TEMPERATURE-DEPENDENT MICROSTRUCTURAL MODIFICATION IN ION-IRRADIATED TL-TYPE HIGH-TEMPERATURE SUPERCONDUCTORS

Ion irradiation damage creation and recovery were examined in TI-based high temperature superconductors, HTSC, using TEM, resistivity, and m agnetic measurements for irradiation temperatures of 20 to 650 K. Duri ng 1.5 MeV Kr+ and Xe+ ion irradiations of single-crystal Tl-1212 and Tl-2212 Tl-Ba-Ca-Cu-O HTSC, microstructural modification was observed in situ by electron diffraction and shows a remarkable temperature dep endence. At selected sample temperatures, irradiations continued until a critical fluence, D-c, was reached where the original structure dis appeared, The temperature dependence of D-c shows a minimum near the s uperconducting transition temperature, T-c, and is correlated with the temperature dependence of the thermal conductivity, which has a maxim um near T-c. At an irradiation temperature near this maximum in therma l conductivity, a minimum amount of damage recovery occurs because hea t can be dissipated away from the displacement cascade, Ion irradiatio n suppresses the T-c. The rate of decrease in the T-c as a function of damage (measured in displacements per atom, dpa) was found to be the same for various incident ions (He+, O2+, Au5+ which shows that the da mage accumulation is a result of atomic collisions. Further, the rate of decrease in T-c was found to be the same for both transport and mag netization measurements, indicating that the displacements effect the bulk of the samples through point defect creation, An activation energ y of 0.4 eV for ion irradiation damage recovery over the temperature r ange from 100 to 650 K was determined from normal. state resistance ve rsus time immediately after irradiation.