Bayreuth researchers have discovered new yttrium-hydrogen compounds

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 T_C (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.”