Beryllium, an s-block element, forms an aromatic network of delocalized Be-Be π bonds in alloys ZrBe2 and HfBe2. This gives rise to a structure that fits description as stacked [Be2]4- layers with tetravalent cations in between. The [Be2]4- sublattice is isoelectronic and isostructural to graphite, as well as the [B]-2 sublattice in MgB2, and it bears identical manifestations of π bonding in its electronic band structure. These come in the form of degeneracies at K and H in the Brillouin zone, separated in energy as the result of interlayer orbital interactions. Zr and Hf use their valence d orbitals to form bonds with the layers, leading to nearly identical band structures. Like MgB2, ZrBe2 and HfBe2 are computed to be phonon-mediated superconductors at ambient pressures, with respective critical temperatures of 11.4 K and 8.8 K. The coupling strength between phonons and free electrons is very similar, so that the difference in critical temperatures is controlled by the mass of constituent interlayer ions.
Bibliographical noteKAUST Repository Item: Exported on 2021-10-29
Acknowledgements: KAUST super computing Lab
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