High pressure structures and superconductivity of AlH3(H2) predicted by first principles

Abstract

Motivated by the potential high-temperature superconductivity in hydrogen-rich materials, the high-pressure structures of AlH₃(H₂) in the pressure range of 25–300 GPa were extensively explored by using a genetic algorithm. We found an insulating P1 phase, a semiconducting P phase and an intriguing sandwich-like metallic phase with a space group of P2₁/m-Z (containing Z shape net layers of Al atoms). We found that the H₂ molecules in the environment of AlH₃ became metallic and showed a molecular semi-molecular phenomenon. The application of the Allen–Dynes to modify the McMillan equation yields remarkably high superconducting temperatures of 132–146 K at 250 GPa, which is among the higher values reported so far for phonon-mediated superconductors. In this paper, we reveal a unique superconducting mechanism, which shows that the direct interactions between H₂ and AlH₃ at high pressure play a major role in the high superconductivity, while the contribution from the H₂ vibration is minor.