Diagnostics of target inhomogeneity and influence of YBCO target oxygen content on properties of HTSC 2G samples fabricated by PLD technique

摘要

The pulsed laser deposition (PLD) targets used for HTSC 2G fabrication should be uniform and chemically suitable to make long tapes with reproducible critical properties. We investigated inner density distribution of flat YBCO targets using non-destructive neutron introscopy and tomography techniques. The methods are based on absorption of monochromatic neutron beam which is going through the specimen. In first set of targets we measured variance of material density (up to 10-25%) with maxima density located in central layer of the target body. After updating of target fabrication technology no significant density inhomogeneity were detected. The dependence of critical current of superconducting films with thickness of 300 nm deposited on sapphire substrate with appropriate buffer layers using PLD YBCO targets with various oxygen content was also investigated. Oxygen index of YBCO targets vary from 6.12 to 6.85. No significant influence of target oxygen index on critical current density of fabricated films was detected.