Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan1
The study of Laves phase, represented by the general formula AB2, is a challenge in solid-state physics and chemistry. Various structures such as C14, C15, and C36 appear, but there is still no systematic understanding of which phase is stable for given elements A and B. In the ternary system, the structure types become more diverse. It shows interesting ordered structures in which two elements occupy B4 tetrahedra in an ordered manner. The ordered structure provides a unique opportunity for material development with a focus on Kagome and triangular networks.
In this talk, we report on the novel ordered Laves phase compounds Li2IrSi3 (P31c, C3v4, No. 159) [1] and Mg2Ir3Si (P63/mmc, D6h4, No. 194) [2] and their superconductivity. They are classified as ordered variants of the C14 Laves phase, where Li and Mg form a hexagonal diamond network of A, while Ir and Si show an ordered configurations in the B4 tetrahedra. We found that the positions of Ir and Si atoms were interchanged between them. Li2IrSi3 has an Ir1/4Si3/4-type ordering, resulting in the breathing Kagome network of Si and triangular network of Ir. On the other hand, Mg2Ir3Si has an Ir3/4Si1/4-type ordering in which the breathing Kagome network of Ir and the triangular network of Si result. The change in the ordered configuration depending on the A-site element significantly influenced superconducting properties: the superconducting transition temperature Tc = 3.8 K for Li2IrSi3 [1,3] and 7 K for Mg2Ir3Si [2]. The results will stimulate the study of parameters to control the structure of the ordered Laves phase. Furthermore, the phase could be a useful platform for the development of superconductors with Kagome and triangular networks.
This work was conducted in collaboration with M. Nohara (Okayama Univ.) and S. Pyon (The Univ. of Tokyo).
[1] S. Pyon, K. Kudo, J. Matsumura, H. Ishii, G. Matsuo, M. Nohara, H. Hojo, K. Oka, M. Azuma, V. O. Garlea, K. Kodama, and S. Shamoto, J. Phys. Soc. Jpn. 83, 093706 (2014).
[2] K. Kudo, H. Hiiragi, T. Honda, K. Fujimura, H. Idei, and M. Nohara, J. Phys. Soc. Jpn. 89, 013701 (2020).
[3] D. Hirai, R. Kawakami, O. V. Magdysyuk, R. E. Dinnebier, A. Yaresko, and H. Takagi, J. Phys. Soc. Jpn. 83, 103703 (2014).
Keywords: New superconductors, Ordered Laves phase, Kagome network