High-pressure synthesis of a ternary yttrium-sulfur hydride superconductor with a high T_(c) of approximately 235 K

Ternary hydrides have attracted considerable worldwide attention owing to their potential high-temperature superconducting phases.In contrast to previously reported alloy-based ternary hydrides,we selected the rare earth metal yttrium and light element sulfur to form new yttrium-sulfur hydride superconductors as the target at high pressure,which also linked the two categories of binary clathrate YH_(6) and covalent H_(3)S high-temperature superconductors.The rare earth metal ions served as carrier donors for the dissociation of H_(2) molecules and the formation of clathrate-like cage structures,while the light elements helped stabilize the materials.By applying high-pre ssure and high-temperature conditions,two possible ternary hydride s,i.e.,Im3m-(Y,S)H_(6+δ) and I4/mmm-(Y,S)H_(4+δ),were discovered.Im3m-(Y,S)H_(6+δ) is a ternary hydride with a record superconducting transition temperature(T_(c)) of 235 K belonging to the single-metal hydride system,exhibiting an 11% increment in T_(c) compared with binary Im3m-YH_(6).In the pressure range of 199-249 GPa,the T_(c) of this phase displayed a decreasing tendency but with an apparent slope change,indicating the possible structural distortions or electronic structure changes at 227 GPa.Concurrently,the extrapolated upper critical magnetic field H_(c2) was determined to be 85 T using the Werthamer-Helfand-Hohenberg formula at199 GPa,with a 37% increment compared with Im3m-YH6.The slight volume expansion(~3 %) of Im3m-(Y,S)H_(6+δ) compared with that of binary Im3m-YH_(6) signified the possible interstitial sites of sulfur atoms filling into the hydrogen cages.The size expansion of the center atoms might attract more hydrogen atoms to stabilize the hydrogen cages,contributing to the enhancement of T_(c) and H_(c2) in Im3m-(Y,S)H_(6+δ).The present study demonstrates that introduction of light elements is an effective way for enhancing T_(c) by forming larger hydrogen cages.