Pressure-Induced Structural Transformations and Electronic Transitions in TeO 2 Glass by Raman Spectroscopy.

TeO glass has been studied by Raman spectroscopy up to the record pressure of 70 GPa. The boson peak frequency ω exhibits a decrease of the ∂ω/∂ slope at 5-6 GPa and saturates above 30 GPa with a practically constant value up to 70 GPa. Experiment and theory indicate that pressures up to 20 GPa induce the transformation of single Te-O-Te bridges to double Te-O-Te bridges, leading to a more compact structure, while Raman activity developing at higher pressures around 580 cm signals the increase of Te coordination from 4- to 6-fold. Natural bond orbital analysis shows that double Te-O-Te bridges favor the s → d transition and promote the increase of Te coordination through dsp hybridization. This transition leads to the formation of TeO octahedra, in strict difference with crystalline TeO at the same pressure range, and to the development of a 3D network that freezes the medium range order.