Superconductivity up to 243 K in the yttrium-hydrogen system under high pressure

The discovery of superconducting H₃S with a critical temperature Tₐ~200 K opened a door to room temperature superconductivity and stimulated further extensive studies of hydrogen-rich compounds stabilized by high pressure. Here, we report a comprehensive study of the yttrium-hydrogen system with the highest predicted Tₐ's among binary compounds and discuss the contradictions between different theoretical calculations and experimental data. We synthesized yttrium hydrides with the compositions of YH₃, YH₄, YH₆ and YH₈ in a diamond anvil cell and studied their crystal structures, electrical and magnetic transport properties, and isotopic effects. We found superconductivity in the Im-3m YH₆ and P6₃/mmc YH₈ phases with maximal Tₐ of ~220 K at 183 GPa and ~243 K at 201 GPa, respectively. Fm-3m YH₁₀ with the highest predicted Tₐ > 300 K was not observed in our experiments, and instead, YH₈ was found to be the hydrogen-richest yttrium hydride in the studied pressure and temperature range up to record 410 GPa and 2250 K.

Panpan Kong, Vasily S. Minkov, Mikhail A. Kuzovnikov, Alexander P. Drozdov, Stanislav P. Besedin, Shirin Mozaffari, Luis Balicas, Fedor Fedorovich Balakirev, Vitali B. Prakapenka, Stella Chariton, Dmitry A. Knyazev, Eran Greenberg, Mikhail I. Eremets