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 str ucture of the samples have been investigated as a function of the Mg c ontent. The results show that all samples exhibit p-type semiconductio n in the P-O2 region 3.8 x 10(-4)-2.6 x 10(-1) atm and temperature ran ge 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 sensitivit y to the change of P-O2 is 7-8.5 and its response and recovery times a re 3 and 28-32 s, respectively. It can be used for monitoring and cont rolling the combustion processes under excess air (lean-burn) conditio ns. In addition, its approximate dependence of sigma proportional to P -O2(1/3) was observed at intermediate temperature. To explain this res ult a new defect structure is proposed, in which a double ionized oxyg en vacancy, V-O double ionized acceptor of Mg, Mg-Ti'', and an associa tion defect formed by Mg-Ti'' trapping one hole, (Mg-Ti'' h .)', are t he important defects. (C) 1997 Elsevier Science S.A.