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Original article (peer-reviewed)

Journal Nature Communications
Volume (Issue) 8
Title of proceedings Nature Communications
DOI 10.1038/ncomms15830

Open Access

URL https://www.nature.com/articles/ncomms15830
Type of Open Access Website

Abstract

Hydration of oxygen deficient metal oxides causes filling of oxygen vacancies and formation of hydroxyl groups with interstitial structural protons, which rotate around the oxygen in a localized motion. Thermal activation from 500 K to 800 K triggers delocalization of the protons by jumping to adjacent oxygen ions, constituting proton conductivity. Our quantitative analyses of the proton dynamics and lattice dynamics reveals direct coupling of protons with the crystal lattice. Moreover, a proton-phonon coupling is revealed. The equation of motion for the proton trapped in the elastic crystal field yields Eigen frequencies and coupling constants, which satisfy Holstein’s polaron model for electrons and thus constitutes first experimental evidence for a proton polaron at high temperature. Specifically, the proton jump rates follow a polaron model for the Ce-O and O-H stretching modes, which are thus vehicles for the proton conductivity. This is confirmation that the polaron mechanism is not restricted to electrons only, but a more universal charge carrier transport process than hitherto acknowledged.
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