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 (ScH_4, 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 T_cs are predicted for ScH₆, ScH₇, ScH₉, ScH₁₀, and ScH₁₂, with superconducting transition temperatures (T_cs) of 120-169 K above 250 GPa, as estimated by the Allen-Dynes modified McMillan equation.