Hysteresis and Thermal Studies on Ferroelectric Transitions in Thiourea

抄録

The hysteresis loop, the specific heat and the thermal expansion of CS (NH₂)₂ have been studied with particular reference to its ferroelectric transitions.
The hysteresis loop in intermediate phase III is transformed into a double loop with a variation of temperature. The field dependence of the transition temperature is given by dTc⁄dE=+ and −0.5 deg. cm/kV for the upper and lower sides of phase III, respectively. Below phase III, a decrease of the critical field is observed by applying a stress on the (100) or (001) face. A new ferroelectric loop is also observed at −102°C with the spontaneous polarization of 2×10⁻⁴μ coul/cm². The specific heat anomaly is found at −106°C with the latent heat of 6.6±01 cal/mol. In [100] and [001] directions, expansion anomalies are found; a jump of 0.9×10⁻³ is observed especially in the [100] direction at −105°C.
The results are examined according to the phenomenological theory. The dipole moment of the molecule in the crystal is discussed and a molecular model of the transition is also introduced.