Enhancement of Critical Current Density by Establishing a YBa2Cu3O7−x/LaAlO3/YBa2Cu3O7−x Quasi-Trilayer Architecture Using the Sol-Gel Method

We developed a solution-derived method to establish a YBa2Cu3O7-x/LaAlO3/YBa2Cu3O7-x 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 (J(c)) of high-quality YBa2Cu3O7-x (YBCO). The improvement in the in-field J(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 YBa2Cu3O7-x surface, the LaAlO3 interlayer is discontinuous due to synchromesh-like growth of the LaAlO3 layer on relatively rough YBa2Cu3O7-x 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 YBa2Cu3O7-x layers. These nanoscale defects could play a role in flux pinning and thus enhancing J(c). The effective non-vacuum solution to induce vortex pinning into YBa2Cu3O7-x films could be a reference for the further design of an optimal pinning landscape for higher J(c).