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

Abstract

Chemical oxygen diffusion coefficient ( D ̃ ) was measured by conductivity relaxation experiments on La 2Cu 0.5Ni 0.5O 4+δ 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 (δ) was computed from thermogravimetric experiments, under different p O2, in order to determined the thermodynamic factor (γ). A quantitative agreement between D ̃ and γ×D*, observed over a wide temperature range (500–900 °C), confirms the validity of the experimental method and of the Wagner's theory, applied to the oxygen diffusion in this compound.