Crystal structure of BiZn2PO6. Filiation between related compounds

The BiZn2PO6 room-temperature crystal structure was determined from powder X-ray data using the Rietveld method. This compound crystallizes in space g roup Pnma, with Z = 4, a = 11.897(2) Angstrom, b = 5.277(1) Angstrom, c = 7 .819(2) A. The structure contains ZnO5 square pyramids associated by edge i n dimers which are connected by corners to form infinite independent [ZnO34 -](infinity) zigzag double chains. The interconnection is achieved by PO43- tetrahedra creating six-sided tunnels parallel to the b axis containing Bi 3+ cations. An intensive discussion about the structural filiation between the different members of the BiM2XO6 series (M = Mg, Ca, Cu, Cd, Pb; X = P, V, As) is given. A thermal investigation showed that BiZn2PO6 undergoes a P-to-B phase transition at about 325 degrees C while this isostructural BiC u2PO6 remains structurally unchanged until 750 degrees C. (C) 2000 Academic Press.