Li₇La₃Zr₂O₁₂ (LLZO) garnet-type materials are regarded as promising candidates for solid electrolytes and have been extensively investigated in the past few years.^[1,2] Several studies report on an increase in conductivity by doping with ions to stabilize the cubic structure.^[3,4] In the present study we focus on the ionic transport processes in Al-doped LLZO single crystals. To investigate ionic motions we used ⁷Li nuclear magnetic resonance (NMR) spectroscopy and impedance spectroscopy. With the help of rotating-frame spin-lock NMR spin-lattice relaxation (SLR) we looked at localized and medium-ranged ionic motions, respectively. Impedance spectroscopy was used to shed light on the long range ion dynamics. At room temperature the total conductivity turned out to be 0.082 mS cm^-1 at, which is remarkably good for LLZO with an Al-content of only 0.34 wt%.^[5]

Most importantly, ⁷Li NMR spin-lock NMR of revealed two overlapping diffusion-induced processes that share almost the same activation energy. A similar behavior has recently been seen for Mo-bearing LLZO.^[6] Overall, activation energies gathered from spin-lock NMR and impedance measurements are in good agreement with each other; both techniques yield values around 0.36 eV. The solid-state coefficient (D) and the self-diffusion coefficient (D_sd), calculated from impedance spectroscopy and NMR spin-lock SLR, respectively, almost coincide. This excellent agreement points out that the two methods are sensitive to very similar motional correlations functions probing magnetic spin fluctuations and electrical relaxation processes, respectively.

References

[1] S. Ohta et al., J. Power Sources, 2012, 202, 332–335.

[2] B. Stanje et al., Ann. Phys. (Berlin), 2017, 529, 1700140.

[3] D. Rettenwander et al., Chem. Mater., 2014, 26, 2617–2623.

[4] J. L. Allen et al., J. Power Sources, 2012, 206, 315–319.

[5] H. Buschmann et al., Phys. Chem. Chem. Phys., 2011, 13, 19378–19392.

[6] P. Bottke et al., Chem. Mater., 2015, 27, pp 6571–6582