Complex hydrogen substructure in semimetallic ruthenium tetrahydride - Drs. Ross Howie, Philip Dalladay-Simpson and Duckyoung Kim
APRIL 26, 2020
The search for polyhydride materials at high pressure has produced numerous predictions focused almost entirely on metallic superconductors. Intriguingly, a series of independent studies have postulated the anomalous emergence of semiconducting and semimetallic polyhydrides unique to the group 8 metals Fe, Ru, Os. Despite extensive study these materials have remained entirely hypothetical to date. A new study, comprised primarily of HPSTAR researchers, report on the discovery and properties of two novel ruthenium polyhydride materials – Ru3H8 and RuH4. This study is published inthe Journal of Physical Chemistry Letters (https://doi.org/10.1021/acs.jpclett.0c00688).
Through the combined application of x-ray diffraction, in situ laser heating, and density functional theory calculations the team explore the synthesis and properties of ruthenium polyhydrides. Conditions of 1000 K and 50 GPa lead to the synthesis of Ru3H8 adopting a simple cubic structure containing H8 units. Our analysis suggests that the formation of these cubic hydrogen units allows for the adoption of an efficient fcc packing.
Applying similar heating conditions at 85 GPa, the synthesis of RuH4 is reported, which adopts a remarkable low-symmetry structure, previously predicted to form in the Fe- H system at more than double the pressure. Calculations indicate that RuH4 is semimetallic and the apparently chaotic structure can be rationalized by observing the layers of corner-sharing H6 octahedra.
Neither of the structures observed have been previously predicted to occur in the Ru-H system – demonstrating the importance of experimental observation in a field extensively driven by structure-prediction methods.
“Our study has experimentally confirmed the existence of nonmetallic polyhydride species in the group 8 metals at high pressures,” said Dr Ross Howie, who led the study, “The underlying mechanism and origin of this anomalous trend remains an intriguing unanswered question.”
Caption: RuH4 synthesized at 85 GPa and 1000 K with its structure containing corner-sharing H6 octahedra and semimetal property comparing to RuH.
富氢化合物由于其潜在的高温超导及其储氢方面的应用是而成为近年来凝聚态物理研究的焦点。近期北京高压科学研究中心的Ross Howie研究员带领的团队首次在高温高压条件下合成了VIII族金属Ru的两种新型富氢化合物Ru3H8，RuH4。他们进一步的理论计算表明Ru3H8具有金属性而RuH4具有半金属性。他们的研究指出增加氢含量及其压力或许是实现高温超导的错误指引。相关研究以“Complex Hydrogen Substructure in Semimetallic RuH4”为题发表于JPCL。