• P Senthil Kumar

      Articles written in Bulletin of Materials Science

    • Theoretical approaches to superionic conductivity

      C S Sunandana P Senthil Kumar

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      Recent theoretical approaches to the understanding of superionic conductivity in polycrystalline, glassy and polymeric materials are briefly reviewed. Phase transitions to the superionic conducting state in the AgI family are apparently triggered by cluster formation and strong mobile ion interaction within the clusters. Anomalous conductivity and related physical properties are explained in the cluster induced distortion model. Ionic composites such as AgX : Al2O3 (𝑋 = Cl, Br and I) involve conducting and non-conducting phases and the all-important interface between the two whose space charge enhances the conductivity and also trigger phase transitions to exotic polymorphic phases, for which the mechanisms are yet to be explored. Ion hopping dynamics controls the conductivity of superionic glasses. Mode coupling and jump relaxation theories account for the non-Debye relaxation observed in a.c. conductivity of these glasses. The theory of conductivity in polymer electrolytes-still in its infancy-involves their complex structure and glass transition behaviour. Preparative and thermal history, composition and crystallinity control ionic conductivity. New approaches to the synthesis of optimal polymer electrolytes such as rubbery electrolytes, crystalline polymers and nanocomposites must be considered before achieving a comprehensive theoretical understanding.

    • Structural and spectral properties of 4-phenoxyphthalonitrile dye sensitizer for solar cell applications

      P M Anbarasan K Vasudevan P Senthil Kumar A Prakasam M Geetha K Lalithambigai

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      The geometries, electronic structures, polarizabilities and hyperpolarizabilities of organic dye sensitizer 4-phenoxyphthalonitrile was studied based on ab initio HF and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet–visible (UV–Vis) spectrum was investigated by time dependent DFT (TDDFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands were assigned to 𝜋 → 𝜋* transitions. Calculated results suggest that the three excited states with the lowest excited energies in 4-phenoxyphthalonitrile was due to photo-induced electron transfer processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer 4-phenoxyphthalonitrile was due to an electron injection process from excited dye to the semiconductor’s conduction band. The role of phenoxy group in 4-phenoxyphthalonitrile in geometries, electronic structures and spectral properties were analysed.

    • Impact of interfacial interactions on optical and ammonia sensing in zinc oxide/polyaniline structures

      Mansi Dhingra Lalit Kumar Sadhna Shrivastava P Senthil Kumar S Annapoorni

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      Zinc oxide/polyaniline (ZnO/PANI) hybrid structures have been investigated for their optical and gas sensing properties. ZnO nanoparticles, prepared by the sol–gel method, pressed in the form of pellets were used for gas sensing. The hybrid ZnO/PANI structure was obtained by the addition of PANI on the surface of ZnO. The UV–Vis absorption of the modified pellets show band edge at 363 nm corresponding to ZnO, while a change in the absorption peaks for PANI was observed. The possible interaction between Zn2+ of ZnO and NH-group of PANI was confirmed using Raman spectroscopy studies. The results reveal that the hybrid structures exhibit much higher sensitivity to NH3 gas at room temperature than blank ZnO, which is sensitive to NH3 gas at higher temperature. This enhancement has been attributed to the creation of active sites on the ZnO surface due to the presence of PANI.

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