Anisotropic Phononic and Electronic Thermal Transport in BeN4

Beryllium polynitride (BeN4) has been recently synthesized under high-pressure conditions [Bykov et al. Phys. Rev. Lett. 2021, 126, 175501]. Its anisotropic lattice structure dependent on the applied pressure motivates exploration of its thermal transport properties with a theoretical framework that combines the Boltzmann transport equation with ab initio calculations. The bonding anisotropy (impacting the phonon and electron group velocities) and bonding anharmonicity (captured through three- and four-phonon scatterings) are reflected in the strong anisotropy of both phononic and electronic components of the thermal conductivity. Moreover, the pressure-driven evolution of the interlayer Be-N bonding, from partially covalent (under high-pressure synthesis conditions) to van der Waals (under ambient pressure), drives a largely interlayer thermal conductivity. These findings highlight an alternative strategy for achieving directional control of the thermal transport in synthetic materials.

Automated summary

Beryllium polynitride (BeN4), synthesized under high-pressure conditions, exhibits an anisotropic lattice structure and thermal conductivity. The bonding anisotropy and bonding anharmonicity contribute to the anisotropic behavior in both phononic and electronic components of its thermal conductivity. The pressure-driven evolution of the interlayer bonding also plays a significant role in the interlayer thermal conductivity.