Ternary phase relations of the chalcopyrite compound CuGaSe2

The ternary Cu-Ga-Se phase diagram has been determined by DTA and x-ray analysis. In addition to two ternary solid solutions based on the binary compounds Cu_2.xSe and Ga₂Se₃, only one ternary phase, the chalcopyrite CuGaSe₂ (peritectic m.p. 1030°C), was encountered. The liquidus contains two regions of liquid immiscibility, one which extends from the Cu-rich (Cu, Se) binary liquid immiscibility to the Ga-rich (Ga, Se) binary immiscibility, and the other which is a minor extension of the Se-rich (Cu, Se) binary liquid immiscibility. The liquidus maxima include those at the binary boundaries: Cu (1087°C), Cu₆₇Se₃₃ (1148°C), GaSe (960°C); and a ternary liquidus maximum at Cu₁₉Ga_28.5Se_52.5 (1112°C), the maximum melting point of a solid solution based on the defect-zincblende phase of Ga₂Se₃. The primary phase fields are identified and the crystal growth of CuGaSe₂ solid solutions from nonstoichiometric melts is discussed, especially the most satisfactory Bridgman growth from the Cu₂Se-CuGaSe₂ join. Subsolidus phase relations are also proposed for the Cu-Ga-Se system, and probable similaritics in all I-III-VI ternary diagrams are suggested.