Exploration of the Structural and Vibrational Properties of the Ternary Molybdate Tl 5 BiHf(MoO 4 ) 6 with Isolated MoO 4 Units and Tl + Conductivity.

The phase relations in the subsolidus region of the Tl ₂ MoO ₄ -Bi ₂ (MoO ₄ ) ₃ -Hf(MoO ₄ ) ₂ system were studied with the "intersecting cuts" method. The formation of the novel ternary molybdate Tl ₅ BiHf(MoO ₄ ) ₆ is found in this ternary system. The compound has a phase transition at T _pt = 731 K (Δ H = -3.15 J/g) and melts at T _m = 871 K (Δ H = -41.71 J/g), as determined by a thermal analysis. Tl ₅ BiHf(MoO ₄ ) ₆ single crystals were obtained by the spontaneous nucleation method. The crystal structure of Tl ₅ BiHf(MoO ₄ ) ₆ was revealed by structure analysis methods. This molybdate crystallizes in the trigonal space group R 3̅ c with the unit cell parameters a = 10.6801(4) Å, c = 38.5518(14) Å, V = 3808.3(2) Å ³ , and Z = 6. The vibrational characteristics of Tl ₅ BiHf(MoO ₄ ) ₆ were determined by Raman spectroscopy. The Tl ₅ BiHf(MoO ₄ ) 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.