Enhancement of critical current density of YBa 2Cu 3O 7 − δ thin films by self-assembly of Y 2O 3 nanoparticulates

Abstract

YBa 2Cu 3O 7 − δ (YBCO) thin films, possessing high critical current density ( J c), have been synthesized by embedding a homogeneous array of Y 2O 3 non-superconducting nanoclusters/nanoparticles using a pulsed laser deposition technique. The size, interparticle spacing, and density of Y 2O 3 nanoparticles in YBCO thin films were tailored by varying the number of laser pulses in order to determine the optimum size for effective immobilization of vortices. Scanning transmission electron microscopy with atomic number contrast and X-ray diffraction techniques were used to determine the size and structure of the nanoparticles. Both techniques indicate that the Y 2O 3 particles are epitaxial with respect to the surrounding YBCO matrix. The information about pinning of vortices by the nanoparticles was obtained by investigating the behavior of critical current density as a function of temperature and applied field, which in turn determines the vortex density in the sample. The superconducting transition temperature ( T c) of YBCO films with the inclusion of nanoparticles was observed to remain almost the same or decrease marginally (1–2 K) with respect to T c of pure YBCO films deposited under identical conditions. However, J cs of YBCO films embedded with self-assembled nanoparticles were found to be significantly higher than that of pure YBCO films. The J c enhancement was up to five times in high magnetic field, which is a key requirement for practical application of high- T c materials.