Figure - available from: Journal of Physics: Condensed Matter
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Ge–Se (red) and Ga–Se (black) partial total correlation functions (solid curves). Ge–Se (red) and Ga–Se (black) coordination number curves (dotted curves).
Source publication
The short and medium range structures of the 80GeSe2-20Ga2Se3 (or Ge23.5Ga11.8Se64.7) chalcogenide glasses have been studied by combining ab initio molecular dynamics (AIMD) simulations and experimental neutron diffraction studies. Structure factor and total correlation function were calculated from glass structures generated from AIMD simulations...
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Citations
... While Ge is considered to be a network glass former in its Ge-Se form, the entities related to Sb-Se or Ga-Se are considered as network modifiers. The glasses containing these elements are mainly constituted of GeSe 4 and GaSe 4 tetrahedra as well as SbSe 3/2 pyramids or Se 2 Sb-SbSe 2 structural motifs following the Sb content [1][2][3]. While the combinations of Ge and Se easily form glasses, the vitreous domain in the Se/Ga or Se/Sb binaries are relatively narrow and occur at very high percentage of Se. ...
This paper deals with the structural investigation of a new class of glasses belonging to the Ga-Sb-Se system. Neutron diffraction and ⁷⁷Se NMR were performed on the Ga8Sb27Se65 glass composition to understand the structural network in this unconventional system. The experimental data were confronted to molecular dynamics simulations and show a good agreement. Detailed analyses are consistent with Ga and Se coordination numbers (CN) of 4 and 2, respectively, as usually obtained in chalcogenide glasses. This study also highlights a variable CN of Sb, ranging from 3 up to 5, allowing to better understand the formation of glasses in a such complex system.
... The average coordination number of Ga atoms is also close to 4, as was found in several Ge-Ga-Ch (Ch ¼ S, Se, Te) glasses: experimentally in Ge-Ga-S glasses [52e59], in Ge-Ga-Se glasses [54,60e65] and in amorphous Ge-Ga-Te [13,26]. Recent FPMD simulations on 80GeSe 2 -20Ga 2 Se 3 glass [66], Ge-Ga-Te liquids [16] and Ge 15 Ga 10 Te 75 glass [14] also reported Ga coordination numbers around 4. ...
Chemical short range order and topology of GexGaxTe100-2x glasses was investigated by neutron- and x-ray diffraction as well as Ge and Ga K-edge extended x-ray absorption fine structure (EXAFS) measurements. Large scale structural models were obtained by fitting experimental datasets simultaneously with the reverse Monte Carlo simulation technique. Models, relying only on experimental data and basic physical information without constraining the average coordination numbers, give 3.9–4.1 for the number of the atoms in the first coordination sphere of Ge atoms, while the average number of first neighbors of Ga atoms scatters around 3.8. The average coordination number of Te atoms is significantly higher than 2 for x = 12.5 and 14.3. It is found that the vast majority of MTe4 (M = Ge or Ga) tetrahedra have at least one corner sharing MTe4 neighbor.
... The average coordination number of Ga atoms is also close to 4, as was found in several Ge-Ga-Ch (Ch=S, Se, Te) glasses: experimentally in Ge-Ga-S glasses [52 -59], in Ge-Ga-Se glasses [54, 60 -65] and in amorphous Ge-Ga-Te [13,26]. Recent FPMD simulations on 80GeSe2-20Ga2Se3 glass [66], Ge-Ga-Te liquids [16] and Ge15Ga10Te75 glass [14] also reported Ga coordination numbers around 4. ...
Chemical short range order and topology of Ge$_{x}$Ga$_{x}$Te$_{100-2x}$ glasses was investigated by neutron- and x-ray diffraction as well as Ge and Ga K-edge extended x-ray absorption fine structure (EXAFS) measurements. Large scale structural models were obtained by fitting experimental datasets simultaneously with the reverse Monte Carlo simulation technique. Unconstrained models (relying only on experimental data and basic physical information) give 3.9 - 4.1 for the average coordination number of Ge atoms, while the average number of neighbors of Ga atoms scatters around 3.8. The average coordination number of Te atoms is significantly higher than 2 for $x$ = 12.5 and 14.3. It is found that the vast majority of MTe$_4$ (M=Ge or Ga) tetrahedra have at least one corner sharing MTe$_4$ neighbor.
A compositional series of GexGa10Se90−x (at.%; x = 20, 23.3, 25, 27.5, and 30), set to cross both the stoichiometric GeSe2–Ga2Se3 tie-line and the pseudo-stoichiometric GeSe2–GaSe2 tie-line compositions, is employed in this study to refine the local structural environments of Se atoms. Our structural analysis reconfirms that the amorphous network of Ge25Ga10Se65 glass consists mainly of [Ge(Ga)Se4] tetrahedral units connected through either corner-sharing or edge-sharing, in addition to involvement of threefold-coordinated Se atoms. Interestingly, however, upon increase of Se content up to Ge23.3Ga10Se66.7, which belongs to the pseudo-stoichiometric GeSe2–GaSe2 tie-line, the excess Se atoms turn out to form homopolar –Se–Se– chain fragments rather than to transform the heteropolar threefold-coordinated Se atoms into the typical heteropolar twofold-coordinated Se atoms bridging two tetrahedra. Coexistence of the homopolar twofold-coordinated and heteropolar threefold-coordinated Se atoms is considered a unique structural characteristic of Ge–Ga–Se glass, which needs to be taken into account in the compositional optimization of its macroscopic properties.
Surface crystallization processes in the 80GeSe2–20Ga2Se3 glasses thermally annealed at 380 °C for 25 and 80 h were studied by both experimental methods and statistical analysis of images using Python scripts. It is shown that GeSe2 phase is formed as a result of annealing unevenly on glass surface in the form of thread-like crystallites with a length of 1–3 μm. The obtained dependences of number crystallites on their geometric parameters indicate a significant increase in their size (area, length and width) with an increase in the duration of annealing up to 80 h. At the same time, the crystallite growth orientation does not change and is 50°, 90° and 130°. Optimal conditions for crystallization processes can be selected based on the obtained results to prepare stable 80GeSe2–20Ga2Se3 glasses with predetermined optical properties.
A comprehensive study of the crystallization of GaxGe100-x-ySey (x = 0–30; y = 60–75) glasses by means of differential scanning calorimetry, X-ray diffraction analysis, optical microscopy and scanning electron microscopy as carried out. Glass transition temperature and stability against crystallization decrease with increasing gallium content in the glasses. During the glass crystallization, phases of variable composition, isostructural to the polymorphic modifications of Ga2Se3, are formed. Samples with ≤10 at.% gallium content contain germanium mono- and diselenide phases. A distinctive feature of the crystallization of GaxGe100-x-ySey glasses is the formation of globules – localized 10–60 µm sized regions with an increased crystalline phase content. The formation of globules at the stage of melt quenching determines the microscopic structure of glasses. Among the studied compositions, glasses with a selenium content of 60 at.% and gallium content up to 15 at.% are recommended as optimum for the preparation of IR glass-ceramic materials.
