Stabilization and highly metallic properties of heavy group-V hydrides at high pressures

Compressed hydrides of the heavy group-15 elements Bi and Sb are investigated using ab initio methods. While the hydrides of Bi and Sb are known to be quite unstable at one atmosphere, our calculations predict that they can be stabilized at high pressures. Thus, at the composition of XH3 (X=Bi or Sb), possible Bi hydrides are BiH2(Pnma) + H beyond 105 GPa and BiH3(I41/amd) beyond 250 GPa; for Sb hydrides, SbH2 + H hardly appears, and SbH3(Pnma) is stabilized beyond 150 GPa. All of these hydrides are metallic with very dispersive electronic structures, this being in accordance with the predictions of the Goldhammer-Herzfeld criterion. Superconducting transition temperatures have also been estimated from the extended McMillan equation, and they turn out to be 39 K for BiH2 at 125 GPa, 65 K for BiH3 at 270 GPa, and 68 K for SbH3 at 170 GPa.