Electronic Structure and Defect Chemistry of Tin(II) Complex Oxide SnNb2O6

Tin(II) complex oxides have unique valence band structures due to the contribution of the Sn 5sp orbitals. We investigate the fundamental electronic, optical, and defect properties of tin(II) niobate (SnNb2O6) via first-principles calculations and the characterization of epitaxial thin films. The calculations reveal its characteristic valence band structure similar to that of SnO. SnNb2O6 is predicted to have an indirect-type band structure with an indirect gap of 2.41 eV and a direct gap of 2.55 eV. Epitaxial thin films of SnNb2O6 with smooth surfaces are fabricated on A1(2)O(3) (0112) substrates using pulsed laser deposition. Experimental and theoretical absorption spectra consistently show an absorption threshold of similar to 2.5 eV. Both undoped thin films and doped sintered samples fabricated by a solid-state reaction show high electrical resistivities. Theoretical defect energetics suggests that the high resistivity is due to the charge compensation by oxygen vacancies and tin-on-niobium antisites.