Low-temperature heat capacity and thermodynamic functions of thulium and lutetium titanates and Schottky anomaly in Tm2Ti2O7

Abstract

The temperature dependence of the heat capacity of Tm2Ti2O7 and Lu2Ti2O7 compounds over the range of 4.5–320 K has been researched by adiabatic calorimetry. Based on the experimental data, the basic thermodynamic functions of the compounds over the range of 5–320 K have been determined. Tm2Ti2O7 sample has revealed an additional component in the heat capacity associated with the presence of the Schottky anomaly. The temperature dependence behavior of the Debye characteristic temperature of Lu2Ti2O7 sample indicates the absence of anomalies in the heat capacity. Standard thermodynamic functions at 298.15 K are: for Tm2Ti2O7 – Cp,298.15 = 221.0 ± 1.2 J·mol−1·K−1, S298.15 = 261.3 ± 2.4 J·mol−1·K−1, ΔH0298.15 = 39.45 ± 0.29 kJ·mol−1; for Lu2Ti2O7 – Cp,298.15 = 206.9 ± 1.1 J·mol−1·K−1, S298.15 = 229.8 ± 2.2 J·mol−1·K−1, ΔH0298.15 = 35.70 ± 0.26 kJ·mol−1.