Unit cell perovskite CaTiO

FIGURE 10.6 The A-type unit cell of the perovskite structure for compounds ABOs, such as CaTiOs. 

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. 

The parent perovskite structure shown in Fig. 10.4 consists of alternating layers of composition AO and BO2, as for example in BaTiOs (23759) and CaTiOs (62149). It is also possible to have several AO layers between each BO2 layer providing each AO layer is sheared by half a unit cell from the adjacent AO layers, as shown for La2Ni04 in Fig. 12.1. This permits a wide range of structures with an even wider range of compositions to be prepared. Which compositions are possible depend on how well the structure can accommodate the bonding requirements of the atoms A and B. 

The perovskite CaTiOs crystallizes in the space group Pm 3 m. The unit cell contains oxygen atoms at the midpoints of every edge of a cube. There is a calcium atom... 

Fig. 5.23 (a) One representation of a unit cell of perovskite (CaTiOs) (b) the Ca ion is 12-coordinate with respect to the ions. Colour code Ca, purple O, red Ti, pale grey. 

Some high-temperature superconductors adopt a crystal structure similar to that of perovskite (CaTiOs). The unit cell is cubic with a Ti" " ion in each comer, a Ca " ion in the body center, and 0 ions at the midpoint of each edge, (a) Is this unit cell simple, body-centered, or face-centered (b) If the unit cell edge length is 3.84 A, what is the density of perovskite (in g/cm ) ... 

Figure 5.35 The cubic unit cells of (a) iridium, (b) CsCl and (c) perovskite (CaTiOs)...

The unit cell of the classical perovskite CaTiOs. The octahedral coordination environment of Site B is indicated. 

The ideal perovskite structure derives from the mineral CaTiOs, which is cubic with a unit cell around 0.39 nm containing one formula unit. The... 

Perovskite is the name given to the mineral CaTiOs. Although this composition is not cubic at room temperature, the structure can be described in a cubic mean unit cell with titanium at the center of the cell, calcium at the corner, and oxygen in the middle of each faces of the cube (Figure 8.3a). It can also be described as slabs of TiOe octahedra with calcium atoms in the 12-fold sites (Figure 8.3b). 

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