Mixed-conducting contributions to electrical transport in Br-doped BaCe0.8Y0.2O3-d

Introduction of halogen anions in protonic-ceramic doped barium cerates has recently been claimed as a successful strategy for improving stability under aggressive environments associated with the presence of CO2 or high... [ view full abstract ]

Introduction of halogen anions in protonic-ceramic doped barium cerates has recently been claimed as a successful strategy for improving stability under aggressive environments associated with the presence of CO₂ or high water-vapour partial pressure [1]. However, the presence of halogens in the oxygen sublattice of the perovskite has an inherent effect on the defect chemistry of the material which may considerably affect the concentration of the electrical-charge carriers. In the current work, mapping of the partial conductivities of BaCe_0.8Y_0.2O_{2.9-(y/2)±δ}Br_y (0 ≤ y ≤ 0.2) has been performed by impedance spectroscopy in wet and dry conditions of O₂, N₂ and H₂/N₂ as a function of temperature. The competition between different charge carriers is reflected in different electrical responses under variations of oxygen and water-vapour partial pressures. The conductivity improves considerably in dry O₂ in comparison to dry N₂ and H₂, confirming a marked influence of electron holes, mainly at high temperature. Moreover, in the intermediate temperature range the system presents an improved conductivity under wet atmospheres in comparison to dry, supporting the existence of a significant protonic contribution in wet conditions. A specific methodology for determination of electrical transport contributions, consisting of the effect of pH₂O on the conductivity dependence with oxygen partial pressure [2,3], was also employed. A higher p-type electronic component as Br content increases supports a mixed compensation mechanism in which the oxygen-vacancy concentration decreases and electron-hole concentration increases.