Structure of semiconducting versus fast-ion conducting glasses in the Ag–Ge–Se system

Abstract

The transition from a semiconductor to a fast-ion conductor with increasing silver content along the Agx(Ge0.25Se0.75)(100−x) tie line (0≤x≤25) was investigated on multiple length scales by employing a combination of electric force microscopy, X-ray diffraction, and neutron diffraction. The microscopy results show separation into silver-rich and silver-poor phases, where the Ag-rich phase percolates at the onset of fast-ion conductivity. The method of neutron diffraction with Ag isotope substitution was applied to the x=5 and x=25 compositions, and the results indicate an evolution in structure of the Ag-rich phase with change of composition. The Ag–Se nearest-neighbours are distributed about a distance of 2.64(1) Å, and the Ag–Se coordination number increases from 2.6(3) at x=5 to 3.3(2) at x=25. For x=25, the measured Ag–Ag partial pair-distribution function gives 1.9(2) Ag–Ag nearest-neighbours at a distance of 3.02(2) Å. The results show breakage of Se–Se homopolar bonds as silver is added to the Ge0.25Se0.75 base glass, and the limit of glass-formation at x≃28 coincides with an elimination of these bonds. A model is proposed for tracking the breakage of Se–Se homopolar bonds as silver is added to the base glass.

Topological Study of Phase-Separated Ag-Conducting Chalcogenide Glasses Using Peak Force Quantitative Nano-Mechanical Characterization

“…Therefore, a last restriction is proposed inspired from the limit of Ag x (Ge 0.25 Se 0.75 ) 100−x glass forming ability proposed by Zeidler et al (2018). This limit corresponds to the consumption of all Se-Se homopolar bonds, can be estimated when the concentration of Ge, Se, and Ag lead to the mean coordination number associated to the number of Se-Se bonds n Se Se = 0.…”

“…where Z Se and Z Ge are the overall coordination numbers of Se and Ge equal to 2 and 4 respectively, and N Broken is the mean number of broken Se-Se bonds per silver atoms estimated around 0.33 (Zeidler et al, 2018). The criteria of n Se Se = 0 has been used to find the limit between the compositions lying within the glass forming ability and those beyond.…”

“…In order to explain the operation of this memory and in particular its very short switching time hardly compatible with the mobility of Ag + ions, various hypotheses have been proposed and among them, the presence of pre-existing silver-rich zones within the amorphous film-which would be heterogeneousand the creation of conduction paths between these zones. To confirm this hypothesis and to better understand the phenomena at the origin of the switching from a resistive state to a conductive state in CB-RAM memories, the electrical, structural, and thermal properties of bulk Ag-Ge-Se glasses have been widely studied (Dejus et al, 1988(Dejus et al, , 1991(Dejus et al, , 1992Kawasaki et al, 1999;Mitkova et al, 1999;Iyetomi et al, 2000;Piarristeguy et al, 2000Piarristeguy et al, , 2003Piarristeguy et al, , 2007aPiarristeguy et al, , 2012Ureña et al, 2003Ureña et al, , 2005Wang et al, 2003;Cervinka et al, 2005;Tafen et al, 2005;Cuello et al, 2007;Prasai and Drabold, 2011;Le Parc et al, 2013;Stellhorn et al, 2016a,b;Zeidler et al, 2016Zeidler et al, , 2018. It was shown that the conductivity of Ag x (Ge 0.25 Se 0.75 ) 100−x glasses with 1 < x < 30 at.…”

“…In Ag x (Ge 0.25 Se 0.75 ) 100−x glasses, when ionic bonds are participating to the structure, the determination of the mean coordination is more complex Zeidler et al (2018). have estimated the nearest-neighbor coordination numbers <N ij > extracted from neutron diffraction experiments on glasses along the Ag x (Ge 0.25 Se 0.75 ) 100−x tie line.…”

Generating large starting configurations for molecular Reverse Monte Carlo modelling of an unique non-linear optical amorphous solid

“…Additionally, different scattering laws of the same substance are often employed. Such functions may be available from neutron scattering using isotopic substitution techniques [11][12][13] or from anomalous x-ray scattering [12,14,15]. Another strong constraint exists if known significant structural correlations exist between certain atoms in the sample as is the case in disordered materials made up of molecular units.…”