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

Abstract The new oxyarsenate Li 0.5 Ni 0.25 TiOAsO 4 has been synthesized and studied by a combination of X-ray powder diffraction, neutrons powder diffraction and vibrational spectroscopy. Li 0.5 Ni 0.25 TiOAsO 4 crystallizes in the monoclinic P 2 1 / c space group with the unit cell parameters: a  = 6.5854(3) A, b  = 7.4665(4) A, c  = 7.4969(4) A, β  = 89.884(6)°, V  = 368.62(1) A 3 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 TiO 6 octahedra and AsO 4 tetrahedra sharing corners. Structural refinement shows a partial and a statistical occupancy of 2a and 2b sites by Li + and Ni 2+ ions. TiO 6 octahedra are linked together by corners and form infinite chains along c -axis. Raman and infrared studies confirm the existence of -Ti O Ti- chains. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Ni 2+ ions.