Superconducting properties and microstructure of electron beam irradiated MgB2 superconductors

The effect of electron beam (EB) irradiation on superconducting properties and microstructures of MgB2 bulk superconductors were investigated. At E-beam doses of 1x10(16) e/cm(2) and 1x10(17) e/cm(2), the effect of irradiation on a superconducting transition temperature (T-c) of MgB2 was weak. As a dose increases to 5x10(17) e/cm(2), T-c decreases by 0.5 K. The critical current density (J(c)) measured at 4.2 K and 20 K, and 0 T - 5 T increases slightly as exposure time increases. X-ray diffraction for the irradiation surface of MgB2 shows that the diffraction intensity of (hkl) peaks decreases proportionally as the exposure time increases. This indicates that the crystallinity of MgB2 was degraded by irradiation. TEM investigation for the irradiated sample showed distorted lattice structure, which is consistent with the XRD results. The J(c) increase and T-c reduction of MgB2 by irradiation are believed to be caused by the lattice distortion.