• T N Guru Row

Articles written in Bulletin of Materials Science

• Structure determination at room temperature and phase transition studies above $T_c$ in ABi4Ti4O15 (A = Ba, Sr or Pb)

The room temperature structure of three compounds belonging to the Aurivillius family (𝑛 = 4), ABi4Ti4O15 (A = Ba, Sr or Pb) has been analysed. BaBi4Ti4O15 crystallizes in a tetragonal 𝐼4/𝑚𝑚𝑚 space group whereas SrBi4Ti4O15 and PbBi4Ti4O15 crystallize in the orthorhombic space group $A2_1am$. The starting model for the Sr and Pb analogues was derived from ab initio methods and refined using the Rietveld method. The cations Ba and Sr are disordered over the Bi sites while the Pb cation is found exclusively in the [Bi2O2]2+ layers. The TiO6 octahedra are tilted with the Ti–O bonds forming zigzag chains along the 𝑐’ axis. The displacement of Bi atoms along the 𝑎’ axis might be responsible for ferroelectricity in these compounds. The high temperature X-ray data above $T_c$ indicate no structural transition for A = Ba and Pb while A = Sr transforms to the tetragonal structure.

• Synthesis, structure and photocatalytic properties of 𝛽-ZrMo2O8

Monoclinic ZrMo2O8 was synthesized via solid state method and single crystals of the title compound have been grown by the hydrothermal method. The crystals belong to monoclinic crystal system with space group 𝐶2/c (No. 15) with 𝑎 = 11.4243(19) Å, 𝑏 = 7.9297(6) Å, 𝑐 = 7.4610(14) Å and 𝛽 = 122.15(2)°, 𝑍 = 4. The bandgap of the compound was 2.57 eV. Unlike the other polymorphs of ZrMo2O8, the monoclinic form has unique crystallographic features with ZrO8 and Mo2O8 polyhedra. The photocatalytic activity of this compound has been investigated for the first time for the degradation of various dyes under UV irradiation and has been compared with the photoactivity of the trigonal form of ZrMo2O8. It has been observed that this compound exhibits specificity towards the degradation of cationic dyes.

• A soluble-lead redox flow battery with corrugated graphite sheet and reticulated vitreous carbon as positive and negative current collectors

A soluble-lead redox flow battery with corrugated-graphite sheet and reticulated-vitreous carbon as positive and negative current collectors is assembled and performance tested. In the cell, electrolyte comprising of 1.5M lead (II) methanesulfonate and 0.9 M methanesulfonic acid with sodium salt of lignosulfonic acid as additive is circulated through the reaction chamber at a flow rate of 50 ml min-1. During the charge cycle, pure lead (Pb) and lead dioxide (PbO2) from the soluble lead (II) species are electrodeposited onto the surface of the negative and positive current collectors, respectively. Both the electrodeposited materials are characterized by XRD, XPS and SEM. Phase purity of synthesized lead (II) methanesulfonate is unequivocally established by single crystal X-ray diffraction followed by profile refinements using high resolution powder data. During the discharge cycle, electrodeposited Pb and PbO2 are dissolved back into the electrolyte. Since lead ions are produced during oxidation and reduction at the negative and positive plates, respectively there is no risk of crossover during discharge cycle, preventing the possibility of lowering the overall efficiency of the cell. As the cell employs a common electrolyte, the need of employing a membrane is averted. It has been possible to achieve a capacity value of 114 mAh g−1 at a load current-density of 20 mA cm-2 with the cell at a faradaic efficiency of 95%. The cell is tested for 200 cycles with little loss in its capacity and efficiency.

• # Bulletin of Materials Science

Volume 44, 2021
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Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020