Impurities and defects of high-Jc YBa2Cu3Ox superconductor with flux jumps

The microstructures of a highly textured bulk YBa2Cu3 (123) superconductor, with the high-transport Jc (≥ (R18)3.7x104 A/cm2 at 77 K) and flux jumps (T<15 K), were characterized by x-ray diffraction, polarized optical microscopy, scanning electron microscopy, and scanning transmission electron microscopy. It was found that the grains of the 123 superconductor are preferentially oriented along the a-b plane of the 123 phase. The Y2BaCuO5 and CuO particles are dispersed uniformly in the 123 matrix, and the highly dense twins run through the matrix everywhere. Some irregular-shaped BaCuO2-CuO mixtures were observed at the 123 grain boundaries. The aligned 123 crystals and microstructural defects in the 123 matrix are considered to be responsible for the high-Jc value and flux jumps