Permanent Ge Coordination Change Induced by Pressure in La2O3–B2O3–GeO2 Glass.

In this study, we report the results of an in situ X-ray absorption spectroscopy investigation of the La₂O₃–B₂O₃–GeO₂ (LBG) glass compressed in a diamond anvil cell until 17 GPa at ambient temperature. A pressure-induced coordination change of germanium from fourfold to sixfold is shown here. The analysis of Ge K-edge X-ray absorption near-edge structure spectra supports a model of mixing of fourfold and sixfold coordinated Ge sites during the compression/decompression cycle. This transformation proves to be irreversible: about 25% of sixfold coordinated Ge still exists at ambient pressure. This phenomenon underlines a polymorphism property of the LBG glass, whose origin lies in the complexity of composition. [ABSTRACT FROM AUTHOR]