IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Melt processing of SmBa2Cu3Oy (Sm-123) is done by infiltrating liquid phases into an Sm-211 preform and allowing the growth of Sm-123 to take place. The melt-textured samples are found to be free of macrodefects, and the microstructure contains uniformly distributed fine-sized Sm-211 particles. The behaviour of the critical current density (Jc) of the samples in high fields is reported here.

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Department Of Physics

Superconductor Science and Technology

Infiltration-growth processing of SmBa2Cu3Oy superconductor

The microstructure of a melt processed YBCO sample reveals the presence of random domains with aligned platelets separated by microcracks inside the domains. The lower critical field (H/sub c1/) and critical current density (J/sub c/) of these boundaries will be less than that of the grains, and their role in determining the bulk properties cannot be neglected. We have employed a sensitive lock-in flat-band detection technique and recorded the low field ac M-H loops at 33 Hz and 77 K and derived the flux profiles. The results show an enhancement in H/sub c1/ due to melt processing. Inclusion of Y/sub 2/BaCuO/sub 5/, and Ag enhances the H/sub c1/ further. The flux profiles show distinct slope changes at certain fields which reflect different coupling strengths of weaklinks that become operative for flux entry at different applied fields. While the low field flux profiles are found to reflect the effect of residual weaklinks (like liquid phase and micropores) and domain boundaries, those at higher fields might reflect the effect of platelet boundaries.

EEE Transactions on Applied Superconductivity

Role of interdomain and interplatelet boundaries on magnetic flux penetration in melt grown YBCO

Melt-processed Sm-123 samples with an excess Sm2BaCuOy (Sm-211) phase is studied by transmission electron microscope (TEM) and superconducting quantum interference device magnetometer, to explain the origin of the peak effect exhibited in the magnetization hysteresis loops of light RE-123 samples in intermediate fields at 77 K. TEM images of the sample showing peak effect reveal dilute concentrations of areas with ortho-II structure distributed on a nanometer scale within the twin regions of the sample. The ortho-II structure is an oxygen deficient 123 with a lower Tcthan the bulk of the material and will be a source of flux pinning by turning normal in high fields, thus contributing to the peak effect. With an increase in Sm-211 concentration, the peak effect disappears from the hysteresis loop, as does the ortho-II structure in the TEM images.&nbsp;

Fulltext

Applied Physics Letters

Origin of peak effect in the magnetization hysteresis loop of melt-processed REBa2Cu3Oy superconductors

The field variations of ac M-H loops are recorded at 77 K and 33 Hz using a lock-in flat-band detection method in sintered and press sintered 110-K-phase samples of the Bi-Sr-Ca-Cu-O system. From the slope of the M vs (Formula presented) curve the flux profiles and the effective relative permeability ((Formula presented)) of the samples are determined. Using this value of (Formula presented) the intergrain and intragrain contributions to the magnetization are separated out. The intergranular loops of the sintered sample could be simulated very well using Kim’s model, while for the press-sintered sample the exponential model gives a better fit. Our results show that the loop closure exhibited by the intergranular loop can be simulated to the critical state models without subtracting the wing portion in contrast to the Dersch-Blatter approach. The intragranular loops of sintered samples show quite a good fit to the exponential model after introducing the surface barrier modification. The intergranular critical current density ((Formula presented)) and the apparent lower critical field ((Formula presented)) of the grains are found to be enhanced due to press sintering. The field variations of the various physical quantities obtained from the loops are analyzed to see the effect of microstructural alterations introduced by the press-sintering method. By doing a fast Fourier transform on the M vs t curve the harmonic components are separated out and their variation with the ac field amplitude is studied. © 1996 The American Physical Society.