On the influence of K 2CO 3 additives in obtaining HTSC materials of the YBCO system (original) (raw)
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Microstructural studies of K2CO3 and Rb2CO3 doped YBCO HTSC
Physica C: Superconductivity, 2003
The influence of Me 2 CO 3 (Me ¼ K or Rb) additions on the microstructural morphology of YBa 2 Cu 3 O x (YBCO) HTSC with nominal composition Y ð1À0:2xÞ Ba ð2À0:2xÞ M x Cu 3 O y (x ¼ 0-2.0) were investigated by means of orientation imaging microscopy which provides a method for measuring a large number of individual grain orientations and relating them directly to the microstructural features by means of evaluating electron backscatter Kikuchi patterns in scanning electron microscopy. We investigated the influence of the alkali additions on the grain orientation distributions of YBCO. The samples are characterized by grain orientation maps, and pole and inverse pole figures. Finally, the grain orientation distribution functions are obtained from the measured data. Within a certain range of doping (up to 5 wt.% in the initial batch), the grain sizes are found to increase as compared to pure YBCO, accompanied by an improvement of the superconducting properties (T c). It is shown that the additions of alkali carbonates do not introduce any preferred grain orientations in YBCO HTSC in the entire doping range.
Physica C: Superconductivity, 2003
YBa 2 Cu 3 O y ceramics having different morphologies: low porosity, composed of well shaped and closely connected large crystal grains, high porosity, composed of badly packed irregularly shaped small grains, and of intermediate microstructure,were investigated with respect to reactions that lead to the deviation of oxygen content from its equilibrium value and loss of homogeneity of oxygen ion distribution. These reactions, which occur during quenching performed after the equilibrium of YBCO with oxygen has been attained, are the oxygen absorption during quenching in liquid oxygen or in common liquid nitrogen (containing 2-3% dissolved oxygen) and the oxygen release during quenching in pure liquid argon. In these reactions and in the reaction with CO 2 impurities during attaining equilibrium (which also leads to an inhomogeneous sample), the reactivity of the investigated ceramics varied from high (in high porosity ceramic) to almost inert (in low porosity ceramic), while even an almost inert ceramic attains equilibrium under 0.01-1 atm O 2 and 450-920°C during less than 35 h. Therefore this ceramic is most suitable for preparation of the samples having any oxygen content. The interrelations found make it easier to search for the proper conditions of ceramic sintering, equilibration with oxygen and quenching for preparation of both homogeneous and inhomogeneous samples having the desired morphology and properties.
Synthesis and Structural Properties Study of YBCO at Room Temperature
YBCO is a family of crystalline chemical compounds famous for displaying high-temperature superconductivity and synthesized YBCO superconductor by using solid state reaction in order to study structural properties. The structural was studied by using scanning electron microscope (SEM) and fourier transform infrared (FT-IR). Scanning electron microscope pictures show uniform and homogeneous distribution, and the effect of the doping of aluminum oxide to the composite samples decreases the grains of the image of the distortion in the shape and structure. fourier transform infrared spectrum showed that the YBa 2 Cu 3 O 7 is pure, and YBa 2 Cu 3 O 7 whichdopped with AL 2 O 3 revealed perfectly.
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.
Superconducting properties of YBa2CanCu3+nOδ ceramics
2000
Extensive experimental studies have been carried out on the Y-Ba-Cu-O system since the discovery of superconductivity above 90 K [1]. It has been well established that there exist three stable phases in the Y-Ba-Cu-O systems, namely; YBa 2 Cu 3 O 7−y (Y-123), and YBa 2 Cu 4 O 8 (Y-124) [2] and Y 2 Ba 4 Cu 7 O 15−y (Y-247) [3] with T C of 90 K, 80 K and 40 K respectively. All of them are characterized by the layered perovskite structure with the possession of the Cu-O chains. The structural difference in these three compounds originates from the difference in the stacking sequence of the Cu-O chain: the repetition of a single chain, that of the double-chain and the alternative repetition of a single and double chain for the Y123, Y124 and Y247 compounds respectively.
Phase equilibria, structure and properties of YBa ceramics
Journal of The Less Common Metals, 1990
X-ray diffraction (XRD), microscopy, chemical and activation analysis, together with measurement of T, and some other properties, have been used to study the changes in phase composition, microstructure, crystal structure, texture and "composition-property" diagrams of the high temperature Y-Ba superconductors (single-crystal and polycrystalline specimens and cold-rolled strips) with variations in the conditions of preparation, heat treatment, deformation and temperature. When prepared by the conventional solid state reactions, specimens of the Y-Ba ceramic are generally poiyphase (the orthorhombic superconducting 123 phase, the 2 115 phase, sometimes BaCuO*, and residual amounts of the initial oxides). The non-equilibrium specimens also contain Y,Ba,O,-type phases. Homogeneous single-phase (as shown by XRD) specimens of the 123-type phase with T,= 88-92 K (containing under 2-5 vol.% second phase, predominantly 2 115) are obtained by repeated wet grinding, mixing and solid state annealing at 920-930 "C, in air and under oxygen, of the initial mixture of oxides, including BaOz. The manner in which the lattice periods of the orthorhombic 123 phase ( T, = 92 K) vary with temperature displays an anomaly near T, that correlates with the thermal behaviour of the Debye temperature. The lattice parameters of a YBa,Cu,O,, orthorhombic crystal have been studied at 9 1 and 293 K to ascertain the occupancy of the oxygen positions. Cooling the orthorhombic crystals involves the compression of the triple layers formed by two sheets of CuO, pyramids, with their vertices facing the Cul-01-Cul chains. The compression is mainly due to a reduction in the Cul-02 distance. Centrally located in the "a" edges, the oxygen atoms may "trigger" the interchain interaction. Rolling of the 123 phase powder and strip with the addition of a plasticizer causes brittle cleavage of the crystals and gives rise to the (00 1) [ 1 lo] basal texture. Reducing the amount of binder to 2%-3% intensifies the process of basal texture development and increases the basal density from 4.5 to 13-15 arbitrary units. An axial basal texture is formed with a small scattering angle (within f 7" normal to the plane of the specimens) and a weak preferred orientation in the "b", "a" or "a + 6" direction along the rolling direction. The orthorhombic structure is distorted and transformed to tetragonal by cold work. This is accompanied by the loss of superconductivity which is reduced by the subsequent annealing.
Applied Superconductivity, 1995
The effects of eutectic (BaCuOl+CuO) additions and sintering temperahue on the morphologr, density and critical current of extruded YBCO wires, were investigated systematically over a wide range of temperatures (800-975°C) and compositions (040 mol%). The YBCO-eutectic system was classified morphologically into five distinct regions, which are influenced strongly by the sintering temperature. The main effect of the eutectic dopant is prevention of the sharp drop of critical current, observed in pure YBCO, at sintering temperatures above 920°C. This effect is facilitated by suppression of exaggerated anisotropic grain growth and the development of visible intergranular cracks in material.
A review on the synthesis of Y–Ba–Cu-oxide powder
Superconductor Science and Technology, 2005
The preparation of Y-Ba-Cu-oxide (YBCO) powder by various techniques is critically reviewed and the synthesis of ultrafine superconducting YBa 2 Cu 3 O x (123) powders is specially emphasized. The fine powder has assumed a large importance, requiring the minimization of processing parameters (time and temperature) during calcination, homogenization and sintering to avoid the problems of evaporation of the constituent oxides. From the voluminous research activities on YBCO it is known that by adopting any preparation technique the superconducting transition temperature (T c) value of ≈92 K could be achieved in the bulk samples, thus in this review the T c values are not emphasized. Also, the other transport properties such as critical current densities (J c) and magnetic properties are not discussed, since these properties are mainly controlled by many other parameters related to the weak link across the grain boundaries of the specimens, and a very little role is played by the synthetic procedure. The weak links across the grain boundaries are known to be the cause for the poor J c values in bulk specimens and those weak links are observed due to the presence of impurities at the grain boundaries, misorientation of grains and oxygenation of the samples. By selecting the proper synthetic procedure, only the impurity problem can be solved, and to remove the other problems, a proper fabrication method needs to be adopted. This review will guide the new researcher to find the appropriate technique to synthesize good quality YBCO powder.