The development of ceramic proton conductors is currently
attracting
great attention, as they might be useful to construct new energy storage
systems. Li6La3ZrTaO12 (LLZTO) is
known for its rapid Li+ diffusivity as has been directly
revealed by 7Li NMR measurements. Exchanging parts of the
highly mobile Li+ ions by protons through treatment of
a single crystal in water or glacial acetic acid yields a mixed proton–lithium
ionic conductor. Here, H+ proton diffusivity and Li+ diffusivity have separately been studied with element-specific 1H and 7Li NMR spectroscopy. While long-range 7Li diffusion is noticeably slowed in Li–H exchanged
LLZTO, we directly observe rather high H+ diffusivity,
which is, however, significantly slower than Li+ dynamics.
With the help of spin–lattice relaxation measurements we were
able to measure local (and long-range) energy barriers (0.20(1) eV
vs 0.45(3) eV) as well as the self-diffusion coefficient D
H of H+ dynamics (1.2 × 10–15 m2 s–1 at 125 °C). These encouraging
results are assumed to open new directories in designing ceramics
offering fast transport pathways for protons.
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