Static dielectric constant measurement on betaine mixed crystals was used to measure the temperature $T_m$, where the 2--dimensional interaction changes to the 3--dimensional interaction. The temperature $T_m$ is near the cell doubling temperature $T_c3$ in BP(Betaine Phosphate). This suggests that the temperature $T_m$ is the intrinsic precursory temperature, triggering the cell doubling in BP. In the relative dielectric constant function a local maximum was found near 0 V bias below the cell doubling temperature $T_c3$. $T_f$ anomaly in $BP_{0.6}A_{0.4}$ dipole glass is derived from terms which give net polarization, and disappears irreversibly once given a thermal cycle below $T_f$.
Nonlinear dielectric constant of thiourea was studied. Only in the 1/8 lock-in phase and ferroelectric phase the nonlinear dielectric constant could be measurable. The magnitute and sign of odd harmonic nonlinear dielectric constants are well explained by the phenomenological Landau theory. For even harmonic nonlinear dielectric constants there is a discrepancy between the same Landau theory and experimental results, including different signs for $ε_2'$ and $ε_2"$. Odd harmonic nonlinear dielectric constants in the 1/8 phase, however, was well fitted by a modified Landau theory.
A first complete study of hysteresis loop as a function of frequency (Ω) and field magnitude ($H_m$) was made in antiferroelectric $BP_{0.9}A_{0.1}$. The area (A) of antiferroelectric hysteresis loop scales as $A=(H_m-642.8)^{0.50} Ω^{0.40}$. The exponent is close to the theoretical result of the 2--dimensional Ising model. Also the area of minor loop was found to scale as $A=(H_m-642.8)^{2.12} Ω^{0.28}$.
