Please use this identifier to cite or link to this item: https://hdl.handle.net/20.500.14279/1379
Title: Structural properties and energetics of amorphous forms of carbon
Authors: Kelires, Pantelis C. 
Major Field of Science: Engineering and Technology
Field Category: Mechanical Engineering
Keywords: Carbon;Monte Carlo method;Density
Issue Date: 1993
Source: Physical Review B,1993, vol. 47, no. 4, pp. 1829-1839
Volume: 47
Issue: 4
Start page: 1829
End page: 1839
Journal: Physical Review B 
Abstract: We have made a comparative theoretical study of the most common forms of unhydrogenated amorphous carbon (α-C), namely, of the dense, diamondlike phase and the low-density evaporated α-C (e-C). Emphasis is given to the connection among the structure, energetics, and stability of these phases. To make the simulations of the amorphous structures (formed by quenching the liquid) tractable, we used the Monte Carlo method, combined with the empirical-potential approach. Our analysis employs a powerful total-energy-partitioning scheme, which is proved very useful in treating the energetics of disordered systems. It is found that threefold sp2 sites are the energetically favorable geometries in e-C, and thus they are by far more numerous. The nonplanar character of sp2 sites and the absence of sixfold rings indicate that medium-range order is rather not significant in e-C. The increasing graphitic character of e-C, as the temperature is raised, is explained by resorting to the effective temperatures T*, at which the atoms freeze in their lattice positions. For diamondlike α-C, the simulations show that there exist two distinctly different dense structures. The ''as-quenched'' one (i-C) is mostly sp3 bonded, but it is metastable. Upon annealing, it converts into a second phase (i-C*), mostly sp2 bonded, with a significant energy gain. A specific mechanism is proposed for this transition. The insensitivity of density to annealing is explained if we use the concept of the ''glass transition temperature'' T*. Finally, by introducing an isotropic bulk modulus for the amorphous phase, it is found that e-C has a much lower compressibility than i-C*, enhancing the distinguishability among the two low-coordinated forms of α-C.
URI: https://hdl.handle.net/20.500.14279/1379
ISSN: 01631829
DOI: 10.1103/PhysRevB.47.1829
Rights: © American Physical Society
Type: Article
Affiliation : University of Crete 
Research Center of Crete 
Publication Type: Peer Reviewed
Appears in Collections:Άρθρα/Articles

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