Chalcogenide Letters Vol. 10, No. 11, November 2013, p. 435 - 441 AGEING EFFECTS IN Ag-Ge-Se BULK GLASSES  P. P. GIMENA a , C. J. M.GARRIDO a , S. DELIA b , M. A URENA a , FONTANA M. a , A. BIBIANA a* a INTECIN, Facultad de Ingeniería, Universidad de Buenos Aires -CONICET, Paseo Colón 850 Buenos Aires, Argentina, b CEQUINOR, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 47 & 115, La Plata, Argentina, e-mail: soria@quimica.unlp.edu.ar Glasses of composition Ag x (Ge 0.25 Se 0.75 ) 100-x and Ag x (Ge 0.25 Se 0.75 ) 100-x doped with 0.5 at% of 57 Fe were analyzed with the aim to evaluate if their structure evidences any effect of ageing, for thousands of hours at room temperature and/or hundreds of hours for sub-Tg thermal treatments. Strong ageing effects were observed by means of Mössbauer spectroscopywhereas Raman spectroscopy contributed to identify the origin of these effects. (Received October 8, 2013; Accepted November 11, 2013) 1. Introduction As well as other chalcogenide glasses, Ag-Ge-Se glasses have attracted much interest in recent years due to their actual or potential applications in fields such as solid electrolytes, electro/opto-chemical sensors, non- volatile memories, etc. As a consequence, the stability of these glasses is one aspect to be controlled. Several authors [1-5] have approached the study of relaxation and ageing of chalcogenide glasses andsome of them even analyzed ageing and relaxation on glasses of composition Ge u Se 1-u from different points of view [3-5]. Among these authors J.M. Saiter et al. [3]reported an interesting result, that is, forGe u Se 1-u samples withu <0.12 at. Fraction,aged for 13 years, differential scanning calorimetric analyzes present two endothermic peaks associated to the glass transition (Tg)instead of the single endothermic peak observed at short ageing duration. On the other hand only one peak occurs for u=0.12. The authors propose that it is neededa long time ageing at temperatures well below Tg for the occurrence of double endothermic peaks. They attribute these two peaks to a transformation of an initial homogeneous glass towards an inhomogeneous one during ageing. The fact that they only occur for low x is attributed to the coexistence, in the initial glass, of Se chains and GeSe 4/2 structural units in a model of local atomic arrangements, and the presence of only one relaxation peak for higher x values is attributed to the gradual disappearing of the Se chains as x increases. The authors propose that the first endothermic peak corresponds to the faster relaxation of Se chains whereas the GeSe 4/2 cells must relax with a slower kinetics and so they need larger ageing duration to be observed. This phenomenon corresponds to the second relaxation peaks in low u samples and to the single peak that appears in DSC patterns for Ge higher concentrations. For higher Ge concentrations the structure of Ge u Se 1-u glasses is characterized by the presence of chains of tetrahedra centered on a Ge (GeSe 4/2 ) which are linked together either sharing vertices (CS) or edges (ES).[6] The presence of rings and chains of Se is also possible [7] whereas ethane type structures (Et) are reported for high Ge concentration[8]. The addition of Ag to the structure of these binary glasses does not alter substantially their structural units. However,  Paper presented at 6 th International Conference on Amorphous and Nanostructured Chalcogenides, Brasov, Romania, June 24-28, 2013 * Corresponding author:barcond@fi.uba.ar