Superconductivity at 253 K in lanthanum–yttrium ternary hydrides

Abstract: Here we report the high-pressure synthesis of a series of lanthanum–yttrium ternary hydrides obtained at pressures of 170–196 GPa via the laser heating of P63/mmc La–Y alloys with ammonia borane. As a result, we discovered several novel compounds: cubic hexahydride (La,Y)H6 and decahydrides (La,Y)H10 with a maximum critical temperature TC?∼?253?K and an extrapolated upper critical magnetic field BC2(0) of up to 135?T at 183 GPa. The current–voltage measurements show that the critical current density JC in (La,Y)H10 is 12–27.7 kA/mm2 at 4.2?K, which is comparable with that of commercial superconducting wires such as NbTi and Nb3Sn. (La,Y)H6 and (La,Y)H10 are among the first examples of ternary high-TC superconducting hydrides. Our experiments show that part of metal atoms in the structures of recently discovered Im3¯m-YH6 and Fm3¯m-LaH10 can be replaced with lanthanum (∼70%) and yttrium (∼25%), respectively, with the formation of unique ternary superhydrides containing metal-encapsulated cages La@H24 and Y@H32, which are specific for Im3¯m-LaH6 and Fm3¯m-YH10. This work demonstrates that hydrides, unstable in pure form such as LaH6 and YH10, may nevertheless be stabilized at relatively low pressures in solid solutions with superhydrides having the desired structure.