Mechanisms of Proton Conduction Undoped, Cubic Perovskites

3 Mechanisms of Proton Conduction (Undoped, Cubic Perovskites) 

From the thermodynamics of such dynamical hydrogen bonds one may actually expect an activation enthalpy of long-range proton diffusion not more than 0.15 eV provided that the configuration O-H... O is linear, for which the proton transfer barrier vanishes at 0/0 separations less than about 250 pm. However, the mobility of protonic defects in cubic perovskite-type oxides has activation enthalpies of the order of 0.4-0.6 eV [35], which raises the question of which interactions are controlling the activation enthalpy of proton transfer. 

The importance of the H/B repulsion is also evidenced by the finding that the activation enthalpies of proton mobility in cubic perovskites with pentavalent B-site cations (I-V perovskites) are significantly higher than for perovskites with tetravalent B-site cations (II IV perovskites) [36]. On this background, proton mobility in III III perovskite may be even higher, provided the oxide shows cubic symmetry. 

---