Li jump process in h-Li0.7TiS2 studied by two-time 7Li spin-alignment echo NMR and comparison with results on two-dimensional diffusion from nuclear magnetic relaxation

Aug 25, 2026

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7Li spin-alignment echo NMR is used to track ultraslow diffusion of Li+ in the layered Li conductor LixTiS2 with x=0.7. Two-time correlation functions at fixed evolution times are recorded while varying the mixing time over temperatures in the 7Li rigid-lattice regime. The extracted decay rates yield Li jump rates from 10−1 to 103 s−1 between 148 K and 213 K, consistent with jump rates inferred from diffusion-induced maxima in spin-lattice relaxation peaks in both laboratory and rotating frames. An Arrhenius behavior is found with activation energy 0.41(1) eV and preexponential factor 6.3(1)×1012 s−1. A solitary Li diffusion process is identified between 148 and 510 K, spanning roughly ten decades. Final-state echo amplitudes indicate a two-site jump pathway involving both occupied octahedral sites and vacant tetrahedral sites within the van der Waals gap. The results are discussed in terms of two-dimensional Li diffusion.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages13

Reading Time33 min

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I. Introduction

NMR for cation dynamics and motivation

SAE NMR for ultraslow jump rates

II. Lithium Titanium Disulfide

Crystal modifications and ion conduction background

PHYSICAL REVIEW B 77, 024311 􀀁2008􀀂 Li jump process in h-Li0.7TiS2 studied by two-time 7Li spin-alignment echo NMR and comparison with results on two-dimensional diffusion from nuclear magnetic relaxation M. Wilkening* and P. Heitjans† Institute of Physical Chemistry, and Center for Solid State Chemistry and New Materials, Leibniz University Hannover, Callinstraße 3A, D-30167 Hannover, Germany 􀀁Received 25 May 2007; revised manuscript received 23 November 2007; published 31 January 2008􀀂 7Li spin-alignment NMR is used to trace ultraslow diffusion of Li+ in the layered Li conductor LixTiS2 􀀁x= 0 .7􀀂 . Two-time correlation functions were recorded for ﬁxed evolution times as a function of mixing time at temperatures within the 7Li rigid-lattice regime. The corresponding decay rates were identiﬁed as Li jump rates 􀀁−1 ranging from 10−1 to 103 s−1 between temperatures T= 148 K and 213 K. The jump rates obtained directly from spin-alignment echo NMR and those from diffusion induced maxima of spin-lattice relaxation peaks, monitored in the laboratory as well as in the rotating frame, are consistent with each other and follow an Arrhenius law with an activation energy of 0 .41􀀁1􀀂 eV and a preexponential factor of 6 .3􀀁1􀀂 􀀂 1012 s−1 . Altogether, a solitary Li diffusion process was found between 148 and 510 K. Li diffusion was investigated ina dynamic range of about 10 orders of magnitude, i.e., 0 . 1􀀃􀀁−1 􀀃7.8 􀀂 108 s−1 . Additionally, the analysis of ﬁnal-state echo amplitudes of the two-time correlation functions revealed information about the Li diffusion pathway in Li0.7TiS2. Obviously, a two-site jump process is present, i.e., besides the regularly occupied octahedral sites also the vacant tetrahedral ones within the van der Waals gap are involved in the overall two-dimensional diffusion process. DOI: 10. 1103/PhysRevB.77.024311 PACS number􀀁s􀀂: 66 .30. 􀀄h, 76 .60. 􀀄k, 76 .60.Lz, 82 .47.Aa I. INTRODUCTION Nuclear magnetic resonance 􀀁NMR􀀂 is a well-known powerful tool for the investigation of structure and dynamics in condensed matter. Especially, it is highly suitable to study cation dynamics in fast Li ion conducting materials which are required for the design of new secondary Li batteries in everyday use.1–7 Moreover, in recent years many studies have focused attention on lithium conductors because of their potential application in electrochromic displays8 as well as in chemical sensors, see, e.g., Refs. 9 and 10. Layered lithium titanium disulﬁde, LixTiS2, is one of the ﬁrst materials which were used as an electrode material in a rechargeable Li ion battery.11, 12 For this reason, it is one of the best investigated intercalation compounds at all.13, 14 Although Li diffusion in LixTiS2 was studied in previous years by others using 7Li NMR relaxation experiments, 15–19 a comprehensive study about the cation dynamics, especially in the regime of ultraslow Li motions which are not accessible by standard measurements, is still missing. Unfortunately, the standard tracer technique is not applicable to study Li dynamics due to the lack of a suitable radioactive Li isotope. Therefore, it is a necessity in general that 7Li NMR methods are steadily developed to overcome this disadvantage. It is the aim of the present paper to show that newly developed20,21 but not yet well-established 7Li spinalignment echo 􀀁SAE􀀂 NMR, i.e., the recording of JeenerBroekaert echoes22 of spin-3 / 2 nuclei, can be used to probe directly Li jump rates with values in the kilohertz to subhertz regime. Such extremely slow Li motions are not or only hardly accessible by other NMR methods. Directly means here that no theoretical model was necessary to convert the measured echo decay rates into microscopic Li jump rates. By applying the SAE technique, it is possible to enlarge the experimental time window for studying 7Li jumps because the well-known 7Li relaxation NMR methods probe Li jump rates on much shorter time scales.23 Here, we repo

FAQs

What technique is used to study Li+ diffusion in h-Li0.7TiS2?

The study uses two-time 7Li spin-alignment echo (SAE) NMR based on Jeener-Broekaert echoes to directly probe Li jump rates.

How are Li jump rates obtained and what range are they found in?

Decay rates from two-time correlation functions are identified as Li jump rates. The measured rates span from 10−1 to 103 s−1 between 148 K and 213 K, with diffusion also observed over 148–510 K.

What does the analysis of echo final states reveal about the diffusion pathway?

It reveals a two-site jump process where Li ions can jump not only from regularly occupied octahedral sites but also involving vacant tetrahedral sites in the van der Waals gap during overall two-dimensional diffusion.

Aug 25, 2026

Uploaded by Ophelia