NMR studies of modified nasicon-like, lithium conducting solid electrolytes

Al-27, P-31 and Li-7 NMR measurements have been performed on lithium conduc ting ceramics based on the LiTi2(PO4)(3) structure with Al, V and Nb metal ions substituted for either Ti or P within the framework NASICON structure. The Al-27 magic angle spinning NMR measurements have revealed that, althou gh Al is intended to substitute for octahedral Ti sites, additional substit ution into tetrahedral environments (presumably phosphorous sites) occurs w ith increasing amount of Al addition. This tetrahedral substitution appears to occur more readily in the presence of vanadium, in Li1-xAlxTi2-x(PO4)(2 .9)(VO4)(0.1), whereas similar niobium additions (in place of vanadium) app ear to stifle tetrahedral substitution. Li-7 static NMR spectra reveal quad rupolar structure with C-q approximately 42 kHz, largely independent of sub stitution. Measurement of the Li-7 central transition linewidth at room tem perature reveals a relatively mobile lithium species (300-900 Hz) with line width tending to decrease with Al substitution and increase with increasing V or Nb. This new structural information is discussed in the context of io nic conduction in these ceramics. (C) 1999 Published by Elsevier Science B. V. All rights reserved.