Positron trapping defects in free-volume investigation of Ge–Ga–S–CsCl glasses

Evolution of free-volume positron trapping defects caused by crystallization process in (80GeS₂–20Ga₂S₃)_100−х(СsCl)_x, 0 ≤ x ≤ 15 chalcogenide-chalcohalide glasses was studied by positron annihilation lifetime technique. It is established that CsCl additives in Ge–Ga–S glassy matrix transform defect-related component spectra, indicating that the agglomeration of free-volume voids occurs in initial and crystallized (80GeS₂–20Ga₂S₃)_100−х(СsCl)_x, 0 ≤ x ≤ 10 glasses. Void fragmentation in (80GeS₂–20Ga₂S₃)₈₅(СsCl)₁₅ glass can be associated with loosing of their inner structure. Full crystallization in each of these glasses corresponds to the formation of defect-related voids. These trends are confirmed by positron-positronium decomposition algorithm. It is shown, that CsCl additives result in white shift in the visible regions in transmission spectra. The γ-irradiation of 80GeS₂–20Ga₂S₃ base glass leads to slight long-wavelength shift of the fundamental optical absorption edge and decreasing of transmission speaks in favor of possible formation of additional defects in glasses and their darkening.     

Raman scattering studies of the GeS2-Ga2S3-CsCl glassy system

Room temperature Raman spectra of samples on four serials within GeS₂-Ga₂S₃-CsCl glassy system have been investigated systematically. Based on the analysis of the local coordination surroundings of Cs⁺ ions, the similarities and changes of Raman spectra for glass Ga₂S₃-2CsCl and bridged molecular GaCl₃ were explained successfully. With a profound consideration of the effect of Cs⁺ ions on mixed anion units (GaS_4−xCl_x) and bridged units (Ga₂S_6−xCl_x) and the corresponding micro-structural model, the Raman spectral evolution of the samples within GeS₂-Ga₂S₃-CsCl glassy system was reasonably elucidated.     

Ge-Ga-Cd硫化物玻璃的超快三阶非线性光学性质与结构关系研究

本文采用飞秒时间分辨光学克尔门技术测量了GeS2-Ga2S3-CdS硫化物玻璃体系的超快三阶非线性光学响应，所用激光波长分别为820nm和640nm。?实验结果证明了GeS2-Ga2S3-CdS组分玻璃具有很大的飞秒超快三阶非线性光学响应，另外，其Kerr信号随摩尔组分的不同呈显著变化。通过拉曼光谱结构分析，探讨了此系列硫化物玻璃的三阶非线性光学性质与结构的关系，结果表明构成玻璃网络的四面体结构单元[GeS4]([GaS4])对其超快三阶光学非线性起重要作用。实验还表明了此硫化物玻璃体系的超快三阶非线性不符合半经验的Miller定律。     

Ag–Ge–Se glasses: a vibrational spectroscopy study

Ag_x(Ge_0.25Se_0.75)_100−x glasses with x varying from 0 to 25 have been shown to exhibit a conductivity threshold around x ~8–10. In this work, the structural changes induced by introduction of Ag in Ge₂₅Se₇₅ glass have been investigated using Raman and infra‐red spectroscopies. In ambient conditions, changes are observed in position, width and intensity for vibrations assigned to Ge–Se bonds, showing that the tetrahedral network is relaxed and gains flexibility as Ag is introduced. High pressure experiments on two glasses containing 5 and 25 at.% Ag confirm that Ag‐rich (25%) glasses clearly exhibit higher compressibility than Ag‐poor (5%) glasses. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman and infrared structural investigation of (PbO)x(ZnO)(0.6−x)(P2O5)0.4 glasses

The structure of ternary (PbO)_x(ZnO)_(0.6−x)(P₂O₅)_0.4glasses was investigated using Raman scattering and infrared spectroscopy over the compositional range x = 0–0.6. No significant change of the average chain length composed by PO₄ tetrahedral units with the substitution of zinc for the lead cation was observed. The linewidth and wavenumber variations of the Raman high‐wavenumber bands reflect the Zn/Pb substitution in these glasses and are correlated with the metal–oxygen force constant and local disorder. The infrared reflectivity spectra have been fitted with the four‐parameter dielectric function model. The variation in the 1000–1200 cm⁻¹wavenumber range has been attributed to an increase of the oscillator damping Γ_LO(PO₃)₂₋ as with PbO content vibrations rather than a variation of the chain length. Copyright © 2008 John Wiley & Sons, Ltd.     

Microstructure and crystallization properties of TeO2?PbF2 glasses

The microstructures of (1 − x)(TeO₂)–xPbF₂, (x = 0.1, 0.15, and 0.25 mol) glasses were investigated by using the Raman spectroscopic technique. The effect of compositions on the TeO₂ glass networks and the intensity ratios of the deconvoluted Raman peaks were determined. The results confirm that the addition of modifiers to the glass network former shifts the Raman intensity and the peak wavenumber values for each band in the 167–165, 652–645, and 747–755 cm⁻¹ wavenumber regions. The structural evaluation was recognized from the Raman spectra, with the structural units described as [TeO₃₊₁] polyhedra, [TeO₃] trigonal pyramids, and [TeO₄] trigonal bipyramids for this binary glass system. Heat‐treatment of the samples shows that the metastable crystalline phase of TeO₂ known as γ‐TeO₂ is formed only when the modifier content is 10 mol% in the glass matrix. Transparent glass properties were not realized when the TeO₂ amount was decreased to less than 10 mol% content. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal conductivity of GexSb(As)ySe100‐x‐y glasses measured by Raman scattering spectra

We systematically measured thermal conductivity of Ge_xSb(As)₁₀Se_90−x, Ge_xSb₁₅Se_85−x, and Ge_xSb(As)₂₀Se_80−x chalcogenide glasses by measuring their Stokes and anti‐Stokes Raman scattering spectra and estimating the temperature raised by laser irradiation via the ratio of Stoke and anti‐Stokes scattering cross‐section. We aimed at demonstrating the viability of Raman scattering method for thermal conductivity measurements, and understanding the role of chemical composition in determining thermal conductivity of the chalcogenide glasses. We found that, while the values of the thermal conductivity measured in the paper are in a range from ~0.078 to 1.120 Wm^‐1K^‐1 that are in agreement with those reported data in the literatures, thermal conductivity increases before it reaches a maximum at the glass with chemically stoichiometric composition, and then decreases with increasing Ge content. We ascribed the threshold behavior of the thermal conductivity to the demixing of the structural units like GeSe₂, As₂Se₃ and Sb₂Se₃ from the main glass network. The present study demonstrated that Raman scattering method is simple and easy to measure thermal conductivity of the material. Copyright © 2014 John Wiley & Sons, Ltd.     

Photoinduced transformations in (As1–xBix)2S3 glass observed by Raman spectroscopy

Raman spectra of (As_1–xBi_x)₂S₃ glass samples with x ≤ 0.2 measured at the excitation with above-bandgap (532 nm) laser light at a relatively low power density (P_exc = 4 kW/cm²) clearly confirm the amorphous character, thereby markedly extending the known compositional interval of existence of the (As_1–xBi_x)₂S₃ glass previously known (x ≤ 0.06). Spectra measured at an increased P_exc (40 kW/cm²) reveal a photostructural transformation in the illuminated area of the glass leading to an additional contribution of Bi–S bonds as well as to an increasing number of cage-type As₄S₄ units with homopolar As–As bonds. A number of new features in a broad range up to about 1,000 cm⁻¹, which emerge in the Raman spectra of the (As_1–xBi_x)₂S₃ glasses with high (x ≥ 0.14) Bi content and increase in intensity with the exposure time, are related to a photochemical transformation, namely, oxidation of arsenic and sulphur on the (As_1–xBi_x)₂S₃ glass surface with formation of units containing arsenate AsO₄³⁻ and sulphate SO₄²⁻ ions. These processes are irreversible and occur only in the presence of a sufficient amount of bismuth.     

Influence of the selenium content on thermo-mechanical and optical properties of Ge–Ga–Sb–S chalcogenide glasses

A number of Ge₁₇Ga₄Sb₁₀S_69−xSe_x (x = 0, 15, 30, 45, 60, and 69) chalcogenide glasses have been synthesized by a melt-quenching method to investigate the effect of the Se content on thermo-mechanical and optical properties of these glasses. While it was found that the glass transition temperature (T_g) decreases from 261 to 174 °C with increasing Se contents, crystallization temperature (T_c) peak only be observed in glasses with Se content of x = 45. It was evident from the measurements of structural and physical properties that changes of the glass network bring an apparent impact on the glass properties. Also, the substitution of Se for S in Ge–Ga–Sb glasses can significantly improve the thermal stability against crystallization and broaden the infrared transmission region.     

Structural investigations of GeS2-Ga2S3-CdS chalcogenide glasses using Raman spectroscopy

Raman investigations were carried out for various compositions of chalcogenide glasses in the GeS₂-Ga₂S₃-CdS system. Addition of Ga₂S₃ into GeS₂ results in the formation of metal-metal bonds and edge-shared GaS_4/2 tetrahedra. Ge²⁺ ions may surround [GaS_4/2]¹⁻ tetrahedra acting as charge compensators. Upon the addition of CdS into the GeS₂-Ga₂S₃ system, the number of the metal-metal bonds and edge-shared GaS_4/2 tetrahedra decreases, resulting in the formation of corner-shared tetrahedra with non-bridging sulfurs (NBS). Cd²⁺ ions can be dissolved into the glass network as charge compensators for these NBS and exited few [GaS_4/2]¹⁻ tetrahedra. The high solubility of CdS is ascribed to the dissociation of metal-metal bonds and edge-shared tetrahedra in these Ga-containing glasses.     

Raman spectroscopy of gallium‐ and zinc‐based hydrotalcites

Insight into the unique structure of hydrotalcites (HTs) has been obtained using Raman spectroscopy. Gallium‐containing HTs of formula Zn₄ Ga₂(CO₃)(OH)₁₂ · xH₂O (2:1 ZnGa‐HT), Zn₆ Ga₂(CO₃)(OH)₁₆ · xH₂O (3:1 ZnGa‐HT) and Zn₈ Ga₂(CO₃)(OH)₁₈ · xH₂O (4:1 ZnGa‐HT) have been successfully synthesised and characterised by X‐ray diffraction (XRD) and Raman spectroscopy. The d(003) spacing varies from 7.62 Å for the 2:1 ZnGa‐HT to 7.64 Å for the 3:1 ZnGa‐HT. The 4:1 ZnGa‐HT showed a decrease in the d(003) spacing, compared to the 2:1 and 3:1 compounds. Raman spectroscopy complemented with selected infrared data has been used to characterise the synthesised gallium‐containing HTs. Raman bands observed at around 1050, 1060 and 1067 cm⁻¹ are attributed to the symmetric stretching modes of the (CO₃²⁻) units. Multiple ν₃ (CO₃²⁻) antisymmetric stretching modes are found between 1350 and 1520 cm⁻¹, confirming multiple carbonate species in the HT structure. The splitting of this mode indicates that the carbonate anion is in a perturbed state. Raman bands observed at 710 and 717 cm⁻¹ and assigned to the ν₄ (CO₃²⁻) modes support the concept of multiple carbonate species in the interlayer. Copyright © 2010 John Wiley & Sons, Ltd.     

Er<Superscript>3+</Superscript> as glass structure modifier of Ga–Ge–S chalcogenide system

Er³⁺ clustering phenomenon in Ga–Ge–S chalcogenide system is studied using Raman spectroscopy. The Raman spectra from 10 to 500 cm⁻¹ for glasses (100−y)[15Ga₂S₃–85GeS₂]–yEr₂S₃ (y=0.08−5.00 mol. %) have been analyzed. To reveal the influence of the chemical composition on the glass structure the intensity of the peak corresponding to Ge–Ge (Ga–Ga) homopolar bonds has been examined. The peak intensity increase with Er₂S₃ concentration change in the region 0<C(Er₂S₃)<2 mol. % has been interpreted in terms of the sulphur deficiency in the glass resulting in the formation of S₃Ge–GeS₃ (S₃Ga-GaS₃) structural units. The further increase in concentration beyond 2 mol. % reduces the sulphur deficiency, which can be attributed to the formation of the ternary compound Er₃GaS₆. The structural units Er₃GaS₆ contain a large mol. fraction of Er³⁺ or, in other words, Er³⁺ clusters. The data obtained from the low-frequency Raman spectra (boson band) indicate strong variations of the medium-range order (MRO) in the glasses induced by Er³⁺. The observed behavior of the MRO size (the correlation length) with increasing of Er₂S₃ concentration provides for additional evidence of the Er³⁺ clustering.     

Inelastic light scattering in strontium borate glasses in the systemxSrO.(1−x)B2O3 and (SrCl2) y .[xSrO.(1−y−x)B2O3]1−y

Raman spectra of strontium borate binary glasses in the systemxSrO.(1-x)B₂O₃ forx=0.20, 0.25, 0.30, 0.35, 0.40, and 0.50 and ternary glasses in the system (SrCl₂) _y .[xSrO.(1−y−x)B₂O₃]_1−y fory=0.10, 0.20, 0.30 and 0.40 andx=0.20 and 0.35, are reported. Raman spectra of the glasses show experimental evidence of glass network modifying nature of SrO in borate matrix. SrO causes a change of boron atom coordination number from 3 to 4 resulting in the complex structural groupings comprising of BO₄ and BO₃ units. Strontium cations are not easily accommodated in the glass structure and tend to break up the network at high concentration (x) of SrO, causing non-bridging oxygens. The effect of temperature variation of binary glasses has also been studied. The introduction of SrCl₂ to the binary stronium borate glass causes a large change in intensity of low frequency Raman scattering whereas there is no change in the vibrational dynamics in the high frequency region. The temperature reduced Raman spectra represents true vibrational density of states. Martin-Brenig model developed for the low frequency region has been discussed to obtain the structural correlation range in the glass.     

Raman spectroscopy of gallium‐based hydrotalcites of formula Mg6Ga2(CO3)(OH)16· 4H2O

Insight into the unique structure of hydrotalcites has been obtained using Raman spectroscopy. Gallium‐containing hydrotalcites of formula Mg₄Ga₂(CO₃)(OH)₁₂· 4H₂O (2:1 Ga‐HT) to Mg₈Ga₂(CO₃)(OH)₂₀· 4H₂O (4:1 Ga‐HT) have been successfully synthesized and characterized by X‐ray diffraction and Raman spectroscopy. The d(003) spacing varied from 7.83 Å for the 2:1 hydrotalcite to 8.15 Å for the 3:1 gallium‐containing hydrotalcite. Raman spectroscopy complemented with selected infrared data has been used to characterize the synthesized gallium‐containing hydrotalcites of formula Mg₆Ga₂(CO₃)(OH)₁₆· 4H₂O. Raman bands observed at around 1046, 1048 and 1058 cm⁻¹ are attributed to the symmetric stretching modes of the CO₃²⁻ units. Multiple ν₃ CO₃²⁻ antisymmetric stretching modes are found at around 1346, 1378, 1446, 1464 and 1494 cm⁻¹. The splitting of this mode indicates that the carbonate anion is in a perturbed state. Raman bands observed at 710 and 717 cm⁻¹ assigned to the ν₄ (CO₃²⁻) modes support the concept of multiple carbonate species in the interlayer. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of gamma irradiation on X‐ray absorption and photoelectron spectroscopy of Nd‐doped phosphate glass

X‐ray absorption near‐edge structure (XANES) and X‐ray photoelectron spectroscopy (XPS) of Nd‐doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of the L₃‐edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d_5/2 peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy‐dispersive X‐ray spectroscopy measurements. The ratio of non‐bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.     

Intrinsic nanoscale phase separation of bulk As2S3 glass

Raman scattering on bulk As _x S_{1? x} glasses shows that vibrational modes of As₄S₄ monomer first appear near x = 0.38, and their concentration increases precipitously with increasing x, suggesting that the stoichiometric glass (x = 0.40) is intrinsically phase separated into small As-rich (As₄S₄) and large S-rich clusters. Support for the Raman-active vibrational modes of the orpiment-like and realgar-like nanophases is provided by ab-initio density functional theory calculations on appropriate clusters. Nanoscale phase separation provides a basis for understanding the global maximum in the glass transition temperature T _g near x = 0.40, and the departure from Arrhenius temperature activation of As₂S₃ melt viscosities.     

CsCl effect on the optical properties of the 80GeS2–20Ga2S3 base glass

Optical properties of chalcogenide glasses belonging to the series (80GeS₂–20Ga₂S₃)_100−x (CsCl) _x with x=0;5;10;15;20 were investigated. The linear refractive indices (n ₀) were determined by prism measurements at four wavelengths: 633 nm, 825 nm, 1311 nm, and 1511 nm. Z-scan experiments were performed at 800 nm to measure the non-linear indices (n ₂) and the absorption coefficients (β). CsCl additions in the base glass (80GeS₂–20Ga₂S₃) are characterized by a white shift of the transmission in the visible range and a strong decrease of both n ₀ and n ₂. As the same time, β is also decreasing and this results in a figure of merit FOM=2βλ/n ₂ that remains relatively low at 800 nm, meaning that this series of highly non-linear glasses should be very suitable for optical switching applications at telecommunication wavelengths.     

Thermal stability and crystallization kinetics of Ge–Se–Cd glasses

The effect is reported of varying cadmium concentration on the glass transition, thermal stability and crystallization kinetics of Ge₂₀Se_{80? x} Cd _x (x = 2.5, 5, 7.5 and 10 at. %) glasses. Differential scanning calorimetry results under non-isothermal conditions for the studied glasses are reported and discussed. The values of the glass transition temperature (T_g ) and the peak temperature of crystallization (T_p ) were found to be dependent on heating rate and Cd content. From the heating rate dependence of T_g and T_p , the values of the activation energy for glass transition (E_g ) and the activation energy for crystallization (E_c ) were evaluated and their composition dependence discussed. The thermal stability of the glasses was evaluated using various thermal stability criteria such as ΔT, H_g and S. The stability calculations emphasize that the thermal stability decreases with increasing Cd content.     

Spin-polarised DFT study of cobalt-doped gallium clusters

The structural, electronic and magnetic properties of small gallium clusters doped with Cobalt have been studied using spin-polarised density functional theory. The binding energy per atom, second-order differences of total energies and fragmentation energies of equilibrium geometries of the host Ga_n+1 and doped Ga_nCo (n = 1–12) clusters are computed. Doped clusters are found to be more stable than pure Ga clusters; Ga₃Co, Ga₅Co and Ga₈Co clusters are exceptionally stable. Doping with Co changes the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) gap, and also affects the magnetic moments of clusters.     

Structural studies and Raman spectroscopy of forbidden zone boundary phonons in Ni‐doped ZnO ceramics

We present X‐ray diffraction and Raman spectroscopy studies of Ni‐doped ZnO (Zn_1−xNi_xO, x = 0.0, 0.03, 0.06, and 0.10) ceramics prepared by solid‐state reaction technique. The presence of the secondary phase along with the wurtzite phase is observed in Ni‐doped ZnO samples. The E₂(low) optical phonon mode is seen to be shifted to a lower wavenumber with Ni incorporation in ZnO and is explained on the basis of force‐constant variation of ZnO bond with Ni incorporation. A zone boundary phonon is observed in Ni‐doped samples at ∼130 cm⁻¹ which is normally forbidden in the first‐order Raman scattering of ZnO. Antiferromagnetic ordering between Ni atoms via spin‐orbit mechanism at low temperatures (100 K) is held responsible for the observed zone boundary phonon. Copyright © 2008 John Wiley & Sons, Ltd.