Abstract
Abstract A linear relationship exists in oxide glasses between glass transition temperature (Tg) and quadrupole splitting (Δ) of Fe3+ . DTA and Mössbauer measurements of silicate and tungstate glasses yielded large slopes of 680 and 260 °C/(mm s-1) from the slope of the straight lines when Fe3+ occupied, as network former (NWF), distorted tetrahedral Si4+ and distorted octahedral W6+ sites, respectively. This linear relationship, named a ‘‘Tg - Δ rule’’, suggests that Tg is in proportion to the distortion of NWF-oxygen polyhedra and a higher activation energy is required for the fragments of glass to have a cooperative movement in the supercooled liquid state. The ‘‘Tg - Δ rule’’ was also valid in the case of potassium silicate glasses heat treated at the temperature close to Tg, indicating a distortion of SiO4 and FeO4 tetrahedra. Substitution of Fe3+ for individual NWF in silicate and tungstate glasses was confirmed from the Fourier transform infrared (FT-IR) spectra because only the absorption bands due to Si and W were respectively observed without the bands due to Fe.
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