An international research team has successfully synthesized a ‘forbidden’ compound made of hydrogen and cerium with a chemical formula CeH9 and superconductivity at a relatively low pressure of 1 million atmospheres. Superconductors can conduct an electric current with no resistance. They are a vital component in particle accelerators, MRI scanners, maglev trains, and can enable power lines that supply electricity without losing any kilowatts to thermal dissipation. To synthesize the superconductor, the researchers, belonging to the U.S., China, and Russia, placed a microscopic sample of the metal cerium into a diamond anvil cell, along with a chemical that releases hydrogen upon heating, for which they used a laser. The cerium sample was pressed between two flat diamonds to enable the pressure required for the reaction.
The team employed an X-ray diffraction analysis to detect the positions of the cerium atoms. Through this process, the team also indirectly discovered the structure of the new compound. The CeH9 crystal lattice includes cage-like formations of 29 hydrogen atoms in a near-spherical configuration. The particles in each cage are bound by covalent bonds, similar to the H2 molecule of the hydrogen gas, but comparatively weaker. Each cage creates a cavity that contains one cerium atom. Professor Artem R. Oganov, Skoltech, Moscow Institute of Physics and Technology (MIPT), and the author of the study, explains that the alternative for metalizing hydrogen is synthesizing these forbidden compounds of some element, such as sulfur, uranium, lanthanum, and cerium, with hydrogen.
Even though they had toyed with a formula like CeH2 or CeH3, the newly synthesized cerium superhydride’s CeH9 is equipped with considerably more hydrogen, which adds new properties to the compound, adds Professor Oganov. With USPEX and other computer algorithms being able to predict the crystal structure of ‘forbidden’ compounds has allowed the researchers to study the single-metal hydrides in minute detail. In the next step, researchers are contemplating adding a third element to the mix, and because the possibilities are vast, researchers might use AI algorithms to select the most promising candidates.