Characterization of the mixed perovskite BaSn1–xSbxO3 by electrolyte electroreflectance, diffuse reflectance, and X-ray photoelectron spectroscopy

Abstract

The band gap of the mixed perovskite BaSn_1–xSb_xO₃ has been reported to be 134 kJ mol^–1(J-M. Hermann, M. R. Nunes and F. M. A. da Costa, J. Chem. Soc., Faraday Trans. I, 1982, 78, 1983), corresponding to 1.4 eV, which is the optimum value for solar-energy conversion. In order to confirm this value, pressed discs of the mixed perovskite were sintered at 1673 K and made into electrodes, and their electrolyte electroreflectance (e.e.r.) spectra measured. The band gap was determined by fitting the e.e.r. spectra to Aspnes' formula for the low-field regime. The band gap of the pure, insulating perovskite BaSnO₃ was determined from its diffuse reflectance spectrum, after application of the Kubelka–Munk formula. The band gap of the mixed perovskite was constant and equal to 330 kJ mol^–1 for Sb concentrations in the range x= 0–10%, in agreement with the observed constancy of the lattice parameter for x= 0–17%, the range over which the perovskite exists as a single phase. The high band-gap energy of this material makes it unsuitable for solar-energy conversion. X-Ray photoelectron spectroscopy measurements showed that all the Sb in the mixed perovskite was present as Sb^V, as would be expected from the high conductivity of the samples. From the atomic ratios it was concluded that probably the surface of the pure BaSnO₃ perovskite is enriched in SnO₂, and that of the mixed perovskite in Sb₂O₅.