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 950-1050degreesC. The product from the reaction is predominantly BaSnO3 with some SnO2 and Ba2SnO4 impurities. Annealing of the SHS powders at 1000degreesC for 2-72 h forms phase pure cubic BaSnO3, a = 4.116 (3) Angstrom. X-ray photoelectron spectroscopy showed the expected Ba: Sn: O ratios with binding energy shifts for Ba 3d(5/2) at 775.8 eV; O 1s at 526.1 eV and Sn 3d(5/2) at 482.7 eV. Scanning electron microscopy showed ca 0.5 mum agglomerates of cubic crystallites of dimension 0.15 mum, 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. (C) 2002 Kluwer Academic Publishers.