferromagnetic transition.
TL;DR: The magnetic and magnetotransport properties of perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound.
Abstract: The magnetic and magnetotransport properties of the perovskite La0.67Ca0.33Mn0.9Fe0.1O3 have been investigated, and the spin-glass behavior with a spin freezing temperature of 42 K has been well confirmed for this compound. A metal-to-insulator transition and colossal magnetoresistance have been observed near its spin freezing temperature; besides, the insulator behavior has been found to reappear at lower temperature. The formation of ferromagnetic and antiferromagnetic clusters and the competition between them with the introduction of Fe3+ ions, which do not participate in the double-exchange process, have been suggested to explain the experimental results.
TL;DR: In this paper, the synthesis and electrical characterisation over a range of oxygen partial pressures (10−20−1 atm) of the A-site deficient perovskites were reported, with a view to establishing their potential as anode materials for solid oxide fuel cells.
Abstract: This work reports the synthesis and electrical characterisation over a range of oxygen partial pressures (10–20–1 atm) of the A-site deficient perovskites Sr1–3x/2LaxTiO3–δ, with a view to establishing their potential as anode materials for solid oxide fuel cells. Single phase samples were observed for synthesis in air for 0≤x≤0.6, and the materials remained phase pure for both high and low oxygen partial pressures at the measurement temperature of 930 °C. Good electrical conductivity, which increased with increasing La content, was observed on reduction in low oxygen partial pressures, with values as high as 7 S cm–1 [ P(O2)= 10–20 atm], similar to values observed for the related system, Sr1–x/2Ti1–xNbxO3–δ, examined previously. The conductivity of the fully reduced samples showed metallic character from 100 to 930 °C. As the oxygen partial pressure was raised, the conductivity dropped, showing an approximate [P(O2)]–1/6 dependence for porous samples. New samples, Sr1–y/2–3x/2LaxTi1–yNbyO3–δ, with both La and Nb substitutions, were also studied, and these phases showed similar electrical behaviour. Further results for the Sr1–x/2Ti1–xNbxO3–δsystem are presented and compared with the La doped systems.
TL;DR: In this paper, the authors investigated oxide ion conduction in A 3+ B 3+ O 3 -type perovskites, (La 0.9 Sr 0.1 )M III O 3− δ (M III =Al, Ga, Sc, In, and Lu) taking the distortion from ''ideal'' cubic structure into consideration.
TL;DR: In this paper, the authors report on experiments that have been conducted on the tantalate relaxor, Pb(Mg1/3Ta2/3)O3(PMT), and its solid solutions with PbZrO3, in which the size of the do-mains and the degree of cation ordering have been in-creased by two orders of magnitude through annealing that has been conducted at a temperature of 1325°C.
Abstract: Extensive studies that have been conducted on the Pb(Mg1/3Nb2/3)O3 (PMN) family of relaxor ferroelectrics have led to the establishment and acceptance of the“space-charge” model as a basis for explaining their structures and dielectric properties. In this model, the arrangement of the metal cations on the octahedral sites of the perovskite structure is interpreted in terms of the formation of nega-tively charged ordered nanodomains that are dispersed in a positively charged disordered matrix. The primary experi-mental support for this interpretation has come from the apparent absence of any growth of the domains or change in the degree of ordering as the heat treatment is extended. Here, we report on experiments that have been conducted on the tantalate relaxor, Pb(Mg1/3Ta2/3)O3(PMT), and its solid solutions with PbZrO3, in which the size of the do-mains and the degree of cation ordering have been in-creased by two orders of magnitude through annealing that has been conducted at a temperature of 1325°C. Moreover, fully ordered ceramics that are comprised of large domains retain relaxor behavior. These results cannot be explained by the space-charge model and support a charge-balanced, “random-site” model for the ordering of the metal cations
TL;DR: In this article, a series of cobalt-containing perovskites LnCoO3(Ln=La, Pr, Nd, Sm, and Gd) has been studied as catalyst precursors for the partial oxidation of methane to synthesis gas.
TL;DR: High-pressure diamond-cell experiments indicate that the iron-magnesium partitioning between (Fe,Mg)SiO3-perovskite and magnesiowustite in Earth's lower mantle depends on the pressure, temperature, bulk iron/magnesium ratio, and ferric iron content.
Abstract: High-pressure diamond-cell experiments indicate that the iron-magnesium partitioning between (Fe,Mg)SiO3-perovskite and magnesiowustite in Earth's lower mantle depends on the pressure, temperature, bulk iron/magnesium ratio, and ferric iron content. The perovskite stability field expands with increasing pressure and temperature. The ferric iron component preferentially dissolves in perovskite and raises the apparent total iron content but had little effect on the partitioning of the ferrous iron. The ferrous iron depletes in perovskite at the top of the lower mantle and gradually increases at greater depth. These changes in iron-magnesium composition should affect geochemical and geophysical properties of the deep interior.
IBM1
TL;DR: The lattice constant for NH 2 CH=NH 2 SnI 3 is found to be a =6.316(1) A, which is approximately 1.2% larger than that for the isostructural compound CH 3 NH 3 SnI3 as mentioned in this paper.
TL;DR: In this article, spin-dependent perpendicular transport in the magnetic trilayer junction structure La0.67Sr0.33MnO3/SrTiO3 was reported.
Abstract: We report spin-dependent perpendicular transport in the magnetic trilayer junction structure La0.67Sr0.33MnO3/SrTiO3/La0.67Sr0.33MnO3. Large (factor of 5) changes of magnetoresistance induced by a field of ∼200 Oe are observed at 4.2 K. Junction I–V characteristics at low temperatures are consistent with a metal–insulator–metal tunneling process with a large spin-polarization factor of 0.81 for the conduction electrons. Above 100 K, a variable range-hopping conduction shunts out the magnetoresistance contribution. This second conduction channel comes from the impurity states within SrTiO3 barrier and therefore is not an intrinsic limit to the magnetoresistance performance of the device at high temperatures.
TL;DR: The perovskite quantum-well films showed strong exciton absorption at around 2.4 eV and sharp exciton emission even at room temperature, and the X ray diffraction measurement on the vacuum-deposited films demonstrated that the layer structure was oriented parallel to the film plane as discussed by the authors.
Abstract: Oriented thin films of layered perovskite compounds (RNH3)2PbI4, which possess a quantum well structure where a two-dimensional semiconductor layer of PbI4 and an organic ammonium layer of RNH3 are alternately piled up, were found to grow in a self-organizing manner on fused quartz substrates through the simple dual-source vapor deposition of organic ammonium iodide RNH3I and lead iodide PbI2. The perovskite quantum-well films showed strong exciton absorption at around 2.4 eV and sharp exciton emission even at room temperature. Further, the X ray diffraction measurement on the vacuum-deposited films demonstrated that the layer structure of the vacuum-deposited film was oriented parallel to the film plane.