Electronic properties and solid-state 87Rb and 13C NMR studies of mesoporous tantalum oxide rubidium fullleride composites

Mesoporous tantalum oxide rubidium fulleride composites were synthesized by solution impregnation and characterized by elemental analysis, X-ray diffraction, Raman spectroscopy, nitrogen adsorption/ desorption, X-ray photoelectron spectroscopy, superconducting quantum interference device magnetometry, room- and variable-temperature electron transport measurements, and solid-state (87)Rb and (13)C NMR. The room-temperature conductivity pattern, as a function of the oxidation state of C(60)(n-), displayed a conductivity minimum at n = 3.0 and a single maximum at n = 4.0, while variable-temperature conductivity measurements indicated that the n = 1.0 composite is a semiconductor and the n = 4.0 material is a narrow band gap semiconductor or a semimetal. Solid-state (87)Rb NMR of the composite materials indicated the presence of two Rb environments associated with the walls or channels of the mesostructure as well as several resonances associated with various fulleride species. The n = 3.0 and n = 4.0 samples showed a substantial increase of Rb ions confined into the walls of mesostructure as well as the buildup of a Rb environment associated with a fulleride species. Solid-state (13)C NMR experiments showed the presence of multiple fulleride species as well as pure fullerene, depending on the level of reduction.