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Perovskites ABO3 perovskite

F can he suppressed hy the high site symmetry of the central atom In many perovskite-like structures of the ABO3 type the lone pair of the B-cat-ion leads not to a structural distortion. In CsPbF3 under ambient conditions no lone-pair activity observed [27], but upon cooling a phase transition is observed that leads to less symmetrical surrounding of Pb by fluoride [28]. [Pg.17]

The perovskite structure, ABO3 (where A represents a large cation and B a medium-size cation) is adopted by many solids and solid solutions between them can readily be prepared. Vacancy-containing systems with the perovskite structure are of interest as electrolytes in solid-state batteries and fuel cells. Typical representatives of this type of material can be made by introducing a higher valence cation into the A sites or a lower valance cation into the B sites. [Pg.37]

It should be mentioned that oxygen vacancies are often formed in the perovskite-type structure ABO3 in cases where the B atom is a transition metal that readily exists in more than one oxidation state. [Pg.105]

The configurational entropy term, given by the degeneracy, gc, is included in AfG but not in AfGc. Let us assume the existence of two compounds with different formal oxidation states for the B atom, ABO3 and ABO2.5. The two compounds have the same (perovskite-type) structure and the non-stoichiometric phase... [Pg.297]

Figure 10. Unit cell of ABO3 perovskite structure. (Reprinted with permission from Nature Materials (http //www.nature.com/nmat), ref 128. Copyright 2003 Nature Publishing Group.)... Figure 10. Unit cell of ABO3 perovskite structure. (Reprinted with permission from Nature Materials (http //www.nature.com/nmat), ref 128. Copyright 2003 Nature Publishing Group.)...
Figure 1. Schematic structure of ideal ABO3 perovskite. Figure 1. Schematic structure of ideal ABO3 perovskite.
In recent years, research on catalysts for the ATR of hydrocarbons has paid considerable attention to perovskite systems of general formula ABO3. In the perovskite stmcture, both A and B ions can be partially substituted, leading to a wide variety of mixed oxides, characterized by structural and electronic defects. The oxidation activity of perovskites has been ascribed to ionic conductivity, oxygen mobility within the lattice [64], reducibility and oxygen sorption properties [65, 66]. [Pg.296]

Various metal and metal oxide nanoparticles have been prepared on polymer (sacrificial) templates, with the polymers subsequently removed. Synthesis of nanoparticles inside mesoporus materials such as MCM-41 is an illustrative template synthesis route. In this method, ions adsorbed into the pores can subsequently be oxidized or reduced to nanoparticulate materials (oxides or metals). Such composite materials are particularly attractive as supported catalysts. A classical example of the technique is deposition of 10 nm particles of NiO inside the pore structure of MCM-41 by impregnating the mesoporus material with an aqueous solution of nickel citrate followed by calicination of the composite at 450°C in air [68]. Successful synthesis of nanosized perovskites (ABO3) and spinels (AB2O4), such as LaMnOs and CuMn204, of high surface area have been demonstrated using a porous silica template [69]. [Pg.383]

Perovskites. Materials of the formula ABO3 having the per-ovskite structure (32) can be prepared in a form containing lanthanum. Some perovskites containing cobalt and strontium, LaCoOa... [Pg.125]

CrFs has the ReOa-structure, which results from the perovskite structure ABO3 by removing the A-cations. [Pg.44]

The familiar cubic perovskite structure of ABO3 has of course just one structural parameter, the unit cell edge a. This requires the ratio of the A-O to the B-O bond lengths to be equal to y/2. When this condition cannot be met, the structme distorts in (one of) a number of well-documented ways . By far the largest of the families of derivative structures that arise when A is too small [/(A-0)//(B-0) < /2] is that of the orthorhombic perovskites (GdFeOa type) exemplified by the mineral perovskite (CaTi03) itself. [Pg.89]

Of the structures with stoichiometry ABO3 that may be derived from that of perovskite (Sect. 2.2), the calcite structure is the simplest in the sense that it requires the fewest parameters to specify it. We earlier described this structure in terms of the parameters obtained with regular BOe octahedra that are rotated (tilted) about their 3 axes from the positions they have in (cubic) perovskite. The coordination of A goes from 12 in the cubic structure to 3 in the rhombohedral calcite structure. [Pg.137]

Figure 1.5. Schematic diagrams of the structures of (a) rutile (Ti02) and (b) a perovskite (ABO3). Figure 1.5. Schematic diagrams of the structures of (a) rutile (Ti02) and (b) a perovskite (ABO3).
Cubic close-packed 12 6 6 ABO3 1/4 oct. (B) Perovskite CoTiOs, SrTi03, SrSn03, SrZr03, SrHf03, BaTiOs... [Pg.58]

The crystal structure of the 1-2-3 superconductor, YBazCusOy- is depicted in Figure 10.8. Figure 10.8(a) depicts only the positions of the metal atoms. If we discuss it in terms of the perovskite structure ABO3, where B=Cu, the central section is now an A-type perovskite unit cell and above and below it are also A-type perovskite unit cells with their bottom and top layers missing. This gives copper atoms at the unit cell corners and on the unit cell edges at fractional coordinates A and Ys. The atom at the body-centre of the cell (i.e., in the centre of the middle section) is yttrium. The atoms in the centres of the top and bottom cubes are barium... [Pg.402]

Draw a packing diagram (Chapter 1, Section 1.4.5) of the perovskite A-type cell (CaTiOs/ABOs), determine the number of ABO3 formula units, and describe the coordination geometry around each type of atom. Repeat this procedure for the perovskite B-type unit cell. [Pg.410]


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See also in sourсe #XX -- [ Pg.259 ]




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ABO3 perovskites

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