• O D Jayakumar

      Articles written in Pramana – Journal of Physics

    • Inelastic neutron scattering and lattice dynamics of GaPO4

      R Mittal S L Chaplot A I Kolesnikov C -K Loong O D Jayakumar S K Kulshreshtha

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      We report here measurements of phonon spectrum and lattice dynamical calculations for GaPO4. The measurements in low-cristobalite phase of GaPO4 are carried out using high-resolution medium-energy chopper spectrometer at ANL, USA in the energy transfer range 0–160 meV. Semiempirical interatomic potential in GaPO4, previously determined using ab-initio calculations have been widely used in studying the phase transitions among various polymorphs. The calculated phonon spectrum using the available potential show fair agreement with the experimental data. However, the agreement between the two is improved by including the polarisability of the oxygen atoms in the framework of the shell model. The lattice dynamical models are also exploited for calculations of various thermodynamic properties of GaPO4.

    • Neutron diffraction studies on Ca$_{1-x}$Ba$_{x}$Zr4P6O24 solid solutions

      S N Achary O D Jayakumar S J Patwe A B Shinde P S R Krishna S K Kulshreshtha A K Tyagi

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      Herein we report the results of detailed crystallographic studies of Ca$-[1-x}$Ba$_{x}$Zr4P6O24 compositions from combined Rietveld refinements of powder X-ray and neutron diffraction data. All the studied compositions crystallize in rhombohedral lattice (space group R-3 No. 148). A continuous solid solution is concluded from the systematic variation of unit cell parameters. The variation of unit cell parameters with the composition indicates decreasing trend in 𝑎 parameter with increasing Ba2+ concentration contrast to an increasing trend in 𝑐 parameter.

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