Formation mechanism of BaZrO3 nanoparticles in Y1−xSmxBa2Cu3Oy-coated conductors derived from trifluoroacetate metal–organic deposition

Abstract

Grains of BaZrO3 (BZO) in REBa2Cu3Oy (REBCO) films exhibit microstructural differences, depending on whether they weredeposited by pulsed-laser deposition (PLD) or metal–organic deposition (MOD). In orderto understand the origins of these differences, we examined the formation mechanism ofBZO nanoparticles in the MOD process with detailed observations of the quenchedfilms by transmission electron microscopy. The BZO nanoparticle was found toform in the precursor during the temperature ramp prior to the formation of theY1−xSmxBa2Cu3Oy (YSmBCO) crystals. The YSmBCO grew layer by layer while entrapping the BZOparticles, which resulted in random dispersion of the BZO particles in the YSmBCO layer.Consequently, uniformly dispersed BZO nanoparticles were formed in the YSmBCO matrixderived from the TFA-MOD process. These findings indicate that a key factor in achievingfine dispersion of BZO nanoparticles in the superconducting matrix is strongly related tonucleation 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-coatedconductors with uniformly dispersed and densely concentrated BZO nanoparticlesshowed striking isotropic magnetic-field angular dependence of critical currents.