First Principles Study on Phonon Energy in SiO_2 Glass with the Incorporation of Al_2O_3

摘要

The aim of this study is to investigate the incorporation of Al_2O_3 in SiO_2 glass with emphasis on reducing the phonon energy in the SiO_2 matrix. Pure SiO_2 glass has very high phonon energy of about 1100 cm~(-1), while Al_2O_3 has 780 cm~(-1). By incorporating Al_2O_3 into SiO_2 glass structure, the relative phonon energy of the SiO_2 matrix is expected to reduce. However, the composition of Al_2O_3 has been limited to a desired amount so as not to perturb other properties of SiO_2, such as optical absorption. The Infrared (IR) spectra for a portion of SiO_2 glass with the Al dopants were simulated at different molar ratio of the composition using Molecular Mechanic and Density Functional Theory (DFT). The Al_2O_3-SiO_2 structures show a significant change in the simulated IR spectra compared to pure SiO_2 glass. The Al_2O_3-SiO_2 structures in the present work were constructed by replacing some Si atoms with Al atoms in the host lattice of SiO_2 glass. In addition, some O atoms were removed from SiO_2 host lattice to get the correct chemical balance. With increasing of Al_2O_3 content, the relative intensity of ～1100 cm~(-1) band associated with the asymmetrical Si-O-Si stretching vibrations is decreased. The decreasing in relative intensity of the IR spectra demonstrates that Al dopants are forming - [Al-O-Si] - linkages in the structure.