Ab initio calculations of the thermal properties of boron arsenide

Abstract

Thermal properties of bulk zinc-blende boron arsenide (BAs) were investigated by performing ab initio calculations using both the local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange-correlation potential. Phonon dispersion relations were studied within the framework of density functional perturbation theory (DFPT) and the subsequent thermal properties were computed using the quasi-harmonic approximation (QHA). We have computed the temperature dependence of lattice constant (ao), isothermal bulk modulus (Bo), linear thermal expansion coefficient (αL), average Grüneisen parameter (γ), and specific heat capacity at constant pressure (CP) as well as at constant volume (CV) of BAs. The calculated LDA values at 300 K of Bo (142.8 GPa), αL (4.01 × 10−1 K−1), γ (0.816), and CP (0.34 J g−1 K−1) are in excellent agreement with the reported experimental values of 148 GPa, 3.85 × 10−6 K−1, 0.82, and 0.4 J g−1 K−1 respectively in the same order. In contrast, the GGA is found to overestimate the values of thermal properties for all the temperatures when compared to LDA, except the isothermal bulk modulus. The discrepancy between the computed LDA and GGA values has been discussed in detail. Results further indicate that the discrepancy between the computed LDA and GGA values of ao,Bo is found to increase with the increase in temperature. In contrast, the discrepancy in the values of CP,CV,γ and αL is found to decrease with the increase in temperature. In the subsequent calculations, the mode-Grüneisen parameter corresponding to various phonon modes has been computed. No negative thermal expansion (NTE) is observed, although, the mode-Grüneisen parameter corresponding to transverse acoustic phonons exhibits a small negative value at the zone-edge of the Brillouin Zone. Finally, the intrinsic lattice thermal conductivity (κℓ) of BAs has been estimated using the Slack’s model. Results indicate that the Slack’s model underestimates the κℓ of BAs, which is possibly due to the low acoustic Debye temperature (θa) obtained for BAs.