Synthesis and structure determination of the disordered V-V-P compound (NH4)(2)(VO)-O-IV((V2-xPxO7)-P-V)

Orange crystals of (NH4)(2)(VO)-O-IV((V2-xPxO7)-P-V) were synthesized hydrothermally. Their structure was solved by X-ray diffraction in the noncentrosymmetric tetragonal space group P4 (No. 75) a = 8.629(2) Angstrom, c = 5.648(4) Angstrom, Z = 2, R1(F-0) = 0.0495, omega R2(F-0(2)) = 0.1125 for 1747 independent reflections. The chemical analysis indicates the presence of phosphorus in the material with a VIP ratio close to 2. The X-ray structural determination confirms the fresnoite-type structure with a disordered occupation of the tetrahedral site by the V-V and P atoms. (C) 1996 Academic Press, Inc.