Transferred hyperfine interaction and structure in LiMn2O4 and Li2MnO3 coexisting phases: A XRD and Li-7 NMR-MAS study

X-ray diffraction (XRD) and Li-7 MMR-MAS measurements have been performed on LiMn2O4 (lithium cationic fraction, x = 0.333), Li2MnO3 (x = 0.667), and the intermediate composition with x = 0.40. The use of magic angle spinning produces complex manifolds of the spinning sidebands. The predominant interaction affecting the NMR spectrum is the transferred hyperfine coupling (TFHI) between the Mn ions and the Li spins. TFHI parameters are extracted from MAS-NMR spectra of oxides containing a large quantity of manganese. We obtained a full spectral assignment for the spinel LiMn2O4, for the rocksalt Li2MnO3, and for the x = 0.40 sample, which contains the rocksalt and both stoichiometric and nonstoichiometric spinel phases. According to XRD data, the rocksalt phase contains three nonequivalent lithium sites whose NMR peaks are shifted upheld from x = 0.667 to 0.40 because of the cell volume expansion. The Li+ ions belonging to the two spinel phases of x = 0.40 are quite mobile and give origin by motional narrowing to a single peak, which is slightly shifted upheld with respect to that of LiMn2O4.