• E Mohandas

      Articles written in Bulletin of Materials Science

    • Details of an imaging atom probe

      V R Seshadri K Neelakantan E Mohandas V S Raghunathan

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      An imaging atom probe has been incorporated in a conventional field ion microscope in our laboratory. The principle and instrumentation of the probe has been discussed.

    • Oxygen diffusion and defect mechanism in c-axis textured thin films of YBa2Cu3O7−x by resistivity measurements

      P Kuppusami E Mohandas S Raju V S Raghunathan

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      Isothermal resistivity measurements have been carried out to study the dynamics of oxygen out- and in-diffusion in thin films of YBa2Cu3O7−x in the temperature range 648–773 K. The activation energies for the out- and in-diffusion were determined to be 1·36 and 0·7 eV respectively. We have modelled the resistance-time plots for the oxygen in-diffusion using an equation for one dimensional diffusion into a plane. The microstructural defects such as low angle grain boundaries associated with the c-axis oriented grains are believed to provide the required diffusion paths in thin films of YBCO.

    • Development of an effective interatomic potential for transition metals and alloys: Modified Wills-Harrison model

      S Raju E Mohandas V S Raghunathan

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      This paper deals with the development of an effective interionic interaction for transition metals and alloys in the spirit of a hybridized pseudopotential tight-binding formalism, developed among others by Wills and Harrison. Stated briefly, the recipe consists in writing the total interionic interaction as a sum of contributions arising from nearly free s-electrons and that of tightly bound d-electrons. The s-d hybridization is also accounted for by allowing for the relative change in the occupancy of s and d electron counts. This potential, although not taking into account the magnetic contribution, contains otherwise all the essentials of a physically meaningful interatomic interaction. In this paper, a modified version of the Wills-Harrison model is used to calculate the structural and cohesive properties of transition metals at 0 K. The calculated values are in reasonable agreement with the experimental ones. This method is also used to derive an effective interatomic interaction for γ-TiAl. The use of this potential in obtaining an estimate of point defect energetics in TiAl is discussed.

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