Phase Transitions and the Heat Capacity Anomalies in Ferroelectric Li ₂Ge ₇O ₁₅ and LiNaGe ₄O ₉

The heat capacity of Li2Ge7O15 and LiNaGe4O9 was measured by adiabatic calorimetry between 13 and 300K. A typical second-order type of anomaly due to the ferroelectric phase transition was observed at 282.4K for Li2Ge7O15 and at 121.6K for LiNaGe4O9, 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.