Stability Of Giant Onion-like Carbon Fullerenes

Onion-like carbon fullerenes(OLCFs)are a promising material for various applications in nanoscale devices,medicine,lubrication and superhard materials.Despite of a large body of experimental and theoretical studies of SWFs and OLCFs,information on the microscopic mechanisms of reversible phase transformations of OLCFs-NTs is still insufficient.Since the intermediate metastable structures generated during the quenching/heating process of OLCFs could give an important clue to the root of reversible formation paths,as well as the formation of NTDs with high hardness.Detailed thermodynamical characterization of melting behaviors of stable OLCFs is highly warranted at this point.To date,most of the theoretical studies have been restricted to address the molecular stability and fragmentation kinematics of small SWFs,and only two available theoretical investigations have been conducted to explore structural and thermal stability of small 2/3 layered OLCFs.To the best of our knowledge,investigations on the high temperature structural behaviors and fragmentation dynamics of giant OLCFs have not been undertaken hitherto,both experimentally and theoretically.Here we hence present direct computer simulation of thermal and dynamics characteristics of 20-shell-OLCF having uniquely arrangement of concentric cages of C60@C240@...@C24000.Knowledge of the pyrolysis chemistry of OLCFs helps understanding the thermally induced erosion of carbon-based materials,the present study provide important knowledge of the pyrolysis chemistry of OLCFs that helps understanding the high-temperature erosion of carbon-based materials,and also may shed some lights onto the synthesis of NTDs transformed from OLCFs.Here,using first-principle-based ReaxFF atomistic simulations,thermal and dynamical characteristics of supergiant 20-shell OLCF having concentric arrangement of C60@C240@...@C24000 are explored.Fullerenes@20-shell OLCF yield slightly larger average radius than isolated ones at the same scale,excluding C60.The average intershell-spacing@OLCF shows a reduction tendency from inner to outer,but is slightly higher than that of bulk graphite.Because of nonbonded intershell forces,fullerenes@20-shell OLCF are energetically favorable over the corresponding isolated ones.In contrast to nonmonotonic variation of melting point with size and shell-index in isolated fullerenes and conventional solid nanoparticles,an anomalous shell-dependent melting instability in the 20-shell OLCF is identified due to the combined effects of size,confinement and surface;Both inner and outer fullerenes are not so resistive against heating,nor are they as strong as the identical-size isolated ones,however,the intermediate shells,locally similar to curved bulk graphite,demonstrate higher heat-resisting property than isolated fullerenes at the same scale.Topological analysis shows the overall morphological transformation of four stages for incipient Stone-Wales rearrangement,heterogeneous defects nucleation,amorphization and fragmentation.