Crystal chemistry, Rietveld refinements and Raman spectroscopy studies of the new solid solution series: Ba_3-xSr_x(VO₄)₂ (0 ≤ x ≤ 3)

The new solid solution series Ba_3-xSr_x(VO₄)₂ (0 ≤ x ≤3) has been synthesized and studied by a combination of X-ray powder diffraction and Raman vibrational spectroscopy. This continuous solid solution crystallise in the hexagonal system with R over(3, ̄) m space group. The structure has been determined at room temperature from X-ray diffraction by the Rietveld method analysis. It is formed by a 3D network of (Ba/Sr)₍₁₎(VO₄)₂^4- layers linked into a crystal network by (Ba/Sr)²⁺₍₂₎ cations. The vibrational spectra of this crystalline orthovanadate solid solution series are interpreted by means of factor group analysis in terms of space group R over(3, ̄) m (D_{3 d}⁵). Assignments of the V-O vibrational stretching and bending modes, as well as some of the external modes, have been made. While all the modes show a monotonous shift as a function of the composition x, a break in the curves of intensities, full width at half maximum and band areas as a function of x is observed and attributed to the statistical distribution of Ba and Sr ions in the same crystallographic sites.