New 3D and 2D Octacarbon C8 and isoelectronic B4N4 having peculiar mechanic and magnetic properties. First-principles identifications

TL;DR

This study uses first-principles calculations to explore the structural, mechanical, and magnetic properties of novel 3D and 2D octacarbon C8 and isoelectronic B4N4, revealing their potential as superhard and magnetic materials.

Contribution

It introduces new 3D and 2D octacarbon C8 and B4N4 structures with unique mechanical and magnetic properties, supported by comprehensive density functional theory analysis.

Findings

Cohesive energies and elastic constants indicate superhard properties.

2D-C8 is stable with ferromagnetic ground state.

B4N4 exhibits similar bandgap to diamond with slightly lower hardness.

Abstract

Cohesive energies, energy-volume equations of states EOS, electron localization ELF maps, elastic constants, and band structures are reported for original octacarbon C8 three dimensional 3D and two-dimensional 2D chemical systems based on density functional theory calculations. Specifically, tetragonal C8 is identified cohesive with hardness close to experimentally identified cubic Ia-3 C8; both exhibiting comparable hardness to diamond. Also, isoelectronic and isostructural B4N4 is calculated with a slightly lower hardness due to the ionocovalent B-N bonding and a bandgap with the same magnitude as Diamond. 2D-C8 on the other side is proposed with interpenetrating two carbon hexagonal substructures, identified from energy calculations as stable in a ferromagnetic ground state. Critical pressure for the collapse of magnetization PC=12 GPa let assign a soft ferromagnetic behavior alike Invar alloys. Electronic band structures analyses identify specific bands differentiating magnetic carbon substructure (C1) from nonmagnetic semi-conducting honeycomb-like C26 layers. These observations let propose spin chemistry perspectives once such multilayered carbon 2D compounds are grown as stand-alone or on selected substrates as thin or thick films