• K R Rao

      Articles written in Bulletin of Materials Science

    • Experimental study of fluctuations in materials

      K R Rao

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      Mechanical behaviour is decided by the structure and kinetics of defects in materials. External forces play an important role in determining the growth, decay and motion of defects. In addition there is an inherent fluctuation in the various microscopic characteristics of the system as the latter acts as a ‘heat bath’. A disturbance that is set up in the system is affected by these fluctuations. The response of the system to external forces can be related to the behaviour of the system due to intrinsic fluctuations in the absence of impressed forces. This is the basis of relation between study of fluctuations in the system and various relaxation phenomena observed. It is proposed to discuss certain features of this subject in relation to various material properties.

    • A computer simulation of LiKSO4

      S L Chaplot K R Rao

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      Molecular-dynamics computer-simulation of an ionic molecular solid LiKSO4 has been carried out at 300 and 1000 K using the atom-atom potentials obtained from lattice dynamical studies. We observe hopping of lithium ions to interstitial positions which is related to reorientations of sulphate tetrahedra.

    • Inelastic neutron scattering from Tl2CaBa2Cu2O8

      S L Chaplot B A Dasannacharya R Mukhopadhyay K R Rao P R Vijayaraghavan R M Iyer G M Phatak J V Yakhmi

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      Coherent inelastic neutron scattering measurements have been carried out on the high temperature superconductors Tl2CaBa2Cu2O8 (Tl-2122,Tc=107 K) and YBa2Cu3O7 (Y-123,Tc=92 K), at the Dhruva reactor at Trombay. The density of phonon states in Tl-2122 is enhanced at 6–17 meV and reduced at 40–70meV compared to that in Y-123.

    • Phonon dispersion relations and densities of states in La2CuO4 and La2NiO4

      Narayani Choudhury K R Rao S L Chaplot

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      Rigid-ion model calculations of phonon dispersion relations, densities of states and partial densities of states of the highTc superconductor La2CuO4 and its isostructural compound La2NiO4 have been carried out both in the tetragonal and orthorhombic phases of La2CuO4 and the tetragonal phase of La2NiO4. The calculations are in fair agreement with reported experiments. The computed phonon dispersion in the tetragonal phase of La2CuO4 reproduces the soft mode behaviour for the lowest Σ4 TO branch which is found to harden in the orthorhombic phase, consistent with experimental data.

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