Spontaneous Polarization of Ferroelectric Triglycine Sulfate between 2.2 and 20 K

The temperature dependence of the spontaneous polarization of ferroelectric triglycine sulfate has been determined in the range 2.2-20 K by measuring the charge released by a large crystalline sample with a Keithley electrometer. Above ∼8 K this temperature dependence is $\Delta P_s=C{e}^{-\frac{\Delta }{\mathrm{kT}}}$, corresponding to a two-level system with energy splitting $\Delta =h{\nu }_{\mathrm{E}}=9.08\mathrm{}\times {10}^{-15\mathrm{}}$ erg, while between 2.2 and 4 K it is $\Delta P_s=A{T}^{\frac{3}{2}}$. Both temperature dependences are consistent with recent specific-heat measurements by Lawless.