SEMINARIO: Glass relaxation probed by ionic conductivity

Ana Cándida Martins Rodrigues, LaMaV, Universidad de San Carlos, Brasil.

Lunes 2 de octubre a las 12h, salón de actos del ICV


Structural relaxation of glass is an intriguing phenomenon from a scientific point of view, which also bears important technological applications, for example in annealing processes, or chemical straightening by ion exchange. Glass relaxation has been experimentally demonstrated by measuring the effect of isothermal aging on different properties, such as density, refractive index, or viscosity. In this talk, we will present results from the variation of isothermal ionic conductivity in silver phosphate (AgPO3) and lithium disilicate (Li2Si2O5) glasses. In both cases, the relaxation phenomenon was well described by the Kohlrausch stretched exponential equation. For the same study temperature (Ts), AgPO3 shows faster relaxation when measured above the initial fictive temperature (Tf), i.e., when the aging experiment is conducted at TsTf. Also, the Kohlrausch exponent is lower when Tf >Ts than in the opposite case. For the Li2Si2O5 glass, the relaxation process was also probed by refractive index. We will show that the Kohlrausch exponent decreases, and the characteristic relaxation time increases when the difference Tf-Ts increases for both properties. Also, the characteristic relaxation time and the stretching exponent resulting from conductivity measurements are shorter than those obtained from the refractive index. This means that, although the very small structural rearrangements induced by isothermal aging are always the same, they have greater influence on ionic conductivity than in refractive index.