Positron lifetime studies of 100-MeV oxygen irradiated Pb-doped Bi-2223 superconductors

Positron lifetime studies have been carried out for unirradiated and 100-MeV oxygen ion irradiated Pb-doped Bi-2223 superconductors. The analysis of positron lifetime spectra revealed three lifetime components: a short lifetime, τ1=153–196 ps; an intermediate lifetime, τ2=269–339 ps; and a long lifetime, τ3=616–812 ps. A decrease in all the lifetime components, τ1, τ2 and τ3 with an increase of the relative intensities of I2 and I3 has been observed with increasing fluence. The positron lifetime results obtained are contradictory to the expected trend for the irradiated samples. This variation has been attributed to the formation of cationic clusters and their segregation at the grain boundaries; and probably in between the Bi–O planes too, where the positron density distribution is a maximum. This is highly possible since the metal atoms have a fair chance to get displaced from their original positions as a result of swift heavy ion irradiation. The growth of the Bi-2212 phase with irradiation supports the positron lifetime results.