In situstudy of amorphization and changes in coordination inSi2N2Oat high pressure

Abstract

Silicon oxynitride was investigated by x-ray powder diffraction and infrared absorption spectroscopy at pressures close to 50 GPa. Gradual amorphization was found to occur above 25 GPa. This process is associated with the disappearance of the strong B 1 Si-O stretching mode of the SiN 3 O tetrahedra at close to 1130 cm −1 and the appearance of additional modes at lower frequencies with respect to the Si-O stretching modes. This is evidence of an increase in the coordination of Si. Whereas the silicon atom appears to revert to a fourfold coordination below 7 GPa, the material remains amorphous.

Si−Ge-based Oxynitrides: From Molecules to Solids

“…Our calculated value for the bulk modulus of Si 2 N 2 O, 129 GPa, is quite close to the value 130 GPa reported recently by Kroll 19 using an almost identical and high-quality computational procedure. Both of these values closely match the experimental value of 127 GPa obtained via neutron diffraction at low-pressures (P < 3 GPa), and somewhat overestimate the value of 115 GPa recently obtained by Haines et al 22 using an extended compression range (P < 50 GPa). The latter authors also report an anomalously small value for the bulk modulus derivative B 0 0 ∼ 1.2, which they ascribe to the possible effect of non-hydrostatic stress in their experiments.…”

“…A similar calculation for the Ge analogue using Ge 3 N 4 (B 0 ∼160 GPa) and GeO 2 (B 0 ∼30 GPa) yields an estimate of ∼95 GPa for B 0 [Ge 2 N 2 O]. Recent high-pressure hydrostatic compression experiments on Si 2 N 2 O corroborate this expectation and report a bulk modulus near 127 GPa, 22 while previous first-principles calculations based on LDA and/or GGA have produced values ranging from 130 to 180 GPa. In view of this latter variability in theoretical values for Si 2 N 2 O, and since experimental compression data for Ge 2 N 2 O is limited (see below), it is of considerable interest to pursue a systematic study of the compression behavior Si-Ge-O-N compounds.…”

“…Our calculated structural data is also quite consistent with values obtained in earlier theoretical studies. 22,25,27 The structural parameters of the hypothetical R-SiGeN 2 O and β-SiGeN 2 O polytypes are predicted to be virtually identical. We note that the molar volume of the β-polymorph is found to be slightly lower than that of its R-counterpart, which may be associated with the slightly different packing obtained upon layering the SiN 3 O and GeN 2 O polyhedral units.…”

The role of oxygen in shockwave-synthesized γ-Si3N4 material

“…Several high pressure studies using crystalline Si 2 N 2 O as a starting material have been published. Compression in a diamond anvil cell at room temperature led to gradual amorphization above 25 GPa [7]. A similar trend was observed in a shock wave study, where the material was subjected to dynamic pressures between 28 and 64 GPa [8].…”

First-principle investigation on the thermodynamics of X 2 N 2 O ( X = C, Si, Ge) compounds

“…Srinivasa and Cariz, [5] and Srinivasa et al [15] determined the lattice parameters, bond properties of Si 2 N 2 O and Ge 2 N 2 O at pressure P = 2.3 and 2.54 GPa by the time-of-flight neutron diffraction. Haines and Santoro [16] found the complete amorphization of Si 2 N 2 O occurs above P = 41 GPa by the x-ray power diffraction and the infrared absorption. Although the electronic properties and thermodynamic properties of some ceramics were reported, [17][18][19][20][21][22] as a widely used refractory, however, few experimental and theoretical data about the thermodynamic properties of X 2 N 2 O (X = C, Si, Ge) compounds have been reported so far.…”