Viscoelastic behavior of alkali and alkaline earth aluminophosphate glasses

ABSTRACT The viscoelastic behavior of alkali and alkaline earth aluminophosphate glasses was studied. The energetic interpretation was based on the Arrhenius behavior of the relaxation modulus. With increasing aluminum content, the activation energy of the relaxation increased in the alkali series but decreased in the alkaline earth series. Dynamic viscoelasticity measurements revealed that the loss modulus, E”(ω), showed a crossover of the relaxation process at the glass transition temperatures. The activation energy below the transition temperature was close to the energies of internal friction or ionic self-diffusion. The energy above the transition temperature corresponded to the dissociation energies of alkali-oxygen or alkaline earth-oxygen single bonds. The different behavior in the energy of the relaxation modulus between alkali and alkaline earth series was due to weak bonds caused by adding alkali ions and the formation of crosslinking by low-coordinate aluminum polyhedra because of the presence of alkaline earth ions.