Conductance and EPR study of the endohedral fullerene Li @C60

Thin films and bulk samples of endohedral fullerenes Li@C-60 are studied using current-voltage (I-V) measurements and electron paramagnetic resonance (EPR). Electrical measurements show a linear behaviour for the I-V curves and give an average resistivity of ca. 1.5 kOmegacm for thin Li@C-60 films deposited in vacuum, four orders of magnitude lower than C-60 samples. A drastic effect on the conductance, lowering it to the values typical for C-60, is observed when the Li@C-60 samples are exposed to ambient atmosphere. No additional paramagnetic centres (PCs) are found for the Li@C-60 compared to C-60 that can be related to the formation of dimers or trimers of the endohedral fullerene molecules. However, the presence of the Li atoms in the fullerene cages contributes to a change of the spin-spin and spin-lattice relaxation times. The spin-lattice relaxation time becomes four orders of magnitude longer compared to the spin-spin relaxation time. (C) 2004 Elsevier Ltd. All rights reserved.