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摘要
The atomic-scale picture of the proton conduction mechanism in tin pyrophosphate, SnP2O7, has theoretically been investigated using first-principles calculations, to clarify the intrinsic proton conductivity in the bulk region. Protons in the crystal lattice reside around oxide ions and migrate by rotation around single oxide ions and hopping between adjacent oxide ions by a mechanism similar to that in other proton-conducting oxides. The calculated proton conductivity has weak anisotropy reflecting the monoclinic structure (unique axis: b), particularly in the ca plane. The main origin of the anisotropic conductivity is the relatively fast long-range migration pathways along the unique b axis and in the [101] direction (potential barrier: 0.57 eV) versus that along the [101] direction (potential barrier: 0.64 eV). The apparent activation energy of the estimated proton conductivity is as high as similar to 1.1 eV with the proton trapping effect by dopants (association energy: 0.59 eV), leading to the low proton conductivity in the bulk region. This suggests that the reported fast proton conductivity in the literature may be due to other unexpected proton migration routes, such as surfaces, grain boundaries, and secondary phases with residual phosphoric acid.
- 出版日期2017-1-26
