Relationship between composition and glass transition temperature in Na2O-M2O3-SiO2 glasses (M=Ga,In,Sc,Y,La)

To compare the role in the glass structure of Sc3+, Y3+, La3+, Ga3+ and In3+ ions with that of Al3+, Mg2+, and Ca2+ ions, the effect on glass transition temperature, Tg, of a progressive substitution of such a cation for Na+ or Si4+ ions (M3+ → 3Na+, M2+→ 2Na+, 4M3+→ 3 Si4+, 2M2+→Si4+) in sodium disilicate glass has been investigated. Sc3+, Y3+, La3+, and In3+ ions behave like Ca2+ ions, wherea the behaviour of Ga3+ ions is more like that of Al3+ and Mg2+ ions. Moreover Tg values have been indirectly related to the degree of cross-linking and of tighness of packing