The effect of nitrogen on viscosity of La-Si-Mg-O-N glasses by compressive creep and dilatometry

Viscosity as a function of temperature and nitrogen content and the glass transition temperature (Tg) were investigated in 20La-60Si-20Mg-O-N glasses with nitrogen contents varying from 0 to 28 eq.% (e/o) using compressive creep and dilatometric experiments. Although Tg obtained from dilatometry were 6–12◦C lower than the lower limit of the transition temperature range from creep, both methods revealed identical and linear dependencies of Tg on N content. The average activation energy was 1184 ± 36 kJ/mol and viscous flow remains the deformation mechanism in all glasses regardless of nitrogen content. Addition of 28 e/o N in oxide glass resulted in an increase of Tg by 94–105◦C and an increase in viscosity of around 5 orders of magnitude. These changes are greater than those reported in similar Al-containing glasses. Linear increase of Tg and compactness of the glass with nitrogen content result from enhanced cross-linking of the glass network.