Thermal investigations of reactive powder mixtures as precursors for melt-processing of YBa2Cu3O7−x (original) (raw)
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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.
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.
Fabrication of melt textured YBa2Cu3O7 samples
Cryogenics, 1994
Textured YBCO samples were produced following the partial-melt method with sample transport. Structural and compositional characterizations, performed by means of XRD and SEM/EDS, show the presence of the 123 with a small amount of 211 inclusions. The investigated samples show a non weak link behaviour in the irreversible magnetic properties at 77 K, with critical current densities Jc = 104 A/c m2 at 2 kOe.
Solid state reactions in the formation of YBa2Cu3O7−δ high Tc superconductor powders
Solid State Ionics, 1989
The synthesis of high Tc superconducting YBa2Cu307 ~ powders obtained by three different schemes has been investigated. The decomposition of metal carboxylates, mixed metal oxalates, and the conventional ceramic method of mixed oxide/carbonate are contrasted. Thermal analysis (TGA, DTA) results as well as X-ray diffraction data are used to follow the progress of the decomposition and solid state reactions leading to the formation of the required perovskite. The effect of cation mixing at the molecular level in the carboxylates and oxalates is compared to the physical mixing of coarser particles in the conventional approach. In the case of the carboxylates and mixed oxalate it is suggested that Ba and Y form a double carbonate that decomposes into barium carbonate and yttrium oxide in the progress of the reaction.
Thermal reactivity of YBa2Cu3O7-δ with Al2O3 addition in air atmosphere
Ceramics International, 2019
The high-temperature thermal reactivity of YBa 2 Cu 3 O 7-δ (Y123) compound with Al 2 O 3 addition (0.5-10 wt%) was investigated and the thermal processes were described. Experimentally obtained results showed that Al 2 O 3 firstly reacted with Y123 at temperatures far below the peritectic melting point of Y123. During this solid state reaction Al partially diffused into Y123 and formed a solid solution. Also, the formation of Al-rich complex oxides, mainly with barium, and basic secondary phases as Y 2 BaCuO 5 and CuO, was observed with increasing Al 2 O 3 content. The formation of additional secondary phases with Al 2 O 3 provoked their reactivity with Y123 or between themselves. After increasing the temperature of the powder mixtures above the peritectic melting point of Y123 it was found that Al was incorporated in Y123 at higher concentrations than during the solid state reaction. The reason for that could be a partial or full dissolution of Al-rich complex oxides formed at lower temperatures which in turn increased the source of Al for the incorporation in Y123. The thermal behaviour of powder mixtures was investigated with the help of simultaneous differential thermal analysis and thermogravimetry. Morphology and microstructure were examined using powder X-ray diffraction and scanning electron microscopy in combination with energy dispersive X-ray spectroscopy.
Study of YBa2Cu3O7−x reaction kinetics by Rietveld method
Powder Diffraction, 2001
Using a recent proposed analysis procedure for quantitative phase determination by X-ray powder diffraction, YBa2Cu3O7−x solid state formation reaction kinetics at 900 °C was studied. Although there was the presence of partial amorphous components, it was possible to determine a reaction route for the synthesis of the title compound from X-ray powder diffraction data collected at various stages of the thermal treatment and using the Rietveld method for the quantitative determination of the phase composition
The thermal decomposition of an organometallic precursor for the preparation of YBa2Cu3O7?x
Advanced Materials, 1997
Within the area of high-temperature superconductors, thin films will play an important role for many interesting technological and commercial applications if it is possible to produce the oxide superconductors in the form of crystallographically orientated thin films. Generally, the deposition of such layers can be produced via a gas phase or a solution. With regard to the solution process, the high-temperature superconducting material YBa2Cu,07,,L11 which is of special interest for the preparation of thin layers for high current density applications,[21 can be prepared from organometallic precursors i.e., carb~xylates,["~~ P-diketones,['] and alkoxides.16] Above all, the YBa2C~307-x thin films prepared via wet-chemical methods exhibit signifi-
Chemical characterization of melt-textured YBCO produced by hybrid powder metallurgy
Materials Science and Engineering: B, 2008
Monolithic YBCO samples were made by traditional top-seeded melt-texturing processes from cold-milled mixtures of Y123 (YBa 2 Cu 3 O 7−δ ) and elemental Y. The bulk composition does not lie on the Y211 (Y 2 BaCuO 5 )-Y123 join so, formation of Y123 from liquid and Y211 is not an essentially isothermal process on cooling. The reaction liquid + Y211 = Y123 is a ternary reaction and occurs over several tens of degrees. The Y123 thus produced has a range in compositions -particularly in Cu:(Y + Ba) -which may reflect crystallization over the thermal interval. The liquid migrates to an invariant point at which CuO also crystallizes with complete loss of liquid. The presence of trains of CuO grains in the YBCO indicates the locations of the last liquids to be preserved in the sample. These trains are dominantly in an annulus 1-3 mm from the edge of the 20-mm diameter sample. Mapping the compositional variation in Y123 may allow mapping the path of crystallization of these monolithic YBCO samples.
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.