Oral
Synthesis and High-pressure Chemistry of Novel Thorium Polyhydrides: ThH4, ThH6, ThH9 and ThH10. A route to room-temperature superconductivity. | Authors: Dmitrii Semenok (SKOLTECH - Skolkovo Institute of Science and Technology) ; Aleksandr Kvashnin (SKOLTECH - Skolkovo Institute of Science and Technology) ; Ivan Troyan (SHUBNIKOV INSTITUTE OF CRYSTALLOGRAPHY RAS - Shubnikov Institute of Crystallography, Federal Research Center Crystallography and Photonics, Russian Academy of Sciences) ; Anna Ivanova (SHUBNIKOV INSTITUTE OF CRYSTALLOGRAPHY RAS - Shubnikov Institute of Crystallography, Federal Research Center Crystallography and Photonics, Russian Academy of Sciences) ; Artem Oganov (SKOLTECH - Skolkovo Institute of Science and Technology) |
Abstract: We have performed targeted high-pressure synthesis of the most promising potential superconductors, thorium nonahydride P63/mmc-ThH9 and thorium decahydride Fm3m-ThH10 with calculated TC up to 241 K, upper critical magnetic fields μ0HC(0) of 71 T SC gap ~ 52 meV [1, 2]. The synthetic conditions (150-170 GPa, ~1800 K) and the stability range (85-186 GPa) of ThH10 are the mildest among all known metal decahydrides predicted or synthesized until now [2]. New high-temperature superconductor P63/mmc-ThH9 was synthesized from lower hydrides at 2100 K by multistage laser heating. This hydride is isostructural to previously reported CeH9 [3], UH9 [4], and predicted YH9 [5] and ScH9 [6], while Fm3m-ThH10 adopts the same crystal structure as recently synthesized near room-temperature superconductor LaH10 and predicted YH10 [5]. Reaction 2/5 ThH9 + 3/5 ThH4 → ThH6 was found to be responsible for instability of ThH9 below 105 GPa. Two other recently predicted Th-H compounds were also synthesized and identified, namely I4/mmm-ThH4 (> 86 GPa) and Cmc21-ThH6 (86-104 GPa). We observed multiple pressure-driven phase transition in ThH4 (P321 → I4/mmm → Fmmm) and ThH10 (Fm3m → Immm). Equations of state of the obtained higher thorium hydrides were measured and found to perfectly agree with theoretical calculations. Electronic and phonon properties of new phases were examined including experimental confirmation of high-temperature superconductivity in Fm3m-ThH10.
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[2] D. Semenok et al. “Synthesis of ThH4 , ThH6 , ThH9 and ThH10 : a route to room-temperature superconductivity”, RG preprint 2019 (doi 10.13140/RG.2.2.31274.88003); https://arxiv.org/abs/1902.10206
[3] N. Salke et al. “Synthesis of clathrate cerium superhydride CeH9 at 80 GPa with anomalously short H-H distance”, arXiv:1805.02060 https://arxiv.org/ftp/arxiv/papers/1805/1805.02060.pdf (2018).
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[6] K. Abe “Hydrogen-rich scandium compounds at high pressures”, Phys. Rev. B 96, 144108 (2017).
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