• P VISHNU KAMATH

      Articles written in Bulletin of Materials Science

    • Electrochemical impedance studies of capacity fading of electrodeposited ZnO conversion anodes in Li-ion battery

      G K KIRAN TIRUPATHI RAO PENKI N MUNICHANDRAIAH P VISHNU KAMATH

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      Electrodeposited ZnO coatings suffer severe capacity fading when used as conversion anodes in sealed Li cells. Capacity fading is attributed to (i) the large charge transfer resistance, $R_{\rm ct}$ (300–700 $\Omega$) and (ii) the low Li$^+$ ion diffusion coefficient, D$^+_{\rm Li}$ (10$^{−15}$ to 10$^{−13}$ cm$^2$ s$^{−1}$). The measured value of R$_{\rm ct}$ is nearly 10 times higher and D$^+_{\rm Li}$ 10–100 times lower than the corresponding values for Cu$_2$O, which delivers a stable reversible capacity.

    • NO$^−_2$ and SCN$^−$-intercalated layered double hydroxides: structure and orientation of anions in the interlayer gallery

      SHIVANNA MARAPPA P VISHNU KAMATH

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      NO$^−_2$ and SCN$^−$ are two common small inorganic anions. The former is a common industrial pollutant. Thelatter is linear and is a good mimic for the toxic CN$^−$ ion. The structures of these two anions are refined within the gallery ofthe [Zn–Al]-layered double hydroxide (LDH). Both LDHs crystallize as mixed anion phases. The nitrite is found to co-existwith the nitrate ion. The nitrite ion is intercalated with its molecular plane inclined to the metal hydroxide layer. In the caseof the SCN$^−$ intercalated LDH, no other anion was detected by ion chromatography, suggesting that the SCN$^−$ deficiencyis compensated by intercalated hydroxyl ions. In this case, the SCN$^−$ ion is found to be intercalated with its molecular axisinclined to the metal hydroxide layer.

    • Reversible hydration of the perchlorate-intercalated layered double hydroxides of Li and Al: structure models for the dehydrated phases

      LATHA PACHAYAPPAN P VISHNU KAMATH

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      Imbibition of lithium sulphate into aluminium hydroxide is known to result in a sulphate-intercalated layered double hydroxide (LDH) of Li and Al. The perchlorate ion has the same size and molecular symmetry as the sulphate ion,but only half its charge. Consequently, twice the number of ClO$^−_4$ ions is needed to balance LDHs the charge on the metal hydroxide layer, compared to the SO$^{2−}_4$ ions. In this work, the ClO$^−_4$-intercalated LDHs were obtained from both the bayerite and gibbsite precursors. Inclusion of the hydration sphere along with the ClO$^−_4$ anion, induced turbostratic disorder in the stacking of the metal hydroxide layers. Temperature-induced dehydration ($T \sim 100$–140$^{\circ}$C) brought about a partial ordering in the interlayer region and the ClO$^−_4$ ion oriented itself with one of its $C_2$-axes parallel to the metal hydroxide layer. The close packing of ClO$^−_4$ ions could be realized by the complete dehydration of LDH and the distribution of the ClO$^−_4$ ions in all the available interlayer sites. In contrast, within the crystal of the sulphate analogue, the sulphate ions occupy only half the number of interlayer sites. The other half is occupied by the residual water molecules, as the sulphate analogue does not fully dehydrate even at elevated temperatures. This difference in the behaviour of the two LDHs has its origin in the largedifference in the hydration enthalpies of the two anions.

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      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
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      Posted on July 25, 2019

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