No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Study of As―Se―Te glasses by neutron-, X-ray diffraction and optical spectroscopic methods
Abstract
The atomic structures of amorphous As 40 Se (60−x) Te x (x= 10 and 15) and As 40 Se 60 glasses have been investigat-ed by neutron and high energy X-ray diffraction methods. The two datasets were modeled simultaneously by reverse Monte Carlo (RMC) simulation technique. The RMC simulations revealed a glassy network built-up from As(Se, Te) 3 pyramids in which Te atoms substitute Se atoms. The As―Se correlation function shows a strong and sharp first peak at 2.4 Å and two broad and much less intense peaks at 3.7 and 5.6 Å, related to 1st, 2nd and 3rd neighbor distances of the As―Se bonds, respectively. They are an evidence for existence of short and medium ordering in the studied glasses. The similarity of Θ Te―As―Te and Θ Se―As―Se bond distributions suggests that Te atoms have a similar role in the structure formation as Se atoms. The FTIR spectra analysis revealed impurity bonds of Se―H, As―O, Se―O, and Te―O in the glasses which contributed to enhanced ab-sorption in visible spectral range. From the ellipsometric data analysis the optical constants and the energetic parameters of the studied glasses were established. The compositional variation of these parameters is explained in terms of chemical bonds formation and change in the density of charged defects.
... Hence, the recorded bands are vibrational bands due to extrinsic impurities being present in the studied glass system. These bands were identified on the basis of the reported data in [30][31][32] and represented in Fig. 1(b). The observed band centered at around 4.24 μm and 6.14 μm can be assigned to the stretching mode of Se-H and Se-O bonds, respectively [30,32] while two vibrational bands of the hydroxyl groups Se-OH are situated at 2.9 μm and 3.45 μm [31,32]. ...
... These bands were identified on the basis of the reported data in [30][31][32] and represented in Fig. 1(b). The observed band centered at around 4.24 μm and 6.14 μm can be assigned to the stretching mode of Se-H and Se-O bonds, respectively [30,32] while two vibrational bands of the hydroxyl groups Se-OH are situated at 2.9 μm and 3.45 μm [31,32]. The broad band positioned around 9.29 μm could be due to a combined frequency of hetero-polar bonds like Se − Sb and Se − Te bonds [33]. ...
The effect of Sb at% on different temperature ranges dc-electrical conductivity are reported for thermally evaporated Se 85− x Te 15 Sb x (x = 2.5, 5 and 7.5 at.%) glassy thin films. The structure and surface morphology of the considered samples were studied by the X-Ray Diffraction (XRD), Differential Thermal Analysis (DTA), Fourier Transform Infrared (FTIR) and Scanning Electron Microscope (SEM) measurements. The electrical conduction in the Se 85− x Te 15 Sb x chalcogenide glass system was found to be determined by different conduction mechanisms with different activation energy values at various temperature ranges. The relation between various structural parameters and the electrical activation energies was investigated. The analysis of the high-temperature conductivity data identified that the conduction mechanism on the basis of thermionic emission occurs over the grain boundaries according to Seto's model. In the amorphous to crystalline phase transition region, a model has been modified to describe the conduction mechanism. The modification is considering the percolation effects alongside with the effect of thermally activated electrical conductivity of the formed crystalline grains embedded in the sample amorphous matrix. The calculated electrical conductivity was found to be effectively fitted to the temperature-dependent electrical conductivity measurements for thermally evaporated Se 85− x Te 15 Sb x films and showed promising candidates to be examined in different chalcogenide systems .
... medium range order (MRO). The first sharp diffraction peak (maximum) (FSDP) in the distribution of Xray diffraction intensity or neutrons, the structural factor determined from them and the repeated maxima in the correlation function [15][16][17][18][19][20], as well as the appearance of the "boson" peak in Raman scattering spectra [21][22][23][24] is explained by the existence of the MRO region in the CVS materials. According to literature data [25], in semiconductors with covalent bonds between constituent atoms, the dominant factor determining the local structural order is the so-called "8-N" rule. ...
... The third weak peaks are at 4.75 Å (As 40 Se 60 ), 4.3 Å (As 40 Se 30 S 30 ) and 5.6 Å (As 40 Se 30 Te 30 ). The obtained values of the bond length for the As 40 Se 60 composition are in good agreement with the results of [5,16,17]. According to the results of [35,36], the second peaks in the g Se-Se (r) and g As-As (r) graphs could give a forecast about the existence of medium- In Table 2 are summarized the short-range order parameters, i.e. "the partial coordination numbers" N ij , i.e. the average number of j atoms around i atom, average number of neighbors, total coordination number, average coordination number. ...
... In the RMC procedure, starting from the initial atomic configuration, the initial atomic configurations are iteratively adjusted for increasingly improved convergence with the S(Q) provided by the experiment. For the starting configuration, we have used the initial atomic configuration constructed according to the protocol already established in our earlier work on similar glassy systems [4,51]. During the RMC runs, cut-off constraints were used, constraining the minimum inter-atomic distances between two atoms. ...
In this work, following our previous work on molybdate glasses, we employ a combination of neutron diffraction and neutron Compton scattering, augmented by ab initio harmonic lattice dynamics and Reverse Monte Carlo modelling to characterise the force-constant disorder in the tungsten oxide-based glasses. Specifically, we discuss the correlations between the average interatomic force constant magnitudes inferred from neutron Compton scattering and the glass formation ability, measured in terms of the value of the glass transition temperature, as well as the average bond-lengths and interatomic distances obtained from diffraction data analysis. Moreover, we provide a comparative analysis of the widths of force-constant distributions of individual atomic species in glasses and their precursor metal oxides based on the distributions of the widths of nuclear momentum distributions. Furthermore, we assess the degree of softening of atom-projected vibrational densities of states induced by the force-constant disorder in the glasses.
Ge4As14Se82, Ge4As14S2Se80, Ge7As16S5Se72, Ge10As20S10Se60, Ge17.5As15S15Se52.5, Ge24As19S20Se37, Ge25As10S25Se40, Ge26As18S30Se26, and Ge33As17S35Se15 chalcogenide glass compositions were synthesized and molar percentage of element have been determined by energy-dispersive X-ray analysis. The parameters study the local structure (d, L), characterizing the chemical regularity (R) and glassy network topology (Nco, f), the glass-forming ability (Hr), the thermal stability (Hʹ, S), the glass and crystallization regions (ΔTg-c) of substances corresponding to different topological glass states (isostatic, rigid, elastic) are determined and physical features of the change of these parameters depending on the composition were studied according to X-ray diffraction, differential scanning calorimetry methods and Tanaka's two-dimensional layered structure approach.
As an extension to part I, Dongol and Elhady (2020), the method of Reverse Monte Carlo simulation has been
used to examine the effect of quenching rate on the structure of glassy AsxSe100 x (x=20, 30, 40, 50 at%). Results
of the partial structure factors indicate that the correlations responsible for medium range order depend strongly
on As-content, and distortion occurs in this structure range with increasing quenching rate. This distortion is
more predominant in case of As50Se50 glass. Results of partial pair distribution function show that, most of short
range order is mainly governed by the chemically ordered network model, and the random covalent network
model plays a relatively small role. Also, it was clarified that the percentage of homopolar bonds increases with
increasing quenching rate. In case of x = 50 at.%, the tendency of As segregation and formation of As–As bonds
is demonstrated. Some Deviation from “8-N” rule was observed in the structure of the investigated glasses.
Lithium-sulfur (Li-S) battery is one of the promising high-energy battery systems for future use. However, the shuttle effect due to the dissolved lithium polysulfides in ether electrolyte hampers its practical application. Applying electrolyte additives in Li-S battery has been widely acknowledged as an effective way to reduce the shuttle effect and improve cycling efficiency. In this work, benzoselenol (PhSeH) is used as an organic electrolyte additive in Li-S battery. It reacts with elemental sulfur to form phenyl selenosulfide, altering the redox pathway of the cathode with the regeneration of S8 at the end of charge and enabling new redox reactions with high reversibility. The Li-S coin cell with an optimized amount of PhSeH in the electrolyte delivers a high discharge capacity of 1,436 mAh·g−1 and a capacity retention of 92.86% in 200 cycles, and exhibits lower discharge overpotential in comparison to the cell with blank electrolyte. The Li-S pouch cell with a low electrolyte/sulfur (E/S) ratio of 4.0 µL·mg−1 shows a discharge capacity of 1,398 mAh and excellent capacity retention for 20 cycles.
In this work, we report the sensitivity of structural, thermal, and electrical properties of Ag30+xAs28-xSe21Te21 (x = 2, 4, 6, 8, 10) chalcogenide glasses to the relative abundance of Ag and As in the compositions. The results show non-linear variation of glass density with linear increase in Ag (or decrease in As), implying structural change at 38 at.% Ag (or 20 at.% As). This structure change was further evident from differential scanning calorimetry (DSC) and Raman analyses, which show distinct characteristic temperatures (Tg, Tx, and Tp) and bonding type with increasing Ag content (decreasing As content). Specifically, at high Ag content beyond 38 at.% (As below 20 at.%), two additional exothermic peaks appear in DSC curves, and a strong As–Se bonding peak appears in Raman. The structural change is closely related to the variation of glass conductivity in a complex way, which first decreases with increasing Ag content, from 1.14 × 10⁻⁶ S cm⁻¹ at 32 at.% Ag to 2.88 × 10⁻⁷ S cm⁻¹ at 36 at.% Ag, but then with further increase in Ag, conductivity increases rapidly and reaches the maximum of 5.20 × 10⁻⁶ S cm⁻¹ at the maximum Ag content 40 at.%. The abnormal change in conductivity is interpreted as due to the mutual effects of Ag doping as well as the degree of deviation from stoichiometry of the glass forming units. The impedance spectra identify little ionic contribution to the total conductivity which is supported from Raman spectra of the glasses and XRD analyses of the samples after thermal crystallization, both showing evidences of the presence of lone pair electrons of the chalcogen atoms. This work highlights the importance of compositional adjustment for the modification of physical properties in chalcogenide glasses, and provides a scientific basis for potential applications of such glasses in electronic devices.
In this work, series of glass samples in the Ag30As28 (SexTe100-x)42 (x = 15, 30, 50, 70, 85) system are prepared. Effects of the Se/Te ratio on density (ρ), glass transition temperature (Tg), room-temperature conductivity (σ298k) and crystallization behaviors of glasses are investigated, and their associations with the structure of glasses are discussed. Results show that with the increased substitution of Se for Te, the molar volume (Mv) decreases and Tg increases, indicating the increased space packing efficiency and the enhanced structure connectivity. The strengthened structure leads to an abnormal increase of ρ when x is lower than 30 mol%. Further increase of the Se/Te ratio results in the reduction of ρ due to the dominant effect of smaller molar weight (Mw). The σ298k of glasses decreases with Se increasing from 15 to 50 mol%, and then interestingly increases up to the level even higher than that of the sample with the lowest Se content (15 mol%). Raman spectra shows the transformation of main glass structure units from Te-based pyramids to Se-based complexes as the Se/Te ratio increases. According to XRD patterns of samples thermally treated at either lower (215 °C) or higher (265 °C) temperature, with the Se/Te ratio increasing, the dominant precipitated crystals suffer an evolution from AsTe to Ag2Te and finally to the AgAsSe2 semiconductor phase, consistent with the variation trend of Raman spectra. In terms of the structural similarity principle, we thus suppose that the formation of structural units similar to AgAsSe2 semiconductor crystals inversely increases the conductivity of glasses, realizing the mutual benefits of the improved thermal stability and increased conductivity of chalcogenide glasses.
The local structures of amorphous As40Se60, As40Se30S30, As33.3Se33.3S33.4 chalcogenide glass semiconductors have been studied by neutron diffraction and Raman scattering methods. The neutron diffraction data-sets were modeled by Reverse Monte Carlo (RMC) simulation technique. Several first and second neighbour distances, coordination numbers and bond-angle distributions have been calculated. It is established that the first neighbour atomic distances are overlapping at three characteristic distances, namely the SS and SeS are centered at 2.2(5) Å, while the AsS and SeSe are centered at 2.35 Å, the AsAs and AsSe are centered at 2.4(5) Å. The average coordination numbers in As40Se60 (ZAs = 3.03; ZSe = 2.02) and As40Se30S30 (ZAs = 3; ZSe = 2.07; ZS = 2) compositions were determined and found to be consistent with, “8-N” rule. The slight deviations from this rule is discovered in case of As33.3Se33.3S33.4 (ZAs = 3.07; ZSe = 2.09; ZS = 1.95) composition. The main role in the formation of medium range order belongs to SeSe bonds. It has been identified that the replacement of Se with S atoms causes a slight change in coordination numbers. The similarity of θSeAsSe and θAsSeAs bond angle distributions suggest that S atoms have a similar role in the structure formation as Se atoms. The RMC models highlighted a glassy network built-up from AsSe3 trigonal bipyramids, in all binary and ternary samples.
In the present work, we report the effect of Te deposition onto As2Se3
film which affects the optical properties. The Te/As2Se3
film was illuminated with 532 nm laser to study the photo induced diffusion. The prepared As2Se3, Te/As2Se3
films were characterized by X-ray diffraction which show a completely amorphous nature. On the basis of optical transmission data carried out by Fourier Transform infrared Spectroscopy, a non direct transition was found for these films. The optical bandgap is found to be decreased with Te deposition and photo darkening phenomena is observed for the diffused film. The change in the optical constants are also supported by the corresponding change in different types of bonds which are being analyzed by X-ray photoelectron spectroscopy.
Neutron and high-energy X-ray diffraction measurements have been performed on As40Se60 and As40Se50Te10 glasses. Both the traditional Fourier transformation technique and the reverse Monte Carlo (RMC) simulation of the experimental data have been applied to model the 3-dimensional atomic configurations. From the analysis of the partial atomic correlation functions and structure factors the first and second neighbour distances, coordination numbers and bond-angle distributions were calculated. It is established that substitution of Se by Te does not change the basic glassy network structure. For the As-Se bonding is revealed that the first neighbour distance is at 2.42 Å, the average coordination numbers are CNAsSe=2.6±0.1 and CNSeAs=1.8±0.1 atoms and the three-atom-bond angle for , configurations is 95°, the same value within limit of error, as obtained from RMC calculations.
A new neutron powder diffractometer with high counting efficiency was put into operation at the refurbished 10 MW Budapest research reactor in 1994. For data collection linear position sensitive 3He detector system is used. The detector assembly is mounted on the diffractometer arm and it spans a scattering angle range of 28°. The entire diffraction spectra can be measured in four steps. The characteristic features of the diffractometer is given and its perfomance is illustrated.
A summary is given of the partial structure factors that have been measured for liquids and glasses in the Ge–Se binary system by using diffraction methods. Information is presented on the pair correlation functions describing the atomic species and use is made of the Bhatia–Thornton formalism to separate those pair correlation functions describing the system topology from those that describe the chemical ordering. The information made available by the measured Bhatia–Thornton partial structure factors on the thermodynamic properties of Ge–Se mixtures is briefly summarized. The properties of the network structures formed in liquid and glassy Ge–Se compounds are investigated as a function of composition, temperature and pressure. For GeSe2 at ambient pressure it is shown that the so-called first sharp diffraction peak, which appears in the measured diffraction patterns at a small scattering wavevector value of ≈1Å−1 and which is associated primarily with Ge–Ge correlations, does account for discernable features of the observed intermediate range order in both the liquid and glassy phase. The first sharp diffraction peak in the measured Ge–Ge partial structure factor for both phases is described by comparable parameters suggesting communality in the underlying intermediate range order which survives the glass transition. Homopolar bonds are found to be a feature in the structure of liquid GeSe and both liquid and glassy GeSe2 with Ge–Ge and Se–Se distances in the ranges 2.33(3)–2.42(2) and 2.30(2)–2.34(2) Å, respectively.
This paper reports optical properties of amorphous chalcogenide thin films of As2Se3 of different thicknesses 2000-6800 Å. The transmittance and reflectance of thin films were measured in the wavelength range 500-1000 nm. It was found that the optical band gap increases with film thickness. Variation of refractive index n and extinction coefficient k with thickness have been studied to analyze optical efficiency of the As2Se3 thin films. The dielectric behavior of the films has also been studied and high frequency dielectric constants \varepsiloninfty has been estimated as a function of thickness of films.
The effect of successive annealing illumination cycles on the structural and optical properties of wedge-shaped As50Se50 amorphous chalcogenide thin films, has been studied. It is observed that illumination increases the thickness and shrinks the bandgap. Annealing of the chalcogenide films, before or after illumination, decreases the thickness. However, although annealing after illumination increases the bandgap, when this treatment is carried out upon the as-evaporated films, the bandgap decreases. The photostructural changes have been explained in terms of two different mechanisms, which can coexist. One of them involving the repulsion and slip motion of the 2D structural layers comprising the pyramidal' network, as a consequence of the negative charging of these structural layers, by electron accumulation in conduction-band tails, and the other, involving the As4Se4 molecules, typical of thermally evaporated As-rich chalcogenides films, and forming particularly the crystalline form of medium-thickness (1+2 %m) AssoSe50 films.
Variable angle spectroscopic ellipsometry (VASE) was employed to study the optical properties of As33 S67-x Sex (x=0, 17, 33.5, 50, and 67 at. %) bulk glasses in the UV-vis-NIR (near infrared) spectral region for photon energies from 0.54 to 4.13 eV (photon wavelengths from 2300 to 300 nm). For data analysis, we employed Tauc-Lorentz (TL) dispersion model in the entire measured near bandgap spectral region and standard Cauchy dispersion model in the spectral region below the bandgap. With increasing Se content (x) in the bulk glass, we observed a linear decrease in optical bandgap energy Egopt from 2.52±0.02 eV for As33 S67 to 1.75±0.01 eV for As33 Se67 and linear increase in refractive index nTL in the NIR spectral region, e.g., at 0.80 eV from 2.327 for As33 S67 to 2.758 for As33 Se67. The amplitude A decreased with increasing Se content. The peak transition energy E0 and broadening C had a maximum value for x=33.5 at. % and systematically decreased for higher S or Se content in glasses. Our study showed that TL model is suitable to describe dielectric functions of studied chalcogenide bulk glasses in the broad spectral region. The bulk glasses had a higher refractive index compared to thin films of corresponding composition. The bulk glasses with high S content had higher value of optical bandgap energy than was previously reported for thin films. The optical bandgap energy of glasses with higher Se content was very similar to the thin films
Modern materials and their properties are of-ten characterized by varying degrees of disorder. Routine crystallographic structure solution only reveals the average structure. The study of Bragg and diffuse scattering yields the local atomic arrangements holding the key to under-standing increasingly complex materials. In this paper we review the pair distribution function technique used to un-ravel the local structure. We aim to give a practical over-view and make this method easily accessible to the wider scientific community.
Compared to oxide-based glasses, vitreous materials involving chalcogens form a rather new family of glasses which have received attention, mainly because of their transmission in the mid-infrared. Indeed as low phonon compounds, these heavy-anion glasses allow the fabrication of molded optics for infrared cameras as well as infrared fibers operating in a large spectral range. These waveguides, when correctly tapered, allows the development of a new generation of sensitive evanescent-wave optical sensors which have been used for biomedical applications. Here we will focus on the spectral analysis of biomolecules present in human lung cells by measuring their infrared signatures. Because they contain heavy polarizable anions as well as lone-pair electrons, these glasses exhibit very large non-linear properties compared to silica and are candidates for fast optical switching and signal regeneration in telecom. Due to the technological interest in chalcogenide glasses, more information is needed on their structural organization and 77Se NMR spectroscopy appears to be a useful tool for checking the local environment of the Se atoms.
The relaxation of persistent infrared spectral holes burned in the SeH vibrational absorption band at 1.5 K is studied for ten glass compositions in the Ge–As–Se system. It is found that the dominant spectral hole relaxation rate increases by over three orders of magnitude as the average atomic coordination number varies from 2.0 to 2.8. Over the composition range studied, the quantitative form of the non-exponential hole relaxation depends solely on the average coordination number, independent of chemical composition.
The paper presents a brief review of optical properties of infrared optical fibers based on chalcogenide glass materials. The most representative results on optical transmission of chalcogenide glasses used for fabrication of IR fibers as well as photo-induced absorption features in chalcogenide glass fibers are presented.
IntroductionShort-Range-Order (SRO) EffectsMedium-Range-Order (MRO) EffectsLong-Range-Order (LRO) EffectsConclusion
References
The IR optical transmission spectra in the 4000-1000 cm-1 (2.5-10 mum) region in the chalcogenide glasses (ChG) of the ternary Ge-Sb-S system of stoichiometric Sb2S3-GeS2 and non-stoichiometric Sb2S3-Ge2S3 compositions are studied. The compositional dependences of the measured IR spectra connected with influence of O-, H- and C-based absorbed impurites are analyzed.
As potential candidates for photonic devices, non-linear materials and coatings, 22 glasses in the TeO2–WO3–PbO system have been formulated and prepared by conventional melting at temperatures ranging between 710 and 750°C. The glass forming area has been determined for a wide region of the corresponding ternary diagram. Structural characterisation of the glasses was conducted through FTIR spectrometry and the variation of density values, which allowed calculation of the glass molar volume and the oxygen molar volume. UV–VIS spectra were recorded to determine optical absorption/transmission and energy gap values. Likewise, such results were correlated with the glasses composition and their ability for optical materials. DTA curves yielded data of transition temperature (Tg), onset crystallisation temperature (Tc) and the thermal stability range of glasses. Crystalline phases formed in devitrified and partially devitrified glasses were detected by X-ray diffraction. The properties and structural features of glasses were discussed in terms of their relative proportion of former/modifier oxides. The main glass former oxide is TeO2, which arranges [TeO4] groups with tetrahedral coordination, while PbO plays as glass modifier oxide. Tungsten oxide is incorporated as network former, alternating with TeO2 and forming mixed linkages Te–O–W and W–O–W. WO3 is the component that contributes most to increase the glass transition temperature, and to decrease both the oxygen molar volume and the thermal expansion coefficient.
The radial distribution function (RDF) of As30Se70−xSnx amorphous films was obtained by X-ray diffraction. Depending on the composition and preparing conditions, the short-range order of the melt-quenched, and thermally evaporated As30Se70−xSnx (x=0, 3at.%) is described. Structural parameters such as interatomic distances and bond angles were derived and proposed as a good statistical description of the glasses under study. Both the disorder network structure of the glass matrix and the transport properties have been studied according to the chemical properties of Sn as a doping element. The activation energies calculated from dc conductivity is obtained. The effect of composition and average coordination number Nc on the number of topological constraints Ncon, the number of lone-pair electrons L, the mean atomic volume Va and the glass transition temperature Tg have been studied, in the light of recent model proposed for covalent random network. The occurrence of this dependence leads to the conclusion that Sn has a marked effect on the electronic state of the host glass.
The short range structure analysis of (1−x)As2Se3–xAg2Se (x=0.05–0.30) glasses were studied by the time-of-flight (TOF) neutron diffraction method, and the effects of Ag2Se addition on the network structure of AsSe3 trigonal pyramid were investigated.The As–Se and Se–Se distances of the AsSe3 trigonal pyramids in As2Se3–Ag2Se glasses were at 2.45–2.54 and 3.72–3.86Å, respectively, and thus the bond angles of ∠Se–As–Se for the AsSe3 trigonal pyramids in these glasses were calculated to be about 99.0°. These results indicate the existence of AsSe3 trigonal pyramid structure in these glasses, but the shape was not as symmetrical as in crystalline As2Se3.
The pair distribution functions G(r)’s of As2S3 and As2Se3 glasses were obtained from the structure factors S(Q)’s. The structural parameters were refined by applying the correlation method in the (Q,Q·i(Q)) space. Although the structural parameters by PND were somewhat different from those by XRD, the peak shape in PND was clearer than in XRD. The local structure of the glasses was similar to that of orpiment (As2S3 crystal) with AsS3 pyramids. However, the nearest neighbor distances of As–S pair were 2.29Å in PND, 2.27Å in XRD, and 2.25Å (average value of As–S bonds in crystal), implying the little expansion of AsS3-type pyramids and the variation in linkage of pyramids.
A comparison of the known structural data, with our quantum-chemical results for a-Se, leads to the conclusion that a neutral four-valence state, Se40, represents the lowest-energy (0.4eV) defect, whose concentration is about 10% in the glass and greater in the melt. These results are expanded to other substances with the conclusion that the ability of a chemical bond system to generate low-energy network-linking alternative bonds (or ‘defects’) is a key property that distinguishes a group of glass-forming substances.
Refractive-index dispersion data below the interband absorption edge in more than 100 widely different solids and liquids are analyzed using a single-effective-oscillator fit of the form n2-1=EdE0/(E02-ℏ2ω2), where ℏω is the photon energy, E0 is the single oscillator energy, and Ed is the dispersion energy. The parameter Ed, which is a measure of the strength of interband optical transitions, is found to obey the simple empirical relationship Ed=βNcZaNe, where Nc is the coordination number of the cation nearest neighbor to the anion, Za is the formal chemical valency of the anion, Ne is the effective number of valence electrons per anion (usually Ne=8), and β is essentially two-valued, taking on the "ionic" value βi=0.26±0.04 eV for halides and most oxides, and the "covalent" value βc=0.37±0.05 eV for the tetrahedrally bonded ANB8-N zinc-blende- and diamond-type structures, as well as for scheelite-structure oxides and some iodates and carbonates. Wurtzite-structure crystals form a transitional group between ionic and covalent crystal classes. Experimentally, it is also found that Ed does not depend significantly on either the bandgap or the volume density of valence electrons. The experimental results are related to the fundamental ε2 spectrum via appropriately defined moment integrals. It is found, using relationships between moment integrals, that for a particularly simple choice of a model ε2 spectrum, viz., constant optical-frequency conductivity with high- and low-frequency cutoffs, the bandgap parameter Ea in the high-frequency sum rule introduced by Hopfield provides the connection between the single-oscillator parameters (E0,Ed) and the Phillips static-dielectric-constant parameters (Eg,ℏωp), i.e., (ℏωp)2=EaEd and Eg2=EaE0. Finally, it is suggested that the observed dependence of Ed on coordination number and valency implies that an understanding of refractive-index behavior may lie in a localized molecular theory of optical transitions.
We have developed a new technique, based on the standard Monte Carlo simulation method with Markov chain sampling, in which a set of three dimensional particle configurations are generated that are consistent with the experimentally measured structure factor. A(Q), and radial distribution function, g(r), of a liquid or other disordered system. Consistency is determined by a standard χ2 test using the experimental errors. No input potential is required, we present initial results for liquid argon. Since the technique can work directly from the structure factor it promises to be useful for modelling the structures of glasses or amorphous materials. It also has other advantages in multicomponent systems and as a tool for experimental data analysis.
Optical properties and conductivity of glassy (As2Se3)3−x(As2Te3)x were studied for 0 ≤ x ≤ 3. The films of the above mentioned compound were prepared by thermal evaporation with thickness of about 250 nm. The optical-absorption edge is described and calculated using the non-direct transition model and the optical band gap is found to be in the range of 0.92 to 1.84 eV. While, the width of the band gap tail exhibits opposite behaviour and is found to be in the range of 0.157 to 0.061 eV, this behaviour is believed to be associated with cohesive energy and average coordination number. The conductivity measurement on the thin films is reported in the temperature range from 280 to 190 K. The conduction that occurs in this low-temperature range is due to variable range hopping in the band tails of localized states, which is in reasonable agreement with Mott's condition of variable range hopping conduction. Some parameters such as coordination number, molar volume and theoretical glass transition temperature were calculated and discussed in the light of the topological bonding structure.
Since the first edition of this highly successful book the field saw many great developments both in experimental and theoretical studies of electrical properties of non-crystalline solids. It became necessary to rewrite nearly the whole book, while the aims of the second edition remained the same: to set out the theoretical concepts, to test them by comparison with experiment for a wide variety of phenomena, and to apply them to non-crystalline materials. Sir Nevill Mott shared the 1977 Nobel Prize for Physics, awarded for his research work in this field. The reissue of this book as part of the Oxford Classic Texts in the Physical Sciences is a reprint of the second edition which was published in 1979.
We develop model interaction potentials for the binary As–Se system using ab initio molecular simulations and a cluster expansion technique. These potentials are used with classical Monte Carlo simulations to characterize the structure of As2Se3, AsSe2, and AsSe glasses. Finally, we compute the fraction of soft modes in the As–Se system as a function of average coordination number. The results show evidence of a rigidity percolation threshold at an average coordination number between 2.3 and 2.4.
The structure of As3Se5Te2 infrared optical glass was investigated by X-ray and neutron diffraction as well as extended X-ray absorption fine structure measurements at the As-, Se- and Te K-edges. The five datasets were modelled simultaneously by the reverse Monte Carlo simulation technique. Experimental data could be fitted satisfactorily by allowing As–Se, As–Te and Se–Te bonds only. It was revealed that the affinity of As is much higher to Se than to Te. The nearest As–Se distance is similar to that found in other vitreous As–Se based alloys, while the As–Te bond length is 0.02–0.04 Å shorter in As3Se5Te2 than in binary As–Te glasses.
Some resolved solid state 77Se NMR spectra are presented in the AsxSe1−x and GexSe1−x glass families at ambient temperature. Three line positions are observed in the arsenic–selenium network assigned to Se–Se–Se, As–Se–Se and As–Se–As selenium neighborhood, whereas only two types of line are exhibited in germanium–selenium glasses assigned to Se–Se–Se and Ge–Se–Ge selenium atom. The relative intensity measurements of these lines are carried out thanks to the reconstruction of the spectra. Then it appears that a scenario involving a selenium clustering process has to be assumed to describe the GexSe1−x medium range order. On the other hand, a structural model based on AsSe3 pyramids homogeneously distributed in the Se network is in better agreement with the NMR results obtained in AsxSe1−x glasses.
A quantitative study of infrared absorption in the 250–4000 cm−1 region of As2Se3 glasses doped with small amounts of As2O3 or purified by various procedures has been carried out with particular attention to absorption in the wavelength regions of the CO2 and CO lasers. The dependence of the relative intensities of the oxide impurity bands in the 650–1340 cm−1 region on the total amount of As2O3 added to the glass indicates the existence of three distinct oxide-impurity species. A number of higher-frequency impurity bands which are due to the presence of hydrogen in the glass and whose intensities are highly dependent on the glass-melting conditions have been observed and classified. Intrinsic multiphonon absorption in the 400–1100 cm−1 region has been interpreted in terms of combination and overtone bands of the two highest-frequency fundamental vibrational modes. Absorption coefficients of As2Se3 glass in the 920–1090 cm−1 CO2 laser region are limited by intrinsic multiphonon absorption to values of around 10−2 cm−1. The lowest absorption coefficients measured in the 1700–2000 cm−1 CO laser region were around 2 × 10−3 cm−1 and may contain contributions from hydrogen-impurity bands.
The data on the present degree of purity of chalcogenide glasses for fiber optics, on their methods of production and on the
properties, which are essential for their actual application, are generalized. The content of limiting impurities in the best
samples of chalcogenide glasses is 10–100 ppb wt.; of heterophase inclusions with size of about 100 nm is less than 103 cm−3. On the basis of chalcogenide glasses the multimode and single mode optical fibers are produced with technical and operation
characteristics sufficient for a number of actual applications. The minimum optical losses of 12–14 dB/km at 3–5 µm are attained
in the optical fiber from arsenic-sulfide glass. The level of losses in standard chalcogenide optical fibers is 50–300 dB/km
in 2–9 µm spectral range. The factors, affecting the optical absorption of glasses and optical fibers, are analyzed, and the
main directions in further development of chalcogenide glasses as the materials for fiber optics are considered.
a b s t r a c t New quaternary chalcogenide Ge x Sb 40Àx S 50 Te 10 (x = 10, 20 and 27 at.%) and Ge x Sb 40Àx S 55 Te 5 (x = 20 and 27 at.%) glasses have been synthesized and the compositions have been characterized applying prompt gamma-ray activation analyses, neutron diffraction, and material density measurements. Using the experimental data, the basic physical parameters, such as average atomic volume, packing density, com-pactness, average coordination number, number of constrains, average heat of atomization and cohesive energy, of the synthesized glasses are evaluated and the results are discussed in a function of glass composition. Ó 2009 Elsevier B.V. All rights reserved.
The use of hard X-rays (60–300 keV) for diffraction studies of disordered materials has several advantages: higher resolution in direct space, smaller correction terms, removal of truncation effects, the possibility for operating in extreme environments and for direct comparison between X-ray and neutron data. A feasibility study of amorphous silica has been performed at 95 keV, using a wiggler synchrotron beam-line at HASYLAB and a cylindrical sample, 3 mm in diameter. The range of Q between 0.8 and 32 Å−1 was covered. A thorough discussion of the experimental challenges is given. The resulting systematic error intrinsic to the scattering process (not including errors in the form-factors) is found to be of the order of 0.2%. The data have been analyzed in terms of a model of the short-range order. The OSiO bond angle distribution is found to be nearly Gaussian, centered around 109.3(3)° with a rms value of 4.2(3)°. For the SiOSi bond angle, several types of distribution V(α) = V1(α) sin(α) were investigated. Best fits were obtained for rather broad distributions with V having its maximum at 147° and V1 at 180°.
- I Kaban
- W Hoyer
- T Petkova
- P Petkov
- B Beuneu
- A Schöps
- M A Webb
I. Kaban, W. Hoyer, T. Petkova, P. Petkov, B. Beuneu, A. Schöps, M.A. Webb, J.
Ovonic Res. 3 (2007) 67.
- G E Snopatin
- V S Shiryaev
- V G Plotnichenko
- E M Dianov
- M F Churbanov
- D Munoz-Martín
- M A Villegas
- J Gonzalo
- J M Fernandez-Navarro
G.E. Snopatin, V.S. Shiryaev, V.G. Plotnichenko, E.M. Dianov, M.F. Churbanov,
Inorg. Mater. 45 (2009) 1439.
[25] D. Munoz-Martín, M.A. Villegas, J. Gonzalo, J.M. Fernandez-Navarro, J. Eur. Ceram.
Soc. 29 (2009) 2903.
- E Sváb
- Gy
- F Mészáros
- Deák
E. Sváb, Gy. Mészáros, F. Deák, Mater. Sci. Forum 228 (1996) 247 http://www.bnc.
hu/.
- Th
- S J L Proffen
- T Billinge
- D Egami
- Louca
Th. Proffen, S.J.L. Billinge, T. Egami, D. Louca, Z. Kristallogr. 218 (2003) 132.
- S P Love
- A J Sievers
- B L Halfpap
- S M Lindsay
S.P. Love, A.J. Sievers, B.L. Halfpap, S.M. Lindsay, Phys. Rev. Lett. 65 (1990) 1792.
- B Bureau
- J Troles
- M Floch
- F Smektala
- J Lucas
B. Bureau, J. Troles, M. Floch, F. Smektala, J. Lucas, J. Non-Cryst. Solids 326–327
(2003) 58.
- D C Sati
- R Kumar
- R M Mehra
- Turk
D.C. Sati, R. Kumar, R.M. Mehra, Turk. J. Phys. 30 (2006) 519.
- R Prieto-Alcón
- J M González-Leal
- R Jiménez-Garay
- E Márquez
- J Optoelectron
R. Prieto-Alcón, J.M. González-Leal, R. Jiménez-Garay, E. Márquez, J. Optoelectron.
Adv. Mater. 3 (2001) 287.
- A Eungho
- G A Williams
- P C Taylor
- D G Georgiev
- P Boolchand
- B E Schwickert
- R L Cappelletti
A. Eungho, G.A. Williams, P.C. Taylor, D.G. Georgiev, P. Boolchand, B.E. Schwickert,
R.L. Cappelletti, J. Non-Cryst. Solids 299–302 (2002) 958.
- A C Hannon
A.C. Hannon, ISIS Disordered Materials Database, 2006, 2006 http://www.isis.rl.
ac.uk/disordered.
- M R Balboul
- S S Fouad
- S A Fayek
M.R. Balboul, S.S. Fouad, S.A. Fayek, M.S. El-Bana, J. Alloys Cmpd. 460 (2008) 570.
- A Andriesh
- M Iovu
- O Shpotiuka
- I Culeac
- J Optoelectron
A. Andriesh, M. Iovu, O. Shpotiuka, I. Culeac, J. Optoelectron. Adv. Mater. 11
(2009) 2172.
- B Bureau
- X H Zhang
- F Smektala
- J.-L Adam
- J Troles
- H.-L Ma
- C Boussard-Plèdel
- J Lucas
- P Lucas
- D Le Coq
- M R Riley
- J H Simmons
B. Bureau, X.H. Zhang, F. Smektala, J.-L. Adam, J. Troles, H.-L. Ma, C. Boussard-Plèdel, J. Lucas, P. Lucas, D. Le Coq, M.R. Riley, J.H. Simmons, J. Non-Cryst. Solids
345&346 (2004) 276.