Complex refractive index of silica, silicate, borosilicate, and boroaluminosilicate glasses – Analysis of glass network vibration modes with specular-reflection IR spectroscopy

A novel mathematical algorithm was developed to calculate refractive index (n + ik) from specular reflectance infrared (SR-IR) spectra in the strongly-absorbing glass network vibration region. The method is named as two-angle SR-IR (TASR-IR), since it is based on the Fresnel equations of specular reflectance at two incidence angles (10° and 45°). The results obtained from TASR-IR are comparable with the values obtained from spectroscopic ellipsometry. The TASR-IR method allows one to obtain the peak positions and intensities of fundamental network vibration modes of glass from the imaginary component (k) of complex refractive index without convolutions from the dispersion effect due to chains in the real component (n) of refractive index. The TASR-IR method is applied to silica, silicate, borosilicate, and boroaluminosilicate glasses; tentative peak assignments of glass network vibrations are proposed. The origin and concept of peaks in the vibrational spectra of glasses is discussed.