Chemical oxygen diffusion coefficient measurement by conductivity relaxation - correlation between tracer diffusion coefficient and chemical diffusion coefficient

Chemical oxygen diffusion coefficient ((D) over tilde) was measured by conductivity relaxation experiments on La2Cu0.5Ni0.5O4+delta ceramics. This method consists of abruptly changing the oxygen partial pressure in the surrounding atmosphere of the sample. The consequent evolution of the electrical conductivity is recorded as a function of time, at fixed temperature. The transient behaviour during the re-equilibration process is analysed on the basis of the second Fick's law. In parallel, the oxygen tracer self-diffusion coefficient (D*) was derived from isotopic exchange experiments monitored by SIMS analysis. Finally, the oxygen over-stoichiometry (delta) was computed from thermogravimetric experiments, under different p(O2), in order to determined the thermodynamic factor (gamma). A quantitative agreement between (D) over tilde and gammaxD*, observed over a wide temperature range (500-900 degreesC), confirms the validity of the experimental method and of the Wagner's theory, applied to the oxygen diffusion in this compound. (C) 2003 Elsevier Ltd. All rights reserved.