Local geometries and energetics of hydrogen in acceptor-doped SrZrO3

The local geometry and chemical bonding around proton and acceptor dopant in perovskite-type oxide SrZrO3 have been investigated by the pseudopotential method and the DV-Xα molecular orbital method. Special attention is directed towards the MO6 octahedron in the perovskite-type structure, where Ms are acceptor dopants (e.g., Y and Al) substituted for Zr ions in the oxide. shown that local electronic state of the constituent ions in the MO6 octahedron is a good measure of the local geometrical change of the octahedron with doping. For example, there is a strong resemblance in the local ionic state and hence the local geometry of the octahedron between the undoped and Y-doped oxides. However, there is little resemblance between the undoped and Al-doped oxides. The calculated activation energy for protonic conduction is higher in the Al-doped oxide than that in the Y-doped oxide, in agreement with experimental results. From these results, it is found that such an acceptor dopant that does not change local electronic state or local geometry of the octahedron is a preferable element for enhancing protonic conductivity in perovskite-type oxides.