Specific heat of tri-glycine sulfate in electric field

Measurements of the specific heat, polarization and dielectric constant are reported in electric fields up to 3 kV/cm in order to investigate domain energetics in the hydrogen-bonded ferroelectric tri-glycine sulfate. Although the shape of the specific-heat anomaly at $T_C = 322.5\, K$ is thermally broadened in unpoled crystals, this shape changes into the characteristic $\lambda$-shape expected for a continuous transition with the application of a 220$\,$V/cm electric field. The $\lambda$ transition below $T_C$ depends on $T-T_C$ in a range $T-T_c\leq~10~K$ with a critical exponent, $\beta$ = - 0.39. Similarly we find that below $T_C$ the experimental dielectric constant obeys an inverse-power law of the form, $\varepsilon(T) = a/(T-T_C)^\beta$, with the constant $a = 1244\, \mathrm{K}$ and the exponent $\beta=0.4$.