Crystal structure and spectroscopic properties of a new oxyarsenate Li0.5Ni0.25TiOAsO4

The new oxyarsenate Li0.5Ni0.25TiOAsO4 has been synthesized and studied by a combination of X-ray powder diffraction, neutrons powder diffraction and vibrational spectroscopy. Li0.5Ni0.25TiOAsO4 crystallizes in the monoclinic P21/c space group with the unit cell parameters: a = 6.5854(3) Å, b = 7.4665(4) Å, c = 7.4969(4) Å, β = 89.884(6)°, V = 368.62(1) Å3 and Z = 4. The structure has been determined at room temperature from neutrons diffraction by the Rietveld method analysis. It is formed by a 3D network of TiO6 octahedra and AsO4 tetrahedra sharing corners. Structural refinement shows a partial and a statistical occupancy of 2a and 2b sites by Li+ and Ni2+ ions. TiO6 octahedra are linked together by corners and form infinite chains along c-axis. Raman and infrared studies confirm the existence of -TiOTi- chains. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Ni2+ ions.