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

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 Mossbauer 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.