First-principles study of protonic conduction in In-doped AZrO3 (A=Ca, Sr, Ba)

The first-principles calculations based on the density functional theory were carried out to investigate the effects of A-cations on the protonic conductivity of AZrO3 (A=Ca, Sr, Ba). The local geometries around proton and dopant ion, formation energies of interstitial proton and activation energies for proton transfer were simulated in the In-doped CaZrO3, SrZrO3 and BaZrO3. The results showed that the crystallographic feature of AZrO3 (A=Ca, Sr, Ba) is an important factor to control the protonic conduction. In the In-doped CaZrO3 or SrZrO3 with the orthorhombic structure, there is a unique stabilized proton site located between two adjacent octahedra. But in the In-doped BaZrO3 with the cubic structure, there exists a certain region of stable sites between them. As the ionic radii of A-cations decrease, the crystal symmetry changes from cubic to orthorhombic, resulting in the rotation of ZrO6 (or InO6) octahedra, which causes the increase of activation energies for proton transfer in the oxides.