Stable multifunctional aluminum phosphides at high pressures.

Phosphides have been used in a wide range of applications due to their excellent optical, mechanical, and catalytic properties. Using an effective unbiased structure searching method combined with first-principles calculations, the phase diagram and physical and chemical properties of aluminum phosphides have been determined at high pressures. The results reveal that the unconventional stoichiometries of AlP, AlP, and AlP remain stable above 66, 91, and 116 GPa, respectively. Interestingly, the analysis of the phonon spectrum suggests that AlP with 2 symmetry can be dynamically stable at atmospheric pressure. In addition, the band gap of 1.51 eV at the HSE06 level and the estimated Vickers hardness of ∼10.54 GPa make 2-AlP a hard photoelectric material. Moreover, our electronic properties show that AlP with symmetry and AlP with 4/ structure are metallic at high pressures and further electron-phonon coupling calculations indicate -AlP and 4/-AlP are superconductors with estimated values of 3.9 K at 150 GPa and 10.2 K at 100 GPa, respectively. Our work provides significant inputs toward understanding novel chemical bonding in aluminum phosphides and gives a direction for the experimental synthesis of multifunctional materials at high pressures.