Two-dimensional negative thermal expansion and ionic conductivity of a new glaserite-like ternary molybdate KZn _0.5 Hf _0.5 (MoO ₄ ) ₂

A new glaserite-like ternary molybdate KZn0.5Hf0.5(MoO4)2 was obtained through a solid-state reaction, and its structure was refined using the Rietveld method. It was found that the compound crystallizes in the trigonal space group P m1 and melts at 656 °C with decomposition. At elevated temperatures, the compound exhibited significant ionic conductivity, reaching 0.39·10–3S/cm at 570 °C with an activation energy Еа = 1.0 eV, with oxygen ions as the probable charge carriers. The infrared spectrum simulated using DFT showed good agreement with experimental data, containing characteristic stretching modes of the MoO4 tetrahedra. The observed negative thermal expansion in the ab plane did not result in a reduction in the volume of the unit cell, with αV = 98∙10–6 °С–1 at 500 °С, indicating that KZn0.5Hf0.5(MoO4)2 can be classified as a material with high thermal expansion properties.