Irradiation-induced oxygen knock-out and its role in bismuth cuprate superconductors

Charged particle irradiations have been carried out on Bi-2212 and Pb-doped Bi-2223 with 40-MeV {α} particles and 15-MeV protons. The purpose was to investigate the knock-out of oxygen caused by particle irradiation and its effects on superconductivity. Studies with respect to x-ray diffraction patterns, Tc, resistivity, oxygen contents, etc., have been undertaken on samples, unirradiated as well as irradiated at various doses for comparison. A remarkable difference has been observed between Bi-2212 and Bi-2223 with respect to the irradiation-induced knock-out of oxygen. In Bi-2212, the oxygen knock-out plays a dominant role and there is an increase in Tc by particle irradiation for the sample overdoped with oxygen. On the other hand, in Bi-2223, there has been a decrease in Tc except for protons at a low dose and the knock-out of oxygen is not significant. There has been an increase in resistivity in general by irradiation. At a high dose of 1×10¹⁶α/cm², there is a change to nonmetallic behavior in resistivity with three-dimensional variable range hopping conductivity in both Bi-2212 and Bi-2223.