- Researchers spotted 14 new uranium hydrides that have superconducting properties.
- UH7 is the highest-temperature superconductor that shows superconducting features at -219° C.
- The temperature can be raised to even more levels via doping.
Uranium is a radioactive element. It has an unstable nucleus, with half-lives varying between 4.5 billion years and 159,200 years. In fact, it was the Uranium that made the discovery of radioactivity possible. Since the element is unstable, it spontaneously reacts with water and ignites in the air.
Its most common isotopes are Uranium-235 (has 143 neutrons) and Uranium-238 (has 146 neutrons and accounts for more than 99 percent). 7 kilograms of Uranium is sufficient to create an atomic bomb. Some of you might know the first nuclear bomb (nicknamed Little Boy) used in war used Uranium fission.
Uranium reacts well with hydrogen. For now, UH3 is the only known compound that is stable at ambient surroundings, though evidence of other uranium hydrides (isolated molecules of U2H4, U2H2, UH4, UH3, UH2, and UH) has also been spotted.
Recently, researches at Moscow Institute of Physics and Technology predicted new compound of uranium and their relationship with superconductivity. They mentioned fourteen new uranium hydrides (including UH3, UH7, UH8) that have superconducting properties.
To prove this via experiments, they collaborated with the Chinese Academy of Sciences and US Carnegie Institution of Washington, where they identified these hydrides by matching theoretically derived and experimental XRD patterns and equations of state.
Superconducting Capabilities of Uranium Hydride
Superconductivity is a phenomenon of complete absence of electrical resistance and expulsion of magnetic flux fields in a material when its temperature is dropped to a certain limit. Initially, the phenomenon was discovered in several base metals, including mercury and aluminum, at temperatures slightly higher than -273° C (absolute zero).
The so-called notion ‘high-temperature superconductor’ also exist, which represents the conductivity at extremely low temperatures. At present, the highest known superconductors function at -183° C. They are extensively used in electric equipment, and for better performance, they require to be continuously cooled.
A couple of years ago, a team of researchers set a new record with sulfur hydride (H3S) high-temperature superconductor. At nearly 1.5 million atmospheric pressure, they achieved superconductivity of -70° C.
After discovering H3C, researchers all over the world stared studying superconducting hydrides in other elements, including non-metals like phosphorus and selenium.
In this study, authors carried out experiments with uranium hydrides and found that UH7 is the highest-temperature superconductor that shows superconducting features at -219° C. The measurements suggest that the temperature can be raised to even more levels via doping.
Crystal structures of predicted phases | Courtesy of researchers
Now you can say that both metal hydrides and non-metals hold the same potential for high-temperature superconductivity. The study underlines the two important factors:
- To generate a rich set of hydrides, you need to use extremely high pressures, which is not common in conventional chemistry.
- It’s possible to sustain superconducting capabilities of these hydrides at very low pressures.
Overall, the work demonstrates the prediction ability of advanced techniques of crystal structure prediction capable of discovering unique compounds with exotic properties.