Solid electrolytes. Extremely fast charge carriers in garnet-type Li₆La₃ZrTaO₁₂ single crystals

The development of all-solid-state electrochemical energy storage systems, such as lithium-ion batteries with solid electrolytes, requires stable, electronically insulating compounds with exceptionally high ionic conductivities. Considering ceramic oxides, garnet-type Li₇La₃Zr₂O₁₂ and derivatives, see Zr-exchanged Li₆La₃ZrTaO₁₂ (LLZTO), have attracted great attention due to its high Li⁺ ionic conductivity of 10^-3 S cm^-1 at ambient temperature. Despite numerous studies focussing on conductivities of powder samples, only few use time-domain NMR methods to probe Li ion diffusion parameters in single crystals. Here we report on temperature-variable NMR relaxometry measurements using both laboratory and spin-lock techniques to probe Li jump rates covering a dynamic time window spanning several decades. Both techniques revealed a consistent picture of correlated Li ion jump diffusion in the single crystal; the data perfectly mirror a modified BPP-type relaxation response being based on a Lorentzian-shaped relaxation function. The rates measured could be parameterized with a single set of diffusion parameters. Results from NMR are completely in line with ion transport parameters derived from conductivity spectroscopy. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)