STRUCTURE AND DISORDER IN SINGLE-CRYSTAL LEAD ZIRCONATE, PBZRO3

The full three-dimensional single-crystal crystal structure of the perovskite material PbZrO3 (M(r) = 346.42) has been refined. It is found that the structure is disordered with two substructure components related by a shear of c/2. Each individual substructure corresponds closely to the tilt system a-a-c(o) of Glazer [Acta Cryst. (1972), B28, 3384-3392; Acta Cryst. (1975), A31, 756-7621. The space group was determined to be Pbam (D2h9) with a = 5.889 (3), b = 11.784 (4) and c = 8.226 (2) angstrom, V = 570.8 (4) angstrom3, Z = 8, D(x) = 8.06 Mg m-3, Mo Kalpha, lambda = 0. 71069 angstrom, mu = 612.68 cm -1, T = 297 K. The structure was refined to R = 0.0596 and wR = 0.0753 for 246 unique reflections, and, apart from the choice of space group, is very similar to that proposed by Whatmore (PhD thesis, Univ. of Cambridge, England, 1976). Comments are made on the relationship between the single-crystal structure of PbZrO3 and that determined from polycrystalline samples.