Synthesis, structural characterization, and conductive properties of new Tl5A0.5Hf1.5(MoO4)6 (A = Ca, Cd) molybdates

https://doi.org/10.1016/j.jssc.2025.125716

Ionic conductivity of triple molybdates Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) is studied by the method of impedance spectroscopy in the frequency range from 1 Hz to 1 MHz and in the temperature range of 300–830 K. The molybdates Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) are prepared in the form of fine crystalline powder by solid state synthesis from Tl₂MoO₄, CaMoO₄ (or CdMoO₄), and Hf(MoO₄)₂ at 723–823 K. The conductivity of Tl₅Ca_0.5Hf_1.5(MoO₄)₆ ceramic samples σ = 2.69‧10⁻⁴ S/cm (at 830 K); Tl₅Cd_0.5Hf_1.5(MoO₄)₆ ‒ 8.5‧10⁻⁵ S/cm (at 830 K). The σ vs. T curve demonstrates an anomaly which corresponds to thermal effects in this temperature range. The ionic conductivity of Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) is due to Tl ⁺ ions localized in channels of the framework structure. The crystal structures of Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) are obtained by Rietveld method. The following unit cell parameters are calculated for Tl₅Ca_0.5Hf_1.5(MoO₄)₆: a = 10.68493(26), c = 38.3943(11) Å, V = 3796.13(22) ų, Z = 6 and for Tl₅Cd_0.5Hf_1.5(MoO₄)₆: a = 10.66890(17), c = 38.25443(73) Å, V = 3770.96(14) ų, Z = 6.