Effects of ambient and humidity exposure on the MgB2 superconductor

Exposure effect of ambient (up to a period of 465 days) and humid atmosphere on stability and the physical properties of bulk samples of MgB2 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 MgB2 superconductor. It has been observed that on initial exposure to ambient for a period of about 2 months, the MgB2 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 MgB2 phase into Mg-deficient phases, viz., MgB6 and MgB12 and also leading to formation of Mg(OH)2 which is accompanied by decrease in the TC 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 MgB2. In sharp contrast to the case of ambient exposure, the exposure of MgB2 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 MgB2 is also presented.