High Temperature Raman Spectroscopy of Glasses and Melts

Raman scattering spectroscopic techniques are presented with emphasis on the high temperature spectra measurements of inorganic materials including molten and glassy metal halides and oxides. Next the basic experimental design for levitation and CO₂   laser melting is described in relation to a) the preparation of oxide glasses and b) the in-situ Raman measurements of high temperature levitated glasses and melts. The role of blackbody radiation, and the important role of materials’ purity on the quality of the spectra is discussed. The Raman spectra at temperatures up to 2300K   of selected   oxide and halide glasses and melts  (e.g.: SiO₂ , ZnX₂) are presented  and discussed in terms of their structural peculiarities.  Finally container-less levitation techniques and CO₂-laser heating were used to prepare a series of  alkaline earth silicate glasses along the compositional join (1-X) MO-XSiO₂ with M=Mg, Ca and  X ranging between 0.60 and 0.27; thus reaching compositions beyond the orthosilicate limit (X=0.33). Polarized and depolarized Raman spectra measured at ambient conditions for all these glasses show systematic and smooth band intensity changes with composition shows the presence  a) of bridging oxygens  in all glasses studied with silica mole fractions down to X=0.33 and b) of free oxygen at all compositions.  Beyond the X=0.33 limit, the connectivity between the SiO₄ tetrahedra decreases drastically and the corresponding glass structures are characterized by isolated negatively charged “tetrahedral” SiO₄^4- and O^2-  anions with M²⁺(M =Mg,Ca) as counter cations, held together by pure Coulombic (ionic) interactions [1,2]

References:

1. N.K. Nasikas, A. Chrissanthopoulos, N. Bouropoulos, S. Sen, G.N. Papatheodorou, Chem. Mater. 23 (2011) 3692.

2.  A. Retsinas, A.G. Kalampounias, G.N. Papatheodorou, J. Non Cryst. Solids 383 (2014) 38.