Superconductivity in the Bi - Sr/K - Ca/Na - Cu - O system
TL;DR: In this article, the role of double doping at the Ca and Sr sites simultaneously in the Bi-2212 composition was studied and it was found that the structure is single-phase Bi-2012.
Abstract: Samples with the stoichiometric composition with x = 0.1 and y = 0.1, 0.2, 0.3 and 0.4 were prepared by the solid state reaction method. The role of Na and K doped at the Ca and Sr sites simultaneously in the Bi-2212 composition was studied. From the x-ray diffraction data it was found that the structure is single-phase Bi-2212. From the resistivity data the varies from 63 to 67 K for different dopant levels. The diamagnetic nature of the samples was confirmed by ac susceptibility measurements. The oxygen content was determined by the two-step iodometric titration technique. The present results on the effect of double doping are compared with those of single dopants published earlier by our group. The microstructures of the samples were examined by scanning electron microscopy.
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TL;DR: In this paper, the superconducting and normal state transport properties of ceramic samples with composition Bi 2 Sr 2−x K x CaCu 2 O y ( x ǫ = 0, 0.1, 0., 0.2, 0, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) have been investigated by measuring thermoelectric power.
Abstract: The superconducting and normal state transport properties of ceramic samples with composition Bi 2 Sr 2− x K x CaCu 2 O y ( x = 0, 0.1, 0.2, 0.3, 0.4) have been investigated by measuring thermoelectric power. The samples were prepared by the solid state route, and single phase Bi-2212 was found for all compositions. The T c (0) and thermoelectric power data were collected from 50 to 300 K. The thermoelectric power changes slightly with increasing doping level and increases linearly with decreasing temperature reaching a maximum value at T c (0). The T c (0), hole concentration and thermoelectric data were correlated. The results obtained are analysed in terms of phenomenological theoretical models that makes it possible to determine the band spectrum parameters in the normal state and to trace their changes with varying composition. Following models applied such as (a) Hubbard model, (b) two-band model, (c) Fermi-liquid behaviour. Applicability of these models to the present HTSC system is discussed and the parameters related to the models have been evaluated.
18 citations
TL;DR: In this article, a combination of Tl 0.3−x Sb x is found to promote the formation of high-Tc (Bi-2223) superconducting phase in Bi 1.7 Pb 0.4 Sr 2 Ca 2 Cu 3 O y compound which consequently results in enhancement of the critical temperatures.
14 citations
TL;DR: In this paper, the superconductivity and critical current density of stoichiometric composition Bi1.8Pb0.4Sr2−xKxCa2−yNdyCu3Oz with x = 0, 0.01,0.02, and y = 0.02 were prepared by the solid state reaction method and postannealing experiments were carried out at 500 °C for 30 h in order to improve the oxygen homogeneity.
Abstract: Samples of stoichiometric composition Bi1.8Pb0.4Sr2−xKxCa2−yNdyCu3Oz with x = 0, 0.01, 0.02, and y = 0, 0.01, 0.02 were prepared by the solid state reaction method. Post-annealing experiments were carried out at 500 °C for 30 h in order to improve the oxygen homogeneity. They were characterized by the x-ray diffraction (XRD) technique, field emission scanning electronic microscopy (FE-SEM), resistivity, magnetization and Raman measurements. The superconducting transition temperature Tczero of the samples varies from 99 to 110 K for different doping. The superconductivity and the critical current density (Jc) of the sample single doped with K are improved compared with the undoped one. We attribute the change of Tc to the variation of carrier concentration. Additionally, the observed change of the normal state resistivity is related not only to carrier concentration but also to the nature of grain boundary links. These analyses are confirmed by Raman and SEM measurements.
13 citations
TL;DR: In this paper, a systematic study of the weak link behavior for (Cu 0.5 Tl 0.25 K 0.6 Tl ) superconductors has been carried out using electrical resistivity and AC-susceptibility techniques, and it is concluded from these studies that potassium atoms appearing at the crystal boundaries enhance inter-grain coupling and pinning mechanism in K-doped (Ba 2 Ca 2 Cu 3 O 10− δ ) supercondors.
Abstract: A systematic study of the weak link behaviour for (Cu 0.5 Tl 0.5− x K x )Ba 2 Ca 2 Cu 3 O 10− δ ( x = 0, 0.25) superconductors samples has been carried out using electrical resistivity and AC-susceptibility techniques. The K-doped (Cu 0.5 Tl 0.5− x K x )Ba 2 Ca 2 Cu 3 O 10− δ samples were synthesized by solid-state reaction method. In magnetic susceptibility measurements, the real ( χ ′) and imaginary ( χ ″) parts of the magnetic susceptibility of (Cu 0.5 Tl 0.5− x K x )Ba 2 Ca 2 Cu 3 O 10− δ ( x = 0, 0.25) samples were measured as a function of temperature under various DC-magnetic fields up to 172 Oe. It is observed from these studies that the magnitude of the diamagnetism is substantially enhanced by K-doping. The possible reasons for the enhanced magnitude of diamagnetism have been investigated. It is observed from in-field magnetic measurements that the inter-grain coupling is improved with the K-doping. It is concluded from these studies that potassium atoms appearing at the crystal boundaries enhance inter-grain coupling and pinning mechanism in K-doped (Cu 0.5 Tl 0.25 K 0.25 )Ba 2 Ca 2 Cu 3 O 10− δ superconductors.
7 citations
TL;DR: In this paper, the authors have successfully synthesized (Cu 0.5 Tl 0.25 )Ba 2 O 4− δ charge reservoir layer to the conducting CuO 2 planes.
Abstract: In order to study the higher carrier’s doping efficiency of (Cu 0.5 Tl 0.5 )Ba 2 O 4− δ charge reservoir layer to the conducting CuO 2 planes we have incorporated Bi in (Cu 0.5 Tl 0.5 )Ba 2 Ca 2 Cu 3 O 10− δ superconductors; the presence of Bi in the charge reservoir layer promotes highest anisotropy to these compounds. For such studies, we have successfully synthesized (Cu 0.25 Tl 0.5 Bi 0.25 )Ba 2 Ca 2 Cu 3 O 10− δ , (Bi 0.5 Tl 0.5 )Ba 2 Ca 2 Cu 3 O 10− δ , (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25 )Ba 2 Ca 2 Cu 3 O 10− δ and (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25 )Ba 2 Ca 2− y Be y Cu 3 O 10− δ superconductors at normal pressure and studied their superconducting properties. These studies have shown that incorporation of Bi at the charge reservoir layer promoted a decrease in the density of carriers in the conducting CuO 2 planes which in turn suppressed the magnitude of diamagnetism of final compound. The decreased density of the carriers in the CuO 2 planes, which most likely promotes inferior superconducting properties, was replenished by doping of Li in the charge reservoir layer and optimizing their number by post-annealing in oxygen atmosphere. It is observed that Bi doping in (Cu 0.5 Tl 0.5 )Ba 2 O 4− δ charge reservoir layer promotes an increase in the c -axis length which in turn increase the anisotropy and decrease the Fermi-vector [ k F = (3 π 2 N / V ) 1/3 ] and Fermi-velocity [ v F = ( π e c Δ / ℏ ) ] of the carriers. We have decreased the c -axis length of Bi doped compounds by doping Be at the Ca sites in (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25 )Ba 2 Ca 2− y Be y Cu 3 O 10− δ superconductors. It is observed from these experiments that Beryllium doping of y = 0.5 has produced excellent superconducting properties in terms of enhancement of T c ( R = 0) and magnitude of diamagnetism in this compound. A maximum decrease in the unit cell volume is observed with this Be doping concentration, which enhance k F , v F and superconducting order parameter of the carriers and hence promote the enhancement of superconducting properties. These studies have also shown that the role of density of the carriers in CuO 2 planes is pivotal in the mechanism of superconductivity in these compounds and Bi doping significantly affects them due to its presence in the charge reservoir layer.
4 citations
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TL;DR: In this paper, the critical current densities for Bi-based superconductors fabricated by normally sintering powder in the tube technique, hot-pressing and hot isostatic pressing, are presented and discussed.
Abstract: AC susceptibility measurements and critical current densities for Bi-based superconductors fabricated by normally sintering powder in the tube technique, hot-pressing and hot isostatic pressing, are presented and discussed. It is argued that the J c of the normally sintered sample is limited by intergrain weak links, while the J c of the mechanically deformed samples is determined primarily by flux pinning. It is shown that the pinning force density is significantly increased through mechanical deformation. For Ag-sheathed tapes and hot-pressed samples, the J c drops 80% when the magnetic field is increased from ambient earth field to 0.5 T, whereas that for the normally sintered samples decreases by two orders in a magnetic field of only 0.01 T. Dislocations may act as effective pinning centres for flux lines in HIPed samples. Uniaxial pressing produces an excellent grain alignment, which allows the crystalline anisotropy to be utilized to strengthen flux pinning. The planar defects along a - b direction may induce internal Josephson weak links leading to a reduction of the J c in the c direction, but not in a - b direction. In the a - b direction, it is believed that the planar defects provide effective pinning. Utilisation of both planar defects and crystalline anisotropy may provide a valuable route towards the goal of high critical current densities.
28 citations
TL;DR: In this paper, the oxygen nonstoichiometry and high temperature conductivity of Bi 2.12 Sr 1.86 Cu 1.02 O y (2201 phase) were determined as a function of temperature (T ) and oxygen partial pressure (P O2 ).
Abstract: The oxygen nonstoichiometry and high temperature conductivity of Bi 2.12 Sr 1.86 Cu 1.02 O y (2201 phase) were determined as a function of temperature ( T ) and oxygen partial pressure ( P O2 ). The dependences of conductivity on T and P O2 were similar to those of oxygen content, and two subphases, α and β, were found in such cases as 2212 and 2223 phases. From the result a close relationship was inferred between conductivity and oxygen content, and the mobility and carrier density were calculated. The carrier density of 2201 phase was smaller than those of the 2212 and 2223 phases.
23 citations
TL;DR: In this article, the effects of Li doping on the superconductivity of Bi-based superconducting whiskers have been investigated, and Li doping is effective in increasing T c of both the Bi 2 Sr 2 CaCu 2 O x (2223) and undoped 2223 whiskers.
Abstract: The effects of Li doping on the superconductivity of Bi-based superconducting whiskers have been investigated. The Li doping is effective in increasing T c of both the Bi 2 Sr 2 CaCu 2 O x (2223) whiskers. The Li-doped 2212 whiskers show a T c at 82 K, which is higher than that of the undoped 2212 whiskers by 5 K. The Li-doped and undoped 2223 whiskers have been prepared by the Conversion by Annealing in Powder (CAP) method. An enhancement of T c by 1.2 K is achieved by Li doping of the 2223 whiskers. The T c of the 2223 phase is commonly accepted to be lowered by a reduction of hole concentration, which is opposite to the situation of the 2212 phase. Therefore, the mechanism of the enhancement of T c is not due to the optimization of the hole concentration. From the compositional analysis and the measurement of the c -axis lattice parameter, the Li doping is thought to be effective in increasing the Sr/Ca ratio for both kinds of whiskers, which causes the enhancement of T c .
18 citations
TL;DR: In this paper, magnetization versus applied field data have been taken up to 5 T over a wide temperature range from 10 K to 77 K for polycrystalline YBa 2 Cu 3 O x with x = 6.98 and x =6.62.
Abstract: Magnetization versus applied field data have been taken up to 5 T over a wide temperature range from 10 K to 77 K for polycrystalline YBa 2 Cu 3 O x with x =6.98 and x =6.62. The intragrain critical current density has been calculated based on the magnetization measurements. The observed temperature dependence of the flux pinning behavior in the x =6.98 sample indicates a new pinning mechanism in the intermediate temperature region, whose strength increases linearly with the applied field above certain field values. The experimental results also suggest that the twin boundary pinning is active only in the low temperature region.
16 citations
TL;DR: In this article, a series of sodium-doped Bi-2212 single-phase high- superconductors have been prepared by the solid state reaction method, and ultrasonic longitudinal velocity studies were undertaken over the temperature range 80 - 300 K using the pulse transmission technique.
Abstract: A series of sodium-doped Bi-2212 single-phase high- superconductors have been prepared by the solid state reaction method. After the usual characterization by XRD, SEM, bulk density porosity etc, ultrasonic longitudinal velocity studies were undertaken over the temperature range 80 - 300 K using the pulse transmission technique. In the temperature range 300 - 230 K, in contrast to normal solids, the velocity of Bi - Na(0) and Bi - Na(3) samples is found to decrease with decreasing temperature (elastic softening) followed by a velocity maximum at around 150 K for all the four samples, signifying the presence of lattice instabilities. Plausible explanations are given for both the elastic softening and the velocity maxima on the basis of microstructure and ordering readjustments of the oxygen atoms among the Cu - O planes of the samples.
10 citations