Effect of hydrostatic pressure on the phase transition temperatures and spontaneous polarization of thiourea monocrystals

Abstract

Hydrostatic pressure‐induced shifts in the phase transition temperatures of monocrystalline thiourea are studied. The transition occurring at 202 K under atmospheric pressure is found to shift linearly downwards. The other transitions behave likewise at pressures up to 0.9 kbar. At 0.9 kbar the phase transitions, lying in the temperature interval from 169 to 180 K under atmospheric pressure, vanish. From hysteresis loop observations, the hydrostatic pressure‐induced change in spontaneous polarization in the region of phases I and III is determined.

Model of Temperature Dependence of Spontaneous Polarization of Thiourea Monocrystal in Phase I

“…Comparing Fig. 12 with the pressure dependence of the Curie temperature from [5] (dT c /dp = 35.35 × 10 −8 deg/Pa), we obtain the value of the compressibility factor of thiourea crystal as κ = 4.02 × 10 −10 Pa −1 . The use of the above formulae makes it easy to obtain the following values of the parameters of the presented theory:…”

“…8 and Fig. 9, can be compared to the experimental results presented in articles [5] and [6] (Figs. 9 and 10).…”

The Model of Ferroelectricity in Thiourea

“…The general problem of dependence of the number of phase transitions upon the form of the intermolecular interactions was described by Hoye and Hemmer [9] and it seems to be of universal character. The distances between the molecules of thiourea and thus the ferroelectric phase transitions are also affected by the hydrostatic pressure which was discovered by Gesi [10] and Klimowski et al [11,12]. The effect of the high hydrostatic pressure on the phase transitions in thiourea was studied by using the Raman scattering method in the article of Banerji and Deb [13].…”

A bibliographical review of the high pressure studies of ferroelectric phase transitions

“…The stabilization of the ferroelectric phase in other (N(CH,),),XY, type of compounds has been elaborately discussed by Gesi (1986). In thiourea all the incommensurate phases at room temperature disappear under pressure (Klimowski et al, 1976) and new commensurate phases appear (Gesi, 1969;Denoyer et al, 1982). The effect of pressure on the crystals exhibiting incommensurate phases will be discussed separately in section (h).…”