Synthesis, structure, and optical properties of BiCuOCh (Ch=S, Se, and Te)

Crystals of BiCuOSe were grown from a salt flux, and the crystal structure was determined by single-crystal X-ray diffraction. BiCuOSe adopts the tetragonal layered structure of LnCuOCh (Ln=lanthanide; Ch=S, Se, and Te) with bond lengths and bond angles in good agreement with those published for powders. Powders comprising mixed chalcogenides across the series BiCuOCh (Ch=S, Se, and Te) were made by reacting Bi2O2Ch and Cu2Ch. Band gaps determined via infrared diffuse reflectance from powders are Eg=0.82 eV for BiCuOSe, 0.89 eV for BiCuOS0.5Se0.5, and 1.07 eV for BiCuOS. The band gap of BiCuOSe inferred from infrared transmission measurements on single crystals is in good agreement with the value obtained from diffuse reflectance from the powder.

Graphical abstractIR absorption of BiCuOCh powders from diffuse reflection (left scale) and polished BiCuOSe single crystal from transmission (right scale). Spectra are normalized to the maximum absorption. Inset: band gap as a function of composition.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► BiCuOSe single crystals are synthesized, and the band gap is measured by direct transmission. ► A new powder synthesis of BiCuOCh1−xCh′x is demonstrated. ► Band gaps of BiCuO(S1−xSex) are determined from diffuse reflection from powders.