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

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. H has a pseudotetragonal (sphalerite type) structure : a = 5.774(2) A, c = 11.617(6) A. The structure of 11 was solved in a reduced unit cell with a = 5.774(2) A b = 5.774(2) A, c = 7.095(6) A, alpha = 113.95(5)degrees ,beta =113.95(5)degrees, gamma= 90.00(4)degrees, Z = 1. sp. gr. P1. III has a triclinic cell (disordered structure of 11): a= 4.088(1) A, b = 4.091(2) A, c = 4.101 (1) A. alpha = 60.05(1)degrees ,beta = 60.08( 1)degrees , gamma = 89.98(4)degrees, Z = 1, sp. ar. 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.