B-cation displacement

Figure 11.14 (a) A cation-centred unit cell (b) cation displacement, r, creating an electric dipole in each cell (c) an array of unit cells and (d) an array of electric dipoles... 

These three modifications, namely, B-cation displacement, BX tilt/rotation and BXg distortion, are not mutually exclusive and they can occur independently or, often, in combination with one another. Moreover, the resulting changes may be cooperative in that they affect all octahedra in a similar way, or non-cooperative, in which case the distortions may cancel out at a macroscopic level although they may still influence microscopic properties. 

The effects of B-cation displacement upon the structures and dielectric properties of perovskite phases have been extensively studied in the important dielectric/fer-roelectric perovskite, BaTiOj. The phase shows transformations from trigonal to... 

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