diffusion-fundamentals The Open-Access Journal for the Basic Principles of Diffusion Theory, Experiment and Application www.diffusion-fundamentals.org, ISSN 1862-4138; © 2005-2010 Diffusion Fundamentals 12 (2010) 97 © A. Kuhn Slow Li Exchange in a Li 3 N Single Crystal Measured by 6,7 Li NMR Selective Quadrupole Satellite Inversion A. Kuhn, * P. Heitjans Leibniz Universität Hannover, Institut für Physikalische Chemie und Elektrochemie, Callinstr. 3a, 30167 Hannover, Germany E-Mail: kuhn@pci.uni-hannover.de Presented at the Bunsen Colloquium: Spectroscopic Methods in Solid State Diffusion and Reactions September 24 th − 25 th , 2009, Leibniz University Hannover, Germany Lithium nitride, Li 3 N, is one of the best Li conductors at room temperature. Unfortunately, its applica- tion as electrolyte in batteries is limited due to the low decomposition potential of only 0.45 V. Never- theless, diffusion in Li 3 N was studied by many groups and various techniques (see [1-3] and refer- ences therein) which predestines it to act as a model system for the establishment of new techniques. Li 3 N crystallizes in a layered structure of the hexagonal space group P6/mmm [3,4] (see Fig. 1). There are two alternating types of layers, one with the stoichiometry Li 2 N, the other containing only Li. As a result, there are two different Li positions, Li(2) in the Li 2 N layer and Li(1) in the Li layer. Li diffu- sion in the Li 2 N layer (ab-plane, intralayer diffusion) is fast, while the Li diffusion parallel to the c- axis is moderate. The mechanism of this interlayer diffusion process is directly associated with a Li exchange between the two Li positions (see Fig. 1) since the Li ions cannot jump from one Li(2) site to the other but transitionally reside on a Li(1) site [5]. This makes it possible to measure the interlayer diffusion process by exchange NMR techniques. In the case of nuclei with spin I = 1/2, an easy and accurate NMR technique to measure slow exchange between two spin reservoirs referring to two non-equivalent sites is the selective inversion technique which uses the pulse sequence π sel – t m – π/2 det . The first pulse π sel selectively inverts the population difference of one of the spin reservoirs and thus the peak in the NMR spectrum referring to that cohe- rence. During the variable mixing time t m the negative amplitude of the inverted peak is partially trans- ferred to the peak corresponding to the inverted one via the exchange process. The detection pulse π/2 det transfers the longitudinal magnetization into a detectable transversal magnetization. When the Fig. 1 The layered structure of Li 3 N [2] with the two differ- ent Li positions Li(1) and Li(2). The interlayer diffusion process consists of an exchange process between Li(1) and Li(2).