Homogeneous-inhomogeneous models of AgGeSe bulk glasses

ARCONDO, B.; MARIA ANDREA UREÑA; PIARRISTEGUY, A.; PRADEL, A.; FONTANA, M.

La Plata

Congreso; International Workshop 35th Anniversary of Hyperfine Interactions at La Plata (HFILP05); 2005

Ge–Se system presents an extensive glass forming composition range even when different metals (Ag, Sb, Bi) are added. In spite that the addition of Ag (up to 30 at%) to Ge–Se does not affect substantially the glass forming tendency, it impacts significantly on the transport properties. (Ge0.25Se0.75)100_xAgx is a fast ionic conductor with xX8 at% whereas it is a semiconductor for xo8 at%. This behavior is also reported in other chalcogenide systems containing Ag. One of the structural models proposed to explain the relation between transport and structure is based on an intrinsically inhomogeneous structure where zones rich in metals coexist with zones of the host material. Field effect scanning electron microscopy (FE-SEM) is performed on amorphous (Ge0.25Se0.75)100_xAgx bulk samples. These results appear to sustain this model. However previous structural and thermal studies oppose it. Mossbauer spectrometry on samples (0pxp25) containing 0.5 at% of 57Fe is performed at Tp300 K. The main contribution to the glasses spectra correspond to low spin Fe2+ in octahedral coordination and high spin Fe2+ in distorted octahedral environments. The relative population of both sites changes continuously as Ag concentration varies denoting that the change in the transport behavior obeys to a percolation phenomenon. The low temperature results are discussed with the aim to throw light on the controversy about the homogeneity–inhomogeneity of the studied bulk glasses.