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Tuning of upper critical field in a vanadium-based A15 superconductor by the compositionally-complex-alloy concept


Compositionally complex alloys (CCAs) are a new category of multi-principal-element materials, which are closely related to high-entropy alloys, but contain more than two phases in an alloy sample. We applied the concept of CCA to a A15-type compound superconductor V3X by aiming to occupy the X site by a mixture of Al, Si, Ga, Ge and Sn. The V3X sample showed bulk superconductivity with a transition temperature Tc of 6.3 K, which is close to the Tc of V3Ge. The upper critical field Bc2(0) of V3X estimated from magnetic susceptibility is 8.8 T, which is ~ 50% higher than that of V3Ge (Bc2(0) = 5.8 T). Using synchrotron X-ray diffraction, the presence of at least five different A15 phases were revealed, which could not be understood by simple phase separation into V3Al, V3Si, V3Ga, V3Ge, and V3Sn. We consider that the CCA states in V3X resulted in the improvement of Bc2. The CCA concept would be useful for improvement of superconducting properties of practical superconductors.

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The authors thank O. Miura, Md. R. Kasem, and T. D. Matsuda for their support in experiments. This work was partly supported by Grant-in-Aid for Scientific Research (KAKENHI) [Nos.: 18KK0076, 21H00151, 21K18834]; and Tokyo Metropolitan Government Advanced Research [H31-1].


Grant-in-Aid for Scientific Research (KAKENHI), 18KK0076, Yoshikazu Mizuguchi, 21H00151, Yoshikazu Mizuguchi, 21K18834, Yoshikazu Mizuguchi, Tokyo Metropolitan Government Advanced Research, H31-1, Yoshikazu Mizuguchi

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YN, AY, and YM: conception and experimental design; All the authors: carrying out measurements; YN and YM: manuscript composition.

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Correspondence to Yuki Nakahira.

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Nakahira, Y., Kiyama, R., Yamashita, A. et al. Tuning of upper critical field in a vanadium-based A15 superconductor by the compositionally-complex-alloy concept. J Mater Sci 57, 15990–15998 (2022).

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