• A V Ravi Kumar

      Articles written in Bulletin of Materials Science

    • Characteristics of laser-induced plasma from highTc superconductor

      G Padmaja A V Ravi Kumar V Vidyalal P Radhakrishnan V P N Nampoori C P G Vallabhan

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      The spectroscopic analysis of the emission from the plasma produced by irradiating a highTc superconducting GdBa2Cu3O7 target with a high power Nd:YAG laser beam shows the existence of the bands from different oxides in addition to the lines from neutrals and ions of the constituent elements. The spectral emissions by oxide species in laser-induced plasma show considerable time delays as compared to those from neutral and ionic species. Recombination processes taking place during the cooling of the hot plasma, rather than the plasma expansion velocities, have been found to be responsible for the observed time delays in this case. The decays of emission intensities from various species are found to be non-exponential.

    • Dielectric properties of LiF-B2O3 glasses doped with certain rare earth ions

      A V Ravi Kumar B Apparao N Veeraiah

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      Dielectric constantɛ, loss tanδ and a.c. conductivityσ of LiF-B2O3: Ln3+ (where Ln=Ce, Pr, Nd and Tb) glasses are studied as functions of frequency (in the range 102–106 Hz) and temperature (range 30–200°C). The dielectric breakdown strength of these glasses was also determined at room temperature in an air medium. The rate of increase ofɛ and tanδ with temperature decreases with decrease in the ionic radius of RE3+ ion whereas the dielectric breakdown strength, the activation energy for a.c. conduction in the high temperature region decreases with increase in the ionic radius of RE3+ ion. An attempt has been made to explain the a.c. conduction in these glasses on the basis of quantum mechanical tunnelling (QMT) model.

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