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

Abstract The systems Tl 2 MoO 4 –AMoO 4 –Hf(MoO 4 ) 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 Tl 5 A 0.5 Hf 1.5 (MoO 4 ) 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 ν 1 vibrational mode and deformation fluctuations has been demonstrated. The bands of the ν 3 ( F 2 ) vibrational mode are split in the IR spectra of the given triple molybdates. This splitting increases with the radius of the divalent cation.