Density-functional calculations of prefactors and activation energies for H diffusion in
- 27 September 2007
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 76 (9), 094301
- https://doi.org/10.1103/physrevb.76.094301
Abstract
Density-functional calculations are used to investigate hydrogen diffusion in the solid-state proton conductor . Activation energies and prefactors for the rate of proton transfer and reorientation are evaluated for a defect-free region of this simple cubic perovskite-structured oxide. Both semiclassical over-barrier jumps and phonon-assisted tunneling transitions between sites are considered. It is found that the classical barriers for the elementary transfer and reorientation steps are both of the order of . The quantum-mechanical zero-point motion effects are found to be sizable, to effectively reduce the barrier heights, and to make the prefactors similar for the transfer and reorientation steps. The Flynn-Stoneham model [Phys. Rev. B 1, 3966 (1970)] of phonon-assisted tunneling yields an activation energy of around and a very small prefactor for proton transfer, whereas the corresponding adiabatic model gives a similar activation energy but a much larger prefactor. It is suggested that the effect of other defects such as dopants has to be included for a proper description of hydrogen diffusion in this material.
Keywords
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