Mat. Res. Bull., Vol. 20, pp. 715-721, 1985. Printed in the USA. 0025-5408/85 $3.00 + .00 Copyright (c) 1985 Pergamon Press Ltd. CRYSTAL STRUCTURE OF KSb2P0 8 Y. PIFFARD, A. LACHGAR and M. TOURNOUX Laboratoire de Chimie des Solides, U.A. du CNRS N ° 279 2, rue de la Houssini~re - F. 44072 NANTES C~dex. (Received March 26, 1985; Communicated by P. Hagenmuller) ABSTRACT KSb_PO 8 crystallizes in the monoclinic system, space group Cc, wit~ a = 12.306(4) ~, b = 7.086(2) ~, c = 15.037(5) ~, 6 : 95.82(3) 0 , Z = 8. The structure was determined from 21,19 reflexions collected on a NONIUS CAD4 automatic diffractometer with MoK~ radiation. The final R index and weighted R index are 0.019 and 0.025 respectively. The structure is builtWup from SbO6 octahedra sharing corners or edges and P04 tetrahedra sharing corners with octahedra to form a three-dimensional network. The potassium atoms are situated in the interconnected channelliKe cavities. Introduction As part of a search Go~ layered or skeleton structures with fast alkali-ion mobility the K-Sb -P -0 system has been investigated. Several phases have been identified (1)(2)(3) among which the compound KSb2PO 8. This paper reports the refinement and description of its crystal structure. Experimental The starting materials for synthesizing KSb2PO£ were NH4H2PO 4 (GR grade, Merck), Sb_O_z J (GR grade, Merck) and KNO 3 (~P ~rade, Pnolabo). The chemicals were weighed out in the stoichiometric ratios. The mixture was heated, in a platinum crucible, at 200°C for 4 hours to decompose the NH4H2F'04 before calcining at 900°C fop 24 hours in air. The crystals obtained are colourless hexagonal-shaped platelets with large (001) and (00~) faces. Single crystal X-Pay study indicates the compound to present the monoclinic symmetry. 715