II. Structure of Perovskites 1982 A. Crystal Structure 1982 B. Nonstoichiometry in Perovskites 1983 1. Oxygen Nonstoichiometry 1983 2. Cation Nonstoichiometry 1984 C. Physical Properties 1985 D. Adsorption Properties 1986 1. CO and NO Adsorption 1986 2. Oxygen Adsorption 1987 E. Specific Surface and Porosity 1987 F. Thermal Stability in a Reducing Atmosphere 1989 III. Acid−Base and Redox Properties 1990 A. Acidity and Basicity 1990 B. Redox Processes 1991 1. Kinetics and Mechanisms 1992 2. Reduction−Oxidation Cycles 1993 C. Ion Mobility 1993 1. Oxygen Transport 1993 2. Cation Transport 1994 IV. Heterogeneous Catalysis 1995 A. Oxidation Reactions 1995 1. CO Oxidation 1995 2. Oxidation of Hydrocarbons 1996 B. Pollution Abatement 2001 1. NOx Decomposition 2001 2. Exhaust Treatment 2002 3. Stability 2004 C. Hydrogenation and Hydrogenolysis Reactions 2004 1. Hydrogenation of Carbon Oxides 2004 2. Hydrogenation and Hydrogenolysis Reactions 2006

Chemical structures and performance of perovskite oxides.

The high-temperature solid oxide fuel cell (SOFC) is the most efficient and environmentally friendly energy conversion technology to generate electricity from fuels such as hydrogen and natural gas as compared to the traditional thermal power generation plants. In the last 20–30 years, there has been significant progress in the materials development and stack technologies in SOFC. Among the electrode materials, lanthanum strontium manganite (LSM) perovskites, till today, are the most investigated and probably the most important electrode materials in SOFCs. The objective of this article is to review and update the development, understanding, and achievements of the LSM-based materials in SOFC. The structure, nonstoichiometry, defect model, and in particular the relation between the microstructure, their properties (electrical, thermal, mechanical, chemical, and interfacial), and electrochemical performance and performance stability are critically reviewed. Finally, challenges and prospects of LSM-based materials as cathodes for intermediate and low-temperature SOFCs are discussed.

Development of lanthanum strontium manganite perovskite cathode materials of solid oxide fuel cells: a review

Stoichiometric RMnO3 perovskites have been prepared in the widest range of R3+ ionic sizes, from PrMnO3 to ErMnO3. Soft-chemistry procedures have been employed; inert-atmosphere annealings were required to synthesize the materials with more basic R cations (R = Pr, Nd), in order to minimize the unwanted presence of Mn4+. On the contrary, annealings in O2 flow were necessary to stabilize the perovskite phases for the last terms of the series, HoMnO3, ErMnO3, and YMnO3, thus avoiding or minimizing the formation of competitive hexagonal phases with the same stoichiometry. The samples have been investigated at room temperature by high-resolution neutron powder diffraction to follow the evolution of the crystal structures along the series. The results are compared with reported data for LaMnO3. The distortion of the orthorhombic perovskite (space group Pbnm), characterized by the tilting angle of the MnO6 octahedra, progressively increases from Pr to Er due to simple steric factors. Additionally, all of the pe...

https://www.icmm.csic.es/jaalonso/seoxidos/oxidos/ic-rmno3.pdf

Evolution of the Jahn-Teller distortion of MnO6 octahedra in RMnO3 perovskites (R = Pr, Nd, Dy, Tb, Ho, Er, Y): a neutron diffraction study.

Results of a detailed investigation of the structure and electron-transport properties of $La_{1-x}A_xMnO_3$ (A =Ca, Sr) over a wide range of compositions are presented along with those of parent $LaMnO_3$ containing different percentages of $Mn^{4+}$. The electrical resistivity $(\rho)$ and magnetoresistance (MR) of polycrystalline pellets have been measured in the 4.2–400 K range in magnetic fields up to 6 T and the Seebeck coefficient (S) from 100 to 400 K. The electrical measurements were supplemented by ac susceptibility and magnetization measurements. MR is large and negative over a substantial range of compositions and peaks around temperatures close to the ferromagnetic transition temperatures $(T_c)$. An insulator to metal-like transition occurs near the $T_c$ and the temperature dependence of $\rho$ below $T_c$ is related to the magnetization although $\rho$ in the metallic state is generally much larger than the Mott’s maximum metallic resistivity. The occurrence of giant magnetoresistance is linked to the presence of an optimal proportion of $Mn^{4+}$ ions and is found in the rhombohedral and the cubic structures where the Mn-O distance is less than 1.97 \AA and the Mn-O-Mn angle is $170^o\pm10^o$. The field dependence of MR shows the presence of two distinct regimes. The thermopower S shows a positive peak in the composition range at a temperature where MR also peaks; S becomes more negative with increase in $Mn^{4+}$.

Structure, electron-transport properties, and giant magnetoresistance of hole-doped LaMnO 3 systems

This article presents a survey of recent applications of advanced computer modelling techniques in the study of ion transport and defect properties of ABO3 perovskite-structured oxides. The principal methodologies are outlined which include techniques based upon both interatomic potentials (static lattice, molecular dynamics) and quantum mechanical methods. The scope of contemporary applications of computer modelling of perovskite oxides (such as LaBO3 and AZrO3) is illustrated by accounts of recent work on oxygen ion transport and defect association, on cation migration, and, finally, on proton incorporation and diffusion.

R.B. Helmholdt

Papers

The Defect Chemistry of LaMnO3±δ: 2. Structural Aspects of LaMnO3+δ