Structures and effects of radiation damage in cuprate superconductors irradiated with several-hundred-mev heavy ions

Abstract

This paper reports a study of the nature and systematic variation of radiation damage to cuprate superconductors caused by several-hundred-MeV heavy ions. While irradiation of YBa₂Cu₃O_7-δ with 300-MeV Au²⁴⁺ and 276-MeV Ag²¹⁺ ions produces columns of amorphous material along the ion trajectories, such defects are only created occasionally during irradiation with 236-MeV Cu¹⁸⁺ and not induced with 182-MeV Si¹³⁺. A comparative study of the defect formation in Bi₂Sr₂Ca₂Cu₃O_x and oxygen-reduced and ozone-treated YBa₂Cu₃O_7-δ, shows that the degree of the radiation damage by the heavy ions depends on (a) the rate at which ions lose their energy in the target; (b) the crystallographic orientations with respect to the incident ion beam; (c) thermal conductivity and chemical state (oxygen concentration for YBa₂Cu₃O_7-δ) of the sample; and (d) the extent of preexisting defects in the crystal. A theoretical model based on ion-induced localized melting and the effects of anisotropic thermal conductivity of these materials provides a basis for understanding the size and shape of the amorphous tracks. Measurements of the superconducting properties of Au²⁴⁺-and Ag²¹⁺-irradiated YBa₂Cu₃O_7-δ thin films show a universal linear scaling between the fractional areal damage versus the superconducting transition temperature and the normal-state resistivity.