• C S Sunandana

      Articles written in Bulletin of Materials Science

    • Ferromagnetic resonance in metallic glasses: study of fracture, stress and thermal stability

      R S Parashar C S Sunandana Anil K Bhatnagar

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      Effects of fracture, stress and isothermal annealing of Fe-Ni based metallic glasses have been investigated using the ferromagnetic resonance technique.fmr linewidth is quite sensitive to changes in the magnetic and structural order in metallic glasses, andfmr lineshape seems to provide useful qualitative information on the mechanical state of these systems. Our observations are compared with recent work of Baianu and co-workers.

    • DTA studies of formation of LaBa2Cu3Ox

      K Sucharitha C S Sunandana

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      The 1:2:3 composition in the La-Ba-Cu-O system has been investigated to understand the formation pathways of the LaBa2Cu3Ox using the static air differential thermal analysis (DTA) as the principal probe and X-ray diffraction and EPR as supporting probes. The major endothermic events observed in DTA are attributed toγα type phase transition of BaCO3 and the formation of “123” phase. It was found necessary to dry the La2O3 at high temperatures to make it crystalline and reactive. BaCo3 was prepared afresh to achieve optimum reactivity. Even after four DTA runs the compound was not single phase as seen in XRD which shows the presence of BaCuO2 as the impurity. The Ba(NO3)2-based mixture appears to react slower than the BaCO3-based mixture.

    • YBa2Cu3O7 superconductor as a mild, deep oxidation catalyst

      Y Srinivasa Rao K Sai Prasad Rao V S Subrahmanyam C S Sunandana

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      Several Y-Ba-Cu-O compositions including the superconducting YBa2Cu3O7 are scanned for their oxygen uptake using low temperature oxygen chemisorption (LTOC) technique as the principal probe at 195 K. BET surface area and pore size distribution were also determined. The results indicate their potential for use as mild, deep oxidation catalysts even under ambient and sub-ambient conditions.

    • Conducting glasses

      C S Sunandana

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      Ion-conducting tellurite glasses are built from trigonal bipyramidal TeO4 units. Neutron diffraction as well as Raman and IR spectroscopic studies have shown that there is a continuous transition from TeO4 → TeO3+1 → TeO3 as the alkali oxide content is progressively increased, non-bridging oxygens being created in the process. Electrical conduction in both single and mixed alkali tellurite glasses is satisfactorily explained by the interchange transport mechanism, based on the site-memory effect exhibited by the glass network.

    • Alkali tellurite glasses: Bonding, structure and conductivity

      C S Sunandana

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      The nature of the Te-O bond and charge transfer between alkali atoms and Te-O polyhedra in alkali-tellurite glasses is discussed in connection with ion transport in these glasses. Experimental results on XPS, neutron and Raman scattering support the empirical picture developed here. The overall kinetics of the interchange transport mechanism for conduction in single and mixed alkali-tellurite glasses is apparently determined by the kinetics of the alkali ion—glass former ion interchange—an aspect to be probed experimentally.

    • Techniques and applications of electron spin resonance

      C S Sunandana

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      A broad-spectrum review of the applications of electron spin resonance to advanced materials is presented. Starting with basic concepts the reader is taken through a quick tour of techniques including continuous-wave and pulse ESR, microscopy and imaging, as well as a few emerging techniques. Applications of spin identification, spin counting, spin mapping and spin imaging of a variety of advanced solid state materials including metals and alloys, semiconductors, inorganics, electroceramics, catalysts, intercalates, polymers, glasses, and organic charge-transfer complexes besides superionic conductors and high-temperature superconductors are included. It is thus demonstrated that the technique is at once specific, sensitive to composition, phase and texture yet accurate enough to be a quantitative but non-invasive tool that promises to be useful in the study of newer and newer materials including multilayers, ferrofluids and nanomaterials.

    • Effect of pre-annealing on the structural evolution and optical response of Ag films exposed to iodine vapours

      R PRAVEENA V SRAVANI SAMEERA N V PRABHAKARA RAO THIRUMALA C S SUNANDANA M GHANASHYAM KRISHNA

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      Ag thin films of 5nm thickness were deposited on glass substrates by thermal evaporation. The films were divided into two sets, out of which, one set was not annealed and the other set was subjected to pre-annealing at 300$^{\circ}$C for2 h in air. The un-annealed and pre-annealed films were exposed to iodine vapours at room temperature for the durations from 5min to 10 h. The un-annealed films were crystallized into the $\beta$ phase of AgI after exposure for 5 h. In contrast, for the pre-annealed films, crystallization into the $\beta$ phase occurred within the first 5 min. Both sets of films, however, exhibit astrong preferential c-axis orientation in the $\beta$-AgI phase. Optical absorption studies reveal that the un-annealed films exhibit a localized surface plasmon resonance (LSPR) with a peak at 545 nm and a long wavelength shoulder at 620 nm, which shifts to 516nm after iodization for a few minutes. This peak position does not change with further iodization. The LSPR for the pre-annealed films has a single peak at 538 nm. After iodization for a few minutes, this peak shifts to 525 nm. Iodization for 3 h results in a further blue-shift of this resonance to 475 nm. The photoluminescence spectrum reveals two peaks, oneat 368 nm and the other at 712 nm. The first one is assigned to the excitons of AgI, whereas the long wavelength peak is attributed to the presence of disorder in the films. The reasons for the difference in behaviour of the un-annealed andpre-annealed films are discussed.

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