Aluminium telluride can be obtained by direct combination of aluminium metal with elemental tellurium at 1,000 °C (1,270 K; 1,830 °F).[1]
2 Al + 3 Te → Al2Te3
Properties
Aluminium telluride is a very air-sensitive[3] dark grey to black solid.[1] It has a band gap of 2.4 eV.[4] The compound decomposes in humid air.[5].
In its pure form, it occurs in at least two phases. The orange-red low-temperature (α) modification transforms into the yellow high-temperature (β) form at 720 °C (993 K; 1,328 °F). The conversion from β- to α-Al2Te3, which is associated with such a small enthalpy change that it cannot be observed with differential thermal analysis, takes place after prolonged annealing just below the conversion point. The α form crystallizes in the monoclinic crystal system with the lattice constants a = 13.885 Å, b = 7.189 Å, c = 4.246 Å, p = 90.21° and an additional superstructure. The β form has a monoclinic crystal structure with space groupP21/c and the lattice constants a = 7.181(1) Å, b = 12.848(3) Å, c = 14.167(3) Å, and b= 90.04(2)°. This form represents a separate structure type. The tellurium atoms form a hexagonal dense packing parallel to the (001) plane; one-third of the tetrahedral vacancies are occupied by aluminium atoms, whereby the tetrahedral vacancies are occupied in such a way that a layered structure is formed. Some sources also report another form of the defect wurtzite type.[3]