SYNTHESIS AND STRUCTURE OF K2XBA2-XSB4O9(PO4)(2) (0-LESS-THAN-X-LESS-THAN-0.4)

The solid solution K2xBa2-xSb4O9(PO4)(2) (0 < x < 0.4) has been prepar ed, and the structures of the end members K0.8Ba1.6Sb4O9(PO4)(2) and B a2Sb4O9(PO4)(2) have been determined from single-crystal and powder di ffraction data, respectively. The compounds crystallize in space group Pnma of the orthorhombic system with Z = 4 in cells of dimensions a = 20.998(3), b = 7.168(1), and c = 9.569(2) Angstrom for K0.8Ba1.6Sb4O9 (PO4)(2) and a = 20.9237(6), b = 7.1836(2), and c = 9.5189(3) Angstrom for Ba2Sb4 O-9(PO4)(2). Their structure consists of a three-dimension al arrangement of corner-sharing SbO6 octahedra and PO4 tetrahedra. In K0.8Ba1.6Sb4O9(PO4)(2), the K and Ba atoms are partially ordered amon g four possible sites, while in Ba2Sb4O9PO4)(2), the Ba atoms occupy o nly two of these sites. Arguments for the distribution of the K and Ba atoms in K0.8Ba1.6Sb4O9(PO4)(2) are presented. (C) 1995 Academic Pres s, Inc.