• S A Hashmi

      Articles written in Bulletin of Materials Science

    • Proton transport in KDP-family of ferroelectric materials

      Ajay Kumar S A Hashmi Suresh Chandra

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      Proton transport in potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) is briefly reviewed. The experimental results of Wagner’s polarization measurement, coulometry, infrared spectroscopy, transient ionic current measurement, the variation of electrical conductivity with temperature and electrogravimetric analysis for KDP and ADP are reported. H+ and OH- ions are ascertained as the mobile ionic species. A new mechanism for the proton transport in KDP and ADP is suggested: A three-fold rotation of H2P4- units about any of the axes of PO4 tetrahedra leads to a configuration like O...H...H...O, the rearrangement of which provides H...O...H bridge that gets electrodissociated on the application of a d.c. electric field.

    • Plastic crystal-incorporated magnesium ion conducting gel polymer electrolyte for battery application

      JYOTI SHARMA S A HASHMI

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      Studies on a novel composition of magnesium ion conducting gel polymer electrolyte (GPE), comprising a solution of Mg-salt, magnesium trifluoromethanesulfonate (Mg-triflate or Mg(Tf)$_2$) in a plastic crystal succinonitrile (SN), entrapped in a host polymer poly(vinylidenefluoride–hexafluoropropylene) (PVdF–HFP) was reported. Small amount of anionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf) was added to stabilize the GPE composition. The electrolyte possesses excellent dimensional integrity in the form of free-standing thick film, which offers the ionicconductivity of $4 \times 10^{−3}$ S cm$^{−1}$ at room temperature $\sim$26$^{\circ}$C. The electrochemical potential window of the electrolyte,observed from the linear sweep voltammetry, is determined to be $\sim$4.1 V. The magnesium ion conduction in the GPE film is confirmed from cyclic voltammetry, electrochemical impedance spectroscopy and dc polarization techniques. Different structural, thermal and electrochemical studies demonstrate the promising characteristics of the polymer film, suitable as electrolyte in rechargeable magnesium batteries. The potential of the GPE as electrolyte/ separator was ascertained by fabricating a prototype magnesium battery of the configuration Mg:graphite composite anode/GPE/MnO$_2$-cathode. Thespecific discharge capacity of 40 mAh g$^{−1}$ (with respect to the MnO$_2$ cathode material) was obtained at the first discharge. The cell shows charge–discharge performance for eight cycles with a substantial fading in capacity.

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