Turkish Journal of Physics

Nonlinear Effects in the Symmetric Phase of Layered Ferroelectric Materials




The layered ferroelectric \rm {TlInS_{2}} possessed a space group of symmetry \rm {C_{2h}^6} at room temperature undergoes succession of phase transitions below T_i=216 K with decreasing temperature [1]. In the present communication the results of nonlinear behaviour of pyroelectric effect and second harmonic generation observation in the symmetric phase of \rm {TlInS_2} were reported. Above of T_i=216K in the paraelectric phase, the unusual behaviour of pyrocurrent as found. The pyrocurrent undergo the maximum at T=238K with abruptly changes its sign with decreasing temperature. The influence of beas field increases the maximum of pyrocurrent considerably. Chang in the sign of applyed field induces the swiching of pyrocurrent peak at T=238K. Besides that, near the above mentioned temperature the appearance of second harmonic generation signal have been founded out. The temperature dependence of second harmonic generation in paraelectric phase exhibits a rather unusual behaviour: the second harmonic intensity undulation is observed with decreasing temperature in the range T_i

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