A part of the research devoted to the preparation and characterization of ternary tetradymite-type crystals, was performed with ternary crystals of Bi_2-xIn_xSe₃ and Bi₂Se_3-xAs_x. The other part of the research devoted to the tetradymite-type crystals doped with transition metals was focused on the effect of doping of with Ti, Zr, V, Mn and Fe on the transport and magnetic properties of the crystals. Sb_2-xV_xTe₃ crystals (x 0.03) and Bi_2-xFe_xTe₃ (x <= 0.08) show at low temperatures a ferromagnetic behaviour, belonging to a new group of dilute magnetic semiconductors.