Defect structure and oxygen sensing properties of Mg-doped SrTiO3 thick film sensors

The preparation of oxygen sensors based on Mg-doped SrTiO3 thick film is described briefly. The oxygen sensing properties and the defect structure of the samples have been investigated as a function of the Mg content. The results show that all samples exhibit p-type semiconduction in the P-O2 region 3.8 x 10(-4)-2.6 x 10(-1) atm and temperature range 400-1000 degrees C. A sensor prepared from the pre-calcined powder of Sr(Mg0.4Ti0.6)O3-delta revealed the best oxygen sensing properties. When the temperature is between 500 and 800 degrees C, its sensitivity to the change of P-O2 is 7-8.5 and its response and recovery times are 3 and 28-32 s, respectively. It can be used for monitoring and controlling the combustion processes under excess air (lean-burn) conditions. In addition, its approximate dependence of sigma proportional to P-O2(1/3) was observed at intermediate temperature. To explain this result a new defect structure is proposed, in which a double ionized oxygen vacancy, V-O double ionized acceptor of Mg, Mg-Ti'', and an association defect formed by Mg-Ti'' trapping one hole, (Mg-Ti'' h .)', are the important defects. (C) 1997 Elsevier Science S.A.