The results of neutron diffraction researches in the temperature region 10 - 290 K as well as thermoelectric, magnetic and electric properties of solid solution Pb0,8Sn0,2Te of high structural perfection within temperature range (4,2-25) K in magnetic fields up to 4T are represented. The analysis of experimental data testifies to the existence of phase transformations at Tc1 = (35 ± 5) K, Tc2 = (110 ± 5) K, Tc3 = (140 ± 5) K and Tc4 = (260 ± 5) K. The temperature hysterenis of thermoelectric power is observed in the interval Tc1 < T < Tc2. It testifies to the ferroelectrics transition of I kind and lowering of crystal symmetry. Phase transformations at Tc3 and Tc4 are transitions of presumable the II kind. The structural perfection improvement of single crystals Pb0,8Sn0,2Te results in the shift of the first phase transition temperature Tc1 from 20 - 25 K to Tc1 = 35 K. This shift can be described by Dingle temperature - TD, which is determine a degree of crystal imperfection at T = O K.