J Supercond Nov Magn (2010) 23: 1313–1323 DOI 10.1007/s10948-010-0775-z

O R I G I N A L PA P E R

Superconducting Properties of Spray Deposited TBCCO Films R.S. Kalubarme · C.J. Park · S.H. Pawar

Received: 24 August 2009 / Accepted: 4 April 2010 / Published online: 1 May 2010 © Springer Science+Business Media, LLC 2010

Abstract The present study shows general characteristic features of processes such as spray pyrolysis and heattreatment, involved in the preparation of Tl-2223/CeO2 / Al2 O3 superconducting coatings by using aerosol pyrolysis method. The importance of the present study, however, lies in a new process to make a thick Tl-2223 superconducting layer by using spray pyrolysis. In the new method, a relatively thick BaCaCuO precursor film is firstly spray deposited on the buffered alumina substrate and then heattreated in the presence of thallium source for phase transformation to superconducting phases to assign conductivity to the film. The thickness of the Tl-2223 layer was 2–3 µm. The crystal symmetry was found to be tetragonal with lattice parameters a = 3.85, and c = 35.7 Å. The T c was found to be 98 K for the samples heat treated at 870 °C for 60 min. Magnetic characterizations were conducted by using a DCSQUID magnetometer. From the magnetization measurements, the intragrain critical-current density, Jc , was calculated to be 2 × 104 A/cm2 at 70 K. Keywords Tl-based superconductor · Spray pyrolysis · Magnetic measurements · CeO2 buffer layer R.S. Kalubarme · S.H. Pawar () Department of Physics, Shivaji University, Kolhapur 416 004, M.S., India e-mail: [email protected] R.S. Kalubarme e-mail: [email protected] S.H. Pawar Department of Technology, D.Y. Patil University, Kolhapur 416 006, M.S., India R.S. Kalubarme · C.J. Park Department of Material Science and Engineering, Chonnam National University, Gwangju 500 757, South Korea

1 Introduction The discovery of superconductivity at high temperatures in thallium cuprates [1] has opened the road to the exploration of a large family of oxides whose structures are closely related to each other and which can exhibit a wide range of critical temperatures, from several Kelvin to 127 K [2, 3]. From a physical point of view, these materials appear as most promising since they are the superconductors that exhibit the highest Tc s. It is seen that their critical temperature can be improved dramatically by adjusting the oxygen pressure during synthesis or by annealing in a reducing atmosphere [4–9]. Thus, there is no doubt that the superconducting properties of these oxides are very sensitive to the nonstoichiometry of oxygen. Another particularity of these phases deals with their difficult synthesis which is due to the enormous volatility of thallium oxide at 600 °C and above. This property of thallium makes disastrous effects not only for the operator who can be intoxicated by thallium loss, but it can also introduce thallium and oxygen non-stoichiometry in the samples, thus drastically modifying the superconducting properties of these materials. The commercial feasibility of any high-temperature ceramic superconductor application is enhanced by the availability of a fabrication process that can produce large amount of high quality materials economically. The chemical processing techniques such as spray pyrolysis is the technique with the potential to fabricate the high quality superconducting thin as well as thick films for the application purpose. In the present paper, the emphasis is given on the synthesis of Tl-2223 thin as well as thick films by spray pyrolysis. The different post deposition treatments were used to study their effect on the structural, morphological, and electrical properties of the Tl-Ba-Ca-Cu-O films.

1314

2 Experimental The thermal spray pyrolysis technique is used for the deposition of Tl-free Ba-Ca-Cu-O thin films and CeO2 buffer layer on Al2 O3 substrate. The precursor used for the deposition of CeO2 buffer layer is cerium nitrate Ce(NO3 )3 (Loba Chemie). The TG-DTA of the cerium nitrate was carried out to know the temperature at which it decomposes and forms the oxide. The parameters used for the deposition of CeO2 are: deposition temperature of 325 °C, spray rate 2 ml min−1 and the deposition time 10 min. After the deposition the films were treated at 500 °C for 30 min to complete the decomposition of the nitrate to form uniform film of ceria on alumina. The formation of the buffer layer was confirmed by recording the x-ray pattern for the spray deposited CeO2 film. These buffered Al2 O3 substrates were used as substrate to deposit Tl-free Ba-Ca-Cu-O thin film. The solution to be sprayed was prepared by dissolving Ba(NO3 )2 , Ca(NO3 )2 and Cu(NO3 )2 (Aldrich chemical 99.9% pure) into double distilled water. The molar concentration of the final solution was adjusted in such a way that the ratio of Ba:Ca:Cu should remain as 2:2:3. This solution was further sprayed by air blast spray pyrolysis unit on the CeO2 buffered polycrystalline Al2 O3 substrates maintained at constant temperature with the nozzle to a substrate distance of 25 cm. The temperature of the substrate is varied from 230 to 310 °C to deposit well adherent and smooth films. The total solution of 60 ml was sprayed. The rate of spray of the solution was found to be 1 ml min−1 . The Ba-Ca-Cu-O alloy film thus deposited in the first step of processing with spray pyrolysis technique were post heat treated at 650 °C for 30 min to convert remaining nitrates of Ba, Ca, and Cu into respective oxide. The process of thalliation was carried out in the one side sealed quartz tube with oxygen environment at ambient pressure. This process was carried out at two different temperatures like 850 °C and 870 °C for time period of 30 min and 60 min accordingly, for three different combinations of temperature and duration; the heat treated samples were nomenclatured as S1 , S2 , and S3 . Sample S1 was allowed to react with thallium oxide at 850 °C for 30 min, sample S2 at 870 °C for 30 min. and sample S3 at 870 °C for 60 min. The source of thallium used is the black powder of thallium oxide from Alfa aesar with 99.9% purity. Sample thicknesses were measured using fully computerized AMBIOS Make XP-1 surface profiler with 1 Å vertical resolution. With a low force stylus mechanism that produces stylus loads as small as 0.05 milligrams, the XP-1 is ideally suited for measurement of soft or delicate films. The films were characterized for their structural properties by Philips PW-1710 powder diffractometer with Cu as target material. Surface morphological and compositional studies were carried out with scanning electron microscope JEOL JSM 6360 equipped

J Supercond Nov Magn (2010) 23: 1313–1323

with EDAX probe. Raman measurements have been performed using a BRUKER-Multi Ram (German make) spectrometer combined with a Germanium diode detector. All Raman data were obtained at nearly back-scattering geometry. The photon excitation was provided by the 106.4 nm (9395 cm−1 ) lines of a Nd:YAG laser. The temperature dependence of resistivity measurement of the sample was done using a conventional four-probe method. All the parameters for the measurement of resistivity were controlled by the personal computer (P-IV) connected to the refrigeration system and the multimeters by means of GPIB cable and IEEE interface. The Oxford made Quantum Design II magnetometer is used for recording the M–H hysteresis loops to determine the critical current density of the superconducting sample.

3 Results and Discussion 3.1 CeO2 Buffer Layer on Al2 O3 Substrate selection is the important part of the thin film synthesis. Substrate enables us to grow thin films as per the required properties for their possible application, depending upon the properties it possesses. For example, if we want to use thin films in high frequency device application, then one must have the substrate with high dielectric constant for the deposition of thin film. Considering this fact, we have decided to use the Al2 O3 substrate for the spray deposition of Ba-Ca-Cu-O films. The unit cell of Al2 O3 is rhombohedral, but the structure is normally expressed in hexagonal notation (a = 4.759 Å, c = 12.991 Å). The physical properties of Al2 O3 make it an excellent substrate for high frequency applications; it has a low dielectric constant, low loss tangent, good mechanical strength, and high thermal conductivity, and it is readily available in the form of large area wafers with good surface finish. It is impossible to fabricate very high performance Tl HTS films directly on Al2 O3 due to its nonorthogonal axes (86◦ ), large lattice mismatch with the HTS phase, and large difference in thermal expansion coefficient. Diffusion of Al from the substrate into the HTS film at processing temperatures also results in the formation of a BaAl2 O4 interfacial layer [10–12] and severe degradation in the superconducting properties of the film. In order to overcome the problem of Al diffusion in the BaCaCuOx layer, a buffer layer will be deposited prior to the deposition of precursor film. There has been much research into suitable buffer layer architectures for YBCO superconducting films; only a few studies have been made on buffers for Tl-based superconductors. Speller et al. has reviewed the different buffer layers used for Tl-based superconductors; out of that, ceria has a cubic fluorite structure with a lattice parameter a ∼ 5.411 Å

J Supercond Nov Magn (2010) 23: 1313–1323

1315

Fig. 1 TG-DTA plot of cerium nitrate

and, therefore, has a good lattice match to HTS phases when the unit cell is rotated by 45◦ in the a–b plane. CeO2 has been used as a buffer layer for TBCCO growth on both MgO [13, 14] and R-plane sapphire [13, 15, 16] substrates. The buffer layers grown on MgO tend to be less structurally perfect than those grown on R-plane sapphire. A buffer layer thickness of 20 nm seems to be sufficient to prevent Al diffusion from sapphire substrates into the HTS films. The precursor used for the deposition of CeO2 buffer layer is cerium nitrate Ce(NO3 )3 . The TG-DTA of the cerium nitrate was carried out to know the temperature at which it decomposes and forms the oxide. The range of temperature used for collecting the data was from room temperature to 1000 °C. The typical TG-DTA of Ce(NO3 )3 is shown in Fig. 1. The thermogravimetric analysis shows the continuous decrease in the weight until it attains the constant value. It is also revealed that the nitrates of cerium totally get converted into its oxide up to 300 °C. This information is important in the sense that one can easily deposit the ceria thin films by spray pyrolysis technique using the deposition temperature above 300 °C. We have deposited the ceria films on alumina by air blast spray deposition technique. The parameters used during the deposition were: deposition temperature of 325 °C, spray rate 2 ml min−1 , and the deposition time 10 min. After the deposition, the films were annealed at 500 °C for 30 min to complete the decomposition of the nitrate to form uniform film of ceria on alumina. The formation of the buffer layer was confirmed by recording the x-ray pattern for the spray deposited CeO2 film, which is given in Fig. 2. The pattern shows the peaks of CeO2 with cubic crystal structure along with the peaks of alumina, i.e., substrate. These ceria buffered alumina were used as a substrate for further experiments.

3.2 Deposition of Ba-Ca-Cu-O Layer on Buffered Al2 O3 The thermal spray pyrolysis technique is used for the deposition of Tl-free Ba-Ca-Cu-O thin films. In order to study the solution chemistries and the effect of other nitrates on chemical reactivity during denitration, the TGA scans were run on the residues precipitated from the aqueous solution containing nitrates of Ba, Ca, and Cu in the proportion of 2.3:2:3 in the air atmosphere. The drying of the residues is performed on alumina substrate at 80◦ C. Figure 3 shows TG-DTA spectra for all of the nitrate dissolved in water in the proportion of Ba:Ca:Cu as 2.3:2:3, respectively. Thermogravemetric changes below 200 °C were attributed to removal of water absorbed in the nitrates from the ambient air. Copper denitration proceeds as explained before [17] and not affected by the presence of the other nitrate complexes. Its characteristic peak of DTA was observed 261 °C. The percentage weight change observed between 208 and 352 °C was roughly 12.8% and is attributed to copper denitration. This is in general agreement with an 11.9% weight differential that would be expected using the fractional weight percentage change observed during Cu2 (OH)3 ·NO3 denitration between 200 to 300 °C. There was a decrease in the weight observed between 360 to 670 °C which roughly matches with the weight loss due to denitration of Ca(NO3 )2 and Ba(NO3 )2 . It appears that Ca(NO3 )2 and Ba(NO3 )2 have chemical affinity for one another and that their mutual denitration is accelerated by each other’s presence or by the copper oxides in the sample. The above discussion reveals that the post deposition treatment to the sample is necessary for the complete denitration of the precursor material and it should be above 650 °C.

1316

J Supercond Nov Magn (2010) 23: 1313–1323

Fig. 2 XRD pattern of spray deposited CeO2 buffer layer on Al2 O3 substrate

Fig. 3 TG-DTA plot of the precipitated powder from aqueous solution of Barium nitrate, Calcium nitrate, and Cupric nitrate in 2.3:2:3 molar proportions

3.3 Thickness Measurement

3.4 Structural Characterization

The BaCaCuO films deposited by spraying the nitrate solutions of Ba, Ca, and Cu on Al2 O3 /CeO2 substrate were scanned for the thickness measurement by surface profiler. The variation of BaCaCuO film thickness is plotted against the substrate temperature used for the deposition, which is given in Fig. 4. It is found that the film deposited at 275 °C gives thickness of the order of 3.4 µm. The films deposited above this temperature have less thickness and more roughness. The thickness of the film is recorded after thallium intercalation and it is found to be 2–3 µm depending upon the post deposition treatment temperature.

The XRD plots for the sample S1 , S2 , and S3 were recorded and shown in the Figs. 5a, 5b, and 5c, respectively. From Fig. 5a, it is seen that there are few peaks belonging to the 2212 phase and the remaining were the substrate peaks and some unidentified impurity peaks. However, from the intensities of the 2212 phase peaks, it is seen that a very small amount of the material having superconducting phase is present in the thin film. From this, it is observed that the temperature, at which this sample annealed, is very low for the formation of the phase. From the above discussion, it is clear that the reaction for the formation is just started at

J Supercond Nov Magn (2010) 23: 1313–1323

1317

Fig. 4 Variation of spray deposited BaCaCuO film thickness as a function of substrate temperature

Fig. 5a XRD pattern of spray deposited Ba-Ca-Cu-O film reacted with thallium oxide at 850 ◦ C for 30 min

850 °C, hence the higher temperature is used for the post deposition treatment of next samples. Figure 5b gives the XRD pattern for the sample annealed at 870 °C for 30 min (S2 ). This pattern shows the peaks of Tl-2223 phase. There are small impurity peaks present in the plot. The peaks observed in the pattern were indexed with help of standard JCPDS data. The peaks belonging to (0010), (105), (112), (114), (1011), (0016), (1013) (1015), (1112), (1019), (1021), (2111), (2115), (305), (312), (1031), (1130), and (3017) planes of Tl-2223 phase with tetragonal symmetry were observed in the diffraction pattern with few substrate peaks. The lattice parameters calculated for this sample are a = 3.84 Å and c = 35.82 Å. This pattern shows most of the reflections of Tl-2223; however, it is observed that the reaction is not yet completed to form single

phase compound as there are some impurity peaks seen in the pattern. Hence, the time period for the post deposition annealing was increased from 30 to 60 min. Bragg’s reflection pattern for the sample annealed at 870 °C for 60 min (S3 ) was shown in the Fig. 5c. This pattern shows the peaks of Tl-2223 phase including the small angle reflections. The peaks observed in the pattern were indexed with help of standard JCPDS data. The peaks belonging to (002), (004), (008), (0012), (110), (112), (114), (118), (200), (1116) (217), (0022), (219), (2111), (2016), (222), (2020), (307), and (314) planes of Tl-2223 phase with tetragonal symmetry were observed in the diffraction pattern having some substrate peaks. The lattice parameters for Tl-2223 were calculated and found to be ‘a’ = 3.84 Å and ‘c’ = 35.74 Å, which are in good agreement with the values

1318

J Supercond Nov Magn (2010) 23: 1313–1323

Fig. 5b XRD pattern of spray deposited Ba-Ca-Cu-O film reacted with thallium oxide at 870 ◦ C for 30 min

Fig. 5c XRD pattern of spray deposited Ba-Ca-Cu-O film reacted with thallium oxide at 870 ◦ C for 60 min

reported earlier [18]. Thus, the two step method of formation of Tl-2223 thin films was successfully attempted. 3.5 Morphological Studies The technological device evidence can be judged by considering the surfaces and interfaces. Surface morphology studies were carried out with scanning electron microscope JEOL JSM 6360 equipped with EDAX probe to understand information about the surface coverage, uniformity, grain connectivity, size, and shapes. Effect of heat treatment on the morphology of all the samples was studied. Sample S0 , i.e., as-deposited, S1 , S2 , and S3 were scanned by using the

electron microscope to form the image with higher resolution of these samples. Figure 6 shows the SEM images of the samples S0 , S1 , S2 , and S3 . In Fig. 6(a) the micrograph of as-deposited film is shown having porous nature of the deposit. In Fig. 6(b), the porous nature of the deposit starts disappearing as thallium start reacting with the film and start occupying interstitial sites. The film after the complete thallium intercalation shows the pore-free continuous morphology for the samples annealed at 870 °C as shown in Fig. 6(c) and 6(d). From the above studies, it is concluded that the grain improvement with increasing processing temperature was observed. The better connectivity was seen in the samples after

J Supercond Nov Magn (2010) 23: 1313–1323

1319

(a)

(b)

(c)

(d)

Fig. 6 SEM micrographs of spray deposited BaCaCuO films on Al2 O3 /CeO2 substrate (a) As deposited film and post heat treated in the presence of thallium source at (b) 850 ◦ C for 30 min, (c) 870 ◦ C for 30 min and (d) 870 ◦ C for 60 min

the intercalation of thallium into the sample upon primary heat treatment. This connectivity of the sample is essential for the superconducting transition temperature which in turn affects the microwave properties as reported elsewhere [17]. 3.6 Compositional Analysis The interactions of electron with solid leads to different signals like secondary electrons, backscattered electrons, and x-rays which are characteristic of atoms in the host lattice. These x-rays can be used for element detection and its quantification for compositional analysis. Compositional analysis for the samples was carried out with EDAX probe attached to the scanning electron microscope JEOL JSM 6360 to quantify the elements present in the samples. Figure 7 shows the typical EDAX pattern taken for the sample S3 .

The graph shows the presence of all the elements in the proper proportion in the film. 3.7 Raman Measurements Raman scattering measurement has been carried out for the spray deposited BaCaCuO film post heat treated at 870 °C for 30 min (S2 ). The Raman shift pattern obtained is given in Fig. 8a. This plot shows the major characteristic peaks related to Tl-based superconductors at wavenumber 418 cm−1 and 613 cm−1 . The peaks observed at 613 cm−1 is due to the scattering of phonons in the CuO2 plane of Tl-2223 material in B1g mode [19, 20]; while the peak at 418 cm−1 is due to the in phase oxygen [21–23]. The other peaks may be due to oxygen rich impurities and adsorbed water. Similar is the

1320

J Supercond Nov Magn (2010) 23: 1313–1323

Fig. 7 EDAX analysis for Al2 O3 /CeO2 /Tl2 Ba2 Ca2 Cu3 O10 thin film

Fig. 8a Raman spectra recorded for spray deposited BaCaCuO film post heat treated in the presence of thallium source at 870 ◦ C for 30 min

plot for Raman shift of the spray deposited BaCaCuO film post heat treated at 870 °C for 60 min as shown in Fig. 8b. The observed peaks are 408, 480, and 608 cm−1 . The Peak at 608 and 408 cm−1 corresponds to the B1g mode and the in phase oxygen for Tl-2223 compound, respectively. The additional peak may be due the bridging oxygen.

3.8 Resistivity Measurements TBCCO films were characterized for the low temperature measurements after their structural and morphological characterizations to test their superconducting properties by determining their transition temperature. Resistivity was

J Supercond Nov Magn (2010) 23: 1313–1323

1321

Fig. 8b Raman spectra recorded for spray deposited BaCaCuO film post heat treated in the presence of thallium source at 870 ◦ C for 60 min

Fig. 9 Variation in the normalized resistance with temperature of spray deposited BaCaCuO film on Al2 O3 /CeO2 substrate post heat treated in the presence of thallium source at (a) 850 ◦ C for 30 min and (b) 870 ◦ C for 30 min

recorded in the temperature range of 300 (R.T.) to 60 K for the samples prepared by spray pyrolysis technique followed by the post deposition heat treatment at 850 °C for 30 min. The plot of normalized dc resistivity as function of temperature is given in Fig. 9(a). From the figure, it is observed that the sample is showing positive coefficient of resistivity, i.e., the resistivity decreases with decrease in the temperature till 120 K, below that temperature resistivity seen to be saturated and the resistance of sample remains constant irrespective of decrease in temperature. However, it does not show any drop in the resistivity. This nature of the resistivity clearly exemplifies the metallic behavior of the films. In order to form the superconducting phase, samples were further heat treated at 870 °C for 30 min. The resistivity for this sample is measured and given in Fig. 9(b).

This sample shows the linear behavior of resistivity with temperature. The linear variation of resistivity as a function of temperature is due to the scattering of charge carriers by phonons, which is the standard behavior in normal metals. But in general, the normal state resistivity changes with higher power law of temperature, having values of the order of TD /5, where TD is Debye temperature. Sometimes, it follows the T 5 law in good crystalline metals, or a T 2 law in disordered metals. In some cuprate superconductors with relatively low values of Tc , the resistivity fails to show the expected flattening at low temperatures [24]. However, in others a transition to a T 2 behavior is observed. The resistivity start deviating from its nature with the rapid fall in it at 93 K, i.e., Tconset = 93 K and drops to zero at Tc = 81 K, which is less than the earlier reported values for the phase.

1322

J Supercond Nov Magn (2010) 23: 1313–1323

Fig. 9 (c) Variation in the normalized resistance with temperature of spray deposited BaCaCuO film on Al2 O3 /CeO2 substrate post heat treated in the presence of thallium source at 870 ◦ C for 60 min

Flatness in the resistivity plot is observed near the transition temperature because the resistivity may follow the power law of temperature. Further, experiments were planned to achieve the greater value of Tc for spray deposited film by increasing the post heat treatment temperature as well as time to vary the oxygen content and hole concentration in the sample. The sample treated at 870 ◦ C for 60 min shows the linear trend in the normal state resistivity and a drop in the resistivity at 105 K and zero resistivity at Tc = 98 K as shown in Fig. 9(c). The greater values of the T c have been achieved by changing the post deposition experimental conditions. Variation in the caxis lattice parameter and T c values with oxidation period is observed for spray deposited sample. The increase in Tc with decrease in the c-axis lattice parameter was observed as oxidation period was increased from 30 min to 60 min. A similar type of result, decrease in c-axis parameter with increase in Tc was reported by the Holstein et al. [9]. The decrease in the c-axis parameter might be due to cation ordering of the lattice and removal of the secondary phases with oxidation period of 60 min. The increase in the transition temperature is found to be dependent on the processing parameters during synthesis of TBCCO films. This is in turn related oxygen stochiometry and the concentration of the holes (p) per Cu atom. In order to understand the variation of transition temperature with the oxygen content or hole concentration in cuprate superconductors, Presland et al. [25] have proposed a universal phase diagram, which shows a parabolic superconducting domain and is given by the equation Tc = 1 − 82.6(p − 0.16)2 Tmax where p is the number of holes per Cu.

(1)

The variation in Tc /Tc(max) with the hole concentration (nh ) for Tl2 Ba2 Can−1 Cun O2n+4 system is given by Liu and Edward [26]. This leads us to predict that n = 1 and 2 compounds lie on the excess hole (overdoped state) site of the Tc maximum, while the n = 3 and 4 lie on the deficient hole (underdoped state) of the maximum in Tc . The increase in the transition temperature was observed in sample S3 than those of S2 , which may be due to oxygen evaluation as Tl2 O3 during the prolong annealing of 60 min. This evaluation of the oxygen causes the change in the carrier concentration, which in turn results to increase the Tc . 3.9 Magnetic measurements The M(H ) plot for sample S3 were recorded at 70 K and 50 K in the applied magnetic field of −10 T ≤ H ≤ 10 T. The M(H ) plot at 70 K was found to be collapsed, which may be due to the decreased pinning. The lack of pinning at higher temperature is a significant drawback with respect to current carrying applications for Tl-2223 as compared to Tl-1223 materials [27]. The Jc (H, T ) is calculated from M(H ) loops by using Beans critical state [28] model using the formula Jc = 30M/d

(2)

where “M” is the width of magnetization curve derived from the behavior of magnetization against field and “d” is the average grain size of the sample. Here, “d” is considered the average grain size of the sample as the critical state of the flux density gradient occurs individually in each one of nearly uncoupled grains of the sample. The Jc values at zero filed is 2 × 104 A cm−2 at 70 K.

J Supercond Nov Magn (2010) 23: 1313–1323

4 Conclusions In conclusion, spray pyrolysis was well demonstrated for the deposition of Tl2 Ba2 Ca2 Cu3 O10 films on ceramic substrates. The spray deposited films annealed at temperature of 870 °C for 60 min gives the single phase Tl-2223 compound with tetragonal crystal structure having lattice parameters a = 3.84 Å and c = 35.7 Å. The modification in the surface morphology for all the samples with changing processing temperature was studied. From these studies, it is concluded that the grain improvement with increasing processing temperature was observed. The better connectivity was seen in the samples after the intercalation of thallium into the sample after primary heat treatment. The compositional analysis confirms the presence of all the elements in proper proportions in the respective samples. The presence of B1g mode in Raman scattering of sample S2 and S3 predicts the presence of 3 CuO2 planes per unit cell. The evolution of B1g can be very well traced in all the samples equally confirming the presence of thallium intercalated superconducting volume fraction. The Tc was found to be 98 K for the S3 sample. The intragrain critical-current density (Jc ), was of the order of 2 × 104 A/cm2 at 70 K. Acknowledgements Authors are thankful to DRDO, New Delhi for the financial support. RSK would like to thank CSIR, New Delhi for financial help in terms of the award of CSIR-SRF to him. (9/816(14)/2008-EMR-I).

References 1. 2. 3. 4.

Sheng, Z.Z., Hermann, A.M.: Nature 332, 138 (1988) Liu, R.S., Tallon, J.L., Edwards, P.P.: Physica C 182, 119 (1991) Kaneko, T., Yamauchi, H., Tanaka, S.: Physica C 178, 377 (1991) Koo, H.S., Ku, H.K., Chen, M., Kawai, T.: Physica C 455, 71 (2007) 5. Matkovicov, Z., Strbik, V., Plesch, G., Valerianov, M., Dujavov, A.: Cent. Eur. J. Phys. 5, 398 (2007) 6. Lee, W.Y.: Appl. Phys. Lett. 60, 772 (1990)

1323 7. Mayers, K.E., Face, D.W., Kuntz, K.J., Nestlerode, J.P.: Appl. Phys. Lett. 65, 490 (1994) 8. Lee, W.Y., Lee, V.Y., Salem, J., Huang, T.C., Savoy, R., Bullock, D.C., Parkin, S.S.P.: Appl. Phys. Lett. 59, 329 (1989) 9. Holstein, W.L., Parisi, L.A.: J. Mater. Res. 11, 1349 (1996) 10. Bramley, A.P., Wilkinson, A.J., Jenkins, A.P., Grovenor, C.R.M.: J. Supercond. 11, 71 (1998) 11. Holstein, W.L., Parisi, L.A., Flippen, R.B., Swartzfager, D.G.: J. Mater. Res. 8, 962 (1993) 12. Collins, B.T., Ladd, J.A., Matey, J.R.: J. Appl. Phys. 70, 2458 (1991) 13. Tsaih, W.C., Huang, C.K., Tseng, T.Y.: J. Am. Ceram. Soc. 78, 1969 (1995) 14. Copetti, C.A., Schubert, J., Klushin, A.M., Bauer, S., Zander, W., Buchal, C., Seo, J.W., Sanchez, F., Bauer, M.: Appl. Phys. Lett. 79, 5058 (1995) 15. Wu, X.D., Foltyn, S.R., Meunchausen, R.E., Cooke, D.W., Pique, A., Kalokitis, D., Pendrick, V., Belohoubeck, E.: J. Supercond. 5, 353 (1992) 16. Denhoff, M.W., Mccaffrey, J.P.: J. Appl. Phys. 70, 3986 (1991) 17. Kalubarme, R.S., Kadam, M.B., Pawar, S.H.: J. Alloys Compd. 479, 732 (2009) 18. Cox, D.E., Totardi, C.C., Subramanian, M.A., Gopalkrishnan, J., Sleight, A.W.: Phys. Rev B 38, 6624 (1988) 19. Gasparov, L.V., Lemmens, P., Brinkmann, M., Hoffmann, A., Kolesnikov, N.N., Thomas, H., Winzer, K., Giintherodt, G.: Physica B 223–224, 484 (1996) 20. Hoffmann, A., Lemmens, P., Guntherodt, G., Thomas, V., Winzer, K.: Physica C 235–240, 1897 (1994) 21. Kulkarni, A.D., de Wette, F.W., Prade, J., Schroder, U., Kress, W.: Phys. Rev. B 41, 6409 (1990) 22. Kress, W., Prade, J., Schroder, U., Kulkarni, A.D., de Wette, F.W.: Physica C 162–164, 1345 (1989) 23. McCarty, K.F., Morosin, B., Ginley, D.S., Boehme, D.R.: Physica C 157, 135 (1989) 24. Allen, P.B., Fisk, Z., Maglori, A.: In: Ginzburg, D.M. (ed.) Physical Properties of High Tc Superconductor-I, p. 213. World Scientific, Singapore (1989) 25. Presland, M.R., Tallon, J.L., Buckley, R.G., Liu, R.S., Flower, N.E.: Physica C 176, 95 (1991) 26. Liu, R.S., Edwards, P.P.: In: Hermann, A.M., Yakhmi, J.V. (eds.) Thallium Based High Tc Superconductors, p. 325. Marcel Dekker, New York (1994) 27. Zheng, D.N., Campbell, A.M., Liu, R.S., Edwards, P.P.: Cryogenics 33, 46 (1993) 28. Bean, C.P.: Rev. Mod. Phys. 36, 31 (1964)