Entrapment of Y2BaCuO5 particles in melt-textured YBa2Cu3O7−δ crystals and its effect on J (original) (raw)
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Physica C: Superconductivity, 1996
A modified melt-textured-growth (MTG) method which has a relatively low working temperature and short reaction time compared with the conventional MTG method has been developed. The number of YBa2CU3OT_y (123) nuclei during the initial slow-cooling process has been minimized which leads to the enhancement of the 123 grain growth rate and a better homogenized and smaller Y2BaCuOs (211) particles over the samples. Magnetization measurement shows that the 123 crystals have a high Jc and a good performance in high magnetic fields.
Physica C: Superconductivity, 1998
Parameters affecting the nucleation and growth of a Y123 single-domained crystal were studied in top-seeded melt processing. Based on the parametric study, the two-step undercooling technique was developed. The key points techniques are the controlled nucleation of Y123 at the primary undercooling step and the accelerated growth at the secondary undercooling temperature. Optimization of the process parameters in the two-step undercooling technique considerably reduced the processing time required for the growth of the Y123 single crystal without degradation of the levitation property.
Growth of Y123 bulk crystals in Y1.5Ba2Cu3Ox system with CeO2 addition
Journal of Crystal Growth, 2012
The growth of YBCO bulk superconductors with Y 1.5 Ba 2 Cu 3 O x composition and 1 wt% CeO 2 addition was studied. It is shown that the window for isothermal growth of single-crystalline sample grown from Sm123 seed is between 988 1C and 1003 1C. At lower temperatures of this window, Y123 crystals grow with higher growth rate but the quality of crystals is worse due to the formation of steps at the growth front. The optimum temperature 996 1C is proposed at which medium growth rate and better crystal quality are obtained. The growth rates in the a-and c-direction were measured and their dependence on undercooling is demonstrated. It is also shown that the growth rate under isothermal conditions is not constant and an epitaxially grown layer is formed during furnace cooling from the temperature of isothermal growth followed by the layer of misaligned Y123 crystals. The rest of not-solidified part of the sample solidifies by spheroidal growth.
Physica C: Superconductivity, 2003
The influence of the ratio of small and large size YBa 2 Cu 3 O x (Y123) starting powders on the microstructure development in the sintered and melt-textured YBa 2 Cu 3 O 7 /Y 2 BaCuO 5 (Y211) bulk superconductors with the CeO 2 addition was studied. It was shown that Y211 low concentration regions in the microstructure of the melt-textured samples are formed due to the presence of large multigrain particles and/or agglomerates of small 123 particles in the starting Y123 powder. Moreover, it was observed that large Y211 particles in the melt-textured samples are nucleated on the surface of large Y123 grains during the sintering stage. It is suggested that the insufficient mixing of the powders with higher portion of small Y123 particles causes that the CeO 2 concentration in the sample is more inhomogeneous. Consequently the Y211 particles can locally grow during peritectic melting and temperature dwell.
Modified growth mechanism in directionally solidified YBa/sub 2/Cu/sub 3/O/sub 7/
IEEE Transactions on Appiled Superconductivity, 1995
Minute amounts of CeO2 additions have a strong effect on the solidification path, physicochemical parameters and final size distribution of Y 2BaCuO5 (21 1) precipitates of directionally solidified YBa2Cu307 (123). Inductive and transport critical currents density (Jc) measurements indicate a clear increase with Ce02 addition.
Direct observation of textured YBa2Cu3O7−δ crystal growth from the melt
Physica C: Superconductivity, 1992
The behavior and kinetics of textured growth of the YBaZCu@_d (123) compound from Y,BaCuO, (21 I) +liquid have been investigated by hot-stage optical microscopy and high-temperature x-ray diffraction methods. The formation of the 123 is found to begin in the liquid of the peritectic melt, not nucleated from 2 11 crystals as is widely assumed. The quantity of the liquid phase strongly influences the crystal growth and final morphology of the 123. Dynamic studies show that the optimum temperature for 001 orientation of 123 is 940°C on an MgO substrate. The growth rate of 123 from the melt is rapid; the rate constant was determined to be 0.526x 10m2 s-l.
Growth and Properties of Large Single Crystals of YBa2Cu3O7-d from BaCuO2/CuO Flux
Australian Journal of Physics, 1991
Large single crystals of YBa2Cu307-o have been grown using a BaCu02/CUO flux whose composition lies close to the eutectic in the Y-Ba-Cu-o phase diagram. While the largest crystals produced were '" 20x20xO• 7 mm 3 , the average size of the remaining crystals was approximately 10x10xO• 5 mm 3. These crystals, both as-grown and oxygen annealed, have been characterised using susceptibility measurements, optical and scanning microscopy and X-ray and neutron diffraction techniques.
Growth of thick YBa2Cu3O7−x single crystals from Al2O3 crucibles
Journal of Crystal Growth, 1989
The growth of large, isometric and free-standing single crystals of YBa2Cu~O7_~using a CuO-BaO self-flux is reported. Within an optimum Concentration range in the phase diagram centered around 4 at% Y. 30 at% Ba and 66 at% Cu. isometric crystals with aspect ratios between 1-10 and sizes of 5 x 5 <2 mm 3 were grown. Outside this range of favourable flux compositions thin platelets up to 8 x 8 mm2 with aspect ratios >~10 were obtained. The thickness of the isometric crystals is essentially determined by the cooling rate: 500~Lm. 1 mm and 2 mm thick crystals were obtained for cooling rates of 0.5, 0.3 and 0.1°C/h, respectively. For cooling rates <0.5°C/h the occurrence of additional crystal faces was observed which were determined as the (101) and (011) faces. At cooling rates > 30°C/h a dendritic non equilibrium morphology with a zigzag-like habit of the edge of the (001) face can he observed. Aluminum impurities arising from the Al 203 crucible have a strong influence on the crystal growth: they considerably reduce the soak time and the viscosity of the melt. The presence of Al also favours the formation of yellow-greenish needles of a new quaternary phase, YBa3AI,073.
Microstructural development of partial-melt processed YBa2Cu3O7−δ
Proceedings of the Samahang Pisika ng Pilipinas, 2002
YBa 2 Cu 3 O 6.5 (YBCO123) was synthesized, subjected to a pre-melt process, and its microstructures were characterized via SEM. The microstructural evolution was observed by pre-melting YBCO123 at the melting temperature onset of 1020°C and cooling it down with crystallization cooling rates (CR) 100, 50, 33.3, 20, 10, 5, and 2°C/hr. Microstructural development from a brittle fissured faceted phase with no defined grain boundary and densified melted features to column-like grains and biphasic grains with hexagonal grain boundaries were observed as the CR was varied from fastest to slowest CR.
Growth and characterization of Y−yPryBa2Cu3O7−x single crystals
Physica C: Superconductivity, 1991
Starting from the recently reported isothermal section of the Y-Ba-Cu-(O) system in air at 950:C the optimum compositional region allowing the growth from a homogeneous melt and a replacement of yttrium for praseodymium in Yt_:.PrrBa2Cu3OT_, single crystals was determined. Besides that the effects of crucibles during the growth and of a post-annealing modification of the oxygen stoichiometry on the resulting electric properties are reported.