Average Single Bond Energy Research Articles

Improvement in spectral range of Sb 2 Se 3 absorption layer on Bi addition

Antimony selenide (Sb 2 Se 3) is a versatile material used in solar cells. The alteration in the physical properties of Sb 2 Se 3 alloys on Bi addition has been analysed. (Sb 2 Se 3)100-x Bi x (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2) system has been studied to examine the structural alterations by computing physical parameters. The increase in parameters, i.e., average coordination number 〈Z〉, total number of constraints per atoms (N c ), and crosslinking density (D cl ) reflect an increase in rigidity of the Sb 2 Se 3 on Bi incorporation. The computed band gap decreases on Bi addition, from 1.095 eV to 1.079 eV, indicating an approximate increase in absorption wavelength from 1132.42 nm to 1149.21 nm. An increase in rigidity reflects reduction in defect states decreasing the recombination rate within absorption layer. There are variations in cohesive energy, electronegativity, and average single-bond energy. The study reveals that this composition can be utilized to develop novel solar absorber layer materials.

Impact of Ag concentration in As-S-Se chalcogenide on physical, topological and resistive switching properties

Physical properties of quaternary chalcogenide Agx(As40S30Se30)100-x, glasses were analyzed. Synthesis of the studied samples x = 6 - 9 at.% Ag was performed by melt quenching in cascade regime of heating. X-ray diffraction analysis verified amorphous character of the synthesized samples. Morphological characterization was carried out using a scanning electron microscopy, and energy-dispersive X-ray mapping. The obtained results show that the density of the system increases upon silver incorporation in the glassy As40S30Se30 matrix, which is manifested through decrease of free volume percentage. Assessment of various physical and topological properties of prepared series of chalcogenide materials was done using theoretical models available in the literature. Specifically, compactness, average coordination number, constraint parameters, cross-linking density, floppy modes, number of lone–pair electrons are analyzed with addition of Ag atoms in the As40S30Se30 matrix. Average single bond energy and the mean bond energy were also discussed. The chemical bond approach model was used to study the cohesive energy of the studied Ag-containing As-S-Se samples. It is found that all studied parameters are dependent upon silver concentrations. Finally, the room-temperature memristive characteristics and compositional dependence on resistive switching properties in a wide range of Ag concentrations were examined in this paper.

Structure of lithium tellurite and vanadium lithium tellurite glasses by high-energy X-ray and neutron diffraction.

xLi2O-(100 - x)TeO2 (x = 20 and 25 mol%) and xV2O5-(25 - x)Li2O-75TeO2 (x = 1, 2, 3, 4 and 5 mol%) glasses were prepared by melt-quenching and their thermal and structural properties were characterized by differential scanning calorimetry, Raman spectroscopy, high-energy X-ray diffraction and neutron diffraction and reverse Monte Carlo (RMC) simulations. The glass transition temperature increases steadily with an increase in V2O5 mol% in lithium tellurite glasses due to an increase in the average single bond energy of the glass network. The X-ray and neutron diffraction structure factors were modelled by RMC technique and the Te-O distributions show the first peak in the range 1.85-1.90 Å, with V-O = 1.75-1.95 Å, Li-O = 1.85-2.15 Å and O-O = 2.70-2.80 Å. The average Te-O coordination number decreases with an increase in Li2O mol% in lithium tellurite glasses, and the V-O coordination decreases from 5.12 to 3.81 with an increase in V2O5 concentration in vanadium lithium tellurite glasses. The O-Te-O, O-V-O, O-Li-O and O-O-O linkages have maxima in the ranges 86°-89°, 82°-87°, 80°-85° and at 59o, respectively. The structural analysis of tellurite glasses reveal significant short-range and medium-range disorder due to the existence of a wide range of Te-O and Te-Te distances in the first coordination shell.

Effect of Sn Incorporation on Physical Parameters of Sb-Se Glassy System

The rationale of this study is to investigate band gap tailoring of Sb-Se-Sn chalcogenide glasses. This study has been accompanied by the assessment of various theoretical parameters such as average co-ordination number, Lone-pair of electrons, number of constraints, average heat of atomization, mean bond energy and glass transition temperature. It has been observed that almost all these physical parameters have been enhanced with the increase in tin (Sn) content except Lone-pair of electrons. The number of lone-pair electrons has been decreased with the increase in Sn content. The glass transition temperature has been observed to increase due to the addition of Sn atom in the Se-Sb glassy system. The band gap is decreasing with increase in Sn content due to overall decrease in the average single bond energy of the Sb-Se-Sn glassy system.

On the structural and thermophysical study of Pb-doped Se-Te-In nanochalcogenide alloys

ABSTRACT Pb additive nanochalcogenide materials are becoming well-known materials in modern optoelectronics. In this paper, multicomponent Se-Te-In-Pb nanochalcogenide alloys are prepared using melt-quenching technique. The physical and submicron structural features of investigated system are reported and discussed. Characteristic peaks in x-ray spectra signify nanorange of each sample under investigation validated by FESEM and HRTEM. Influence of Pb content on examined composition has been deliberated with respect to their physical characterization namely average coordination number (<r>), mean bond energy (<E>), cross-linking density (X), lone-pair electrons (L), fraction of floppy modes (f), constraints (Nc ), electronegativity (χ), cohesive energy (CE), glass transition temperature (Tg ), and heat of atomization (Hs ). It is realized that addition of Pb content, enhanced Nc, X, and <r>. Whereas, <E>, L, f, χ, CE, Tg , and Hs decrease with Pb addition. Cohesive energy is analyzed through chemical-bond approach. Tg is estimated by Tichy-Ticha and Lankhorst approaches and are found in consistent with experimental results. The band gap of investigated system has been calculated theoretically by Shimakawa’s relation and deduced results are analyzed through cohesive energy, electronegativity, and average single-bond energy. Also the compositional dependence of experimentally derived optical band gap has been analyzed and discussed.

Study of amorphous Sn–Se–Bi–Te semiconducting materials at an average coordination number = 2.4

Amorphous chalcogenide materials are of great importance owing to their excellent properties in infrared and thermoelectrics. A complex system of (SnSe4)95-x(Bi2Te3)5+x (x = 0, 5, 15, 25, 35, 45 at%) chalcogenide materials have been synthesized. A semi-empirical approach has been employed to study the various physical parameters corresponding to the synthesized samples. All the compositions correspond to an average coordination number 〈r〉 = 2.4. Structural, morphological and elemental studies using XRD, FESEM, and EDS respectively have been performed for all the compositions. The density of the system increases with the addition of Bi2Te3 replacing SnSe4 in the system. The calculations of free volume percentage show an increase with increasing Bi2Te3 content. The semi-empirical energy gap values show a decrease from 1.57 eV to 1.04 eV. This decrease in energy gap values is well supported by a decrease in average single bond energy. The high percentage covalent character above the benchmark supports the glass forming ability. The glass transition temperature is determined from Tichy-Ticha approach and shows an increase with increasing x at%.

Topological behavior and glassy framework of GeTeSeGa chalcogenide glasses

Te-based chalcogenide glasses own the most comprehensive infrared window among amorphous materials and have far-infrared applications such as CO2 detection. Nevertheless, the glass forming ability and thermal stability decrease for higher Te content chalcogenide glasses. Here, we report the effect of Ga addition on Te-based chalcogenide glasses by presuming that the addition of Ga may develop the configurational disorder and hence may improve the glass forming ability and thermal stability. Ge10Te80Se10-xGax (x = 0, 2, 4, 6, 8, 10 at %) bulk chalcogenide glassy alloys have been synthesized via melt quench technique. The role of Ga is studied through a semi-empirical approach. The result shows that the system is in rigid mode (total number of mechanical constraints >3). The density of the system shows an increase which is further supported by a decrease in free volume percentage. Mean bond energy and glass transition temperature have also been investigated. The energy gap shows a decrease with increase in Ga at. % and the behavior are correlated with the decrease in average single bond energy (72.7 kJ/mol to 69.7 kJ/mol) and electronegativity (2.14–2.06) of the system. From the results of covalent character (>90%), it is estimated that the compositions may be used to form stable glasses, which may be helpful in the development of an infrared system.

Optical investigation of vacuum evaporated Se80−xTe20Sbx (x = 0, 6, 12) amorphous thin films

Amorphous thin films of Se80−xTe20Sbx (x=0, 6, 12) chalcogenide glasses has been deposited onto pre-cleaned glass substrate using thermal evaporation technique under a vacuum of 10−5Torr. The absorption and transmission spectra of these thin films have been recorded using UV spectrophotometer in the spectral range 400–2500nm at room temperature. Swanepoel envelope method has been employed to obtain film thickness and optical constants such as refractive index, extinction coefficient and dielectric constant. The optical band gap of the samples has been calculated using Tauc relation. The study reveals that optical band gap decreases on increase in Sb content. This is due to decrease in average single bond energy calculated using chemical bond approach. The values of urbach energy has also been computed to support the above observation. Variation of refractive index has also been studies in terms of wavelength and energy using WDD model and values of single oscillator energy and dispersion energy has been obtained.

Glass-forming ability and rigidity percolation in SeTePb lone-pair semiconductors

Correlating the various physical parameters of known semiconductors and pointing the properties of new ones, a number of parameters have been employed recently with different levels of success. Taking this into account an attempt has been made to correlate the physical properties of Pb-doped Se–Te lone-pair semiconductors. The small band gap and large Bohr radius of lead (Pb) containing lone-pair semiconductors assist them with specific optical, electrical and thermal properties. The various physical parameters like number of constraints, lone pair of electron, heat of atomization, density, compactness, free volume percentage have been analyzed in terms of mean coordination number for (Se90Te10)100−x Pb x (x = 0, 4, 8, 12, 16, 20, 24). The band gap for the compositions has been determined theoretically, and the obtained results are very well explained in terms of cohesive energy, electronegativity and average single bond energy.

Correlation of some opto-electrical properties of Se–Te–Sn glassy semiconductors with the average single bond energy and the average electronegativity

Studies of some electrical and optical properties of Se90Te10−xSnx (x = 2, 4, 6 and 8) glassy alloys, in bulk and thin film forms, were performed at room temperature. Pellets of a diameter ∼1.3 cm and different thicknesses ranging from 0.04 cm to 0.06 cm of these compositions were obtained. Measurements of I–V characteristics of these pellets have been carried out at room temperature. Ohmic behavior was observed in low voltage range (0–5 V) while a deviation from ohmic towards non-ohmic behavior was observed at higher voltage range (6–20 V). This deviation can be interpreted in terms of space charge limited conduction (SCLC) mechanism whereas the plots of ln (I/V) vs. V were found to be straight lines. The room temperature DC electrical conductivity σDC has been calculated from the linear region of the I–V characteristic curves. In addition, thin films of a thickness ∼1100 Å of the alloys under investigation were prepared and the optical band gap Eopt of these thin films is obtained from Tauc plot (αhν)2 = B (hν − Eopt) after the determination of the absorption coefficient α over a wavelengths range of 440–1100 nm. Analysis of the experimental data shows that σDC increases while Eopt decreases with increasing Sn content. These results are explained in terms of the decrease in the values of average single bond energy HS/<r> and average electronegativityχm.

Effects of Al3 +, W6 +, Nb5 + and Pb2 + on the structure and properties of borotellurite glasses

The effects of addition of Al3+, W6+, Nb5+ and Pb2+ on the density, thermal, optical properties of borotellurite glasses and on the B–O, Te–O and Al–O speciation are studied. Density maximizes in glasses containing Pb2+ and minimizes in glasses with Al3+. The optical absorption cut-off wavelength increases with the addition of heavy metal ions while Al3+ shifts it to lower wavelengths. W6+, Nb5+ and Al3+ strengthen the borotellurite network and enhance the glass transition temperatures, however Pb2+ decreases it. The glass transition temperature is a linear function of the average single bond energy of the glass network. 11B Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared studies found that the BO4 structural units are unstable in the presence of Al3+, W6+ and Nb5+, however Pb2+ has an opposite effect and promotes the formation of BO4. 27Al MAS NMR showed that alumino-borotellurite glasses contain AlO6, AlO5 and AlO4 structural units whose relative concentrations depend on alumina mol%. Raman spectroscopy was used to determine Te–O coordination in glasses, the later decreased on adding metal ions and Al3+ produced a maximum suppression of TeO4 units.

Estimation of some physical characteristics of chalcogenide bulk Cd50S50 − xSex glassy systems

This work reports the determination of many of the physical properties of ternary chalcogenide bulk Cd50S50−xSex (30≤x≤50) glasses as well as the study of their dependence upon the Se-content. Mechanical milling technique was used to get a solid-state solution from elemental powders of Cd, S and Se. The phase formation of Cd–S–Se mixture was obtained by using a high energy ball milling for 48h. The product of the milling process was pressed as pellets using a compressor of pressure about 6.5MPa. The amorphous nature of bulk pellet samples has been checked using X-ray diffraction. It was found that, the values of mass density, molar volume, excess volume, field strength, compactness and the atomic density were increased, whereas the values of polaron radius and the average spacing of Se–Se, average heat of atomization, average single bond energy, mean bond energy, cohesive energy and glass transition temperature were decreased with increasing the Se concentration percent in CdSSe matrix. Heat of atomization was correlated to cohesive energy of the present Cd50S50−xSex glasses. Chemical bond approach model was used to analyze the heat of atomization, the mean bond energy and the glass transition temperature values.

Analysis of chemical ordering and fragility for Ge–Se–In glasses

Decreasing the band gap of a material due to metal impurities has been approved through several studies, and this subject is considered as a major area of interest within the optoelectronic applications. Indium-based chalcogenides have been considered good candidates in nonlinear optics due to their ability to transmit in the infrared region. Hence, Ge18Se82 has been alloyed with In. The nature of the chemical ordering of amorphous samples of Ge18Se82−xInx (x = 0, 2, 4 and 6) have been systematically studied. The aim of present investigation is to understand the role of chemical composition and mean-coordination number in determining their structural and physical properties. The compactness, δ, of alloyed samples has been calculated from their measured densities, and values obtained have been interpreted using the topological model proposed to describe the atomic arrangements in these alloys. The variation of the glass transition temperature, Tg, with the average coordination number, Z, has been investigated. The compositional dependence of the mean atomic volume, Vm, has also been determined. The free volume percentage, FVP, in Ge18Se82−xInx amorphous samples and their fragility indices, m, have been determined to examine the relationship with the mean-coordination number. We have also analyzed the obtained results on the basis of average single bond energy and electronegativity.

Theoretical prediction of physical parameters of GexSb20−x Te80 (x = 11, 13, 15, 17, 19) bulk glassy alloys

Abstract Physical properties of GexSb20−x Te80 (x = 11, 13, 15, 17, 19) bulk glassy alloys are examined theoretically. Lone pair electrons are calculated using an average coordination number (〈r〉) and the number of valence electrons, and are found to decrease with an addition of Ge. Mean bond energy (〈E〉) is proportional to glass transition temperature (Tg) and shows maxima near the chemical threshold. Cohesive energy of the system is calculated using chemical bond approach. A linear relation is found between cohesive energy, band gap (calculated theoretically and confirmed experimentally) and average heat of atomization. All these parameters are increasing with an increase in Ge content. A relation between average single bond energy and photon energy is discussed. Compactness of the structure is measured from the calculated density of the glass. An attempt is made to discuss the results in terms of structure of the glass or equivalently with average coordination number.

Chemical bond approach to optical properties of some flash evaporated Se100−XSbXchalcogenide alloys

Amorphous thin films of Se 100 − X Sb X ( X = 1, 5, 10, 15 and 20) were synthesized by flash evaporation of the premelt quenched bulk samples. The optical properties were investigated from spectrophotometric measurements in the UV-VIS-NIR spectral region using Swanepoel’s standard envelope method and related techniques. The optical band gap energy ( E g opt ) was evaluated from the Wemple-Didomenico (WDD) single oscillator model and Tauc’s extrapolation method in the region where the absorption coefficient, α ≥ 10 4 cm –1 . The observed values of E g opt and oscillator energy E o were found to decrease monotonously with increasing Sb additive. The complex dielectric constant ( e ), Urbach energy ( E u ), optical conductivity ( σ ), plasma frequency ( ω p ) and lattice dielectric constant ( e L ) were deduced for each alloy composition. The complex refractive index ( n ) fitted well to Sellmeier function which can allow extrapolation of n outside the measured spectral range. The observed changes in optical parameters with Sb content were explained on the basis of increased defect states and changes in cohesive energy indicators (average heat of atomization ( H s ), mean coordination number 〈 Z 〉 and average single bond energy (H s /〈Z〉).

Structural and short-range order analysis of glassy system

To understand the effects of structural features and to locate their signatures in the As–Ag–Te glassy system, various properties were studied as a function of average coordination number, 〈 r〉. The structure of the sample is analyzed by X-ray diffraction technique and is found to be crystalline. The d-spacing and the lattice parameters of the samples were calculated. The structural parameters were discussed on the basis of Ag (silver) effect on As–Ag–Te glassy system. Structural investigations on these compositions revealed the polycrystalline nature of compositions with the presence of hexagonal As–Ag–Te phases. Grain size increased with the Ag content and parameters of unit cell are determined. The variations in the mean atomic volume, V, and the glass transition temperature, T g, for glass transition, with composition have been reported. The change in thermal parameters was measured using differential thermal analysis (DTA). The results of the program are in agreement with those of analytical method and realized by binding energy represented by the cohesive energy values. The generalized ‘8- n’ rule was used to estimate the average coordination number. Obtained results were treated in the frame of chemical bond approach. We estimated some of physical parameters viz. mean bond energy, glass transition temperature, cohesive energy, average single bond energy, density, compactness and molar volume of all bulk samples. Our experimental and theoretical results were discussed in light of the topological bonding structure, which involves a hierarchy of correlation ranges in short-range order.

Experimental investigation on some electrical parameters of In 10− xSn xSe 90 ( x = 2, 4, 6, and 8) chalcogenide glasses before and after γ-irradiation

Some electrical parameters of In 10− x Sn x Se 90 ( x = 2, 4, 6, and 8) chalcogenide glasses before and after γ-irradiation, at doses of 8, 16 and 32 kGy, are reported and discussed. I– V measurements, for both un-irradiated and gamma irradiated glasses, have been carried out in the temperature range of 170–290 K for different electric fields. The recorded I– V characteristics reveal that the studied glasses exhibit ohmic and non-ohmic behavior at low and high fields, respectively. Analysis of the experimental data, for un-irradiated and gamma irradiated samples, in the high field range confirms the presence of space charge limited conduction (SCLC) in the glasses under investigation, while conduction mechanism in low temperature region occurs via variable range hopping (VRH) of charge carriers in the band tail of the localized states. The DC conductivity is found to increase with Sn concentration up to 6 at.% of Sn, after which it decreases. The post gamma irradiation conductivity is, in general, improved at moderated doses i.e., 8 and 16 kGy. The density of localized states N( E F), before and after irradiation, is increased with incorporation of Sn up to 6 at.%, after which a drastic decrease is observed to occur. This is attributed to an increase in the average single bond energy of In 2Sn 8Se 90 which decreases the conductivity and the density of localized states for this particular composition. The hopping energy W and hopping distance R hop have also been calculated and their values agree fairly well with the concept of (VRH) model and are in support of our results regarding the behavior of the electrical conductivity.

Optical properties of a-Se 90In 10− x Sn x chalcogenide thin films before and after gamma irradiation

Amorphous Se 90In 10− x Sn x ( x=2, 4, 6, and 8) thin films of thickness 1000 Å were prepared on glass substrates by the thermal evaporation technique. Optical parameters of the films were investigated, in the wavelength range 400–700 nm, before and after irradiation by 4, 8, and 12 kGy doses of γ-ray. The optical absorption coefficient α for as-deposited and gamma irradiated films was calculated from the reflectance R and transmittance T measurements, which were recorded at room temperature. From the knowledge of α, at different wavelengths, the optical band gap E g was calculated for all compositions of Se–In–Sn thin films before and after gamma irradiation. Results indicate that allowed indirect optical transition is predominated in as-deposited and irradiated films. Besides, it is found that the band gap decreases with increasing Sn concentration and this is attributed to the corresponding decrease in the average single bond energy of the films. The band gap, after irradiation at different doses of γ-ray, was found to decrease for all compositions of the studied films. This post-irradiation decrease in the band gap was interpreted in terms of a bond distribution model.