Formation mechanism of BaZrO₃nanoparticles in Y_1−<i>x</i>Sm_<i>x</i>Ba₂Cu₃O_<i>y</i>-coated conductors derived from trifluoroacetate metal–organic deposition

Abstract

Grains of BaZrO3 (BZO) in REBa2Cu3Oy (REBCO) films exhibit microstructural differences, depending on whether they were deposited by pulsed-laser deposition (PLD) or metal–organic deposition (MOD). In order to understand the origins of these differences, we examined the formation mechanism of BZO nanoparticles in the MOD process with detailed observations of the quenched films by transmission electron microscopy. The BZO nanoparticle was found to form in the precursor during the temperature ramp prior to the formation of the Y1−xSmxBa2Cu3Oy (YSmBCO) crystals. The YSmBCO grew layer by layer while entrapping the BZO particles, which resulted in random dispersion of the BZO particles in the YSmBCO layer. Consequently, uniformly dispersed BZO nanoparticles were formed in the YSmBCO matrix derived from the TFA-MOD process. These findings indicate that a key factor in achieving fine dispersion of BZO nanoparticles in the superconducting matrix is strongly related to nucleation of the BZO phase crystals in the precursor before growth of the YSmBCO layer, which is unique to the MOD process. In subsequent testing, YSmBCO-coated conductors with uniformly dispersed and densely concentrated BZO nanoparticles showed striking isotropic magnetic-field angular dependence of critical currents.