• A S Vaingankar

      Articles written in Bulletin of Materials Science

    • Influence of Nd3+ substitution on thermoelectric power of Zn-Mg ferrite system

      B P Ladgaonkar P N Vasambekar A S Vaingankar

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      Polycrystalline ferrites, ZnxMg1−xFe2−yNdyO4 (x = 0.00, 0.20, 0.40, 0.60, 0.80 and 1.00;y = 0.00, 0.05 and 0.10) were prepared by standard ceramic method. X-ray diffraction study of these compositions revealed the formation of single phase spinels. Seebeck coefficient was obtained from thermo emf measurement by keeping constant temperature difference of 10 K across the pellet. The values of Seebeck coefficient were found to be negative showing majority charge carriers ofn-type, suggesting the mechanism of conduction to be predominantly by electron hopping. The substitution of Nd3+ ion, which perhaps resides at the B-site, resulting in a decrease in the Seebeck coefficient. This decrease was assigned to the decrease of population of Fe3+ ion at the B-site. The activation energies calculated both from mobility plots and from dc resistivity plots were found comparable. The Fermi energy,EF(0), which was estimated by intrapolation ofEF-T curves toT = 0 K, was found less than the activation energy. This difference was attributed to electron hopping energy.

    • Infrared absorption spectroscopic study of Nd3+ substituted Zn–Mg ferrites

      B P Ladgaonkar C B Kolekar A S Vaingankar

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      Compositions of polycrystalline Zn𝑥Mg1-𝑥Fe2–𝑦Nd𝑦O4 (𝑥 = 0.00, 0.20, 0.40, 0.60, 0.80 and 1.00; 𝑦 = 0.00, 0.05 and 0.10) ferrites were prepared by standard ceramic method and characterized by X-ray diffraction, scanning electron microscopy and infrared absorption spectroscopy. Far infrared absorption spectra show two significant absorption bands, first at about 600 cm–1 and second at about 425 cm–1 , which were respectively attributed to tetrahedral (A) and octahedral (B) sites of the spinel. The positions of bands are found to be composition dependent. The force constants, $K_T$ and $K_O$, were calculated and plotted against zinc concentration. Compositional dependence of force constants is explained on the basis of cation–oxygen bond distances of respective sites and cation distribution.

    • A.c. susceptibility study of CaCl2 doped copper–zinc ferrite system

      A Y Lipare P N Vasambekar A S Vaingankar

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      Polycrystalline soft ferrites, Zn$_x$ Cu$_{1–x}$ Fe2O4 (𝑥 = 0.30, 0.50, 0.70, 0.80 and 0.90), doped with controlled amount of calcium chloride (CaCl2) were prepared by standard ceramic route and studied for a.c. susceptibility. X-ray diffraction studies of the compositions reveal formation of single-phase cubic spinel. The values of lattice constant increase as doping percentage of CaCl2 increased from 0.01% to 0.05% and afterwards decrease slightly. The presence of chlorine ions is confirmed by absorption peak in far IR spectra near 650 cm-1 for all the samples. The variation of a.c. susceptibility with temperature shows the existence of single domain structure for 𝑥 = 0.3 and exhibits transition from single domain to multidomain structure with increased Ca2+ contents from 0.01 to 0.1%. The composition, 𝑥 = 0.5, shows multidomain structure independent of Ca2+ content. The samples for 𝑥 = 0.70, 0.80 and 0.90 show paramagnetic behaviour at and above room temperature.

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      Posted on October 12, 2020

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      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
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