Crystal field and lattice disorder effects on the low-temperature thermodynamic properties of TmF3

Abstract

The temperature dependence of the heat capacity Cp(T), (2–300 K), and the lattice parameters a(T), b(T), and c(T) (5–300 K) TmF3 were experimentally studied. Anomalies in the studied characteristics were identified due to the influence on the thermal properties of trifluoride of the crystal field, and at the lowest temperatures (2–10 K), of a possible glass-like contribution due to disorder in the crystal lattice. As a result of our analysis of the excess contribution to the heat capacity (Schottky contribution, CSch(T)), we proposed a simplified scheme based on 1-1-7-5 splitting of the ground state of the Tm3+ ion, and determined the splitting parameters. The influence of the crystal field is also manifested through anomalies in the thermal expansion of TmF3. The temperature dependences of the unit cell volume of thulium trifluoride, and its heat capacity, were analysed using the Debye-Einstein model, and the model parameters are determined.