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A series of FeSe 0.5 Te 0.5 bulk samples have been prepared using the high gas pressure and high-temperature synthesis (HP-HTS) method to optimize the growth conditions for the first time and investigated for their superconducting properties using structural, microstructure, transport, and magnetic measurements to reach the final conclusions. Ex situ and in situ processes are used to prepare bulk samples under a range of growth pressures using Ta-tube and without Ta-tube. The parent compound synthesized by convenient synthesis method at ambient pressure (CSP) exhibits a superconducting transition temperature of 14.8 K. Our data demonstrate that the prepared FeSe 0.5 Te 0.5 sealed in a Ta-tube is of better quality than the samples without a Ta-tube, and the optimum growth conditions (500 MPa, 600 °C for 1 h) are favorable for the development of the tetragonal FeSe 0.5 Te 0.5 phase. The optimum bulk FeSe 0.5 Te 0.5 depicts a higher transition temperature of 17.3 K and a high critical current density of the order of >10 4 A/cm 2 at 0 T, which is improved over the entire magnetic field range and almost twice higher than the parent compound prepared using CSP. Our studies confirm that the high-pressure synthesis method is a highly efficient way to improve the superconducting transition, grain connectivity, sample density, and pinning properties of a superconductor.

The enhanced performance of superconducting FeSe 0.5 Te 0.5 materials with added micro-sized Pb and Sn particles is presented. A series of Pb- and Sn-added FeSe 0.5 Te 0.5 (FeSe 0.5 Te 0.5 + x Pb + y Sn; 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 ( T c onset ) of pure FeSe 0.5 Te 0.5 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 T c onset 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. FeSe 0.5 Te 0.5 samples with 2 wt% of cometal additions show the best performance with their critical current density, J c , and the pinning force, F p , 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.