Institute of High Pressure Physics

Experimental data collected for the preparation of the manuscript: "Effect of spark plasma sintering on the superconducting properties of Sm-based oxypnictide"

Title: Effect of spark plasma sintering on the superconducting properties of Sm-based oxypnictide

Authors: Mohammad Azam, Tatiana Zajarniuk, Konrad Kwatek, Paolo Mele, Shiv J. Singh

Cryogenics 150 (2025) 104125

Abstract:

We optimize the superconducting properties of Sm-based oxypnictide (Sm1111: SmFeAsO_0.80F_0.20) by using the Spark Plasma Sintering (SPS) technique under various synthesis conditions, including heating temperatures ranging from 600 to 1000 ^◦C for durations of 5 to 30 min at the applied pressure of 45 MPa. All prepared bulks are characterized by structural and microstructural analysis as well as transport and magnetic measurements to conclude our findings. SmFeAsO_0.80F_0.20 bulks are also prepared using the conventional synthesis process at ambient pressure (CSP) and the high gas pressure and high temperature (HP-HTS) methods at 500 MPa, which exhibit a superconducting transition temperature (T_c) of 53–54 K. Interestingly, the SPS process of SmFeAsO_0.80F_0.20 increases the sample densities up to 97–98 % and confirms the optimized synthesis conditions of 900 ^◦C for 5–10 min; however, the increased sintering temperature or duration reduces T_c due to the possible evaporation of lighter elements, particularly fluorine. Furthermore, the SPS technique is unable to reduce the observed impurity phases for the Sm1111, which is similar to the CSP and HP-HTS processes. A slight increment in the J_c by the SPS process is observed due to the enhancement of sample density. A comparative analysis of Sm1111 superconductors prepared by SPS is performed with CSP and HP-HTS processes, suggesting that an increased sample density is ineffective on the superconducting properties in the presence of the impurity phases. This finding can be beneficial for the fundamental and applied research of iron-based superconductor (FBS).

[In the published article, Figure 2 and Figure 3 are elemental mapping for the constituent elements and scanning electron microscope (SEM) image of SmFeAsO_0.80F_0.20, samples, respectively]

Fig. 1. (a) Powder XRD pattern of SmFeAsO_0.80F_0.20 bulks prepared by CSP, HP-HTS and various SPS-1 to SPS-8 bulks prepared by spark plasma sintering (SPS) with various sintering temperatures and time. (b) An enlarged view of the main peak (102) position is depicted for different samples. The variation of (c) lattice parameter (a), (d) lattice parameter (c), and (e) unit cell volume (V) with the various synthesis pressures for all SmFeAsO_0.80F_0.20 samples.

Fig. 4. (a) The temperature variation of resistivity (ρ) up to the room temperature for various SPS bulks. The inset image depicts the temperature dependence of the resistivity for the parent, HIP, SPS-1 and SPS-2 up to room temperature. (b) Low-temperature variation of the resistivity up to 60 K for various SPS samples. The inset figure shows the low-temperature dependence of the resistivity for the parent, HIP, SPS-1, and SPS-2.

Fig. 5. (a) The temperature dependence of the normalized magnetic moment in ZFC and FC modes under a magnetic field of 20 Oe. (b) The variation of the critical current density (Jc) at a temperature of 5 K with the applied magnetic field up to 9 T for the parent, HIP, SPS-4, SPS-5, SPS-6, SPS-7 and SPS-8 bulks. The inset of the figure (b) illustrates the magnetic hysteresis loop for the parent, HIP and SPS-7 samples at a temperature of 5 K under the magnetic field up to 9 T.

Fig. 6. The variations of (a) the onset transition temperature (T_c^onset), (b) the transition width (ΔT), (c) the room temperature resistivity (ρ_{300 K}), (d) the Residual Resistance Ratio (RRR = ρ_{300 K}/ρ_{60 K}), and (e) the critical current density (J_c) of different SmFeAsO_0.80F_0.20 bulks prepared by CSP, HP-HTS and SPS processes under the different growth pressures.

Fig. 7. The magnetic field dependence of the critical current density (Jc) at ~5 K for our F-doped Sm1111 (Sm1111), (Ba,K)Fe₂As₂ (Ba122) and CaKFe₄As₄ (1144) bulks prepared by CSP process at ambient pressure (AP) and SPS method. The details about the Jc and other parameters for these bulks are mentioned in Table 4 of the Supplementary Data File.