• K J Rao

      Articles written in Journal of Chemical Sciences

    • Electrical conductivity studies in K2SO4-ZnSO4 glasses

      P S L Narasimham Sudha Mahadevan K J Rao

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      The d.c. conductivities of K2SO4-ZnSO4 glasses have been measured over a wide range of temperature. It has been found that two different subglassy activation energies are present which may be associated with K+ and Zn++ ions. Also a conductivity maximum occurs as a function of composition. These features have been discussed in the light of the random close packed model of sulphate glasses.

    • Infrared absorption spectra of As-Se glasses

      R Mohan K J Rao

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      IR absorption spectra of As-Se glasses have been studied over a wide range of compositions. Various two-phonon, multiphonon (combination tones) and impurity absorptions have been identified. Compositional variation of relative band intensities has been explained in terms of the chemically ordered network model.

    • Dielectric studies of As-Se glasses

      R Mohan K J Rao

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      Dielectric constants and loss tangents of As-Se glasses have been measured between 300 K and the respective glass transition temperatures and between 1 kHz and 20 kHz. The variation of dielectric constants has been interpreted in terms of both heteropolarity of bonds and average bond energies employing a chemically ordered network model. Various contributions to total molar polarizations have been estimated. Rapid rise of loss tangent in the vicinity of glass transitions has been interpreted in terms of rapid increase; of d.c. conductivity.

    • EXAFS studies of cobalt oxides and oxide glasses

      R Parthasarathy Ravi V Prasad P R Sarode K J Rao

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      The exafs of Co2+ has been studied in rare earth cobaltites and in sulphate and borate glasses. It has been found that the environment of Co2+ ions is very similar in these cases. It appears feasible to study local structures in glasses using probe ion exafs.

    • Electrical conductivity studies in sulphate glasses and the mixed alkali effect

      H G K Sundar K J Rao

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      Electrical conductivities of alkali sulphate-zinc sulphate glasses have been measured. The variation of conductivity with compositon confirms the presence of the mixed alkali effect. The origin of mixed alkali effect has been explained on the basis of structural considerations reported earlier by us.

    • Glass transition. A new approach based on cluster model of glasses

      K J Rao

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      The structure of real glasses has been considered to be microheterogeneous, composed of clusters and connective tissue. Particles in the cluster are assumed to be highly correlated in positions. The tissue is considered to have a truly amorphous structure with its particles vibrating in highly anharmonic potentials. Glass transition is recognized as corresponding to the melting of clusters. A simple mathematical model has been developed which accounts for various known features associated with glass transition, such as range of glass transition temperature,Tg, variation ofTg with pressure, etc. Expressions for configurational thermodynamic properties and transport properties of glass forming systems are derived from the model. The relevence and limitations of the model are also discussed.

    • Particle motion in glasses

      K J Rao R Parthasarathy

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    • Electron spin resonance of transition metal ions in glasses

      K J Rao B G Rao

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      Electron spin resonance (ESR) studies of transition metal ions in glasses have been briefly reviewed. The known relations of spin Hamiltonian parameters to structural geometries around the transition metal ion probes in glasses are summarized. RecentESR studies in glasses based on the use of Ti3+, VO2+, Mo5+, Cr3+, Fe3+, Mn2+ and Cu2+ have been emphasized. Merits ofESR in the context of structural elucidation have also been discussed.

    • Formation of lead pyrophosphate glass and the role of anion disproportionation

      S Ananthraj K J Rao

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      Thermal, spectroscopic and electrical properties of lead pyrophosphate glass prepared by melt quenching have been examined. A model based on the structural disproportionation of the P2O74− ions has been proposed and is shown to consistently explain all the observations. The equilibrium of various anionic species has been discussed on the basis of their electronegativities which are in turn related to their basicities.

    • Distribution of ionic charge carriers and migration barriers in binary alkali silicate glasses

      K J Rao S R Elliott

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      Likely spatial distributions of network-modifying (and mobile) cations in (oxide) glasses are discussed here. At very low modifier concentrations, the ions form dipoles with non-bridging oxygen centres while, at higher levels of modification, the cations tend to order as a result of Coulombic interactions. Activation energies for cation migration are calculated, assuming that the ions occupy (face-sharing) octahedral sites. It is found that conductivity activation energy decreases markedly with increasing modifier content, in agreement with experiment.

    • Infrared and Raman spectroscopic studies of glasses with NASICON-type chemistry

      K J Rao K C Sobha Sundeep Kumar

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      Structures of NASICON glasses of the general formula AB2(PO4)3, where A = Li, Na or K and B = Fe, Ga, Ti, V or Nb, have been investigated using vibrational (IR and Raman) spectroscopies. Phosphate species appear to establish an equilibrium via a disproportionation reaction involving a dynamical bond-switching mechanism where both charge and bonds are conserved. B ions in the system acquire different coordinations to oxygens. Alkali ions cause absorptions due to cage vibrations. All the observed spectroscopic features are consistent with speciation involving disproportionation reactions.

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