Microstructure and Flux Pinning of Reacted-and-Pressed, Polycrystalline Ba0.6K0.4Fe2As2 Powders

Abstract

The flux pinning properties of reacted-and-pressed Ba0.6K0.4Fe2As2 powder were measured using magnetic hysteresis loops in the temperature range 20 K ≤ T ≤ 35 K. The scaling analysis of the flux pinning forces ( F p = j c × B , with j c denoting the critical current density) following the Dew-Hughes model reveals a dominant flux pinning provided by normal-conducting point defects ( δ l -pinning) with only small irreversibility fields, H irr , ranging between 0.5 T (35 K) and 16 T (20 K). Kramer plots demonstrate a linear behavior above an applied field of 0.6 T. The samples were further characterized by electron backscatter diffraction (EBSD) analysis to elucidate the origin of the flux pinning. We compare our data with results of Weiss et al. (bulks) and Yao et al. (tapes), revealing that the dominant flux pinning in the samples for applications is provided mainly by grain boundary pinning, created by the densification procedures and the mechanical deformation applied.

Visualization of the grain structure in high-performance Ba1−x K x Fe2As2 superconducting tapes

“…Due to the outstanding features of EBSD, the application has experienced rapid acceptance in the investigation of superconducting materials in recent years. The EBSD technique has been adopted to analyze and view the grain structure, grain size, and grain boundary in Nb 3 Sn multifilament, Bi2212 and Bi2223 wires, MgB 2 bulks and polycrystalline Ba-122 reacted-and-pressed powders [26][27][28][29], and these results can help researchers better understand the microstructure of superconductors.…”