Design of High‐<i>T</i>_c Quaternary Hydrides Under Moderate Pressures Through Substitutional Doping

Abstract In recent years, there has been considerable interest in exploring high‐temperature superconductors in hydrides at low‐pressure conditions. A series of quaternary XAZ 2 H 16 compounds (X, A = La, Ca, Sr, Ba, Ac, Ce, Th, Na or K; Z = Be, B, Si or P) are constructed based on ternary Fm ‐3 m LaB/BeH 8 ‐type structure. Eight hydrides are found to be thermodynamically stable, with LaThBe 2 H 16 and AcBaSi 2 H 16 exhibiting lower pressures of 92 and 81 GPa, respectively. All investigated hydrides display dynamical stability at pressures below one million atmospheres, with LaThBe 2 H 16 remaining stable even as low as 8 GPa. Moreover, LaSrB 2 H 16 , AcBaSi 2 H 16 , AcSrSi 2 H 16 , and Ba 2 SiPH 16 exhibit clear covalent bonding characteristics between Z and H atoms, while Be atoms tend to form ionic bonds with H atoms. Electron‐phonon coupling calculations indicate that all of these quaternary hydrides have potential as superconductors. LaThBe 2 H 16 , AcBaSi 2 H 16 , AcSrSi 2 H 16 and YCeBe 2 H 16 exhibit superconducting transition temperatures ( T c s) of 126, 137, 123, and 104 K at 10, 30, 30, and 45 GPa, respectively, while LaYBe 2 H 16 exhibits the highest T c of 221 K at 75 GPa. These findings provide valuable insights for the search for high‐ T c superconductors under lower pressure conditions and encourage further exploration of polynary superconducting hydrides.