Theoretical prospects for alkali intercalation of hexagonal boron nitride

Although alkali intercalation of graphite is well-known, the large bandgap of its sister compound hexagonal boron nitride would appear to preclude a similar charge-transfer-based mechanism for alkali intercalation of hBN. Recent experimental results on potassium intercalation of bulk hBN motivate a computational reassessment of possible driving forces towards alkali intercalation of this large-gap 2D material [1].

Different areal densities of potassium or sodium with and without defects in the underlying hBN layers were explored, with careful consideration of van der Waals contributions through DFT-D3 [2] or DFT-TS [3] methods. The intercalated state appears to support a 2D electron gas resident on the alkali layer with limited charge transfer. Boron vacancies strongly favor intercalation and also act to “pillar” the hBN to facilitate further alkali infiltration. Due to the reduced dimensionality and delocalized nature of the alkali-derived electron gas, significant ambiguity remains around the quantification of vdW contributions to the thermodynamic balance, expressible as a threshold areal density of hBN defects needed to drive intercalation.

References:

1. S. Okada and M. Otani , Phys. Rev. B: Condens. Matter Mater. Phys., 2010, 81, 233401

2. S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J. Chem.Phys, 2010, 132, 154104

3. A. Tkatchenko, M. Scheffler, Phys. Rev. Lett., 2009, 102, 073005