A theoretical analysis of the ground state of long-chain(K&at;C60)nis presented. Within mean field theory, a ferroelectric ground state is found to be stable because of the pseudo-Jahn-Teller mixing of theb1uand theb2gband with a zone-center optical phonon involving the displacement of the endohedralK−ions. A phase diagram for this model is derived in the narrow bandwidth regime. ©2000 American Institute of Physics.