Aging effects in Ag-Ge-Se bulk glasses

P. PEREZ; J.M. CONDE-GARRIDO; D. SORIA; M.A. UREÑA; M. FONTANA; B. ARCONDO

Brasov

Conferencia; 6 International Conference 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 in fields such as solid electrolytes, electrochemical sensors, non-volatile memories, etc. As a consequence, the stability of these glasses is one aspect to be 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) studies show the presence of 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 composition Ag0.05(Ge0.25Se0.75)0.95, which were heat treated, were analyzed by Raman spectroscopy. The spectra obtained were compared with those of 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 theRaman spectra are thebands centered at 197 cm-1 and 213 cm-1 and those centered at 240 cm-1 and 261cm-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 and rings 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 evolution towards a more rigid structure, with fewer degrees of freedom, compatible with an increased Lamb-Mössbauer fraction, consistent with the results obtained by MS.   References   [1] Edwards T.G.; Sen S., J. Phys. Chem B 2011, 115, 4307. [2] Chakravarty S.; Georgiev D.G.; Boolchand P. and Micoulaut M., J. Phys.: Condens. Matter  2005, 17, L1.