I. Tomeno et M. Oguchi, NMR-STUDY OF LICO1-XCRXO2 AND LI-1-XNAXCOO2 (X = 0 AND 0.05), Journal of the Physical Society of Japan, 67(1), 1998, pp. 318-322
The Li-7 and Li-6 nuclear spin-lattice relaxation rates, (T-7(1))(-1)
and (T-6(1))(-1), have been measured for LiCoO2 as a function of tempe
rature. Comparison between Li-7- and Li-6- rich samples shows that the
ratio (T-6(1))(-1)/(T-7(1))(-1) = 0.06 is considerably larger than th
e value expected for quadrupolar relaxation processes. Furthermore (T-
7(1))(-1) decreases significantly as 7Li is replaced by Li-6. These ob
servations indicate that (T-7(1)) is dominated by the nuclear magnetic
dipole-dipole interaction between the Li-7 nuclei. The substitution o
f Cr for Co has no effect on (T-7(1))(-1) in the range below 200 K, wh
ereas the substitution of Na for Li enhances (T-7(1))(-1). The substit
ution effect supports the view that the two-dimensional Li ion motion
is dominant in LiCoO2. The weak dependence of (T-7(1))-1 upon temperat
ure and frequency suggests the presence of a broad distribution of bar
rier heights for ionic motion in LiCoO2.