A high-temperature Raman spectroscopic investigation of the potassium tetrasilicate in glassy, supercooled, and liquid states

Raman spectra of K 2 Si 4 O 9 were measured over a broad temperature range including the glassy, supercooled, and molten states in an effort to follow the structural changes caused by temperature variation. Potassium tetrasilicate glass has been prepared using a containerless method and a C O 2 laser for heating and melting the samples and thus avoiding contamination induced by the walls of the crucibles. Systematic Raman intensity measurements caused by temperature variation have been performed in order to elucidate the induced structural changes in the high-frequency stretching and in the three- and four-membered ring breathing vibration regions. The high-frequency symmetric stretching vibrations of the nonbridging Si-O bond are associated to the presence of two distinct types of tetrahedral units with terminal oxygen atoms. The low-frequency Raman spectra reveal the, well resolved, presence of the boson peak at temperatures above the melting point. The temperature dependence of the boson peak energy has also been determined and compared with that of the sound velocities of potassium tetrasilicate. The results are discussed in the context of recent experimental and theoretical works.