STRUCTURE AND DISORDER IN SINGLE-CRYSTAL LEAD ZIRCONATE, PBZRO3

The full three-dimensional single-crystal crystal structure of the per ovskite material PbZrO3 (M(r) = 346.42) has been refined. It is found that the structure is disordered with two substructure components rela ted by a shear of c/2. Each individual substructure corresponds closel y 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 determin ed 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 K alpha, lambda = 0. 71069 angstrom, mu = 612.68 cm -1, T = 297 K. The s tructure was refined to R = 0.0596 and wR = 0.0753 for 246 unique refl ections, and, apart from the choice of space group, is very similar to that proposed by Whatmore (PhD thesis, Univ. of Cambridge, England, 1 976). Comments are made on the relationship between the single-crystal structure of PbZrO3 and that determined from polycrystalline samples.