Structure and phase relations of the Zn2x(CuIn)1−xS2 solid solution series

Powder samples of Zn2x(CuIn)1−xS2 alloys were prepared by solid state reaction of the elements (T = 950 °C) and annealed with cooling rates between 2 and 42 K/h in the entire composition range. Structural parameters (e.g. lattice parameter, tetragonal deformation η) were investigated by X-ray diffraction (XRD) studies, the chemical composition was determined by EDX analysis on a transmission electron microscope. The room temperature results showed that mixed crystals in the interval 0 ≤ x < 0.1 crystallize in the tetragonal chalcopyrite-type structure and in the interval 0.4 < x ≤ 1 in the cubic sphalerite-type structure. In between, i.e. for 0.1 ≤ x ≤ 0.4, a miscibility gap was found, indicated by the coexistence of two phases, resulting in crystals containing tetragonal domains in a cubic matrix. In the single-phase regions the lattice parameter follows Vegard's rule, whereas in the 2-phase field the phases try to match in the a-b-plane (atetr ∼ acub), causing an increase of the tetragonal lattice parameter c and herewith a strong increase of the tetragonal deformation η. Thus the tetragonal deformation η = c/2a in 2-phase samples is significantly larger than in tetragonal single-phase samples and even larger than in the end member CuInS2.