Structural Changes and Annealing Behavior of Ar-Ion-Irradiated Superconducting BiSrCaCuO Thin Films

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Abstract
Superconducting mixed phase BiSrCaCuO thin films containing mainly the low-T c phase were irradiated with 100 keV Ar ions up to 4×1017 ions/cm2 at 10 K or 300 K and were subsequently annealed below 800°C. The irradiated thin film was considered to consist of a heavily damaged surface layer and an underlying partially displaced crystalline layer. X-ray diffraction studies showed that a specific phase transformation occurs during postannealing at relatively low temperatures, 700-730°C, i.e., irradiated layer→high-T c (2223) phase+Ca-free (2201) phase. The high-T c phase ratio and the T c of the films were markedly improved by an Ar ion dose of 2×1016 ions/cm2 at 10 K, prior to the low temperature annealing. Preirradiation at 10 K was more effective for improving superconducting properties of the films than preirradiation at 300 K.