Chemical diffusion of oxygen in tin dioxide: Effects of dopants and oxygen partial pressure

Tin dioxide SnO2-delta is a pronounced n-type electron conductor due to its oxygen deficiency. This study investigates the rate of chemical diffusion of oxygen in SnO2-delta single crystals, which is a crucial step in the overall stoichiometry change of the material. The chemical diffusion coefficient D was determined from conductivity- and EPR-relaxation methods. The temperature dependence was found to be D-delta = exp(-4 +/- 2) cm(2) s(-1) exp(-(1.1 +/- 0.3) eV/kT). The dependence on crystal orientation, dopant content and oxygen partial pressure was below experimental error. The latter observation leads to the conclusion that the chemical diffusion coefficient is close to the diffusion coefficient of oxygen vacancies. Along with the relaxation process resulting from the chemical diffusion of oxygen, additional processes were observed. One of these was attributed to complications in the defect chemistry of the material. The relevance of the results for the kinetics of drift processes of Taguchi sensors is discussed. (c) 2005 Elsevier Inc. All rights reserved.