Boron arsenide phonon dispersion from inelastic x-ray scattering: Potential for ultrahigh thermal conductivity

Cubic boron arsenide (BAs) was predicted to have an exceptionally high thermal conductivity (k)~20000.16em0exW0.16em0exm^-1K^-1 at room temperature, comparable to that of diamond, based on first-principles calculations. Subsequent experimental measurements, however, only obtained a k of ~2000.16em0exW0.16em0exm^-1K^-1. To gain insight into this discrepancy, we measured phonon dispersion of single-crystal BAs along high symmetry directions using inelastic x-ray scattering and compared these with first-principles calculations. Based on the measured phonon dispersion, we have validated the theoretical prediction of a large frequency gap between acoustic and optical modes and bunching of acoustic branches, which were considered the main reasons for the predicted ultrahigh k. This supports its potential to be a super thermal conductor if very-high-quality single-crystal samples can be synthesized.