Raman spectrum of vitreous As2S3

The spontaneous Stokes and anti-Stokes Raman spectrum of vitreous As₂S₃ is reported. The spectrum was recorded with both HeNe and Ar ion laser excitation lines in the transmission and reflection modes respectively. Spectra were recorded at various temperatures between 20°K and 465°K, the softening temperature of As₂S₃ glass. It is shown conclusively that the quasicontinous scattering observed at low wave number shifts (< 100 cm⁻¹) is real in agreement with the theory of Shuker and Gammon and not an arbitrary background as previously reported. An approximate density of vibrational states is deduced from the polarized Raman spectra.     

Local structure and vibrational spectra of vAs2O3

We discuss the atomic displacements of the optically active vibrational modes of vitreous (v-)As₂O₃ through comparisons of the infrared (ir) and Raman response with the corresponding spectra of the two crystalline polymorphs, claudetite, a layer crystal similar to orpiment, and arsenolite, a molecular crystal based on the As₄O₆ molecule. We conclude from these comparisons that the structure of the glass is composed of $\text{AsO}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ pyramidal units that are corner connected to form a continuous random network. The character of the strong ir and polarized Raman modes in the vitreous form, suggests that the interconnection of these pyramidal units cannot be described by a random distribution of dihedral angles, but rather has peaks at angles characteristic of the different ordering in two-dimensional macromolecular layer basis of claudetite, and the As₄O₆ molecule. The comparisons are extended to v-As₂S₃ and vAs₂Se₃ where we conclude the dihedral angle distributions characteristic of an As₄O₆-like local geometry are less prevalent.     

Raman scattering of the mixed chalcogenide glass system As2SxSe3-x

Polarized room temperature Raman spectra of glassy As₂S_xSe_3-x for 0≦×≦3 have been measured. Spectra for crystalline As₂S₁Se₂ are reported. The polarization and intensity dependence upon composition are consistent with mixed pyramids of composition As₂S_nSe_3-n and preclude phase separation in the glassy system.     

Bulk and impurity infrared absorption in 0.5 As2Se30.5 GeSe2 glass

A study of infrared absorption in the 250–4000 cm^?1 region has been carried out for 0.5 As₂Se₃0.5 GeSe₂ glasses quantitatively doped with oxide impurity. The frequencies of the intrinsic 2- and 3-phonon absorption bands at 490 and 690 cm^?1 correspond well to those predicted from combinations of the high frequency bands in the first order IR and Raman spectra of As₂Se₃ and GeSe₂ glasses.Glasses doped with As₂O₃ exhibit the same oxide impurity absorptionbands as those doped with GeO₂. Unlike As₂Se₃ glass, at impurity concentrations up to 1000 ppm As₂O₃, 0.5 As₂Se₃0.5 GeSe₂ glass exhibits only one major oxide impurity species, characterized by absorption bands at 780 and 1260 cm^?1 and due to oxygen bonded to network Ge. The observation of a much weaker network AsO vibration band at 670 cm^?1 confirms that oxygen bonds preferentially to Ge in this glass. The same minor oxide species appears to determine excess IR absorption at the CO₂ laser wavelength of 10.6 μm in both As₂Se₃ and 0.5 As₂Se₃ 0.5 GeSe₂ glasses. The frequencies and intensities of absorption bands due to hydrogen impurities are also quite comparable for these two materials.     

Raman and infrared spectra of As2Sx chalcogenide glasses with x ⩽ 3

Raman laser and far infrared spectra of As₂S_x glasses with x ? 3 are given and discussed. The purpose of the work is to bring a vibrational spectroscopic contribution to the study of these glasses and to the hypothesis, still under discussion in the literature, that they might be constituted either by a homogeneous vitreous phase or by a mixture of As₂S₃ and As₄S₄.Our results confirm a phase separation, with formation of ß-As₄S₄, below a certain value of x, which depends not only on the preparation method of the samples but also on other factors such as melting time. Laser irradiation of ß-As₄S₄ modifies its Raman spectrum. Such a phenomenon is attributable to two principal factors, either a partial polymerization or formation of a species richer in arsenic. A structural and formation model of the As₂S_x glasses is given, starting from a more generalized structural model of vitreous As₂S₃ which is an accord with the vibrational results and those by the diffraction method in the literature.     

Structure and bonding in the mixed chalcogenide system As2SxSe3−x

⁷⁵As Nuclear Quadrupole Resonance (NQR) lineshape measurements for the amorphous mixed chalcogenide system As₂S_xSe_3?x are reported. The line-shapes are asymmetric and approximately 8 MHz in width (full width at half maximum). The peak resonance frequency is observed to increase approximately linearly with x. The NQR results indicate the presence of mixed As₂(S, Se)₃ pyramidal structural units and are thus not consistent with models that predict the occurrence of anion subsite segregation. NQR measurements performed on crystalline As₂SSe₂ lend support to the structural model proposed for the glasses.     

A photoelectric study on the interface between metallic silver and vitreous As2S3

The electrostatic potential at the AgAs₂S₃ interface was investigated. In the dark, cells of a structure, Ag/As₂S₃/Al behaved like and an electrochemical battery. When light fell onto the cells, short-circuit currents were observed, but their appearancesvaried much, depending on the excitation wavelength and the material of the illuminated electrode. At wavelengths longer than the absorption edge of As₂S₃ glass, photocurrents were characteristic of the polarization current and little influenced by the external field. A model for explaining these findings was proposed on an assumption of an interface reaation between silver and vitreous As₂S₃ in the dark. The interfacial reaction was supposed to accompany a charge separation leading to formation of a potential barrier at the interface.     

Structural, electrical, and optical properties of As2S3-Cu6PS5I nanocomposites

As₂S₃-Cu₆PS₅I nanocomposites are prepared by incorporation of nanocrystals of Cu₆PS₅I superionic conductor in As₂S₃ glass matrix. Their structural studies by scanning electronic microscopy are performed and the electrical conductivity of the nanocomposites is investigated. The temperature dependence of the nanocomposite optical absorption edge is studied; a non-Urbach behaviour of the absorption edge is revealed. Influence of different types of disordering on the optical absorption edge is studied.     

X-ray photoelectron spectroscopic studies on Se/As2S3 and Sb/As2S3 nanomultilayered film

Photoinduced diffusion in Se/As₂S₃ and Sb/As₂S₃ nanomultilayered thin films are studied by X-ray photoelectron spectroscopy (XPS). The XPS measurements show the atomic movements during photoinduced diffusion in Se/As₂S₃ and Sb/As₂S₃ nanomultilayered film. The analysis of experimental data describes the nature of light induced changes in different structural units.     

Properties and structure of glasses in the system AsS

In obtaining the glass, at first, the raw materials were mixed up and melted by using porcelain crucible, but in this case it was found by infra-red absorption method that the glass contains some oxygen impurities. Then a range of glasses was prepared by melting elementary pure As and S in definite proportions in a sealed vacuum tube. The infra-red absorption, molecular volume, molecular refraction, hardness, thermal expansion and viscosity of sample glasses with various compositions were investigated and, additionally, solubility of these glasses into CS₂ was measured. The structure of glasses in the system AsS was studied by X-ray diffraction and a structural model was set up. From the measurements the following conclusions were made. The structure of As₂S₃ glass is a distorted form of the crystalline orpiment structure. With increasing S content above As₂S₃, S is likely to exist in the chain-like form, but when the S content is greater than that in As₂S_8–10, both chain-like and ring type forms co-exist. With decreasing S content below As₂S₃, S between As and As is eliminated and AsAs bonds are formed. Consequently a deformation of layer occurs and an expansion of the layer distance was observed.     

Raman spectroscopy studies of xNa2S+(1−x)B2S3 glasses and polycrystals

The Raman spectra of binary xNa₂S+(1−x)B₂S₃ glasses and polycrystals have been measured for the first time and are used to develop a structural model of the sodium thioborate glasses. The Raman spectra confirm our previous infrared (IR) experimental conclusions that the structure of vitreous (ν-B₂S₃) is comprised of B3(0) groups and six-membered rings. It was also found that as sodium sulfide is added to the glass in the low alkali (x<0.35) glass forming region, the B4 groups are formed at the expense of the B3(0) groups first and then from the six-membered ring groups. The Raman spectra are also consistent with the presence of a pyramidal structural arrangement of B4 groups with trigonally coordinated sulfur atoms. This structure could explain the existence of the super-stoichiometric amounts of B4 groups found using nuclear magnetic resonance (NMR). Glasses in the high alkali region (0.50<x<0.80) progressively change from being comprised of metathioborate rings to being comprised of B3(3) groups. The Raman spectra also confirms the IR spectra which saw no evidence of B3(2) groups in these sodium thioborate glasses.     

Structural study of (As2S3)0.6(GeS2)0.4 glass

(As₂S₃)_0.6(GeS₂)_0.4 glass in non-irradiated and γ-irradiated states has been studied by using high-energy synchrotron X-ray diffraction, extended X-ray absorption fine structure spectroscopy, and positron annihilation lifetime spectroscopy. The experimental results are explained by the local changes around As and Ge atoms upon irradiation. These changes are suggested to involve chemical bonds distortion, formation of defective bonds with wrong coordination, rotation of structural units and appearance of additional free volume in the glass network.     

Structure and properties of glasses in the MI + M2S + (0.1Ga2S3 + 0.9GeS2), M = Li, Na, K and Cs, system

The structure and properties of glasses in the MI + M₂S + (0.1Ga₂S₃ + 0.9GeS₂), M = Li, Na, K and Cs, system were studied using Raman, IR spectroscopy, DSC and density measurements to help better understand the ionic transport in these glasses. The glass forming ranges of these ternary glasses were compared to those of the binary alkali sulfide and germanium sulfide systems. The more extensive glass forming range in the Na₂S system was used to examine the more extensive changes of structure and properties of these glasses as a function of Na₂S content. As expected, non-bridging sulfurs (NBS) form with the addition of alkali sulfide. Unlike their oxide counterparts, however, the alkali sulfide doped glasses appear to support longer-range super-structural units. For example, evidence that the adamantine-like structure exists in the K₂S and Cs₂S modified glasses is found in the Raman spectra of the glasses. The structural role of the alkali iodide addition was also explored since the addition of alkali iodide helps to improve the conductivity. For most of these glasses, as observed in many other oxide glasses, the added MI dissolves interstitially into the glass structure network without changing the alkali sulfide network structure. In 0.6Na₂S + 0.4(0.1Ga₂S₃ + 0.9GeS₂) glasses, however, the added NaI may affect the glass structure as it causes systematic changes in the frequency of the Ge-S network mode as seen in the Raman spectra.     

Preparation of mixed arsenic/antimony chalcogenide glasses and some optical and thermo-physical properties

The preparation of mixed glasses of As₂S_3−xSe_x (x = 0–3) and (1 − y) · As₂S₃y · Sb₂S₃ (y = 0–1) has been carried out by an in situ pouring technique. X-ray diffraction (XRD) was used to confirm the glassy nature of the materials and monitor devitrification. Visible-IR transmission, photoluminescence, refractive index and micro-Raman were measured as a function of composition. Microhardness (MH) and thermal expansion coefficient (TEC) were also measured. Raman peaks in As₂S₃ and As₂Se₃ were observed around 338 cm⁻¹ and 230 cm⁻¹, respectively in this first composition series in which S was replaced by Se. When As was replaced by Sb, in the case of second composition series, the As₂S₃ related Raman peak became broader and shifted to lower wave number, reflecting some structural change/devitrification. MH increased (1.31–1.50 GPa) with Se and Sb content while the TEC was found to decrease (2.5–1.4 × 10⁻⁵/K). The progressive increase in the content of either Se or Sb in As₂S₃ is anticipated to modify bond lengths and bond angles. The combined effect of these structural modifications would change the local structure of the glass forming a more rigid glass network thereby increasing the hardness and decreasing TEC.     

Glass formation, physico-chemical properties, and structure of glasses based on Ga2S3-GeS2-Sb2S3 system

We prepared sulfide glasses based on a Ga₂S₃-GeS₂-Sb₂S₃ system and investigated the compositional dependences of their physico-chemical properties and structure. Additivities were observed for density and refractive index; i.e., these properties were presented by the summation of the contribution from each component. With the increase of Sb₂S₃ content, the density, refractive index, and thermal expansion coefficient increased while the glass transition and softening temperatures decreased, and the short-wavelength absorption edge shifted to the longer wavelength side. These variations are expected from the incorporation of a heavy element (Sb) into the glasses. On the other hand, the replacement of GeS₂ by Ga₂S₃ increased the density and refractive index, and shifted the short-wavelength absorption edge to the longer wavelength side. These variations were explained by the increase of the number densities of the cations with the replacement and the formation of metal-metal bonds. The latter was confirmed from the Raman spectra. We also investigated the effects of Ag₂S incorporation on the optical properties. The incorporation of Ag₂S increased the density and refractive index whereas the position of the short-wavelength absorption edge varied little. These results show the possibility of fabricating an optical waveguide by Ag incorporation into the glasses.     

Nanocrystallites in Bi–As–S system

Bi₂S₃–As₂S₃ composite formation was performed by two methods: by the direct insertion of Bi₂S₃ nanocrystals into a molten As₂S₃ glass which was further solidified and by the crystallization of a rapidly quenched (As₂S₃)_1−x (Bi₂S₃)_x glasses with x = 0.005, 0.01, 0.02 and 0.04 at different conditions. Fine tuning of the annealing of the quenched glass as well as the mixing of nanocrystals in to the molten glass resulted glass-crystalline composites with different amounts and distribution of 20–50 nm large Bi₂S₃ nanocrystals as well as larger, up to few micrometer long, needle-like crystals. Structural and optical investigations support the presence of the Bi₂S₃ crystalline phase in all composites. Optical absorption and the photoconductivity of bulk composite samples follow the structural changes of the structure in the amorphous and amorphous-crystalline phase. In addition, the 290 cm⁻¹ characteristic band in Raman spectra may be used for tracing the formation of the nanocomposites.     

Ac conductivity of Ag-doped bulk,glassy As2S3

Measurements of the electrical conductivity of Ag-doped bulk As₂S₃ glasses have been made as functions of temperature, pressure, frequency and Ag doping level. A Debye-like loss peak was observed near 10⁴ Hz. The frequency of the loss peak is dependent on temperature, pressure and doping level, but these dependences are different from those of the dc conductivity. The ac loss is attributed to the Maxwell-Wagner losses characteristic of inhomogeneous materials. The materials are presumed to be inhomogeneous mixtures of As₂S₃ and Ag₂S. We have also searched unsuccessfully for ac conductance in several bulk chalcogenide glasses.     

Effect of hydrostatic pressure on the elastic moduli of As2S3 and As2Se3 glasses at 195 and 296 K

Velocities of 30 MHz longitudinal and shear ultrasonic waves have been measured in As₂S₃ and As₂Se₃ glasses as a function of hydrostatic pressure up to 1.5 kbar at 195 K and 3 kbar at 296 K. The elastic stiffness moduli are found to have relatively large, positive, pressure dependences which are about the same at both temperatures for both glasses. This behavior is attributed to the weakness of bonding between layers comprised of AsS₃ and AsS₃ pyramids.Inspection of data for a variety of glasses reveals a correlation between the value of C_L/3C_T and whether the elastic moduli are increased or decreased by pressure. (C_L is the longitudinal modulus and C_T the shear modulus.)Using the pressure dependences of the elastic moduli obtained in the present work, it is found that volume change is responsible for most of the temperature dependences of the moduli. In addition elastic gammas are obtained which are consistent with thermal Grüneisen gammas at 12 K. The pressure dependence of the volume of As₂S₃ glass at 296 K is calculated using the present results in the Murnagham equation. Agreement with volumetric data of Weir is obtained.     

Structure and physical properties of the glassy As2S3Gex system

Spectroscopical and structural investigations directly reveal the presence of those structural units which were predicted by Myuller and coworkers to form the continuous network of As-S-Ge glasses. After refining Myuller's model to some extent, the variation with x of several physical properties (density, microhardness, electrical dark conductivity, photoconductivity, optical gap and first-neighbour coordination) in the whole series of As₂S₃Ge_x glasses can be either understood qualitatively or even calculated quantitatively with the aid of additivity laws.     

Intrinsic and impurity infrared absorption in As2Se3 glass

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.