• G N Subbanna

      Articles written in Bulletin of Materials Science

    • Determination of the composition of binary systems by the ratio method employing SEM-EDAX

      G N Subbanna

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      By employing x-ray emission in a scanning electron microscope (SEM), it has been shown that compositions of binary systems such as As-Se glasses, Al-Zn alloys and copper sulphides can be determined.

    • High resolution electron microscopy of bismuth oxides with perovskite layers

      G N Subbanna L Ganapathi

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      Layered bismuth oxides of the general formula (Bi2O2)2+ (An−1BnO3n+1)2− whereA = Bi or Ba,B = Ti, Fe, W andn = number of perovskite layers have been investigated by high resolution electron microscopy. Lattice images obtained forn = 1 to 6 members show stacking of (n − 1) perovskite layers sandwiched between dark bands due to the (Bi2O2)2+ layers. It has been possible to resolve the perovskite layer structures in some of the oxides. A highly ordered structure is observed upto then = 3 member, whereas higher members show superstructures, dislocations and stacking faults arising from the side-stepping of (Bi2O2)2+ layers as well as ferroelectric domain walls.

    • Electron microscopic investigation of high-temperature oxide superconductors

      G N Subbanna

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      Electron microscopic investigations have been carried out on superconducting YBa2Cu3 O7−δ, NdBa2Cu3 O7−δ and related oxides. All these orthorhombic oxides exhibit twin domains. Based on high resolution electron microscopy, it is shown that there is no significant change in the structure across the twins. Oxides of the La2−xSrx(Bax)CuO4 system do not show twins, but exhibit other types of defects. Twins appear to be characteristic of only the orthorhombic 123 structures.

    • SrB4O7:Bi2VO5·5 — A novel nanocomposite

      M V Shankar G N Subbanna K B R Varma

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      Glass composites of strontium tetraborate, SrB4O7(SBO) with bismuth vanadate, Bi2VO5·5 (BiV) of the composition (1 −x) SBO-x BiV (0 ≤x ≤ 0·75), have been synthesized. X-ray powder diffraction and electron microscopy indicate as-quenched composites to be amorphous and the annealed samples showed the presence of nanometer sized particles of BiV dispersed in the glassy matrix of SBO. The dielectric constant of these composites increases with increase in the volume fraction of BiV, at 300 K. The measured dielectric constant of the composite very nearly obeys the Maxwell’s relationship. Optical transmission studies confirm a steady shift in the optical absorption edge towards longer wavelengths with increase inx.

    • Synthesis, structure and IR absorption studies of LnBaCuCoO5 (Ln=rare earth) oxides

      C Shivakumara M S Hegde G N Subbanna

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      A series of oxides LnBaCuCoO5 (Ln=Pr, Nd, Sm, Dy, Gd, Ho and Er) have been synthesized by ceramic method. The oxides crystallize in a tetragonal structure, isostructural to YBaCuCoO5. All the oxides in the series are semiconducting. IR spectra of these oxides show distinct absorption bands at 630 cm−1, 550 cm−1 and 330 cm−1 which are assigned toE,A2 andA1 modes respectively. Doping of holes in these oxides, by calcium substitution in Er1−xCaxBaCuCoO5−x (up tox ⋍ 0·3) was done but, these oxides did not show metallic behaviour.

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