Pentagonal Monolayer Crystals of Carbon, Boron Nitride, and Silver Azide

TL;DR

This paper presents a theoretical study of pentagonal monolayer crystals of carbon, boron nitride, and silver azide, revealing their structural, electronic, and mechanical properties through first principles calculations.

Contribution

It introduces new pentagonal monolayer structures of carbon, boron nitride, and silver azide and analyzes their stability, electronic behavior, and mechanical properties.

Findings

p-graphene and p-AgN₃ are semiconductors with indirect bandgaps.

p-BN structures exhibit metallic behavior.

Only p-graphene and p-B₂N₄ are dynamically stable.

Abstract

In this study we present a theoretical investigation of structural, electronic and mechanical properties of pentagonal monolayers of carbon (p-graphene), boron nitride (p-B$_{2}$N$_{4}$ and p-B$_{4}$N$_{2}$) and silver azide (p-AgN$_{3}$) by performing state-of-the-art first principles calculations. Our total energy calculations suggest feasible formation of monolayer crystal structures composed entirely of pentagons. In addition, electronic band dispersion calculations indicate that while p-graphene and p-AgN$_{3}$ are semiconductors with indirect bandgaps, p-BN structures display metallic behavior. We also investigate the mechanical properties (in-plane stiffness and the Poisson's ratio) of four different pentagonal structures under uniaxial strain. p-graphene is found to have the highest stiffness value and the corresponding Poisson's ratio is found to be negative. Similarly, p-B$_{2}$N$_{4}$ and p-B$_{4}$N$_{2}$ have negative Poisson's ratio values. On the other hand, the p-AgN$_{3}$ has a large and positive Poisson's ratio. In dynamical stability tests based on calculated phonon spectra of these pentagonal monolayers, we find that only p-graphene and p-B$_{2}$N$_{4}$ are stable, but p-AgN$_{3}$ and p-B$_{4}$N$_{2}$ are vulnerable against vibrational excitations.