Single crystals of undoped Li2WO4 and Li2W1−0.0125Mo0.0125O4: formation enthalpies, heat capacity in the temperature range 320–997 K

Abstract

The Li₂WO₄ single crystal was first grown by applying the Czochralski technique with weight control and low-temperature-gradients. A single crystal of Li₂WO₄ is one of the perspective materials for researching rare events. The heat capacity for a Li₂W_1−0.0125Mo_0.0125O₄ single crystal has been determined by DSC calorimetry in the temperature range 320–997 K for the first time. No anomalies in the heat capacity associated with phase transitions were found. The standard formation enthalpy for the Li₂WO₄ single crystal was studied using reaction calorimetry. It has been shown that the relation of standard formation enthalpies for Li₂W_1−xMo_xO₄ (x = 0.15–0) with function (1−x)W + xMo are close to linear, which allows one to predict the thermodynamic properties for single crystals with isotopes Li₂W¹⁸⁶_1−0.0125Mo¹⁰⁰_0.0125O₄ and Li₂W¹⁸⁶O₄. It was shown that single crystals with isotopes are more thermodynamically stable than without isotopes.