METAL-LIKE BEHAVIOR OF LITHIUM INTERCALATED IN MOLYBDENUM CLUSTER CHALCOGENIDES

Li-7 solid-state NMR studies have been carried out on the molybdenum cluster chalcogenides (''Chevrel phases'') Li3Mo6X8, Li3.8Mo6X8, and Li4Mo6X8 at 16 and 117 MHz and various temperatures. The low-temperature spectra of Li3Mo6X8, Li3.8Mo6X8, and Li4Mo6X8 can be interpreted in terms of chemical shift (CS), nuclear quadrupole (Q), and dipole-dipole (D) interaction, where the principal axes of the CS and Q tensors do not coincide. The spin-lattice relaxation of these compounds is governed by contributions from the lithium diffusion and from the interaction with conduction electrons. The latter part is connected with the isotropic (Knight) shift by a Korringa relation. The formation of lithium triclusters with partial charge transfer to the host lattice, short Li-Li distances and remaining electron density in the 2s orbitals is concluded from the various data. In Li4Mo6X8, by contrast, the intercalated lithium is completely ionized. Models for structure and motion have been developed in connection with recent neutron diffraction studies.