Positron annihilation study of the high-Tc (Bi,Pb)2Sr2Ca2Cu3Ox superconductor

Positron lifetime spectroscopy (PLS) and positron Doppler-broadening spectroscopy (PDBS) were applied to the high-Tc lead-doped Bi2Sr2Ca2Cu3Ox (BPSCCO 2223) superconductor as a function of temperature. Neither positron lifetimes nor Doppler parameters ( S, W, and S W ) showed significant change through Tc. This may result from having the highest positron density in the open BiO2 double layers and no significant positron density in the superconducting CuO2 layers where positrons, if mainly present, are known to be sensitive to the transition in other high-Tc superconductors. Doppler parameters showed that the probability of positron annihilations with core electrons in the lattice slightly increased and that the probability of positron annihilations with conduction electrons slightly decreased as temperature decreased from ambient temperature to 20 K. The lifetime associated with positron annihilations in the perfect lattice of the sample (τ1) was 209 ps and, due to the annihilations at internal surfaces or voids in the sample (τ2) was about 540 ps, independent of temperature. Finally, the mean lifetime for BSCCO 2223 was about 307 ps.