Recently, perovskite hydrides have received great attention due to their excellent superconductivity at moderate pressures. Based on perovskite structure $Pm\overline{3}m\text{−}{\mathrm{KInH}}_3$, a series of quaternary double perovskite hydrides $A_2{\mathrm{In}Z\mathrm{H}}_6$ $(A=\mathrm{Li}, \mathrm{Na}, \mathrm{K}, \mathrm{Rb}, \mathrm{Cs}, Z=\mathrm{Cu}, \mathrm{Ag} \mathrm{Au}, \mathrm{Zn}, \mathrm{Cd}, \mathrm{Hg}, \mathrm{Ga}, \mathrm{Tl}, \mathrm{Ge}, \mathrm{Sn}, \mathrm{Pb}, \mathrm{As}, \mathrm{Sb}, \mathrm{Bi})$ were designed. High-throughput screening show that 27 compounds are dynamically stable below 50 GPa. Double perovskite hydrides $A_2{\mathrm{In}Z\mathrm{H}}_6$ which are dynamically stable at moderate pressures are all superconductors. Four hydrides exhibit high-temperature superconductivity, including ${\mathrm{K}}_2{\mathrm{InCuH}}_6$ (92 K at 0 GPa), ${\mathrm{K}}_2{\mathrm{InAuH}}_6$ (108 K at 6 GPa), ${\mathrm{Cs}}_2{\mathrm{InGeH}}_6$ (82 K at 20 GPa), and ${\mathrm{Cs}}_2{\mathrm{InAuH}}_6$ (104 K at 20 GPa). Additionally, ${\mathrm{K}}_2{\mathrm{InAgH}}_6$ has a superconducting $T_c$ of 75 K, which is approaching liquid nitrogen temperature. The flat band of ${\mathrm{K}}_2{\mathrm{InCuH}}_6$ at Γ point is governed by $\mathrm{H}\text{−}s$ and $\mathrm{Cu}\text{−}{e}_{1g}$ orbitals hybridization. Further analysis indicates that there is strong coupling between electrons and hydrogen-dominated optical phonons. This strong electron-phonon coupling (EPC) plays a critical role in high-temperature superconductivity for ${\mathrm{K}}_2{\mathrm{InCuH}}_6$. Our results enhance confidence in the exploration of high-temperature superconducting perovskite hydrides at moderate pressure, and stimulates further exploration of quaternary superconducting hydrides.

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• Chemical bonding
• Crystal structure
• Pressure effects
• Superconductivity
• High-temperature superconductors
• Hydrides
• Superconductors
• BCS theory
• Density functional theory