Аннотация:An x-ray diffraction study 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 Pb0.8Sn0.2Te and PbTe0.95S0.05 showed no lattice distortions at temperatures T>100 K. Incorporation of In and S impurities into Pb1-xGexTe solid solutions reduced the temperature Tc of the ferroelectric phase transition Oh5->C3v5. A study was made of the influence of the Te->Se substitution on the phase transition in Pb1-xGexTe: it was found that in the case of Pb0.92Ge0.08Te1-ySey the temperature Tc 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 strain and quasielectric fields on the ordering of the dipole moments of the off-center Ge atoms.