DOI: 10.18150/r6xyfb
title: Praseodymium doping effect on the superconducting properties of FeSe0.5Te0.5 bulks under ambient and high-pressure growth conditions

description: Experimental data collected for the preparation of the manuscript: "Praseodymium doping effect on the superconducting properties of FeSe0.5Te0.5 bulks under ambient and high-pressure growth conditions"Physica C: Superconductivity and its applications 633 (2025) 1354729Abstract:A series of Pr-doped FeSe0.5Te0.5 (Fe1-xPrxSe0.5Te0.5; x = 0 to 0.3) bulks are prepared by conventional synthesis process at ambient pressure (CSP), and high gas pressure and high temperature synthesis (HP-HTS) methods. These bulks are well characterized by structural and microstructural analysis, Raman spectroscopy, transport, and magnetic measurements. The HP-HTS process of the parent bulks has enhanced the onset transition temperature (Tconset) by 1.5 K and the critical current density (Jc) by two orders of magnitude compared to the CSP method. Pr-doped FeSe0.5Te0.5 up to 10 % doping content prepared, either CSP or HP-HTS, slightly increases the unit cell volume, and high-pressure growth produces an almost pure superconducting phase, which confirms the successful Pr-doping at Fe sites. Raman spectroscopy measurements and DFT calculations suggest the substitution of Pr-atoms in the interlayer spacing of Fe(Se,Te) lattice. High-pressure growth of Fe1-xPrxSe0.5Te0.5 also makes the sample less dense compared to the parent sample grown by HP-HTS. Transport and magnetic measurements depict that Tconset is almost unaffected by Pr-doping, whereas Jc of Pr-doped FeSe0.5Te0.5 is enhanced by one order of magnitude relative to the parent sample developed by CSP but lower than that of the parent sample grown by HP-HTS. Hence, Pr- doping at Fe sites preserves Tconset and improves Jc of FeSe0.5Te0.5 regardless of the doping contents and growth conditions. These results are promising for the practical application of iron-based superconductors to improve Jc properties without affecting Tconset through CSP process and congruent with discoveries from other superconductors, like cuprates and MgB2.[In the published article, Figure 3, Figure 4 and Figure 5, Figure 6 are elemental mapping for the constituent elements and scanning electron microscope (SEM) image of PrxFe1-xSe0.5Te0.5, samples, respectively]Fig. 1. Powder X-ray diffraction (XRD) patterns of PrxFe1-xSe0.5Te0.5 bulks (x = 0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1 and 0.2 and 0.3) prepared at the room temperature by (a) CSP and (b) HP-HTS process. The variation of the calculated lattice parameters (c) ‘a’ (d) ‘c’ and (e) the lattice volume (V) with the nominal Pr substitution level (x) for all Pr-doped samples either prepared by CSP (closed symbol) or HP-HTS (open symbol) process. The lattice parameters and lattice volume for Gd-added FeSe0.5Te0.5 are also included in the previously published paper in Figure 1(c), (d) and (e). The tetragonal phase of FeSe0.5Te0.5 was observed as the superconducting phase.Fig. 2. Raman scattering study of polycrystalline FeSe0.5Te0.5 doped with Pr. (a) Experimental Raman spectrum collected at room temperature from the surface of parent FeSe0.5Te0.5 using high laser power (4 mW). Green spectrum from the paper of Zargar et al. 2015 [30] illustrates one of many examples of misinterpreted phonon assignments for FeSe0.5Te0.5. (b) Experimental Raman spectrum collected at low-temperature, under gaseous nitrogen atmosphere using medium laser power (0.8 mW). (c) Representative low-temperature Raman spectra of FeSe0.5Te0.5 with addition of Pr: 5 at. % (x = 0.05) acquired using low and medium laser power of 0.08 mW and 0.8 mW (red and blue spectrum respectively). The assignment of detected signals related to molecular rotation of nitrogen and lattice vibrations of Pr-doped FeSe0.5Te0.5 is shown for the spectrum collected at medium laser power. For comparison, positions of Fe related lattice modes in both spectra are indicated by arrow headed lines. An enlarged fragment of the red spectrum along with peaks fitted by Lorentz shape are shown in the inset. (d) Raman frequencies of respective lattice modes measured in parent compound (FeSe0.5Te0.5) and materials with Pr addition (5 and 10 at. %) were observed for two series of samples synthesized at ambient and high-pressure conditions (full and empty symbols respectively). Experimental data on the frequency of Se/Te and Fe related phonons modes from earlier reported studies for single crystalline materials Fe0.95Se0.56Te0.44 [31], Fe1.09Te [31] and FeSe0.5Te0.5 [32] are included for comparison.Fig. 3. Elemental Mapping of the constituent elements of various PrxFe1-xSe0.5Te0.5 bulks prepared by CSP: (i) Parent x = 0 (ii)x = 0.02 (iii)x = 0.05 (iv)x = 0.1 (v)x = 0.3 samples.Fig. 4. Elemental Mapping of the constituent elements of various PrxFe1-xSe0.5Te0.5 bulks prepared by HP-HTS: (i) Parent x = 0_HIP (ii)x = 0.02_HIP (iii)x = 0.05_HIP (iv)x = 0.1_HIP.Fig. 5. Back-scattered (BSE) images of PrxFe1-xSe0.5Te0.5 polycrystalline samples prepared by CSP where pores and hexagonal phases (H) are marked using arrows: (a)-(c) for parent x = 0; (d)-(f) for x = 0.02; (g)-(i) for x = 0.05; (j)-(l) for x = 0.1; and (m)-(o)x = 0.3.Fig. 6. Back-scattered (BSE) images of PrxFe1-xSe0.5Te0.5 polycrystalline samples prepared by HP-HTS where pores and hexagonal phases(H) are marked using arrows: (a)-(c) for parent x = 0_HIP; (d)-(f) for x = 0.02_HIP; (g)-(i) for x = 0.05_HIP; (j)-(l) for x = 0.1_HIP.Fig. 7. (a) The temperature dependence of resistivity for PrxFe1-xSe0.5Te0.5 (x = 0, 0.01, 0.02, 0.03, 0.05, 0.07, 0.1) samples prepared by CSP up to room temperature (b) The variation of the resistivity (ρ) with the temperature for PrxFe1-xSe0.5Te0.5 bulks for x = 0.2 and 0.3. The inset figure shows the low-temperature variation of the resistivity for these samples. (c) Low-temperature resistivity up to 16 K temperature of PrxFe1-xSe0.5Te0.5 bulks prepared by CSP (d) The temperature variation of the resistivity under different currents (I = 5, 10 and 20 mA) for PrxFe1-xSe0.5Te0.5 samples x = 0, 0.02, 0.05 and 0.1 prepared by CSP method.Fig. 8. (a) Samples prepared by HP-HTS: (a) the temperature dependence of the resistivity of PrxFe1-xSe0.5Te0.5 bulks up to room temperature for x = 0, 0.02, 0_HIP and 0.02_HIP. The inset figure shows the low-temperature resistivity of these samples in the temperature range 10–16 K. (b) The variation of resistivity of PrxFe1-xSe0.5Te0.5 bulks for x = 0.01_HIP, 0.05_HIP and 0.1_HIP till 250 K (c) The temperature dependence of the resistivity under different currents (I = 5, 10 and 20 mA) for x = 0_HIP and 0.02_HIP x = 0_HIP shows no dependence on applied current.Fig. 9. The temperature dependence of the normalized magnetic susceptibility (χ = 4πM/H) measured under zero field-cooled (ZFC) and field-cooled (FC) modes in an applied magnetic field H = 50 Oe for PrxFe1-xSe0.5Te0.5 bulks prepared by (a) CSP and (b) HP-HTS. (c) The variation of critical current density (Jc) with respect to the applied magnetic field for PrxFe1-xSe0.5Te0.5 bulks (x = 0, 0_HIP, 0.01, 0.01_HIP, 0.02, 0.02_HIP, 0.05 and 0.1) up to 9 T and at 7 K. The inset figure shows the hysteresis loop (M-H) for the sample x = 0.02 and 0.02_HIP.Fig. 10. The variation of (a) the onset transition temperature (Tc) (b) the transition width (ΔT) (c) the room temperature resistivity (ρ300K) (d) residual resistivity ratio (RRR = ρ300K / ρ20K) (e) the critical current density (Jc) at 7 K for H = 0 T (closed symbol) and 3 T (open symbol) for PrxFe1-xSe0.5Te0.5 bulks prepared by CSP with respect to the nominal contents (x) of Pr-doping or Gd-additions.Fig. 11. The variation of (a) the onset transition temperature (Tc) (b) the transition width (ΔT) (c) the room temperature resistivity (ρ300K) (d) residual resistivity ratio (RRR = ρ300K / ρ20K) (e) the critical current density (Jc) at 7 K for H = 0T (closed symbol) and 3 T (open symbol) for PrxFe1-xSe0.5Te0.5 bulks prepared by HP-HTS with respect to the nominal contents (x) of Pr substitutions or Gd- additions.