Crystal Structure of CuIn3Se5 Semiconductor Studied Using Electron and X-ray Diffractions

Abstract
The crystal structure of CuIn3Se5 is investigated by complementary use of electron and X-ray diffractions. The lattice parameters are a=5.7539(3) and c=11.519(1) Å and the space group is uniquely determined to be I42m. The crystal is not constructed of a rigid unit cell but by three kinds of local Se tetrahedrons, such as CuIn2Se4, CuIn3Se4 and In3Se4, which minimize the numbers of electron excess and deficient bonds. The average unit cell is represented by Cu0.8In0.4In2Se4, where Se and some In atoms fully occupy the 8i site with x≈1/4 and z≈1/8, and the 4d site, respectively, and Cu and the remaining In atoms partially occupy 2a and 2b sites, respectively. Since the space group I42m is not a subgroup of I42d which is the space group of CuInSe2, CuIn3Se5 is not related to CuInSe2 from the viewpoint of crystal symmetry. It is neither a vacancy ordered compound nor of a defect chalcopyrite structure.