Superconductivity & Particle AcceleratorS 2026

Enhancing the critical current density (Jc) of polycrystalline SmFeAsO1-xFx (Sm1111) superconductors remains a major challenge because intergranular current transport is severely limited by weak-link grain boundaries, porosity, and incomplete phase formation. High-pressure processing offers a unique opportunity to overcome these limitations by simultaneously controlling phase evolution, densification, and microstructural connectivity [1-2]. In this work, we present a comprehensive investigation of high-pressure engineering of Sm1111 superconductors using three complementary processing routes: high-gas-pressure and high-temperature synthesis (HP-HTS) [3], cubic-anvil high-pressure processing (CA-HP) [4], and spark plasma sintering (SPS) [5]. The superconducting, structural, and microstructural properties of these materials are systematically compared with those of conventionally synthesized ambient-pressure samples to establish clear processing–structure–property relationships [3-5]. By independently tuning pressure (up to 4 GPa), temperature (up to 1600 °C), and processing conditions, distinct optimization strategies are identified for intrinsic and extrinsic superconducting performance. In-situ synthesis at 4 GPa and 1400 °C enables complete phase formation and enhances the superconducting transition temperature (Tc) by approximately 3 K. In contrast, ex-situ high-pressure densification at moderate pressure (~0.5 GPa) preserves a high transition temperature (Tc ≈ 53 K) while producing nearly an order-of-magnitude enhancement in Jc. Detailed structural, magnetic, and microstructural analyses demonstrate that this remarkable improvement originates from enhanced densification, reduced porosity, improved phase purity, and substantially strengthened intergrain connectivity, leading to effective suppression of weak-link behavior. These results demonstrate that high-pressure engineering provides independent yet complementary control over intrinsic superconducting properties and intergranular current transport. The established processing framework offers a scalable route toward high-performance Sm1111 superconductors and provides practical design principles for the development of iron-based superconducting wires and tapes intended for high-field magnet and particle accelerator applications [3-5].

Acknowledgments
This research was supported by the National Science Centre (NCN), Poland through the SONATA-BIS 11 project (2021/42/E/ST5/00262) and the Weave-UNISONO project (2025/07/Y/ST5/00116). SJS acknowledges financial support from NCN Poland through Project numbers 2021/42/E/ST5/00262 and 2025/07/Y/ST5/00116.

References
1) S. J. Singh and M. I. Sturza, Crystals 12, 20 (2022)
2) Priya Singh and Shiv J. Singh et al., Cryogenics (Elsevier) 147, 104028 (2025)
3) M. Azam and Shiv J. Singh et. al., Crystals 13 (10), 1525 (2023) and Ceramics International 51, 13734-13751 (2025)
4) M. Azam, T. Zajarniuk H. Ogino, Shiv J. Singh, Materials Research Express 12 (11), 116001 (2025) and J Mater Sci: Mater Electron 37, 385 (2026)
5) M. Azam, T. Zajarniuk, K. Kwatek, Paolo Mele, Shiv J. Singh, Cryogenic 150, 104125 (2025)