Composition-structure-property relationships for Si-Al-O-N glasses containing mixed modifiers

This paper examines composition - property relationships for La-Y, La-Er, Nd-Y and Mg-Y mixed modified Si-Al-O-N glasses. For the La-Y, La-Er and Nd-Y glasses, the following properties: molar volume (MV), glass compactness (C), Young's modulus (E), microhardness (Hv), glass transition onset (Tg_on.) and midpoint (Tg_mid.) temperatures, dilatometric softening temperature (T_DS) and coefficient of thermal expansion (CTE), were all linearly related to the effective cation field strength of the mixed modifiers. For the mixed Mg-Y glasses no such correlations existed due to the fact that the valencies (Mg²⁺ and Y³⁺) were different. In this case, glass transition temperatures (using dilatometry) and T_DS values were linearly related to the average number of (Si,Al)(O,N)₄ tetrahedra coordinated to the modifiers. A further observation for Mg-Y-SiAlON glasses was that the effects of N substitution for oxygen were exactly the same for each mixed modifier composition, indicating that property changes induced by either changing nitrogen or modifier contents are totally independent. Accordingly, when choosing glass compositions, cation and anion contents must be varied independently if clear conclusions are to be drawn as to the effects of nitrogen substitution and modifier changes.