Temperature dependent microstructural modification in ion-irradiated Tl-type high temperature superconductors

Abstract

Ion irradiation damage creation and recovery were examined in Tl-based high temperature superconductors, HTSC, using TEM, resistivity, and magnetic measurements for irradiation temperatures of 20 to 650 K. During 1.5 MeV Kr + and Xe + ion irradiations of single-crystal Tl-1212 and Tl-1212 TlBaCaCuO HTSC, microstructural modification was observed in situ by electron diffraction and shows a remarkable temperature dependence. At selected sample temperatures, irradiations continued until a critical fluence, D c, was reached where the original structure disappeared. The temperature dependence of D c shows a minimum near the superconducting transition temperature, T c, and is correlated with the temperature dependence of the thermal conductivity, which has a maximum near T c. At an irradiation temperature near this maximum in thermal conductivity, a minimum amount of damage recovery occurs because heat can be dissipated away from the displacement cascade. Ion irradiation 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 +, O 2+, Au 5+ which shows that the damage 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 magnetization measurements, indicating that the displacements effect the bulk of the samples through point defect creation. An activation energy of 0.4 eV for ion irradiation damage recovery over the temperature range from 100 to 650 K was determined from normal state resistance versus time immediately after irradiation.