Gallium(III) sulfide

Gallium(III) sulfide, Ga₂S₃, is a compound of sulfur and gallium, that is a semiconductor that has applications in electronics and photonics.

Structure

There are four polymorphs, α (hexagonal), α' (monoclinic), β(hexagonal) and γ(cubic). The alpha form is yellow. The crystal structures are related to those of ZnS with gallium in tetrahedral positions. The alpha and beta forms are isostructural with their aluminium analogues. The similarity in crystal form of gamma- with sphalerite (zinc blende), ZnS is believed to explain the enrichment of gallium in sphalerite ores.

Preparation and chemical properties

Ga₂S₃ can prepared by reacting the elements at high temperature or as a white solid by heating Ga in a stream of H₂S at high temperature (950 Ã‚°C).

It may also prepared by a solid state reaction of GaCl₃ and Na₂S.

The method of production can determine the polymorphic form produced, the reaction of Ga(OH)₃ with H₂S at different temperatures is reported to produce a different polymorph depending on the temperature, α- 1020 K, β- 820 K and γ- above 873 K

Ga₂S₃ decomposes at high temperature forming the non-stoichiometric sulfide, Ga₄S_x (4.8 < x < 5.2). Ga₂S₃ dissolves in aqueous acids and decomposes slowly in moist air forming H₂S.

Ga₂S₃ dissolves in aqueous solutions of potassium sulfide, K₂S to form K₈Ga₄S₁₀ containing the (Ga₄S₁₀)^{8−} anion which has an adamantane, molecular P₄O₁₀ structure.

Ternary sulfides M^IGaS₂, M^IIGa₂S₄ and M^IIIGaS₃ respectively have been of interest due to their unusual electrical properties and some of these can be prepared by reactions of Ga₂S₃ with metal sulfides e.g. CdGa₂S₄:-

Although by itself Ga₂S₃ is not a glass former it can be reacted with rare earth sulfides to form glasses e.g. the reaction with lanthanum sulfide, La₂S₃, forms gallium lanthanum sulfide glass which has interesting optical properties and is a semiconductor.

References