New generation of superconductors use high entropy alloys

In a recent Science Daily article, Japanese researchers presented the first of a new generation of superconductors. These highly-conductive materials incorporate a high-entropy alloy made from not just one or two or even three, but five separate rare earth metals (REMs).

The researchers combined layers of bismuth sulfide (BiS₂) superconductor with high-entropy REM alloy oxyfluoride. This allows the dimensions of the crystals that make up the structure of the new superconductor to vary more widely while still retaining the ability to conduct electricity with zero electrical resistance.

The results of the Tokyo Metropolitan University (TMU) study offer a new way to create layered superconductors. This, in turn, may lead to the development of high-temperature superconductors that can retain their properties at room temperature.

Superconductors are better than normal conductors in most ways. For one thing, they have no electrical resistance. No electrons are lost during the transfer, which translates to very efficient transmission of electricity and strong electromagnets.

The primary weakness of superconductors is that they require extremely cold temperatures. As the temperature goes up, the dimensions of the superconductor’s crystal lattices start changing. This disrupts their superconducting properties.

None of the known superconductors can operate at ambient temperatures. A significant amount of time and effort has been directed at ways to overcome this problem. (Related: MIT researchers working on a nuclear fusion superconductor that will generate carbon-free limitless energy within 15 years.)

High-entropy rare earth alloys can shield superconductors from destabilizing heat

One of the better ideas to improve their performance is layered superconductor material. Each layer would be the thickness of a molecule. Superconducting layers would alternate with “blocking layers” that serve to insulate them against temperature changes.

Yoshikazu Mizuguchi, a professor from the TMU’s Department of Physics who led the research effort, explained that his team came across a significant development for the insulating layer. They combined different proportions of five rare earth metals (cerium, lanthanum, neodymium, praseodymium, and samarium) to create a “high-entropy alloy.”

High-entropy alloys are substances made from at least five different metals. Their ductility, resistance to fatigue, and toughness drew the attention of superconductor researchers during the 2010s.

The new rare earth alloy was added to the blocking layers that sandwich the BiS₂ superconductor layers. The researchers then tested the performance of the resulting layered superconductor material in various temperatures.

Layered superconductors can maintain their properties at higher temperatures

The TMU research team reported that the new layered materials were even better at superconducting than usual. In addition, materials with the same periodic configuration of electrons were able to perform superconducting transition at higher temperatures, although none still approached room temperature.

It so happens that the five rare earth metals used for the high-entropy alloy occupy the same periodic group, being elements number 51 to 60 and 62. (Element number 61, promethium, was skipped because it is radioactive and thus very rare in nature.)

That means the rare earth metals have the same energy levels, with electrons occupying the same orbits, the periodic configuration mentioned earlier.

Mizuguchi’s team attributed these improvements to the high-entropy alloy in the blocking layer. They believe the alloy is stabilizing the crystal structure of the superconducting BiS₂ layer. This effect allows the superconductor to maintain its resistance-free qualities even though its crystals are changing size due to the increasing temperature.

Rare earth oxides are not just compatible with bismuth sulfide, a common compound that can be turned into a superconductor at very low temperatures. They will work with many other types of materials, which may lead to a true high-temperature superconductor.

You can read more stories about the newest inventions at Invention.news.

Sources include:

ScienceDaily.com

IOPScience.IOP.org

PTable.com