Superconductivity with interstitial hydrogen atoms in HfAl₂ Laves phase compound

Laves phases are AB₂ intermetallic compounds discovered by Fritz Laves, characterized by a specific atomic size ratio between elements A and B, which ranges from 1.05 to 1.67. This size ratio allows A atoms to form diamond, hexagonal diamond, or related structures, while B atoms occupy tetrahedral positions around A atoms. The Laves phase compounds exhibit high hydrogen storage capacities, up to 3.6 hydrogen atoms per formula unit, due to the presence of both tetrahedral and octahedral interstitial sites. It can be expected that this large uptake in hydrogen will alter the phonon spectrum of the compound, which will consequently influence its electronic properties. Despite the growing interest in these materials for potential hydrogen storage applications in energy generation, their physical properties remain relatively unexplored. In this context, HfAl₂ is a Laves phase compound that crystallizes in a hexagonal structure with MgZn₂ prototype, known as C14, one of the three classes of Laves phases, in which a superconducting state was successfully identified after hydrogenation through conventional metal-gas interaction, with critical temperatures reaching as high as 8.0 K. These results suggest promising potential regarding superconductivity in hydrogen-storing compounds.