The crystal structure of bismuth compounds was established by Aurivillius and the general formula (Bi2O2)2+(Mn-1RnO3n+1)2- indicates that n (1 to 6) perovskite-like layers. M is a cation of 1, 2 or 3 valency and R is a smaller cation of 3, 4, 5 or 6 valency. The properties of a large number of compounds of this family (lattice parameters, ferroelectric Curie temperature, etc.) are correlated with composition, ionic size, value of n, etc. Attention is drawn to their low values of lattice distorition, coercive field and electric fatigue, while possessing high Curie temperatures. The recently discovered cuprate superconductors have compositional (R = Cu) and structural similarity to bismuth layer ferroelectrics.
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