The evolution of properties and microstructure of Bi-2212 wires after gamma-ray irradiation

Among various high-temperature superconducting materials, Bi₂Sr₂CaCu₂O_8+x (Bi-2212) is considered as one of the most promising candidates to fabricate superconductors for magnetic confinement fusion reactors. Considering that the superconductors will be subject to irradiation in nuclear reactors, the effects of gamma-ray irradiation on the superconducting properties of Bi-2212 wires is studied in the present work. Critical current (I _c) tests have been done for Bi-2212 wires with different gamma-ray irradiation doses and the variation of I _c is correlated to the change of microstructures. During the 12 T I _c tests, the normalized I _c first rises to 1.15 then decreases to 0.89 with the increase of irradiation time. Results from x-ray diffraction, Raman spectroscopy and x-ray photoelectron spectroscopy indicate that defects are produced within the gamma-ray irradiated samples. From the images of high resolution transmission electron microscopy, amorphous structure in the gamma-ray irradiated sample is discovered as well. (paper)