Dielectric Loss Spectrum of Hydrated Vitreous Silica
The dielectric properties of all insulating materials at liquid helium temperatures are sensitive to the presence of certain impurities. The hydroxyl group as an impurity is known to have a very strong influence on the low-temperature dielectric properties of three widely differing materials: the alkali halides, polyethylene, and vitreous silica. In the highly ionic and crystalline alkali halide salts, OH− substitutes for an anion and can reorient under the influence of an electric field down to temperatures less than 1 K [1,2]. In the almost purely covalent and semicrystalline polyethylene, two known dielectric relaxations have each been associated with an OH− group [3–6], and it is possible that impurity OH− groups may also be involved in the low-temperature dielectric behavior of other, more amorphous polymers. In the semiionic, semicovalent compound silica in the vitreous state, water can combine at broken bond defects, forming hydroxyl pairs whose spectrum includes a weakly Raman, but strongly infrared active mode around 30 cm−1 . Hydroxyl content has been shown to weakly influence the low-frequency ambient temperature dielectric constant of vitreous silica , but it strongly influences the low-temperature dielectric loss at 100 kHz  and 1 kHz  and the dielectric constant variation at 11 GHz . In this study, the low-temperature loss angle, δ, was determined over a wide spectral range to further examine the incidence of this characteristic impurity on the dielectric response of a noncrystalline solid.
KeywordsDielectric Relaxation Alkali Halide Wide Spectral Range Loss Angle Vitreous Silica
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