Properties and crystallization of rare-earth Si-Al-O-N glasses containing mixed trivalent modifiers

Thirteen glasses of the general formula (M1, M2) _9.33Si ₁₄ Al _5.33O _41.5N _5.67 where M1 = La or Nd and M2 = Y or Er have been prepared with M1/(M1+M2) fractions of 1, 0.75, 0.5, 0.25, and 0. Data for molar volume (MV), glass compactness (C), Young's modulus (E), microhardness (H), glass transition temperatures (T _g), and dilatometric softening temperatures (T _d) have been recorded. In addition, temperatures at which crystallization exotherms arise have also been determined as well as crystalline phases present after the glasses had been heat treated to 1300°C in nitrogen. The results clearly demonstrate that glass properties vary linearly with effective cation field strength (CFS) of the combined modifiers (M1, M2), which is calculated from the atomic fractions of M1 and M2 and their associated CFSs. Glass stability in both the La-Y and La-Er systems reaches a maximum at Ml and M2 fractions of 0.5 because of the relative stability of different oxynitride and disilicate phases with changes in ionic radius. Furthermore, La appears to stabilize the α polymorph of yttrium disilicate because of combined La-Y ionic radius effects.