Abstract
A high-temperature Raman study of alloys is reported up to a temperature close to the melting point, including both Ge-rich and S-rich glasses, as well as the compound glass The variation in the Raman spectra indicates that above certain temperatures gradually crystallizes, first to the three-dimensional (3D) phase and then to the layered two-dimensional (2D) phase, with the latter being maintained up to melting point and upon subsequent cooling to room temperature. There is evidence that the controversial companion band of evolves to a counterpart band of the 2D crystalline phase, implying that this band is due to symmetric stretch vibrations of S atoms in bridges of edge-sharing tetrahedra, in agreement with a previous prediction. Similar two step irreversible crystallization to the 3D and 2D phases of have been observed above for the moderately rich in Ge or in S glasses, but at lower thresholds of crystallization temperature. In the strongly enriched in S glass, though, crystallization takes place only to the 3D phase of a process which is reversible after cooling the alloy to room temperature, i.e., the material returns to its initial amorphous phase. This reversible crystallization is explained in terms of the three-dimensional network of S-rich glasses which evolves only to the respective 3D crystalline phase lattice at high temperatures. It is pointed out that all glasses studied undergo a first-step transition to the 3D crystalline phase, which shows that the network of these glasses is, by large, three dimensional.
- Received 27 December 2000
DOI:https://doi.org/10.1103/PhysRevB.64.125210
©2001 American Physical Society