PC-P-7
Na-catalyzed rapid synthesis and superconducting properties of intercalated graphite CaC6
16:45-18:15 29/11/2023
*Akira Iyoa, Hiroshi Fujihisaa, Yoshito Gotoha, Shigeyuki Ishidaa, Hiroshi Eisakia, Hiraku Oginoa, Kenji Kawashimaa,b
a. National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
b. IMRA JAPAN Co., Ltd., Kariya, Aichi 448-8650, Japan
Graphite interlayer compounds (GICs) are a class of materials in which atoms or molecules are inserted between the layers of graphite. Among these, CaC6 is known to exhibit a high superconducting transition temperature (Tc) of as high as 11.5 K [1]. However, its physical properties and application potential have not been fully evaluated due to the extreme difficulty of sample synthesis. Recently, the metal Na has been reported to have catalytic properties that dramatically enhance the formation of alkali metals or alkaline earth metals GICs [2]. CaC6 is formed simply by mixing powdered Ca and graphite with Na and heating at low temperature (250℃) for several hours.
In this study, we conducted experiments on CaC6 for elucidating the Na-catalyzed formation mechanism and achieving rapid mass synthesis of graphite intercalation compounds (GICs). Rapidly synthesized CaC6 was characterized by analysis of its crystal structure and physical properties. A Na-to-C molar mixing ratio of 1.5–2:6 was suitable for the efficient formation of CaC6 under heat treatment at 250 °C for 2 h, and the catalytic Na remaining in the sample was demonstrably reduced to a Na:Ca ratio of approximately 3:97.
The upper critical field Hc2 was enhanced approximately three times compared to those of previous reports. Based on X-ray diffraction and experimental parameter analysis, we concluded that the enhancement of Hc2 was attributed to the disordered stacking sequence in CaC6, possibly because of the rapid and low-temperature formation. Physical properties derived from specific heat measurements were comparable to those of high-quality CaC6, which is slowly synthesized using the molten Li-Ca alloy method. This study provides new avenues for future research and exploration in the rapid mass synthesis of GICs as practical materials, for applications such as battery electrodes and superconducting wires.
[1] T. E. Weller, M. Ellerby, S. S. Saxena, R. P. Smith, and N. T. Skipper, Nature Physics 1 (2005) 39.
[2] A. Iyo, H. Ogino, S. Ishida, H. Eisaki, Advanced Materials 35 (2023) 2209964.
This study was partly supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI) (No. 22K04193 and JP19H05823).
