Synthesis, structure, magnetic susceptibility and Mössbauer and Raman spectroscopies of the new oxyphosphate Fe0.50TiO(PO4)

A new iron titanyl oxyphosphate Fe_0.50TiO(PO₄) was synthesized by both solid-state reaction and Cu²⁺-Fe²⁺ ion exchange method. The material was then characterized by X-ray diffraction, Mössbauer spectroscopy, magnetic susceptibility measurements and Raman spectroscopy. The crystal structure of the compound was refined, using X-ray powder diffraction data, by Rietveld profile method; it crytallizes in the monoclinic system, space group P2₁/c (No.14), with , , , β=120.36°(1), and Z=4. The volume of the title compound is comparable to those of the M_0.50^IITiO(PO₄) series, where M^II=Mg, Co, Ni and Zn. The framework is built up from [TiO₆] octahedra and [PO₄] tetrahedra. [TiO₆] octahedra are linked together by corners and form infinite chains along the c-axis. Ti atoms are displaced from the center of octahedral units showing an alternating short distance (1.73 Å) and a long one (2.22 Å). These chains are linked together by [PO₄] tetrahedra. Fe²⁺ cations occupy a triangle-based antiprism sharing two faces with two [TiO₆] octahedra. Mössbauer and magnetic measurements show the existence of iron only in divalent state, located exclusively in octahedral sites with high spin configuration (t_2g⁴e_g²). Raman study confirms the existence of Ti-O-Ti chains.