In situRaman spectroscopy of pressure-induced changes in LaBGeO₅glass: hysteresis and plastic deformation

Abstract

In situ micro-Raman spectroscopy was performed on lanthanum borogermanate (LBG) glasses, compressed in a diamond anvil cell at ambient temperature. Up to 5.6 GPa the structural changes are reversible, whereas experiments performed at 10 GPa and higher are characterized by hysteresis loops. A noticeable change of evolution of the main Raman band at 800 cm(-1) has been evidenced around 8 GPa. Indeed, at such a pressure, this Raman band is shifted in the opposite direction while the pressure is still increasing. This change of slopes may be the sign of a pressure-induced coordination number change. Upon decompression the Raman shift of this band follows a different path from the one during compression. When the sample is returned to ambient pressure, it shows a shifted and lightly modified Raman spectrum, suggesting that a new amorphous phase for LBG glass is reached under high pressure and still exists at atmospheric pressure. However, a comparison with LaBGeO(5) crystals with the same composition shows that this material has a full elastic behaviour in the same pressure range.

High pressure elastic and plastic deformations of silica: In situ diamond anvil cell Raman experiments

“…In situ Raman experiments within a diamond anvil cell lead to a better understanding of polyamorphism [24,25] through the polyamorphic transition of silica. The mode Grü neisen parameters of both low density amorphous silica in the reversible domain, and high density amorphous silica above the irreversible transition were determined.…”

Polyamorphism: Path to new high density glasses at ambient conditions

“…We studied a ternary 25La 2 O 3 -25B 2 O 3 -50GeO 2 (LBG) glass under compression/decompression at different peak pressures. Detailed results will be published elsewhere [25], but in this paper we will focus on the Raman spectra of the main band at 800 cm À1 which is attributed to the stretching of both B-O and Ge-O bands in BO 4 and GeO 4 tetrahedra [26]. From IR spectra Sigaev et al [27] deduced that LBG glass contains both BO 4 and BO 3 units whereas Germanium is only four-fold coordinated.…”

“…The shift of the 800 cm À1 Raman band as function of the applied pressure in a Diamond Anvil Cell is shown in (Fig. 3) in quasi-hydrostatic conditions [25] using methanol as liquid for pressure transmis- sion. For compression below 7.5 GPa the line shift is linear and corresponds to an elastic response.…”

Comprehensive study of crystallization and phase formation in (La,Gd)BGeO5 glass

“…According to Ref. 25, the Raman band observed around 800-900 cm -1 , 500-600 cm -1 , and 300-400 cm -1 are attributed to the antisymmetric stretching of BO4 and GeO4 tetrahedra, the bending vibrations of T-O-T (T: B or Ge) bonds, and the La-O vibration, respectively. This indicates that the structural units of (La,Gd)BGeO5 glasses is very close to that of stillwelite-type …”