Transport critical current in electron and ion irradiated sintered samples of YBa2Cu3O7

Polycrystalline samples of YBa2Cu3O7 were irradiated by 2.5 MeV electrons at low temperature and by 155 MeV oxygen ions at room temperature. The evolutions of critical temperature Tc, resistivity and transport critical current jc were followed as a function of particle fluences and, in the case of electron irradiation, annealing temperatures. It is shown that decrease rates of Tc can be well described in terms of the number of atomic displacements in these two irradiations. We find experimental conditions which lead to an increase of jc by respectively 5 % and 16 % for electron and O irradiation. In the latter case, the increase of jc is accompanied by a reduction in the resistivity of the sample. We show that the presence of grain boundaries plays a role in these phenomena which are due to mobile irradiation-induced defects. Whereas the resistance increase is found to be only due to the damage of intragrain properties for electron irradiation, modification of grain boundaries seems to contribute to the resistance increase after 155 MeV O irradiation.