Chemical diffusion of oxygen in tin dioxide

Tin(IV) oxide is widely used in the Taguchi sensor for the detection of red ox-active gases. The performance of the sensor critically depends on oxygen transport parameters since perceptible values of the chemical diffusion co efficient of oxygen cause severe drift effects. The present work investigat es the kinetics of oxygen exchange by two independent methods, an EPR relax ation technique and the well-known conductivity relaxation technique. The e xperiments were performed on nominally undoped single crystals which contai ned traces of iron and aluminum. In the temperature range from 700 to 1000 degreesC the chemical diffusion coefficient is obtained as D-delta = 0.02 c m(2) s(-1) exp(-0.9 eV/kT). The results of the relaxation experiments were complicated by additional processes occurring on different time scales. A d oping independence assumed, we conclude that the kinetics of drift processe s are determined by the surface exchange reaction of oxygen on SnO2 rather than by the chemical diffusion of oxygen. (C) 2001 Elsevier Science B.V. Al l rights reserved.