Pressure induced superconductivity in ternary yttrium borohydride system

Abstract

Driven by the excitement of the high temperature superconductivity in hydrides, we systematically investigated the structures, electronic properties, and superconductivity of ternary Y-B-H compounds by first-principles calculations combined with genetic algorithm for structure search. Five stable phases (YBH, YBH2, YBH10, YB2H6 and YB2H10) were predicted at a specified pressure. Several structure building units such as boron ring, folded boron chain, BH4 tetrahedron, and dumbbell shaped B2H6 are observed in these stable phases. The metallic phase C2-YB2H6 with dumbbell shaped B2H6 units is found to be dynamically stable at 50 GPa, and thermodynamically stable at 100 GPa. Compared to binary B-H superconducting system, the addition of rare earth element Y significantly reduces the stabilization pressure for the ternary phases. Electronic phonon coupling calculation showed that C2-YB2H6 and the metastable YBH5 (P3m1 and F-43m) and YB2H12 (P1) phases with tetrahedral BH4 units are superconductors at pressure of 50 GPa. Among them, the F-43m-YBH5 exhibits strong electron-phonon coupling which drives the superconducting Tc up to ~50 K at 50 GPa. Our work provides useful guidance for expanding the directions in searching for conventional superconductors under lower pressures.