First-Principles Calculations to Investigate the Structural, Electronic, Optical, and Elastic Constants; Thermal Conductivity; Raman Scattering; Mulliken Population; and XPS Loss Features of Boron Nitride Polytypes

We systematically studied the structural properties, energetics, charge density, electronic structure, optical properties, hardness, elastic anisotropy properties, mechanical properties, lattice dynamics, thermodynamics, thermal conductivity, Raman scattering, Mulliken population, and core-level X-ray photoelectron spectroscopic (XPS) loss features of boron nitride polytypes and implemented CAmbridge Serial Total Energy Package (CASTEP) code for first-principles calculations based on density functional theory (DFT) along with generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation potential. Our findings on structural parameters agree strongly with the experimental values, with an average error of less than 1%. The acoustic Debye temperature of the boron nitride (BN) polytype is about 1680 K for h-B2N2, 1877 K for c-B4N4, and 1880 K for w-B2N2. The specific heat capacities of h-B2N2, w-B2N2, and c-B4N4 are about 9.437, 7.895, and 3.91 J/(mol K) at 300 K, respectively. To identify significant features and understand the sensitivity of BN polytypes, we estimate that the thermal conductivities for h-B2N2, w-B2N2, and c-B4N4 are 3.905, 10.156, and 22.038 W/(m K) at 300 K, respectively. The elastic constants state that the BN polytypes are mechanically stable and h-B2N2 has a strong anisotropy. The electronic structures reveal that w-B2N2 has a direct band gap of 5.232 eV, while h-B2N2 and c-B4N4 are wide- and indirect-band-gap semiconductors with band gaps of 4.329 and 4.530 eV, respectively. The maximum absorption coefficients in the investigated energy range are 538.50 and 513.66 cm^-1 for c-B4N4 and w-B2N2, respectively. The spectra of the K-edge (1s) of the B and N sites have a sharp π* and a broader σ* in the energy region between 5 and 50 eV. These results indicate that BN is a promising material for heat dissipation and has a lot of potential in the development of novel microelectronic devices because of their low density, exceptional strength, high flexibility and stretchability, good thermal stability, and excellent impermeability. © 2023 American Chemical Society.