Structural disorder and phase transition in Pb_1-xSn_xTe_1-ySe_y

Studies of the temperature dependence of electrical resistivity in Pb_1-xSn_xTe_1-ySe_y samples, carried out in the whole range of existence of the solid solution, was used to establish the dependence of the phase transition temperature on the solid solution composition. The phase transition was attributed to the presence of off-center Sn atoms with dipole moments, which could not be ordered at low values of x because of the high rate of tunneling. Under statistical disorder created by the random substitution of atoms in the anion sublattice the tunnel transition rate decreases, and the phase transition becomes possible. At higher x the phase transition acquires the characteristics of a displacive phase transition, in agreement with the theoretical predictions of the properties of a system of interacting particles moving in a multi-well potential with shallow wells.

Keywords: lead tin telluride selenide solid solution, IV-VI narrow-gap semiconductors, ferroelectric phase transition, Curie temperature, tunneling