Ionic Conducting Glasses of the Ag-Ge-Se System

Abstract

In this presentation the AgGeSe ionic conducting glasses are analysed. Previous works are reviewed with the aim to stand out the relationships that can exist between their structural, thermal and electrochemical characteristics. A new insight is presented in order to contribute to the glass structure model. Mössbauer spectrometry in transmission geometry with 57 Fe radiation has been performed on bulk glasses of composition (Ge 0.25 Se 0.75 ) 100-x Ag x with x≤25, doped with 57 Fe, in order to explore the local order in the network. These new results are discussed in connection with structural aspects (radial distribution function obtained by X-ray diffractometry with Mo (Kα) radiation), electric transport (ionic conductivity measurements) and thermal properties (differential scanning calorimetry).

Conductivity percolation transition of Agx(Ge0.25Se0.75)100−x glasses

“…These structural studies show that the key of the ionic conduction is the gradual decrease of the intermediate range order produced by the addition of silver. It generates paths for the ionic conduction [8]. These facts point out the percolation nature of the transition.…”

“…Although the fast ionic conductivity composition threshold (x * % 8) does not coincide with the value reported by Kawasaki et al, we confirm that the transition from semiconductor to fast ionic conductor is abrupt and occurs in a very narrow composition range. Structural studies: X-ray diffractometry, radial distribution function [6] and Mö ssbauer spectrometry [8] do not show any abrupt structural change on glasses in the composition range studied. These structural studies show that the key of the ionic conduction is the gradual decrease of the intermediate range order produced by the addition of silver.…”

“…For samples with x P 8 the resistive impedance of the bulk electrolyte, R 1 , was determined from the cross point of the arc, fitted according to the cell equivalent circuit, with the horizontal line [8]. The conductivity values at different temperatures are calculated following r = d/R 1 A, where d is the thickness of the sample and A its area.…”

Phase separation in Ag–Ge–Se glasses

“…Bulk Ag-Ge-Se glasses have already been widely studied for their electrical, structural and thermal properties [6][7][8][9][10][11][12]. In particular it was shown that the conductivity of Ag x (Ge 0.25 Se 0.75 ) 100Àx glasses with 1 < x < 30 at.% changed suddenly by seven orders of magnitude for x = 10 at.%.…”

Neutron thermodiffractometry study of silver chalcogenide glasses

“…In particular the electrical properties in these glasses are strongly affected by the addition of metals (Li + , Na + , Ag + ) [2]. For example AgGeSe glasses evolve from semiconductor for the chalcogenide matrix to superionic conductor for Ag 25 Se 56.25 -Ge 18.75 glass (r = 10 À4 X À1 cm À1 at room temperature) [3][4][5]. Moreover thin layers of chalcogenide glasses, deposited by thermal evaporation or RF sputtering, exhibit photo-induced phenomena which are at the basis of many interesting applications [6].…”