Enhancement of Critical Current Density by Establishing a YBa₂Cu₃O_7−<i>x</i>/LaAlO₃/YBa₂Cu₃O_7−<i>x</i> Quasi-Trilayer Architecture Using the Sol-Gel Method

• Main Authors: Chuanbao Wu, Yunwei Wang
• Format: Article
• Language: English
• Published: MDPI AG 2019-07-01
• Series: Coatings
• Subjects: quasi-trilayer; sol-gel; flux pinning; defects
• Online Access: https://www.mdpi.com/2079-6412/9/7/437

We developed a solution-derived method to establish a YBa₂Cu₃O_{7&#8722;<i>x</i>}/LaAlO₃/YBa₂Cu₃O_{7&#8722;<i>x</i>} quasi-trilayer architecture. Using the method, nano-scale pinning sites were induced into the quasi-trilayer architecture and yielded an apparent improvement in the in-field critical current density (<i>J</i>_c) of high-quality YBa₂Cu₃O_{7&#8722;<i>x</i>} (YBCO). The improvement in the in-field <i>J</i>_c of the films was closely related to the thickness of the LaAlO₃ (LAO) interlayer. In this paper it is demonstrated that when the nominal interlayer thickness approximates 20 nm, which is slightly higher than the roughness of the YBa₂Cu₃O_{7&#8722;<i>x</i>} surface, the LaAlO₃ interlayer is discontinuous due to synchromesh-like growth of the LaAlO₃ layer on relatively rough YBa₂Cu₃O_{7&#8722;<i>x</i>} surface resulting from the mobility of the solution. Nanoscale defects, such as particles, some amorphous phases, and especially their concomitant lattice defects (such as stacking faults and plane buckling) arise in YBa₂Cu₃O_{7&#8722;<i>x</i>} layers. These nanoscale defects could play a role in flux pinning and thus enhancing <i>J</i>_c. The effective non-vacuum solution to induce vortex pinning into YBa₂Cu₃O_{7&#8722;<i>x</i>} films could be a reference for the further design of an optimal pinning landscape for higher <i>J</i>_c.