1 8 A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 2 in the glass network for silicate tetrahedra (SiO4), however the AlO4 - tetrahedra has a negative charge that achieves charge compensation though alkali or alkaline earth cations, e.g., CaO. Adding both CaO and Al2O3 creates a neutral charge glass system. CaO ultimately results in depolymerization of the glass network through formation of nonbridging oxygen (NBO) atoms, while also producing over-coordinated or five-fold coordinated aluminum (AlV) and triclustered oxygen (TBO). It is important to note that compositions along the tectosilicate join should contain minimal or near zero NBO atoms. The refractive index of pristine and high repetition rate laser irradiated tectosilicate glasses was studied to densification or rarefaction of CAS, CaO-Al2O3-SiO2, glasses[25]. These are CAS glasses along the tectosilicate, xCaO·xAl2O3·(100-2x)SiO2, where the addition of both calcium and aluminum creates a charge neutral system (R = CaO/Al2O3 = 1). SiO2, Al2O3, and CaO are termed network former, intermediate network former, and network modifier, respectively. CAS glasses are used for display glass applications due to superior mechanical and physical properties, specifically based on the role aluminum plays in the glass network. Aluminum is traditionally four-coordinated (AlIV) along the tectosilicate join and these Al species are in the form of tetrahedrally coordinated aluminum (AlO4 -). Aluminum tetrahedra substitute STUDYING CAS GLASSES FOR DISPLAY APPLICATIONS The authors have reported highlighted refractive index changes from 0.3-0.8 THz of SLS and ABS glasses that had been irradiated using a high repetition rate femtosecond laser system[24]. SLS and ABS measured reduced and increased refractive index consistently throughout the THz region (Fig. 4). Refractive index changes at THz frequencies, obtained using THz-TDS, reflect densification or rarefaction of the glass network due to femtosecond laser exposure. In addition, the researchers correlated changes in the refractive index, at THz frequencies from THz-TDS, Fig. 3 — Refractive index at 0.5 THz of Nd2Ti2O7 and CaZrTi2O7 as a function of temperature from 25-200°C. Fig. 2 — Refractive index as a function of frequency for titanate materials for nuclear waste applications.
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