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ION-IRRADIATION EFFECTS IN Tl2Ca 2 Ba2Cu3OlO SUPERCONDUCTORS J. C. Barbour, J. F. Kwak, E. L. Venturini, D. S. Ginley, Sandia National Laboratories, Albuquerque, NM 87185.

and P.

S.

Peercy

The effects of oxygen and helium ion irradiation on the superconducting properties of Tl2Ca2Ba 2 Cu3OlO thin films were investigated. The transition temperature and width were monitored as a function of ion fluence using both magnetization and resistivity measurements. These data suggest that superconductivity is completely suppressed at 0.020 dpa for both He and 0 ion irradiation. Further, the rate of decrease in Tc as a function of deposited energy showed that the dominant mechanism causing damage-induced suppression of Tc in these films was from atomic collisions.

INTRODUCTION Devices made from high temperature superconducting (HTSC) thin films depend on patterning techniques to control electrical transport properties. The Tl 2 Ca 2 Ba 2 Cu 3 O1 0 phase (TI-2223) has the highest transition temperature 2 5 [1] (Tc up to 110 K) and critical current density (2] (Jc up to 6x10 A/cm at 76 K) of the polycrystalline thin film HTSCs, and is therefore a good candidate for device quality material. Whereas true epitaxial Y-123 films on 2 (001) SrTiO3 have [3] Jc values >106 A/cm at 76 K, the more easily grown polycrystalline Y-123 films have Jc's which are much lower. The lower Jc is usually due to the disruption of the superconducting phase by impurities and defects at the grain boundaries, a problem which is apparently less severe for the Tl-based films. Grain misalignments can present a fundamental limitation on Jc for polycrystalline HTSC films, but the ultimate severity of this limit is not clear [4]. Reports on the irradiation of Y-123 films have shown that displacements by elastic collisions, rather than ionization, are predominantly responsible for the irradiation-induced decrease in the room temperature conductivity [5]. Therefore, we have begun a study using conventional ion implantation technology to investigate the effects of ion-irradiation on polycrystalline Tl-2223 thin films. The objective of this study is threefold: 1) to understand the damage mechanism in TI-2223 (atomic collisions vs. ionization effects), 2) to characterize the parameters (ion species, fluences, and energies) which are useful for patterning devices, and 3) to investigate the use of ion-beam damage for creating fluxoid pinning centers. Our previous work [6) showed the useful limits of oxygen ion irradiation for control of Tc in Tl-2223 films. Superconductivity, as determined from resistivity measurements, was suppressed for a level of deposited energy between 0.014 and 0.028 dpa. The present study extends that investigation to lighter He ions.

EXPERIMENT The samples were highly oriented (c-axis normal to the substrate) polycrystalline Tl-2223 films on (001) SrTiO3 . The films were deposited by sequential electron beam evaporation of the metals in an 02 overpressure of 5 Ixl0" mbar. Then the samples were sintered in air for 15 minutes at 850°C, and