Thermoelectric Properties of 2-D B₄C Nanosheets

Bulk Boron Carbide(B₄C) has encouraging properties as a high temperature thermoelectric material, it is extremely hard with a high melting temperature of 2763^oC and a high Seebeck coefficient in the range of 100-300 μV/K. Calculating similar properties for the 2-D form can allow us to establish more varied applications of the material. We start by generating the theoretical structures for non-polar and symmetric 2-D slabs of B4C along multiple cleavage directions and all possible terminations. We then use Van der Waals corrected DFT as implemented in the plane wave code VASP to compute their formation energies and determine the bonding scheme in the slab. Our results show the formation energies for slabs in various directions are similar, indicating that there isn’t a significant preference in the choice for a cleavage direction. Also, three selected planes (001), (012) and (101) have formation energies of 0.056 eV/atom, 0.105 eV/atom and 0.116 eV/atom, respectively, which are all below the threshold energy of 0.2 eV/atom for free-standing single/few-layer nanosheets. We finally compute the thermoelectric coefficients using the open source code BoltzTrap2. Our results indicate that B4C nanosheets are promising thermoelectric materials.