Metastability and high-Tc superconductivity in A15-type ternary hydride YSbH6 at moderate pressure

TL;DR

This work identifies YSbH$_{6}$ as a promising high-$T_{ m c}$ superconductor in the A15 framework at moderate pressure by integrating a multi-stage high-throughput screening with data-driven interatomic potentials and first-principles calculations. The predicted $T_{ m c}$ is $\approx 118$ K at $50$ GPa, but thermodynamic stability places the compound above the convex hull ($E_h = 108$ meV/atom at 50 GPa, reducing to 26 meV/atom at 120 GPa), indicating metastability and a potential megabar synthesis route. Dynamic, kinetic, and elastic stability analyses—supported by custom ED DPs and phonon/Eliashberg calculations—reveal robust dynamical stability across $20$–$120$ GPa, strong kinetic resilience at 50–120 GPa, and elastic stability at lower pressures but instability at 120 GPa. The study highlights the necessity of combining thermodynamic, dynamical, kinetic, and elastic criteria, along with refined $T_{ m c}$ calculations (notably using variable DOS approaches), to guide experimental pursuit of metastable superconductors. Overall, YSbH$_{6}$ serves as a benchmark for balancing high-$T_{ m c}$ performance with limited thermodynamic stability in ternary hydrides.

Abstract

The discovery of high-temperature superconductors remains a central challenge in materials science. Hydrogen-rich compounds are among the most promising candidates, as they can exhibit phonon-mediated superconductivity at elevated critical temperatures, though their stabilization typically requires extreme pressures. % Here, we report the identification of YSbH$_{6}$ as a promising superconductor by a multi-stage high-throughput screening on ternary A15-type hydrides, followed by a high-throughput computational search of the Y--Sb--H system, accelerated by ephemeral data derived potentials. % The cubic $Pm\Bar{3}$ YSbH$_{6}$ phase exhibits a predicted critical temperature of 118\,K at 50\,GPa, among the highest $T_{\rm c}$ reported to date for an A15-hydride at this pressure. Thermodynamic analysis shows that YSbH$_{6}$ lies $\sim$100\,meV/atom above the convex hull at 50\,GPa, but only 26\,meV/atom above the hull at 120\,GPa, suggesting possible metastability and synthesis at similar high pressure conditions. The phase is dynamically stable over a wide pressure range (20--120\,GPa), displays kinetic stability at 50\,GPa and elastic stability at 20 and 50\,GPa, key ingredients for long-lived metastable behaviour at moderate pressures. % These results highlight YSbH$_{6}$ as a benchmark case illustrating the balance between high-$T_{\rm c}$ performance and limited thermodynamic stability in ternary hydrides, and underscore the importance of combined dynamic, thermodynamic, kinetic and elastic stability analyses for guiding experimental synthesis of metastable superconductors.

Figures (4)

• Figure 1: The crystal structure of $Pm\Bar{3}$ YSbH$_{6}$. Y, Sb and H atoms are indicated as green, orange and light pink spheres respectively. Y and Sb are surrounded by 12 hydrogen atoms forming a cage. For clarity, only the cage encircling Sb is showcased in orange.
• Figure 2: Ternary convex hull at 120 GPa, calculated with the PBEsol functional. Dark green circles indicate the thermodynamically stable phases, solid lines are ridges connecting thermodynamically stable points. Metastable phases are shown as squares, their size is set according the energy distance from the convex hull, the smaller the marker size the larger the distance from the convex hull. The convex hull displays 391 structures collected from different searches, with a total of 311 different compositions. Structures shown on the plot have been relaxed with DFT and showcase an energy distance from the hull E$_h$$\leq$ 169 meV/at. Structures are color-coded according to their formation enthalpy (eV/f.u.) relative to Y, Sb and H elements. At 120 GPa, YSbH$_{6}$ is 26 meV/at from the hull and is indicated by a purple square. The list of all stable structures at 120 GPa is provided in the Supplementary Material (Table ST4) along with the convex hull at 50 GPa (Fig. S4 and ST5).
• Figure 3: The left panels show the phonon dispersion along a high symmetry path in the Brillouin zone, for different pressures from 10 to 120 GPa. The $Pm\Bar{3}$ YSbH$_6$ structure is dynamically unstable at 10 GPa inferred by the presence of imaginary mode, but is stable above 20 GPa pressure. The right panels show the corresponding phonon density of states (phDOS).
• Figure 4: (a) Electronic band structure of $Pm\Bar{3}$ YSbH$_6$ at 50 GPa. (b) The total electron density of states (eDOS) projected onto hydrogen-1s (blue), yttrium-4d (green), and antimony-5s (pink) and antimony-5p (purple). H (s), Y (d), Sb (s) and Sb (p) orbitals all make contributions to the peak in the density of states at the Fermi energy. Black dashed line indicates the Fermi level.