Dynamics of mixed alkali metaphosphate glasses and liquids

Dynamic mechanical, stress relaxation, and oscillatory shear experiments we re performed to examine relaxation processes in a series of mixed alkali me taphosphate glasses and liquids. At temperatures less than the glass transi tion temperature, T-g, dynamic processes are dominated by hopping of alkali ions and local network relaxations that accommodate the motion of the cati ons. The average relaxation times associated with these dynamic processes w ere sensitive to the molar ratio of alkali ions in the glass. For T > T-g, viscous relaxations were controlled primarily by the translational dynamics of P-O-P chains. These longer time viscous relaxation processes also appea r to be affected by the dynamics of the alkali ions. The high frequency ela stic modulus, G(0), the fragility of the liquid, the heat capacity changes at T-g, Delta c(p)(T-g), and the breadth of the distribution of relaxation times, W, were all dependent on the molar ratio of the alkali oxides. Corre lations between the fragility, W and Delta c(p)(T-g), which were found to d escribe the effects of single alkali oxide modified glasses, failed to desc ribe related properties in these mixed alkali metaphosphates. (C) 1999 Publ ished by Elsevier Science B.V. All rights reserved.