The influence of structural defects on intra-granular critical currents of bulk MgB2

TL;DR

This study investigates how structural defects, specifically Mg(B,O)2 precipitates formed during slow cooling, enhance the intra-granular critical current density in bulk MgB2 by acting as flux pinning centers.

Contribution

It demonstrates that controlled synthesis conditions induce nanometer-sized precipitates that improve flux pinning and critical current density in MgB2.

Findings

Nanometer-sized Mg(B,O)2 precipitates act as flux pinning centers.

Slow cooling promotes oxygen segregation and precipitate formation.

Enhanced critical current density observed due to precipitates.

Abstract

Bulk MgB2 samples were prepared under different synthesis conditions and analyzed by scanning and transmission electron microscopy. The critical current densities were determined from the magnetization versus magnetic field curves of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow cooling process, the oxygen dissolved in bulk MgB2 at high synthesis temperatures can segregate and form nanometer-sized coherent precipitates of Mg(B,O)2 in the MgB2 matrix. Magnetization measurements indicate that these precipitates act as effective flux pinning centers and therefore significantly improve the intra-grain critical current density and its field dependence.