The Bismuth Titanates

The Bismuth Titanates. This family of materials was one of the first complex perovskite groups to be discovered the early studies being made by Aurivillius and reported in 1949. The structures are well known and described in standard texts such as Wells. The general architectural principle of these materials is a repetition of perovskite layers n octahedra thick cut parallel to (110) as in the Sr +iTi 03 +i oxides described above. Instead of being held together by a sequence of SrO layers, the perovskite layers in the bismuth titanates are joined by (Bi202) layers. The perovskite slabs have an overall formula where /I is a large cation that can readily 

Structural Inorganic Chemistry , Oxford University Press, 4th Edition, 1976. 

This material is an ordered intergrowth of = 2 and n = 3 perovskite layers. The genera formulae of such intergrowth phases can be written as (Bi202)  

There have been attempts by Kikuchi to prepare more complex intergrowths, but so far with no reported successes. Working by analogy with the perovskite phases described in the preceding parts of this Section, it would seem highly probable that 

Horiuchi, T. Kikuchi and M. Goto, Acta Crystallogr., Sect. A, 1977, 33, 701. 

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Perovskite-related Oxides.—The perovskite-related oxides have been studied extensively in recent years because of the large variety of device applications for which these materials are suited. The interaction between structure, properties, and stoicheiometry is significant at all levels, but here we will discuss only the narrow areas where intergrowth is a dominant structural feature. We will not, therefore, consider solid solutions typified by the Pb(Zr Tii )03 ferroelectrics, and neither will we discuss the structurally complex but stoicheiometric phases related to hexagonal BaTiOj, which includes BaNiOj, which has a simple two-layer repeat in the c-direc-tion, the nine layer BaRuOj, the twelve layer Ba4Re2CoOj2, and the twenty-four layer Sr5Re20ig phase. The crystal chemistry of these phases is treated in detail by Muller and Roy. The materials we shall discuss are the two series of phases A B 0 +2 and A + B 02n+, and the bismuth titanates. Some of the anion deficient perovskites, ABO -x, will be considered in Section 5. 

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