INTECIN   20395
INSTITUTO DE TECNOLOGIAS Y CIENCIAS DE LA INGENIERIA "HILARIO FERNANDEZ LONG"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Analyzes of the structure of Agx(Ge0.25Se0.75)1-x bulk glasses employing 119Sn Mössbauer effect and XAFS
Autor/es:
CONDE GARRIDO, J. M.; LEDE, E.J.; MARIA ANDREA UREÑA; ROCCA, J.; ARCONDO, B.
Reunión:
Conferencia; HK2011, Humboldt Kolleg (Argentine- Germany; 2011
Resumen:
The zone rich in Se in the equilibrium phase diagram of Ag-Ge-Se system presents a large gap of miscibility in the liquid phase that solidifies, upon a fast cooling process, as an intrinsically inhomogeneous glass. The non-homogeneous morphology of these glasses depends on the atomic fraction of Ag (x). These glasses consist of Ag rich zones surrounded by a Ag depleted matrix for x < 0.08 whereas they consist of Ag depleted zones surrounded by a Ag rich matrix for x > 0.10. Evidence of a spinodal decomposition is observed for 0.08 ≤ x ≤ 0.10. On the other hand, these glasses present an abrupt change in their conductivity at x ≈ 0.08. They are semiconductors for x<0.08 whereas they are fast ionic conductors for x ≥ 0.08. This fact has been attributed to their particular morphology. In this work, the structure of these glasses is analyzed for 0 ≤ x ≤ 0.25 employing Mössbauer spectroscopy, on samples doped with substitutional 119Sn, and X-ray absorption spectroscopy (Ge and Se K edges). In the Mössbauer spectra two main 119Sn (i.e. Ge) environments were observed. One of them, corresponding to Sn4+ tetrahedrally coordinated by 4 Se, is the main contribution for all sample spectra. The other contribution, present in the spectrum of sample with x=0.25, may be attributed to Sn2+. In agreement with these results the best fit of Xanes spectra (Ge edge) corresponded to a superposition of two Ge environments that may be correlated to those mentioned above. Xanes spectra (Se edge) provides a complementary insight revealing two different environmentsof Se, whoserelative abundance depends almost linearly on theconcentration of Ag. Accordingly, these environments may be asociated to Se-Ge and Se-Ag. These results suggest that the structure of both glassy phases that coexist in each non homogeneous sample, that is the phase with high Ag concentration and that with lower Ag concentration, are not qualitatively different as Ge and Se environments are practically the same in both phases.