Title: Structural relaxation dynamics of phosphate glasses: The effects of network topology on the glass transition
Abstract: Scanning calorimetry measurements were made on a series of lead ((y)PbO + (1−y)P2O5, 0.3 < y < 0.55) and lead-iron phosphate glasses ((1−xPb(PO3)2 + (x)Fe2O3, 0 < x < 0.25) over a temperature range encompassing the glass transition. The apparent activation energy for structural relaxation, ΔH, determined for each composition from plots of the inverse of the glass transition temperature, Tg vs. the log of the cooling rate, was found to increase with the metal-to-phosphorus ratio. The value of ΔH increased from 44 kcal/mol for P2O5 to 350 kcal/mol for a lead-iron phosphate glass with x = 0.25. The calorimetry data were analyzed using the Adam-Gibbs-Scherer model of the glass transition. This analysis suggests that these glasses undergo a transition from ‘strong’ to the ‘fragile’ glass regime as the metal-to-phosphorus ratio is increased. It is also shown that this transition may be related to the phase transition predicted by He and Thorpe for glasses with underconstrained networks. From scanning calorimetry data on P2O5, B2O3 and a lead-iron phosphate glass (x = 0.15), the temperature dependence of the shear viscosity for each material above Tg was calculated and compared with published viscosity data.
Publication Year: 1990
Publication Date: 1990-04-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 33
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