Thermodynamic functions of erbium orthophosphate ErPO4 in the temperature range of 0–1600 K

Low temperature heat capacity of erbium phosphate ErPO4 was measured by relaxation calorimetry (2–35 K) and adiabatic calorimetry (5–345 K). High-temperature enthalpies of this substance were studied by drop calorimetry in the region of 357–1575 K. Smoothed thermodynamic properties (heat capacity, entropy, enthalpy change and derived Gibbs energy) were calculated in the range of 0–1600 K. Gibbs energy of formation of ErPO4 was estimated using the standard entropy S0(298.15 K) from this work: ΔfG0(ErPO4, 298.15 K) = −1855.3 ± 2.1 kJ mol−1. The Schottky heat capacity anomaly was observed in the range from 2 to 300 K.

► Heat capacity and enthalpy change of erbium orthophosphate were investigated in the region of 2–1575 K by relaxation, adiabatic and drop calorimetric methods. ► Double-maximum Schottky anomaly of ErPO4 heat capacity was revealed. ► Thermodynamic functions in the studied temperature range were estimated. ► The standard Gibbs energy of erbium orthophosphate was calculated from literature data and results of this study.