Solids with Two Mobile Ions: Proton H<sup>+</sup> Self-Diffusion in Li–H Exchanged Garnet-Type Li<sub>6</sub>La<sub>3</sub>ZrTaO<sub>7</sub> as Seen by Solid-State <sup>1</sup>H NMR Relaxation
Maria Gombotz, Caroline Hiebl, Florian Stainer, Martin Wilkening
Abstract
High Resolution Image Download MS PowerPoint Slide The development of ceramic proton conductors is currently attracting great attention, as they might be useful to construct new energy storage systems. Li 6 La 3 ZrTaO 12 (LLZTO) is known for its rapid Li + diffusivity as has been directly revealed by 7 Li 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 1 H and 7 Li NMR spectroscopy. While long-range 7 Li 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 m 2 s –1 at 125 °C). These encouraging results are assumed to open new directories in designing ceramics offering fast transport pathways for protons.