Self-propagating solid state routes to BaSnO3; investigation of gas sensing properties

Thermal initiation of mixed powders of a tin source (Sn, SnCl2, SnO2) and barium peroxide in air produce a self propagating high temperature synthesis (SHS) wave of velocity 2–5 mms−1 and temperature 950–1050°C. The product from the reaction is predominantly BaSnO3 with some SnO2 and Ba2SnO4 impurities. Annealing of the SHS powders at 1000°C for 2–72 h forms phase pure cubic BaSnO3, a = 4.116 (3) A. X-ray photoelectron spectroscopy showed the expected Ba: Sn: O ratios with binding energy shifts for Ba 3d5/2 at 775.8 eV; O 1s at 526.1 eV and Sn 3d5/2 at 482.7 eV. Scanning electron microscopy showed ca 0.5 μm agglomerates of cubic crystallites of dimension 0.15 μm, whilst energy dispersive analysis by X-rays showed the expected barium to tin ratios. Infra-red spectra of the annealed products were equivalent with commercial samples. The SHS prepared barium stannates were good sensors for carbon dioxide, showing n-type response.