The effects of very long physical ageing up to 13 yr on vitreous chalcogenide glasses have been investigated for GexSe1−x glasses, x = 4 , 8 and 12 at%, by means of calorimetric methods. We show that the rejuvenation of such very old materials can be performed without any problem. More importantly, we find that a long ageing leads to a phase separation process. This could explain why the configurational (or conformal entropy) does not apparently reach its equilibrium value as already observed by Gomez Ribelles et al. (Macromolecules 28 (1995) 5867) on other polymeric materials.

Very long physical ageing in inorganic polymers exemplified by the GexSe1−x vitreous system

About the coordination number of indium in GexSe1 − x − y Iny glasses

This paper shows that, using an adapted protocol, measurements of the glass-transition-temperature displacements lead to a quantification of relaxation processes which occur during ageing of glassy chalcogenides. The application of this method to a-Se1-x Gex alloys shows that the behaviour is different in two ranges of composition (x=0·04 then x = 0–0·04–0·12), which is not evident from the phase diagram. The results are discussed in terms of molecular movements and network dimensionality.

Relaxation processes and structural models in glassy chalcogenide materials: Application to the Se,-xGex alloys

Differential thermal analysis results on BixSe1−x alloys (0 < x < 0.27) show that Bi atoms may be either three- or four-fold coordinated. Further measurements of dark conductivity show a sharp decrease of both resistivity and activation energy of conductivity between 1 and 2 at% of Bi. Comparison with other Bi-based alloys and chalcogenide alloys without Bi leads to the conclusion that Bi plays a particular role when allied with chalcogen materials. Considerations on the metallic character and electronegativity of Bi enable us to confirm that in Bi-based chalcogen alloys the Bi defects are four-fold coordinated and positively charged.

J.P. Larmagnac

Papers

Structural relaxation below Tg of amorphous germanium-selenium alloys