X-ray diffraction investigations of phase transitions in narrow-gap semiconductors

An X-ray diffraction investigation was made of the distortions of the fcc lattice in a series of solid solutions of IV-VI semiconductors in which low-temperature phase transitions were expected. Samples of Pb_0.8Sn_0.2Te and PbTe_0.95S_0.05 showed no lattice distortions at temperatures T>100 K. Introduction of In and S impurities into Pb_1-xGe_xTe solid solutions reduced the temperature T_c of the ferroelectric phase transition O_h->C_3v. A study was made of the influence of the Te->Se substitution on the phase transition in Pb_1-xGe_xTe: it was found that in the case of Pb_0.92Ge_0.08Te_1-ySe_y the temperature T_c and the temperature coefficient of the rhombohedral distortion angle d(alpha)/dT varied nonmonotonically with y. These effects were explained by the influence of random deformation and quasielectric fields on the ordering of the dipole moments of the noncentral Ge atoms.

Keywords: semiconductor solid solutions, lead tin telluride, lead telluride sulfide, lead germanium telluride, lead germanium telluride selenide, indium, sulfur, Curie temperature