• V Ganesan

      Articles written in Bulletin of Materials Science

    • Magnetic shielding using high-temperature superconductors

      V Ganesan R Srinivasan S Aswathy K D Chandrasekaran B Srinivas U V Varada Raju G V Subba Rao R Gopalan T Rajasekaran

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      Magnetic shields of various high-temperature superconductors, YBa2Cu3O7−x (YBCO), YBa2Cu3O7−x-Ag composites (random inclusions as well as non-random coatings) and Bi2Sr2Ca2Cu3Ox (BSCCO) were prepared by uniaxial as well as isostatic compression with various dimensions. The shielding properties were measured at 77 K for dc and ac magnetic fields in the range of frequencies from 100 Hz to 10 kHz. The critical penetration field (CPF), defined as the value of the applied magnetic field at which a detectable field was observed inside the cylinder, varied from cylinder to cylinder and also with the ageing of the cylinders in the case of YBCO shields. The highest value of CPF was 16 G at 77 K for YBCO shield prepared by isostatic compression. Even though the stability of BSCCO shields with respect to ageing is good, the CPF values are very low compared to those for YBCO. Detailed studies were performed in the case of YBCO shields. The CPF decreased as a function of time over a period of 90 days. The CPF decreased as the frequency of the applied field was increased. The wave form of the field inside the pot for a sinusoidal applied field was highly distorted and showed the presence of higher harmonics with appreciable amplitude. The wave form was Fourier-analysed to yield the field inside the shield along with the harmonics. The shields with Ag addition seem to give better performance at high fields.

    • Critical exponent of the electrical conductivity in the paracoherence region of a thin film of YBa2Cu3O7−x

      Manmeet K Marhas K Balakrishnan V Ganesan R Srinivasan D Kanjilal G K Mehta G K Muralidhar G Mohan Rao Senthil Nathan S Mohan

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      Critical exponent of the electrical conductivity in the paracoherence region (γ) of the high temperature superconductor YBa2Cu3O7−x (YBCO) has been estimated for high quality thin film on ZrO2 substrate prepared by high pressure oxygen sputtering. High energy ion irradiation was carried out using 100 MeV16O7+ ions at liquid nitrogen temperature to see the effects of disorder on the value of the exponent. The critical exponent (γ) changes from a value of about 2 to 1·62 upon irradiation. Studies were also carried out on this film to see the effect of ageing and annealing.

    • Magneto-heat capacity study on Kondo lattice system Ce(Ni$_{1−x}$Cu$_x$)$_2$Al$_3$


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      Heat capacity studies on the Kondo lattice system Ce(Ni$_{1−x}$Cu$_x$)$_2$Al$_3$, in the presence of magnetic fields, were reported for $x = 0.0−0.4$. The physical properties of the intermediate compositions like $x = 0.3$ and 0.4 were known for their enhanced thermoelectric power and hence have been analysed with an extra interest. It was also shown from the X-ray diffraction that these systems with $x = 0.3$ and 0.4 were in single phase in terms of sample purity and it stabilized the phases easily with the increase in the Cu doping in the system. The low temperature risein $C_p/T$ below 10 K under the influence of high magnetic fields was analysed using a multi-level Schottky effect. A gradual decrease of the total angular momentum (J) with the increase of applied magnetic fields indicated ascenario of screening of Ce$^{3+}$ magnetic moment while simultaneously the system settled for the Fermi liquid state. The screening thus seen was in line with the expectations of electrical conductivity measurements on these samples.

    • Tuning of structural, morphological, optical and electrical properties of SnO$_2$ by indium inclusion


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      A complete range of indium-doped (In:SnO$_2$) thin films prepared by spray-pyrolysis technique have been studied and characterized by different techniques to get information about structure, surface and electrical properties. The influence of indium filler concentration (i.e., 0–15 wt%) on the properties of SnO$_2$ has been explored. Structural study reveals that the inclusion of indium after a certain optimum value leads structural distortion which causes the films’ expansion along c-axis direction. The extract of electrical study helps to understand that what should be the optimum value to switch from n- to p-type, which is further confirmed by Hall measurement. A deep analysis of electrical data confirms that the solid solution of indium into SnO$_2$ should not be completely excluded and its range should not be >12 wt% as we got saturation in the electrical behaviour after it. Variable range hopping mechanism has been found to be best fitted for low temperature range and comes out with valuable information that increase in density of states near Fermi level are responsible for decrease in resistivity in case of higher doping and also confirms that 6 wt% is the optimum value to switch from n- to p-type conductivity.

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    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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