Crystal structure of tetragonal bismuth arsenate, BiAsO₄

Abstract

The complete crystal structure of the tetragonal form of bismuth arsenate has been determined by X-rays. The crystal has the scheelite structure. The body-centered cell, containing four molecules, has the following dimensions: a = 5.08 ± 0.02 A., c = 11.70 ± 0.02 A., c/a = 2.30. The calculated density is 7.6 g.cm−3. The space group is C4h6–I41/a. The arsenic and bismuth atoms are in fourfold special positions (a) and (b) of the space group, while the oxygen atoms are in the sixteenfold general positions (f). The oxygen parameters, given in fractions of the unit cell, are x = 0.213, y = 0.149, z = 0.080. Bismuth is in eight co-ordination, the average Bi—O distance being 2.54 A.