“…2, 3 and 4, for all crystals, the experimental points of the temperature dependence ln(σ·T) in the range of the sharp jump of conductivity are described well by a straight line, which is given by the following equation: (1) where is the conductivity of sample, 0 is the constant within the experimental interval of temperature, ΔE is the conductivity activation energy, T is the temperature in Kelvins and k is the Boltzmann constant. It is known that this temperature dependence of conductivity indicates the dominant character of ionic conductivity above the critical temperature [2][3][4][5]. The values of critical temperatures and activation energies for TlS, TlSe, and TlInS2 crystals are shown in Table 1.…”