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

Tin dioxide SnO2−δ is a pronounced n-type electron conductor due to its oxygen deficiency. This study investigates the rate of chemical diffusion of oxygen in SnO2−δ single crystals, which is a crucial step in the overall stoichiometry change of the material. The chemical diffusion coefficient Dδ   was determined from conductivity- and EPR-relaxation methods. The temperature dependence was found to be Dδ=exp(-4±2)cm2s-1exp(-(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.

Graphical abstractMeasurements of the oxygen chemical diffusion coefficient indicate that rather the sluggish oxygen incorporation at the surface than the bulk diffusion causes the drift of SnO2−δ-based Taguchi sensors.Figure optionsDownload full-size imageDownload as PowerPoint slide