Fused silica glass, with its large transparency range, low thermal expansion, high resistance to optical damage, high refractive index homogeneity, and ease of finishing has found use as an optical material in applications as varied as space shuttle windows, optical fiber, and deep UV lens elements. Its widespread role as an optical material has been enabled by manufacturing the glass from pure liquid precursor compounds, thereby minimizing impurities, and maximizing refractive index homogeneity. As a technical material, silica glass exhibits anomalous properties with respect to volume as a function of temperature and cooling rate, among other properties; these anomalies remain under investigation to this day. This article describes the manufacture of silica glasses and some of their varied optical applications. Silica is often used in demanding environments, an example of which is its use as a lens material for lithography systems using high photon excimer lasers. Static and dynamic properties of silica glass are discussed here.
Glass‐ceramics in the tungsten‐titanium‐phosphate system were first reported in 1992. The glass‐ceramics exhibited electrical resistivity as low as log(ρ) = −1.8 Ω·cm, which was attributed to an interconnecting network of tungsten suboxide crystals, WO3−x. A new identification of the conducting phase as a phosphate tungsten bronze, (PO4)2(WO3)2m, is reported. High‐temperature x‐ray diffraction and electron microscopy have been used to provide a detailed description of the crystalline phases and their development. As the ceramming temperature was raised, the phase assemblage progressed from cubic tungsten oxide and titanium pyrophosphate to phosphate tungsten bronzes. The m‐values of the bronzes ranged from 2 to 7 depending on composition.
Inelastic neutron scattering was used to study the vibrational dynamics of fused silica and its mixed binary glasses that were doped with either T iO2 or K2O. The energy transfer were measured from zero to 180 meV where the so-called Boson peaks (BP) at low energy and molecular vibrations at high energy are included. Although most of the vibrational spectra at the high energy resemble those reported in earlier literatures, a defect mode like peak is observed for the doped binary systems near 120 meV. At very low temperature, the BP intensity increases rapidly with temperature and then, at higher temperature, the peak intensity decreases. As a result, a maximum is observed in the temperature dependence of the BP intensity. This maximum was shown in all four samples but the pure SiO2 sample shows the highest intensity peak and the lowest temperature for peak position. Broadband energy spectra reveal a shift of intensity from BP to the more localized modes at higher energy. Temperature evolution of BP and its relationship with heat conduction and thermal expansion are discussed.
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