On orientational relief of inter-molecular potential and the structure of domain walls in fullerite C60

TL;DR

This paper models the orientational ordering and domain wall structures in fullerite C60, revealing narrow domain walls and significant barrier reductions near defects, which impact molecular orientation dynamics.

Contribution

It introduces a simple planar model for fullerite C60's orientational ordering on a triangular lattice, highlighting the effects of domain walls and potential barrier reductions.

Findings

Narrow interdomain walls observed.

Significant barrier reduction near defects.

Strong correlation effects in triangular lattice.

Abstract

A simple planar model for an orientational ordering of threefold molecules on a triangular lattice modelling a close-packed (111) plane of fullerite is considered. The system has 3-sublattice ordered ground state which includes 3 different molecular orientations. There exist 6 kinds of orientational domains, which are related with a permutation or a mirror symmetry. Interdomain walls are found to be rather narrow. The model molecules have two-well orientational potential profiles, which are slightly effected by a presence of a straight domain wall. The reason is a stronger correlation between neighbour molecules in triangular lattice versus previously considered square lattice A considerable reduction (up to one order) of orientational interwell potential barrier is found in the core regions of essentially two-dimentional potential defects, such as a three-domain boundary or a kink in the domain wall. For ultimately uncorrelated nearest neighbours the height of the interwell barrier can be reduced even by a factor of 100.