Einstein, Debye, and Fermi Temperatures, Electron‐Phonon Coupling Constant and Parabolic Pressure Dependence of the Transition Temperature in the Y _0.5 Ce _0.5 H ₉ Hydride Superconductor

ABSTRACT Ternary and quaternary hydride superconductors have been the focus of intensive experimental and first‐principles calculations studies in recent years. A primary approach in experimental synthesis of ternary and quaternary hydrides is to substitute La or Ce ions by other rare‐earth elements in LaH 10 and CeH 9 phases, respectively. The choice of CeH 9 as a matrix phase to synthesise ternary and quaternary hydrides is because this phase exhibits transition temperatures above 70 K at a relatively low‐pressure p = 90–130 GPa. One of the synthesized phases by this approach, where cerium is substituted by yttrium, is the ternary P6 3 /mmc ‐Y 0.5 Ce 0.5 H 9 hydride phase. This phase exhibits the onset of superconducting transition temperature T c = 100–140 K in the pressure range of p = 98–155 GPa. Here, based on the analysis of reported experimental data by Chen et al. ( https://doi.org/10.1038/s41467‐024‐46133‐x ), I found that the onset of the superconducting transition temperature in Ce 0.5 Y 0.5 H 9 obeys the parabolic dependence on pressure, T c,onset ( P )/ T c,onset,max = (1–95*( P ‐0.145) 2 ), where T c,max = 140 K, and P is in TPa. The revealed dependence of T c ( P ) is remarkably similar to that of T c ( p ) in cuprates, where p is the doping state. Furthermore, the evolution of the Einstein and Debye temperatures and the electron‐phonon coupling strength with pressure have been derived for the P6 3 /mmc ‐Y 0.5 Ce 0.5 H 9 phase.