Formation enthalpy and thermodynamic functions of Li2W1-xMoxO4 single crystals (x = 0.025 and 0.05)

Highlights: • Single crystal of Li₂W_0.975Mo_0.025O₄ has been grown by low-temperature-gradient Czochralski technique. • Formation enthalpy for Li₂W_0.975Mo_0.025O₄ single crystal has been measured. • Relation for lattice energy of Li₂W_1-xMo_xO₄ has been derived for low doping: U = A + B⋅x_Mo⋅r_Mo. • The heat capacity of Li₂W_0.95Mo_0.05O₄ has been measured (T = 193–915 K). • Dependence of Li₂W_1-xMo_xO₄ lattice enthalpies on tolerance factor has been constructed. A single crystal of lithium tungstate doped by 2.5% molybdenum was grown by low-temperature-gradient Czochralski technique (LTG CZ) with weight control for the first time. The solution enthalpy of Li₂W_0.975Mo_0.025O₄ was measured by solution calorimetry in aqueous KOH solvent. Based on experimental data obtained and reference values, the standard formation enthalpy of Li₂W_0.975Mo_0.025O₄ single crystal was calculated as following: Δ_fH⁰ (Li₂W_0.975Mo_0.025O₄, s, 298.15 K) = − 1599.77 ± 1.88 kJ mol⁻¹. The dependence of lattice enthalpy for Li₂W_1-xMo_xO₄ single crystals on tolerance factor for x = 1; 0.15; 0.1; 0.05; 0.025 was constructed. It was shown that dependence of lattice enthalpy on tolerance factor was linear. For low doping of molybdenum, a relation that connected the lattice energy in Li₂WO₄-Li₂MoO₄ system with molybdenum content was derived as following: U = A + B · x_Mo · r_Mo. The heat capacity of Li₂W_0.95Mo_0.05O₄ single crystal was measured in two temperature ranges: (193–370) K; (320–915) K. Heat capacity in both temperature ranges was well described by cubic polynomials. It was shown that there were no phase transitions in both temperature ranges. It is important from a practical point of view for promising application of investigated compounds.