Tunneling Motion and Antiferroelectric Ordering of Lithium Cations Trapped inside Carbon Cages

Dielectric and X-ray diffraction measurements of [Li@C60](PF6) single crystals reveal the motion of the Li+ cations inside the C60 cages at low temperature. An increase in the dielectric permittivity below 100 K is consistent with a combined tunneling and hopping motion of the Li+ cation between two positions inside the C60 cage. A phase transition accompanied by a decrease in the dielectric permittivity at TC = 24 K is explained by an antiferroelectric ordering of the Li+ cations. The Li+ ordering is caused by interactions among electric dipole moments formed between the Li+ cations inside and the PF6− anions outside the C60 cages. The electric dipole moments that are switched by the Li+ tunneling and interact with each other are potential qubits in a quantum computer using electric dipole moments.