A novel glass-synthesis route involving the reaction of electropositive elements in their metallic state with Si 3 N 4 and SiO 2 in N 2 atmosphere is presented. New silicate glass compositions have been obtained in this way with nitrogen contents higher than 70 e/o (N content in equivalents; e = [N]/ 3[N] + 2 [O], where [N] and [O] are the atomic concentrations of N and O, respectively), compared to previously reported oxynitride glasses typically that have concentrations below 30 e/o. [1][2][3][4][5][6][7][8] The new glasses constitute a significant extension of silicate glass compositions and also show high chemical flexibility. Samples have been prepared with high concentrations of alkaline-earth and rare-earth elements such as Ca, Sr, Ba, La, Pr, and Sm (higher than 50 % cations; hereafter cation %). The glasses can easily be obtained in macroscopic quantities. They demonstrate high refractive indices, up to 2.30, and Vickers hardness values up to 13.3 GPa, which are the highest values reported for any silicate glass. The technological use of silicate glasses constitutes an important part of modern civilization. They have, however, inherent compositional limitations that inhibit further improvements of their various properties, e.g., the attainable amount of network-modifier elements (Na, Ca, Ba, etc.) is rather small and restricted by the Si/O ratio. One way of increasing the amount of electropositive elements in silicates is to substitute oxygen with nitrogen. Such oxonitridosilicates do not occur in nature and investigations of them originated from efforts to prepare new Si 3 N 4 -based ceramic materials with improved mechanical properties, i.e. sialons.[1±4] Sialon and oxonitridosilicate crystal chemistries are similar to that of oxosilicates, but differ in that nitrogen, unlike oxygen, may bond to three or even four Si atoms, [5,6] resulting in higher connectivity and condensation of the networks. Due to the high formal charge of ±3 for nitrogen, more or higher valent cations can be incorporated in the phases for a given network connectivity. Studies of oxynitride glasses over the last few decades [7±14] have demonstrated that an increase in nitrogen content increases the glass-transition temperature, T g , viscosity, elastic modulus, hardness, and refractive index. [6,15±17] This can be partly attributed to a higher crosslinking of the Si(Al) network. Increased nitrogen contents have been desired by both academic and industrial sectors to improve physical properties, but efforts so far have had limited success. The glass modifiers have mainly been added as oxides, [1±7] typically leading to nitrogen contents less than 30 e/o. In the synthesis method presented here, rare-earth and/or alkaline-earth elements are introduced instead as metals. Precursor mixtures of electropositive elements, Si 3 N 4 , and SiO 2 , are ground in an oxygen-and water-free atmosphere and then heat treated, using graphite or radiofrequency furnaces, at 1500±1800 C in N 2 atmosphere, which serves as the nitridation source f...

Six oxide and oxynitride glasses were synthesized in the Y-Mg-Si-Al-O-N, Nd-Mg-Si-Al-O-N and La-MgSi-Al-O-N systems. As already known, nitrogen introduction increases the T g , packing factor and mechanical properties of the glasses. Cationic substitution also has an influence on the glasses' behavior, particularly in terms of sensitivity to indentation load/size effect (ISE). The structure of the yttrium-containing glasses was investigated by mean of 27 Al and 29

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