Presentation Information
[WBP2-24]Magnetically bi-axial aligned Dy123 superconducting ceramics by colloidal process
*Futo Fukuyama1, Tohru S. Suzuki2, Shintaro Adachi1, Fumiko Kimura1, Noriyuki Hirota2, Tetsuo Uchikoshi2, Shigeru Horii1 (1. Kyoto University of Advanced Science (Japan), 2. National Institute for Material and Science (Japan))
Keywords:
RE123,Magnetic alignment,colloidal process
[Introduction]
To achieve the high critical current densities (Jc) of REBa2Cu3Oy (RE123) superconductors (SCs) for practical use, bi- or tri-axial grain alignment and densification are essential. The thin film epitaxial growth technology is used for the production of RE123 coated conductors with high Jc. However, the thickness of the RE123 layer has the order of microns and material cost of the coated conductors is very high. Our group focuses on the magnetic alignment technique to improve critical current by fabricating the thick RE123 films (> 100 µmt) with biaxially aligned microstructures. Biaxial alignment of RE123 grains with twinned microstructure has been achieved under the modulated rotating magnetic field (MRF) of a solenoidal SC magnet (SC-MRF) and linear drive type MRF (LDT-MRF) in an epoxy resin . As the next step, in this study, the fabrication of the magnetically biaxial aligned Dy123 ceramics is attempted.
[Experimental method]
Dy123 (y ~ 7) polycrystals were synthesized by the standard solid-state reaction and oxygen annealing. Incidentally, the average particle size is ~ 0.5 μm. Dispersant (polyethyleneimine, 1 wt%, PEI) was mixed with the butanol. Then, the binder (Hydroxypropyl Cellulose H type, HPC-H) and fined Dy123 powder (5 – 15 vol%) were added to the mixture of butanol and PEI, and were mixed thoroughly. Prepared Dy123 colloidal solutions were dried in a mold under LDT-MRF with ambient pressure. The magnetically aligned green compacts were sintered at 900 – 950℃ in air and annealed in flowing O2 gas. The microstructures of the green compact and the ceramic were observed by SEM. Degrees of bi-axial orientation of the magnetically aligned Dy123 ceramics were determined from (103) pole figure measurements. Magnetic Jc was determined by PPMS (Quantum Design, Versa Lab).
[Results and discussion]
As-casted green compact of magnetically aligned Dy123 has ~ 0.5 μm of average grain size and ~ 35% of relative density. The sintered ceramic of magnetically aligned Dy123 has ~15 μm of average grain size and ~ 80 % of relative density. This ceramic was obtained by sintering at 950℃ in air for 24 h on the green compact. On SEM image, stacking of grains with the planer shape was observed. Compared to the as-casted green compact, Dy123 grains were clearly grown by the introduction of the sintering process. The (103) pole figure of this ceramic shows clearly four-fold symmetric spots, and the FWHM value of this pole figure is ~17 deg, indicating that Dy123 grains are biaxially aligned. In this study, we will report the details of the fabrication process of Dy123 ceramics using the colloidal process and the change in Jc on the bi-axial aligned Dy123 ceramics with LDT-MRF as functions of relative density and bi-axial orientation degrees on the biaxial aligned Dy123 ceramics with LDT-MRF.
To achieve the high critical current densities (Jc) of REBa2Cu3Oy (RE123) superconductors (SCs) for practical use, bi- or tri-axial grain alignment and densification are essential. The thin film epitaxial growth technology is used for the production of RE123 coated conductors with high Jc. However, the thickness of the RE123 layer has the order of microns and material cost of the coated conductors is very high. Our group focuses on the magnetic alignment technique to improve critical current by fabricating the thick RE123 films (> 100 µmt) with biaxially aligned microstructures. Biaxial alignment of RE123 grains with twinned microstructure has been achieved under the modulated rotating magnetic field (MRF) of a solenoidal SC magnet (SC-MRF) and linear drive type MRF (LDT-MRF) in an epoxy resin . As the next step, in this study, the fabrication of the magnetically biaxial aligned Dy123 ceramics is attempted.
[Experimental method]
Dy123 (y ~ 7) polycrystals were synthesized by the standard solid-state reaction and oxygen annealing. Incidentally, the average particle size is ~ 0.5 μm. Dispersant (polyethyleneimine, 1 wt%, PEI) was mixed with the butanol. Then, the binder (Hydroxypropyl Cellulose H type, HPC-H) and fined Dy123 powder (5 – 15 vol%) were added to the mixture of butanol and PEI, and were mixed thoroughly. Prepared Dy123 colloidal solutions were dried in a mold under LDT-MRF with ambient pressure. The magnetically aligned green compacts were sintered at 900 – 950℃ in air and annealed in flowing O2 gas. The microstructures of the green compact and the ceramic were observed by SEM. Degrees of bi-axial orientation of the magnetically aligned Dy123 ceramics were determined from (103) pole figure measurements. Magnetic Jc was determined by PPMS (Quantum Design, Versa Lab).
[Results and discussion]
As-casted green compact of magnetically aligned Dy123 has ~ 0.5 μm of average grain size and ~ 35% of relative density. The sintered ceramic of magnetically aligned Dy123 has ~15 μm of average grain size and ~ 80 % of relative density. This ceramic was obtained by sintering at 950℃ in air for 24 h on the green compact. On SEM image, stacking of grains with the planer shape was observed. Compared to the as-casted green compact, Dy123 grains were clearly grown by the introduction of the sintering process. The (103) pole figure of this ceramic shows clearly four-fold symmetric spots, and the FWHM value of this pole figure is ~17 deg, indicating that Dy123 grains are biaxially aligned. In this study, we will report the details of the fabrication process of Dy123 ceramics using the colloidal process and the change in Jc on the bi-axial aligned Dy123 ceramics with LDT-MRF as functions of relative density and bi-axial orientation degrees on the biaxial aligned Dy123 ceramics with LDT-MRF.