Phase Transitions and the Heat Capacity Anomalies in Ferroelectric Li_2Ge_7O_15 and LiNaGe_4O_9

Abstract

The heat capacity of Li₂Ge₇O₁₅ and LiNaGe₄O₉ 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 Li₂Ge₇O₁₅ and at 121.6, K for LiNaGe₄O₉, and the entropy of transition was determined as 1.50 and 1.95, JK^-1mol^-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.