Discovery of Ferroelectricity in the Fullerene Adduct C₆₀S₈

Fullerenes offer versatile functionalities and are promising materials for a widespread range of applications from biomedicine and energy to electronics. Great efforts have been made to manipulate the symmetries of fullerene and its derivatives for studying material properties and novel effects, such as ferroelectricity with polar symmetry; however, no documentary report has been obtained to realize their ferroelectricity. Here, for the first time, we demonstrated clear ferroelectricity in a fullerene adduct formed by C₆₀ and S₈. More is different: the combination of the most symmetric molecule C₆₀ with the highest I symmetry and molecule S₈ with high D₄ symmetry resulted in the polar C₆₀S₈ adduct with a low crystallographic symmetry of the C₂ (mm2) point group at room temperature. The presented C₆₀S₈ undergoes polar-to-polar ferroelectric phase transition with the mm2Fm notation, whose ferroelectricity was confirmed by a ferroelectric hysteresis loop and ferroelectric domain switching. This finding opens up a new functionality for fullerenes and sheds light on the exploration of more ferroelectric fullerenes.