Stability and electronic structure of potassium-intercalated hexagonal boron nitride from density functional calculations

By using the local-density approximation in density functional theory, we explore the possibility of a metallic layered compound derived from hexagonal boron nitride (h-BN). We find that the intercalation process of potassium atoms into the interlayer spacing of h-BN is exothermic with a formation energy of approximately 1.6 eV per potassium atom, and that the electronic structure of potassium-intercalated h-BN under equilibrium interlayer distance is metallic, in which electrons are injected into unoccupied, nearly-free-electron states. The calculated Fermi surfaces of the compound exhibit characteristics similar to that of graphite intercalation compounds doped with alkali/alkali-earth metals.

Figure 1

Schematic (a) top and (b) side views of K-intercalated h-BN compound. White, pale shaded, dark shaded circles denote K, B, and N atoms, respectively. (c) The formation energy of K-intercalated h-BN as a function of interlayer spacing of h-BN per unit cell $\left[\text{K}{\left(\text{BN}\right)}_4\right]$.

Figure 2

(Color online) Energy diagrams of (a) h-BN monolayer and (b) graphene. The dark and pale shaded areas denote the valence and conduction bands, respectively. A red (pale) line denotes the energy position of the bottom of the nearly-free-electron state. Energies are measured from that of the vacuum level. The vacuum level is evaluated by the energy level at the region far from the layers where the local potential is almost constant.

Figure 3

(Color online) (a) Electronic energy band of K-intercalated h-BN compound. Energy is measured from that of the Fermi level. Distribution of wave function of (b) the nearly-free-electron state denoted by $\alpha$ and of (c) the electronic energy band denoted by $\beta$ (the top of valence band and a nondegenerate state) at the $\Gamma$ point, respectively. Black and red contours characterize the sign of the wave functions. Each contour represents twice (or half) the density of the adjacent contour lines.

Figure 4

The Fermi surfaces of K-intercalated h-BN compound on (a) $k_x\text{−}{k}_y$, (b) $k_x\text{−}{k}_z$, and (c) $k_y\text{−}{k}_z$ planes in the Brillouin zone. Dotted line in (a) denotes the zone boundary of the hexagonal Brillouin zone.