Flux Pinning by BaCeO₃ Nanoparticles in Single-Grain YBCO Superconductors

The current study explores the effect of adding BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles to Y-Ba-Cu-O (YBCO) composites, synthesized by the infiltration and growth process (IGP). BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles synthesized using a wet-chemical method are added in two ways: directly to Y<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>BaCuO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (Y-211) preform (set A) and indirectly through infiltrated liquid phase by adding to the YBa<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>Cu<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-</sub><italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_δ</i> (Y-123) source pellet (set B). The sol-casting technique was used for the uniform distribution of nanoparticles in the precursor powders by polymerization. Further processing of the preform pellets of composites by IGP led to single-grain growth in the composites, except at the highest (1 wt.%) BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> content (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i>) in set A. It has been observed through detailed magnetization and microstructural studies that the addition of BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles enabled interesting effects on the flux pinning landscape within the material. A systematic reduction in Y-211 particle size in both cases (sets A and B) indicates that BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles react and refine the Y-211 phase significantly. Fishtail effect was observed at moderate concentrations and the optimum content of 0.5 wt.% BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> addition enabled to achieve best critical current density and pinning force density at two studied temperatures of 50 and 77 K. Performance observed at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> = 1 wt.% BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> addition in set B is similar to that of 0.5 wt.% sample in set A. This shows that the properties are generally governed by the final BaCeO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> content present in the YBCO matrix. A study of flux pinning mechanisms suggests point pinning at low <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i>, whereas <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">δk</i> pinning is operative at medium <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i>, where the fishtail effect is observed. Higher concentrations (1 wt.%) limited the single-grain growth, leading to a very broad diamagnetic transition and deteriorated the superconducting properties within the samples.