• D D Sarma

      Articles written in Journal of Chemical Sciences

    • Nature of dependence of spin-orbit splittings on atomic number

      D D Sarma

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      It has been shown that Dirac equation employing a constant value of the screening constant Z0 does not explain the variation of spin-orbit splittings of 2p and 3p levels with atomic number Z. A model which takes into account the variation of Z0 withZ is shown to satisfactorily predict the dependence of spinorbit splittings onZ.

    • Adsorption of carbon monoxide and oxygen on transition metal surfaces: A comparative study of the results from electron spectroscopy and theoretical calculations

      P Vishnu Kamath D D Sarma C N R Rao

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      Results of investigations on the adsorption of CO andO2 on transition metal surfaces by employinguv and x-ray photoelectron spectroscopy and electron energy loss spectroscopy (eels) are presented. Results of molecular orbital calculations on adsorbed CO and O2 are also discussed. Some of the interesting aspects discussed are, satellites in the O(ls) region due to adsorbed CO, vibrationaleels of adsorbed O2 and dissociation energy profiles of adsorbed O2 on clean surfaces as well as surfaces covered with potassium or presorbed atomic oxygen.

    • Origin of the insulating state in NaCuO2

      Seva Nimkar N Shanthi D D Sarma

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      We study the electronic structure of NaCuO2 by analysing experimental core level photoemission and X-ray absorption spectra using a cluster as well as an Anderson impurity Hamiltonianincluding the band structure of the oxygen sublattice. We show that the X-ray absorption results unambiguously establish a negative value of the charge transfer energy, Δ. Further, mean-field calculations for the edge-shared one-dimensional CuO2 lattice of NaCuO2 within the multiband Hubbard Hamiltonian show that the origin of the insulating nature lies in the band structure rather than in the correlation effects. LMTO-ASA band structure calculations suggest that NaCuO2 is an insulator with a gap of around 1 eV.

    • Properties of a new magnetic material: Sr2FeMoO6

      D D Sarma Sugata Ray

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      Recently, there have been a large number of investigations of the physical properties of Sr2FeMoO6 and related compounds, in view of their significant negative magnetoresistive property at room temperature and in low applied magnetic fields. We review these investigations, detailing the microscopic mechanism controlling the electronic and magnetic properties of this system.

    • Electron spectroscopic investigation of metal-insulator transition in Ce1-xSrxTiO3

      U Manju S R Krishnakumar Sugata Ray S Raj M Onoda C Carbone D D Sarma

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      We have carried out detailed electron spectroscopic investigation of Ce1−x SrxTiO3 exhibiting insulator-metal transition withx. Core level X-ray photoelectron spectra of Ce3d as well as resonant photoemission spectra obtained at the Ce4d→4f resonant absorption threshold establish Ce as being in the trivalent state throughout the series. Using the ’off-resonance’ condition for Ce 4f states, we obtain the Ti3d dominated spectral features close toEF, exhibiting clear signatures of coherent and incoherent peaks. We discuss the implications of our findings in relation to the metalinsulator transition observed in this series of compounds.

    • A microspectroscopic study of the electronic homogeneity of ordered and disordered Sr2FeMoO6

      Dinesh Topwal U Manju Sugata Ray S Raj D D Sarma S R Krishnakumar M Bertolo S La Rosa G Cautero

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      Disordered Sr2FeMoO6 shows a drastic reduction in saturation magnetization compared to highly ordered samples, moreover magnetization as a function of the temperature for different disordered samples shows qualitatively different behaviours. We investigate the origin of such diversity by performing spatially resolved photoemission spectroscopy on various disordered samples. Our results establish that extensive electronic inhomogeneity, arising most probably from an underlying chemical inhomogeneity in disordered samples, is responsible for the observed magnetic inhomogeneity. It is further pointed out that these inhomogeneities are connected with composition fluctuations of the type Sr2Fe1+xMo1-xO6 with Fe-rich (x > 0) and Mo-rich (x < 0) regions.

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