High Hydrides of Scandium under Pressure: Potential Superconductors

In a systematic investigation of scandium hydrides with high hydrogen content we predict seven phases of scandium hydrides (ScH4, ScH6, ScH7, ScH8, ScH9, ScH10, and ScH12), which are stable above 150 GPa. Zero point energies are essential in determining the phases and pressure ranges within which they are stable. The interconversion of the various hydrides is intriguing; in one case there is a “return” to a lower hydrogen content hydride with increasing pressure. We argue that these hydrides may be synthesized by compressing mixtures of ScH3 and H2 above 150 GPa. New H bonding motifs are uncovered, including “H5” pentagons or “H8” octagons in ScH9, ScH10, and ScH12. High Tcs are predicted for ScH6, ScH7, ScH9, ScH10, and ScH12, with superconducting transition temperatures (Tcs) of 120–169 K above 250 GPa, as estimated by the Allen–Dynes modified McMillan equation.