Gallium(III) sulfide
# Gallium(III) sulfide

Gallium(III) sulfide, $Ga_2S_3,$ 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

$Ga_2S_3$ can prepared by reacting the elements at high temperature or as a white solid by heating Ga in a stream of $H_2S$ at high temperature (950 °C).

It may also prepared by a solid state reaction of $GaCl_3$ and $Na_2S.$

The method of production can determine the polymorphic form produced, the reaction of $Ga(OH)_3$ with $H_2S$ 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

$Ga_2S_3$ decomposes at high temperature forming the non-stoichiometric sulfide, $Ga_4S_x$ (4.8 < x < 5.2). $Ga_2S_3$ dissolves in aqueous acids and decomposes slowly in moist air forming $H_2S.$

$Ga_2S_3$ dissolves in aqueous solutions of potassium sulfide, $K_2S$ to form $K_8Ga_4S_{10}$ containing the $(Ga_4S_{10})^{8−}$ anion which has an adamantane, molecular $P_4O_{10}$ structure.

Ternary sulfides $M^IGaS_2,$ $M^{II}Ga_2S_4$ and $M^{III}GaS_3$ respectively have been of interest due to their unusual electrical properties and some of these can be prepared by reactions of $Ga_2S_3$ with metal sulfides e.g. $CdGa_2S_4:-$

    $Ga_2S_3$ + CdS → $CdGa_2S_4$

Although by itself $Ga_2S_3$ is not a glass former it can be reacted with rare earth sulfides to form glasses e.g. the reaction with lanthanum sulfide, $La_2S_3,$ forms gallium lanthanum sulfide glass which has interesting optical properties and is a semiconductor.

