New crystal structure for hydrogen compounds
Ishikawa, Japan – Superconductivity is the disappearance of electrical resistance in certain materials below a certain temperature, known as the “transition temperature”. The phenomenon has enormous implications for revolutionizing technology as it is known, allowing low loss power transmission and maintenance of electromagnetic force without a power supply. However, superconductivity generally requires extremely low temperatures ~ 30 K (the temperature of liquid nitrogen, in comparison, is 77 K) and, therefore, expensive cooling technology. To have any chance of realizing superconducting technology at low cost, superconductivity must be achieved at much higher transition temperatures.
Materials scientists have made a breakthrough on this front with crystalline materials containing hydrogen, known as “metal hydrides.” These are compounds formed by a metal atom bonded to hydrogen that have been predicted and realized as suitable candidates to achieve superconductivity even at room temperature. However, for this they require extremely high pressures, which limits their practical applications.
In a new study published in Materials chemistry, a group of researchers led by Professor Ryo Maezono of the Japan Advanced Institute of Science and Technology (JAIST) performed computer simulations to extend the search for high-temperature superconductors, looking for potential candidates among ternary hydrides (combined hydrogen with two other elements).
“In ternary hydrides, the number of elements goes from two to three. While this greatly increases the number of possible combinations and may make the problem of predicting suitable materials more difficult, it also increases our chances of encountering a potential high temperature superconductor ”, explains Prof. Maezono.
Using the university’s supercomputer, the researchers examined possible crystal structures for (LaH6) (YH6)Yes compounds (y = 1-4), in search of configurations which would give stable structures, allowing their synthesis in the laboratory at high pressure. Starting from a random structure, the simulations went through various possible combinations of elements, testing their stability at extremely high pressures ~ 300 GPa.
The simulations revealed the clathrate (Cmmm-) LaYH structures12 and LaY3H24, composed of LaH24 and YH24 cages stacked on top of each other (Figure 1), as viable candidates for high temperature and high pressure superconductors. “Longer stacking for Cmmm-LaY3H24 lead to a slightly increased transition temperature ”, explains Prof. Maezono. Among the possible structures, the highest transition temperature (145.31 K – 137.11 K) was observed for LaY3H24. The researchers attributed the origin of a higher transition temperature to a high “density of states” and a high “phonon frequency”, two parameters used to assess superconductivity in materials.
The findings have excited researchers, who are optimistic about finding more of these high-temperature superconductors. “It is entirely possible to predict, using simulations, other new combinations of elements which would further improve the desired properties”, said Professor Maezono.
With potential new discoveries on the horizon, practical superconductor-based technology may not be a pipe dream after all!
About Japan Advanced Institute of Science and Technology, Japan
Founded in 1990 in Ishikawa Prefecture, the Japan Advanced Institute of Science and Technology (JAIST) was the first independent national graduate school in Japan. Today, after 30 years of steady progress, JAIST has grown into one of the top universities in Japan. JAIST has several satellite campuses and strives to develop capable leaders with a cutting-edge education system where diversity is key; around 40% of its alumni are international students. The university has a unique style of higher education based on a carefully designed curriculum to ensure that its students have a solid foundation on which to conduct cutting-edge research. JAIST also works in close collaboration with local and foreign communities by promoting collaborative industry-university research.
About Professor Ryo Maezono from the Japan Advanced Institute of Science and Technology, Japan
Dr Ryo Maezono has been a professor at the School of Information Science, Japan Advanced Institute of Science and Technology (JAIST) since 2017. He received his PhD from the University of Tokyo in 2000 and worked as researcher at the National Institute of Materials Science in Ibaraki, Japan from 2001 to 2007. His research areas include materials informatics and condensed matter theory using high performance computing. He is a principal investigator and has 105 publications to his credit.
This study was funded by the HPCI System Research Project (Project ID: hp190169), MEXT-KAKENHI (JP16H06439, JP17K17762, JP19K05029 and JP19H05169), the Air Force Office of Scientific Research (award numbers: FA2386-20-1 -4036), MEXT-KAKENHI (21K03400 and 19H04692), and the Office of Air Force Scientific Research (AFOSR-AOARD / FA2386-17-1-4049; FA2386-19-1-4015).
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High Tc superconducting hydrides formed by LaH24 and YH24 cage structures as basic building blocks
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