Ternary Gold Hydrides: Routes to Stable and Potentially Superconducting Compounds

In a search for gold hydrides, an initial discouraging result of no theoretical stability in any binary AuH<sub><i>n</i></sub> at <i>P</i> < 300 GPa was overcome by introducing alkali atoms as reductants. A set of AAuH<sub>2</sub> compounds, A = Li, Na, K, Rb, and Cs, is examined; of these, certain K, Rb, and Cs compounds are predicted to be thermodynamically stable. All contain AuH<sub>2</sub><sup>–</sup> molecular units and are semiconducting at <i>P</i> = 1 atm, and some form metallic and superconducting symmetrically bonded AuHAu sheets under compression. To induce metallicity by bringing the Au atoms closer together under ambient conditions, we examined alkaline earth ion substitution for two A, i.e., materials of composition AE­(AuH<sub>2</sub>)<sub>2</sub>. For AE = Ba and Sr, the materials are already marginally metallic at <i>P</i> = 1 atm and the combination of high and low phonon frequencies and good electron–phonon coupling leads to reasonably high calculated superconducting transition temperatures for these materials.