Ideal perovskite ABO3 structure

The ideal perovskite (ABO3) structure which is a simple cubic structure with the space group Pm3m, provides the basis for the structures of a large variety of inorganic solids. The perovskits structure is conventionally described as consisting of a BO3 array... 

Figure 6.1 Different presentations of the ideal perovskite ABO3 structure and the projections of structure along [1 0 0], [1 1 0], and [1 1 1].

Figure 6.3 (a) The ideal perovskite ABO3 structure (b-e) Changes ofthe environ merit ofTi " " ions... 

In an ideal perovskite structure for an ABO3 compound, the larger, A, ions are surrounded by twelve oxygens and the smaller, B, ions by six oxygens. Eq. (31) shows the ionic radii relationship for a close-packed arrangement. 

Figure 7 The structure of ABO3 ideal perovskite. A-site B-site oxide ion...

ABO3 compounds containing lanthanum are closer to the ideal perovskite than those containing smaller rare earth ions. Compounds of the smaller rare earth ions appear to have a distorted perovskite structure of lower symmetry. When, however, the relationship between the radii is very far from being ideal (eq. 31), strong distortion may result giving an entirely different structure. The Goldschmidt tolerance factor, t, for the perovskite structure is related to the ionic radii by... 

Fig. 4 Ideal perovskite structure for ABO3 type oxides.

The majority of new materials for SOFCs are perovskite stmctured oxides of general form ABO3.5 [23]. The ideal perovskite structure is a cubic close-packed ABO3 structure where the B-site cation sits within the octahedral interstices. Fig. 3.5. This stmcture is very flexible toward cation composition and tolerates large substitution fractions on either cation site. The Goldschmidt factor, a ratio of A, B, and O ionic radii, is often utilized to predict if a metal oxide will crystallize into the perovskite structure [24]. The A site of the commonly utilized perovskites is typically occupied by La, Ca, Sr, or Ba. The B site is typically a transition metal. Other stmctures investigated include double perovskites, apatites, and fluorites. 

Figure 15.18. ABO3 ideal perovskite structure showing oxygen octahedron containing the B ion lined through comers to form a tridimensional cubic lattice [119]. (Reprinted with permission from Chem Rev 2001 101 1981-2017. Copyright 2001 American Chemical Society.)...

Fig. 13.24 Ideal structure of perovskite ABO3 the cation in the center of the unit cell cation B in the center of an octahedron whose vertices are oxygen anions (Adapted from Fierro JLG, Pena MA. Chem Rev.

Ideal, cubic ABO3 perovskite structure belongs to Pm3m (no. 221) space group. It can be described as a 3-dimensional network of corner sharing BOg octahedra. In such a structure bigger, 12-fold A cations occupy aU available positions. Alternatively, it can be described as a cubic close-packed iccp) array of AO3, in which one quarter of all octahedral positions is occupied by smaller B cations. Fig. 1 shows graphical representation of perovskite stmcture. 

Figure 1. Schematic structure of ideal ABO3 perovskite.

Figure 4. ABO3 perovskite structure (left) and an idealized representation of LaSrCuA105 (right).

Here, R is the radius of the ions, and the subscripts A, B and O represent the corresponding ions in ABO3. This factor serves as a structure parameter to describe the extent of distortion of the perovskite structure from the ideal cubic prototype due to mismatch between the A-O and B-O bond lengths. Figure 2.10 shows the relationship of AHj n. the heat of formation of ABO3 from oxide precursors, to the perovskite tolerance factor, t. As indicated in Fig. 2.10, the stability of the perovskite structure increases as the tolerance factor increases towards 1, because... 

Subsequently we present the main experimental results about size effects of different physical properties of nanoferroelectrics with perovskite structure [16]. Latter ferroelectrics constitute large group of the materials with structure ABO3. The majority of them have wide band gap so that pure samples (i.e. those without specially added impurities) are almost ideal insulators. Note that the predominant part of modern technological applications of ferroelectrics belong to the substances of perovskite family. 

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