Structure of amorphous carbon quenched from liquid in the pressure range 1–40 GPa: Molecular dynamic modeling

Abstract

It is well known, that quenching from the liquid state is the basis of many methods for creating new materials with unique properties. Liquid and amorphous carbon are a mixture of atoms with different states of hybridization (sp1, sp2, sp3) owing to polymorphism. It is claimed that there is a tendency of growth of sp1 atoms in liquid and amorphous carbon at decreasing pressure. Great interest has been shown recently to carbyne and pseudocarbynes, consisting of sp1-hybridizing atoms. These materials have unique optical and mechanical properties. In the present work a pressure dependence of the structure of amorphous carbon, quenched from liquid is studied by molecular dynamics simulation in the pressure range 1–40 GPa. The interaction between carbon atoms was determined by two bond-order potentials: Airebo and ReaxFF. These two potentials take into account the type of a chemical bond as well as breaking and formation of new chemical bonds during the modeling process. We study a bulk quenching from liquid carbon in the NPT ensemble at a constant pressure and determine the distribution of chemical bonds sp1–sp2–sp3 in amorphous carbon during the quenching. Quenched liquid structure modeling at a pressure of 1 GPa and the structure of an amorphous carbon sample obtained experimentally at a pressure of 25 MPa by Raman spectroscopy showed that the sp1 fraction of carbon was significant.