Structure and rheological properties of the RE-Si-Mg-O-N (RE = Sc, Y, La, Nd, Sm, Gd, Yb and Lu) glasses

Structure, viscosity, glass transition temperature, Littleton temperature and elastic moduli were investigated by MAS-NMR spectroscopy, compressive creep, dilatometry and ultrasound velocity experiments, in order to reveal the effects of rare earth elements and nitrogen on the behavior of RE-Si-Mg-O-N glasses (RE = Sc, Y, La, Nd, Sm, Gd, Yb and L) with different nitrogen contents. NMR showed that nitrogen modifies the glass structure depending on RE type via increasing content of SiO3N(+Q(1)) units at the expense of Q(2) units and Lu seems to be more effective in their formation than La. Despite that, the effects of rare-earth modifiers and nitrogen as network former are independent, additive and a synergy effect was not observed. Approximately linear dependencies of most properties on molar volume (and ionic radii) suggest that glass network is tightened proportionally to ionic radius of corresponding modifier and cross-linking is proportional to nitrogen content. However, the mechanism involved in lanthanide effect is different from that of Sc and Y additives, although they result in properties similar to those of Lu-containing glasses. Irregularities found for Yb and Sm additives at elevated temperatures may be related to the change of valence state. (C) 2004 Published by Elsevier B.V.