Lattice-gas model for alkali-metal fullerides: face-centered-cubic structure

TL;DR

This paper introduces a lattice-gas model for alkali-metal fullerides with face-centered-cubic structure, analyzing phase diagrams and ordering phenomena using mean-field and cluster-variation methods.

Contribution

It proposes a new lattice-gas model incorporating ion-site energies and interactions, providing insights into phase behavior of alkali-metal fullerides.

Findings

Large variety of phase diagrams observed

Effect of site energy parameter on ordering phenomena

Model captures key features of alkali-metal fullerides

Abstract

A lattice-gas model is suggested for describing the ordering phenomena in alkali-metal fullerides of face-centered-cubic structure assuming the electric charge of alkali ions residing in either octahedral or tetrahedral interstitial sites is completely screened by the first-neighbor C_60 molecules. This approximation allows us to derive an effective ion-ion interaction. The van der Waals interaction between the ion and C_60 molecule is characterized by introducing an additional energy at the tetrahedral sites. This model is investigated by using a three-sublattice mean-field approximation and a simple cluster-variation method. The analysis shows a large variety of phase diagrams when changing the site energy parameter.