Critical Behavior of Ferroelectric Triglycine Sulfate

The ferroelectric behavior of triglycine sulfate, which can be considered the best example of a nearly ideal second-order-transition ferroelectric, has been analyzed. Accurate measurements of the temperature dependence of spontaneous polarization and dielectric constant in the vicinity of the phase transition from the ferroelectric to the nonpolar state were performed, yielding the following results: $P_s=\mathrm{const}\times {\left(\Delta T\right)}^{\beta }$ with $\beta =0.51\mathrm{}\pm 0.05$ and $\frac{1}{\epsilon }=\mathrm{const}\times {\left(\Delta T\right)}^{\gamma }$ with $\gamma =1.00\mathrm{}\pm 0.05$, both above and below, but close to, the critical temperature $T_c$. These results are in good agreement with predictions of the thermodynamic theory for ferroelectric crystals.