Molecular Dynamics Study of Na‐Si‐O‐N Oxynitride Glasses

Abstract

The structure and properties of Na-Si-0-N oxynitride glasses have been studied by molecular dynamics calculations using a pair potential of the Busing approximation of the Born-Mayer-Huggins type. Nitrogen atoms bonded to one, two, and three silicon atoms coexist in the glass structure. The mean of the number of silicon atoms bonded to a nitrogen atom ranges from 2.4 to 2.1, decreasing with increasing Na,O content from 15 to 30 mol%. It has been assumed that nitrogen atoms bonded to two or fewer silicon atoms are formed when nitrogen atoms substitute for nonbridging atoms. The bond angle LSi-N-Si exhibits a bimodal distribution around 105-135" and 140-170", roughly corresponding to the nitrogen atoms bonded to three and two silicon atoms, respectively. The dependences of the density, the bulk thermal expansion, and the bulk modulus on the nitrogen content are consistent with those observed in real systems.

La–Si–O–N glasses

“…A recent investigation by us of a series of these glasses by solid state NMR 47 indicates accordingly, that for glasses with high X:M ratios, the O and N atoms play similar structural roles, i.e. a predominant fraction of the nitrogen atoms are present as N [1] and N [2] . It may be noted that anomalously high X:M ratios could be a result of the glasses containing significant amounts of isolated X [0] species, i.e.…”

“…Cross-linking of SiX 4 tetrahedra X [1] X [2] X [3] La 5 Concurrently there is an increase in the average connectivity of N and a decrease in the X:M ratios. However, the compositional trends clearly differ between these crystalline compounds and the glasses, which make further comparisons difficult.…”

“…The importance of an oxynitride liquid phase during sintering and densification of Si 3 N 4 based ceramics is well known. This has led to studies on the preparation and property characterization of bulk oxynitride glasses in the systems M-Si-(Al)-O-N (M = Na, [1][2][3][4][5] Li, 3,6,14 Sc,7,15 Ba, 3,8 Mn, 3,9,10 Y, 11,16,17,18 La, 12,17,18 Mg, 8,[13][14][15][16] Ca, 5,9,10,14 Nd, 9,17,18,20,22 Ce, 18,20,21 Sm, 17,20,22 Gd, 17,19,22 Eu, 20 Dy, 17,18,20,22 Ho, <...>…”

Glass-forming region in the Ca–Si–O–N system using CaH2 as Ca source

“…15 Oxynitride glass formation occurs in a number of M-Si-O-N and M-Si-Al-O-N systems, where M is a modifying cation such as one of the alkali metals (Li, Na, K), [16][17][18][19] the alkaline earths (Mg, Ca, Ba) 17,[19][20][21][22] or Y and the rare earth lanthanides. 16,20,[23][24][25][26][27] It has been found that addition of nitrogen in the form of Si 3 N 4 promotes glass formation and that the glassforming regions are relatively small. 28 In the case of Mg, glasses comprising 15-28 e/o of Mg and 10-12 e/o of nitrogen have been obtained.…”

Viscosity of high-nitrogen content Ca–Si–O–N glasses

“…The nitrogen content induces indeed an increase of the atomic packing density. 15,28,29 But, even if high e/o N induce high Poisson's ratio -up to 0.29 for the glass with 42 e/o N -the Poisson's ratio is largely controlled by the cation modifier contents. As the cation modifier content increases, the Poisson ratio increases 15 (almost linearly, from 0.276 for 33.2 e/o Ca to 0.291 for 38.0 e/o Ca).…”