Leap forward in superconductivity achieved

A new material that could be used as a superconductor and for hydrogen-fuel cell storage has been created by US scientists.

The research published in Nature Communications, details how scientists have managed to force hydrogen into a metallic state. Scientists are interested in creating metallic hydrogen as it will allow superconductors to be used at higher temperatures – currently they only work at temperatures lower than -210°C.

Victor Struzhin, from The Carnegie Institution for Science in Washington D.C. who led the research, said: “The challenge is temperature. The only superconductors that have been produced can only exist at impractically cold temperatures. In recent years, there have been predictions of compounds with several atoms of hydrogen coupled with alkali metals that could exist at more practical temperatures. They are theorised to have unique properties useful to superconductivity.”

Lithium and sodium samples were compressed in a diamond anvil cell while being heated by a laser. At pressures between 30-40 gigapascals and temperatures of 1704°C, structures of polyhydrides, sodium with three hydrogen atoms (NaH₃) and sodium with seven hydrogen atoms (NaH₇) in unusual configuration were seen for the first time.

Duck Young Kim, also from Carnegie and involved in the research, said: “This configuration was originally predicted to exist in 1972, more than 40 years ago. It turns out that our experiments are in complete agreement with the theory, which predicted the existence of NaH₃. The bonus is that we also observed the compound with seven hydrogen atoms.”

The team used X-ray diffraction and Raman spectroscopy to ascertain the structure of the samples. The sodium/hydrogen material should be stable under pressure while exhibiting metallic characteristics and displaying superconducting properties, predict scientists.