In this study, the effects of Nb substitution on the Bi-based superconducting materials have been investigated. The X-ray diffraction measurement indicated coexistence of Bi-2212, Bi-2223 phases and some impurity phases of CuO, CuNb 2O 6, CaNb 2O 6, CaCuO 2, and Sr 5Nb 5O 16. With increasing Nb content, impurity phases consistent with the Nb element appeared in the samples. Also with increasing Nb content, the Bi-2223 phase of samples gradually was decreased and in contrast, the Bi-2212 phase was increased. From the SEM, results have been seen that with increasing of Nb contents, the crystal structure of the samples was slightly changed because of the disrupted grain growth. From the electrical resistivity measurements, it has been found that with increasing of Nb contents, critical temperature decreases and the superconducting transition width ( Δ T) increases. Estimated critical current density showed that J c decreases with increasing Nb content, as expected.
In high-temperature superconductors, there is a group which is called the Bi-based superconductors. Following the discovery of Bi-based superconductors [
Before, the researchers have studied the effect of the high-valency cations, like Ta5+, V5+, Nb5+ and Nd3+ for obtaining of Bi-2223 single phase and found that doping any one of them can significantly enhance the formation of Bi-2223 phase. These cation roles are quite similar to Pb for stabilizing the Bi-2223 phase [
In this research, our aims are:
1) To answer this question that substitution of Pb with Nb in BPSCCO systems increases or decreases the critical temperature.
2) To explore the magnetic behavior of the modified BPSCCO systems. In other words, this substitution improves or depresses the superconductivity of BPSCCO systems.
Our simple are BPSSCO system with general formula of Bi1.65Pb0.35−xNbxSr2- Ca2Cu3O10+δ and x = 0.0, 0.05, 0.15, 0.25, 0.35.
Bi1.65Pb0.35−xNbxSr2Ca2Cu3O10+δ samples, with x = 0.0, 0.05, 015, 0.25 and 0.35 substitutions were prepared from ultra-fine and high grade purity powders Bi2O3 (99.99%), PbO (99.99%), SrCO3 (99.99%), CaCO3 (99.9%), Nb2O5 (99.99%) and CuO (99.99%) using the conventional solid-state reaction method [
For measurement of the DC resistivity of samples as a function of temperature, the standard four-point probe method with silver point contacts was used. The transition temperature TC was determined as the temperature at zero resistivity. The structure of the samples was checked by SIMENS X-ray diffractometer with CuKα (1.54 Å) radiation in the range of 2θ = 2˚ - 60˚. Lattice parameters were determined from the XRD patterns by using Match 3.3 software based on Cohen’s least square method. Scanning electron microscope (SEM) photographs for the study of the microstructure were taken by using MIRA3 TESCAN. Magnetic measurements of samples were done by a Quantum Design PPMS model 6000.
diffraction angle 2θ range between 2˚ - 60˚. Comparison of five highest peaks and detected impurity phases of samples by using Match 3.3 software are given in
For determining the volume fraction of the present phases of the samples, following equations were used by means of corresponding XRD peaks of Bi-2223 and Bi-2212 phases [
where I(Bi-2223) and I(Bi-2212)) are the intensity of present phases in the samples which were indicated in
Small impurity peaks of samples were identified by using Match 3.3 Software. For example,
Sample (Nb substation) | Nominal Composition | 2θ | d-values | Peak name | (hkl) |
---|---|---|---|---|---|
4.73 | 18.677 | Bi-2223 | H(002) | ||
27.5 | 3.241 | Bi-2223 | H(115) | ||
28.80 | 3.097 | Bi-2223 | H(117) | ||
A (x = 0.00) | Bi1.65Pb0.35Sr2Ca2Cu3O10+δ | 31.87 | 2.806 | Bi-2223 | H(119) |
33.13 | 2.701 | Bi-2223 | H(200) | ||
18.56 | 4.777 | SrCu2O2 | I(011) | ||
36.24 | 2.477 | CaCuO2 | I(101) | ||
4.80 | 18.382 | Bi-2223 | H(002) | ||
26.25 | 3.392 | Bi-2223 | H(115) | ||
28.86 | 3.091 | Bi-2223 | H(117) | ||
31.91 | 2.870 | Bi-2223 | H(119) | ||
B (x = 0.05) | Bi1.65Pb0.3Nb0.05Sr2Ca2Cu3O10+δ | 33.80 | 2.696 | Bi-2223 | H(200) |
16.50 | 5.367 | CaNb2O6 | I(110) | ||
17.05 | 5.197 | CuNb2O6 | I(110) | ||
19.12 | 4.637 | Sr5Nb5O16 | I(070) | ||
5.76 | 15.336 | Bi-2212 | L(002) | ||
23.95 | 3.712 | Bi-2212 | L(008) | ||
27.56 | 3.234 | Bi-2212 | L(115) | ||
28.97 | 3.079 | Bi-2223 | H(0012) | ||
C (x = 0.15) | Bi1.65Pb0.2Nb0.15Sr2Ca2Cu3O10+δ | 33.19 | 2.697 | Bi-2212 | H(200) |
16.72 | 5.305 | CaNb2O6 | I(110) | ||
19.10 | 4.643 | Sr5Nb5O16 | I(070) | ||
36.31 | 2.472 | CaCuO2 | I(101) | ||
5.83 | 15.137 | Bi-2212 | L(002) | ||
23.28 | 3.818 | Bi-2212 | L(008) | ||
27.61 | 3.228 | Bi-2212 | L(115) | ||
29.18 | 3.058 | Bi-2223 | H(0010) | ||
D (x = 0.25) | Bi1.65Pb0.1Nb0.25Sr2Ca2Cu3O10+δ | 31.17 | 2.867 | Bi-2212 | L(117) |
17.42 | 5.087 | Sr5Nb5O16 | L(031) | ||
28.41 | 3.138 | Ca2CuO3 | I(101) | ||
36.43 | 2.464 | CaCuO2 | I(101) | ||
23.20 | 3.830 | Bi-2212 | L(008) | ||
24.86 | 3.579 | Bi-2212 | H(013) | ||
27.49 | 3.241 | Bi-2212 | L(115) | ||
31.03 | 2.879 | Bi-2212 | L(117) | ||
E (x = 0.35) | Bi1.65Nb0.35Sr2Ca2Cu3O10+δ | 33.16 | 2.699 | Bi-2223 | H(200) |
17.02 | 5.213 | CuNb2O6 | I(110) | ||
19.11 | 4.639 | Sr5Nb5O16 | I(070) | ||
38.82 | 2.318 | CuO | I(200) |
Volume fraction of phases (%) | |||
---|---|---|---|
Sample (Nb content) | Nominal Composition | Bi-2223 (%) | Bi-2212 (%) |
A (x = 0.00) | Bi1.65Pb0.35Sr2Ca2Cu3O10+δ | 63.7 | 36.3 |
B (x = 0.05) | Bi1.65Pb0.3Nb0.05Sr2Ca2Cu3O10+δ | 64.8 | 35.2 |
C (x = 0.15) | Bi1.65Pb0.2Nb0.15Sr2Ca2Cu3O10+δ | 56.4 | 43.6 |
D (x = 0.25) | Bi1.65Pb0.1Nb0.25Sr2Ca2Cu3O10+δ | 46.2 | 53.8 |
E (x = 0.35) | Bi1.65Nb0.35Sr2Ca2Cu3O10+δ | 48.7 | 51.3 |
and impurity phases of the A and E samples [
Many properties of the polycrystalline materials depend on the grains size. So, by using of the Debye-Scherer formula in Match 3.3 software and the XRD data, grains size were calculated [
where β is the full width at half maximum of X-ray peaks (radians), λ is the wavelength of the incident radiation, and θ is the angle of the peak. With using Debye-Scherer formula, the size of the grains calculated lies between 250 Å and 360 Å.
With calculation of crystal lattice parameters by using Match 3.3 software, were found that all of the samples have an orthorhombic structure which has been reported also by other groups [
Sample (Nb substation) | ΔTc (K) | a (Å) | b (Å) | c (Å) | P-values | ||
---|---|---|---|---|---|---|---|
A (x = 0.00) | 95.1 | 111.4 | 16.3 | 5.40038 | 5.40882 | 37.12406 | 0.120 |
B (x = 0.05) | 91.7 | 109.3 | 17.6 | 5.40546 | 5.40534 | 37.10640 | 0.115 |
C (x = 0.15) | 74.9 | 112.2 | 37.3 | 5.24895 | 5.59561 | 37.05370 | 0.098 |
D (x = 0.25) | 51.4 | 109.1 | 57.7 | 5.40020 | 5.40112 | 36.96917 | 0.080 |
E (x = 0.35) | 50.3 | 107.9 | 57.6 | 5.40031 | 5.41910 | 36.95215 | 0.079 |
Satyavathi et al. and Zandbergen et al. [
Normalized resistivity versus temperature for all samples and the variation of
A sharp drop of resistivity was seen for samples A (x = 0.00) and B (x = 0.05), this means that these samples consist of predominantly of Bi-2223 phase. As was indicated by Bolat et al., once the volume fraction of Bi-2223 within the sample is sufficient to make this possible that a one-step resistivity transition is observed even in the samples which contain a rather large amount of Bi-2223 phase [
Sample with x = 0.25 showed the two-step resistivity transition. It is possible that the both Bi-2223 and Bi-2212 phases exist within one grain in such a way that low-Tc (Bi-2212) phase can play important role in the weak link [
The zero field cooled (ZFC) magnetization versus temperature curve of samples were measured under external applied magnetic field of 50 Oe. These results are illustrated in
For determining the intergranular critical current density, the magnetic-hysteresis cycles were measured at 10 K for all samples between applied fields of ±9000 Oe. These results are shown in
In this formula, Jc is the critical current density in amperes per square centimeter of a sample and
curves are illustrated in
In ceramic high-temperature superconductors, one of the most important properties is their grain structure. These grain structures can be illustrated and explained by the SEM micrographs. These SEM micrographs provide us with data about the formation of the surface morphology of the samples. Surface morphology micrographs taken by SEM for all samples are shown in
Superconducting transition temperature has a parabolic relationship with the hole concentration p (the number of holes per Cu atom) can be calculated by using this relation which is given by Presland et al. [
In this formula for the Bi-2223 and Bi-2212 systems the value of
superconducting properties degrade. p-values versus Nb substitution is shown in
In summary, the nominal composition of the Bi1.65Pb0.35−xNbxSr2Ca2Cu3O10+δ (x = 0.0, 0.05, 0.15, 0.25 and 0.35) compounds has been prepared by the solid-state reaction method and the effects of Pb2+ substitution by Nb5+ in (Bi-Pb)-2223 superconducting samples have been investigated. The obtained results from XRD, resistance measurements, DC magnetization and hysteresis measurements showed that with increasing of Nb content volume fraction of the high-Tc (Bi-2223) phase, the critical temperature
The authors would like to thank Superconductivity Research Center of Urmia University and Gebze Technical University for supporting and helping us with the all the related measurements of this project. The authors would also like to express their thanks to Professor Ali Gerncer, Center of Excellence for Superconductivity Research, Ankara University, Turkey for helpful discussions.
Asghari, R., Sedghi, H., Arsalan, L.Ç. and Naghshara, H. (2017) Investigation of Niobium (Nb) Substitution on Structural and Superconducting Properties of (Bi, Pb)-Based Superconductors. Advances in Materials Phy- sics and Chemistry, 7, 277-293. https://doi.org/10.4236/ampc.2017.77022