Network Rearrangement in AgI-Doped GeTe4 Glasses
Résumé
The structure of (GeTe4)1-x(AgI)x (x = 0.15 and 0.25) glasses has been investigated by X-ray and neutron diffraction as well as extended X-ray absorption spectroscopy (EXAFS) and Raman spectroscopy. Large-scale structural models have been obtained by fitting simultaneously the exptl. datasets in the framework of the reverse Monte Carlo simulation technique (RMC). Short-range order parameters have been calcd. and compared with that of GeTe4. Doping with AgI affects the structure of the host GeTe4 matrix in two ways. First, while Te is essentially twofold coordinated in GeTe4, its coordination no. is as high as ∼2.9 ± 0.3 for x = 0.25. The change is mainly due to the increased fraction of Te-Te bonds. Second, Ge atoms remain fourfold coordinated but the tetrahedral symmetry is distorted due to the elongation of some Ge-Te bonds. The incorporation of AgI in the GeTe4-based host covalent matrix and the Te coordination increase explains the enhanced thermal stability of (GeTe4)1-x(AgI)x in the supercooled liq.-state hindering the crystn. of Te found in case of GeTe4 glass.