Dielectric spectroscopy and nonequilibrium phase transitions in TlGaSe ₂ layered crystals

The real and imaginary parts of the dielectric function of TlGaSe ₂ single crystals are investigated in the frequency range 30 Hz-13 MHz and at temperatures 80 K-300 K. A low frequency dispersion due to the interfacial polarization within the crystals is observed. The temperature dependence of relaxation time is obtained in a wide temperature region. A well- distinguished anomalous rise of relaxation time has been established in the 145 K-190 K temperature range for the first time far from the traditional phase transitions known in TlGaSe₂ crystals. It is shown that the observed behaviour of relaxation time is due to instabilities in the electronic subsystem revealing themselves as a non-equilibrium phase transition. A close relationship between the observed anomaly and anomalous behaviour of the various physical parameters of the investigated crystals is proposed.