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 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 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.