n- to p-Type Conductivity Transition of LuN@C Due to Anisotropic Deformation of Fullerene and Pyramidalization of Endohedral Clusters.

The endohedral fullerene LuN@C was examined using in situ high-pressure measurements, which included electrical transport, Fourier-transform infrared spectroscopy, and Raman spectroscopy, in combination with theoretical calculations. LuN@C was found to undergo a reversible n- to p-type conversion at ∼8.9 GPa. This p-type semiconductor remains stable up to 25 GPa. The fullerene cage collapses at ∼29 GPa, resulting in an irreversible p- to n-type conversion. Raman, infrared, and X-ray absorption spectroscopy reveal that an anisotropic distortion of the carbon cage and a pyramidalization of the planar LuN clusters occur during compression. Density functional theory simulations indicate that the p orbitals of C atoms in the fullerene cage primarily contribute to the density of states (DOS). Pressure-induced deformation of the fullerene cage dominates the DOS changes in the conduction and valence bands close to the Fermi level. The findings elucidate the relationship between the conductivity and structural changes in the endohedral clusters.