• C Shivakumara

      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, structural and ferromagnetic properties of La1–𝑥K𝑥MnO3 (0.0≤ 𝑥 0.25) phases by solution combustion method

      C Shivakumara Manjunath B Bellakki

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      We describe the solution combustion synthesis and characterization of La1–𝑥K𝑥MnO3 (0.0 ≤ 𝑥 ≤ 0.25) perovskite phases, which is a low temperature initiated, rapid route to prepare metal oxides. As-synthesized compounds are amorphous in nature; crystallinity was observed on heating at 800°C for 5 min. Structural parameters were determined by the Rietveld refinement method using powder XRD data. Parent LaMnO3 compound crystallizes in the orthorhombic structure (space group 𝑃𝑏𝑛𝑚, No. 62). Potassium substituted compounds were crystallized with rhombohedral symmetry (space group 𝑅–3c, No. 167). The ratio of the Mn3+/Mn4+ was determined by the iodometric titration. The Fourier transform infrared spectrum (FT–IR) shows two absorption bands for Mn–O stretching vibration (𝜈s mode), Mn–O–Mn deformation vibration (𝜈b mode) around 600 cm-1 and 400 cm-1 for the compositions, 𝑥 = 0.0, 0.05 and 0.10. Four-probe electrical resistivity measurements reveal a composition controlled metal to insulator transition (𝑇M–I}}$), the maximum 𝑇M–I was observed for the composition La0.85K0.15MnO3 at 287 K. Room temperature vibrating sample magnetometer data indicate that for the composition up to 𝑥 = 0.10, the compounds are paramagnetic whereas composition with 𝑥 = 0.15, 0.20 and 0.25 show magnetic moments of 27, 29 and 30 emu/g, respectively.

    • Spherical and rod-like Gd2O3:Eu3+ nanophosphors—Structural and luminescent properties

      N Dhananjaya H Nagabhushana B M Nagabhushana B Rudraswamy C Shivakumara R P S Chakradhar

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      A comparative study of spherical and rod-like nanocrystalline Gd2O3:Eu3+ (Gd1.92Eu0.08O3) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of Gd2O3:Eu3+. Upon calcinations at 800°C for 3 h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH)3:Eu3+ phase and it converts to pure cubic phase of Gd2O3:Eu3+ on calcination at 600°C for 3 h. TEM micrographs of hydrothermally prepared cubic Gd2O3:Eu3+ phase shows nanorods with a diameter of 15 nm and length varying from 50 to 150 nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50–250 nm. Dominant red emission (612 nm) was observed in cubic Gd2O3:Eu3+ which has been assigned to ${}^{5}D_{0} \rightarrow {}^{7}F_{2}$ transition. However, in hexagonal Gd(OH)3:Eu3+, emission peaks at 614 and 621 nm were observed. The strong red emission of cubic Gd2O3:Eu3+ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap (𝐸g) was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.

    • Effect of TiN particulate reinforcement on corrosive behaviour of aluminium 6061 composites in chloride medium

      H C Ananda Murthy V Bheema Raju C Shivakumara

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      In the present investigation, the corrosive behaviour of Al 6061–TiN particulate composites prepared by liquidmetallurgy has been studied in chloride medium using electroanalytical techniques such as Tafel, cyclic polarization and electrochemical impedance spectroscopy (EIS). Surface morphology of the sample electrodes was examined using scanning electron micrography and energy dispersive X-ray methods. X-ray diffraction technique was used to confirm inclusion of TiN particulates in the matrix alloy and identify the alloying elements and intermetallic compounds in the Al 6061 composites. Polarization studies indicate an increase in the corrosion resistance in composites compared to the matrix alloy. EIS study reveals that the polarization resistance (𝑅p) increases with increase in TiN content in composites, thus confirming improved corrosion resistance in composites. The observed decrease in corrosion rate in the case of composites is due to decoupling between TiN particles and Al 6061 alloy. It is understood that after the initiation of corrosion, interfacial corrosion products may have decoupled the conducting ceramic TiN from Al 6061 matrix alloy thus eliminating the galvanic effect between them.

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