Nominal Composition Bi Research Articles

Dielectric Behavior and Impedance Spectroscopy of Bi2Sr2GdCu2Oy

Samples with the nominal composition Bi 2 Sr 2 GdCu 2 O y in Bi -2212 where Gd replaces Ca as well as samples without Gd were prepared by solid-state reaction method. From the room temperature X-ray diffraction data, the samples were found to be similar to the single phase Bi -2212 structure. Impedance studies were performed from room temperature to 423 K at different frequencies in the range of 10 to 700 KHz. The AC conductivity increases with temperature and frequency, exhibiting frequency dispersion at low temperature region. The activation energy from AC conductivity in the high temperature region is found to be 0.432 eV. The permitivity increases with the increase in temperature and at 373 K it shows a maximum value exhibiting a dielectric loss. Complex impedance spectra are analyzed in terms of bulk relaxation and interfacial effects. The activation energy of the dipoles involved in the relaxation was estimated to be 0.482 eV. The universal power law of Jonscher is verified in the present system.

Characterization of (1- x)[Bi 12In 0.5O 18.75+γ-Bi 2O 3]:( x)PbTiO 3 ceramics

The ceramic system with composition (1- x)[Bi 12In 0.5O 18.75+γ-Bi 2O 3]:( x)PbTiO 3 with x=0.0, 0.3, 0.5 and 0.8 was synthesized and subsequently characterized for its crystal structure and dielectric properties. X-ray diffraction showed that the ceramic with nominal composition Bi 12In 0.5O 18.75+γ-Bi 2O 3 has sillenite structure, which is an uncommon metastable mineral phase with composition Bi 12In 0.5O 18.75. The dielectric constants and loss tangents were measured at different frequencies and temperatures. The dielectric properties of the sample with x=0.0, Bi 12In 0.5O 18.75+γ-Bi 2O 3, showed strong frequency and temperature dependence of dielectric constant and loss tangent. The high value of both the dielectric constant and loss tangent showed a conductivity value similar to a typical semiconductor. The addition of PbTiO 3 significantly reduced the temperature and frequency dependence at the low frequency range. For the sample x=0.8 (80% PbTiO 3) the dielectric properties are similar to a typical dielectric material and the conductivity was not revealed in the loss tangent. The results indicate that the electrical properties of (1- x)[Bi 12In 0.5O 18.75+γ-Bi 2O 3]:( x)PbTiO 3 ceramics can be tuned from a conducting oxide to an insulator and to dielectric, depending on the amount of PbTiO 3.

The properties of Bi-2223 precursor powders ground by fluid energy comminuting

A fast and high grinding-efficiency method to grind superconducting powders, named fluid energy comminuting, was studied. The sintered powder with a nominal composition of Bi 1.8Pb 0.33Sr 1.87Ca 2Cu 3O y was ground by a fluid energy comminuter on different conditions. Compared with other milling methods, this method does not contaminate the treated powder and grinds fast, so it can save a lot of time and energy, and increase hardly carbon content during comminuting. Powders ground by this process has a narrow particle size distribution (<5 μm) and low carbon content. Scanning electron microscopy and X-ray diffraction were used to characterize the obtained powder.

Investigation on synthesis of Bi-based thin films on flat sputter-deposited Ag film by melting process

We report on the fabrication of ribbon-like thin films on flat sputter-deposited Ag films whose surface smoothness remained within the order of tens of nm. It was found that the addition of Pb to the starting material improves the wettability of molten phase and facilitates the growth of Bi-2212 ribbon-like thin films on a flat Ag substrate, and that the increase of Ca and Cu in starting material suppresses the intergrowth of the Bi-2201 phase in ribbon-like thin films. By using (Bi,Pb)-2246 powders, with nominal composition of Bi 1.6Pb 0.4Sr 1.6Ca 3.2Cu 4.8O y , as the starting material, the superconducting Bi-2212 ribbon-like thin films with an onset T c at 74 K on a very flat Ag substrate were successfully synthesized. Additionally, the growth mechanism of ribbon-like thin films on flat Ag substrate was investigated by in situ high temperature microscope observation.

Superconducting properties of Bi-based ceramics with column 3A elements

Samples with the nominal composition Bi 1.8− x A x Pb 0.26Sr 2Ca 2Cu 3O y ( x=0–0.5; A=B, Al, Ga, In) were prepared. Measurements of resistivity, AC susceptibility, critical current density and magnetization have been used for characterization of the samples. All boron-substituted samples had a 2223 phase and narrow transition with the critical temperature T c≈106–108 K and the critical current density J c (77 K)≈10 5 A/m 2. The presence of aluminium caused decrease of T c. The 2212 phase became evident and J c (77 K) sharply decreased at x⩾0.3. The resistivity curves of all the samples with Ga were steeper. The T c values ranging from 103 to 60 K were considerably influenced by the amount of dopant. The volume of 2212 phase increased rapidly at x=0.2 and J c decreased to zero below 77 K. Introducing indium into the samples had a rather positive effect on T c since the resistivity–temperature curves were always shifted towards higher temperatures with the narrow transition at ∼107 K although the XRD patterns showed that the samples also contained the 2212 phase. The samples with x=0.05–0.4 had J c (77 K)≈10 5 A/m 2. The highest content of In worsened the quality of the samples and decreased the J c (77 K) to zero.

Comparative study on the transport critical current density of Bi-2223 and Tl-1212 Ag-sheathed superconductor tapes in low magnetic fields

High- T c superconductor tapes with nominal compositions of Bi 1.8Pb 0.4Sr 2Ca 2.2Cu 3O 10− x (Bi-2223) and (Tl,Cr 0.15)Sr 2(Ca 0.9,Pr 0.1)Cu 2O 7− x (Tl-1212) were fabricated using the powder-in-tube method. The T c zero ’s of the tapes, which were subjected to various thermo-mechanical treatments, ranged from 100–103 K for the Bi-2223/Ag tapes and 84–86 K for the Tl-1212/Ag tapes. Their transport critical current densities in low magnetic fields (0.15 T) were compared. All the tapes are dominated by weak links where this is more severe in the Tl-1212/Ag tapes. No significant anisotropic transport properties were observed in Tl-1212/Ag tapes when the magnetic field was applied perpendicular or parallel to the tape plane (i.e. J c( H ⊥)/ J c( H ∥)=0.75–1.0). The Bi-2223/Ag tapes however show a pronounced anisotropic transport properties in applied magnetic field (i.e. J c( H ⊥)/ J c( H ∥)=0.15–0.65). This can be associated with the microstructural difference between these two types of tapes. Scanning electron micrographs reveal the slightly aligned grains in the Bi-based tapes while randomly orientated grains were observed in the Tl-based tapes.

Crystallization activation energy and hole concentration properties of the Bi2Sr2Ca1-xCdxCu2O8+y glass-ceramic superconductor rods

The glass rods with the nominal compositions of Bi 2 Sr 2 Ca 1-x Cd x Cu 2 O 8+y , where x = 0.0, 0.4, and 0.8, were prepared by melt-casting method. XRD studies exhibited that the Cd substitution caused a transition from Bi-2212 phase to Bi-2201 phase. The multiphase structure was obtained for higher Cd concentration cases. It was determined that the activation energy for crystallization was decreased with the increase of the Cd concentration. When the Cd concentration was increased in the system the superconducting properties decreased. The hole concentration, p, was calculated using the Presland's method. The increase in the Cd concentration increased the hole concentration and the results showed that the Cd-substituted samples were highly in the overdoped region.

Study of Nd substitution in Bi–(Pb)–Sr–Ca–Cu–O high-Tc superconductors

Measurements of complex AC susceptibility χ=χ′+χ″ as a function of temperature and AC field amplitude have been carried out on rectangular bar-shaped high-temperature superconductors with nominal composition of Bi1.6Pb0.4Sr2(Ca1−xNdx)2Cu3Oδ superconducting samples prepared by the solid-state reaction method. The effect of Nd-substitution on the Bi–(Pb)–Sr–Ca–Cu–O system has been investigated in terms of an AC susceptibility study. It was found that as the amount of Nd content x increases, the transition temperature decreases. Temperature-dependent critical current density was deduced from AC susceptibility data. In spite of a slight decrease of Tc, the highest pinning strength parameters (Jcm (T=0) and temperature exponent n) were obtained for the sample with x=0.02.

Synthesis of Bi-2212 ribbon-like thin films on flat Ag substrates

Using (Bi,Pb)-2223 pellets, with nominal composition of Bi 1.8Pb 0.34Sr 1.9Ca 2Cu 3O 8+ δ , as starting materials, nearly phase-pure and highly c-axis oriented Bi-2212 ribbon-like thin films were synthesized on flat Ag thin films with tens nm order of root-mean-square surface roughness. The melting growth processes of Bi-2212 ribbon-like thin films were studied by in situ high-temperature microscope observations. A thin liquid layer spread mechanism of the growth of ribbon-like thin films was revealed. The addition of Pb to the starting materials increases the wettability of melting phase on the Ag thin films surface and facilitates the growth of Bi-2212 ribbon-like thin films. Excess Ca and Cu in starting materials sufficiently suppress the formation of Bi-2201 phase in the ribbon-like thin films.

Structural and magnetic properties of NiS doped Bi-2212 superconductors

In this work we have studied the effect of NiS doping on the superconducting properties of the Bi-2212 (nominal composition Bi 2.1Sr 2.1Ca 0.8[(CuO) 1− x (NiS) x ] 2O 8+ δ ), superconductors. Our studies show that NiS doping stabilizes superconductivity in the system but all the NiS doped samples gave a T c lower than the superconducting transition temperature of pure Bi-2212 superconductors. It appears that NiS substitution for CuO planes and modification of the oxygen content due to S substitution on O places jointly produce strong localization of charge carriers and at the same time increase the hole concentration of the system. These combined phenomena occurring in the Bi 2.1Sr 2.1Ca 0.8[(CuO) 1− x (NiS) x ] 2O 8+ δ system are responsible for the deterioration of superconductivity of NiS doped Bi-2212 superconductors.

Dependence of some Bi1.7Pb0.3Sr2Ca2Cu3Oyphysical properties on the annealing period

By using solid state ceramic synthesis technique, we have produced high- T c superconducting ceramics with a fixed nominal composition of Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 3 O y (BSCCO). Annealing treatments in air at 800 °C for different time periods from 6 to 30 h were carried out for the BSCCO samples. The influence of annealing time on the superconducting and mechanical properties were examined by measurements of thermoelectric power (TEP), X-ray diffraction, surface morphology, bulk density and Vickers microhardness ( V H N ). The results reveal that the most appropriate annealing time to obtain the highest peak intensity of high- T c phase (2223), highest and sharpest transition temperature (), maximum value of density and maximum of V H N is 18 h. Prolongation of the annealing time was associated with a reduction of all these parameters. These observations show that the annealing treatment plays an important role for producing consolidate superconducting compounds with improved mechanical properties.

Effects of Texturing Mechanisms on the Critical Current Density in Sintered High-Tc Bi-2223 Superconductors

Ac susceptibility measurements on ceramic samples with the nominal composition of Bi1.8Pb0.4Sr2Ca2Cu3O10—δ prepared by various pressing pressures on the pellets (355, 533, 711 and 1067 MPa) and different directional cooling temperature rates (20, 10, and 5 °C/h) using a directional solidification approach with a stationary Pt crucible in a strong temperature gradient have been carried out. The intergranular critical current density (Jcm) distribution has been calculated from ac susceptibility measurements by using Bean's and Kim's critical state models. It is observed that the critical current density improved with increasing pressing pressure and decreasing directional cooling temperature rates.

Effect of secondary phases in the precursor powders on the transformation to the (Bi,Pb)-2223 phase

ABSTRACTThe (Bi,Pb)2Sr2Ca2Cu3O2 system [also know as (Bi,Pb)-2223] has shown promise for use in superconducting tapes and wires due to its high transition temperature and high critical current density. The tapes and wires are usually fabricated by the powder-in-tube method, after which they are subjected to thermal and mechanical treatments. Depending on the nature of the heat treatment, phase transformations occur in the powder and it is of paramount importance to understand the response of the powders to different processing conditions. In this study, we have synthesized a precursor powder of the nominal composition Bi1.8Pb0.33Sr1.87Ca2Cu3Oyby spray pyrolysis. The powder was then calcined under controlled conditions between 760 and 800°C in an atmosphere between 0 and 21% O2for 2 to 24 hours with controlled heating and cooling, such that different amounts of Pb are incorporated into the majority phase. The resultant powders were then converted to the (Bi,Pb)-2223 phase with suitable heat treatments. Using powder Xray diffraction and magnetization measurements, the volume fractions of the secondary phases in the precursors were estimated and the effect of the phases on the conversion to the (Bi,Pb)-2223 phase was studied. We show that the ratio of the intensity of the (020) and (115) reflections of the (Bi,Pb)-2212 phase can be used to tune the precursor powders for optimal conversion. While a lower fraction of the secondary phases such as CaO and CuO is desirable in the precursor powders, a higher volume fraction of Ca2PbO4 seems to help in the rapid conversion to the (Bi,Pb)-2223 phase.

AC susceptibility of the sintered Bi1.6Pb0.4Sr2(Ca1-xMx)2Cu3Oδbulk high-Tc superconductors

ABSTRACTAC susceptibility measurements as a function of temperature, frequency and applied ac field amplitude were performed on two rectangular bar shaped samples of nominal composition Bi1.6Pb0.4Sr2(Ca1-xMx)2Cu3Oδ, with M=Pr, Gd, and x=0.01, obtained by the usual solid state reaction route. The incorporation of the rare earth elements at low concentration stage results in an improvement of grain connectivity for the sample doped with Pr. On the other end, the ac field amplitude and frequency dependence of the susceptibility curves disclosed bulk pinning hystersis loss feature. The potential barrier height, activation energy at the grain boundary extracted from the low temperature peak revealed that flux creep is governing the pinning mechanism inside the samples. Qualitative discussion in the framework of the critical state model was highlighted

EDX analysis, microstructure and magnetic properties of CuS doped Bi-2212 superconductors

In this work we have studied the effect of CuS doping on Bi-2212 (nominal composition Bi 2+ySr 3−y−nCa n[(CuO) 1−x(CuS) x] 2O 6+δ, (0 < x 0.1, < y < 0.1 and 0.8 < n < 1) superconductors. An improvement in T c of the CuS doped Bi-2212 superconductors is observed in these studies. Most likely improvement in T c of the CuS doped Bi-2212 superconductors is caused by the modifications in the oxygen stoichiometry of the samples due to incorporation of S in the Bi-2212 lattice, with a consequent improvement in hole concentration.

Chemical stability of the Bi(Pb)-Sr-Ca-Cu-O superconductors

The changes in volume of superconducting high-T c (2223) phase of the high-temperature superconductors (HTSC) with nominal composition Bi 3.2 Pb 0.8 Sr 4 Ca 5 Cu 7 O x are studied by magnetic susceptibility during soaking of material in water and more aggressive aqueous solutions. The apparent volumes of the 2223 superconducting phase after long-term (168 hr) soaking in H 2 O, NaCl (aq) , and NaOH (aq) decreased to 22%, 17%, and 57%, respectively. The atomic absorption analysis of resulting solutions showed high amounts of Sr 2+ and Ca 2+ in H 2 O and NaCl (aq) and lower amounts of Sr 2+ and Ca 2+ in NaOH (aq) , The highest content of Pb 2+ and Cu 2+ was detected in NaOH (aq) .

Doping of Bi-Sr-Ca-Cu-O Compounds with Mn

Formation of the superconducting phases Bi-2212 and Bi-2223 has been studied for samples with nominal composition Bi a Pb b Mn c Sr 4 Ca 5 Cu 7 O x (a + b + c = 4). The influence of the stoichiometric replacement of Bi and/or Pb by Mn on the electric and magnetic properties of the Bi-based superconductors has been studied. The partial substitution of Mn for Bi in the samples without Pb did not promote the growth of the Bi-2223 phase. The samples with double substitution Pb-Mn for Bi revealed a large amount of the Bi-2223 phase.

INFLUENCE OF TECHNOLOGICAL PARAMETERS ON THE QUALITY OF THE Bi-BASED SUPERCONDUCTORS

The effect of the sintering temperature, the cooling rate and the additive on the critical parameters was studied on samples with nominal composition Bi 1.8( Pb 0.26) Sr 2 Ca 2 Cu 3 O 8+x both undoped and with addition of 5, 9, 12.7 mol % of boron (as B 2 O 3), respectively. The sample with 5 mol % of boron cooled slowly had the critical current density five times higher than undoped sample. The rapid cooling of the samples caused enhancement of the volume of the 2223 phase.

Bi-2223 PHASE DEVELOPMENT UNDER INFLUENCE OF ADDITIONS OF 5B METAL OXIDES

Formation of the high temperature Bi-2223 phase has been studied for samples with nominal composition Bi 3,2-x Pb 0.8 M x Sr 4 Ca 5 Cu 7 O y. M represented V, Nb, Ta, their contents was altered from 0 to 0.6 mol %. The effect of the additives on the growth of the phase 2223, lattice parameters and the superconducting properties of the samples was detected. It was found that the additives enhanced the volume of the 2223 phase, improved the intergrain connection resp. the critical current density. The additives did not affect the lattice parameters and T c significantly.

Texturing of precursor Bi1.6Pb0.4Sr2Ca3Cu4Ox (2234) rod by resistive-heat floating-zone method

Abstract We have studied the superconducting properties of nominal composition of Bi1.6Pb0.4Sr2Ca3Cu4Ox (2234) rods grown by the resistive-heat floating-zone (RHFZ) method. Oriented crystalline samples of 2212 were successfully obtained from the 2234 glassy rod using this method. In order to improve the physical properties of superconductors, the influence of growth rate on their microstructure has been analyzed, and it was found that the ratio of superconducting phase of 2212 increased with the lowest growth rates which results in better grain alignment in the samples. The magnetic behavior of textured BSCCO was determined by measurements of the resistivity, ρ, in an external magnetic field. The normalized resistance as a function of temperature and of applied field of the samples was plotted and the low temperature peaks show the energy dissipation due to the flux flow within the grains at a given field. In addition, the activation energy, U0, for thermally activated flux flow (TAFF) was estimated for samples from the slope of the Arrhenius plot of ln ρ vs. 1/T. It was found that the activation energy of samples decreases with increasing magnetic field.