LI-6 AND LI-7 NMR IN THE LINI1-YCOYO2 SOLID-SOLUTION 0-LESS-THAN-OR-EQUAL-TO-Y-LESS-THAN-OR-EQUAL-TO-1)

A series of phases belonging to the LiNi1-yCoyO2 (0 less than or equal to y less than or equal to 1) solid solution have been studied by Li- 6 and Li-7 NMR. Static and magic-angle-spinning (MAS) spin-echo NMR ex periments have been carried out at two magnetic field strengths (4.7 a nd 7.1 T). The Li-6 and Li-7 high-speed MAS spectra are found to be se nsitive to hyperfine couplings with both the nearest and next nearest nickel neighbors. These short distance interactions are used to yield information on the distribution of the transition metal atoms in the ( Ni, Co)O-2 slabs. While deviations from a random Ni/Co distribution ca nnot be quantified by NMR experiments on static samples, the MAS spect ra clearly demonstrate that the LiNi1-yCoyO2 phases have a tendency to form cobalt clusters. These results show that, in favorable circumsta nces, MAS NMR of paramagnetic materials permits the accurate detection of short scale heterogeneities that cannot be observed by X-ray diffr action.