Structure and dynamics of the fullerene polymer Li4 C60 studied with neutron scattering

TL;DR

This study combines neutron scattering experiments and ab-initio calculations to elucidate the structure, lattice dynamics, and ionic behavior of the Li4 C60 fullerene polymer, revealing its bonding, charge transfer, and high ionic mobility.

Contribution

It provides detailed structural and dynamical insights into Li4 C60 using neutron scattering and theoretical modeling, highlighting its unique bonding and ionic diffusion properties.

Findings

Confirmed the bonding architecture of Li4 C60

Observed partial charge transfer from Li to C60

Identified high ionic diffusivity and lattice instability at 200 K

Abstract

The two-dimensional polymer structure and lattice dynamics of the superionic conductor Li4 C60 are investigated by neutron diffraction and spectroscopy. The peculiar bonding architecture of this compound is definitely confirmed through the precise localisation of the carbon atoms involved in the intermolecular bonds. The spectral features of this phase are revealed through ab-initio lattice dynamics calculations and inelastic neutron scattering experiments. The neutron observables are found to be in very good agreement with the simulations which predict a partial charge transfer from the Li atoms to the C60 cage. The absence of a well defined band associated to one category of the Li atoms in the experimental spectrum suggests that this species is not ordered even at the lowest temperatures. The calculations predict an unstable Li sublattice at a temperature of 200 K, that we relate to the large ionic diffusivity of this system. This specificity is discussed in terms of coupling between the low frequency optic modes of the Li ions to the soft structure of the polymer.