“Improved Substance Aids in Quest for Superconductivity at Room Temperature”

Scientists from Jilin University, Advanced Research Center for High-pressure Science and Technology, and Skoltech have synthesized lanthanum-cerium polyhydride, a material that promises to facilitate studies of near room temperature superconductivity. It provides a middle ground between the polyhydrides of lanthanum and cerium in terms of the amount of cooling and pressure it requires. This allows for easier experiments, which may one day lead scientists to vehicles that conduct electricity without resistance in ambient conditions — an engineering dream many years in the making. The study has been published in Nature Communications.

One of the most interesting unresolved questions in modern physics is: can we make a material that conducts electricity without resistance (superconductors) at room temperature and atmospheric pressure? Such a superconductor would enable power grids with unprecedented efficiency, ultrafast microchips, and electromagnets so powerful they can lift trains or control fusion reactors.

In their research, scientists sift through multiple classes of materials, slowly raising the temperature they recommend ultra-high and decreasing the pressure they need to remain stable. One of these groups of substances is polyhydrides – compounds with a very high hydrogen content. At -23 ° C, the current champion of high-temperature superconductivity is lanthanum polyhydride with the formula LaH₁₀. The trade-off: It requires 1.5 million atmospheres of pressure. At the opposite end of the spectrum, coppers are a class of materials that are superconductive at normal atmospheric pressure but require much cooler temperatures—no higher than 140 degrees.

Now, Skoltech researchers and their Chinese colleagues have been able to ease the pressure requirements for polyhydride superconductors. To do this, the team modified the lanthanum-hydrogen system by adding some cerium to the mix. Physically, this meant making an alloy of lanthanum and cerium and heating it in a high-pressure cell with ammonia-borane, a substance that releases a lot of hydrogen as it decomposes.

Lanthanum and cerium are two very similar atoms that form similar compounds and can often be substituted for each other. However, while the superconductivity of LaH₁₀ and CeH₁₀as well as CeH₉and the corresponding LaH₉ Experimenters rarely see the stage. The scientists decided to test the hypothesis: it should be possible to stabilize LaH₉ By supplementing it with an appropriately selected additive, such as cerium, provided that this alters the structure of the original substance. And it worked.

Very high pressure forces pure lanthanum and hydrogen into LaH₁₀ building. But if you replace 1 in 4 lanthanum atoms with cerium, this rearranges the structure into the arrangement seen in CeH₉. In this sense, the introduction of the third element alters the structure that would otherwise be assumed by pure matter. And this additive contributes to stability: compared to the 1.5 million atmospheres you need for LaH₁₀Our lanthanum and cerium polyhydrides are stable at only 1 million atmospheres. This is the same pressure required by cerium polyhydride, however that superconductivity only appears below -158°C, while the new superconductor operates at -97°C. So it’s a good compromise, but more importantly, it’s reassuring that our reasoning is correct,” comments Professor Artem R. Oganov of Skoltech, co-author of the study.

Working in a field not so long ago that many suspected that so-called conventional superconductors – such as those found in polyhydrides – could exist at temperatures above -230 degrees Celsius or so, Oganov attaches particular importance to testing the rules that They make it possible to discover and improve superconductors in a reliable and systematic way. So, although he believes that polyhydrides in general will never be synthesized into superconductivity at atmospheric pressure (a necessary condition for large-scale applications such as magnetic trains or lossless power grids), he says their study provides insight into superconductivity. That requires we come closer to achieving this ultimate goal by using other materials.

“The Eldorado polyhydride is essential for superconducting research under pressure,” says Oganov. “By synthesizing our new compound, we tested and refined the tools and tricks useful in this endeavor and provided suitable material for further studies.”

“The work is also interesting for two main experiments: it demonstrates the potential anisotropy of the upper critical field of hydrides. That is, the dependence of the critical temperature on the direction of the magnetic field. It also shows that with decreasing pressure, a pseudophase manifests itself in polyhydrides,” study co-author and Ph.D. Skoltech. said graduate student Dmitry Semenok, adding that both properties are characteristic of copper superconductors. “Thus, upon closer examination, it becomes clear that the polyhydrides are very similar to the coppers despite the different mechanisms of superconductivity.”

When asked about other promising compounds that current polyhydride research leads to, the researchers replied that the hydrides and borohydrides of calcium, yttrium, lanthanum, and magnesium seem to deserve research attention at this point.