In their study, published in the Proceedings of the National Academy of Sciences,
a group of researchers used inelastic neutron scattering as a local probe of the hydrogen interactions of ZrV2Hx
, a well-studied and prototypical metal hydride. Together with electronic structure modelling, their results provide evidence for hydrogen–hydrogen distances as short as 1.64 Å
In conventional transition metal hydrides containing atomic hydrogen, the minimum hydrogen–hydrogen distances are around 2.1 Å at ambient conditions, although then can get closer at higher pressures. Achieving closer hydrogen-hydrogen distances could lead to a new generation of materials that could store much hydrogen for hydrogen fuel cells for automobiles, for example.
Another application is creating new superconductors based on the near-room temperature lanthanum hydride superconductor discovered by the group of Professor Russell J. Hemley, of the University of Illinois at Chicago, one of the authors of the new study.
"Lanthanum hydride superconducts up to record high temperatures of 260 K, but at close to 2 million times atmospheric pressure, or equivalent to the pressures found in the outer core of the Earth," said Professor Hemley.
Superconductors carry electricity without any energy loss due to resistance. Superconductors that could operate at, or near, room temperature would revolutionize energy efficiency in a broad range of consumer and industrial applications. The smaller spacing between hydrogen atoms, as shown in this study, might enable the packing of significantly more hydrogen into the material, to the point where it begins to superconduct.
Although hints of H–H distances below 2.1 Å in some alloys have been reported, evidence is inconclusive as hydrogen positions are difficult to locate by diffraction techniques. This is where Inelastic Neutron Scattering (INS) came in. Preliminary INS spectra were measured on the TOSCA and MARI beamlines at ISIS, followed by high-resolution measurements at BL16-B (VISION) at the SNS, based at Oak Ridge National Laboratory.
The study illustrates the utility and importance of INS as a probe of the structures of hydrogen-rich materials with potentially novel properties. "For decades, the 'holy grail' for scientists has been to find or make a material that superconducts at room temperature and atmospheric pressure, which would allow engineers to design it into conventional electrical systems and devices," explains Professor Hemley; “We're hopeful that an inexpensive, stable metal like zirconium vanadium hydride can be tailored to provide just such a superconducting material."
The full paper can be found online at: https://www.pnas.org/content/117/8/4021