Aluminium sulfide

Crystal structure

More than six crystalline forms of aluminium sulfide are known and only some are listed below. Most of them have rather similar, wurtzite-like structures, and differ by the arrangement of lattice vacancies, which form ordered or disordered sublattices.

The β and γ phases are obtained by annealing the most stable α-Al₂S₃ phase at several hundred degrees Celsius. Compressing aluminium sulfide to 2–65 bar results in the δ phase where vacancies are arranged in a superlattice of tetragonal symmetry.

Unlike Al₂O₃, in which the Al(III) centers occupy octahedral holes, the more expanded framework of Al₂S₃ stabilizes the Al(III) centers into one third of the tetrahedral holes of a hexagonally close-packed arrangement of the sulfide anions. At higher temperature, the Al(III) centers become randomized to give a "defect wurtzite" structure. And at still higher temperatures stabilize the γ-Al₂S₃ forms, with a structure akin to γ-Al₂O₃.

Molecular derivatives of Al₂S₃ are not known. Mixed Al-S-Cl compounds are however known. Al₂Se₃ and Al₂Te₃ are also known.