• Angelos G Kalampounias

      Articles written in Bulletin of Materials Science

    • Low-frequency Raman scattering in alkali tellurite glasses

      Angelos G Kalampounias

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      Raman scattering has been employed to study the alkali-cation size dependence and the polarization characteristics of the low-frequency modes for the glass-forming tellurite mixtures, 0.1M2O–0.9TeO2 (M = Na, K, Rb and Cs). The analysis has shown that the Raman coupling coefficient alters by varying the type of the alkali cation. The addition of alkali modifier in the tellurite network leads to the conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. Emphasis has also been given to the lowfrequency modes and particular points related to the low-frequency Raman phenomenology are discussed in view of the experimental findings.

    • IR and Raman spectroscopic studies of sol–gel derived alkaline-earth silicate glasses

      Angelos G Kalampounias

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      IR and Raman spectroscopies have been utilized to study the structure and vibrational modes of sol–gel-derived binary silicate glasses. The present study is motivated by the immense geological significance and focuses on the MO–SiO2 (M = Ca, Mg) binary systems in an effort to unveil the role of the CaO and MgO modifiers when incorporated to the 3D silica structure. Glasses in the composition range 𝑥 = 0, 0.1, 0.2, 0.3 and 0.4 prepared by the sol–gel method were compared with the corresponding glasses formed by appropriate mixing of SiO2 and MO powders through melting and fast cooling. The vibrational spectra of the sol–gel-derived glasses have revealed considerable changes in relative intensities as a function of the MO mole fraction. These changes signify structural modifications on the silica network. The population of the 𝑄3 species was found to increase for both modified silicate systems. The rate of increase is more pronounced in the CaO–SiO2 glasses. The extent of network depolymerization in the porous glass is higher at the same content of alkaline earth oxide compared to the bulk glass. The results are indicative of a more `defective’ nature of the sol–gel glasses compared to the corresponding melt-quenched ones.

    • Low-energy excitations in a low-viscous glass-forming liquid

      Angelos G Kalampounias

      More Details Abstract Fulltext PDF

      Polarized and depolarized low frequency Raman spectra of a liquid mixture, viz. 0.15LiCl–0.85H2O, has been analysed in detail in order to elucidate the temperature and polarization characteristics of quasi-elastic line and Boson peak. The employed fitting procedure shows more convincingly that the Boson peak contribution to the overall low frequency Raman pattern is present even in this low-viscous liquid. The degree of disorder in this liquid is not so high and certain micro-ordering effects may take place due to hydrogen bonding. The results are discussed in the framework of the current phenomenological status of the field.

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