Superconducting Phase Diagram of Sm-Based Oxypnictides by Cubic-Anvil High Pressure Technique
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In collaboration of AIST Japan, Prof. Shiv J. Singh’s research team (from NL-6 Laboratory of Superconductors and Hydrogen Technologies) has successfully extended the superconducting phase diagram of fluorine-doped SmFeAsO (Sm1111) up to an unprecedented 40% fluorine substitution using a cubic-anvil high-pressure (CA-HP) technique (pressure up to 6 GPa).
A series of SmFeAsO1-xFx (Sm1111) samples (0.05 ≤ x ≤ 0.40) were synthesized using this CA-HP technique, allowing controlled and homogeneous fluorine incorporation across a wide composition range, including the overdoped regime. Structural, Raman, transport, and magnetic measurements confirmed the stability of the tetragonal Sm1111 phase and effective fluorine substitution throughout the series. Compared to conventionally synthesized samples, the high-pressure growth method significantly enhances superconducting performance: in the underdoped region, the superconducting transition temperature (Tc) increases by 10–17 K, and the critical current density (Jc) improves by up to an order of magnitude. The upper critical field approaches 200 T, highlighting strong paramagnetic limitation and multiband superconductivity. For the first time using a high-pressure technique, an extended dome-shaped superconducting phase diagram has been established for the Sm1111 system. These findings demonstrate that high-pressure synthesis is a powerful materials-engineering strategy for extending the substitution range and optimizing superconducting properties in iron-based superconductors.
For more details, please refer to the publication: M. Azam, T. Zajarniuk, R. Diduszko, T. Palasyuk, C. Jastrzebski, A. Szewczyk, H. Ogino, and S. J. Singh entitled “Fluorine substitution‑dependent phase diagram and superconducting properties of Sm‑based oxypnictides synthesized by a high‑pressure growth technique” J Mater Sci: Mater Electron 37, 385 (2026).
Figure: (a) Superconducting onset Tc obtained from resistivity measurements and (b) Jc derived from magnetization measurements for SmFeAsO1-xFx samples prepared by the CA-HP process, are plotted as a function of nominal fluorine content (x). Three shaded colour regions depict the underdoped, optimal (Opt.) and overdoped regimes. Previous data are also included for a comparison.
