High-Frequency Behavior of Hydrogen-Bonded Ferroelectrics: Triglycine Sulphate and KD2PO4

The small signal dielectric coefficient of triglycine sulfate (TGS) and K${\mathrm{D}}_2$P${\mathrm{O}}_4$ has been determined as a function of frequency, temperature, and dc bias field in both the ferro- and paraelectric regions. The data for TGS are found to agree with a heuristic model involving a Gaussian distribution of relaxation times when the spontaneous and induced polarization are properly taken into account. It is suggested that the clamping out of the electrostrictive contribution to the polarization is a non-negligible factor. For K${\mathrm{D}}_2$P${\mathrm{O}}_4$ a large domain-associated loss is found in the ferroelectric region. This loss persists up to 2 kMc/sec indicating piezoelectric coupling to very small domains. The data for K${\mathrm{D}}_2$P${\mathrm{O}}_4$ suggest that the usual designation of first- or second-order transition is not sufficient.