Topological characteristics of local atomic arrangements at crystalline-amorphous structural transition in graphite

Abstract

Quasi-continuous structural transformation from the crystalline to amorphous state takes place in graphite during ball-milling. The quantitative characteristics of a short- and a medium-range orders in carbon nanomaterials structure are determined by a combined application of X-ray diffraction analysis, reverse Monte Carlo modeling and Voronoi diagram method. High resolution TEM images revealed formation of globular carbon materials having onion-like structure. The Voronoi polyhedra (VP) constructed for simulated atomic configurations of the ball-milled graphite have an extraordinary variety in their topological and metric characteristics and contain a lot of 5-fold faces. The analysis of VP sphericity coefficient Ksph enables a conclusion about the change of the local atomic arrangement in a structure of ball-milled carbon from graphite- to diamond-like. The sphericity coefficient is proposed to be as a parameter of the topological order to quantitative estimation of disordering degree in amorphous structures.