Abstract
The phase equilibrium in the Bi2S3 – YbS system was studied by the methods of physicochemical analysis – DTA, XRD, MSA through measuring the micro-hardness and density, and a state diagram was plotted. It has been found that this system is a quasi-binary cross-section of the Yb-Bi-S ternary system. The formation of the two ternary compounds with YbBi2S4 and YbBi4S7 compositions was detected and the areas of solid solutions determined.