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Resume Le diagramme de phase du systeme ternaire Ag-Ga-Te a ete etudie par analyse thermique differentielle, diffraction de rayons X et analyse metallographique. Sur la ligne Ag2Te-Ga2Te3, trois combinaisons ternaires ont ete observees: Ag9GaTe6, a fusion congruente, presentant une transition de phase a 29 °C, hexagonale de part et d'autre de cette temperature; AgGeTe2, quadratique de type chalcopyrite, egalement a fusion congruente; une phase lacunaire Ag x Ga (4−x 3 □ (2−2x) 3 Te 2 , presentant un domaine d'homogeneite pour x compris entre 0,63 et 0,75, quadratique, stable entre 585 et 700 °C, a decomposition peritectique de type binaire. En outre, on note la presence de deux solutions solides ternaires, l'une de type blende situee sur la ligne Ag2Te-Ga2Te3 et s'appuyant sur Ga2Te3, et l'autre de type GaTe, sur la ligne GaTe-Ag. Enfin, une zone de demixtion ternaire liquide-liquide, interne au systeme, est observee. Dans nos conditions experimentales, aucune zone formatrice de verres n'a pu etre decelee. Seize invariants ternaires sont mis en evidence: huit eutectiques, dont l'un est degenere sur le sommet gallium, et huit peritectiques, sept transitoires et un vrai de type binaire.

Two isostructural compounds are observed in the phase diagrams of the systems Ga2Te3-SnTe and Ga2Te3-PbTe. They have the general formula MGa6Te10 (M = Sn″ or Pb). They present a peritectic decomposition, at respectively 695 et 725°. The crystal structure is solved for SnGa6Te10. The rhombohedral cell, space group R32, contains 2 formulas ; a = 10.207 A, α = 89,74°. Gallium atoms are inside fully occupied tetrahedral sites. Tin atoms partially occupy, in a disordered way, 2 octahedral sites. The same structural type is observed for In2Ga6Te10, in which all the octahedral sites are filled.

Three phases are present in the GaTe system: Ga 2 Te 5 , Ga 2 Te 3 , and GaTe. Ga 2 Te 5 is stable in a narrow temperature domain, between about 400 and 495°C (its peritectic decomposition). The phase diagram is established from DTA and X-ray diffraction studies. The crystal structures of GaTe and Ga 2 Te 5 are described. The first one contains GaGa pairs and the second one a square plane coordination of Te, in which the atoms are bonded by covalency. The formation of compounds involving monovalent Ga is discussed, in connection with the existence of SnGa 6 Te 10 , in which Sn can be substituted by other monovalent or divalent cations.