Effect of Bi and Sr concentrations on the formation of the 2223 phase in Bi-Pb-Sb-Sr-Ca-Cu-O materials, obtained under different conditions of thermal treatment

The superconducting properties and the phase and chemical composition of Bi _x Pb_0.3Sb_0.1Sr _y Ca₂Cu₃O_z (x=1.5, 1.6, and 1.7;y=1.9, 2.0, and 2.1) materials synthesized by one-step and multistep thermal treatments have been investigated. The multistep annealing between 825–875°C promotes the 2223 phase. The change of Bi concentration has little effect on the 2223 phase formation, regardless of the kind of thermal treatment used, but increasing the Sr concentration (y> 2) strongly inhibits this phase. It has also been established that the loss of Pb after synthesis depends on the initial Bi concentration. The loss of Pb decreases when the initial Bi content is lower.     

BPSCCO Superconductor with Addition of Ag2O Synthesized Under Electrical Field

Ag₂O-doped (1.2% wt.) nitrate freeze-dried powders (Bi : Pb : Sr : Ca : Cu = 1.7 : 0.3 : 2 : 2.5 : 3.5) were processed under an external electrical field and 17.5 MPa pressure at 800°C, for 4 min in vacuum. Final heat treatments (HT) were applied at 835–850°C for 70 h. in air (Bi, Pb)₂Sr₂CaCu₂O _x (2212-phase) was formed by electrical field processing in just 4 min. Electrical field application enhanced (Bi, Pb)₂Sr₂Ca₂Cu₃O _y (2223-phase) formation during final HT. Ag₂O additions to field sintered BSCCO ceramics increased the amount of 2223-phase and the zero resistance critical temperature (T _e(R=0)) by 4 k.     

Enhancement of (Bi,Pb)-2223 HTS Formation by Boron-Doping

Influence of boron-doping on the superconducting properties of (Bi,Pb)-2223 HTS ceramics prepared in an alumina crucibles has been investigated. X-ray diffraction, resistivity, and AC susceptibility measurements were performed on the undoped and boron-doped compounds. Obtained results have shown that B₂O₃ addition in the Bi_1.7Pb_0.3Ca₂Sr₂Cu₃O _y precursor enhances the formation of high-T _c phase. The boron-doped samples with starting composition Bi_1.7Pb_0.3Ca₂Sr₂Cu₃B _x O _y (x=0.05 and 0.5) reveal significant improvement in the zero resistivity temperature compared to the undoped sample (from 72 K up to 100 K). Boron-doping level x=1.5 results in a substantial degradation of the (Bi,Pb)-2223 phase.     

Superconducting Bi-Sr-Ca-Cu-O films formed diffusion of metallic bismuth on Sr2Ca2Cu4O y substrates

Superconducting Bi-Sr-Ca-Cu-O films have been prepared on Sr₂Ca₂Cu₄O _y substrates by thermal evaporation of metallic Bi layer and heat-treatment at 830°C for a few minutes in air. The zero resistance temperature of Bi₂Sr₂Ca₁Cu₂O _y film of 1–μm in thickness is about 70 K. The surface diffusion process of Bi on the granular structure of Sr₂Ca₂Cu₄O _y was observed by scanning electron microscope and thermogravimetry analysis. The stripe pattern of superconducting film, typically 2μm thick and 0·3 mm wide, is formed by using a mask.     

Evolution of 2223 phase in the Bi2Pb0.6Sr2Ca2Cu3.1Oy system

The role of cationic ratios (Sr/Ca and Bi/Pb) in the evolution of high-T _c phase (2223) in samples prepared under different sintering conditions, starting with a composition of Bi₂Pb_0.6Sr₂Ca₂Cu_3.1O_y, has been investigated by employing energy-dispersive X-ray analysis, scanning electron microscopy and X-ray diffraction. As manifested by the observed decrease in Sr/Ca ratio, an increase in sintering temperature from 822 to 852 °C increases the disorder in Sr-O and Ca layers. The observed increase in the volume fraction of 2223 phase and the contraction inc-axis parameter have been explained on the basis of the observed decrease in Sr/Ca ratio. It thus appears that the disorder caused by the intersubstitution of Ca and Sr in SrO and Ca layers and partial replacement of Bi by Pb in the structure promote the evolution and growth of 2223 phase.     

Formation and growth studies of the (Bi,Pb)<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10</Subscript> phase in Ag sheathed tapes

The formation and the thickness growth of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ phase in Ag-sheathed tapes have been investigated by scanning electron microscopy on samples sintered at 840°C in a flow of 8.5% O₂ (rest N₂) and quenched in air after sintering for 1 to 50 h. The thickness of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ grains was measured statistically after different sintering times. The experimental results show that the average thickness of these grains increases during the entire sintering period, while the average thickness growth rate decreases exponentially with sintering time. The volume fractions of the various phases present during the heat treatment were also measured from micrographs. Detailed studies of the microstructure and phase formation kinetics support the view that the formation of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀ phase proceeds via a nucleation and growth process. Based on the present observations, a model describing the microstructure evolution is presented.     

Phase Assemblage in PBSSCO OPIT High‐Temperature Superconductor Precursor Powders – Rietveld Analysis of X‐ray Diffractograms

The phase assemblage in PBSCCO‐2223, (Bi, Pb)₂Sr₂ Ca₂Cu₃O_{10 + x}, precursor powders used for the production of long lengths of superconducting tapes by the oxide powder in tube (OPIT) technology has been determined by Rietveld analysis of powder x‐ray diffractograms. The effects of grain alignment, structure modulation and anisotropic line broadening have been taken into account in the Rietveld analysis. The phase assemblage of the air‐annealed precursor is typically Pb‐free 2212 (Bi, Pb)₂Sr₂CaCu₂O_{8 + x}, Pb₃Sr₃Ca₂CuO₁₂, Ca₂PbO₄, Sr₆Ca₈Cu₂₄O₄₁, and Ca_0.79Sr_0.04CuO₂. If the annealing is done in N₂, the Pb⁴⁺ phases disappear and Pb²⁺ enters the 2212 phase, which is accompanied mainly by Ca₂CuO₃ and CuO. Pb‐2223 formation occurs above 830°C in air.     

BPSCCO Superconductor with Addition of Ag2O Synthesized Under Electrical Field

Ag₂O-doped (1.2% wt.) nitrate freeze-dried powders (Bi : Pb : Sr : Ca : Cu = 1.7 : 0.3 : 2 : 2.5 : 3.5) were processed under an external electrical field and 17.5 MPa pressure at 800°C, for 4 min in vacuum. Final heat treatments (HT) were applied at 835–850°C for 70 h. in air (Bi, Pb)₂Sr₂CaCu₂O _x (2212-phase) was formed by electrical field processing in just 4 min. Electrical field application enhanced (Bi, Pb)₂Sr₂Ca₂Cu₃O _y (2223-phase) formation during final HT. Ag₂O additions to field sintered BSCCO ceramics increased the amount of 2223-phase and the zero resistance critical temperature (T _e(R=0)) by ～ 4 k.     

Effect of the fluctuation range of formation temperature on the preparation and superconductivity of Bi(Pb)2223 single-phase

Effects of the fluctuation range of formation temperature on preparation and superconducting properties of the Bi(Pb)2223 phase have been investigated in detail. Our results show that knowledge about the temperature distribution and fluctuation in the muffle furnace is necessary for preparation of the Bi(Pb)2223 single-phase. Single-phase samples from Bi_0.17Pb_0.3Sr₂Ca₂Cu₃O_y were obtained by a solid-state reaction in air at 835±5C. The best superconducting property of the as-prepared samples shows a one-step transition of a.c. susceptibility withT _c=109 K. Using this optimum sintering temperature and keeping the temperature fluctuation less than 5C, we have prepared pure Bi(Pb)2223 single-phase samples with good reproducibility.     

Effect of Ba Substitution on the Formation of (Tl,Bi)-1234 Superconducting Phase

(Tl_1−x Bi _x )(Sr_2−y Ba _y )Ca₃Cu₄O _z ((Tl,Bi)-1234) samples (x=0.1–0.3, y=0.4–1.5) were synthesized under ambient pressure by using a two-step solid-state reaction method to investigate the effect of Ba substitution on the formation and superconducting properties of the (Tl,Bi)-1234 phase. X-ray diffraction analysis shows that nearly single-phased samples are obtained for (Tl_0.8Bi_0.2)(Sr_2−y Ba _y )Ca₃Cu₄O _z (0.8≤y≤1.2), suggesting that control of the composition ratio of Sr and Ba in the bridging layer is a key to stabilizing the 1234-type structure. The critical temperature for the nearly single-phased samples remained between 106.9 K and 109.1 K and was not significantly affected by the change in the Ba content.     

Phase evolution and gas-phase particle size distributions during spray pyrolysis of (Bi,Pb)SrCaCuO and Ag(Bi,Pb)SrCaCuO powders

Phase evolution, gas-phase particle size distributions and lead loss were studied during formation of (Bi,Pb)SrCaCuO powders and their composites with silver by spray pyrolysis starting from nitrate solutions. The 10 wt% Ag/90 wt% Bi_1.8Pb_0.44Sr₂Ca_2.2Cu₃O_x composite powders made at 700°C consisted of 20–60 nm grains of silver and mixed-oxide phases with a fine dispersion of Ag grains within the particles. At 700°C, the primary phases present in (Bi,Pb)SrCaCuO powders were (Bi,Pb)₂Sr₂CuO_x (2201), Ca₂PbO₄ (plumbate), (Bi,Pb)₂Sr₂CaCu₂O_x(2212), and (Bi,Pb)₃Sr₂Ca₂Cu₁O_x(3221). For T≥800°C, the powders were considerably depleted in lead, and the plumbate and 3221 phases were absent. For T = 900°C, a large number of ultrafine particles (<30 nm) were formed, probably from the PbO vapor released from the reactor walls. Using spray pyrolysis, it is easy to control stoichiometry and limit the phase segregation at the nanometer-scale so that homogeneous and phase-pure materials can be obtained rapidly during subsequent processing.     

Oxygen release process of BSCCO powder during heat treatment

In this paper, we report a new method to investigate the oxygen release process during heat treatment of (Bi,Pb)₂Sr₂Ca₂Cu₃O _x (BSCCO) powder, based on oxygen partial pressure measurement (OPPM) using an oxygen analyzer. The influence on oxygen release process of various processing parameters has been studied. Experimental results show that OPPM is a suitable method for investigation of the oxygen release process during heat treatment of BSCCO powder. It is suggested that oxygen release is related to decomposition of the Ca₂PbO₄ phase.     

Effect of composition on critical current density of Bi2212/Ag round wires

We have fabricated Bi2212/Ag round wires using three kinds of precursor to study the effect of a narrow variation of composition. Slightly different compositions - Bi_2.17Sr_1.94Ca_0.89Cu_2.0O_x(N13), Bi_2.15Sr_1.94Ca_0.89Cu_2.0O_x(N14), and Bi_2.17Sr_1.98Ca_0.89Cu_2.0O_x(N15) - were used and Sr/Ca ratio of them were 2.18, 2.18, and 2.22, respectively. The Ag ratios of the wires were 2.7-2.8 and average filament diameter was 19-21 μm. DTA analysis of the wire showed the peritectic temperature of three wires was very similar value of the range of 880-881 °C. The best engineering critical current density (J_e) of three wires at 4.2 K and 0 T was 414-448 A/mm² at the maximum process temperature range of 884-892 °C. The n-value of N14 showed 13.6, whereas other two wires showed lower n-value, estimating the existence of micro-cracks. Although Bi2212/Ag round wires fabricated by three kinds of composition showed similar J_e value, n-value was quite different. It is likely that the fabrication process such as the drawing as well as the composition of precursor will affect on J_e of Bi2212/Ag round wire.     

Detection and stimulation of impulse electromagnetic radiation (IEMR) of radio-frequency (rf) range (∼200 khz) by sensitive element based on a resonant circuit with HTSC element

 The abnormally high sensitivity to low power impulse electromagnetic radiation (IEMR) systems that include a sensing element consisting of a resonant circuit with secondary coil and high-temperature superconductor (HTSC) core was experimentally investigated. The core was produced using epoxied composites containing HTSC powders [YBa₂Cu₃O_x and Bi(Pb)₂Sr₂Ca₂Cu₃O_x composition]. Received: 22 July 1998 / Reviewed and accepted: 28 August 1998     

Possibility of Superconductivity of the 2212 Phase in the Bi(Pb)-Sr-Ce-Cu-O System

Synthesis of the Bi-2212 compound in the Bi-Sr-Ce-Cu-O system has been already known. But, there has been no report on superconductivity of the compound yet. We have prepared many Bi-2212 samples partially substituted by Pb for Bi in the Bi-Sr-Ce-Cu-O system. The nominal composition is (Bi_2−y Pb _y )Sr₂(Sr_1−x Ce _x )Cu₂O _z . Then, we have investigated possibility of superconductivity for the samples. As a result, we find that a sample with nominal composition ofx=0.23 andy=0.1, which is of almost the single 2212 phase, shows an anomaly at about 70 K in addition to temperature dependence of the resistivity like a semiconductor. Furthermore, the sample also shows a decrease of magnetic susceptibility starting at about 70 K with decreasing temperature. These experimental results can be considered to result from superconductivity of the 2212 phase in the Bi(Pb)-Sr-Ce-Cu-O system.     

Possibility of Superconductivity of the 2212 Phase in the Bi(Pb)-Sr-Ce-Cu-O System

Synthesis of the Bi-2212 compound in the Bi-Sr-Ce-Cu-O system has been already known. But, there has been no report on superconductivity of the compound yet. We have prepared many Bi-2212 samples partially substituted by Pb for Bi in the Bi-Sr-Ce-Cu-O system. The nominal composition is (Bi_{2− y} Pb _y )Sr₂(Sr_{1− x} Ce _x )Cu₂O _z . Then, we have investigated possibility of superconductivity for the samples. As a result, we find that a sample with nominal composition of x=0.23 and y=0.1, which is of almost the single 2212 phase, shows an anomaly at about 70 K in addition to temperature dependence of the resistivity like a semiconductor. Furthermore, the sample also shows a decrease of magnetic susceptibility starting at about 70 K with decreasing temperature. These experimental results can be considered to result from superconductivity of the 2212 phase in the Bi(Pb)-Sr-Ce-Cu-O system.     

Effect of annealing on properties of bismuth based highT c superconductors

A novel method to increase the amount of the 110 K phase in the Bi-Sr-Ca-Cu-O system was examined. After the sample with composition of Bi₂Sr₂CaCu₂O_x had been calcined, it was soaked in ethanol containing copper acetate and calcium acetate, the amounts of which were determined to give the composition of Bi₂Sr₂Ca₂Cu₃O_y after sintering. Subsequently, annealing at about 400 °C was conducted to examine the stability of the 110 K phase. The sample containing mainly the 80 K phase and a small amount of the 110 K phase showed an increase in the amount of the 110 K phase while that containing only the 80 K phase showed no change. Therefore, it is presumed that the 110 K phase may grow when the excess calcium and copper coexist adjacent to the 80 K phase at relatively low temperatures such as 400 °C.     

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

The optimal composition for synthesizing the high-T_c 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 Bi_{2.1 – x}Pb_xSr_1.9Ca_2.05Cu_3.0O_z, 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.     

Synthesis of (Hg,X)Ba2Ca2Cu3Ox Superconductors

Synthesis and processing parameters for (Hg_1–xBi_x)Ba₂Ca₂Cu_3.1O_y were optimized for growth at temperatures suitable for growth on Ag and Au substrates (<850° C). Use of Bi₂CuO₄ as a Bi source combined with variations of BaCaCuO precursor phase assemblages allowed the formation of some liquid phase during the reaction and resulted in dense (Hg_1–xBi_x)Ba₂Ca₂Cu_3.1O_y samples with aligned colonies of grains. Magnetization measurements in fields up to 30 T indicated good intergrain coupling within the large grain colonies. The results of the Bi doped samples are compared with those of previously reported Re doped samples.     

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

By the magnetically modulated microwave absorption method (MAMMA) we observed the modifications induced by different calcination temperatures (between 830°C and 870°C) on the 2223 phase formed in a system sintered at (855±5)°C with the starting composition Bi_1.7Pb_0.3Sr₂Ca₂Cu₃O _y . The presence of the 2223 phase in almost distinct states (consequently, multiple 2223 phases) in the same sample was observed. As the calcination temperature was increased up to 850°C, the highest temperature state of the 2223 phase intensified. Higher calcination temperatures resulted in the enhancement of other lower-temperature states. The homogeneity of the 2223 phase was greatly improved by annealing the samples at, 800°C for 5 min in a flowing nitrogen atmosphere. We labeled as metastable the lower-temperature states having excess oxygen, which, by easily losing the supplementary oxygen under the above annealing procedure, were shifted to higher temperatures.