Bayreuth Researchers Have Discovered New Yttrium-Hydrogen Compounds

Researchers at the University of Bayreuth have made a significant scientific breakthrough by discovering new yttrium-hydrogen compounds having serious implications for the research on high-pressure superconductivity. High-pressure superconductivity refers to the property of materials to become superconducting, which means conducting electrical current without resistance, when exposed to certain pressure conditions. The comprehensive high-pressure study of the Bayreuth Researchers shedding light on the complex nature of yttrium hydrides under extreme conditions was published in “Science Advances” journal.

What for?
The results of research at the Bavarian Research Institute of Experimental Geochemistry and Geophysics (BGI) at the University of Bayreuth have an impact on various areas: The discovery of new yttrium-hydrogen compounds and the comprehensive high-pressure study provide an insight into the complex nature of these materials under extreme conditions. This contributes to the further development of our understanding of material behaviour at high pressure. Several rare-earth superhydrides could also lead to a revolution in energy transmission and storage. Identifying new yttrium hydrides and understanding their structure and composition under extreme conditions could drive the development of high-temperature superconductors. Overall, these results have the potential to deepen our understanding of materials under extreme conditions and drive the development of technologies that can benefit from new superconducting materials.

Several rare-earth superhydrides are known for being reported to be near-room-temperature superconductors at high pressures. Superconducting materials allow current to flow without any resistance. In most cases they are products of chemical reactions realized in diamond anvil cells at extreme pressures and temperatures. Their phase and chemical compositions are often unknown, making claims of superconductivity not quite justified, as the measurable critical temperature TC (the temperature below which the material’ electrical resistivity drops to zero) depends on many factors, including the phase purity of the sample and hydrogen content in hydrides. Therefore, the existence of near-room temperature high-pressure superconductors is still under scrutiny.

The use of the modern method of so-called synchrotron single-crystal X-ray diffraction from multiphase microcrystalline samples, developed in the group of Prof. Natalia Dubrovinskaia and Prof. Leonid Dubrovinsky at the University of Bayreuth, enabled unravelling the chemical complexity and richness of the yttrium-hydrogen system under high-pressure high-temperature conditions. At pressures up to about 170 GPa, PhD student Alena Aslandukova and co-authors identified five novel yttrium hydrides with unique structures. These compounds were synthesized in diamond anvil cells through the laser heating of Y-H samples (yttrium with hydrogen-rich ammonia borane or paraffin oil) up to 3500 K.

Single-crystal X-ray diffraction provides valuable insight into the arrangement of yttrium atoms in the crystal structures of these newly discovered phases. Hydrogen content was estimated using empirical relations and ab initio calculations that revealed the specific composition for each compound pointing towards the richness of the Y-H system and diversity of yttrium hydrides under high-pressure conditions.

“The study emphasises the complexity of the yttrium-hydrogen system and its multiphase character at high pressure,” explains Alena Aslandukova. “The results make a significant contribution to our understanding of materials behaviour at extreme conditions and the nature of potentially superconducting hydrides.”