X-ray studyes of phase transitions in narrow gap A4B6 semiconductors

X-ray investigations of fcc lattice distortions in some solid solutions of A4B6 group semiconductors, in which the occurrence of low-temperature phase transitions (PT) is expected, are presented. No lattice distortions at T>100 K is detected in Pb0.8Sn0.2Te and PbTe0.95S0.05 samples. In and S impurity introduction into the Pb1-xGex solid solution is shown to decrease temperature, Tc, of segnetoelectric PT, Oh5→C3v5. The effect of Te→Se substitution to PT in Pb1-xGexTe is studied. Nonmonotonous change of temperature, Tc, and the temperature coefficient of the rhombohedrical distortion angle, da/dT, with composition, y, is detected in Pb0.92Ge0.08Te1-ySey. These phenomena are explained by the effect of random deformed and quasielectric fields on the ordering of dipole moments of noncentral Ge atoms