Formation and Properties of Ln‐Si‐O‐N Glasses (Ln = Lanthanides or Y)

Homogeneous Y‐Si‐O‐N glasses containing 15 or 20 eq% nitrogen (N) were prepared from compositions with Y/Si ratios in the vicinity of that of the lowest eutectic point on the Y₂O₃–SiO₂ phase diagram. The liquidus on the phase diagram shifted toward lower temperatures by incorporation of N. The density, the elastic moduli, and the glass transition temperature of the Y‐Si‐O‐N glasses increased with incorporation of N. This is due to the closer packing of atoms in the glasses by the substitution of N, which is in three‐fold coordination with Si, for O which is in two‐fold coordination, and the stronger covalent nature of the Si–N bond compared with the Si–O bond. The coefficient of thermal expansion of the Y‐Si‐O‐N glasses increased with increasing Y content, because the discontinuity of the glass network developed with increasing nonbridging anions by the introduction of Y. In contrast, the glass transition temperature and the elastic moduli increased with Y content due to the high coordination of Y for O, and the relatively high cationic field strength of Y. Furthermore, the effect of cationic field strength on properties of Ln‐Si‐O‐N glasses (Ln = lanthanides or Y) is discussed.