TY - JOUR

T1 - Solid-State NMR to Study Translational Li Ion Dynamics in Solids with Low-Dimensional Diffusion Pathways

AU - Volgmann, Kai

AU - Epp, Viktor

AU - Langer, Julia

AU - Stanje, Bernhard

AU - Heine, Jessica

AU - Nakhal, Suliman

AU - Lerch, Martin

AU - Wilkening, Martin

AU - Heitjans, Paul

N1 - We appreciate financial support by the Deutsche Forschungsgemeinschaft, grants no. DFG FOR 1277 molife HE1574/11-1, 11-2, WI3600/2-1, 2-2, and LE781/15-2. We are grateful to Prof. F. Fujara and his group at TU Darmstadt for help with the FC NMR measurements and the permission to show Fig. 12b prior to publication

PY - 2017/7/26

Y1 - 2017/7/26

N2 - Fundamental research on lithium ion dynamics in solids is important to develop functional materials for, e.g. sensors or energy storage systems. In many cases a comprehensive understanding is only possible if experimental data are compared with predictions from diffusion models. Nuclear magnetic resonance (NMR), besides other techniques such as mass tracer or conductivity measurements, is known as a versatile tool to investigate ion dynamics. Among the various time-domain NMR techniques, NMR relaxometry, in particular, serves not only to measure diffusion parameters, such as jump rates and activation energies, it is also useful to collect information on the dimensionality of the underlying diffusion process. The latter is possible if both the temperature and, even more important, the frequency dependence of the diffusion-induced relaxation rates of actually polycrystalline materials is analyzed. Here we present some recent systematic relaxometry case studies using model systems that exhibit spatially restricted Li ion diffusion. Whenever possible we compare our results with data from other techniques as well as current relaxation models developed for 2D and 1D diffusion. As an example, 2D ionic motion has been verified for the hexagonal form of LiBH4; in the high-temperature limit the diffusion-induced 7Li NMR spin-lattice relaxation rates follow a logarithmic frequency dependence as is expected from models introduced for 2D diffusion. A similar behavior has been found for LixNbS2. In Li12Si7 a quasi-1D diffusion process seems to be present that is characterized by a square root frequency dependence and a temperature behavior of the 7Li NMR spin-lattice relaxation rates as predicted. Most likely, parts of the Li ions diffuse along the Si5 rings that form chains in the Zintl phase.

AB - Fundamental research on lithium ion dynamics in solids is important to develop functional materials for, e.g. sensors or energy storage systems. In many cases a comprehensive understanding is only possible if experimental data are compared with predictions from diffusion models. Nuclear magnetic resonance (NMR), besides other techniques such as mass tracer or conductivity measurements, is known as a versatile tool to investigate ion dynamics. Among the various time-domain NMR techniques, NMR relaxometry, in particular, serves not only to measure diffusion parameters, such as jump rates and activation energies, it is also useful to collect information on the dimensionality of the underlying diffusion process. The latter is possible if both the temperature and, even more important, the frequency dependence of the diffusion-induced relaxation rates of actually polycrystalline materials is analyzed. Here we present some recent systematic relaxometry case studies using model systems that exhibit spatially restricted Li ion diffusion. Whenever possible we compare our results with data from other techniques as well as current relaxation models developed for 2D and 1D diffusion. As an example, 2D ionic motion has been verified for the hexagonal form of LiBH4; in the high-temperature limit the diffusion-induced 7Li NMR spin-lattice relaxation rates follow a logarithmic frequency dependence as is expected from models introduced for 2D diffusion. A similar behavior has been found for LixNbS2. In Li12Si7 a quasi-1D diffusion process seems to be present that is characterized by a square root frequency dependence and a temperature behavior of the 7Li NMR spin-lattice relaxation rates as predicted. Most likely, parts of the Li ions diffuse along the Si5 rings that form chains in the Zintl phase.

KW - diffusion

KW - dimensionality

KW - lithium

KW - solid-state NMR

KW - spin-lattice relaxation

UR - http://www.scopus.com/inward/record.url?scp=85024900575&partnerID=8YFLogxK

U2 - 10.1515/zpch-2017-0952

DO - 10.1515/zpch-2017-0952

M3 - Article

AN - SCOPUS:85024900575

VL - 231

SP - 1215

EP - 1241

JO - Zeitschrift fur Physikalische Chemie

JF - Zeitschrift fur Physikalische Chemie

SN - 0942-9352

IS - 7-8

ER -