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Abstract <p>Novel orthorhombic carbon allotropes with original topologies: 4<sup>4</sup><b>T</b>39 C<sub>12</sub>, <b>mog</b>-C<sub>12</sub> and <b>cbs</b>-C<sub>16</sub> were devised from crystal structure rationale of <i>C4</i> tetrahedra stacking and connections backed by density functional theory DFT-based calculations of ground state structures and energy derived physical properties. Specifically, the structures were identified with distorted <i>C4</i> tetrahedra versus perfect tetrahedra characterizing diamond, accompanied by small atom-averaged volumes resulting into high densities and subsequent ultra hard mechanical behaviors. Dynamically, the allotropes were found stable with positive frequencies revealed from their phonons represented in band structures. Pertaining thermodynamic properties showed specific heat <i>C</i><sub><i>V</i></sub> = <i>f</i>(<i>T</i>) calculated curves close to diamond’s experimental values from literature. The closest agreement with experiment was found for the most cohesive allotrope in the series, <b>cbs</b>-C<sub>16</sub>, concomitantly with the largest electronic indirect band gap, like diamond. From the investigation, a holistic interrelationship: “crystal structure ↔ mechanical ↔ dynamic ↔ electronic properties” is deducted for carbon materials.</p>

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High-Density Ultrahard Novel Orthorhombic Carbon Allotropes C12 and C16 with Physical Properties Close to Diamond: Structural and DFT Investigations

  • 期刊论文

  • 发表日期：

    2025年6月1日

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  • Samir F. Matar

摘要

Abstract

Novel orthorhombic carbon allotropes with original topologies: 44T39 C12, mog-C12 and cbs-C16 were devised from crystal structure rationale of C4 tetrahedra stacking and connections backed by density functional theory DFT-based calculations of ground state structures and energy derived physical properties. Specifically, the structures were identified with distorted C4 tetrahedra versus perfect tetrahedra characterizing diamond, accompanied by small atom-averaged volumes resulting into high densities and subsequent ultra hard mechanical behaviors. Dynamically, the allotropes were found stable with positive frequencies revealed from their phonons represented in band structures. Pertaining thermodynamic properties showed specific heat CV = f(T) calculated curves close to diamond’s experimental values from literature. The closest agreement with experiment was found for the most cohesive allotrope in the series, cbs-C16, concomitantly with the largest electronic indirect band gap, like diamond. From the investigation, a holistic interrelationship: “crystal structure ↔ mechanical ↔ dynamic ↔ electronic properties” is deducted for carbon materials.