Aging effects in Ag-Ge-Se bulk glasses

PEREZ , PAULA GIMENA; CONDE GARRIDO, J. M.; SORIA, DELIA; MARIA ANDREA UREÑA; FONTANA, M.; ARCONDO, B.

Brasov

Conferencia; 6th International Conference On Amorphous and Nanostructured Chalcogenides (ANC 6); 2013

Ag-Ge-Se glasses have attracted much interest in recent years due to their actual or potential applications infields such as solid electrolytes, electrochemical sensors, non-volatile memories, etc. As a consequence, the stability of these glasses isone aspect tobe controlled. Several authors [1,2] have approached the study of relaxation and aging of glasses of composition GexSe1-x even from different points of view. In the present work, the aging of Ag-Ge-Se glasses as well as the effect of thermal treatments below Tg are analyzed. In a first stage, Mössbauer spectroscopy (MS) studiesshow the presenceof strong effects of long-term relaxation that could be attributed to an increase in the fraction of Lamb-Mössbauer. These effects were inversely proportional to the Ag concentration of the samples. In order to understand the relaxation effects observed by MS, samples of compositionAg0.05(Ge0.25Se0.75)0.95, which were heat treated, were analyzed by Raman spectroscopy. The spectra obtained were compared with thoseof samples of the same composition, aged at room temperature for 8 years. In order to have a reference to the effect of the composition in the structure of the glass, a sample of composition Ag0.10(Ge0.25Se0.75)0.90 was analyzed as well. In all tested samples, the most important contributions to the Raman spectraare the bands centered at 197 cm-1 and 213 cm-1 and those centered at 240 cm-1 and 261 cm-1. The first two are attributed to tetrahedra joined by vertices and by edges respectively and the latter two are attributed to chains and rings of Se atoms. The most notable effect observed after aging the sample consists of a decrease in the relative contribution of chains andrings to the spectra and a blue shiftof their centers. On the other hand, no clear impact was detected after sub-Tg thermal treatments. Accordingly, aging can be interpreted as an evolutiontowards a more rigid structure, with fewer degrees offreedom, compatible with an increased Lamb-Mössbauer fraction, consistent with the results obtained by MS.