The structure of lithium silicate melts revealed by high-temperature Raman spectroscopy

The structure of lithium silicate glasses and melts was studied by in situ Raman spectroscopy at temperatures from 293 to 1423 K. The composition range of the studied melts varied from 33 to 60 mol. % of lithium oxide. A curve-fitting procedure was applied for data analysis taking into account the second coordination sphere of silica atoms. To obtain a correct interpretation of all bands in the Raman spectra, additional types of structural unit, carrying the information about the neighbors, were introduced into a description of glasses and melts structure. It was shown that structural units possessing two non-bridging oxygen atoms are typical of almost all the melts of the lithium silicate system, with their content in the system being higher than that in the melts of the sodium silicate system of the same composition. Such an unusual behavior of these melts under increased temperature as well as the elevated concentration of species with two non-bridging oxygen atoms may significantly affect the viscosity value of lithium silicate melts.