BiSrCaCuO System Research Articles

Reinforcing Increase of ΔTc in MgB2 Smart Meta-Superconductors by Adjusting the Concentration of Inhomogeneous Phases.

Incorporating with inhomogeneous phases with high electroluminescence (EL) intensity to prepare smart meta-superconductors (SMSCs) is an effective method for increasing the superconducting transition temperature (Tc) and has been confirmed in both MgB2 and Bi(Pb)SrCaCuO systems. However, the increase of ΔTc (ΔTc = Tc ‒ Tcpure) has been quite small because of the low optimal concentrations of inhomogeneous phases. In this work, three kinds of MgB2 raw materials, namely, aMgB2, bMgB2, and cMgB2, were prepared with particle sizes decreasing in order. Inhomogeneous phases, Y2O3:Eu3+ and Y2O3:Eu3+/Ag, were also prepared and doped into MgB2 to study the influence of doping concentration on the ΔTc of MgB2 with different particle sizes. Results show that reducing the MgB2 particle size increases the optimal doping concentration of inhomogeneous phases, thereby increasing ΔTc. The optimal doping concentrations for aMgB2, bMgB2, and cMgB2 are 0.5%, 0.8%, and 1.2%, respectively. The corresponding ΔTc values are 0.4, 0.9, and 1.2 K, respectively. This work open a new approach to reinforcing increase of ΔTc in MgB2 SMSCs.

Thermal and structural characterization of the Bi2‐xSmxSr2Ca2Cu3O10+δ glass‐ceramic system

AbstractIn this work, investigations on the crystallization and oxidization kinetics of the Sm substituted BiSrCaCuO glass‐ceramic system were performed. It has been shown that the Sm ions changed the glassification properties of the BiSrCaCuO system. While fully glass samples were obtained for low Sm‐substitution levels (x=0.2 and x=0.4), the Sm containing particles on the surface have grown especially at high Sm‐substitution levels (x>0.6) and glassification problem increased. Nonisothermal crystallization kinetics including activation energy for crystallization, Ea, and Avrami parameter, n, of the samples prepared was investigated using differential thermal analysis (DTA) at four different uniform heating rates. The values of glass transition temperature and crystallization temperature exhibited compositional and heating rate dependence. Ea value of the samples showed an increase with increasing the Sm concentration. The Avrami parameter, n, was found approximately 4.5, suggesting the growth of small particles with an increasing nucleation rate. The calculated values of the oxidization rates and the activation energy for oxygen out‐diffusion process, E, indicated that the oxygen deficiencies by the Sm substitution in the unit cell of BiSrCaCuO were formed and more oxygen atoms were absorbed to fill the oxygen deficiencies in the system.

Magnetic relaxation behavior in the Bi2Sr2Ca2Cu3−xMoxO10+δ system fabricated by glass-ceramic technique

In this paper, we present a study on the critical current density and magnetic relaxation behavior of the Mo-substituted BiSrCaCuO system. The Bi2Sr2Ca2Cu3−xMoxO10+y, where x=0, 0.5, 1.0 and 1.5 have been fabricated using glass-ceramic technique. It was found that the Mo-substitution to the BiSrCaCuO system lead to the formation of pinning centers and hence an increase of critical current density. The magnetic relaxation experiments were performed to understand physical phenomena behind of flux motion. Time dependence of the magnetization exhibited thermally activation flux motion in the samples. It was found that the normalized magnetic relaxation rate, S, did not vary linearly with temperature, especially at high temperatures, which is attributed to the collective creep theory. In addition, the characteristic pinning energy, Ue/KB, in the samples was calculated using Maley's method. Correlation between the pinning energy and the magnetization showed that obtained experimental results can be fitted to the collective creep theory.

Planejamento e produção de um criostato de baixo custo para caracterização elétrica de materiais

Os supercondutores a base de BiSrCaCuO apresentam três fases principais, Bi2Sr2CuO, Bi2Sr2CaCu2O e Bi2Sr2Ca2Cu3O com temperaturas críticas de 20 K, 80 K e 110 K, respectivamente. Desta forma, torna-se fundamental a caracterização elétrica de tais materiais a baixas temperaturas. Com este objetivo confeccionou-se um criostato para medidas de caracterização elétrica. Utilizando-se nitrogênio líquido (77 K), e controlando a pressão sobre o refrigerante, atingiu-se uma temperatura da ordem de 64 K (baseado em princípios termodinâmicos) abrangendo uma maior faixa de temperatura de medida, que permitiu identificar pelo menos duas fases supercondutoras no sistema BSCCO (2212 e 2223). Neste contexto, este sistema propicia uma relação custo/beneficio mais favorável, pois evita o uso de refrigerantes mais custosos como o hélio líquido. O criostato mostra experimentalmente a aplicação dos diagramas de fase PxT (Lei de Gay-Lussac) vistos nos cursos de termodinâmica, propiciando demonstrações experimentais que raras vezes são vistas em sala de aula.

Investigation of Sm → Ca substitution in Bi(Pb)SrCaCuO high temperature superconductor by low field AC magnetic susceptibility

We have investigated the effect of Sm substitution in Bi(Pb)SrCaCuO system by performing AC susceptibility ( \(\chi = \chi ' + i\chi ''\)), XRD (X Ray Diffraction) and SEM (Scanning Electron Microscopy) measurements. The Sm → Ca substitution (Bi1.6Pb0.4Sr2Ca2−xSmxCu3Oy) was carried out by conventional solid-state reaction method. The susceptibility measurements were carried out at different values of the AC field amplitudes. The imaginary part of susceptibility is used to estimate the intergranular critical current density by means of the Bean’s model. The intergranular critical current density (Jc) of pure sample is found to be about 68 A/cm2 at 95 K. The intergranular Jc is seen to decrease with increasing Sm substitution. XRD pattern and SEM micrographs are given to provide information about Bi-2223 phase and grain size respectively.

Growth of superconducting and non-superconducting whiskers in the Bi-Sr-Ca-Cu-O (BSCCO) system

Growth of such non-superconducting whiskers [Sr2.24Ca0.4Al2Ox, (Ca0.8–0.85Sr0.15–0.1)2CuO3,CuO, or Bi2.44Sr2Ca1.3–2Cu6.9–9.95Al0.35–0.46Ox (Cu-rich whiskers)] formed during the growth of Bi-2212 superconducting whiskers from powder or glassy substrates, is discussed. These whiskers are likely to grow from the bottom end, and there is a tight relationship with the growth of the Bi-2212 whiskers. A general reaction-path model for the whisker growth in the BSCCO system, independent of the type of the catalytic impurity and substrate, is proposed. When whiskers are grown under magnetic fields, up to 10 T, changes in the whisker size, aspect ratio, and morphology are observed.

Melting Equilibria of the Bi-Sr-Ca-Cu-O (BSCCO) System in Air: The Primary Crystallization Phase Field of the 2212 Phase and the Effect of Silver Addition

The subsolidus and primary crystallization phase field of the 2212 (Bi:Sr:Ca:Cu) phase in the BSCCO system have been investigated. At 830 C, this phase was observed to be in equilibrium with ten phases. Sixteen four-phase equilibrium regions that surround the 2212 phase have been identified at this temperature. The melting events associated with these four-phase regions were studied with differential thermal analysis, quenching experiments, and wicking experiments, in which samples of the liquid for analysis were absorbed by capillary action. The melt compositions were obtained by using quantitative energy-dispersive X-ray spectrometry. The 2212 phase melts incongruently, beginning at {minus}825 C. Its primary crystallization field encompasses a compositional range of 24--42 mol% BiO{sub 1.5}, 7--33 mol% SrO, 2--27 mol% CaO, and 19--43 mol% CuO. The compositions of melts in equilibrium with the 2212 phase were mostly on the calcium-deficient side of the 2212 solid solution. An approximate polygonal model of the 2212 primary crystallization field has been presented. The addition of silver depresses the melting temperatures in the vicinity of the 2212 phase, from 4 C to 22 C. Silver entered the melt at a saturation level of 2--8 mol%. In the more copper-rich liquids, silver replaced some of the copper,more » which resulted in a shift of the 2212 crystallization field away from the copper oxide corner.« less

Influence of B, Al, Ga, In on the composition of Bi(Pb)SrCaCuO system

Samples with partial cationic substitution for bismuth in Bi(Pb)–Sr–Ca–Cu–O system were prepared to systematically examine phase formation due to different concentrations of B, Al, Ga and In. The elements were substituted in the range x=0–0.5 in the nominal formula Bi 1.8− x A x Pb 0.26Sr 2Ca 2Cu 3O y . X-ray diffraction analysis was carried out for phase analysis with special emphasis to detect impurity phases. All the samples were mixed phases of 2212 and 2223. Rietveld analysis was used to find out the ratio of the phases. Boron enhanced the formation of the 2223 phase up to x=0.5, but gallium deteriorated the high-temperature phase 2223 and the 2212 phase became dominant. The amount of 2223 phase was increased with increasing content of Al and In (up to x=0.2) and then was decreased. The lattice parameters of the superconducting phases were obtained, and no systematic variations with the dopant level were found. Scanning electron microscopy observations revealed the presence of small and irregular amounts of Ga and In in the chemical composition of superconducting grains and the existence of the various non-superconducting phases. Superconducting properties of the samples were characterized by the measurement of the temperature dependence of the electrical and magnetic properties.

ANOMALOUS BEHAVIORS OF NON-RESONANT MICROWAVE ABSORPTIONS OF SUPERCONDUCTORS

The non-resonant microwave absorption (NRMA) measurements have been intensively performed for superconducting thin films of YBa 2 Cu 3 O y fabricated on MgO (100) substrates and powder samples of LaSrCuO systems. In order to complement the study, we also review the NRMA of BiSrCaCuO system. A particular attention has been paid to the following phenomena: (i) phases, (ii) effect of current, (iii) directional effect of applied magnetic field, (iv) hysteresis, (v) microwave power absorbed as a function of magnetic field, (vi) linewidth in the vicinity of T c , and (vii) modulation amplitude effect. A preliminary study on ( La 0.98 Dy 0.02)1.85 Sr 0.15 CuO 4 was also reported.

Melting of the 2212 phase in Bi(Pb)SrCaCuO system

The melting behavior of the 2212 phase in the Bi(Pb)SrCaCuO system has been investigated using DTA, XRD and EPMA. The effect of Pb and Ca on the melting of 2212 have also been discussed. The results indicate that the melting point of 2212 decreases monotonicaly with increasing Pb, however it reaches a peak value with the increase of Ca. 2212 melts incongruently into a liquid and (Sr,Ca)CuO2, and the crystals formed when the liquid is quenched in air vary with the starting concentrations of Pb and Ca.

Optimization of the composition for synthesizing the high-Tc phase in Bi(Pb)SrCaCuO system

The optimal composition for synthesizing the high-Tc phase 2223 in the Pb-doped bismuth oxide system has been presented. It was shown by using DTA, SEM (EDAX) and XRD that a single 2223 phase could be fabricated when the sample of a Bi2.1 − xPbxSr1.9Ca2.05Cu3.0Oz, where x is between 0.2 and 0.3 (not including the loss of Pb), was sintered at 850–860 °C. It was also indicated that excessive Pb is more effective than excessive Cu in promoting the formation of 2223.

The effect of vanadium doping on superconducting properties of (Bi, Pb) 2Sr 2Ca 2(Cu 1− xV x) 3O y ceramics

We report on the studies of doping vanadium with (Bi, Pb) 2Sr 2Ca 2(Cu 1− x ,V x ) 3O y at low concentration of x=0.01–0.03. The superconductivity of the samples were determined by employing a.c. resistivity, a.c. susceptibility and X-ray diffraction measurements. For the low concentration range of vanadium we have observed some enhancement effects in stabilizing the high T c phase, resulting in increase in the volume fraction of it. The role of the presence of two additives in BiSrCaCuO system is discussed in modifying the superconductivity of this system.

Effect of Hg addition on synthesis of Bi-based superconductors

We have investigated the effect of Hg addition on the superconducting properties of BiSrCaCuO system. Polycrystalline samples with nominal composition Bi 2Sr 2− x Hg x Ca 1Cu 2O y and Bi 2Sr 2− x Hg x Ca 2Cu 3O y ( x=0.3) were synthesized and used to investigate the phase evolution by XRD, superconducting behaviour by R– T measurement and the structural grain boundary effects by SEM. From these measurements, it has been noticed that the phases obtained with both types of compositions are the same as Bi2212 but the T c values are different. With additional annealing, T c zero values were raised from 60 to 72 K in Bi 2Sr 2− x Hg x Ca 1Cu 2O y and 64 to 92 K in Bi 2Sr 2− x Hg x Ca 2Cu 3O y . Also, an improved grain boundary linkage has been observed by SEM for the 92 K sample.

The melting behaviour of the lead-doped 2223 phase in Bi(Pb) SrCaCuO system

The melting behaviour of the lead-doped 2223 phase in the bismuth oxide system has been investigated by using DTA, XRD and EPMA techniques. The results indicated that 2223 phase began to decompose into liquid, (Ca, Sr)2CuO3 and (Sr, Ca)14Cu24O41 phases when fired at T ≥ 860 °C in air. The liquid composition is located on the line between 2212 and 2201 phases. When the liquid was cooled in air, 2212 and 2201 phases crystallized from it.

Fast flowing and formation of superconducting Bi 2Sr 2Ca 1Cu 2O x layers on metallic copper wires and plates

A new phenomenon on the fast transportation of the melt-quenched Bi–Sr–Ca–Cu–O (BSCCO) was found. The BSCCO melts were cast and quenched into a metallic copper vessel. The melt-quenched materials consisting of BSCCO systems such as the compositions around Bi 2Sr 2Ca 1Cu 2O x (2212 phase) and Bi 2Sr 2Ca 1O x (2210 phase) crawled at an extraordinarily high speed up the wall of the metallic copper vessel when the vessel filled with the cast materials was reheated at high temperature around 850°C in air; the heat treatment results in the formation of a superconducting thin layer on the copper vessel. When the metallic copper wires or plates are in contact with the copper vessel, then the cast materials crawled up to form a superconducting 2212 layer on the copper surface.

Synthesis of Hg-added Bi2212 superconductors using various routes

We have studied the effect of Hg addition in the BiSrCaCuO system. Polycrystalline samples with nominal compositions and (x = 0.3) were synthesized in an open atmosphere by three different synthesis routes, i.e. solid-state reaction, matrix method and double-matrix method. The samples were characterized through XRD, R - T measurement and SEM. The phase ultimately obtained was mainly Bi2212. Almost identical depressions were observed in all the samples as a consequence of overdoping of charge carriers due to the high-oxygen ambient provided by HgO decomposition. Additional air annealing was found to be useful in attaining proper tuning of charge carriers, while quenching to room temperature had an adverse effect. Improvement in grain boundary linkage was observed for additionally annealed samples.

Characteristics and Determination of the Invariant Reactions in Multicomponent Systems

Characteristics which can be used to determine the type of invariant reactions in the multicomponent system have been discussed. They are: (i) the relations among solidus temperatures; (ii) the position of the liquid phase; (iii) the phase present after incipient melting: the number of univariant phase regions can be observed in partially melting samples or the solid phases which can occur in partially melting samples which originally consist of other solid phases. Several aspects which must be considered in using the above principles: the sensitivity and accuracy of experimental methods; the solubility of solid phases; the consistence among invariant reactions are also discussed. An example of using these principles in determination of the invariant reactions in the vicinity of the (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O 10-x (2223) phase in the Bi(Pb)SrCaCuO system is given.

Metastable states of the 2223 phase in the Bi(Pb)SrCaCuO system

By the magnetically modulated microwave absorption method (MAMMA) the authors observed the modifications induced by different calcination temperatures (between 830{degree}C and 870{degree}C) on the 2223 phase formed in a system sintered at (855 {plus_minus} 5){degree}C with the starting composition Bi{sub 1.7}Pb{sub 0.3}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y}. The presence of the 2223 in almost distinct states (consequently, multiple 2223 phases) in the same sample was observed. As the calcination temperature was increased up to 850{degrees}C, the highest temperature state of the 2223 phase intensified. Higher calcination temperatures resulted in the enhancement of other low-temperature states. The homogeneity of the 2223 phase was greatly improved by annealing the samples at 800{degree}C for 5 min in a flowing nitrogen atmosphere. The authors labeled as {open_quotes}metastable{close_quotes} the lower-temperature states having excess oxygen, which, by easily losing the supplementary oxygen under the above annealing procedure, were shifted to higher temperatures.

Crystallisation kinetics for melt quenched Bi 1.4Tl 0.6Sr 2Ca 2Cu 3O 10+y superconducting glass-ceramic

A glass in the BiSrCaCuO (BSCCO) system with nominal Bi 1.4Tl 0.6Sr 2Ca 2Cu 3O 10+y composition, prepared by the melt-quench (glass) method. Using an analysis already developed for non-isothermal crystallisation studies, based on DTA, TGA and DSC, information on some aspects of crystallization has been obtained. The result obtained indicated that substitution of the Tl for Bi increased the activation energy for crystallisation and enhanced the Superconducting phase formation largely.

Effect of V, Nb, and Ta Doping on the 2223 Phase Formation and the Crystal Structure in the BiSrCaCuO System

X-ray diffraction and electrical and diamagnetic analyses revealed that the 2223 phase was significantly enhanced by high-valence cation (V5+, Nb5+, Ta5+, etc.) doping in BiSrCaCuO samples. The optimum nominal composition was Bi1.6M0.4Sr2Ca2Cu3 Oy(M = high-valence cations) for all three elements. A quasi-high-valence peak of Cu2p3/2 (∼534.5 eV) has been observed. A reversible reaction, Bi3+⇆annealedquenched Bi5+ + Bi+, was also encountered in the sample doped with Nb5+. The effects of doping high-valence cations on the high-Tc phase formation and the crystal structure are two-fold: (1) The high-valence cation substitution for the fourfold-coordinated Cu site in the CuO2 sheet strengthens the coupling among the Ca-CuO2-Ca layers of the 110 K phase, and (2) the cations incorporated into the Bi-O layers increase the oxygen bonding, which is beneficial for the formation of the Aurivillius-type structures and stabilizes the structure of the 2223 phase. We argue that the beneficial effect for promoting the formation of the 2223 phase might be a general property of doping with high-valence cations.