Investigation of Structural and Superconducting Properties of BiSrCa(Ti)CuO Superconducting Ceramics from Sol-Gel Method
S. Menassel1, M-F. Mosbah1, 2, A.Varilci3, S.P.Altintas3.
1Materials Science and Applications Research Unit, Physics Department, Constantine 1 University, B.P. 325 Route d’Ain El Bey, 25017 Constantine. Algeria.
2National Polytechnic School of Constantine, Ville universitaire, Nouvelle Ville Ali Mendjeli, Algeria
3Abant Izzet Baysal University, Department of Physics, 14280Bolu, Turkey [email protected]
Abstract
Superconducting Bi2Sr2Ca1-xTixCu2O8ceramics samples have been prepared by Sol-Gel methods; (using citrate process).The influences of the preparation conditions of compound oxide powder on structural and superconducting properties have been investigated by x ray diffraction (XRD), Scanning Electron Microscopy (SEM) equipped with EDS.The critical transition temperatures Tc have been determined by resistivity versus temperature measurements. Cell parameters samples were calculated from XRD patterns. The polyacrylamid gel makes the citrate process easier, more rapid and affords the possibility of synthesis of high quality oxide powders.
Key words:Superconducting, Sol-Gel - Polyacrylamide Gel Introduction
The Bi-based superconductor system actually consists of three different superconducting phases with very similar crystal structures. The general chemical formula for these phases can be written as Bi2Sr2Can-1CunO4+2n ,with n=1, 2, 3 corresponding to the 22K (2201 phase), 80K (2212 phase; low Tcphase) and 110K (2223 phase; high Tcphase) respectively[1,2].
In order to study the behavior of the Bi2212 cuprate, there is a many methods for synthesis high TC bismuth, such as, sol-gel process [3-6], co-precipitation method [7, 8], citrate gel process [9, 10], solid state reaction, oxidation of liquid quenched precursor alloys, and matrix reaction. Each of these techniques has limitations and problems associated with the actual process and the quality of the material produced. Bismuth powders were prepared by solid- state reaction at high calcinations temperatures over 860°, which many process to reduce particle size generally nonhomogenous mixtures to a microscopic scale, contrary to the solid state reaction, sol-gel colloid solution combustion synthesis, the process synthesis on high- purity multi compoument and it involves a low temperature initiated combustion process which is found to save for the preparation of very fine and homogeneous powders.
Various types of ceramics were prepared by sol-gel processes and it is well known that this method has the potential for obtaining pure and homogeneous products in a shorter reaction time and at a lower reaction temperature [11]. This process goes through a liquid-phase polymerization reaction to form a homogeneous intermediate. After a series of drying and calcinations processes, this liquid-phase intermediate can form a prophase thad leads to the formation of the final ceramic products. A fine crystalline ceramic might be obtainable by this process and it is used in the present experiment for the preparation of fine crystalline 2212.
[12-15] In general, the sol-gel using organometallic compound has advantage in the preparation of homogeneous ceramic materials because the precursors consist of small particles that exhibit a very high chemical activity and they are sintered easily into the oxide
at relatively low firing temperatures. It procedure use a specific gelling reagent, the approach is as follows : first prepare the gel from a homogeneous solution, which can then be decomposed to the oxides under mild thermal conditions, these oxides react to form the ceramic.
In this paper, we prepared the phase Bi2Sr2Ca1-xTixCu2O8superconductor by sol-gel method, and study the Ti substitution for Ca will be discussed through the paper, the doping of Ti into Ca will change the transition temperature with concentration of Ti.
2. Experimental details
Bismuth, strontium, calcium and copper nitrates were dissolved in distilled water in a stoichiometric ratio. Ti powder dissolved in nitric acid was added to the Bi solution. A solution of triammonium citrate with a concentration of 2 mol/Kg, was prepared by reacting citric acid with ammonia solution. The organic gels were made with acrylamide CH2=CHCONH2 and N, N methylene diacrylamide CH2=CHCONHCH2NHCOCH=CH2 was added in order to complex the Bi, Ca, Sr and Cu cations. The obtained solution was mixed, stirred and heated at 80°-90°C with a magnetic stirrer on a hot plate. Few drops of a solution of AIBN in acetone were added to accelerate the formation of the gel. This later is transformed to Bi2212 powder after heating at 400°C for 2h and 6h at 700°C, respectively.
The obtained powder is ground in an agate mortar and calcined during 12h at 860°C reached with a rate of 5°C/min. After calcinations, the samples were ground again, and then pelletized under a pressure of 300MPa.The pellets were then sintered during 12h at 860°C reached with a rate of 5°C/min.
Samples are noted as Ti0, Ti 0025, Ti0050, Ti0075 and Ti 010, where the number following Ti indicates the values of the rate x of Ti. The formation of the Bi-2212 phase was analyzed by XRD with Cukα radiation in the range 2θ=7-50°. Microstructural and surface morphology of the samples were investigated using scanning electron microscopy (SEM, JEOL 6390-LV).
The resistivity was measured for all samples in the temperature range 10K to 150K using a standard DC four-probe technique with a constant current of 5 mA. The current contacts and voltage were made with a silver paste. The magnetic field was applied parallel to the surface of the pellet and perpendicular to the current flow direction.
10 15 20 25 30 35 40 45 50
0 500 1000 1500 2000 2500 3000
: Bi2201
: Bi2212
2 Theta Ti0
Ti0025 Ti0050 Ti0075 Ti010
I(u.a)
Fig. 1The XRD patterns for Ti0, Ti 0025, Ti005, Ti0075 and Ti 010 samples.
Fig. 2SEM images of the samplesTi0, Ti 0025, Ti005, Ti0075 and Ti 010.
Ti005 Ti0075
Ti010 Ti0025
Ti0
20 40 60 80 100 120 140 0.00
0.01 0.02 0.03 0.04
0.05 Ti0
Resistivity
T(k)
20 40 60 80 100 120 140
0.00 0.02 0.04 0.06 0.08
T(k)
Resistivity
Ti0025
20 40 60 80 100 120 140
0.00 0.01 0.02 0.03 0.04 0.05
0.06 Ti005
Resistivity
T(k)
20 40 60 80 100 120 140
0.00 0.05 0.10 0.15 0.20
T(k)
Resistivity
Ti0075
20 40 60 80 100 120 140
0.00 0.02 0.04 0.06 0.08 0.10
Resistivity
T(k)
Ti010
Fig.3. resistivity
( ) versus temperature (T)
3. Results and discussion
The XRD patterns of samples are shown in Figure 1. The diffraction results show the presence of phase Bi2212 as major component. The structure of Bi2201 was also detected.
Indexing is done by matching the obtained result with the Janna 2006. The major peaks corresponds to the BSCCO 2212 phase. Besides these prominent peaks, there are some additional peaks corresponding to BSCCO-2201 phase, for Ti doped samples.
Microstructural features were studied using SEM (Figure 2). The SEM images of all the samples, (Bi2Sr2Ca1-xTixCu2O8) having magnification of ×7000. The grain morphology shows clear and flaky grains with layered growth, typical of BSCCO 2212. One can observe that doping with Ti decreases the size of the grains and the flaky nature of the grains gradually disappears with decreasing grain size and increasing porosity.
The electrical resistivity was measured using the standard four-probe dc technique, in the temperature range between 10 and 150 K. Fig. 3 shows the resistivity versus temperature of pure Ti0 and Ti 0025, Ti005, Ti0075, Ti 010 doped samples. Theρ– Tcurves show metallic behaviour in the normal state: the resistivity of samples decrease with decreasing temperature until the superconducting transition for undoped sample, it’s clearly seen that the transition width (Tc-onset– Tc0) increases with Ti-doping in BSCCO, indicating the doping induced disorder in the sample. This is in support of the SEM results, which shows the destruction of flaky nature of BSCCO and creation of more porosity, on doping with Ti.
Conclusion
In this paper, the Bi2Sr2Ca Cu2Oy superconductor synthesized by a sol-gel method using citric acid and nitrate acid as an oxidant, the phase was observed on calcining powders at 700°c for 6h by XRD. We have investigated the effect of substitution of Ti in Bi2Sr2Ca(1-x)
TixCu2Oy superconductor with x =0, 0.025, 0.05, 0.075 and 0.10 Superconducting proprieties.
Our results suggested that sol-gel method is an efficient route to prepare Bi2212 samples and it is found to be a very simple and convenient to obtain fine powder samples of bismuth superconductor at relatively low temperature with higher degree of homogeneity.
From the XRD analysis, BSCCO phase formation is confirmed.
Acknowledgement. This work was made under support of CNEPRUD00920110014 Algerian Government Project in Abant Izzet Baysal University of Bolu in Turkey.
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