Thermal expansion and ionic conductivity of K5A0.5Hf1.5(MoO4)6 (A = Sr, Pb)

Compounds K5A0.5Hf1.5(MoO4)6 (A = Sr, Pb) were synthesized using solid-state ceramic method. The sequence of chemical reactions that occur during the formation of these compounds has been elucidated. It was determined that the compounds melt incongruently at 628 degrees C, and their crystal structures were refined using the Rietveld method. Theoretical IR spectra were calculated using the obtained structural data and DFT modeling results. These spectra exhibited a high degree of correlation with the experimental data, thereby confirming the presence of isolated MoO4 groups within the structure. It has been shown that the electrical conductivity of K5A0.5Hf1.5(MoO4)6 (A = Sr, Pb) reached about 10-4 S/cm, which exceeds the conductivity of previously studied similar ternary molybdates. BVSE calculations indicated a high probability of oxygen transport in the studied compounds. Thermal deformations were studied by high temperature powder X-ray diffraction in the temperature range of 30-500 degrees C. The results showed that the ternary molybdates K5A0.5Hf1.5(MoO4)6 (A = Sr, Pb) are materials with high thermal expansion (alpha V = 40-56 x10-6 degrees C-1) and exhibit anisotropy along the crystallographic c-axis.