Polyamorphism of GeO₂ Glass at High Pressure

Abstract

Polyamorphism of network‐forming SiO2 and GeO2 glasses at high pressures is a puzzling topic in condensed matter physics and has long‐standing interest because of their important geophysical and geochemical implications. Molecular dynamics simulations suggest that there are multiple amorphous–amorphous transitions at high pressure with parallel high‐pressure crystalline counterparts. However, it is very challenging to experimentally distinguish the pressure‐induced subtle change in the amorphous state at high pressure. Recently, a high‐pressure X‐ray absorption fine structure (HP‐XAFS) method is developed using a diamond anvil cell (DAC) to measure the local structure of polyamorphs in GeO2 glass at high pressure. The results indicate that GeO2 glass shows multiple polyamorphs at high pressure with a local structure, in general, similar to their high‐pressure crystalline states in the first coordination shell but with increasing differences in the distant coordination shells. Three pressure‐induced polyamorphs in GeO2 glass are recognized unambiguously at high pressure, i.e., α‐quartz‐like, rutile‐like, and pyrite‐like amorphous structures. The obtained knowledge of these polyamorphs is helpful for understanding the mechanisms of network compression behavior and physical properties of SiO2 and GeO2 glasses and melts under extreme conditions.

Pressure-Driven Changes in the Electronic Bonding Environment of GeO2 Glass above Megabar Pressures

“…Such similarities indicate that the CN O of GeO 2 glass above 55 to 148 GPa is expected to be similar to that of the pyrite-type phase. Although there is no experimental result for compressed GeO 2 glass beyond 101 GPa, earlier elastic X-ray studies up to ∼90 GPa also suggested the formation of pyrite-like amorphous structures. ,,, As our IXS results distinguish the PDOS features for [3] O and [3+1] O topologies, and the current IXS results of GeO 2 glass show characteristic pattern for [3+1] O topology toward and beyond Mbar, the oxygen environments in amorphous structures may not be fully described with [3] O only. Although there is no experimental study on oxygen configurations in GeO 2 glass at high pressures, particularly above 100 GPa, information regarding CN O can be obtained from CN Ge ; pressure-induced decrease in the O–Ge–O angle in the glass above 50 GPa from simulations indicates an increase in average CN Ge > 6, consistent with experimental results .…”

“…16 X-ray absorption spectroscopy (XAS) and molecular dynamics (MD) studies have reported a gradual transformation of [6] Ge to [7] Ge up to 100 GPa. 20,26,30,31 In contrast, a recent X-ray-emission study indicated that CN Ge remains at 6 up to ∼101 GPa. 32 Such a discrepancy may be due in part to the structural complexity of amorphous oxides under extreme compression.…”

“…The reported transition pressure for [7] Ge in GeO 2 glass is also much lower than that for [7] Si in SiO 2 glass at ∼100 GPa; ,,− an elastic X-ray-scattering study demonstrated an increase in CN Ge beyond ∼6 above ∼50 GPa, reaching ∼7.4 at ∼90 GPa . X-ray absorption spectroscopy (XAS) and molecular dynamics (MD) studies have reported a gradual transformation of [6] Ge to [7] Ge up to 100 GPa. ,,, In contrast, a recent X-ray-emission study indicated that CN Ge remains at 6 up to ∼101 GPa . Such a discrepancy may be due in part to the structural complexity of amorphous oxides under extreme compression.…”

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

“…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]. Mainly based on the SRO, pressure-induced multiple polyamorphs in GeO 2 glass have been recognized, e.g.…”

Effects of Ag2O Nanosheets on the Structural, Optical, and Dielectric Properties of GeO2 Stacked Layers

“…Studies which targeted the exploring the polymorphic phases of GeO 2 -SiO 2 glasses indicated the existence of three polymorphic phases, named, α-quartz-like, rutile-like, and pyrite-like amorphous structures. [11] The occurrences of these pressure-induced polymorphic structures in the GeO 2 -SiO 2 system are still ambiguous and of unknown reasons. However, it is mentioned that the accumulation of positively charged ions around oxygen atoms in SiO 2 is more pronounced than the accumulation around oxygen atoms in GeO 2 [12] for cations having the same ionic radius.…”