The degradation of MgB2 under ambient environment

TL;DR

This study investigates how MgB2 superconductors degrade in ambient environments, revealing that surface decomposition and grain connectivity influence stability, with well-sintered samples showing notable resistance to degradation.

Contribution

The paper provides new insights into the degradation mechanisms of MgB2, highlighting the role of surface chemistry and sample preparation methods in stability under ambient conditions.

Findings

Degradation involves surface oxidation and formation of Mg hydroxide.

Poorly connected and smaller grain samples degrade faster.

Well-sintered samples remain stable for several months.

Abstract

The superconductivities of samples prepared by several procedures were found to degrade under ambient environment. The degradation mechanism was studied by measuring the change of surface chemical composition of dense MgB2 pellets (prepared by hot isostatic pressure, HIPed) under atmospheric exposure using X-ray Photoelectron Spectroscopy (XPS). Results showed that samples with poor connectivity between grains and with smaller grain sizes degrade with time when exposed to ambient conditions. In these samples, the Tc did not change with time, but the superconducting transition became broader and the Meissner fraction decreased. In contrast, our well-sintered and the HIPed samples remained stable for several months under ambient condition. The degradation was found to be related to surface decomposition as observed by XPS. We observed the formation of oxidized Mg, primarily in the form of a Mg hydroxide, the increase of C and O contents, and the reduction of B concentration in the surface layer of MgB2 samples.