Potassium Structures in Carbon Nanotubes

Abstract

We have systemically investigated structural phases of potassium in carbon nanotubes using a structural optimization process applied to an atomistic simulation method. As the radius of the carbon nanotubes is increased, the structures are found in various phases from an atomic strand to multi-shell packs composed of coaxial cylindrical shells and in helical, layered, and crystalline structures. Binding energy variations of encapsulated nanowires as a function of radius were identical with those of freestanding nanowires as a function of radius. Freestanding potassium nanowires of the same structures corresponding to the potassium nanowires encapsulated in carbon nanotubes were unstable and broken at the low temperature. However, when the potassium nanowires were encapsulated in carbon nanotubes, the stability of the K nanowires increased because the walls of carbon nanotubes guarded the encapsulated K nanowire. Numbers of helical atom rows composed of coaxial tubes and orthogonal vectors of a circular rolling of a triangular network can explain multi-shell phases of potassium in carbon nanotubes.