Dielectric and Thermal Study of Tri-Glycine Sulfate and Tri-Glycine Fluoberyllate

The dielectric constants ${\epsilon }_b$ of tri-glycine sulfate and tri-glycine fluoberyllate show a pronounced anomaly at the Curie temperature of 48°C and 70°C, respectively. The dielectric constants ${\epsilon }_a$ and ${\epsilon }_c$ are practically temperature-independent. In the vicinity of the Curie point, the square of the spontaneous polarization increases linearly with decreasing temperature. The transition of both salts is of the second order. Measurements of the specific heat as a function of temperature yield $\Delta S=0.48\mathrm{}$ cal/mole degree for tri-glycine sulfate, and $\Delta S=1.17\mathrm{}$ cal/mole degree for tri-glycine fluoberyllate. The results are discussed on the basis of Mueller's thermodynamic theory for ferroelectric transitions.