Synthesis and Superconductivity of Hexagonal Zr₆MBi₂

d-electron compounds are promising in the exploration for unconventional superconductors due to their various characteristic features, such as high electronic density of states, strong electron-electron interactions, and spin and orbital degrees of freedom. Recently, Sc₆MTe₂ with various transition metals M was found to be a new d-electron superconductor family with the highest critical temperature of T_c = 4.7 K for M = Fe [1]. One of the features of the A₆MX₂ family is that many elements can occupy not only M site but also A and X sites, raising expectations for finding new superconductors.

In this study, we discovered that Zr₆RuBi₂ is a new superconductor with T_c = 4.9 K [2]. First, we synthesized polycrystalline samples of Zr₆RuBi₂ by the arc melting method. The powder X-ray diffraction data indicated the presence of the Zr₆RuBi₂ phase with Zr₆CoAl₂-type crystal structure. However, scanning electron microscopes and energy dispersive X-ray spectroscopy data showed that there is also an amorphous phase including Zr, which is a superconductor with similar T_c to that of Zr₆RuBi₂, so it was difficult to reveal the superconducting properties of Zr₆RuBi₂. By changing the synthesis and annealing conditions, we succeeded in synthesizing the Zr₆RuBi₂ sample without superconducting impurity phases and found that Zr₆RuBi₂ is a bulk superconductor with T_c = 4.9 K. We also found that Zr₆FeBi₂ and Zr₆RuTe₂ are bulk superconductors with T_c = 1.4 K [2] and 1.1 K [3], respectively, by using the similar synthesis procedure for Zr₆RuBi₂.



[1] Y. Shinoda et al., J. Phys. Soc. Jpn. 92, 103701 (2023).

[2] K. Yuchi et al., J. Phys. Soc. Jpn. 94, 013701 (2025).

[3] K. Yuchi et al., J. Phys. Soc. Jpn. 94, 085001 (2025).