La₂Br₂H_n: a hydrogenated two-dimensional electride material

Electrides are materials with electrons localized on interstitial sites in the crystal lattice. Some materials exhibit this behaviour at high pressure when it becomes energetically more favourable for some electrons to occupy states localized in the voids between atoms rather than atomic orbitals.

LaBr, a layered magnetic material that is weakly bound by van der Waals interactions, is an ambient pressure electride¹ and, using first-principles electronic structure calculations, we show that monolayer LaBr is potentially exfoliable, stable, retains the magnetic ordering of bulk LaBr and could also be an electride at ambient pressure.

Furthermore, in monolayer LaBr, we show that the two interstitial sites occupied by electrons have a strong tendency to bind with, e.g., hydrogen and we propose several new structures with composition of La, H and Br. We have calculated the composition phase diagram of LaBr with hydrogen, finding LaBr to be a potential promising candidate material for high-density hydrogen storage, and monolayer La₂HBr₂ to be a potential promising candidate 2D multiferroic material.

1. M. Hirayama, S. Matsuishi, H. Hosono and S. Murakami, “Electrides as a New Platform to Topological Materials”, Phys. Rev. X, 8, 031067 (2018)