Balancing Structure and Performance: Optimized BZO Nanorod Doping in Ca-Interlayered YBCO Multilayers

Abstract

This study demonstrates the enhancement of critical current density over a wide temperature and magnetic field range in BZO-doped YBCO multilayer structures using a Ca-doped YBCO intermediate layer. Compared to single-layer BZO-doped YBCO films, the Ca-doped interlayer improves crystalline quality and reduces non-uniform strain, particularly at low BZO doping concentrations, and promotes better growth of BZO nanorods. Additionally, multilayering slightly increases YBCO's oxygen content across all BZO concentrations, contributing to a higher critical temperature and zero-field critical current density. Besides of this, multilayering enhances critical current density across the magnetic field range, especially at low fields and high BZO concentrations. However, the highest absolute zero-field critical current density is achieved in undoped multilayered YBCO, whereas in fields above 2 T and up to 50 K, the best performance is obtained with 4% BZO-doped YBCO layers separated by Ca-doped interlayers. At around 1 T, 2% BZO doping yields the highest critical current density. This paper also explores the possible mechanisms behind these effects, proposing that multilayering BZO-doped YBCO with a crystal structure-balancing interlayer could be key to next-generation YBCO coated conductors for high-temperature superconductor applications. Optimising the BZO concentration is crucial when tailoring YBCO compositions for different operating conditions.