Behavior of the layered crystals TlInS2 and TlGaSe2 near phase transitions in a static electric field

The effect of an orienting electric field on the anomalies of the temperature dependence of the dielectric constant epsilon of the crystals TlInS2 and TlGaSe2 and of the pyroelectric current i in TlInS2 near phase transitions is investigated. It is found that the epsilon(T) profile of both crystals undergoes the same transformation at the point of the phase transition to the incommensurate phase under the influence of a static electric field applied in the plane of the layer. It is established that the maximum of epsilon(T) in TlGaSe2 and of i(T) in TlInS2 at the point of the phase transition to the commensurate polar phase is shifted in a certain range of orienting electric fields and that the sign of the temperature shift depends on the value of the external electric field. An interpretation is offered for the experimental results. (C) 2000 American Institute of Physics. [S1063-777X(00)00801-X].