Synthesis, structure, magnetic susceptibility and Mössbauer and Raman spectroscopies of the new oxyphosphate Fe 0.50TiO(PO 4)

Abstract

A new iron titanyl oxyphosphate Fe 0.50TiO(PO 4) was synthesized by both solid-state reaction and Cu 2+–Fe 2+ 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 P2 1/ c (No.14), with a = 7.4039 ( 3 ) Å , b = 7.3838 ( 3 ) Å , c = 7.4083 ( 3 ) Å , β = 120.36 ° ( 1 ) , V = 349.44 ( 2 ) Å 3 and Z = 4 . The volume of the title compound is comparable to those of the M 0.50 IITiO(PO 4) series, where M II=Mg, Co, Ni and Zn. The framework is built up from [TiO 6] octahedra and [PO 4] tetrahedra. [TiO 6] 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 [PO 4] tetrahedra. Fe 2+ cations occupy a triangle-based antiprism sharing two faces with two [TiO 6] octahedra. Mössbauer and magnetic measurements show the existence of iron only in divalent state, located exclusively in octahedral sites with high spin configuration (t 2g 4e g 2). Raman study confirms the existence of Ti–O–Ti chains.