In situ Raman spectroscopy of pressure-induced changes in LaBGeO5 glass:: hysteresis and plastic deformation

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 LaBGeO5 crystals with the same composition shows that this material has a full elastic behaviour in the same pressure range.