Superconductivity at 253 K in lanthanum–yttrium ternary hydrides

Polyhydrides offer intriguing perspectives as high-temperature superconductors. Here we report the high-pressure synthesis of a series lanthanum-yttrium ternary hydrides: cubic hexahydride $(La,Y)H_{6}$ with critical temperature $T_{C}$ = 237 +/- 5 K and decahydrides $(La,Y)H_{10}$ maximum ~${253 K}$ an extrapolated upper magnetic field $B_{C2(0)}$ up to ${135 T}$ at 183 GPa. This is one first examples high-$T_{C}$ superconducting hydrides. Our experiments show that part atoms in structures recently discovered ${Im3m}$-$YH_{6}$ ${Fm3m}$-$LaH_{10}$ can be replaced lanthanum (~70 %) yttrium (~25 %), respectively, formation unique superhydrides containing incorporated $La@H_{24}$ $Y@H_{32}$ which are specific for ${Im3m}$-$LaH_{6}$ ${Fm3m}$-$YH_{10}$. Ternary La-Y hydrides were obtained pressures 170-196 GPa via laser heating $P6_{3}$${/mmc}$ alloys ammonia borane medium temperatures above 2000 K. A novel tetragonal $(La,Y)H_{4}$ was impurity phase synthesized $(La,Y)H_{6}$. The current-voltage measurements current density $J_{C}$ may exceed $2500 A/mm^{2}$ 4.2 K, comparable commercial wires such ${NbTi}$, $Nb_{3}$${Sn}$. Hydrides unstable pure form nevertheless stabilized relatively low solid solutions having same structure.