The role of deep acceptor levels in hydration and transport processes in BaZr1 − x Y x O3 – δ and related materials

Abstract

A statistical theory of hydration and defect formation in acceptor-doped proton-conducting perovskites has been developed taking into account contributions of the electron hole and vibrational subsystems. Using yttrium-doped BaZrO3 as an example, we show that deep acceptor states can significantly affect hydration, oxidation, and transport processes in proton-conducting oxides. The impact of these states on defect thermodynamics strongly depends on their energy and becomes negligible at a depth less than a certain value. We demonstrate that the experimental data on the hole conductivity of barium zirconates can be described both in the band transport model and in the model of small polaron hopping. These scenarios correspond to a somewhat different depth of the acceptor levels, but in both cases, the concentration of bound holes at the acceptor centers can be high enough and these states must be taken into account in the defect formation considerations. The results obtained agree well with experimental data on the hydrogen solubility and the contributions of different carriers (protons, oxygen ions, holes) to the charge transfer in barium zirconates with different doping levels.