Phase Transitions and the Heat Capacity Anomalies in Ferroelectric Li2Ge7O15and LiNaGe4O9

The heat capacity of Li 2 Ge 7 O 15 and LiNaGe 4 O 9 was measured by adiabatic calorimetry between 13 and 300 K. A typical second-order type of anomaly due to the ferroelectric phase transition was observed at 282.4 K for Li 2 Ge 7 O 15 and at 121.6 K for LiNaGe 4 O 9 , and the entropy of transition was determined as 1.50 and 1.95 JK -1 mol -1 , respectively. Smoothed heat capacity values at selected temperatures and some other thermodynamic functions such as enthalpy, entropy and Gibbs energy were calculated from the experimental data and tabulated in a table.