Mixed Perovskite Oxides Research Articles

Local electronic and atomic structures of the mixed B-site ions in SrFe1−xMnxO3−δ studied with X-ray absorption spectroscopy

Local electronic and atomic structures of the B-site ions in perovskite SrFe[Formula: see text]Mn[Formula: see text]O[Formula: see text] were evaluated with X-ray absorption spectroscopy (XAS) at Mn, Fe [Formula: see text]- and [Formula: see text]-edges and O [Formula: see text]-edge. The energy of [Formula: see text]- and [Formula: see text]-edge peaks for Mn and Fe ions stayed unchanged against the change in Mn content [Formula: see text]. The analysis of Mn [Formula: see text]-edge extended X-ray absorption fine structure (EXAFS) revealed that Mn−O polyhedra was kept as an octahedron with Mn[Formula: see text] irrespective of the [Formula: see text] value, agreeing with the results of [Formula: see text]-edge spectra. The Fe [Formula: see text]-edge EXAFS analysis showed that the Fe–O distance decreased with decrease of the Mn contents, suggesting that the ratio of FeO5 polyhedra to FeO6 octahedra is increased due to smaller oxygen amount. By analyzing both the [Formula: see text]-edge and [Formula: see text]-edge spectra, we clarified the local electronic and atomic structural changes particularly occurred in the B-site mixed perovskite oxides.

Origin of Improved Photoelectrochemical Water Splitting in Mixed Perovskite Oxides

AbstractOwing to the versatility in their chemical and physical properties, transition metal perovskite oxides have emerged as a new category of highly efficient photocatalysts for photoelectrochemical (PEC) water splitting. Here, to understand the underlying mechanism for the enhanced PEC water splitting in mixed perovskites, ideal epitaxial thin films of the BiFeO3–SrTiO3 system are explored. The electronic structure and carrier dynamics are determined from both experiment and density‐functional theory calculations. The intrinsic phenomena are measured in this ideal system, contrasting to commonly studied polycrystalline solid solutions where extrinsic structural features obscure the intrinsic phenomena. It is determined that when SrTiO3 is added to BiFeO3 the conduction band minimum position is raised and an exponential tail of trap states from hybridized Ti 3d and Fe 3d orbitals emerges near the conduction band edge. The presence of these trap states strongly suppresses the fast electron–hole recombination and improves the photocurrent density in the visible‐light region, up to 16× at 0 VRHE compared to the pure end member compositions. This work provides a new design approach for optimizing the PEC performance in mixed perovksite oxides.

Field Effect on Displacive First-Order Transition in Relaxor Ferroelectrics

As preliminaries of a microscopic theory for displacive phase transition, the first-order transition is investigated within a phenomenological study that provides a good explanation of experimental results on the electric field dependence and pressure effect in relaxor ferroelectrics. The morphotropic phase boundary (MPB) region in mixed perovskite oxides is described in the same phase diagram corresponding to individual perovskite oxides with successive phase transitions. On the basis of the calculated field-dependent phase transitions, the origin of the MPB is examined in comparison with that in the case of BaTiO3 with the first-order displacive transition.

Conditions of Morphotropic Phase Boundary in Perovskite-Oxides

In order to search for Pb-free relaxor substances, the conditions to derive morphotropic phase boundary (MPB) are studied in perovskite-oxides. Before a microscopic theory for displacive type phase transition, the phenomenological approach is extended by combining with a first-principles computer simulation in several perovskite compounds. The MPB region in mixed perovskite-oxides is described by an anisotropy of the fourth-order term of polarizations, S, as 0 ≤ S ≤ 1.7, which is the region corresponding to individual perovskite-oxides with successive phase transitions. Basing on the present theoretical results, the definition of the MPB is discussed with explaining the pressure effect and the electric-field dependence in relaxor ferroelectrics.

Synthesis and Magnetic Properties of Double B Mixed Perovskite Series La0.75K0.25Mn1−xFexO3

Abstract A series of double B mixed perovskite oxides La0.75K0.25Mn1−xFexO3 (x = 0.2–0.5) were synthesized under mild hydrothermal conditions and characterized by powder X-ray diffraction, SEM, ICP, XPS, iodometric titration, and SQUID. All the compounds corresponded to orthorhombic structure of space group Pnma and presented a cuboid morphology. The oxidation state of Fe is +3 whereas Mn is a mixed valence of Mn3+/Mn4+. The curves M vs. T for all the compositions indicated the coexistence of ferro- and antiferromagnetic contribution.

Polypropylene HomoPolymer Oxidation in the Molten State Using Mixed Perovskite (La0.9Sr 0. 1Ni(1 - x)CrxO3)

To achieve oxidized polypropylene (OPP), polypropylene in molten state was reacted with mixed perovskite oxides (La0.9Sr 0.1Ni(1− x) CrxO3) using different concentration of oxidizing agent and varying reaction time. The modified polymer structure was then characterized using different experimental techniques such as Fourier transforming infrared (FTIR), Differential Scanning Calorimetry (DSC) and tensiometry and the melt flow index (MFI). FTIR results revealed that polar groups mainly carboxylic acids, ketones and esters have been performed in the OPP polymer structure while DSC analysis showed a decrease in the fusion temperature and an increase in glass transition temperature, compared to the original PP. In addition, solubility tests show that in contrast to the initial PP, OPP can be partially dissolved in polar solvents. Finally, it was concluded that by increasing the molar concentration of the oxidizing the agent and time of reaction, the number of polar groups increased.

“Hot Spot” Hydrocarbon Oxidation Catalysed by Doped Perovskites—Towards Cleaner Diesel Power

Spot the difference: Oxidation of propane/CO mixtures is efficiently catalysed by mixed perovskite oxides heated directly using microwave irradiation (see figure). A set of twelve catalysts is screened for activity, selectivity and stability towards SO2 poisoning. LaSrMn shows good activity, selectivity and heating capabilities, while LaSrCr is found to be superbly resistant to SO2 poisoning.

Erratum to “Calculated electronic properties of the mixed perovskite oxides: CaCu3T4O12 (T=Ti, Cr, Mn, Ru) within the DFT”

Erratum to “Calculated electronic properties of the mixed perovskite oxides: CaCu3T4O12 (T=Ti, Cr, Mn, Ru) within the DFT”

Calculated electronic properties of the mixed perovskite oxides: CaCu 3T 4O 12 (T=Ti, Cr, Mn, Ru) within the DFT

Electronic and magnetic properties of the mixed perovskites CaCu 3T 4O 12 (T=Ti, Cr, Mn, Ru) are calculated ab initio starting from the experimental crystal data. Using the self-consistent band-structure augmented spherical wave (ASW) method built within the local spin-density approximation (LSDA) to the density functional theory (DFT), calculations of the density-of-states (DOS) and of the covalent-energy ( E cov translating the chemical bonding) are performed. From the analyses of the results of the chemical bonding and the DOS at the top of the valence band (VB), an interpretation of the experimental physical properties evidenced experimentally particularly the large dielectric constant for the Ti member and valence degeneracy between Cu and Ru is proposed.

Induction of bidimensionality in mixed CuTi perovskites

Control of structure and order in oxides is essential for the design of new superconducting cuprates. The intergrowth of perovskite and rock salt layers, as found in bismuth, thallium and, very recently, the record breaking mercury cuprates, is just one way to induce bidimensionality. Defect “all perovskite” oxides, such as Ln2Ba2C2Ti2O11 (Ln = La, Nd, Eu) are discussed as examples of a crystal ‐chemical approach to the induction of bidimensionality and order in mixed perovskite oxides of copper.

Dynamical properties, sequence and mechanism of the phase transition and non-linearities in ABO3 ferroelectrics

The paper proposes a comparative analysis of the relations between the lattice dynamics, both of phononic and relaxational character, the structural phase transitions, their nature and sequence, as well as the ferroelectric properties of several ABO3 solid solutions. These considerations are illustrated by significant experimental and theoretical results obtained on pure and mixed perovskite oxides such as KTa1-xNbxO3, BaTiO3, AgTa1-xNbxO3 and PbZr1-xTixO3. The origin of the non-linear terms in the dielectric susceptibilities, their dispersive behaviour and their magnitude are discussed.