Crystal structure and electronic transport of Dy@C₈₂

The crystal structure of Dy@C₈₂ isomer I at 298 K has been determined by Rietveld refinement for x-ray powder diffraction with synchrotron radiation. Isomer I shows a simple cubic structure (sc: Pa3) with a lattice constant a of 15.78(1) Å. The C₂ axis of a C_2v-C₈₂ cage aligns along the [111] direction of this crystal lattice. The C₈₂ cage is orientationally disordered to satisfy a 3 symmetry along [111], which is requested in this space group. The large thermal parameter for the Dy atom estimated from the x-ray diffraction probably reflects a large disorder caused by a floating motion of the Dy atom inside the C₈₂ cage as well as a ratchet-type motion of the Dy@C₈₂ molecule. The electronic transport of thin film of Dy@C₈₂ shows a semiconducting behavior. The energy gap E_g is estimated to be 0.2 eV. Further, the variation of valence from Dy³⁺ to Dy²⁺ is found by metal doping into the Dy@C₈₂ crystals.