High resolution structural refinement and band gap characterization of the defect chalcopyrites CuIn₅Te₈, AgIn₅Te₈ and AuIn₅Te₈

The AIn₅Te₈ compounds (A ​= ​Cu, Ag, Au), charge balanced defect chalcopyrites, are characterized. Synchrotron powder diffraction shows that the Cu and Ag analogs are tetragonal to high precision at room temperature, with classic 158 (I-III₅-VI₈) defect chalcopyrite structures in space group I4¯2m. These materials display ordered vacancies but disordered cations. The degree of cation intermixing is more significant in the Cu case than in the Ag case. In contrast, AuIn₅Te₈, a previously unreported 158 defect chalcopyrite, exhibits a tetragonal P4¯2c structure with disordered vacancies and cations, displaying poorer crystallinity than the other two materials. The direct optical band gaps (E_g), determined from UV–vis absorption measurements, are estimated to be 0.94, 0.99, and 0.77 ​eV, respectively. Comparison to the corresponding sulfides and selenides for 158 and standard 112 (I-III-VI₂) type chalcopyrites is reported where the data are available.