X-Ray Studies of Molybdenum and Tungsten Phosphides.

Abstract : The Mo-P and W-P systems were studied by X-ray powder methods. In addition to previously reported phases, Mo3P, MoP, MoP2, WP and WP2, the occurrence of a phase with the approximate composition MoP0.75 was established. The unit cell dimensions f r Mo3P, MoP and WP were redetermined. Some data supporting the hypothesis of an ordered distribution of P atoms in WoP (WC-type structure) are given. Structures of the isostructural MoP2 and WP2 were determined, and the MoP2 structure was refined from X-ray powder data. The orthorhombic unit cell dimensions (in angstroms) are for MoP2 : a = 3.145; b = 11.184; c = 4.984; and for WP2 : a = 3.166; b = 11.161; c = 4.973. The space-group comprises four metal atoms and eight P atoms in three sets of fourfold positions. The structure is related to the ZrSi2 (C 49) type. (Author)