The high-temperature heat capacity of LnPO4 (Ln = La, Ce, Gd) by drop calorimetry

The high-temperature heat capacity of three lanthanide orthophosphates of monazite structure have been measured in the temperature range (450 to 1570) K. The data have been analysed in terms of a lattice term, represented by the 4f0 and 4f7 compounds LaPO4 and GdPO4, and an electronic term for CePO4. The calculated excess heat capacity thus obtained is in reasonable agreement with that calculated from the crystal field energies.