Superconductivity in barium hydrides via incorporation of light elements

Barium hydrides are of interest for their potential in both ionic conductivity and superconductivity. Recently, a superconducting hydride BaH$_{12}$ containing H$_2$ and H${_3}^{-1}$ molecular units was experimentally reported with a critical temperature $T_\text{c}$ of 20 K at 140 GPa [Nat Commun 12, 273 (2021)]. Herein, we combine ab initio methods with a rapid calculator of $T_\text{c}$ based on the networking value model to predict that the introduction of light elements, such as Be, can effectively expand the structure diversity and structure space of barium hydrides. Although molecular hydrogen units are still widely present in thermodynamically stable and metastable crystal structures, we find that a metastable phase of BeBaH$_8$ shows a high $T_\text{c}$ of 49 K at 100 GPa, which is only 38 meV/atom above the thermodynamic stability energy. This BeBaH$_8$ remains dynamically stable at 15 GPa. Furthermore, our study shows that increasing pressure can further elevate $T_\text{c}$ beyond 100 K by enhancing the electron-phonon coupling constant. Our study proposes a feasible method for broadening the structural landscape in the exploration of superconducting phases of barium hydrides.