Preparation of BaSnO3 and Ba0.96La0.04SnO3 by reactive core–shell precursor: formation process, CO sensitivity, electronic and optical properties analysis

Abstract

We propose a facile and economic strategy for preparing BaSnO₃ particles from a room-temperature fabricated BaCO₃@SnO₂ core–shell precursor. The core–shell structure promoted the mixing degree of the reactants and effectively suppressed sintering of the particles, therefore, pure BaSnO₃ was obtained at 800 °C, nearly 400 °C lower than traditional solid-state reaction (SSR) method, and showed better CO sensitivity than BaSnO₃ prepared by SSR route. The phase transformation, morphology changes, and structure evolution from the precursor to the final BaSnO₃ were systematically investigated, and a clear picture of the formation mechanism of BaSnO₃ was given. Slightly La doped BaSnO₃ was prepared through the same procedure as BaSnO₃, which proved the availability of this method for synthesis of slightly doped BaSnO₃ materials. The optical properties and total conductivity of pure and La doped BaSnO₃ were compared. The results showed that the band gap of the La-doped sample was slightly increased, while the resistivity was more than six orders of magnitude lower than that of pure BaSnO₃. The underlying reason was studied for the first time by directly monitoring the electron structure of Sn cations at the atomic scale using ¹¹⁹Sn Mössbauer spectroscopy. It was found that the introduction of La in BaSnO₃ solid solution would induce electron donating to the 5s orbital of Sn⁴⁺, and Sn cations were slightly reduced. This result gave clear evidence of conduction band filling in La-doped BaSnO₃, which accounted for the change in the electric and optical properties.