Instytut Wysokich Ciśnień

The properties of high T_c superconductors can be significantly improved by the chemical pressure effect and high-pressure synthesis process. Dr. Singh's research group (NL-6) has published three very interesting IEEE articles that summarize the impact of chemical pressure on iron-based superconductors (FBS) using both ambient and high-pressure growth methods.

In the first paper, researchers show that the superconducting properties of the stoichiometric CaKFe₄As₄ (1144) are improved by high-gas pressure and high-temperature synthesis (HP-HTS) process. The transition temperature is increased up to 35.2 K with a transition width of 1 K, which is comparable to 1144 single crystals. Additionally, the critical current density (J_c) is enhanced by almost one order of magnitude compared with 1144 prepared by the conventional synthesis process at ambient pressure (CSP). This study is published by Manasa Manasa, Mohammad Azam, Tatiana Zajarniuk, Ryszard Diduszko, Tomasz Cetner, Andrzej Morawski, Andrzej Wiśniewski, Shiv J. Singh entitled “Enhancement of Superconducting Properties of Polycrystalline CaKFe₄As₄ by High-Pressure Growth” (IEEE Transactions on Applied Superconductivity (2023)) DOI: 10.1109/TASC.2023.3345821

Figure 1: The variation of (a) the onset transition (T_c^onset) (b) transition width (ΔT) (c) the residual resistivity ratio (RRR = ρ_{300 K} /ρ_{40 K} and (d) the critical current density (J_c) at 0 T and 5 T at 5 K for the samples prepared at different pressures for CaKFe₄As₄ bulks. The data are also included from the previous reports for 1144 bulks.

In the second paper, scientists have shown that the sample quality and superconducting properties of GdFeAs(O,F) prepared by CSP have been improved by the optimization of its growth conditions. This investigation concluded that highly pure precursors, particularly gadolinium metal, are required to achieve high superconducting properties of F-doped Gd1111. A high growth pressure of 1 GPa reduces the superconducting properties of F-doped Gd1111. This study has been published in the paper: Mohammad Azam, Manasa Manasa, Tatiana Zajarniuk, Svitlana Stelmakh, Tomasz Cetner, Andrzej Morawski, Andrzej Wiśniewski, Shiv J. Singh entitled “Optimization of Synthesis Parameters and Superconducting Properties of GdFeAsO_1-xF_x” (IEEE Transactions on Applied Superconductivity 34, 7300205 2023).  DOI: 10.1109/TASC.2023.3341858

Last but not least, researchers studied the twin doping effects on the superconducting properties of SmFeAs(O,F) caused by fluorine (F) incorporation at the O-site in SmO layer and antimony (Sb) substitution at the As-site in the superconducting layer (FeAs). Interestingly, a large size of dopants reduces their superconducting properties, systematically. The detailed studies are published by Mohammad Azam, Manasa Manasa, Tatiana Zajarniuk, Ryszard Diduszko, Tomasz Cetner, Andrzej Morawski, Andrzej Wiśniewski, Shiv J. Singh entitled “Antimony Doping Effect on the Superconducting Properties of SmFeAs(O,F) ” (IEEE Transactions on Applied Superconductivity (2023)) DOI: 10.1109/TASC.2023.3343328

Figure 2. The onset transition temperature T_c and (b) residual resistivity ratio (RRR = ρ_300K / ρ_55K) variation with Sb-doping contents (x) for SmFeAs_1-xSb_xO_0.8F_0.2 bulks.