Exploration of the Structural and Vibrational Properties of the Ternary Molybdate Tl5BiHf(MoO4)6 with Isolated MoO4 Units and Tl+ Conductivity

The phase relations in the subsolidus region of the Tl2MoO4–Bi2(MoO4)3–Hf­(MoO4)2 system were studied with the “intersecting cuts” method. The formation of the novel ternary molybdate Tl5BiHf­(MoO4)6 is found in this ternary system. The compound has a phase transition at Tpt = 731 K (ΔH = −3.15 J/g) and melts at Tm = 871 K (ΔH = −41.71 J/g), as determined by a thermal analysis. Tl5BiHf­(MoO4)6 single crystals were obtained by the spontaneous nucleation method. The crystal structure of Tl5BiHf­(MoO4)6 was revealed by structure analysis methods. This molybdate crystallizes in the trigonal space group R3c with the unit cell parameters a = 10.6801(4) A, c = 38.5518(14) A, V = 3808.3(2) A3, and Z = 6. The vibrational characteristics of Tl5BiHf­(MoO4)6 were determined by Raman spectroscopy. The Tl5BiHf­(MoO4)6 conductivity was measured at frequencies of 0.1, 1.0, and 10 kHz in the temperature range of 293–773 K; in this temperature range, the conductivity level was 10–12–10–7 S/cm.