Enhancing in-field current-carrying capability through Ca-doping in BZO-doped YBCO multilayers

Abstract

This study aims to showcase the improvements of barium zirconium oxide (BZO) - doped yttrium barium copper oxide (YBCO) superconductors which can be achieved with 30% calcium-doped YBCO intermediary layers. This study also aims to explain the possible causes for these improvements as they may be useful in designing new and improved coated conductors in high temperature superconductor applications. Two sets of samples were fabricated using pulsed laser deposition. One set of samples were single layered samples with BZO concentrations ranging from 0% to 10% in 2% increments. The second set of samples were the multilayer samples, which had a Ca-doped intermediary layer between the substrate and the first YBCO layer, and another Ca-doped layer between the second YBCO layer. The multilayered sample were also made with varying BZO concentrations in the same way as the single layered samples. The YBCO thin films were analyzed using x-ray diffraction (XRD) in various measurement modes to achieve thorough information on the structural characteristics and differences the Ca-doping causes. Atomic force microscopy was also used in the structural analysis. The magnetic properties were analyzed using a physical properties measurement system to determine the critical temperature (Tc), critical magnetic field (Hc) and the critical current density (Jc) of the samples. The samples were then patterned using photolithography for further analysis into their current carrying capabilities. In the XRD measurements we found that the Ca-doping improved the crystalline quality through reduced microstrain in BZO concentrations of 2% and 4%. All multilayer samples experienced narrowing in their Δϕ and Δω values, indicating improved in-, and out-of-plane quality, respectively. Ca-doping also improved oxygen saturation in the samples, as can be seen by a decrease in the ratio between the XRD peak intensities of the (004) and (005) peaks in the 2θ-scan. Improvements in Jc were observed in almost all samples, especially those of higher BZO concentration. Overall the highest absolute Jc values were observed with Ca-doped samples of 0%BZO at low magnetic field strengths and at higher field strengths Ca-doped YBCO with 4%BZO had the highest Jc.