Superconductivity & Particle AcceleratorS 2026

High-pressure synthesis is an effective strategy for enhancing the superconducting performance of iron-based superconductors by improving phase formation, microstructure, and grain connectivity [1-2]. In this work, we systematically investigate the effect of in-situ synthesis pressure on the structural, microstructural, and superconducting properties of the optimally fluorine-doped Pr-based oxypnictide superconductor PrFeAsO0.7F0.3 (Pr1111) [3]. Polycrystalline samples are synthesized under the in-situ pressures ranging from 174 to 1131 MPa using a hydraulic high-pressure synthesis technique. The phase formation and crystal structure are examined by X-ray diffraction (XRD), while the microstructure is characterized by scanning electron microscopy (SEM). Lattice dynamics are studied by Raman spectroscopy, and the superconducting properties are evaluated through electrical resistivity, magnetoresistance, and dc magnetization measurements. The critical current density is estimated from magnetic hysteresis loops using the Bean critical-state model. XRD analysis confirms the formation of the tetragonal Pr1111 phase for all samples with only minor variations in the lattice parameters as the synthesis pressure increases. Raman spectra exhibit the characteristic Pr(A1g), As(A1g), and Fe(B1g) phonon modes, whose frequencies remain nearly unchanged within the experimental uncertainty, indicating that the local lattice dynamics are essentially unaffected by the applied synthesis pressure supporting the structural analysis. Microstructural observations reveal a pronounced improvement in grain connectivity and sample densification with increasing synthesis pressure. Electrical transport measurements show that the superconducting transition temperature increases by approximately 6 K with increasing synthesis pressure, reaches a maximum for the samples synthesized at around 1000 MPa, and decreases rapidly at higher pressures [4]. Magnetization measurements corroborate the transport results, while the estimated critical current density exhibits a significant enhancement for the optimal in-situ synthesis pressure, indicating improved flux pinning and stronger intergranular coupling. These results demonstrate that in-situ synthesis pressure provides an effective route for optimizing the superconducting performance of PrFeAs(O,F) through microstructural improvement without altering its chemical composition [4].

Acknowledgement:
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.
We would like to thank Priya Singh for helping in some experiments and analysis.
References:
1. S. J. Singh and M. I. Sturza, Crystals 12 20 (2022).
2. Priya Singh and Shiv J. Singh et al., Cryogenics (Elsevier) Vol 147, pp 104028, 2025.
3. P. Singh et al. Journal of Alloys and Compounds 1072, 188942 (2026); Physica B: Condensed Matter 740, 419025 (2026), Journal of Physics and Chemistry of Solids 218 113933 (2026)
4. Jayant et al. Submitted to a Journal (2026).