Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

The preparation and structural studies in the (80 − x)TeO2–20ZnO–(x)Er2O3 glass system

Er³⁺-doped tellurite glasses of the (80 ? x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ? x ? 2.5 mol%) have successfully been made by melt-quenching technique and their structure has been investigated by means of DTA and Raman spectroscopy. The DTA results show the thermal parameters; such as the glass transition temperature (T_g) and crystallization temperature (T_c) were determined. It is found that this system provides a stable and wide glass formation range in which the glass stability around 99–140 °C may be obtained. The Raman spectroscopy used the structural studies in the glass system. Two Raman shift peaks were observed around 640–670 cm^?1 and 720–740 cm^?1, which correspond to the stretching vibration mode of TeO₄ tbp and TeO₃ tp, respectively. It is found that the spectral shift in Raman spectra is depending on the Er₂O₃ content. This evolution is an indication of the changes in the basic unit of the glass structure.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Thermal and optical properties of CuO–BaO–B2O3–P2O5 glasses

CuO-doped barium borophosphate glasses in a series of xCuO–(45 − x)BaO–10B₂O₃–45P₂O₅ in molar ratio with x = 0–15 mol% were prepared by a melt-quenching technique. All the glasses had excellent thermal stability against crystallization. Glass transition temperature, thermal expansion coefficient and molar volume decrease with increasing CuO concentration. The linear relationship between the absorption coefficient and CuO concentration exists for a peak wavelength in the transitions of ²A_1g → ²B_1g, ²B_2g → ²B_1g, ²E_g → ²B_1g. The relationship between the properties and glass structure evaluated by Raman spectroscopy is discussed.     

Thermally reversing window in Ge15Te85 − xInx glasses: Nanoindentation and micro-Raman studies

Nanoindentation studies on Ge₁₅Te_85 ? xIn_x glasses indicate that the hardness and elastic modulus of these glasses increase with indium concentration. While a pronounced plateau is seen in the elastic modulus in the composition range 3 ≤ x ≤ 7, the hardness exhibits a change in slope at compositions x = 3 and x = 7. Also, the density exhibits a broad maximum in this composition range. The observed changes in the mechanical properties and density are clearly associated with the thermally reversing window in Ge₁₅Te_85 ? xIn_x glasses in the composition range 3 ≤ x ≤ 7. In addition, a local minimum is seen in density and hardness around x = 9, the chemical threshold of the system. Further, micro-Raman studies reveal that as-quenched Ge₁₅Te_85 ? xIn_x samples exhibit two prominent peaks, at 123 cm^? 1 and 155 cm^? 1. In thermally annealed samples, the peaks at 120 cm^? 1 and 140 cm^? 1, which are due to crystalline Te, emerge as the strongest peaks. The Raman spectra of polished samples are similar to those of annealed samples, with strong peaks at 123 cm^? 1 and 141 cm^? 1. The spectra of lightly polished samples outside the thermally reversing window resemble those of thermally annealed samples; however, the spectra of glasses with compositions in the thermally reversing window resemble those of as-quenched samples. This observation confirms the earlier idea that compositions in the thermally reversing window are non-aging and are more stable.     

ArF laser induced pulse absorption in fused silica (type III): Modeling the fluence and repetition rate dependence

At 193 nm, weak stationary bulk absorption coefficients α^stat in standard and experimental grade fused silica (type III) are measured in dependence on the laser fluence H and repetition rate f. The samples show non-linear increases α^stat(H) for 0.2 ? H ? 5 mJ cm^?2 pulse^?1 (f = const.) and α^stat(f) for 100 ? f ? 1000 Hz (H = const.). An absorption model, focussing on ArF laser induced E′ center generation and annealing, and the associated rate equations are applied to simulate the experimental data quantitatively. From the simulations, material parameters like the 2-photon absorption (TPA) coefficient, the E′ center absorption cross section σ_E′ and the hydrogen related E′ annealing rate are calculated. TPA coefficients values of 9.7 · 10^?9 cm/W (standard grade material) and 1.4 · 10^?8 cm/W (experimental grade material), E′ center cross sections of 4.5 · 10^?18 and 3.6 · 10^?18 cm² and hydrogen annealing rates of 1.5 s^?1 (standard grade) and 3.4 s^?1 (experimental grade) are found.     

EPR and optical studies of Mn2+ ions in Li2O–Na2O–B2O3 glasses – An evidence of mixed alkali effect

EPR and optical absorption spectra of 0.5 mol% MnO₂ doped xLi₂O–(30 − x)Na₂O–69.5B₂O₃ (5 ⩽ x ⩽ 25) glasses have been studied. The EPR spectra exhibit resonance signals characteristic of Mn²⁺ ions. The resonance signal at g ≅ 2.0 is due to Mn²⁺ ions in an environment close to octahedral symmetry, whereas the resonances at g ≅ 4.3 and g ≅ 3.3 are attributed to the rhombic surroundings of the Mn²⁺ ions. The ionic character (A), the number of spins participating in resonance (N), optical band gap energies (E_opt) and Urbach energies (ΔE) show the mixed alkali effect (MAE) with composition. The present study gives an indication that the size of alkalis we choose, is also an important contributing factor in showing the MAE. The variation of N with temperature obeys the Boltzmann law. The optical absorption spectra show a single broad band at ∼21 000 cm⁻¹ corresponding to the transition ⁶A_1g(S) → ⁴T_1g(G) which exhibits a blue shift with x. The theoretical values of optical basicity (Λ_th) have also been evaluated.     

Raman investigation of ZnO and Zn1−xMnxO nanocrystals synthesized by precipitation method

Zn_1?xMn_xO nanocrystal samples have been successfully synthesized using the chemical precipitation method in aqueous solution. Comparing with pure ZnO NC, the Raman data recorded from the manganese-doped nanocrystals shows an enhancement of the peaks located at 334 and 439 cm^?1. Besides, a new feature at 659 cm^?1 emerges. X-ray diffraction (XRD) of the as-precipitated nanocrystal samples illustrates that Mn-doping only makes the XRD peaks of the as-precipitated Mn-doped nanocrystals shift towards lower angle values, but the crystal structure of bulk ZnO is still preserved in the Mn-doped samples. Hence, the high quality Zn_1?xMn_xO (x ? 0) nanocrystals are formed through the replacement of zinc ions by manganese ions.     

Octahedral fluoride glasses: Raman spectra and structure of niobium pentafluoride

Raman spectroscopy is used to characterize the NbF₅ phases in the temperature range 80–500 K. A new clear glass is formed by quenching the melt to liquid nitrogen temperatures having a glass transition at ～206 K and crystallization at ～233 K. For all phases including the melt, the glass, the supercooled liquid, the crystalline solid and the gas, the Raman spectra show a rather common high frequency band at ～760 cm^?1 which is attributed to the Nb–F terminal frequency of partially bridged ‘NbF₆’ octahedra. Based on the systematics of the Raman spectra for all phases and the literature physicochemical data a model is proposed for the glass and the liquid phases where ‘NbF₆’ octahedral bridged in cis and/or trans configurations form a variety of cyclic and/or chain structures which intermix building up the overall structure. At exceptionally low energies (<11 cm^?1) a rather weak in intensity Boson peak is observed in the glass which shifts to even lower energies with increasing temperature. Librational and/or tortional motions of the bridged octahedra participating in the glass structure are possible candidates for the origin of this peak.     

Characterization of deep levels in a-plane GaN epi-layers grown using various growth techniques

To study the correlation between defects and deep levels in a-plane GaN films grown on r-plane sapphire substrates, transmission electron microscopy (TEM) and deep level transient spectroscopy (DLTS) have been performed on three types of a-plane GaN samples grown using modified two-step growth (sample I), SiN_x interlayer (sample II), and patterned insulator on sapphire substrate (sample III). From the microstructure evolution in cross-sectional TEM images, it was shown that combination of growth techniques is highly efficient in the reduction of dislocation densities. Average dislocation densities of samples I, II, and III were about 2.2×10⁹ cm^?2, 1.1×10⁹ cm^?2, and 3.4×10⁸ cm^?2, respectively. The trap a_t E_c–E_t～0.13 eV (E1) was observed in only sample I, and three electron traps at 0.28–0.33 eV (E2), 0.52–0.58 eV (E3), and 0.89–0.95 eV (E4) from the conduction band edge were measured common to all the samples. The analysis of trap properties indicated that E2 and E3 trap levels are strongly associated with the partial dislocations in a-plane GaN films.     

Synthesis and structure–property relations in xCuO–(1 − x)Bi2O3 (0.5 ⩽ x ⩽ 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses

Synthesis of the xCuO–(1 ? x)Bi₂O₃ (0.5 ? x ? 0.9) (C1–C5: x = 0.5, 0.6, 0.7, 0.8, 0.9) glasses was done via nitrate–citrate gel route. Glassy phase is ascertained by XRD studies. Magnetic susceptibility results in the range 4.2–400 K show weak paramagnetic nature with exchange integrals ～0.024–0.13 eV in the glasses. The electron paramagnetic resonance (EPR) in the range 4.2–363 K shows g ≈ 2.0 and the trend of the g-matrix elements g_|| > g_⊥ > g_e for the glasses C1–C5 at 4.2 K are due to the Cu²⁺ (3d⁹) paramagnetic site in the glasses which is in a tetragonally elongated octahedron [O_1/2–CuO_4/2–O_1/2] having D_4h symmetry. IR spectroscopic results show the presence of octahedron [BiO_6/2]^3? and [CuO_6/2]^4? units and pyramidal [BiO_2/2O]^? unit in the glasses.     

Low symmetry centers in LiNbO3 doped with Yb and Er

Electron paramagnetic resonance spectroscopy studies of LiNbO₃ single crystal doped with 1 wt% of Yb³⁺ and 0.1 wt% Er are reported. Additionally, Raman spectra of the following crystals are presented: LiNbO₃:Nd, Yb (0.5 wt%, 0.7 wt%), LiNbO₃:Nd, Mg (2 wt%, 6 wt%), and LiNbO₃:Er (0.3 wt%). Raman spectra have revealed bands in the 50–220 cm^?1 range, suggesting the presence of localized phonons. The localized phonons may be considered as indirect evidence of local perturbations around Yb/Er ions, possibly due to formation of Yb/Er ion pairs. EPR spectra are interpreted basing on this presumption using a spin Hamiltonian for the Yb³⁺ dissimilar ion pairs. This model explains the observed spectral features, apparently due to the C₁ symmetry of Yb ions. In the case of the LN:Er sample, the angular dependence of EPR lines enabled distinguishing the presence of several non-equivalent centers. After deconvolution of the main EPR line into several Lorentzian components, the Er³⁺ center with the lowest C₁ point group symmetry was resolved and values of the g tensor were estimated.     

Optical band gap and Raman spectra in some (Bi2O3)x(WO3)y(TeO2)100−x−y and (PbO)x(WO3)y(TeO2)100−x−y glasses

The glasses representing (Bi₂O₃)_x(WO₃)_y(TeO₂)_100?x?y and (PbO)_x(WO₃)_y(TeO₂)_100?x?y systems were prepared. The dilatometric glass-transition temperatures of examined glass samples were found in the region 383–434 °C, the coefficient of thermal expansion varied from 12 to 16 ppm/°C and the density ranged from 6.30₂ to 6.80₈ g/cm³. From the optical transmission measurements of thin glassy bulk samples prepared by a glass blowing, the optical gap values were found in the narrow region 3.21–3.36 eV. For the temperature interval 300–480 K, the values of the temperature coefficient of the optical band gap varied from 3.7 × 10^?4 to 5.24 × 10^?4 eV/K. It is suggested that Raman feature observed at around 350 cm^?1 can be assigned to an overlap of Raman bands attributed to WO₆ corner shared octahedra and to the following three atomic linkages: Bi–O–Te, Pb–O–Te and W–O–Te.     

Properties of sodium-based ternary phosphate glasses produced from readily available phosphate salts

Three series of phosphate glasses were produced by melting together sodium phosphate salt (NaH₂PO₄) and the phosphate salts of either calcium (CaHPO₄), magnesium (MgHPO₄ · 3H₂O) or iron (FePO₄ · 2H₂O) in a 5% gold/95% platinum crucible at 1200 °C. The glass compositions were confirmed by EDX and XRD analysis. Glass transition temperature (T_g), density and durability in water were determined for all the compositions. Maximum metal oxide contents before devitrification were between 55% and 59% for CaO + Na₂O and 59% and 62% for MgO + Na₂O. The normalized equivalent for Fe₂O₃ + Na₂O was between 55% and 61%. Density values for the glasses lay between 2.49 and 2.75 g cm⁻³. T_gs lay between 295 °C and 470 °C. Degradation rates in deionized water at 37 °C lay between 0.03 g cm⁻² h⁻¹ for Na phosphate glasses and 9 × 10⁻⁶ g cm⁻² h⁻¹ for Ca phosphate glasses, 3 × 10⁻⁶ g cm⁻² h⁻¹ for Mg phosphate glasses and <3 × 10⁻⁶ g cm⁻² h⁻¹ for Fe phosphate glasses. The effect of metal addition on properties goes as Fe > Mg > Ca for degradation rates and T_g and Fe > Mg ≈ Ca for density. The change in properties with metal addition was seen to be linear for Fe and Ca additions but not with Mg addition. This is in agreement with the anomalous behavior of magnesium phosphate glasses.     

Ab initio calculation of vibrational frequencies of GexSe1−x glass

We have used the density functional theory to make the models of Ge_xSe_1?x glass for which the energy is a minimum. The clusters, Ge₂Se₂, Ge₂Se₃, Ge₃Se, Ge₃Se₂, Ge₄Se, GeSe₃, GeSe₄, chain mode zig-zag Ge₄Se₃, corner sharing GeSe₄, and edge sharing Ge₂Se₆, have been made successfully and their vibrational spectra have been calculated from the first principles. We are able to optimize the bond distances as well as the bond angles. The calculated values of the frequencies of vibrations of the various clusters have been compared with those obtained from the experimental Raman spectra of actual glasses, Ge_xSe_1?x(0 < x < 0.3). The local concentration, x within 0.25 nm is nonuniform in the amorphous material. When the same cluster occurs in two stable configurations, low frequency vibrations of frequency, ν < 100 cm^?1, are found. The corner sharing GeSe₄ has low frequency modes at 54 cm^?1 and 93 cm^?1 whereas these modes disappear in the pyramidal configuration. The low frequency modes are therefore associated with the breaking of C₄ symmetry of the pyramidal configuration. The computed vibrational frequencies of clusters Ge₃, Ge₄Se₃, Ge₂Se₃, GeSe₃ and Ge₃Se₂ are actually present in the Raman spectra of the glass, Ge_xSe_1?x(0 < x < 0.3).     

Improved method for preparation of anhydrous silica by microwave irradiation with spectroscopic characterization and toxicity assay

Amorphous anhydrous silica SiO_{2 (mw)} (99.99%) is successfully synthesized through microwave irradiation technique and time of reaction is reduced up to 1 h. The dehydration phase study of Si–water, Si–OH, Si–O–Si networking, elemental analysis and surface morphology was carried out by FTIR, FTNIR, SEM and EDAX spectroscopic techniques. The broad absorption stretching and bending of Si–OH and H₂O at 3695.38–2832.96 cm^? 1, 1638 cm^? 1 and 1191.20–1017.14 cm^? 1 completely disappeared and appearance of new bands at 946.93 and 797.63 cm^? 1 confirmed the amorphous anhydrous silica with Si–O–Si networking. The SEM images of SiO_{2 (mwc)} described the smooth and fine particle texture and confirmed 99.99% Si–O–Si networking of anhydrous silica. The 99.99% purity was verified by EDAX spectra which exhibited sharp signals only for oxygen and silicon. Toxicity against Monomorium minimum and Tribolium castaneum with 100% mortality and LT₅₀ 91 min and 7.5 h respectively is being reported. It can be used for long storage of grains in the future.     

Structure and crystallization behavior of mixed potassium-lithium niobiosilicate glasses

Potassium-lithium niobiosilicate (KLiNS) glasses with a composition of (27 ? x)K₂O · xLi₂O · 27Nb₂O₅ · 46SiO₂ (x = 0, 3, 12 and 20) have been synthesized by a melt-quenching method. The glass structure and devitrification behavior have been studied by Raman spectroscopy, DTA, and XRD. By increasing the lithium content, less distorted niobium octahedra increase, indicating a niobium clustering. This change strongly affects the crystallization behavior. In the glasses x = 0 and x = 3, just above T_g, only nanocrystals of an unidentified phase are formed, while for x = 12 and x = 20 potassium lithium niobate (KLN) solid solutions with tetragonal tungsten–bronze structure crystallize by bulk nucleation. In these glasses, LiNbO₃ crystallizes at higher temperature by surface nuclei. Ultimately, it is possible to produce nanostructured glasses based on KLN nanocrystals, by partial replacement of K by Li.     

Quantitation of sulfate solubility in borosilicate glasses using Raman spectroscopy

Raman spectroscopy is used here as an innovative technique to investigate sulfate content in borosilicate glasses. Using Raman spectroscopy after having heated the material, the evolution of sulfate amounts can be followed as a function of temperature, time and chemical composition of the starting matrix. The accuracy of this technique was verified using electron probe micro analysis (EPMA), on two systems of glasses (SiO₂–B₂O₃–Na₂O (SBNa) and SiO₂–B₂O₃–BaO (SBBa)) in order to compare the effect of alkaline or alkaline-earth elements on sulfur speciation and incorporation. To quantitate sulfate content with Raman spectroscopy, the integrated intensity of the sulfate band at 990 cm^?1 was scaled to the sum of the integrated bands between 850 and 1250 cm^?1, bands that are assigned to Qⁿ silica units. Calibration curves were then determined for different samples. The determination of sulfate contents with Raman spectroscopy analysis is possible with an accuracy of approximately 0.1 wt% depending on the composition of the glass. It mainly allows us to follow sulfate removal during the elaboration process and to establish kinetic curves of sulfate release as a function of the viscosity of the borosilicate glass.     

Characterization of a-B5C:H prepared by PECVD of orthocarborane: Results of preliminary FTIR and nuclear reaction analysis studies

The electronic properties of a-Si:H vary with hydrogen passivation of dangling bond defects. It appears this effect is also operative in semiconducting amorphous hydrogenated boron carbide (a-B₅C:H). Therefore, the ability to quantify the amount of hydrogen will be key to development of the materials science of a-B₅C:H. The results of an initial investigation probing the ability to quickly correlate hydrogen concentration in a-B₅C:H films with infrared spectroscopy are reported. a-B₅C:H thin films were growth on Si (1 1 1) substrates by plasma-enhanced chemical vapor deposition (PECVD) using sublimed orthocarborane and argon as the precursor gas. Nuclear reaction analysis (NRA) was performed to quantify the atomic concentration of H in the a-B₅C:H films. While the observed vibronic structure does not show stretches due to terminal C–H or bridging B–H–B, analysis of the terminal B–H stretch at ～2570 cm^?1 gives a proportionality constant of A = 2 × 10²² cm^?2. We conclude that the methods previously developed for correlating H concentration to infrared data in a-Si:H are similarly viable for a-B₅C:H films.