Ab initio determination and Rietveld refinement of the crystal structure of Ni0.50TiO(PO4)

The structure of the oxyphosphate Ni0.50TiO(PO4) has been determined nb ini tio from conventional X-ray powder diffraction data by the "heavy atom" met hod. The cell is monoclinic (space group P2(1)/c, Z=4) with a=7.3830(5) Ang strom, b=7.3226(5) Angstrom, c=7.3444(5) Angstrom, and beta=120.233(6)degre es. Refinement of 46 parameters by the Rietveld method, using 645 reflexion s, leads to kcR(wp)=0.1521 cR(p)=0.120, and R-B=0.043. The structure of Ni0 .50TiO(PO4) can be described as a TiOPO4 framework constituted by chains of tilted corner-sharing TiO6 octahedra running parallel to the c axis, cross linked by phosphate tetrahedra and in which one-half of octahedral cavities created are occupied by Ni atoms. Ti atoms are displaced from the center o f octahedra units in alternating long (2.231) and short (1.703 Angstrom) Ti -O bonds along chains. (C) 1999 International Centre for Diffraction Data. [S0885-7156(98)00303-0].