High-pressure spinel type Al 2S 3 and MnAl 2S 4

New spinel type forms of Al ₂S ₃ and MnAl ₂S ₄ were prepared at pressures from 2 to 65 kb. The Al ₂S ₃ was shown to exhibit a structure similar to β-In ₂S ₃ in which ordered vacancies result in a super lattice with a tetragonal cell. The cell dimensions are a = 7.026 ± 0.001 Å, c = 29.819 ± 0.001 Å. Electrical measurements show semiconducting behavior with ϱ _{298° K} = 10 ⁹ Ω cm, Ea = 0.3 eV. The spinel form of MnAl ₂S ₄ exhibits a range of stoichiometry as indicated by a range of cell dimension from a = 10.092 ± 0.001 Å to a = 10.010 ± 0.001 Å. Resistivity and magnetic measurements indicate semiconducting and paramagnetic behavior.