Thermodynamic properties and phase transition of monoclinic terbium orthophosphate

Abstract Thermodynamic functions of monoclinic terbium orthophosphate were determined based on the results of measurements of low temperature heat capacity (adiabatic calorimetry) and high temperature heat capacity (DSC). An irreversible exothermal effect accompanying the phase transition from monoclinic to tetragonal modification in the range 1350–1450 K was detected. A study of magnetic susceptibility in the temperature range 2–300 K indicated a lack of phase transformations in this region. Stability regions of monoclinic and tetragonal structural modifications were evaluated based on the temperature dependences of Gibbs energy of formation for both phases.