Perovskite and related compounds

Perovskites and related compounds also have a three-dimensional structure. In perovskites of formula ABOj, the octahedra of BOj lie on a cubic lattice, and are joined at the corners. Between these octahedra are large sites for the A atoms. In ReOj, the A atoms are missing, so guests can be added to the A positions. Because adjacent octahedra are joined together by only one oxygen they can rotate relative to one another, changing the shape of the A site. In LijReOj, the rotation splits the large A sites into two smaller sites more suitable for Li ions (Cava et al, 1982). Bronzes of WO3 also have a perovskite structure. 

Perovskites and related compounds Barium titanate Lead titanate Potassium niobate Potassium tantalate niobate Lithium niobate Lithium tantalate Barium titanium niobate Ba-Na niobate ( Bananas )... 

The erystal La2-xBaiCu04 was the first high-temperature superconductor which was discovered in 1986 [1], Since then a whole series of imusual magnetic and transport properties was foimd in lanthanum cuprate perovskites and related compounds. In particular, one of the most interesting features of the inelastic neutron scattering in these crystals is that for hole concentrations x > 0.04, low temperatures and small energy transfers the scattering is peaked at incommensurate momenta (, -5 + ), in the reciprocal lattice units... 

In Section II the perovskite and related structures are briefly introduced. In Section III the methods most frequently used for perovskites preparation are described comparatively. Sections IV, V, and VI refer to the bulk and surface properties of perovskites. Some of these properties will facilitate understanding of the catalytic action of these compounds. Section VII includes a review of the reactions where perovskite oxides were used as catalysts. Some of them are described separately (Sections VII,A-H). These include reactions that were more extensively studied or reactions that may have an increasing interest in the near future. Section VII,I includes less studied reactions such as oxygen homomolecular exchange, hydrogen and NH3 oxidations, N20 decomposition and dehydro-... 

Perovskite-type layered cuprates (high-rc superconductors and related compounds)... 

A good review on perovskites and related structures is given in Ref. [3]. The symmetry of CaTiOs is orthorhombic at room temperature (Pbnm), it transforms to a tetragonal polymorph at 1100°C (I4/mcm), and then to the cubic form at 1250 °C (Pm-3m) [4]. BiMnOs is triclinic at room temperature [5] and compounds such as LaCrOs transforms to a rhombohedral (trigonal) polymorph at high temperatures [6]. 

Perovskite Materials and Related Compounds Oxygen Transport Parameters... 

Overall, some of these perovskites exhibit a coloration that is comparable to inorganic pigments currently utilized by the industry (Figure 12.1). In other cases, however, the color strength is too weak to support their use as colorants. At all events, the only perovskite pigment produced at industrial scale is the red Cr-YAlOs [9,10,12,29,44-47]. Thus, the following sections will focus on yttrium orthoaluminate and related compounds. 

Under these conditions, mixed oxide systems of well-defined ABO3 structure (perovskites) resulted as a reasonable alternative. Based on this, the aim of this chapter is to highlight and compare selected examples of perovskites and related oxides in total oxidation of VOCs. Their potential application as catalysts for the conversion of organic compounds containing carbon and hydrogen to CO, CO2,... 

Magnetic and Other Properties of Oxides and Related Compounds (Garnets and Perovskites). Landolt-Bomstein, new series, K.H. Hellwege and A.M. Hellwege Eds., Vol. lll/12a (Springer, Berlin 1978). 

Numerous investigators have attempted to control the precursor structure and related solution chemistry effects with varying degrees of success, to influence subsequent processing behavior, such as crystallization tempera-ture.40-42,78,109 110 Particular attention has been given to precursor characteristics such as structural similarity to the desired product and the chemical homogeneity of the precursor species. For multicomponent films, this latter factor is believed to influence the interdiffusional distances associated with the formation of complex crystal structures, such as perovskite compounds. Synthetic approaches have been geared toward the preparation of multimetal species with cation stoichiometry identical to that of the desired crystalline phase.40 42 83 84... 

In addition to these perovskite-related compounds, Raveau and Michel have prepared a series of Cu-containing phases which are structurally related to the perovskite structure. Certain of these derivatives have been discussed in a previous section. 

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