Endohedral fullerites: A new class of ferroelectric materials

Endohedral fullerites, composed of periodic lattices of endohedral complexes with polar molecules trapped inside the ${\mathrm{C}}_{60}$ cluster, constitute a new class of ferroelectric materials and the first practical realization of ideal electric dipolar lattices. In these substances, interactions between the partially screened and freely rotating dipole moments of the guest molelcules give rise to dipole-ordered low-temperature phases. The respective transition temperatures for the endohedral fullerites with LiF, LiCl, NaF, and NaCl as the guest molecules are estimated to be at 25, 36, 51, and 60 K, respectively.