Electronic properties and effective masses of hexagonal Bi9O7.5S6: First-principles calculations

Abstract

The electronic band structure, density of states, bond character and effective masses of hexagonal Bi9O7.5S6 crystal have been systematically investigated by applying first-principles calculations based on the density functional theory. Approving agreement between experimental and computational results for lattice parameters shows that the GGA-PBE method is suitable. Bi9O7.5S6 is an indirect band gap semiconductor with the value of 1.383eV using the GGA-PBE functional. The detailed analysis of Mulliken populations in Bi9O7.5S6 demonstrates the covalent nature orders for Bi1–S1, Bi2–O1(1), Bi2–O1(3) and Bi2–O2 bond are Bi1–S1>Bi2–O1(3)>Bi2–O2>Bi2–O1(1) on account of bond population values. More interestingly, the electron effective masses are larger in the interlayer direction than in the intralayer one, while the hole effective masses are lower in the interlayer direction than in the intralayer one. The photoinduced carriers for Bi9O7.5S6 have the high mobility that can be inferred from the effective masses of electron and hole in comparation with Bi2O3 and Bi2S3. The Bi9O7.5S6 is a strong photo-oxidation catalyst but the reduction power is limited in aqueous solutions.