Evidence for the intramolecular motion of Gd atoms in a Gd2@C92 nanopeapod

Atoms in a confined space can be regarded to represent a completely new phase because it should behave differently than the atoms in a solid or in a free-space. The metallofullerene provides an ideal case of the confined atoms since a number of metal atoms are imprisoned in a subnanometer void of the carbon cage. Here we give direct evidence of the dynamic behavior for the confined atoms in metallofullerenes by observing individual atoms using the high-resolution transmission electron microscopy. Rapid movement of Gd atoms in Gd-2@C-92 peapod is identified for the first time. By comparison with simulation, the amplitude of the motion is roughly quantified as 0.2 nm at room temperature and is reduced to almost half at 100 K.