Domain Structural Transition and Structural Heterogeneity in GeO₂ Glass Under Densification

Abstract

The domain structural transition and structural heterogeneity (SH) in GeO2 glass at 300 K and pressures up to 100 GPa are studied by means of molecular dynamics (MD) simulation. The results demonstrate that the structure of GeO2 glass comprises domain D4, domain D5, or domain D6, which depends strongly on pressure, where domain Dx (x = 4, 5, or 6) is a cluster of connected GeO x units, in which all Ge atoms possess the same coordination number of x. In the range of 9–18 GPa, GeO2 glass undergoes a structural transformation from domain D4 to domain D6 via domain D5. Under densification, structural evolution occurs along with the O xx → O xy atom variation, which comprises the processes of both merging and splitting of domain Dx and the exchange of domain-boundary (DB) atoms. The densification leads to a decrease of the Voronoi polygon (VP) volume of atoms. We found that the coexistence of separate domain structures is the origin of spatial SH in GeO2 glass. Pressure-dependent structural heterogeneity in GeO2 glass is also discussed in detail.

Local structural investigation of non-crystalline materials at high pressure: the case of GeO2 glass

“…The full [5] Ge species have been considered as a precursor for the subsequent octahedral transition [11]. The result of up to 58% [5] Ge species at 15 GPa (figure 5(d)) confirms this precursor and is in agreement with other recent AIMD [32] and classical molecular dynamics (MD) [29] simulations. The conflicting results for or against the existence of [5] Ge coordination may be due to the different sensitivity to the local structure by different experimental probes of xray/ND (e.g.…”

“…An intermediate state of GeO 2 glass has been identified at 6-9 GPa by XRD, Raman and density measurements [12,34]. The presence of significant amount of [5] Ge units (figures 5(b) and (d)), which coexist with other [4] Ge and [6] Ge units as the glass undergoes a transition from the tetrahedral to the octahedral state, provides a microscopic basis for the understanding of glass behavior at high pressure [11,12,29,32]. Further experimental and theoretical work on the pressureinduced coordination changes at ultrahigh pressure in GeO 2 glass will is required and will be reported elsewhere.…”

“…GeO 2 glass is of particular interest because the local structure of Ge atoms at high pressure can be determined by x-ray absorption fine structure (XAFS) technique in diamond anvil cell (DAC). The pressure-induced local structural changes of GeO 2 glass have been extensively studied using x-ray-absorption spectroscopy [7][8][9][10], x-ray diffraction (XRD) [11][12][13][14][15][16], neutron diffraction (ND) [17][18][19][20][21], inelastic x-ray scattering [22,23], x-ray Raman scattering at the oxygen K-edge [24,25], x-ray emission spectroscopy [26], and a number of theoretical studies such as classical [27][28][29] and first-principles molecular dynamics simulations [30][31][32]. Important structural and spectroscopic details on the local short-range order (SRO) and the intermediate-range order (IRO) of GeO 2 glass under compression have been successfully revealed [3,6,18,33].…”

The Structural Characteristics and Phase Transformation in Al2O3 Glass. A Molecular Dynamics Simulation

“…We take fAl=0.34493×10 -14 m, fO= 0.58053×10 -14 m as used in ref. [5,13]. Figure 1 shows that the calculated GN(r) (at ambient pressure) is in good agreement with the experimental data [4].…”

“…Therefore, in this work, we focus on studying the structural characteristics and indicating the existence of two phases with high-and low-density of Al2O3 glass. The properties of Al2O3 can be inferred from simulated models by the bond length, bond-angle, coordination number, and cluster function [13,14].…”