Study of ageing in YBa 2 Cu 3 O 7−δ superconductors prepared by different chemical routes (original) (raw)
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The effect of calcination conditions on the superconducting properties of Y−Ba−Cu−O powders
Journal of Thermal Analysis, 1995
Calcination conditions of the precursor powders, i.e. temperature, type of atmosphere and duration, were determined with a view to obtain superconducting powders with the most advantageous physico-chemical properties. Investigated were powders in the Y-Ba-Cu-O system prepared by the sol-gel method. Thermogravimetrie examinations of the powders have revealed that the decomposition kinetics of BaCO3 determines the formation rate of the superconducting phase. It follows from the decomposition kinetics of BaCO3 that the process is the most intensive in argon, whereas in static air and oxygen it is the slowest. The phase composition analysis (XRD) and low-temperature magnetic susceptibility measurements of t.he calcinated powders, confirm the above mentioned changes in the decomposition kinetics. The reaction of barium carbonate can be completed if the calcination process is conducted at the temperature of 850~ for 25 h, yielding easily sinterable powders for obtaining single-phase superconducting bulk samples with advantageous functional parameters.
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.
Journal of Thermal Analysis, 1988
solution) and of oxalates (obtained in aqueous, partly aqueous and nonaqueous media) were investigated as concerns the yield and stoichiometry of the precipitates, including their transmission electron microscopy and DTA characteristics: Oxalates copreeipitated from acetate solutions in non-aqueous media provide fine samples with increased reactivity. For comparison, when thermally treated, an oxide ceramic mixture containing aged BaO (with some Ba(OH)2 and BaO2) exhibits increased reactivity due to the formation of a liquid phase in the temperature range 400-500 ~ .
Characteristics of Y 1 Ba 2 Cu 3 O 7- x highT c superconductor prepared by partial melting process
Korean Journal of Chemical Engineering, 1998
The superconducting Y1Ba2Cu3O7-x (123) and the Y2Ba1Cu1O5(211) powders in this study were prepared by pyrophoric synthesis method with Y2O3 (99.9 %), BaCO3 (99.9 %), and CuO (99.9 %) powders. Samples of 123 and 211 pellets were first prepared and then piled to have a 123/211/123 arrangement before a partial melting process was applied for phase change of the center piece
High Temperature Superconductors (${\rm Y}_{1-x}{\rm Nd}_{x}$ )Ba2Cu3O7-δ Obtained by Acetate Method
IEEE Transactions on Applied Superconductivity, 2018
Bulk ceramic samples with chemical composition (Y 1 −x ,Nd x)Ba 2 Cu 3 O 7 −δ , where x = 0, 0.1, 0.2, 0.5, and 1 were sintered by a proposed acetate method. The samples were then submitted to structural characterization by X-ray diffraction with crystal structure refining using the Rietveld method. AC electrical resistivity measurements from ambient temperatures down to 4.2 K were performed, as well as magnetic measurements of magnetic moment as function of temperature and magnetic hysteresis loop. Results have shown superconductivity with critical temperatures of about 91 and 60 K for pure YBa 2 Cu 3 O 7 −δ (x = 0) and pure NdBa 2 Cu 3 O 7 −δ (x = 1) samples, respectively. Scanning electron microscopy images were also analyzed, revealing a regular parallel-piped grain shape. The proposed method showed as an advantage to reduce the grinding time without any considerable degradation on structural or superconducting properties of pure YBa 2 Cu 3 O 7 −δ (x = 0) or pure NdBa 2 Cu 3 O 7 −δ (x = 1), as related to samples prepared by a conventional solid state route.
Simultaneous coprecipitation of the hydroxides for preparing YBa2Cu3O7 superconductors
Journal of Materials Science Letters, 1989
The recently discovered YBazCu307 superconducting material is generally prepared using the standard ceramic technique. The practical limitations of the standared ceramic technique however make it difficult to achieve homogeneous fine particles of the oxide mixture, which is one of the prerequisites for making a good-quality superconductor.
Formation of Superconducting YBa2Cu3Oy through Sol-Gel Method
Journal of the Ceramic Society of Japan, 1988
The preparation of superconducting YBa2Cu3Oy through sol-gel method was performed using an acetate aqueous solution. Conditions of gelation and conversion of gel to YBa2Cu3Oy ceramics were investigated, applying thermal analysis, infrared absorption spectroscopy and X-ray diffraction techniques. Transparent gel was obtained from the acetate solution with cation mole ratio of Y:Ba:Cu=1:2:3 by adjusting the initial pH of the solution. Formation of Cu metal, Cu2O and BaCO3 below 400•Ž was found to occur during heat treatment of the gel. Above 600•Ž the heated sample turned into a mixture of Y2O3, BaCO3 and CuO, which finally transformed into the single phase of YBa2Cu3Oy at 910•Ž. The resultant material showed good high Tc superconductivity.
A study on the stability of superconducting YBa2Cu3O7?x phase
Journal of Materials Science: Materials in Electronics, 1990
The thermal stability of the superconducting phase of nominal composition YBa2Cu307 xsintered pellets has been studied with respect to different temperatures (ranging from 300 to 950 °C), time (ranging from 1 to 72 h), oxygen partial pressure (from 4 Pa to 1 atm) and carbon dioxide partial pressure (from 10 -4 Pa to 1 atm). Annealed samples were characterized by X-ray diffraction analysis, optical microscopy, and resistive measurements of the superconductive transition temperature. A stability field of the orthorhombic and tetragonal phases was obtained, showing a region of coexistance. The decomposition of the 1 23 phase is found to be strongly influenced by the presence of a small amount of CO2 (1 p.p.m.) in the sintering atmosphere. A sintering process is proposed to avoid the formation of by-products.
Synthesis and characterization of YBa2Cu3O7−x. Superconducting materials
Materials Research Bulletin, 1988
YBa2Cu307. X superconducting materials have been obtained from oxalate coprecipitation and metalloorganic decomposition. Resistivity and magnetic measurements confirm the superconducting behavior below 90 K. Calorimetric measurements reveal the role of impurities in the specific heat evolution.