Fig. 1. Temperature dependence of resistivity R(T) for Pb_0.8Sn_0.2Te_1-ySe_y samples. 1 - y=0, 2 - y=0.05, 3 - y=0.25, 4 - y=0.33, 5 - y=0.5, 6 - y=0.67, 7 - y=0.83. Curves 3-7 are shifted up by 35, 55, 75, 130, and 165 units, respectively. All samples are of n-type. Arrows indicate the direction of temperature change during recording the curves. The insert shows the dependence of T_c on y.