The low-temperature heat capacity of some lanthanide zirconates

The heat capacities of the lanthanide zirconates Gd2Zr2O7 and Eu2Zr2O7 with pyrochlore structure were measured by adiabatic calorimetry and the hybrid adiabatic relaxation method in the temperature range (0.3 to 400) K. A thermal anomaly was observed for Gd2Zr2O7 below T=15 K. From the measurements the thermodynamic functions of Gd2Zr2O7 and Eu2Zr2O7 were determined. By combining our results with the heat capacity data of La2Zr2O7, the lattice component of the heat capacity and the entropy were derived for the lanthanide series Ln2Zr2O7 (Ln=La to Gd). The Schottky contributions were derived for Ce2Zr2O7, Nd2Zr2O7 and Eu2Zr2O7 by subtracting the lattice component from the experimental data, and compared to the values calculated from the crystal field energy levels