Synthesis and Structure of Bi₁₄O₂₀(SO₄), A New Bismuth Oxide Sulfate

A new bismuth oxide sulfate of stoichiometry Bi 14 O 20 (SO 4 ) has been synthesized from thermal treatment of an intimate mixture of α-Bi 2 O 3 and (NH 4 ) 2 SO 4 in the mole ratio 1:0.14, and its structure determined using a combination of electron diffraction, X-ray powder diffraction, and neutron powder diffraction. The body-centered tetragonal unit cell ( I 4/ m; a = 8.664(1) Å, c = 17.282(2) Å) is a commensurate superstructure of the cubic fluorite subcell of δ-Bi 2 O 3 ( a 0 ): a = ( /2) a 0, c = 3 a 0 . The structure contains discrete sulfate anions at the unit cell corners and body center, and a Bi−O framework of linked BiO 4 e (e = lone pair of electrons) square pyramids and trigonal bipyramids. The square pyramids are aggregated into clusters of composition Bi 6 O 8, comprising O 2 - ions arranged in the form of a cube, the faces of which are capped by Bi 3+ ions. In contrast, the trigonal bipyramids are corner linked to form layers perpendicular to [001]. The structure is thought to represent just one of several related phases in this system.