Researchers forge ‘impossible’ superconductor using ‘forbidden’ compound

1 Oct 2019

Image: © michelmond/

An international team of researchers has bent the rules of chemistry to create a ‘forbidden’ compound with unprecedented superconductivity.

The race is on to forge a superconductor that can transfer electricity from one place to another without the loss of precious kilowatts, while at room temperature. So far, today’s superconductors are limited to working at temperatures close to absolute zero or at extremely high atmospheric pressure, making them totally unfeasible for mass adoption.

However, a team of researchers from the US, Russia and China has announced the creation of a “forbidden” compound that exhibits superconductivity at a relatively low pressure of 1m atmospheres.

Writing in Nature Communications, the team said this rule-breaking compound comprises cerium and hydrogen (CeH9). While theories have shown hydrogen to be a potential candidate for room-temperature superconductivity, coaxing it into such a state would require tremendous pressure of approximately 5m atmospheres, at which point it would then turn into a metal. For comparison, the centre of the Earth experiences pressure of nearly 3.6m atmospheres.

Contains ‘exciting’ properties

The alternative to metallizing hydrogen is the synthesis of so-called forbidden compounds of an element – such as sulphur, uranium and cerium – and hydrogen, with more atoms of the latter than classical chemistry allows, the team said.

“Normally, we might talk about a substance with a formula like CeH2 or CeH3,” said Prof Artem R Oganov of Skoltech and the Moscow Institute of Physics and Technology, one of the authors of the study.

“But our cerium superhydride – CeH9 – packs considerably more hydrogen, endowing it with exciting properties.”

To forge the superconductor, the team placed a microscopic sample of the metal cerium into a diamond anvil cell, along with a chemical that releases hydrogen when heated with a laser. This sample was then squeezed between two flat diamonds to create immense pressures, resulting in larger amounts of hydrogen being formed.

The team then used x-ray diffraction analysis to discern the positions of the cerium atoms and thus indirectly reveal the structure of the new compound.

While limited in a sense due to the compound still requiring temperatures of minus 200 degrees Celsius to function, only needing 1m atmospheres to remain stable is less than what the previously synthesised sulphur and lanthanum superhydrides require.

Colm Gorey was a senior journalist with Silicon Republic