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

Abstract

Acceptor and donor doped SrTi 1− x Fe x O 3− δ 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°C and 1000°C. Doped and undoped samples with x=0.3 obey an R∝ pO 2 −1/5 power law. Undoped samples show negligible temperature dependence in a small oxygen partial pressure ( pO 2) range between 10 −2 and 3×10 −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°C and 975°C TCR=0 can be found.