Local electronic structures and chemical bonding in proton conducting Perovskite type oxide, SrZrO3

Local electronic structures around hydrogen and acceptor ions in SrZrO3 are simulated by the DV-Xalpha molecular orbital method. It is shown that the nature of local chemical bonding changes largely with the acceptor dopant and affects the protonic conductivity. Namely, the protonic conductivity decreases as the ionicity difference increases between the dopant and Zr ions. Also, the activation energy increases as the local charge states of oxygen ions neighboring the dopant ion deviate further from those of oxygen ions neighboring the Zr ion. These calculated results are consistent with the measured protonic conductivity and activation energy. These trends are also seen in the other oxides, BaZrO3 and CaZrO3.