Investigations on Structure and Properties of Ge-as-se Chalcogenide Glasses PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Investigations on Structure and Properties of Ge-as-se Chalcogenide Glasses PDF full book. Access full book title Investigations on Structure and Properties of Ge-as-se Chalcogenide Glasses by Ting Wang. Download full books in PDF and EPUB format.
Author: Ting Wang Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Germanium-Arsenic-Selenium chalcogenide glasses are considered as good candidates for photonic applications due to their excellent transparency in the infrared range and high optical nonlinearities. A deep understanding of composition-structure-property relationship in Ge-As-Se ternary system is thus becoming increasingly important, which can serve as a guideline for materials selection. In this work, the structure and various physical properties of GexAsySe100-x-y bulk glasses have been systematically investigated. Raman spectra and EXAFS measurements reveal that chemically ordered network model can be applied to Selenium-rich glasses, but fails to explain bonding characterization of Selenium-poor compositions. Atomic arrangements are more sensitive to the changes in chemical compositions. A tight association between the fragility and the deviation from stoichiometry has been found in the Ge-As-Se system by differential scanning calorimetry. It is shown that chemical compositions with the lowest values of fragility index are far less likely to incur structural relaxation. Those strong glasses are normally chosen as ideal materials for fabrication of stable photonic devices. The variation of density and elastic modulus as a function of mean coordination number both show two transition thresholds, which correlate with floppy-to-rigid phase transition and 2D-to-3D structure transition respectively. The results provide clear evidence that some physical properties of Ge-As-Se chalcogenide glasses are significantly determined by their mean coordination numbers, but could be further tuned by the chemical compositions. The detailed optical investigation shows that the generalized Miller's rule is a simple but effective approach to estimate the nonlinearities of a broad variety of chalcogenide glasses. Nonlinear properties of these materials exhibit strong dependence upon their optical bandgap in the near infrared. It seems that the highest nonlinearity at telecommunications wavelengths is predictable in chalcogenide glasses.
Author: Ting Wang Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Germanium-Arsenic-Selenium chalcogenide glasses are considered as good candidates for photonic applications due to their excellent transparency in the infrared range and high optical nonlinearities. A deep understanding of composition-structure-property relationship in Ge-As-Se ternary system is thus becoming increasingly important, which can serve as a guideline for materials selection. In this work, the structure and various physical properties of GexAsySe100-x-y bulk glasses have been systematically investigated. Raman spectra and EXAFS measurements reveal that chemically ordered network model can be applied to Selenium-rich glasses, but fails to explain bonding characterization of Selenium-poor compositions. Atomic arrangements are more sensitive to the changes in chemical compositions. A tight association between the fragility and the deviation from stoichiometry has been found in the Ge-As-Se system by differential scanning calorimetry. It is shown that chemical compositions with the lowest values of fragility index are far less likely to incur structural relaxation. Those strong glasses are normally chosen as ideal materials for fabrication of stable photonic devices. The variation of density and elastic modulus as a function of mean coordination number both show two transition thresholds, which correlate with floppy-to-rigid phase transition and 2D-to-3D structure transition respectively. The results provide clear evidence that some physical properties of Ge-As-Se chalcogenide glasses are significantly determined by their mean coordination numbers, but could be further tuned by the chemical compositions. The detailed optical investigation shows that the generalized Miller's rule is a simple but effective approach to estimate the nonlinearities of a broad variety of chalcogenide glasses. Nonlinear properties of these materials exhibit strong dependence upon their optical bandgap in the near infrared. It seems that the highest nonlinearity at telecommunications wavelengths is predictable in chalcogenide glasses.
Author: Derrick Charles Kaseman Publisher: ISBN: 9781369343144 Category : Languages : en Pages :
Book Description
Chalcogenide glasses constitute an important class of materials that are sulfides, selenides or tellurides of group IV and/or V elements, namely Ge, As, P and Si with minor concentrations of other elements such as Ga, Sb, In. Because of their infrared transparency that can be tuned by changing chemistry and can be actively altered by exposure to band gap irradiation, chalcogenide glasses find use in passive and active optical devices for applications in the areas of photonics, remote sensing and memory technology. Therefore, it is important to establish predictive models of structure-property relationships for these materials for optimization of their physical properties for various applications. Structural elucidation of chalcogenide glasses is experimentally challenging and in order to make predictive structural models, structural units at both short and intermediate -range length scales must be identified and quantified. Nuclear Magnetic Resonance (NMR) spectroscopy is an element-specific structural probe that is uniquely suited for this task, but resolution and sensitivity issues have severely limited the applications of such techniques in the past. The recent development of multi-dimensional solid-state NMR techniques, such as Phase Adjusted Spinning Sidebands (PASS) and Magic Angle Turning (MAT) can potentially alleviate such issues. In this study novel two-dimensional, high-resolution 77Se and 125Te MATPASS NMR spectroscopic techniques are utilized to elucidate quantitatively the compositional evolution of the short- and intermediate- range atomic structure in three binary chalcogenide glass-forming systems, namely: Ge[subscript x]Se[subscript100-x], As[subscript x]Se[subscript 100-x], and As[subscript x]Te[subscript 100-x]. The spectroscopic results provide unambiguous site speciation and quantification for short- and intermediate-range structural motifs present in these glasses. In turn, for all systems, robust structural models and the corresponding structure-property relationships are successfully established as a function of composition. The results indicate that the physical properties are intimately tied to the topology and chemical order present in each system. Finally, a dynamic version of the two-dimensional 31P PASS NMR spectroscopy is used to study the molecular motion in a supercooled chalcogenide liquid of composition P5Se3. The results clearly display the presence of isotropic rotational reorientation of the constituent molecules at timescales significantly decoupled from that of the structural relaxation near and above T[subscript g]. This behavior is atypical of conventional molecular glasses in organic systems in which rotational and translational dynamics remain coupled near T[subscript g]. When taken together with previous reports on the dynamics of other globular inorganic molecules, the results support the existence of a “plastic glass” phase where the molecules perform rapid rotation without significant translation.
Author: Alvin W. Mao Publisher: ISBN: 9781339824819 Category : Languages : en Pages :
Book Description
Chalcogenide glasses exhibit unique optical properties such as infrared transparency owing to the low-phonon energies, optical non-linearity, and photo-induced effects that have important consequences for a wide range of technological applications. However, to fully utilize these properties, it is necessary to better understand the atomic-scale structure and structure-property relationships in this important class of materials. Of particular interest in this regard are glasses in the stoichiometric system Na2Se/BaSe--Ga2Se3--GeSe2 as they are isoelectronic with the well-studied, oxide glasses of the type M2O(M'O)--Al2O3SiO2 (M = alkali, M' = alkaline earth). This dissertation investigates the structure of stoichiometric Na2Se/BaSe--Ga2Se3--GeSe2 and off-stoichiometric BaSe--Ga2Se3--GeSe2±Se glasses using a combination of Fourier-transform Raman and solid state nuclear magnetic resonance (NMR) spectroscopies. The spectroscopic data is then compared to composition-dependent trends in physical properties such as density, optical band gap, glass transition temperature, and melt fragility to develop predictive structural models of the short- and intermediate-range order in the glass network. These models significantly improve our current understanding of the effects of modifier addition on the structure and properties of chalcogenide glasses, and thus enable a more efficient engineering of these highly functional materials for applications as solid electrolytes in batteries or as optical components in infrared photonics. In general, the underlying stoichiometric Ga2Se3--GeSe2 network consists primarily of corner-sharing (Ga/Ge)Se4 tetrahedra, where the coordination numbers of Ga, Ge, and Se are 4, 4, and 2, respectively. Some edge-sharing exists, but this configuration is relatively unstable and its concentration tends to decrease with any deviation from the GeSe2 composition. Due to the tetrahedral coordination of Ga, the initial addition of Se-deficient Ga2Se3 to GeSe2 results in the preferential formation of Ge-Ge bonds, which are distributed such that the clustering of ethane-like (Se3)Ge-Ge(Se3) units is avoided to the maximum extent. This behavior is entirely consistent with the continuously-alloyed structural scenario of chalcogenide glasses. However, for contents of Ga2Se3 greater than about 25--30 mol%, the avoidance of Ga-Ga and mixed Ga-Ge bonds results in the appearance of three-coordinated Se as an alternate mechanism to accommodate the Se deficiency. The addition of either Na2Se or BaSe to Ga2Se3--GeSe2 glasses introduces an ionic bonding character to an otherwise largely covalently bonded network. As a result, the structure responds by adopting characteristics of the charge-compensated structural scenario of oxide glasses. In the stoichiometric Na2Se/BaSe--Ga2Se3--GeSe2 glasses, the ratio of Na2Se/BaSe:Ga2Se3 = 1 serves as a chemical threshold, where the network consists predominantly of corner-sharing (Ga/Ge)Se4 tetrahedra, and the charge on the Na(Ba) cations is balanced by the GaSe4− tetrahedra. For glasses with Na2Se/BaSe:Ga2Se3 1, the addition of Se-deficient Ga2Se3 induces the formation of Ge-Ge bonds. However, for glasses with Na2Se/BaSe:Ga2Se3 1, the addition of Na2Se/BaSe results in the formation of non-bridging Se atoms, which break up the connectivity of the glassy network. The major difference between the modifying elements Na and Ba is that the high field strength of the Ba cation induces a higher degree of chemical disorder in the glass network. This conclusion is evidenced by the presence of some Ge-Ge bonds in BaSe--Ga2Se3--GeSe2 glasses even at the chemical threshold composition of BaSe:Ga2Se3 = 1. The structural duality of the Na2Se/BaSe--Ga2Se3--GeSe2 system is best observed in the off-stoichiometric BaSe--Ga2Se3--GeSe2±Se glasses. Here, the removal of Se from a stoichiometric glass with BaSe:Ga2Se3 > 1 results in Ge-Ge bonds, while its addition in excess of stoichiometry forms Se-Se bonds. Although such behavior is consistent with the continuously-alloyed structural model, it should be contrasted with the response of the network to the removal or addition of BaSe. In the latter case especially, the network responds with the formation of non-bridging Se atoms, which is reminiscent of the charge-compensated structural scenario. The aforementioned structural conclusions are supported by trends in physical properties. Of all the properties measured, the glass transition temperature Tg responds most predictably to changes in glass structure in the sense that the removal of heteropolar (Ga/Ge)-Se bonds from the glassy network consistently results in a decrease in Tg. Indeed, Tg is observed to be maximized around chemical threshold compositions that are expected to have a fully-connected network of (Ga/Ge)Se4 tetrahedra. The formation of homopolar Ge-Ge bonds causes Tg to drop by ~40-80 °C, while the formation of Se-Se and/or non-bridging Se causes Tg to decrease by at least 120 °C. Trends in density reflect both the packing efficiency of the structural units within the glassy network as well as the masses of the constituent elements, and are generally observed to increase or decrease monotonically. As a result, an increase in density is associated with: 1) the removal of inefficiently packed structural units such as edge-sharing tetrahedra, 2) the formation of efficiently packed units such as three-coordinated Se atoms, 3) the removal of lighter elements like Na, and 4) the addition of heavier elements like Ba. Optical band gap is related to the bonding character within the glassy network, and tends to decrease as the bonding character becomes increasingly metallic. Therefore, a decrease in optical band gap is observed with the formation of homopolar Ge-Ge bonds when Ga2Se3 is added to GeSe2. However, the stoichiometric BaSe--Ga2Se3--GeSe2 glasses show an anomaly in this regard because optical band gap decreases with the addition of BaSe, and consequently the removal of Ge-Ge bonds. This observation was ascribed instead to the formation of Ba-Se bonds, which are associated with a lower bandgap compared to the (Ga/Ge)-Se bonds that they replace. Finally, there is no straightforward structural explanation for trends in fragility, because it is related to the number of structural configurations dynamically available to the supercooled liquid. In the binary Ga2Se3--GeSe2 glasses, the fragility tends to increase with the formation of homopolar Ge-Ge bonds, which is consistent with other chalcogenide systems in which fragility increases with the removal of heteropolar bonds within corner-sharing tetrahedra and pyramids. In the stoichiometric BaSe--Ga2Se3--GeSe2 glasses on the other hand, a shift in trend near the compositions where BaSe:Ga2Se3 = 1 coincides with a structural shift between the formation of Ge-Ge bonds and Se-Se/non-bridging Se.
Author: K.J. Rao Publisher: Elsevier ISBN: 0080518036 Category : Science Languages : en Pages : 585
Book Description
Structural Chemistry of Glasses provides detailed coverage of the subject for students and professionals involved in the physical chemistry aspects of glass research. Starting with the historical background and importance of glasses, it follows on with methods of preparation, structural and bonding theories, and criteria for glass formation including new approaches such as the constraint model. Glass transition is considered, as well as the wide range of theoretical approaches that are used to understand this phenomenon. The author provides a detailed discussion of Boson peaks, FSDP, Polymorphism, fragility, structural techniques, and theoretical modelling methods such as Monte Carlo and Molecular Dynamics simulation. The book covers ion and electron transport in glasses, mixed-alkali effect, fast ion conduction, power law and scaling behaviour, electron localization, charged defects, photo-structural effects, elastic properties, pressure-induced transitions, switching behaviour, colour, and optical properties of glasses. Special features of a variety of oxide, chalcogenide, halide, oxy-nitride and metallic gasses are discussed. With over 140 sections, this book captures most of the important and topical aspects of glass science, and will be useful for both newcomers to the subject and the experienced practitioner.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Abstract: We have prepared three groups of Ge–As–Se glasses in which the Se content is 5.5 mol%, 10 mol%, and 20 mol% rich, respectively. We explored the possibility of suppressing the formation of the Ge–Ge and As–As homopolar bonds in the glasses. Thermal kinetics analysis indicated that the 5.5 mol% Se-rich Ge11.5 As24 Se64.5 glass exhibits the minimum fragility and thus is most stable against structural relaxation. Analysis of the Raman spectra of the glasses indicated that the Ge–Ge and As–As homopolar bonds could be almost completely suppressed in 20 mol% Se-rich Ge15 As14 Se71 glass.
Author: Ting Wang
Author: Ting Wang
Author: Derrick Charles Kaseman
Author: Yogesh Mehrotra
Author: Alvin W. Mao
Author: Sezen Soyer-Uzun
Author: K.J. Rao
Author: Guang Yang
Author: Amin Ismail Amin Abdel-Latif
Author: Yves Bernard Verhelle
Author: