Synthesis, structure and vibration spectra of the triple molybdates Tl5A0.5Hf1.5(MoO4)6, A = Ca, Sr, Ba, Pb

The systems Tl2MoO4–AMoO4–Hf(MoO4)2 (A = Ca, Sr, Ba, Pb) have been studied in their subsolidus regions using X-ray powder diffraction and differential thermal analysis. Intermediate phases of composition 5:1:3 are formed in these systems. The crystallographic and thermal characteristics of these phases have been determined. The vibration spectra of Tl5A0.5Hf1.5(MoO4)6 (A = Ca, Sr, Ba, Pb) have been considered and analysed for each new compound. In the Raman spectra, the influence of the divalent cation on the bands of the ν1 vibrational mode and deformation fluctuations has been demonstrated. The bands of the ν3(F2) vibrational mode are split in the IR spectra of the given triple molybdates. This splitting increases with the radius of the divalent cation.