Materials for temperature independent resistive oxygen sensors for combustion exhaust gas control

Acceptor and donor doped SrTi1-xFexO3-delta materials for novel temperature independent resistive oxygen sensors for lean-burn engine exhaust gases were prepared and characterized by X-ray diffraction. Their electrical resistance, R, was investigated in the oxygen partial pressure range from 10(-4) to 1 bar between 700 degrees C and 1000 degrees C. Doped and undoped samples with x = 0.3 obey an R alpha pO(-1/5) power law. Undoped samples show negligible temperature dependence in a small oxygen partial pressure (pO(2)) range between 10(-2) and 3 X 10(-2) bar. Acceptor (Ga) doping shifts the pO(2) range of negligible temperature dependence to lower pO(2), whereas donor(La) doping results in a right-hand shift to higher pO(2). Combined acceptor and donor doping leads to an extended pO(2) range of negligible temperature dependence. At pO(2) = 10(-1) bar the temperature coefficient of resistance (TCR) of this material composition is always below 250 ppm/K in the complete investigated temperature range. At about 725 degrees C and 975 degrees C TCR = 0 can be found. (C) 2000 Elsevier Science S.A. All rights reserved.