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Current flow without resistance? For a long time, this effect only existed in freezing temperatures. Now it also works at room temperature. Applications are still a long way off.
Laboratory to demonstrate the superconductivity of materials.
In superconductors, electrons run freely: charge carriers tirelessly run through the material without being slowed by atomic nuclei as in conventional conductors and without losing energy. These conductors have the potential to revolutionize the energy industry and electrical engineering.
This is why superconductivity has been a hot story since its discovery over a hundred years ago, if not for the cold: resistance-free current flow has only worked reliably in the basement of the temperature scale. , generally well below minus 200 degrees Celsius. However, the cooling technology required for this is not suitable for everyday use. For this reason, scientists have been feverishly searching for decades for materials that allow electrons to move freely even at higher temperatures, ideally room temperature.
Solid compounds of carbon, sulfur and hydrogen
A research group has now apparently found what they were looking for: Ranga Dias from the University of Rochester, USA, and his colleagues report a material that has superconducting properties at 15 degrees Celsius in the trade journal Nature. For their experiment, the scientists used a very fine powder made of carbon and sulfur, as well as hydrogen gas. The laser light split the sulfur compounds and generated free sulfur radicals, which reacted with hydrogen to form hydrogen sulfide. This was eventually transformed with additional carbon and hydrogen under extreme pressure into a transparent solid with superconducting properties.
However, like similar high-temperature superconductor developments in recent years, the featured version has a new problem: Dias and his colleagues had to compress their material samples with an incredible pressure of 267 billion Pascals, roughly a million times higher than the pressure of a typical car tire. Such conditions can only be achieved with great technical effort in a tiny diamond drilling cell, in which two almost indestructible diamond tips are pressed ever closer together with a vise. Daily eligibility is zero.
Search for metallic hydrogen
As early as 1968 it was theoretically predicted that pure hydrogen would turn into a metal under high pressure. In 2017, Dias and Harvard professor Isaac Silvera reported that they had observed this effect for the first time at a pressure of 500 billion Pascals, but there are still serious doubts about this claim. Under such conditions, according to the theory, the hydrogen molecules dissolve and the individual hydrogen atoms organize themselves in a rigid three-dimensional network and thus form a solid body. Through this, the electrons can move undisturbed.
The same appears to be true for certain hydrogen compounds with other elements, but at slightly lower pressures. For this reason, scientists have begun testing the superconducting potential of such gaseous hydrogen compounds. Researchers led by Mikhail Eremets from the Max Planck Institute for Chemistry in Mainz were successful for the first time in 2015: their hydrogen sulfide (sulfur hydride) compound exhibited superconducting properties at a pressure of around 150 billion Pascals and a temperature minus 70 degrees Celsius.
“These binary materials, which consist of hydrogen and another element, have been carefully studied in recent years,” says Eremets. And a real competition has developed: Which connection is superconducting at room temperature? Last year, Eremets’ team reported a temperature of around minus 23 degrees Celsius for a compound made up of the chemical element lanthanum and hydrogen; Researchers led by Russell Hemley at George Washington University previously reported a temperature of minus 13 degrees for a similar system.
But only the addition of carbon to the sulfur hydride, resulting in a ternary compound, raised the superconductivity to the rank of more degrees. Eremets believes that the results presented by Dia’s research group are credible. However, to be 100% certain, you have to wait and see if other labs can confirm the measurements. He also believes that other combinations of elements could lead to superconductivity at room temperature.
Open questions about the structure and function of materials.
However, it is still unclear how exactly such solids look under high pressure. The spectroscopic examination only worked up to about 60 billion Pascals, the Dias scientists write. Their analysis showed that after the photochemical process, neither pure sulfur nor carbon was present in the sample. This points to the synthesis of a new molecular compound.
The lack of knowledge about the structure of materials also explains why the physical mechanisms of high-temperature superconductivity are not yet understood. However, a theoretical model has been established for conventional superconductivity, which occurs in certain metals or metal compounds at very low temperatures below zero, generally close to absolute zero of minus 273.15 degrees Celsius: Electrons that move freely in the metal form what is known as below a critical temperature. Cooper pairs. These act like a collective, so to speak, and wander step by step through the material without resistance.
Superconductors in MRT systems and magnetic levitation trains
Today, superconducting coils are used, for example, in particle accelerators or magnetic resonance tomography (MRT), where they generate strong magnetic fields. Since magnetic field lines always run around a superconductor, it can be made to float. In Japan, for example, the technology is already being used in a test magnetic levitation train. Meanwhile, high-performance cooling is always included.
Superconductors based on hydrogen compounds would not need that. Therefore, Dias and his colleagues want to look for variants that become superconducting with significantly lower pressure. Mikhail Eremets is also optimistic that this could work especially with ternary hydrogen compounds. The next target of high-temperature superconductor research is called “ambient pressure.”
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