K. J. Rao

Physico chemical investigation of fast ion conducting AgI-Ag2SeO4 glasses

Fast ion conducting glasses in the system xAgI−(1−x)Ag2SeO4 (0·5≤x≤0·75), prepared by melt quenching route have been investigated in detail. Spectroscopic, thermal and electrical properties including dielectric relaxation have been studied. An attempt is made to understand the variation in these properties by using a structural unpinning model.

Electron spin resonance of transition metal ions in glasses

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.

Dielectric studies of As-Se glasses

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.

Formation of lead pyrophosphate glass and the role of anion disproportionation

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.

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

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.

Infrared absorption spectra of As-Se glasses

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.

Magnetic susceptibility studies of lead oxyhalide glasses containing transition metal oxides

Magnetic susceptibility studies of lead oxyhalide glasses containing high concentrations of transition metal oxides such as MnO and Fe2O3 have been performed. While they exhibit predominantly antiferromagnetic interactions, the low temperature (<100K) region is dominated by paramagnetic contributions. The behaviour in these glasses is found to be similar to that of covalent oxide glasses and is different from that of purely ionic sulphate glasses.

On the coordination of molybdenum in AgI−Ag2O−MoO3 glasses usingxanes andexafs

Abstractxanes andexafs analysis of the MoK-edge spectra in a series of AgI−Ag2O−MoO3 glasses has been performed in order to determine the coordination of molybdenum in the glass. Mo has been found to exist in a tetrahedrally coordinated shell of four oxygens. Limitation of theexafs technique in discerning small distance differences in the first shell has also been discussed.

Photoacoustic spectra of As2S3−As2Se3 glasses

Photoacoustic spectra of As−S, As−Se glasses as well as the As2(S,Se)3 glasses have been investigated. Photoacoustic spectra of powdered samples give results comparable to those obtained from transmission spectra, the latter studies requiring preparation of thin films. Temperature-dependent studies of the As2S3 glass have been carried out. Optical behaviour of these glasses has been interpreted in terms of homoatomic bonding defects.

EXAFS studies of cobalt oxides and oxide glasses

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.