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

Al-27, P-31 and Li-7 NMR measurements have been performed on lithium conducting 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, although Al is intended to substitute for octahedral Ti sites, additional substitution into tetrahedral environments (presumably phosphorous sites) occurs with 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) appear to stifle tetrahedral substitution. Li-7 static NMR spectra reveal quadrupolar structure with C-q approximately 42 kHz, largely independent of substitution. Measurement of the Li-7 central transition linewidth at room temperature reveals a relatively mobile lithium species (300-900 Hz) with linewidth tending to decrease with Al substitution and increase with increasing V or Nb. This new structural information is discussed in the context of ionic conduction in these ceramics. (C) 1999 Published by Elsevier Science B.V. All rights reserved.