SPring-8, the large synchrotron radiation facility

Release Date

12 Jun, 2013

National Institute of Advanced Industrial Science and Technology
Osaka University
Japan Synchrotron Radiation Research Institute (JASRI)

Key points
• The crystal structure of phase VII calcium under high pressure, having the highest superconducting transition temperature of 29 K among all elements, was analyzed.
• Calcium, while being a single element, was found to show a complex and new host-guest structure.
• The results of this study will lead to the design of new high-temperature superconducting materials and improvement in the performance of superconducting magnets.

Hiroshi Fujihisa (senior research scientist) and his colleagues in Accurate Crystal Structure Analysis Group, Research Institute of Instrumentation Frontier (Director, Masataka Ohkubo), National Institute of Advanced Industrial Science and Technology (President, Ryoji Chubachi) determined the crystal structure of calcium under ultrahigh pressure, which has the highest superconducting transition temperature (Tc*1) among all elements. This was achieved in collaboration with the Center for Quantum Science and Technology under Extreme Conditions (Director, Yoshito Tobe), Osaka University (President, Toshio Hirano), and JASRI (Director, Tetsuhisa Shirakawa). In 2011, researchers in Osaka University discovered the presence of phase VII calcium under an ultrahigh pressure of 210 GPa or more and reported that this phase of calcium has the highest Tc of 29 K among all elements. However, the crystal structure of phase VII calcium has not been determined. In this study, the crystal structure of phase VII calcium was analyzed by X-ray powder diffraction*3 experiment at SPring-8*2 and quantum chemical calculation and, as a result, a unique and complex host-guest structure*4 was discovered. It is expected that the highest Tc of this calcium among all elements will be logically explained on the basis of the crystal structure determined in this study. Such work will also lead to the design of materials with higher Tc, which are desired in the scientific and industrial world. This achievement was published in the American scientific journal Physical Review Letters on 7 June 2013. Figure Crystal structure of phase VII calcium analyzed in this study The host structure indicated in green and the guest structures indicated in blue and brown are combined.

<<Figures>>

<<Glossary>>
*1 Superconducting transition temperature (Tc)
The temperature at which the electrical resistance of a material becomes zero (superconducting state) upon cooling.

*2 SPring-8
SPring-8 is a synchrotron radiation facility that provides the world’s highest-brilliance synchrotron radiation. It is owned by RIKEN and located in Harima Science Park City, Hyogo Prefecture, Japan. JASRI is responsible for the operation, management, and promotion of the use of SPring-8. The name “SPring-8” is derived from “Super Photon ring-8 GeV”. When the direction of the electron beams accelerated to nearly the speed of light is changed by magnets, electromagnetic waves are emitted in the tangential direction; these waves are synchrotron radiation. When the electron beam has a higher energy and the change in the traveling direction is large, synchrotron radiation contains shorter-wavelength lights such as X-rays. In particular, the following three facilities are known as the third-generation large synchrotron facilities: SPring-8 in Japan, the Advanced Photon Source (APS) in the USA, and the European Synchrotron Radiation Facility (ESRF) in France. Because the ring at SPring-8 enables an electron acceleration energy of 8 giga-electronvolts to be generated, synchrotron radiation in a wide range of wavelengths can be obtained including far-infrared light, visible light, vacuum ultraviolet light, soft X-rays, and hard X-rays. SPring-8 is used by researchers both in Japan and overseas for joint research in various fields such as materials science, earth science, life science, environmental science, and industrial applications.

*3 X-ray powder diffraction
When a powder sample irradiated with X-rays, the X-rays are diffracted in various directions. The inner structure of a sample can be determined without destroying the sample by measuring the intensity of diffracted X-rays and the angle of the diffraction direction.

*4 Host-guest structure
A structure with a host framework having interior cavities that encapsulate guest atoms or guest molecules smaller than the cavities.