Irradiation effects in high temperature superconductors

Irradiation effects on T1- and Y-based high temperatures superconductors (HTS) are compared. Ion irradiation can enhance the critical current density (Jc) at low fluences through the interaction of defects with the flux lattice, and at higher fluences ion irradiation can degrade the superconducting transition temperature (Tc) and increase the normal state resistivity (ρ). Low-fluence irradiation of T12Ca2Ba2Cu3O10 (T1-2223) single crystals was shown to increase Jc by an order of magnitude over Jc for unirradiated crystals. Similarly, irradiated YBa2Cu3O7-δ (YBCO) crystals have increased by factors of 2 to 100; however the effects of irradiation on thin-film HTS from these two materials depends greatly on their crystalline quality. Ion irradiation of millimeter grain-size T1-2223 films was shown to increase Jc while similar irradiation of ∼10 μm grain-size T1-2223 films had little effect on Jc. For ions with energies less than ∼MeV/amu, the dominant mechanism causing irradiation-induced degradation of Tc is collisional damage. Both T1-based and YBCO superconductors behave similarly in that Tc decreases linearly with the level of damage; yet, the rate of decrease in Tc for T1-based superconductors (5000 K/dpa) was approximately twice that for irradiated YBCO. An examination of the temperature behavior and rate of damage recovery of ρ yielded an activation energy of 0.36 eV for annealing defects. 31 refs., 7 figs., 1 tab