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

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).