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

Abstract

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 Li2W0.975Mo0.025O4 was measured by solution calorimetry in aqueous KOH solvent. Based on experimental data obtained and reference values, the standard formation enthalpy of Li2W0.975Mo0.025O4 single crystal was calculated as following: ΔfH0 (Li2W0.975Mo0.025O4, s, 298.15 K) = − 1599.77 ± 1.88 kJ mol−1. The dependence of lattice enthalpy for Li2W1-xMoxO4 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 · xMo · rMo. The heat capacity of Li2W0.95Mo0.05O4 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.