Effect of mixed Ge/Si cross-linking on the physical properties of amorphous Ge-Si-Te networks

Abstract

Amorphous GexSixTe1−2x glasses are studied as a function of composition by a combination of experimental and theoretical methods, allowing for a full description of the network structure in relationship with physico-chemical properties. Calorimetric and thermal measurements reveal that such glasses display an anomalous behavior across a range of compositions xc1=7.5% and <x<xc2=9%, in which is manifested a deep minimum in molar volume, non-reversing enthalpy, and liquid fragility. These anomalies allow defining an intermediate phase, where network rigidity onsets as the content x of Group IV atoms (Ge, Si) are increased. The structural manifestation of these anomalies is understood from 119Sn Mössbauer spectroscopy and First Principles Molecular Dynamics at selected compositions (Ge20Te80, Si20Te80, and Ge10Si10Te80). The numerical models reveal the quite different roles played by the modifier or network cross-linker Ge or Si atoms, Si being more tetrahedral in sp3 geometry, whereas Mössbauer spectroscopy shows that the nature of chemical bonding is dramatically changed around x≃ 8%. The precise evolution of the local structure and chemical bonding ultimately allows understanding the origin of the intermediate phase in these complex tellurides.

Relaxation and physical aging in network glasses: a review

“…absence of stress [352]), which manifests by a minimum in the molar volume ( Fig. 40a and c), a salient feature that has been reported for various systems [15,41,42,43,314,330,349,354]. The stress-free nature of such RWs has been detected from pressure experiments [352] showing the vanishing of a threshold pressure (Fig.…”

“…Using MD simulations, the number of topological constraints has been investigated as a function of temperature in a certain number of glass-forming systems such as GeSe 2 [320], Ge-Te [315], Ge-Si-Te [314] or SiO 2 -2SiO 2 [279,311,316]. Figure 34 shows the analysis for 300 K and 1050 K for GeSe 2 , using either an average count (left) or indiviual constraints giving the distribution f(σ) (right) [320].…”

“…Such methods based on angular standard deviations have also proven to be efficient in order to enumerate the fraction of tetrahedra in amorphous telluride networks [314,315]. To calculate the population of GeTe 4/2 or SiTe 4/2 tetrahedra in binary Ge-Te, Si-Te or ternary Ge-Si-Te glasses, one detects atoms having six low standard deviations σ θ around an Ge/Si atom.…”

Concepts and applications of rigidity in non-crystalline solids: a review on new developments and directions

“…This situation contrasts with the Si-Te binary which contains a large fraction of SiTe 4/2 tetrahedra reminiscent of the local structure of the crystalline Si 2 Te 3 polymorph [126] which is 100% tetrahedral. In the ternary Ge-Si-Te system [124], the calculated tetrahedral fraction is found to be somewhat lower (33.7%) when compared to its isovalent compound (Ge 20 Te 80 , 54.6%) but is very close to the one determined experimentally from Mössbauer spectroscopy (40.8%). The detail of the numerical analysis permits to determine the different contributions, and it is found that Si sites dominate the population of tetrahedra (42.74% for Si against 24.6% for Ge).…”

“…The detection and quantification of tetrahedral germanium can be made from angular standard deviations which are associated with BB interactions [123,124]. The method offers, indeed, the advantage to focus on angular excursions rather than working directly on angles [115].…”