2, Shanghai Superconductor Technology Corporation, Shanghai, , China
REBCO superconducting tapes with different oxide nanoparticle additions have been fabricated on IBAD/MgO tapes by pulsed laser deposition process (PLD). For stoichiometric (123) REBCO films, it was found that when REBCO film thickness was smaller than 1.0 micrometer, REBCO superconducting films had a high critical current density Jc of 5.0x106 A/cm2 (at 77 K, self magnetic field) . As REBCO film thickness increased over 1.0 micrometer, the Jc values of REBCO films decreased with increasing of REBCO film thickness. X-ray diffraction (XRD) and high resolution scanning electron microscope (SEM) observation showed that a-axis orientation was easily formed in thick REBCO films. At higher substrate temperatures, BaCuO3 particles were also found in REBCO films. The main reason for lower Jc of REBCO thick films was broad grain boundaries. SEM and AFM observations showed that thick REBCO films had micrometer-scale grains and relatively broad grain boundaries which blocked superconducting current paths. In order to control the grain size and grain boundary width of REBCO thick films as well as to improve in-field superconducting properties, Y2O3, BaHfO3 and BaZrO3 addition effects were investigated. AFM, SEM and TEM images showed the presence of nano-scale Y2O3, BaHfO3, and BaZrO3 oxide particles in REBCO superconducting film. During deposition, these nanoparticles on REBCO film surface changed REBCO epitaxial growth process and acted as new crystal nucleus. By adding oxide nanoparticles into REBCO films, not only in-field superconducting properties but also surface morphology of REBCO films were obviously improved, which makes the growth of REBCO thick films to be easier. Four probe I-V curve measurements showed REBCO tapes with artificial pinning centers had excellent in-field performance. For 1.0 cm wide tapes, Ic was over 1000A (4.2K and 12T, H//c).