Cometal Addition Effect on Superconducting Properties and Granular Behaviours of Polycrystalline FeSe0.5Te0.5

Abstract

The enhanced performance of superconducting FeSe0.5Te0.5 materials with added micro-sized Pb and Sn particles is presented. A series of Pb- and Sn-added FeSe0.5Te0.5 (FeSe0.5Te0.5 + xPb + ySn; x = y = 0–0.1) bulks are fabricated by the solid-state reaction method and characterized through various measurements. A very small amount of Sn and Pb additions (x = y ≤ 0.02) enhance the transition temperature (Tconset) of pure FeSe0.5Te0.5 by ~1 K, sharpening the superconducting transition and improving the metallic nature in the normal state, whereas larger metal additions (x = y ≥ 0.03) reduce Tconset by broadening the superconducting transition. Microstructural analysis and transport studies suggest that at x = y > 0.02, Pb and Sn additions enhance the impurity phases, reduce the coupling between grains, and suppress the superconducting percolation, leading to a broad transition. FeSe0.5Te0.5 samples with 2 wt% of cometal additions show the best performance with their critical current density, Jc, and the pinning force, Fp, which might be attributable to providing effective flux pinning centres. Our study shows that the inclusion of a relatively small amount of Pb and Sn (x = y ≤ 0.02) works effectively for the enhancement of superconducting properties with an improvement of intergrain connections as well as better phase uniformity.

High Gas Pressure and High-Temperature Synthesis (HP-HTS) Technique and Its Impact on Iron-Based Superconductors

“…The selected composition FeSe0.5Te0.5 is prepared at 600 °C for 21 h in the first step, and in the second stage, the sample is grounded and heated again at 600 °C for 4 h, as more detail was discussed in our previous studies [12,23]. This FeSe0.5Te0.5 sample shows the transition temperature up to 15 K by the convenient synthesis method at ambient pressure, as reported by the previous report [23] and depicted in Figure 8a. The temperature dependence of the resistivity (ρ) for (a) FeSe0.5Te0.5 prepared by in-situ and ex-situ processes using HP-HTS, where the samples were sealed in a Ta-tube before being placed inside the high-pressure chamber.…”

“…Before using the high-pressure technique for these complicated families, the HP-HTS technique was applied to the simplest FBS, i.e., the 11 (FeSe) family. Tellurium (Te) doping at Se-sites, i.e., Fe(Se,Te), provides the highest transition temperature T c of 15 K for FeSe 0.5 Te 0.5 [23]. First, we synthesized the high-quality Fe(Se,Te) sample by the solid-state reaction method at ambient pressure (0 GPa).…”

“…First, we synthesized the high-quality Fe(Se,Te) sample by the solid-state reaction method at ambient pressure (0 GPa). The selected composition FeSe 0.5 Te 0.5 is prepared at 600 • C for 21 h in the first step, and in the second stage, the sample is grounded and heated again at 600 • C for 4 h, as more detail was discussed in our previous studies [12,23]. This FeSe 0.5 Te 0.5 sample shows the transition temperature up to 15 K by the convenient synthesis method at ambient pressure, as reported by the previous report [23] and depicted in Figure 8a.…”

High-Pressure Synthesis and the Enhancement of the Superconducting Properties of FeSe0.5Te0.5

“…Iron-based superconductors (FBS) were discovered in 2008 [1], and since then, numerous compounds have been identified belonging to this family [2,3]. These high T c materials can be categorized into six families based on the structure of the parent compounds, such as REFeAsO (RE1111; RE = rare earth), AFe 2 As 2 (122; A = Ba, K, Ca), (Li/Na)FeAs (111), thick perovskite-type oxide blocking layers, such as Sr 4 V 2 O 6 Fe 2 As 2 (22,456), Sr 4 Sc 2 O 6 Fe 2 P 2 (42,622), etc., and chalcogenide FeX representing 11 (X = chalcogenide) [4][5][6]. Eleven is the simplest family of FBS and has the highest T c of around 15 K for FeSe 1-x Te x (x = 0.5) samples at ambient pressure [3,7,8].…”

“…Due to these stable phases, it's always challenging to prepare a completely pure superconducting phase either in single crystal [14,15] or polycrystalline samples [3,7,16,17]. Some of these stable phases, particularly hexagonal δ-Fe x Se and hexagonal Fe 7 Se 8 , typically coexist with the predominant tetragonal β-Fe x Se phase [18] during the growth process and are not suitable for superconducting properties [19][20][21][22][23]. Recent research has demonstrated that convenient synthesis methods at ambient pressure (CSP) are inefficient for improving the critical current properties, grain connectivity, and phase purity of the bulk samples, as well as for practical applications [19][20][21][22].…”