Intergranular structure of nanocrystalline layered LixTiS2 as derived fromLi-7 NMR spectroscopy

Li-7 NMR spectra of ball-milled nanocrystalline LixTiS2, have been recorded in the temperature range 140 less than or equal to T less than or equal to 500 K. Above 250 K, the central transition of the spectra decomposes into a broad and a narrow component at the same centre frequency. The relative i ntensity of the narrow line increases with temperature, finally reaching a saturation value of 50%. The narrow line is attributed to more mobile spins in the interfacial regions between the nanocrystalline grains. The tempera ture dependent intensity of the narrow component is interpreted in terms of an inhomogeneous interface structure. The average particle size of nanocry stalline LixTiS2 as obtained from X-ray diffraction (XRD) is 11.8 nm. A sim ple geometrical model involving the particle diameter d (from XRD), the int erface fraction f(from NMR), and the interface thickness g predicts unreaso nably thick interfaces but is in accordance with the measured data for d an d f when it is adapted to account for a disk-like particle shape. On the ba sis of the disk model, which is likely to apply for a layered structure lik e LixTiS2, the interface thickness is limited by 1 less than or equal to g less than or equal to 3 nm. The results are compared to those obtained for some three-dimensional structures, to which the standard spherical model is applicable in most cases. (C) 2001 Elsevier Science B.V. All rights reserv ed.