• M Ramanadham

      Articles written in Pramana – Journal of Physics

    • Structure determination of Ls-threonine by neutron diffraction

      M Ramanadham S K Sikka R Chidambaram

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      The structure of the aminoacid, Ls-threonine [NH3+ CH(CHOHCH3)COO], space groupP212121,a=13.630(5),b=7.753(1),c=5.162(2) Å,z=4, has been determined from neutron diffraction data using direct methods. The intensities of 1148 neutron Bragg reflections were measured from a single crystal. The structural parameters were refined by the method of least squares using anisotropic temperature factors. The finalR(F2) is 0.068. The structure was also refined from the x-ray data of Shoemakeret al (1950J. Am. Chem. Soc.72 2328); there is good agreement between the two sets of heavy atom parameters. The parameters of hydrogen atoms are of course more precisely determined in our neutron study. The molecular conformation and the hydrogen bonding scheme are discussed. Weighted average values of bond distances and angles from 14 aminoacid structures with ionized carboxylic groups studied by neutron diffraction at Brookheven and Trombay are also presented.

    • Structural studies and Tc dependence in La2−xDyxCayBa2Cu4+yOz type mixed oxide superconductors

      S Rayaprol Krushna Mavani CM Thaker DS Rana Keka Chakravorty SK Paranjape M Ramanadham Nilesh A Kulkarni DG Kuberkar

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      A new series of mixed oxide superconductors with the stoichiometric composition La2−xDyxCayBa2Cu4+yOz (x=0.0 − 0.5, y=2x) has been studied for structural and superconductiong properties. Our earlier studies on La2−x(Y/Er)xCayBa2Cu4+yOz series, show a strong dependence of Tc on hole concentration (psh). In the present work, the results of the analysis of the neutron diffraction measurements at room temprerature on x=0.3 and 0.5 samples are reported. It is interesting to know that Ca substitutes for both La and Ba site with concomitant displacement of La onto Ba site. Superconductivity studies show that maximum Tc is obtained for x=0.5, y=1.0 sample (Tc ∼ 75 K), for La1.5Dy0.5Ca1Ba2Cu5Oz (La-2125).

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