Predicting Superconducting Crystal Structures | Eurek alert!

image: Newly discovered crystal structure of superconductor achieving higher transition temperature.
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Credit: Ryo Maezono of JAIST.

Isikawa, Japan — Superconductivity refers to the loss of electrical resistance of a material and requires extremely low temperatures (

A breakthrough has been achieved with hydrogen-rich compounds (called hydrides) containing rare earths or alkali metals, which exhibit room temperature superconductivity at high pressures (100-200 GPa). These metal hydrides have cage-like structures of hydrogen atoms stacked on top of each other allowing them to withstand the high pressures necessary for the phenomenon of superconductivity. Many crystal structures and compositions of these hydrides have been predicted by combining various binary metal hydrides together.

However, in a study published in The Journal of Physical Chemistry On January 26, 2022, a group of researchers led by Professor Ryo Maezono of the Japan Advanced Institute of Science and Technology (JAIST) used a supercomputer to make similar predictions for viable high-temperature ternary metal hydride superconductors containing magnesium ( Mg), an alkali metal and Scandium (Sc), a rare earth element. “MgH2 and ScH2 are known to be stable phases at ambient pressure. Therefore, MgH2 and ScH2 can be used to chemically synthesize the ternary compounds Mg−Sc−H“, explains Professor Maezono.

For their research, the researchers initially started from certain Mg-Sc-H compounds (MgSc3HXMgSc2HXMgScHXmg2ScHXand Mg3ScHX, where x = 2−12, 14, 16 and 18). Starting from random initial structures, they used the supercomputer to determine the possible combinations and crystal structures that would yield a valid superconductor in a pressure range of 100 to 200 GPa.

To reach superconductivity, the predicted compound must meet certain conditions: it must be thermodynamically stable, i.e. it cannot degrade into its elementary components, have a high transition temperature, have a of valid synthesis and possess a structure capable of withstanding high temperatures. pressures where the phenomenon occurs. In the simulations, four hydrogen-rich structures were found to meet the criteria: R3̅m-MgScH6C2/m-Mg2ScHten, Immm-MgSc2H9and Pm3̅m-Mg-(ScH4)3.

Outside crystal structures, R3̅m-MgScH6 was found to have the highest transition temperature of (23.3 K) at 200 GPa and 41 K at 100 GPa. The compound was found to possess a hexagonal crystal structure, in which each Mg and Sc atom is surrounded by 14 H atoms (Figure 1). The transition temperature was, however, much lower than that of the binary halide counterparts (LHten and YHten) and this low temperature was attributed to the low density of states at the Fermi level due to the low hydrogen content.

Among metal hydrides, ternary metal hydrides that contain hydrogen bonded to two other metals are promising candidates for superconductivity at low pressure and room temperature. However, it was a difficult and time-consuming process to predict the proper elements and crystal structure that resulted in a superconducting ternary hydride due to the large number of possible combinations with metals. With the help of supercomputers, researchers are now able to quickly identify potential superconductor candidates. The discovery of Mg-Sc-H compounds as valid superconductors is the third such prediction for ternary hydrides made by the research group using computer simulations. “This is the third news with ‘Mg/Sc’ compounds after previous discoveries with ‘La/Y’ in December 2021 and ‘Y/Mg’ in January 2022. New discoveries are launched one after another“, explains Professor Maezono.

Despite low transition temperatures, the predicted Mg-Sc-H compounds remain stable at pressures lower than those normally observed for high-temperature superconductors. Simulations like these allow researchers to understand the contributions of each element to the phenomenon of superconductivity, accelerating the development of high-temperature superconductors.

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Reference

Original article title:

High pressure Mg-Sc-H phase diagram and its superconductivity from first principles calculations

Newspaper:

The Journal of Physical Chemistry

DO I:

10.1021/acs.jpcc.1c08743

About Japan Advanced Institute of Science and Technology, Japan

Founded in 1990 in Ishikawa Prefecture, 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 become one of Japan’s top universities. JAIST has several satellite campuses and strives to develop competent leaders with a state-of-the-art educational system where diversity is key; about 40% of its alumni are international students. The university has a unique style of higher education based on a carefully designed and course-oriented curriculum to ensure that its students have a solid foundation on which to conduct cutting-edge research. JAIST also works closely with local and overseas communities by promoting collaborative industry-university research.

About Professor Ryo Maezono from Japan Advanced Institute of Science and Technology, Japan

Dr. Ryo Maezono has been a professor at the School of Information Science at Japan Advanced Institute of Science and Technology (JAIST) since 2017. He received his doctorate from the University of Tokyo in 2000 and worked as a 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 senior researcher with 107 publications to his credit.

Funding Information

The calculations for this work were performed using facilities at JAIST’s Research Center for Advanced Computing Infrastructure (RCACI).

Dr. Ryo Maezono is grateful for financial support from MEXTKAKENHI (19H04692 and 16KK0097), FLAGSHIP2020 (Project Nos. hp190169 and hp190167 at K-computer), Toyota Motor Corporation, I−O DATA Foundation, the Air Force Office of Scientific Research (AFOSR -AOARD/ FA2386-17-1-4049; FA2386-19-1-4015) and JSPS bilateral joint projects (with India DST).


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