Mechanochemical synthesis of pnictide compounds and superconducting Ba0.6K0.4Fe2As2 bulks with high critical current density

TL;DR

This study presents a novel mechanochemical synthesis method for Ba-122 and K-doped Ba-122 superconductors, achieving high critical current density in bulk samples through optimized heat treatments.

Contribution

It introduces a mechanochemical reaction approach for synthesizing pnictide superconductors and demonstrates how specific heat treatments enhance their superconducting properties.

Findings

Mechanochemical synthesis successfully produces Ba-122 compounds.

Optimized low-temperature heat treatment yields high critical current density.

Bulk samples exhibit global current flow with proper heat treatment.

Abstract

BaFe2As2 (Ba-122) and (Ba0.6K0.4)Fe2As2 (K-doped Ba-122) powders were successfully synthesized from the elements using a reaction method, which incorporates a mechanochemical reaction using high-impact ball milling. Mechanically-activated, self-sustaining reactions (MSR) were observed while milling the elements together to form these compounds. After the MSR, the Ba-122 phase had formed, the powder had an average grain size < 1 {\mu}m, and the material was effectively mixed. X-ray diffraction confirmed Ba-122 was the primary phase present after milling. Heat treatment of the K-doped MSR powder at high temperature and pressure yielded dense samples with high phase purity but only granular current flow could be visualized by magneto optical imaging. In contrast, a short, low temperature, heat treatment at ambient pressure resulted in global current flow throughout the bulk sample even though the density was lower and impurity phases were more prevalent. An optimized heat treatment involving a two-step, low temperature, heat treatment of the MSR powder produced bulk material with very high critical current density above 0.1 MAcm-2 (4.2 K, 0 T).