Observation of coherent oxide precipitates in polycrystalline MgB2

TL;DR

This study reveals that oxygen forms ordered precipitates within MgB2, which enhance its superconducting properties by acting as pinning centers, as shown through atomic resolution imaging.

Contribution

It provides detailed atomic-scale insights into oxygen incorporation and precipitate formation in MgB2, linking microstructure to superconducting performance.

Findings

Oxygen precipitates are 20-100 nm and ordered on boron sites.

Precipitates improve critical current density and transition behavior.

Oxygen ordering occurs mainly in the (010) plane.

Abstract

Here we describe the results of an atomic resolution study of oxygen incorporation into bulk MgB2. We find that ~20-100 nm sized precipitates are formed by ordered substitution of oxygen atoms onto boron lattice sites, while the basic bulk MgB2 crystal structure and orientation is preserved. The periodicity of the oxygen ordering is dictated by the oxygen concentration in the precipitates and primarily occurs in the (010) plane. The presence of these precipitates correlates well with an improved critical current density and superconducting transition behavior, implying that they act as pinning centers.