Syntheses and characterization of two new selenides Ba5Al2Se8 and Ba5Ga2Se8

Two new barium selenides Ba5Al2Se8 and Ba5Ga2Se8 have been synthesized by solid-state reactions. The structures of Ba5Ga2Se8 and Ba5Al2Se8 were determined by single-crystal X-ray diffraction method and the Rietveld method, respectively. The two isostructural compounds crystallize in space group Cmca of the orthorhombic system with isolated MSe4 (M = Al, Ga) tetrahedra separated by Ba atoms. The optical band gap of 2.51(2) eV for Ba5Ga2Se8 was deduced from the diffuse reflectance spectrum. Band structure calculation indicates that Ba5Ga2Se8 is a direct-gap semiconductor. The valence band maximum is dominated by Se 4p orbitals, while the Ba 5d orbitals have the largest contribution to bottom of the conduction band.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ Two new compounds Ba5M2Se8 (M = Al, Ga) have been synthesized for the first time. ▶ The crystal structures contain isolated MSe4 tetrahedra separated by Ba atoms. ▶ The measured optical band gap is 2.51(2) eV for Ba5Ga2Se8. ▶ The Ba 5d orbitals were found to have significant contribution to the energy bands around Fermi level.