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Abstract
Studies of temperature dependences of linear permittivity and third harmonic generation were carried out for ferroelectric thiourea, SС(NH2)2, particles embedded into molecular sieves SBA-15 and МСМ-41 with pore sizes of 7.5 nm and 4.0 nm, respectively. Temperatures of the ferroelectric phase transition and transition from the incommensurate phase into paraphase were shown to be higher than in bulk thiourea. The shifts of the transitions increased with decreasing pore size. Both phase transitions were strongly diffused. The obtained data evidenced that the third harmonic generation can be used to find temperatures of the diffused ferroelectric transition.