Defect chemistry and proton-dopant association in BaZrO3 and BaPrO3

Abstract

Defect reactions, water incorporation and proton-dopant association in the BaZrO₃ and BaPrO₃ perovskite materials are investigated using well-established atomistic simulation techniques. The interatomic potential models reproduce the experimental cubic BaZrO₃ and orthorhombic BaPrO3 structures. The high defect energies suggest that significant intrinsic disorder (either Frenkel, Schottky or reduction) in BaZrO₃ is unlikely, which is consistent with the relative chemical stability of this system. In contrast, favourable redox processes are found for intrinsic reduction of BaPrO₃, and oxidation of acceptor-doped BaPrO₃, the latter leading to p-type conduction properties as observed experimentally. Binding energies for dopant-OH pairs in BaZrO₃ indicate the weakest association for Gd and Y dopants, and the strongest association for Sc. The high binding energies for all the dopant-OH pair clusters in BaPrO₃ suggest strong proton trapping effects, which would be detrimental to proton conductivity. The water incorporation or hydration energy is found to be less exothermic for BaZrO₃ than for BaPrO₃, the higher exothermic value for the latter suggesting that water incorporation extends to higher temperatures in accord with the available thermodynamic data. The energies and pathways for oxide ion migration in both materials are also investigated.