Ion dynamics in Al-Stabilized Li7La3Zr2O12 single crystals - Macroscopic transport and the elementary steps of ion hopping

Patrick Posch*, Sarah Lunghammer, Stefan Berendts, Steffen Ganschow, Gunther J. Redhammer, Alexandra Wilkening, Martin Lerch, Bernhard Gadermaier, Daniel Rettenwander, H. Martin R. Wilkening*

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

Li 7La 3Zr 2O 12 (LLZO) garnet-type ceramics are considered as very promising candidates for solid electrolytes and have been extensively studied in the past few years. Several studies report on an increase in ionic conductivity by doping with ions, such as Al 3+ and Ga 3+, to stabilize the cubic modification of LLZO. Unfortunately, so far ion dynamics have mainly been studied using powdered samples. Such studies may suffer from chemical heterogeneities concerning Al distribution. Here, we took advantage of Al-stabilized LLZO single crystals to throw light on the elementary steps of ion hopping. We used 7Li nuclear magnetic resonance (NMR) spin-lattice relaxation measurements and conductivity spectroscopy to probe dynamic parameters from both a microscopic and macroscopic point of view. At 293 K the total conductivity turned out to be 0.082 mS cm −1, which is remarkably good for LLZO exhibiting an Al-content of only 0.37 wt%. Most importantly, 7Li NMR spin-lock transients revealed two overlapping diffusion-induced processes. Overall, activation energies from spin-lock NMR excellently agree with that from conductivity measurements; both techniques yield values around 0.36 eV. The corresponding diffusion coefficients deduced from NMR and conductivity measurements almost coincide. The magnetic spin fluctuations sensed by NMR provide an in-depth look at the elementary jump processes, which can barely be revealed by macroscopic impedance spectroscopy providing average values. In particular, we were able to precisely measure the local hopping barrier (0.20 eV) characterizing forward-backward jumps between the sites 24d and 96h.

Original languageEnglish
Pages (from-to)220-228
Number of pages9
JournalEnergy Storage Materials
Volume24
DOIs
Publication statusPublished - Jan 2020

Keywords

  • Garnets
  • Single crystal
  • NMR
  • Dynamics
  • Conductivity

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Materials Science(all)
  • Renewable Energy, Sustainability and the Environment

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