Substitution of Y, Ce, and Th for La in LaBeH8 as a path towards lower synthesis pressures of superconducting hydrides

Abstract

Recent theory-guided discoveries of hydrides exhibiting high superconducting temperatures (Tc) exceeding 200 K above 150 GPa have sparked the enthusiasm for the pursuit of room-temperature ambient-pressure superconductors. While efforts to increase the Tc's of these hydrides are underway, optimizing the demanding high-pressure synthesis conditions remains a challenge. Several studies suggested that a multielemental alloying strategy could be a feasible approach to tackle this formidable task. Here, we present an example using LaBeH8 to establish several alloy hydrides via the substitution of La atoms with similar metal atoms, such as Y, Ce, and Th. Quasiquaternary alloy hydride (La,Y,Ce,Th)BeH8 is computed to become thermodynamically stable at 70 GPa and a typically realistic temperature of ∼2000 K for synthesizing high-Tc hydrides, compared with the calculated results showing thermodynamic instability above 300 GPa without considering entropy. Our in-depth analysis revealed that not only does entropy play a crucial role in stabilizing alloy hydrides at moderate pressures and high temperatures, but also the energy contribution from vibrational entropy is much more significant than configurational entropy, where configurational entropy has long been believed to play a key role in the stability of multielemental alloy. Furthermore, extensive electron-phonon simulations indicate that the estimated Tc of (La,Y,Ce,Th)BeH8 could reach near ∼100 K at 70 GPa. The present work offers a fresh perspective on the design and realization of high-Tc multielemental alloy hydrides towards near-ambient pressure.

Source-reported materials — not catalogue approval

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