Computational Modeling of Lanthanum Hexaboride Materials: Interatomic Potentials and Molecular Dynamics

Abstract

Lanthanum hexaboride is a ceramic with current utilization as a field electron emitter in electron microscopes. Considering that ionic diffusion occurs within this substance while in operation as an electron source, this property can potentially be exploited to produce an evacuated hexaboride lattice with interesting electrical and mechanical behavior for gas storage and separation processes. Density functional theory is employed to understand and determine the energetics of this system, and pairwise interaction potentials are subsequently developed for application in a molecular dynamics framework. Lattice inversion techniques are combined with other optimization procedures to yield potentials which are able to capture the correct equilibrium energetics and lattice dynamics of the crystal at varying temperatures. Electric fields are then applied within molecular dynamics to gain insight into the underlying mechanisms involved in electromigration of the cation through the hexaboride lattice. It is found that reasonable field strengths can induce cation migration within the ceramic at lower temperatures than those required for electron emission using this simplified approach. In addition, preliminary evidence shows that coherent effects of the cation motion may aid in overcoming diffusive energetic barriers, suggesting a coupling between electrical fields and thermal energies can lead to efficiency gains in the transport process.