Figure 6. Temperature dependence of resistivity for Pb_1-xSn_xTe_1-ySe_y crystals with fixed Sn concentration (x=0.2) and variable y /15/. 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. The insert shows the dependence of T_c on y.