Effects of ambient and humidity exposure on the MgB 2 superconductor

Abstract

Exposure effect of ambient (up to a period of 465 days) and humid atmosphere on stability and the physical properties of bulk samples of MgB 2 has been carried out based on ac-susceptibility and X-ray diffraction measurements performed at different times during the aging. The motivation of this study came from the device application potential of MgB 2 superconductor. It has been observed that on initial exposure to ambient for a period of about 2 months, the MgB 2 samples neither show any sign of phase decomposition nor any significant degradation of superconducting parameters. However, on further exposure to ambient for a period greater than 4 months duration, the samples progressively exhibited the partial conversion of MgB 2 phase into Mg-deficient phases, viz., MgB 6 and MgB 12 and also leading to formation of Mg(OH) 2 which is accompanied by decrease in the T C and poor connectivity of the superconducting grains. When exposed to humid environment for a period of 30 days, a significant degradation was observed in the superconducting properties of MgB 2. In sharp contrast to the case of ambient exposure, the exposure of MgB 2 to humid atmosphere (for 30 days) did not result in any noticeable phase decomposition. A comparison of the magnetically inferred critical current density behavior before and after the humidity exposure of MgB 2 is also presented.