[en] Monocrystals of Cd₄GeS₆, Cd₄GeSe₆ compounds and solid solutions on their base are synthesized and grown. By the investigation of physicochemical and photoelectric properties of alloys the existence in the Cd₄GeS₆-Cd₄GeSe₆ system of continuous series of solid solutions is proved. It has been found that the specific resistance and photosensitivity of alloys drop with the increase of selenium content. For Cd₄GeS₆ and Cd₄GeSe₆ polycrystalline compounds the low-temperature specific heat is determined and standard entropy, enthalpy and entropy of their formation are calculated