Diagramme de phases gallium-soufre et études structurales des phases solides

A description of the phase diagram for Ga-S and structural studies of all the solid phases are given. Two types of compounds are found (1). "Ga2S3" occurs in four forms. The monoclinic form α' is exactly stoichiometric and stable from room temperature to melting. The hexagonal form α and the wurtzite-type form β exist only at high temperature; their formation requires a very small defect of sulfur. Passage from the hexagonal form α to the wurtzite form β is progressive. The γ-blende-type form is clearly substoichiometric and only exists in a small domain of temperature. Gallium atoms are in tetrahedra for all the crystallographic forms. (2) Two varieties of GaS are found: 2H and 3R. A structural study is made using powder data for GaS 3R; this form is metastable for all temperatures of the solid state. Pairs of Ga are inside antiprisms of sulfur atoms for the 3R form and inside triangular prisms for the 2H form. Two liquid-liquid immiscible phases are observed between Ga and GaS and between Ga2S3 and S.