Phase equilibria in the (SnSe)_1-x(ErSe)_x system have been studied using the methods of physico-chemical analysis –  differential-thermal, X-ray diffraction, microstructural, microhardness and density measurements and its state micro­diagram has been plotted. It was established
that at room temperature in the (SnSe)_1-x(ErSe)_x based on SnSe the solid solutions reach 5 mol. % ErSe. Microhardness and density dependences on composition have been examined.  As well temperature dependences of electrical conductivity and electromotive force for alloy
of (SnSe)_1-x(ErSe)_x have been studied