Different regions of fluctuation conductivity in unirradiated and alpha-irradiated Bi2Sr2CaCu2O8+δ and (Bi,Pb)2Sr2CaCu2O8+δ superconductors

• Published in: Physica. C, Superconductivity Superconductivity, 2000-10, Vol.339 (2), p.113-119
• Main Authors: De, Udayan, Mandal, K, Sanyal, D, Majumdar, C.K
• Format: Article
• Language: English
• ISSN: 0921-4534
• DOI: 10.1016/S0921-4534(00)00337-3

Radiation damage in Bi-2212 and (Bi0.92Pb0.17)-2212 superconducting pellets due to irradiation by 40 MeV He++-beam has been studied, as these two compounds differ with respect to lattice strain in their Bi-O and (Bi,Pb)-O layers. These samples were prepared with excess O that accounts for their lowered Tc of 59.5 and 64.5 K, resp. Irradiation to 8.14x1015 He++/cm2 raised Tc by 4.5 and 5.5 K, resp., and also their normal state resistivities. Excess conductivity analysis for the unirradiated and irradiated samples showed (i) a transition of the conductivity fluctuation from 2-D (lambda=1.0) to 3-D (lambda=0.5) behavior, on cooling across a temperature T0, and (ii) also the signature (lambda=3.0) of critical fluctuations in a network of superconducting microregions, for temperatures below Tcr, where Tcr is 5-10 K lower than T0. The rise in Tc has been explained from irradiation-induced removal of O taking the hole concentration towards the value for the peak in Tc. 18 refs.