In this paper we present a model of spontaneous polarization appearing in the crystal of thiourea in phase I, constructed on the basis of the molecular field theory, with the use of the Boltzmann statistics. The model employs the potential energy of interaction between two nonpunctual molecular electric dipoles performing reorientations within the constraints specified by the experimentally determined structural data. The temperature dependences of the spontaneous polarization for different values of the hydrostatic pressure and for different γ-ray doses were obtained. A comparison between theoretical and experimental results permitted calculation of the parameters of the theory presented.
In this paper we propose a mechanism of the phenomenon of ferroelectricity in the molecular crystal of thiourea (SC(NH_2)_2). The mechanism is based on the model of interaction between two molecular electric dipoles. The dipoles are not idealized to points - they have a finite length. Besides, they can reorient mutually and the reorientation is determined by the crystal structure specified by the experimental structural research. On the basis of this theory, a formula for the potential energy of interaction of a pair of two nonpunctual dipoles as a function of the angle of reorientation is derived and discussed.
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