In this paper, samples of antimony doped Bi-based superconductor with stoichiometric composition Bi 1.7Pb 0.2Sb 0.1Sr 2Ca 2Ca 3O 10 were prepared by a solid state reaction method. The effect of sintering time on the superconducting properties was studied; all samples were sintered in air at 850°C for different sintering time (80, 100, 120, 140, and 160) h. X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements were performed for determination of the crystal structure and surface morphology of samples, respectively. All samples showed an orthorhombic structure with two phases, high-Tc phase (2223) and low-T c phase (2212) in addition to an impure phase. It has been observed that the critical temperature and the high-T c phase increases and appears to be the dominant phase when the sintering time is increased to 140 h, while with increasing sintering time to 160 h, both T c and the high phase started to decrease. (SEM) results show that increasing sintering time enhances the growing of superconducting phase unidirectional and suppresses the high phase intrusion which leads to the production of nearly single Bi-2223 phase with higher T c.
Among high-Tc superconductors, Bi-2223 compound with the superconducting critical temperature Tc ≈ 110 K is one of the promising candidates for practical applications, such as power transmission cables, flexible wire or tape carrying high density of current at liquid nitrogen temperature [
The superconducting properties of BiSrCaCuO compounds can be controlled by the addition or substitution of impurity atoms with different ionic radius and different bonding characters that produces atomic level crystal defects, lattice strains, non-superconducting inclusions and other structural defects. These inhomogeneties can improve Tc. For successful results different receipts can be found in the literature [
The role of Antimony appeared to be the enhancement of low-Tc to high Tc phase reaction beyond that achievable by lead incorporation alone [
Bi1.7Pb0.2Sb0.1Sr2Ca2Ca3O10 samples were prepared by a standard solid state reaction method. The stoichiometric amounts of high purity powders (99.999%) of Bi2O3, Pb3O4, Sb2O3, Sr(NO3)2, CaO, and CuO were used as starting materials. The powders of precursor were mixed together by using agate mortar. The mixture homogenization takes place by adding a sufficient quantity of 2-propanol to form a paste during the process of grinding for about 1 h. The mixture was grounded to a fine powder and then calcined in air by using a tube furnace at 800˚C for 30 h with a rate of 2˚C/min. The mixture then pressed into pellets by using hydraulic press type (SPECAC) under pressure of 0.7 GPa. Five sets of samples were sintered at 850˚C for 80, 100, 120, 140, and 160 h in order to study the effect of sintering time on the superconducting properties of the prepared samples. In this work all samples were subjected to gross structural characterization by X-ray diffraction (XRD) (Philips, with CuKalpha source). A computer program was used to calculate the lattice parameters, based on Cohen’s least square method. Resistance-temperature data were obtained by using four point probe DC method at temperature range (77 - 300) K to determine the critical temperature (Tc). Scanning electron microscopy (SEM) was performed by (JEOL JSEM-5910).
The X-ray diffraction analysis was performed for all samples as shown in
Volume fraction of phases formed (%) | Tc | c/a | V(Å)3 | c(Å) | b(Å) | a(Å) | ts(h) | |
---|---|---|---|---|---|---|---|---|
Bi-2212 phase | Bi-2223 phase | |||||||
43.9 | 56.1 | <77 | 6.878 | 1.083 | 37.081 | 5.418 | 5.391 | 80 |
43.3 | 56.7 | <77 | 6.888 | 1.079 | 37.120 | 5.394 | 5.389 | 100 |
37.9 | 62.1 | 84 | 6.892 | 1.078 | 37.139 | 5.387 | 5.388 | 120 |
17.4 | 82.6 | 110 | 6.895 | 1.084 | 37.148 | 5.417 | 5.387 | 140 |
35.8 | 64.2 | <77 | 6.881 | 1.078 | 37.091 | 5.397 | 5.390 | 160 |
phase, and this leads to an increase in the Tc value. Such result was also obtained by Kocabas [
We have used all the peaks of Bi-(2223) and Bi-(2212) phases for the estimation of the volume fraction of the phases using the following formulas [
where: I (2223), I (2212) and Iother are the intensities of Bi-2223 and Bi-2212 and other phases respectively. The volume fractions of the phases and lattice parameters a, b, c and c/a for all samples are given in
The percent volume fraction of the 2223 and 2212 phases as a function of sintering temperature were calculated from the XRD patterns of the Bi1.7Pb0.2Sb0.1Sr2Ca2Ca3O10 samples and are shown in
The electrical resistivity versus temperature plots at different sintering time is shown in
120 to 140 h, which is related to the increasing of (2223) phase volume fraction. The increase in the Tc value is mainly due to the strong link and increasing of the contact areas between grains, which have higher alignment along the c-axis as inferred from both XRD and SEM analyses. Such result was also obtained by Mizauno et al. [
The surface morphology for the prepared samples is shown in Figures 4(a)-(e). The grains of all samples are randomly plate-like grains and their size is found to increase with increasing sintering time. The occurrence of
grains with plate-like structure is a signature of the Bi-2223 phase formation from the Bi-2212 matrix mostly due to the prolonged sintering process [
The effect of sintering time on the phase formation and superconducting properties were investigated. Results revealed that prolonged sintering time up to a certain maximum time could improve the critical temperature of stoichiometry composition and increase the high-Tc (2223) phase. A remarkable increase in the critical temperature from 84 to 110 K was obtained with increasing sintering temperature from 120 to 140 h. Our results also show that samples sintered for 140 h had the highest critical temperature Tc = 110 K and highest volume fraction of Bi(Pb)-(2223) high-Tc phase 82.6%. On the other hand, increasing sintering temperature to 160 h decreases the critical temperature and the volume fraction of the high Tc phase.