CALORIMETRIC MEASUREMENTS ON RARE-EARTH PYROHAFNATES RE2HF2O7 (RE = LA,EU,GD)

Enthalpy increment measurements have been carried out on La2Hf2O7, Eu2 Hf2O7 and Gd2Hf2O7 in the temperature range 980-1740 K by using a high temperature differential calorimeter. From the enthalpy values, other thermodynamic functions, such as heat capacity, entropy and free ener gy functions have been generated. The high temperature C-p data of the rare earth pyrohafnates obtained in this study are discussed in relat ion to the crystal chemistry of these pyrochlores. (C) 1998 Elsevier S cience S.A.