A LI-7 NUCLEAR-MAGNETIC-RESONANCE STUDY ON SPINEL LIMN2O4-DELTA

A Li-7 nuclear magnetic resonance (Li-7-NMR) study was carried cut to investigate the magnetic properties of powder samples of LiMn2O4 and L iMn2O3.9 in the temperature range between 160 and 400 K. Lowering the temperature from 400 K to similar to 300 K, the width of the Li-7-NMR line was found to increase monotonically, then increased rapidly at te mperatures below 260 K for LiMn2O4 and 290 K for LiMn2O3.9. Combining these results with those of differential scanning calorimetry (DSC) an alyses, the transition temperature (T-C) was determined to be similar to 250 K for LiMn2O4 and similar to 290 K for LiMn2O3.9. This indicate d that the magnitude of T-C of LiMn2O4-delta depends on the oxygen def iciency (delta). In addition, at temperatures below T-C, the NMR line seemed to decompose into two Gaussian peaks; it was a symmetrical sing let at temperatures above T-C. Thus, it is deduced that there are two possible sites for the lithium ions in the sample at temperatures belo w T,, and one equivalent site above T-C. (C) 1997 Elsevier Science S.A .