CRYSTAL-STRUCTURE OF CUIN3SE5 SEMICONDUCTOR STUDIED USING ELECTRON AND X-RAY DIFFRACTIONS

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)Angstrom and the space group is uniquely dete rmined to be I (4) over bar 2m. The crystal is not constructed of a ri gid unit cell but by three kinds of local Se tetrahedrons, such as CuI n2Se4, CuIn3Se4 and In3Se4, which minimize the numbers of electron exc ess and deficient bonds. The average unit cell is represented by Cu0.8 In0.4In2Se4, where Se and some In atoms fully occupy the 8i site with x approximate to 1/4 and z approximate to 1/8, and the 4d site, respec tively, and Cu and the remaining In atoms partially occupy 2a and 2b s ites, respectively. Since the space group I (4) over bar 2m is not a s ubgroup of I (4) over bar 2d which is the space group of CuInSe2, CuIn 3Se5 is not related to CuInSe2 from the viewpoint of crystal symmetry. It is neither a vacancy ordered compound nor of a defect chalcopyrite structure.