Thermo-mechanical characterization of 2D hexagonal Boron Phosphide (h-BP)

Introduction: Two-dimensional hexagonal boron phosphide (h-BP) has attracted interest because of its predicted thermal stability, electronic properties, and potential for electronic, sensing, and energy applications. However, its finite-temperature mechanical behavior, anisotropy, fracture response, and sensitivity to structural defects remain insufficiently understood.

Materials and methods: A classical force field for monolayer h-BP was developed using density functional theory (DFT) calculations. The resulting bond, angle, dihedral, and non-bonded interaction parameters were implemented in molecular dynamics (MD) simulations using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). Tensile loading was applied along the zigzag and armchair directions at temperatures ranging from 300 to 900 K. The effects of Stone–Wales defects, single-atom vacancies, and two-atom vacancies on the mechanical response and fracture behavior were also investigated.

Results: The simulations reveal mechanical anisotropy, with the zigzag direction exhibiting higher tensile strength and elastic modulus than the armchair direction across the investigated temperature range. Increasing temperature progressively reduces both tensile strength and elastic modulus because of thermal softening. Structural defects further degrade the mechanical performance, with Stone–Wales defects and vacancies reducing both tensile strength and failure strain. The two-atom vacancy produces the most severe degradation.

Conclusions: The results demonstrate that the thermo-mechanical response of monolayer h-BP is strongly dependent on temperature and defect structure. The developed force field enables finite-temperature atomistic simulations of deformation and fracture in h-BP, while the observed temperature- and defect-dependent degradation provides useful guidance for evaluating the mechanical reliability of h-BP in future high-temperature electronic, energy, and sensing applications.