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In the context of high temperature superconductors, pulsed laser deposition derived GdBa2Cu3O7-δ sample with BaHfO3 nanoparticles has been reported to achieve high current density and good IC-B-θ characteristics at high temperatures. Herein, we have carried out a thorough nanostrucural characterization of BaHfO3 nanoparticles embedded in GdBCO matrix using scanning transmission electron microscopy, with an emphasis on the dispersion behavior, morphologies and nanostrain, to understand the role of BaHfO3 nanoparticles.
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IntroductionSince the discovery of REBa2Cu3O7-y (RE: Rare Earth element, REBCO) superconductors, they have been expected as the best candidates for the power cable application due to its high critical temperature (Tc) and critical current density (Jc). Among those REBCO superconductors, GdBa2Cu3O7-y (GdBCO) have been receiving great interest because they have higher Tc and Jc than YBa2Cu3O7-y [1].GdBCO with various types of precipitates as artificial pinning centers (APCs) have been proposed to minimize the anisotropy of Jc characteristics under the magnetic field. Among those precipitates, BaHfO3 (BHO) was found most effective precipitates as APCs in GdBCO film prepared by pulsed laser deposition (PLD) method [2]. It is therefore necessary to investigate not only the morphologies but also the dispersion of BHO precipitates within the GdBCO, to understand the role of BHO for the superconducting characteristics. In this study, morphologies and dispersions of BHO precipitates were characterized three-dimensional by scanning transmission electron tomography ExperimentalBHO dispersed GdBCO films were fabricated on Hastelloy C-276TM substrates with buffer layers of CeO2/LaMnO3/MgO/ Gd2ZrO7 by PLD method.To observe microstructure of GdBCO film with BHO precipitates, cross-section TEM specimens were prepared by FIB method using Quanta 3D-200 (FEI, USA) with acceleration voltage from 2 to 30 kV. Three-dimensional information such as morphology and dispersion, of BHO precipitates were characterized by electron tomography using STEM-HAADF. Result and discussionFigure 1 shows three-dimensional reconstructed volume of BHO precipitates in GdBCO, which revealed that fine BHO precipitates have rod- and plate-like morphologies with homogeneous dispersion in GdBCO. In addition, growth directions of these precipitates were found with wide angular distributions from growth direction of GdBCO. Anisotropy of Jc in the magnetic fields was probably enhanced by various growth directions and homogeneous dispersion of nanosized BHO within GdBCO.jmicro;63/suppl_1/i26/DFU080F1F1DFU080F1Fig. 1.Three-dimensional reconstructed volume of BHO.
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Y(1-x)Gd(x)Ba2Cu3O(7-y) with BaZrO3 film was fabricated on CeO2 buffered LaMnO3/ion beam assisted deposition-MgO/Gd2Zr2O7/Hastelloy C276TM substrates by the metal organic deposition process using trifluoroacetates. Both microstructural and analytical characterizations were performed by transmission electron microscopy with selected area electron diffraction method and energy dispersive X-ray spectroscopy. The thickness of Y(1-x)Gd(x)Ba2Cu3O(7-y) with BaZrO3 film was found approximately 700 nm and the film was composed of c-axis oriented Y(1-x)Gd(x)Ba2Cu3O(7-y) grains. Several types of particles, (Y,Gd)2Cu2O5, CuO and BaZrO3, were formed within the Y(1-x)Gd(x)Ba2Cu3O(7-y) film, whose sizes were about 100-200 nm for (Y,Gd)2Cu2O5 and CuO particles, and about 10-20 nm for BaZrO3 particles, respectively. In the Y(1-x)Gd(x)Ba2Cu3O(7-y) film, (Y,Gd)2Cu2O5 and CuO particles were dispersed heterogeneously, whereas BaZrO3 nanoparticles were found dispersed homogeneously with random orientation. In addition, electron tomographic observation was carried out to attain the three-dimensional information of polyhedral BaZrO3 nanoparticles.
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Crystals of the title compound, samarium barium copper oxide, were prepared by a modified top-seeded solution-growth method. The crystals thus prepared showed no superconductivity down to 4.2 K. A careful examination showed that the structure closely resembles that of tetragonal YBCO, and there is no atom mixing at the Ba or other sites, within experimental accuracy. A bond-valence-sum calculation at the Ba site also indicated the absence of Sm. Each site is fully occupied by a single atom, except for the oxygen site in the basal plane of the CuO(6) octahedron. The occupancy of this oxygen site is significantly reduced [0.13 (2)], as is commonly observed in the 123 system. The atomic displacement parameters of the atoms in the CuO(2) plane, as well as of the Sm atom, are very small, indicating that two equivalent CuO(2) planes tightly sandwich the Sm atom.
