We have verified the effectiveness of applying the concept of combinatorial chemistry (CC) to the exploration of superconductors through bulk inorganic material synthesis [1–5]. Using this exploration concept, we have discovered a new superconductor, AuCu3-type (Ba1-xNax)Bi3. BaBi3 is a known superconductor that can be described within the framework of BCS theory[6]. For superconductors with the AuCu3-type structure, the superconducting transition temperature Tc is known to vary as a result of changes in the density of states at the Fermi energy, which is controlled by the valence electron number in accordance with the Matthias rule. Therefore, we investigated the dependence of Tc on the Na substitution level at the Ba site in this system.

Sample synthesis with varying Ba/Na ratios revealed that (Ba1-xNax)Bi3 can be synthesized over the compositional range 0.1 ≤ x ≤ 0.6. Tc increases with increasing Na content and reaches a maximum of Tc ~ 8.5 K near x = 0.5. This enhancement of Tc is attributed to hole-carrier doping induced by partial substitution of Ba²⁺ with Na⁺, leading to an increased density of states at the Fermi energy. Furthermore, density functional theory (DFT) calculations indicate that the Bi(1) atoms forming octahedra are metastable, while (Ba1-xNax)Bi3 stabilizes in a nearly cubic structure (c/a ≈ 1) for x = 0 and x > 0.

In this presentation, we will report the sample synthesis method, normal- and superconducting-state properties, and electronic band structures obtained from first-principles calculations.

References [1] A. Iyo et al., Sci Rep 5, 10089 (2015). [2] T. Kinjo et al., Supercond. Sci. Technol. 29 03LT02 (2016). [3] A. Iyo et al., Phys. Rev. Materials 3, 124802 (2019). [4] A. Iyo et al., Inorg. Chem. 59, 12397 (2020). [5] A. Iyo et al., Inorg. Chem., 61, 12149 (2022). [6] T. Koshinuma et al., Intermetallics 148, 107643 (2022). [7] T. Koshinuma et al., Intermetallics 181, 108748 (2025). [8] N. Haldolaarachchige et al., Supercond. Sci. Technol. 27 105001 (2014).