Predictions of high-temperature superconducting ternary hydrides under high pressure using density functional calculations

The abundant chemical compositions in ternary hydrides bring much more possibility to explore high-temperature superconductors under lower pressure. Here we constructed 115 ternary hydrides on the basis of the element substitution using 16 metal elements within five reported prototype structures. We conducted a three-step approach to screen and study these candidate structures in the aspects of dynamical stability, formation energy, and relative enthalpy, respectively. Based on this approach, we found three metastable compounds with hydrogen clathrate cages in the space group of $P\overline{3}m1$, including ${\mathrm{Y}}_{2}{\mathrm{CdH}}_{18}$, ${\mathrm{Y}}_{2}{\mathrm{InH}}_{18}$, and ${\mathrm{Ca}}_{2}{\mathrm{SnH}}_{18}$. All of the structures are superconductive under high pressure with ${T}_{\mathrm{c}}$ above 110 K, which is larger than the superconductive temperature of liquid nitrogen. By comparing the bonding factors with other 12 reported ternary hydride systems, we proposed that the bond strength alone is limited to evaluate the stable pressure and the H-H bond strength could provide prospects on the ${T}_{\mathrm{c}}$ values. Our study enriches the database of novel ternary hydrides under high pressure, and provides insight to consider relatively active elements than I B, II B, and III A elements or $f$ electron elements for ternary hydrides designing, shedding light on future theoretical and experimental research.