TRAVELS THROUGH PEROVSKITE SPACE

Perovskite and perovskite-related structures are organized in a diagra mmatic form called Perovskite Space. The principal axes show variable oxygen content, variable A/B ratio, and compensated substitutions on e ither the A or B sites. In many cases, large excesses or deficiencies of a component relative to the ideal perovskite composition are accomm odated in uniformly spaced layers separated by two-dimensional slabs o f perovskite structure of various thicknesses. The defect chemistry of compositions along the axis of variable oxygen content is discussed i n detail. There are homologous series of structures in the oxygen-defi cient direction with the generic formula A(n)B(n)O(3n-1), and in the o xygen-excess direction with the generic formula A(m)B(m)O(3n+2). The d efect chemistry is discussed in terms of the effects of forming ordere d structures vs. the dispersal of the oxygen-excess or deficiency as r andomly distributed point defects in the perovskite structure.