Some Anion-deficient Perovskite-related Structures

Some Anion-deficient Perovskite-related Structures.—In this Section we will consider some anion-deficient perovskite phases which can be written as There has 

These phases seem to form a natural bridge between the perovskite related structures described in Section 2 and classical point-defect containing non-stoicheiometric compounds, and as such would seem to merit further study. 

Intergrowths in MO2-LH2O3 Systems.—There have been a large number of structural studies of the rare-earth oxides in recent years and the basic principles of the structures to be found are reviewed by Eyring add Tai. As a general rule, the oxide structures can be considered to be derived from an MO2 fluorite structure parent which contains 

Eyring and L.-T. Tai, Treatise on Solid State Chemistry , Vol. 3, Crystalline and Non-crystalline Solids , ed. N. B. Hannay, Plenum, New York, London, 1976, p. 167. 

Two groups of compounds appear to show this latter type of behaviour. The first of these is the group of phases formed when La203 is allowed to react with 

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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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