Sr‐Doped Superionic Hydrogen Glass: Synthesis and Properties of SrH₂₂

Abstract

experimental metallization limit moving step by step from 150 [4] to 430-500 GPa. [1,5] A consistent increase in pressure leads to a series of phase transitions in solid hydrogen (phases Ι-V [1,5] ), gradual quenching of the Raman signals, and darkening of the sample down to a complete loss of transparency. Despite a significant progress in achieving ultrahigh pressures in the last five years, detecting superconductivity of metallic hydrogen remains an unsolved problem. Studies of the electrical conductivity at pressures above 400 GPa remain very challenging.In 2004, N. Ashcroft suggested that the precompression effects caused by chemical bonding to other atoms may help to convert hydrogen to a metallic state. Fifteen years later, this idea was confirmed in the synthesis of many metallic and superconducting hydrides such as H 3 S, [6,7] LaH 10 , [8,9] YH 6 , [10,11] YH 9 , [11,12] ThH 10 , [13] CeH 9 , [14] PrH 9 , [15] NdH 9 , [16] and so forth. It is believed now that the superconducting properties of these compounds are due to the presence of a sublattice of metallic hydrogen, which is formed in pure hydrogen only at pressures of 500-700 GPa.There must be an intermediate link between these two forms of hydrogen, metallic and superconducting, and a molecular Recently, several research groups announced reaching the point of metallization of hydrogen above 400 GPa. Despite notable progress, detecting superconductivity in compressed hydrogen remains an unsolved problem. Following the mainstream of extensive investigations of compressed metal polyhydrides, here small doping of molecular hydrogen by strontium is demonstrated to lead to a dramatic reduction in the metallization pressure to ≈200 GPa. Studying the high-pressure chemistry of the Sr-H system, the formation of several new phases is observed: C2/m-Sr 3 H 13 , pseudocubic SrH 6 , SrH 9 with cubic F m 43 -Sr sublattice, and pseudo tetragonal superionic P1-SrH 22 , the metal hydride with the highest hydrogen content (96 at%) discovered so far. High diffusion coefficients of hydrogen in the latter phase D H = 0.2-2.1 × 10 −9 m 2 s −1 indicate an amorphous state of the H-sublattice, whereas the strontium sublattice remains solid. Unlike Ca and Y, strontium forms molecular semiconducting polyhydrides, whereas calcium and yttrium polyhydrides are high-T C superconductors with an atomic H sublattice. The discovered SrH 22 , a kind of hydrogen sponge, opens a new class of materials with ultrahigh content of hydrogen.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202200924.

Chemically Assisted Precompression of Hydrogen Molecules in Alkaline-Earth Tetrahydrides

“…After an initial laser heating at 75 GPa, SrH 2 is formed, and after a subsequent heating, SrH 2 transforms to another compound adopting an structure; see Figure S6. We find that the lattice parameters and volumes agree well with those for the recently reported cubic SrH 9 ; see Figure S1 . Upon decompression, we find that SrH 9 does not decompose to at least 30 GPa.…”

“…We find that the lattice parameters and volumes agree well with those for the recently reported cubic SrH 9 ; see Figure S1. 29 Upon decompression, we find that SrH 9 does not decompose to at least 30 GPa.…”

“…27 , 28 Strontium polyhydrides have been reported above 70 GPa with a range of stoichiometries: SrH 22 , SrH 9 , Sr 8 H 46 , SrH 6 , Sr 3 H 13 , and Sr 2 H 3 . 29 Barium polyhydrides have also emerged, with Ba 8 H 46 at 50 GPa 30 and BaH 10 , BaH 6 , BaH 21–23 , and BaH 12 all above 90 GPa. 31 …”

“…27,28 Strontium polyhydrides have been reported above 70 GPa with a range of stoichiometries: SrH 22 , SrH 9 , Sr 8 H 46 , SrH 6 , Sr 3 H 13 , and Sr 2 H 3 . 29 Barium polyhydrides have also emerged, with Ba 8 H 46 at 50 GPa 30 and BaH 10 , BaH 6 , BaH 21−23 , and BaH 12 all above 90 GPa. 31 Here, we synthesize CaH Elemental Ca (99.9%, Alfa Aesar), Sr (99.99%, Sigma-Aldrich), and Ba (99%,Sigma-Aldrich) (or BaH 2 (99.5%, ABCR)) were loaded into diamond anvil cells in an argon atmosphere glovebox and subsequently gas loaded with research grade hydrogen (99.9995%) at 0.2 GPa (see Supporting Information for detailed methods).…”

“…Through a combination of both high temperature and high pressure, interesting compositions were observed in the alkaline-earth-metal–hydrogen system. Superconducting CaH 6 was produced at pressures greater than 160 GPa. , Strontium polyhydrides have been reported above 70 GPa with a range of stoichiometries: SrH 22 , SrH 9 , Sr 8 H 46 , SrH 6 , Sr 3 H 13 , and Sr 2 H 3 . Barium polyhydrides have also emerged, with Ba 8 H 46 at 50 GPa and BaH 10 , BaH 6 , BaH 21–23 , and BaH 12 all above 90 GPa …”