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 role of Na and the effect of various heat treatments in the 2212 composition were studied and it was found that the samples annealed for longer duration have shown a single phase 2212.
Abstract: Samples with the nominal composition Bi 2 Sr 2 Ca 1− x Na x Cu 2 O y (if with x = 0.05, 0.2, 0.4 and 0.5) were prepared by the solid state reaction method. The role of Na and the effect of various heat treatments in the 2212 composition were studied. From the X-ray diffraction data it is found that the samples annealed for longer duration have shown a single phase 2212. From the DC four-probe resistivity data, it was found that the T c (zero) varies from 79 to 89 K. It is believed that doping with an alkali element would reduce the oxygen content due to monovalency and gives an effect similar to that during heat treatment under low oxygen pressure or quenching. The presence of sodium in the samples was confirmed by electron probe microanalysis.
9 citations
TL;DR: In this article, the role of Li at both Ca-and Cu sites in the Bi-2212 composition was studied and the presence of Lithium was confirmed by inductive the coupled plasma method.
Abstract: Samples with the nominal composition Bi 2 Sr 2 Ca 1−x Li x Cu 2 O y (x = 0.2, 0.4, and 0.6) and Bi 2 Sr 2 CaCu 2−x Li x O z (x = 0.4, 0.6, and 1.0) were prepared by the solid state reaction method. The role of Li at both Ca-and Cu sites in the Bi-2212 composition were studied. From the X-ray diffraction data it was found that the Li-doped at the Ca site increases the c-axis and that doped at the Cu site decreases the c-axis. From the D.C. four-probe resistivity data it was found that Li-doped at the Ca site reduces the T c and the Li-doped at the Cu site gives T c (0) above the liquid nitrogen temperature. It was observed that the Li doping reduces the melting point of Bi-2212 composition. The presence of Lithium was confirmed by inductive the coupled plasma method
6 citations
TL;DR: In this paper, the nominal composition Bi2Sr2Ca1−x.............. Na x.............. Cu2O fixme y.............. (x=0, 0·1, 0 ·2 and 0·3) were prepared by solid-state reaction of the individual compounds and X-ray diffraction patterns indicate that the samples have a majority 2212 phase.
Abstract: Samples with the nominal composition Bi2Sr2Ca1−x
Na
x
Cu2O
y
(x=0, 0·1, 0·2 and 0·3) were prepared by solid-state reaction of the individual compounds. X-ray diffraction patterns indicate that the samples have a majority 2212 phase with 2223 also being present. From the DC four-probe resistance data, we have observed that the furnace-cooled samples show metallic behaviour while the quenched samples show superconductivity up to 97 K.
6 citations
TL;DR: The role of potassium at the Sr-site and the effect of various heat treatments in the 2212 composition were studied in this paper, where the X-ray diffraction data was found that the samples annealed for longer have shown a single phase 2212 up to x = 0.4 dopant level.
Abstract: Samples with the nominal composition Bi2Sr2−xKxCaCu2Oy ( with x = 0.1, 0.2, 0.3, 0.4 and 0.5 ) were prepared by the solid state reaction method. The role of potassium at the Sr-site and the effect of various heat treatments in the 2212 composition were studied. From the X-ray diffraction data it is found that the samples annealed for longer have shown a single phase 2212 up to x = 0.4 dopant level. From d.c. four probe electrical resistance data, it was found that the T c (0) varies from 76 to 93 K for different dopant levels. The diamagnetic nature of the samples was confirmed by a.c. susceptibility measurements. The phase formation of 2212 and the presence of potassium in the doped samples was confirmed by electron microprobe analysis.
5 citations
TL;DR: In this article, the effect of co-doping of Ca for Y and Al for Cu(1) in YBa 2 Cu 3 O 7− z (YBCO) leads to a gradual depression in the T c due to counterbalancing effects of Ca and Al doping.
Abstract: Chemical substitution on different sites in superconducting phases affects the layer spacing and electric charge distribution along the c -axes and hence the charge carrier density in the Cu O 2 planes. Alkali element doping in Bi 2 Sr 2 CaCu 2 O 8+ z (BSCCO) and Bi 2 Sr 2 YCu 2 O 8+ z (BSYCO) raises the T c while co-doping of Ca for Y and Al for Cu(1) in YBa 2 Cu 3 O 7− z (YBCO) leads to a gradual depression in the T c due to counterbalancing effects of Ca and Al doping.
5 citations