Pressure-induced superconducting ternary hydride H3SXe： A theoretical investigation

In general, heavy elements contribute only to the superconductivity of hydrides. However, it acoustic phonon modes, which are less important for was revealed that the heavier elements could enhance the phonon-mediated superconductivity in ternary hydrides. In the H3S-Xe system, a novel H3SXe compound was discovered by first-principle calculations. The structural phase transitions of H3SXe under high pressures were studied. The R-3m phase of H3SXe was predicted to appear at pressures above 80 GPa, which transitions to C2/m, P-3m1, and Pm-3m phases at pressures of 90, 160, and 220 GPa, respectively. It has been anticipated that the Pm-3m-H3SXe phase with a similar structural feature as that of Im-3m-H3S is a potential high-temperature superconductor with a Tc of 89 K at 240 GPa. The Tc value of H3SXe is lower than that of H3S at high pressure. The ＂H3S＂ host lattice of Pm- 3m-H3SXe is a crucial factor influencing the Tc value. The Xe atoms could accelerate the hydrogen-bond symmetrization. With the increase of the atomic number, the Tc value linearly increases in the H3S- noble-gas-element system. This indicates that the superconductivity can be modulated by changing the relative atomic mass of the noble-gas element.

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.

Mild-condition synthesis of A2ZnH4(A = K, Rb, Cs) and their effects on the hydrogen storage properties of 2LiH-Mg(NH2)2

In this paper, A2ZnH4(A = K, Rb and Cs) have been synthesized for the first time by a new approach involving in two-step reactions, in which the target samples can be produced under mild conditions(160 ℃ for 4 h). What’s more, the additive effects of A2ZnH4 on the hydrogen storage properties of 2LiH-Mg(NH2)2 composite have been investigated systematically. Experimental results show that K2ZnH4 has the best comprehensive modification effects among these hydrides. The 2LiH-Mg(NH2)2-0.1 K2ZnH4 sample shifts dehydrogenation peak temperature downwards by ca. 30 ℃ as compared to the pristine sample. In addition, about 70% extent of the theoretical hydrogen is able to desorb from the 0.1 K2ZnH4 doped sample at 140 ℃ within 2 h, however, only 20% extent of hydrogen is liberated from the pure sample under the same conditions. The improved desorption kinetics is indicated by the reduced dehydrogenation activation energy(Ea), the Ea of the 0.1 K2ZnH4 doped sample is around 68 ± 1.0 kJ mol-1 which is 28% lower than that of the pristine one. Furthermore, the dehydrogenation mechanism of the K2ZnH4 doped sample has been proposed.