Exploring the superconductivity of CaSrB5: high-pressure stability and electron–phonon interactions

Abstract

High-temperature superconductivity remains a key focus in materials research, with boron compounds considered promising candidate materials due to their unique electronic properties. In this work, we present a systematic investigation of the CaSrB₅ compound within the CaSrB_x (x = 3–12) system, focusing on its structural stability, electronic properties, and superconducting behavior through first-principles calculation. While the Pm1 CaSrB₅ compound lies on the convex hull at 40 GPa, confirming its thermodynamic stability, it exhibits negligible superconductivity (critical temperature T_C < 1 K) due to weak electron–phonon coupling (EPC). In contrast, the metastable F3m phase demonstrates exceptional superconducting properties with an estimated T_C of ≈120 K, as predicted by anisotropic Migdal–Eliashberg theory. At low pressures, it may be dynamically unstable due to the Jahn–Teller effect. Despite the energy of the F3m phase being higher than that of the Pm1 phase across 0–70 GPa, the F3m phase achieves a lower Helmholtz free energy than that of the Pm1 phase at approximately 1700 K at 40 GPa, this suggests that with the inclusion of other thermodynamic quantities, the F3m phase could potentially become stable.