Mechanism of electric conductivity change in BaCo0.7Fe0.2Nb0.1O3 - δ at intermediate temperature

In this paper, the change mechanism of electric conductance behavior of BaCo0.7Fe0.2Nb0.1O3 - delta (BCFN) materials at the temperature range 550-650 degrees C is studied. The ionic conductivity separated by the electrode-blocking method exhibits a gradual increase at this temperature range. However, the electronic conductivity shows a steady curve. According to the characterization of thermogravimetry (TG) and O-2-Temperature Programmed Desorption (O-2-TPD), the desorption of oxygen and the formation of oxygen vacancies also occur at this temperature range. Using the oxygen vacancy diffusion coefficients D-chem (obtained by Electric Conductivity Relaxation (ECR)) and the oxygen vacancy content (obtained by TG), the theoretical ionic conductivity is calculated by Einstein-Nernst equation. The theoretical value is in good agreement with the experimental results, which means that the increase of BCFN ionic conductivity can be explained by the mostly ionized oxygen vacancies. The defect reaction of BCFN suggests that there's consumption of 4+ charge B sites ions accompanied with the formation of oxygen vacancies, which will stabilize the electrical conductivity according to the Zner double exchange effects. Besides, the X-ray photoelectron spectroscopic (XPS) results suggest that the B sites ions are also greatly influenced by the formation of oxygen vacancies. This may increase the exchange energy in the Zener double exchange effect and stabilize the electrical conductivity. (C) 2015 Published by Elsevier B.V.