Promotion of tin oxide gas sensor by aluminum doping

Effects of Al-doping on tin oxide based elements were investigated in the Al content range 0.001-5.000%. Gas sensitivity to H₂ and i-C₄H₁₀ was found to be promoted extensively when 1 or 5% Al was doped, while promotion was modest with doping up to 0.1% Al. Seebeck coefficients indicated that carrier concentration decreased with Al-doping, resulting in an increase in Debye length. At the same time, the crystallite size of tin oxide was found to decrease especially drastically when Al was doped excessively. It was concluded that the increased Debye lengths and decreased crystallite sizes were combined to produce the microstructure responsible for extremely high gas sensitivity of 1 and 5% Al-doped elements.