High pressure structures and superconductivity of AlH 3 (H 2 ) predicted by first principles

Motivated by the potential high-temperature superconductivity in hydrogen-rich materials, the high-pressure structures of AlH 3 (H 2 ) in the pressure range of 25–300 GPa were extensively explored by using a genetic algorithm. We found an insulating P 1 phase, a semiconducting P 1̄ phase and an intriguing sandwich-like metallic phase with a space group of P 2 1 / m -Z (containing Z shape net layers of Al atoms). We found that the H 2 molecules in the environment of AlH 3 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 H 2 and AlH 3 at high pressure play a major role in the high superconductivity, while the contribution from the H 2 vibration is minor.