Synthesis, structure refinement and characterisation of a new oxyphosphate Mg0.50TiO(PO4)

A new titanium oxyphosphate Mg0.50TiO(PO4) has been synthesized and characterized by several physical techniques: X-ray diffraction, P-31 MAS-NMR, Raman diffusion, infrared absorption and diffuse reflectance spectroscopy. It crystallizes in the monoclinic system with unit cell parameters: a = 7.367(9), b = 7.385(8), c = 7.373(9) angstrom, beta = 120.23(1), with the space group P2(1)/c (no. 14), Z = 4. The crystal structure has been refined by the Rietveld method using X-ray powder diffraction. The conventional R indices obtained are R-wp = 0.138, R-p = 0.096 and R-B = 0.0459. The structure Of Mg0.50TiO(PO4) consists of infinite chains of corner-shared [TiO6] octahedra parallel to the c-axis, crosslinked by corner-shared [PO4] tetrahedra. These infinite chains have alternating short (1.74 angstrom) and long (2.26 angstrom) Ti-O bonds and are similar to those found in titanium oxyphosphate (M0.50TiO)-Ti-11(PO4) (M2+ = Fe2+, CO2+, Ni2+, Cu2+, Zn2+). The magnesium atom is located in an antiprism between two [TiO6] octahedra. P-31 MAS NMR showed only a single P-31 resonance line, in a good agreement with the crystal structure. Raman and IR spectra show strong bands respectively at 765 and 815 cm(-1), attributed to the vibration of -Ti-O-Ti-O- bonds in the infinite chains. The gap due to the Oxygen-Titanium(IV) charge transfer is 3.37 eV. (c) 2006 Elsevier Ltd. All rights reserved.