P Guruswamy

National Institute for Interdisciplinary Science and Technology

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U. Syamaprasad

National Institute for Interdisciplinary Science and Technology

R.P. Aloysius

Council of Scientific and Industrial Research

A. D. Damodaran

National Institute for Interdisciplinary Science and Technology

P. Mukherjee

All India Institute of Medical Sciences Bhubaneswar

A Sobha

Cochin University of Science and Technology

K. G. K. Warrier

National Institute for Interdisciplinary Science and Technology

P.M. Sarun

Indian Institute of Technology Dhanbad

S. Vinu

Kanyakumari Government Medical College

Mārtiņš Sarma

Helmholtz-Zentrum Dresden-Rossendorf

A. Biju

Amrita Vishwa Vidyapeetham

Cooperative Institutions

National Institute for Interdisciplinary Science and Technology

Institute of Minerals and Materials Technology

Council of Scientific and Industrial Research

Advanced Materials and Processes Research Institute

Academy of Scientific and Innovative Research

University of Kerala

Cochin University of Science and Technology

Pallium India

MSSCORPS (Taiwan)

National Chemical Laboratory

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Enhanced Flux Pinning of an Nd‐Added (Bi,Pb)‐2212 Superconductor

Journal of the American Ceramic Society (2007)

P.M. Sarun Alikunju Biju P Guruswamy U. Syamaprasad

The flux pinning properties of a (Bi,Pb)‐2212 superconductor by the addition of a rare‐earth element Nd with varying concentrations were studied. The Nd content of the samples was varied from x =0.0 to 0.5 on a general stoichiometry of Bi 1.7 Pb 0.4 Sr 2.0 Ca 1.1 Cu 2.1 Nd x O y . The samples were characterized by powder X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray analysis, and transport critical current measurements at 64 K. Both self‐field J C and J C in the presence of an applied magnetic field ( J C –B ) of Nd‐added samples were found to be much better than those of the pure sample. Also, the peak values of the bulk pinning force density ( F Pmax ) of Nd‐added samples shift toward higher magnetic fields, indicative of the enhanced flux pinning strength of the samples. The results are explained based on the replacement of cations such as Sr 2+ , Ca 2+ , and Bi 3+ by Nd 3+ ions and the associated distortion of the lattice and change in hole concentration in the system. The replacement produced point‐like defects due to the difference in the ionic radii of Sr 2+ (1.12 Å), Ca 2+ (0.99 Å), Bi 3+ (0.96 Å), and Nd 3+ (1.04 Å). The nanoscale secondary phase precipitates produced due to Nd addition may also act as flux pinners.

Ionic radius

Stoichiometry

10.1111/j.1551-2916.2007.01896.x

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Citations (9)

Enhanced critical current density in (Bi,Pb)-2223 superconductor by Nd addition in low percentages

Physica C Superconductivity (2005)

R.P. Aloysius P Guruswamy U. Syamaprasad

Stoichiometry

10.1016/j.physc.2005.05.017

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Citations (16)

Influence of Ho-Doping on the Electromagnetic Field-Dependent $E$–$J$ Characteristics of (Bi,Pb)-2212 Superconductor

IEEE Transactions on Applied Superconductivity (2009)

P.M. Sarun S. Vinu R. Shabna A. Biju P Guruswamy

The magnetic field ($B$ ) dependence of electric field versus transport current density ($E\hbox{–}J$ characteristics) of $\hbox{Bi}_{1.6}\hbox{Pb}_{0.5}\hbox{Sr}_{2-{x}}\hbox{Ho}_{x}\hbox{Ca}_{1.1}\hbox{Cu}_{2.1}\hbox{O}_{8+\delta}$ superconductor was studied for $x$ from 0.000 to 0.200. The behavior of supercurrent flow under magnetic fields in Ho-doped (Bi,Pb)-2212 is explained using thermally activated flux-creep. The $n$ -value and characteristic pinning energy ( ${U}_{c}$) estimated from $E\hbox{–}J$ characteristics show that at applied fields, the flux-lines in Ho-doped samples are in the glass-state. A correlation is observed between $n$ -index and ${J}_{c}$ of doped samples. The highly enhanced critical current density (${J}_{c}$) and $n$-index in both self- and applied-fields due to Ho-doping is of great scientific and technological significance.

Supercurrent

10.1109/tasc.2008.2010866

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The effect of substitution of Eu on the critical current density and flux pinning properties of (Bi, Pb)-2212 superconductor

Superconductor Science and Technology (2008)

S. Vinu P.M. Sarun A. Biju R. Shabna P Guruswamy

The critical current density and flux pinning properties of Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1Oy (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) prepared by solid state synthesis in bulk polycrystalline form were studied. The samples were characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive x-ray analysis (EDS) and superconductivity measurements. The critical temperature (TC), critical current density (JC) and field dependence of JC of the Eu-substituted samples were found to be highly enhanced for optimum doping levels. The peak position of the normalized pinning force density (Fp/Fpmax) is found to shift to higher fields (0.88 T) for optimally doped samples in contrast to 0.2 T for the undoped sample. The enhancement of the JC–B characteristic and pinning force density FP (FP = JC × B) due to Eu substitution is of great technological significance.

10.1088/0953-2048/21/4/045001

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Citations (82)

Journal of Materials Science Letters (1997)

Mārtiņš Sarma U. Syamaprasad C. Pavithran P Guruswamy P. Mukherjee

10.1023/a:1018525814242

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Citations (9)

Effect of Sintering Temperature on the Microstructural and Flux Pinning Characteristics of Bi_1.6Pb_0.5Sr_1.8La_0.2Ca_1.1Cu_2.1O_8+δ Ceramics

Journal of the American Ceramic Society (2009)

P.M. Sarun S. Vinu R. Shabna Alikunju Biju P Guruswamy

We evaluated the microstructure, superconducting, and flux pinning properties of La‐doped (Bi,Pb)‐2212 bulk sample by varying its sintering temperature ( T sinter ) between 846° and 860°C. Significant variations in microstructure, self‐ and in‐field J C s at 64 K and flux pinning properties have been observed for La‐substituted samples with respect to T sinter . The sample sintered at 858°C shows best self‐field J C while that sintered at 846°C shows the best in‐field J C due to the changes in microstructure. The activation energy of flux motion (pinning potential U o ) is estimated from the field dependent resistivity–temperature curves, and the flux pinning force ( F P ) from the field‐dependent J C values. It is found that the La‐doped samples, sintered at 846°C show maximum F P and U o of 463 kN/m 3 and 0.380±0.001 eV as against 93.6 k/Nm 3 and 0.140±0.001 eV, respectively, for the sample sintered at 858°C. The undoped (Bi,Pb)‐2212 shows a maximum F P and U o of 12.7 k/Nm 3 and 0.074±0.001 eV, respectively. The origin of these enhanced properties is mainly from the normal‐like defects introduced by optimum La‐doping at the Sr‐site, at an optimum sintering temperature.

10.1111/j.1551-2916.2008.02895.x

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Phase evolution, microstructure and transport property of (Bi, Pb)-2223/Ag tapes prepared using powders of varying particle size distribution

Superconductor Science and Technology (2001)

A Sobha R.P. Aloysius P Guruswamy U. Syamaprasad

(Bi, Pb)-2223/Ag sheathed tapes were prepared using precursor powders with different particle size distributions which were obtained by grinding the calcined powder for different durations. DTA results revealed that the reaction temperature of the precursor powder depends on the particle size and is at a minimum for the finest powder. Phase evolution studies, transport current measurement at 77 K with and without the application of an external field, microstuctural examination etc, were carried out in order to evaluate the relative performance of the tapes. The results showed that the particle size has significant effects on the reaction kinetics, ultimate phase fraction, microstructure and transport critical current density. For the tapes fabricated using coarser powder, the reaction kinetics were found to be slower and the microstructure contained smaller grains with many misalignments and voids. On the other hand use of extremely fine precursors yielded tapes with a large fraction of secondary phases due to the degradation of the crystallinity of the precursor and a consequent change in the reaction sequence. The tape prepared using a precursor with an average particle size of 3-4 µm showed the best results with respect to JC, high-TC phase fraction, microstructure and JC-B characteristics.

Particle (ecology)

10.1088/0953-2048/14/6/317

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Citations (11)

Enhanced critical current density in (Bi,Pb)-2223/Ag tapes prepared using precursors calcined in dynamic vacuum with oxygen partial pressure

Materials Letters (2005)

V.G. Prabitha R.P. Aloysius P Guruswamy U. Syamaprasad

Partial pressure

Vacuum induction melting

10.1016/j.matlet.2005.04.007

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Enhanced flux pinning in (Bi, Pb)-2223 superconductor by Nd addition

Superconductor Science and Technology (2005)

R.P. Aloysius P Guruswamy U. Syamaprasad

Bi1.8Pb0.35Sr2.0Ca2.1Cu3.1NdxOy (x = 0.00, 0.010, 0.020 and 0.030) superconductors were prepared in bulk form. Phase analysis by XRD, microstructural examination by SEM, superconductivity measurements at 77 K, etc were carried out to evaluate the relative performance of the samples. Both the self-field JC and JC in the presence of an applied magnetic field of the Nd-added samples are found to be much better than those of the undoped one. Also the peak value of the bulk pinning force density, Fp max, of Nd-added samples get shifted towards higher magnetic fields, indicative of enhanced flux pinning strength in these samples. For the sample with Nd = 0.030, small fractions of (Bi, Pb)-2212 were found even after the last stage of sintering. Accordingly the microstructure of this sample shows considerable difference from the other samples, wherein the natural layered growth mechanism of (Bi, Pb)-2223 is disrupted by grain growth and coarsening in random directions. It is likely that Nd ions are substituting at the Ca site, and the point defects thus created act as flux pinners, enhancing the self-field JC as well as the JC–B characteristics of the Nd-added samples.

10.1088/0953-2048/18/4/009

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Citations (15)

Preparation of dense, highJ_CBi-2223 superconductors by multistage cold pressing

Superconductor Science and Technology (2005)

Rohit Kumar R.P. Aloysius R. Jolly Bose P Guruswamy U. Syamaprasad

The effect of multistage cold uniaxial pressing on Bi-2223 bulk superconductors with varying fractions of Bi-2223 in the precursor powder has been studied. The results show that the final density, grain orientation, JC and JC–B characteristics depend greatly on the fraction of Bi-2223 contained in the precursor and increase with increasing Bi-2223 fraction. In a three-stage repeated press–sinter schedule, density and JC (77 K) values as high as 5.76 g cm−3 and 3110 A cm−2 respectively could be achieved with 80% Bi-2223 precursor, whereas the values are only 5.31 g cm−3 and 1860 A cm−2 for 22% Bi-2223 precursor under identical conditions. The likely reasons for the wide variation of microstructural and superconducting properties are discussed.

10.1088/0953-2048/18/5/018

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Citations (4)