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Understanding and controlling Li-ion transport in garnet-type oxides is central to advancing solid electrolytes for all-solid-state energy storage systems. Garnet electrolytes have long been recognized for their high ionic conductivity, and the availability of large single crystals now enables a direct, frequency-resolved view of Li-ion dynamics over a broad time window. In such structurally and chemically homogeneous systems, responses from electrical and nuclear magnetic resonance measurements are expected to align, yielding a consistent picture of frequency-dependent Li-ion hopping processes. Here, we investigate single-crystalline Li6.5La3Zr1.5Ta0.5O12 and probe ion dynamics from the kHz to GHz range using a combination of 7Li nuclear spin relaxation (NSR) and electrical conductivity spectroscopy. Long-range transport (5 × 10–4 S cm–1 at 293 K) is consistently described by activation energies in the range of 0.41 to 0.47 eV, whereas localized ion dynamics, observed, e.g., by laboratory-frame NSR, are associated with much lower barriers of approximately 0.22 eV. In comparison with single-crystalline Li6La3ZrTaO12, which exhibits reduced ionic mobility, we propose that changes in ionic mobility are compensated by a higher effective charge-carrier concentration Nc in systems with lower Li contents. For Li6.5La3Zr1.5Ta0.5O12, the Li+ mobility is higher by approximately 1 order of magnitude; however, the resulting conductivity only slightly exceeds that of Li6La3ZrTaO12, presumably due to a lower density of mobile charge carriers. This finding highlights that Nc is a key parameter to consider in these systems that indeed sensitively governs the practical ionic conductivity.

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• Creative Commons BY Attribution 4.0 International
  

Keyword: lithium, dynamics, diffusion, NMR, solid electrolytes, garnet, single crystals

Date published: 2026-07-28

Publisher: American Chemical Society (ACS)

Journal:

• Chemistry of Materials (ISSN: 08974756) vol. 38 issue. 14 p. 7254-7266

Funding:

• Austrian Science Fund 10.55776/ESP1533525
• German Research Council (DFG) WI3600 4-1

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1021/acs.chemmater.6c00979

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Updated at: 2026-07-29 09:34:13 +0900

Published on MDR: 2026-07-29 12:29:21 +0900