Praseodymium doping effect on the superconducting properties of FeSe0.5Te0.5 bulks under ambient and high-pressure growth conditions

Abstract

A series of Pr-doped FeSe_0.5Te_0.5 (Fe_1-xPr_xSe_0.5Te_0.5; 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 (T_c^onset) by 1.5 K and the critical current density (J_c) by two orders of magnitude compared to the CSP method. Pr-doped FeSe_0.5Te_0.5 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 Fe_1-xPr_xSe_0.5Te_0.5 also makes the sample less dense compared to the parent sample grown by HP-HTS. Transport and magnetic measurements depict that T_c^onset is almost unaffected by Pr-doping, whereas J_c of Pr-doped FeSe_0.5Te_0.5 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 T_c^onset and improves J_c of FeSe_0.5Te_0.5 regardless of the doping contents and growth conditions. These results are promising for the practical application of iron-based superconductors to improve J_c properties without affecting T_c^onset through CSP process and congruent with discoveries from other superconductors, like cuprates and MgB₂.