Synthesis, crystal structure and vibrational spectra of Sr 0.5 Zr 2 "AsO 4 … 3

Sr 0.5 Zr 2 (AsO 4 ) 3 arsenate was prepared and structurally characterized by powder X-ray diffraction and by Raman and infrared spectroscopies. Its structure, which belongs to the Nasicon-type family, was refined by the Rietveld method in the R-3 space group, from X-ray powder diffraction data. The hexagonal unit-cell parameters were determined to be a h =8.965(2) A, c h =23.955(6) A, V =1667.43(6) A 3 , and Z =6. The structure is formed by an ionic three-dimensional network of AsO 4 tetrahedra and ZrO 6 octahedra linked by corners with Sr 2+ ions occupying half of the M1 sites in an ordered manner. Raman and infrared spectra were recorded and assignments of the stretching and bending vibrations of the AsO 4 3− tetrahedra were made. The number of the peaks observed is in good agreement with that predicted by the factor-group analysis of the R-3 space group.