A first–principles study on polar hexagonal Cs 2 Te M 3 O 12 ( M = W, Mo): New visible–light responsive photocatalyst

The crystal structures, electro–optical properties, and charge carrier effective masses of Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 with hexagonal, polar and non–centrosymmetric crystal structure were investigated based on density functional theory. Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 are found to be indirect K (1/3, 1/3, 0) → G (0, 0, 0) band gap semiconductors ( E g > 3 eV) with small effective masses of photogenerated charge carriers. The mixing of octahedrally coordinated d ° transition metal cations (W 6+ and Mo 6+ ) with the filled p orbitals of the oxygen ligands leads to the formation of some W 5+ /Mo 5+ sites and splitting of d orbitals into the partially filled t 2g ( dxy , dyz , and dzx ) orbitals and empty e g ( dz 2 and dx 2 – y 2 ) orbitals. The top of the valence bond is mainly contributed by O 2 p orbital of the oxygen ligands mixed with the partially filled t 2g orbitals of W 5 d /Mo 4 d , while the conduction band mainly consists of empty e g orbitals of W 5 d /Mo 4 d with a little contribution of O 2 p orbitals. The dielectric function exhibits a slight anisotropic behavior and optical absorption peak for Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 belonging to the strong electronic transition O 2 p → W 5 d /Mo 4 d within the octahedral units. According to the estimated valence band and conduction band edges, Cs 2 TeW 3 O 12 and Cs 2 TeMo 3 O 12 can be applied as visible−light−responsive photocatalysts for the decomposition of organic pollutants and dye molecules. Also, Cs 2 TeMo 3 O 12 can be used in water splitting for hydrogen generation but Cs 2 TeW 3 O 12 requires further experimental studies to confirm its ability for water splitting.