• A S Prakash

      Articles written in Bulletin of Materials Science

    • Solution-combustion synthesis of Bi1–𝑥Ln𝑥O1.5 (Ln = Y and La–Yb) oxide ion conductors

      Manjunath B Bellakki A S Prakash C Shivakumara M S Hegde A K Shukla

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      Cubic fluorite related Bi1–𝑥Ln𝑥O1.5 (Ln = Y and La–Yb) phases are synthesized by solutioncombustion method using glycine as the fuel. The cubic fluorite phase is stabilized with 25 mole% of rare earth cations. The lattice parameter of cubic phase increases linearly with size of the lanthanide ion. The synthesized powders are nano-metric in size and exhibit excellent compactability and reach 98% densification even on short period of sintering. The oxides with relatively larger cations Nd, Sm, Eu, Pr and Gd with 25 mole% composition transform to rhombohedral structure while others retain cubic upon sintering. All the phases show high oxide–ion conductivity and the values obtained are in good agreement with the reported values.

    • Synthesis of new (Bi, La)3MSb2O11 phases (M = Cr, Mn, Fe) with KSbO3-type structure and their magnetic and photocatalytic properties

      K Ramesha A S Prakash M Sathiya Giridhar Madras A K Shukla

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      Synthesis and structure of new (Bi, La)3MSb2O11 phases (M = Cr, Mn, Fe) are reported in conjunction with their magnetic and photocatalytic properties. XRD refinements reflect that Bi3CrSb2O11, Bi2LaCrSb2O11, Bi2LaMnSb2O11 and Bi2LaFeSb2O11 adopt KSbO3-type structure (space group, 𝑃𝑛$\bar{3}$). The structure can be described through three interpenetrating networks where the first is the (M/Sb)O6 octahedral network and other two are the identical networks having Bi6O4 composition. The magnetic measurements on Bi2LaCrSb2O11 and Bi2LaMnSb2O11 show paramagnetic behaviour with magnetic moments close to the expected spin only magnetic moments of Cr+3 and Mn+3. The UV-Visible diffuse reflectance spectra are broad and indicate that these materials possess a bandgap of ∼ 2 eV. The photocatalytic activity of these materials has been investigated by degrading Malachite Green (MG) under exposure to UV light.

    • Nitrates–melt synthesized LiNi0.8Co0.2O2 and its performance as cathode in Li-ion cells

      M Sathiya K Hemalatha K Ramesha A K Shukla A S Prakash

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      Layered LiNi0.8Co0.2O2 crystallizing in 𝑅$\bar{3}$𝑚 space group is synthesized by decomposing the constituent metal–nitrate precursors. Oxidizing nature of metal nitrates stabilizes nickel in +3 oxidation state, enabling a high degree of cation ordering in the layered LiNi0.8Co0.2O2. The powder sample characterized by XRD Rietveld refinement reveals < 2% Li–Ni site exchange in the layers. Scanning electron microscopic studies on the as-synthesized LiNi0.8Co0.2O2 sample reflect well defined particles of cubic morphology with particle size ranging between 200 and 250 nm. Cyclic voltammograms suggest that LiNi0.8Co0.2O2 undergoes phase transformation on first charge with resultant phase being completely reversible in subsequent cycles. The first-charge-cycle phase transition is further supported by impedance spectroscopy that shows substantial reduction in resistance during initial de-intercalation. Galvanostatic charge–discharge cycles reflect a firstdischarge capacity of 184 mAh g-1 which is stabilized at 170 mAh g-1 over 50 cycles.

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