Y doping of BaZrO3 may lead to optimum conditions for proton conduction at operating temperature of solid oxide fuel cells: a first principles study

Abstract

First-principle calculations are performed to investigate Y substitutional defects at ground state and at 1000 K, for Ba- and Zr-rich chemical environments. In dependence on the Fermi level, at ground state singly positively charged Y may be potentially stable on Ba site () and neutral as well as singly negatively charged Y on Zr site ( and ). However, using recent results for the doubly positively charged oxygen vacancy () and taking account charge compensation, Fermi level pinning occurs, so that under Ba-rich conditions and are really stable. A similar consideration yields and as stable defects in the Zr-rich case. Concerning which occurrence is a prerequisite to obtain a good proton conductor, by Y doping, at ground state only in the Ba-rich case a moderate concentration can be formed. At 1000 K the situation is improved importantly. The consideration of vibrational contributions to the free formation energy of Y on Zr site shows an increase of the stability of and Under Ba-rich conditions Fermi level pinning results in a free formation energy for the doubly positively charged O vacancy of 0.481 eV which corresponds to a high concentration and optimum conditions for proton conduction. In Zr-rich case the respective value is 0.863 eV which leads also to relatively high occurrence but the situation is less favourable than for the Ba-rich environment.