The effect of an orienting electric field on the anomalies of the temperature dependence of the dielectric constant ε of the crystals TlInS2 and TlGaSe2 and of the pyroelectric current i in TlInS2 near phase transitions is investigated. It is found that the ε(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 ε(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.

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In this study, internal friction (IF) measurements in the temperature interval of 20 -600 °C are investigated for p-PbTe and n-PbTe : Cr crystals with the use of a torsion pendulum at low frequencies such as 1 Hz. The corresponding processes of diffusion of oscillation energy are characterized by values of activation energy and frequency factor. We consider that relaxation processes of IF may be the result of the dislocations that slip on the different planes. The influence of chromium doping to PbTe causes the creation of additional barriers with the oscillation of dislocations and increment of cohesion forces within the nuclei of the dislocations. The latter significantly influences the increase of shear modulus from 1.3 × 10 4 N/m 2 for pure PbTe to 3.14 × 10 4 N/m 2 for Cr-doped PbTe. Moreover, IF exhibits different characters in different temperature intervals.