X-ray diffraction study of the Cu2Se-In2Se3-Cr2Se3 system near CuInCr2Se5

Abstract

The structure of three compounds in the Cu2Se-In2Se3-Cr2Se3 system near CuInCr2Se5 is determined by single-crystal x-ray diffraction: CuInCr4Se8 (I), Cu2In2Se4 (II), and Cu0.5In0.5Se (III). I has a cubic (spinel type) structure: a = 10.606(4) A, Z = 4, sp. gr. F43m. II has a pseudotetragonal (sphalerite type) structure: a = 5.774(2) A, c = 11.617(6) A. The structure of II was solved in a reduced unit cell with a = 5.774(2) A, b = 5.774(2) A, c = 7.095(6) A, α = 113.95(5)°, β= 113.95(5)°, γ= 90.00(4)°, Z = 1, sp. gr. P1. III has a triclinic cell (disordered structure of II): a = 4.088(1) A, b = 4.091(2) A, c = 4.101(1) A, α = 60.05(1)°, β = 60.08(1)°, γ = 89.98(4)°, Z = 1, sp. gr. P1. The Cu and In atoms in I sit in inequivalent tetrahedral sites, and the Cr atoms reside in octahedral interstices of the close packing of Se atoms. The bond lengths are In−Se = 2.538(6), Cr(1)−Se(1) = 2.514(7), Cr(1)−Se(2) = 2.576(8), and Cu−Se = 2.437(5) A. In II, all of the atoms sit in tetrahedral sites; the mean bond lengths are In−Se = 2.578(6) and Cu−Se = 2.44(1) A. In III, the Cu and In atoms are fully disordered in the same tetrahedral site; the mean Cu(In)−Se bond length is 2.508(6) A.