High-pressure growth effects on the superconducting properties of Sm-based oxypnictide superconductors

TL;DR

This study investigates how high-pressure synthesis affects the superconducting properties of SmFeAsO0.8F0.2, finding that it slightly improves sample quality but does not significantly alter critical temperature or current density.

Contribution

It provides the first comprehensive analysis of high-pressure growth effects on Sm1111 superconductors, highlighting the robustness of impurity phases and their limited impact on superconducting properties.

Findings

Optimal growth at 900°C, 1 hour, 0.5 GPa slightly improves sample quality.

Superconducting transition temperature remains around 53-54 K across methods.

Impurity phases are robust and unaffected by high-pressure synthesis.

Abstract

High-pressure synthesis can be an effective method for improving the sample quality of materials as well as their superconducting properties. In this paper, the synthesis process of F- doped SmFeAsO has been optimized by preparing a series of bulk SmFeAsO0.8F0.2 (Sm1111) using the high gas pressure and high-temperature synthesis (HP-HTS) method, considering various growth parameters like growth pressures (0-1 GPa) and heating time (0.5-2 h). Structural, microstructural, Raman spectroscopic, transport, and magnetic measurements are employed to comprehensively analyze these bulks and derive the conclusive findings. The parent SmFeAsO0.8F0.2 prepared by the conventional synthesis process at ambient pressure (CSP) has a transition temperature (Tc) of around 53-54 K, and the critical current density (Jc) of 103 A/cm2 at 5 K with a small amount of the impurity phases (SmOF and SmAs), consistent with previous reports. Interestingly, all bulks synthesized by HP-HTS have almost the same Tc and Jc as the parent sample. The optimal growth conditions are obtained as 900C, 1 hour, and 0.5 GPa with the sealed Ta-tube, which slightly improved the sample quality and the superconducting properties compared to other bulks grown by HP-HTS. Our study confirms that the existence of the impurity phases in the 1111 family is very robust and cannot be reduced by HP-HTS, leading to only a small variation in the observed superconducting properties of Sm1111 whether prepared by CSP or HP-HTS. This is the first comprehensive investigation of the high-pressure development of Sm1111, which shows distinct behaviour from other families of iron-based superconductors.