Defect chemistry and proton-dopant association in BaZrO3 and BaPrO3

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.