Solid solution between lead fluorapatite and lead fluorvanadate apatite: mixing behavior,Raman feature and thermal expansivity

The solid solution between lead fluorapatite and lead fluorvanadate apatite, Pb₁₀[(PO₄)_6-x (VO₄) _x ]F₂ with x equal to 0, 1, 2, 3, 4, 5 and 6, was synthesized by solid-state reaction at 1 atm and 700°C for 72 h and characterized by scanning electronic microprobe, electronic microprobe analysis, micro-Raman spectroscopy, and powder X-ray diffraction. The volume-composition relationship at ambient temperature does not show significant deviation from the Vegard’s Law. The Raman spectrum data suggest that both P and V are identical on a C _s site and both end-members show no apparent factor-group effect. The Raman frequency shift of the symmetric stretching vibration is linearly dependent on the composition. High temperature X-ray diffraction data, up to 600°C, suggest that the thermal expansion coefficients α _a , α _c , and α _V also vary linearly with the compositions of the apatites.