Tensile Strengths of Se, As2S3, As2Se3, and Ge30As15Se55 Glass Fibers

The strengths of as-drawn, abraded, and pristine Se, As₂Se₃, As₂S₃, and Ge₃₀As₁₅Se₅₅ fibers are reported. Pristine strength values range from an average of 80 MPa for Se and Ge₃₀As₁₅Se₅₅ to 100 and 180 MPa for As₂Se₃ and As₂S₃, respectively. Although these values are considerably higher than those reported previously for bulk samples, in no case does the maximum observed strength reach more than about 6% of that expected from simple theoretial calculations. Several factors that can control the strength are discussed. The overall behavior is interpreted in terms of the glass structures which permit localized stress relaxation effects in regions of weak, nondirectional bonds. These effects occur at temperatures well below the glass-transition region.     

Physical Properties of Chalcogenide and Chalcohalide Glasses

The physical properties of glasses in the Ge₃₀As₁₀Se_{(60— x )}Te _x system with x = 25, 28, 30, and 35 at.% Te, the Ge₃₀As₁₀Se₃₀Te_{(30— y )}I _y system with y = 5, 10, 20, and 30 at.% I, the Ge₃₀As₁₀Se₃₅Te_{(25— z )}I _z system with z = 2, 6, 10, and 20 at.% I, and the [Ge₃₀As₁₀Se₃₀Te₃₀]_{(100— w )}I _w system with w = 0, 5, 10, and 20 at.% I have been investigated. The changes in the glass transition temperature, density, coefficient of thermal expansion, hardness, and viscosity are attributed to the delocalized metallic bonding character of Te in the substitution of Te for Se in the Ge-As-Se-Te glass system and the network-terminating role of iodine in the substitution of I for Te in the Ge-As-Se-Te-I glass system, respectively.     

In Situ Measurements of X-Ray-Induced Silver Diffusion into a Ge30Se70 Thin Film

High-resolution X-ray photoelectron spectroscopy is used to identify the mechanism of X-ray-induced Ag diffusion into Ge₃₀Se₇₀ chalcogenide glass thin films, which are prepared in situ to avoid oxygen contamination. From the analysis of Ge 3d, Se 3d, and Ag 3d core levels, and valence band spectra, changes in the electronic structure are determined as Ag diffuses gradually with increasing irradiation. The ternary phase based on Ge₂Se₆ units, which contains homopolar Ge–Ge bonds, forms when diffusion approaches equilibrium where Ag content ∼30 at.%. The formation of a Se-rich composition is indicated in the near-surface region at the initial stage of the process, but the previously assumed Ag₂Se phase is not detected.     

Glass Formation in the Pseudobinary Metallic Selenide Systems MmSen-Ge1.5As0.5Se3

The glass-forming regions were investigated for pseudobinary systems of the composition X M _m Se _n -(1– X )Ge_1.5As_0.5Se₃ (M _m Se _n =PbSe, CdSe, BaSe, ZnSe, or La₂Se₃). Systems containing PbSe, CdSe, and BaSe contain substantial regions of glass formation, and differential scanning calorimetry, electron microscopy, and water corrosion tests were used to characterize these glasses. The glasses were generally phase-separated, and the available data suggest that for PbSe melts the region of liquid-liquid immiscibility spans almost the entire pseudobinary composition range. A few studies of glass formation were conducted for CdSe-M _m Se _n -Ge_1.5As_0.5Se₃ pseudoternary and M _m Se _n -GeSe₂ binary melts.     

Structure and Properties of Long-Wavelength-Transmitting Halide Glasses

The lower halides of zinc, namely, ZnCl₂, ZnBr₂, and ZnI₂, may act as network formers in glasses that also contain modifying alkali halides such as KCI, KBr, KI, NaI, or CsI. Compositions which contain only Br⁻ or I⁻ anions are of particular interest because of their extended infrared transmission, which includes the ∼10-μm region, in addition to full visible transparency. A series of modified zinc halide glasses were prepared and characterized by differential scanning calorimetry, middle and far Fourier transform infrared spectroscopy, and polarized Raman spectroscopy. T _g values were characteristically low, around 40°C. Bulk glass infrared transmission up to 15 to 20 μm was recorded. The most probable glass structures are discussed and compared to oxide glass models. An attenuation of  0.001 dB/km has been projected as a possible intrinsic minimum for optical fibers operating near ∼6 μm.     

Formation and Properties of GeSe2–Ga2Se3–PbI2 Novel Chalcohalide Glasses

The glass-forming region of the GeSe₂–Ga₂Se₃–PbI₂ system was determined and homogeneous glasses were prepared. The maximum dissolvable PbI₂ can be up to 50 mol%. The structures of glasses were characterized by Raman spectroscopy. The thermal, optical, and some basic physical properties of the glasses were investigated. The results show that GeSe₂–Ga₂Se₃–PbI₂ glasses have a wide region of transmission window (0.7–16 μm) and high refractive index (∼2.5) with the addition of PbI₂. The glasses have good glass-forming ability and high glass transition temperatures. Consequently, these novel glasses may be promising candidate materials for infrared optics and nonlinear optical field.     

Absorption and Scattering Losses in Glasses and Fibers for Light Guidance

Fiber optics for telecommunications applications require very high purity glass. Light loss in glass results primarily from absorption and scattering. Transition metal ions and OH ions cause most of the absorption, whereas scattering is caused by microheterogeneity. Scattering losses vary from 1 to 4 dB/km at 850 nm; absorption losses are high near 630 nm, because of Cr³⁺ and Ni²⁺ impurities, but are lower near 850 nm, making this a preferred wavelength region. Flint glass with a total loss of 50 dB/km at 850 nm, prepared using pure material and special techniques, was used as the core of thin-clad optical fibers 70 μm in diameter; these fibers had an internal loss at 850 nm of ∼450 dB/km.     

Limitations of the Augis and Bennett Method for Kinetic Analysis of the Crystallization of Glasses and Conditions for Correct Use

The equation proposed by Augis and Bennett for determining the kinetic exponent of the Johnson–Mehl–Avrami (JMA) model is thoroughly analyzed; a new expression, calculated accurately with no assumptions introduced, is proposed. This new method of calculation has been extended to the different kinetic models more commonly used in the literature for describing solid-state reactions. However, determining the JMA exponent from the Augis and Bennett method can lead to an incorrect interpretation of the reaction mechanism unless an additional, independent test is used. A testing method for verifying the applicability of the Augis and Bennett method is proposed. The kinetic analysis of the crystallization of Ge_0.3Sb_1.4S_2.7 has been used for checking this method.     

Hardness, Toughness, and Scratchability of Germanium–Selenium Chalcogenide Glasses

Ge–Se chalcogenide glasses are characterized by relatively low hardness (0.39–2.35 GPa) and low fracture toughness (0.1–0.28 MPa·m^1/2). Actually, the hardness of chalcogen-rich glasses is low enough so that the brittleness parameter, B = H / K _c , is lower than that of silicate glasses. Whereas hardness and Young's modulus increase with increasing germanium contents, fracture toughness follows a trend similar to that of the density and exhibits a maximum for the Ge₂₀Se₈₀ composition, which corresponds to the rigidity percolation threshold. Optical microscopy and atomic force microscopy observations suggest that the indentation deformation proceeds by a localized shear deformation phenomenon. Glasses in the chalcogen-rich region behave viscoelastically at room temperature. As a consequence, an increase of the loading time results in a decrease of hardness and toughness.     

Reaction and Diffusion in Silver-Arsenic Chalcogenide Glass Systems

The diffusion of Ag from the metal or Ag₂Se in amorphous As₂S₃ and As₂Se₃ at 175°C is accompanied by the reduction of As from a valence of 3+ to 2+ or 2+ to 1 + to maintain charge neutrality in the glass. Only Ag⁺ diffuses at this temperature; all other ions are essentially immobile. An amorphous reaction-product phase is formed in the diffusion zone with a composition range of 28.6 to 44.4 at % Ag. The lower limit corresponds to all As cations of 2+ valence (equivalent to amorphous Ag₂As₂S₃); the upper limit, the maximum solubility of Ag in these glasses, corresponds to all As cations of 1 + valence (equivalent to amorphous Ag₁As₂S₃). The diffusivity of Ag in these glasses at 175°C for concentrations of 10 to 35 at.% Ag is
Sulfide 4× 10⁻¹⁴ exp[(+0.23±0.01)(at.% Ag)]cm²/s
Selenide 2' 10⁻¹¹ exp[(+0.14±0.01)(at.% Ag)]cm²/s     

Visible Transparent GeSe2–Ga2Se3–KX (X=I, Br, or Cl) Glasses for Infrared Optics

GeSe₂–Ga₂Se₃–KX (X=I, Br, or Cl) chalcohalide glasses are synthesized, and their optical properties and thermo-mechanical properties are investigated. A structural model is put forward to elucidate the interesting compositional dependences of the short-wavelength absorption edge (λ_s) and glass transition temperature ( T _g). These glasses are transparent in the red-light region in addition to the 3–5 and 8–14 μm atmospheric windows. Most of their T _g exceed 300°C, and they also present good thermal stability. These properties make them attractive materials for infrared optics.     

Formation and Properties of the Novel GeSe2–In2Se3–CsI Chalcohalide Glasses

The glass-forming region of the GeSe₂–In₂Se₃–CsI system was reported firstly. The dependence of glass properties on compositions as formulas of (1−2 x )GeSe₂− x (In₂Se₃–CsI) and (0.8− x )GeSe₂−0.2In₂Se₃− x CsI was investigated. Properties measurements include density, DTA, Raman spectra, visible and near infrared, and infrared (IR) transmission spectra. Raman spectra show that [GeSe_4/2] and [InSe_{4− x} I _x ] tetrahedra are the main structural units in the network of the present glass system. Glasses show larger density (4.29–4.51 g/cm³), wider optical transmission window from 0.56 to 16 μm, and higher thermal stability characterized by the bigger Δ T (Δ T = T _x – T _g>110°C), which make them the promising candidate materials for IR optics.     

Glass Formation and Crystallization Behavior of a Novel GeS2–Sb2S3–PbS Chalcogenide Glass System

In the present work, a large glass-forming region was found in the novel GeS₂–Sb₂S₃–PbS system, in which up to 58 at.% PbS could be incorporated without deteriorating the thermal and physical properties of glasses. Infrared (IR) transmitting glass ceramics with a large amount of small-sized crystals (<100 nm) were then produced by choosing sub-stable compositions and annealing at fairly low temperatures (15°–30°C above T _g) for long durations (up to 100 h). Crystals were identified by X-ray diffraction as Pb₂GeS₄, PbGeS₃, PbS, PbSb₂S₄, etc., depending on base glass compositions. Compared with base glasses, glass ceramics showed much improved thermal shock resistance and fracture toughness, making them good candidate materials for IR optics.     

Fracture Strength–Fracture Resistance Response and Damage Resistance of Sintered Al2O3–ZrO2 (12 mol% CeO2) Composites

The fracture strengths of sintered Al₂O₃ containing 20 and 40 vol% ZrO₂(12 mol% CeO₂)—zirconia-toughened alumina (ZTA)—composites along with the fracture resistance can be increased (e.g., to ∼900 MPa and >12 Mpa·m^1/2, respectively), by increasing the mean grain size of the t -ZrO₂ (and the Al₂O₃) from ∼0.5 μm to ∼3 μm. At these lower t -ZrO₂ contents, the fracture strength-fracture resistance curves show a continuous rise as opposed to the strength maxima observed in polycrystalline t -ZrO₂(12 mol% CeO₂), CeTZP, and ZrO₂(12 mol% CeO₂) ceramics containing ≤20 vol% Al₂O₃. The toughened composites also exhibit excellent damage resistance with fracture strengths of 500 MPa retained with surfaces containing ∼150- N Vickers indentations which produce cracks of ∼160-μm radius. Greater damage resistance correlates with an increase in the apparent R -curve response of these composites.     

Formation and Properties of Chalcogenide Glasses in the GeSe2–As2Se3–CdSe System

The glass-forming region in a GeSe₂–As₂Se₃–CdSe system and the dependence of properties on glass compositions as a formula of 70GeSe₂–(30− x )As₂Se₃– x CdSe ( x =0–25) were investigated. Measurements included density, micro-hardness, differential scanning calorimetry (DSC), X-ray diffraction, and IR transmission spectra. A large glass-forming region was shown while addition of Cd increases the crystallization trend of the system. Besides, the Cd content accommodated by the system to form glass is found to be lower in the As₂Se₃-rich region than in the GeSe₂-rich region. With the introduction of CdSe, density, micro-hardness, and T _g of glasses increase whereas an exothermal peak in the DSC curve appears and thermal stability (Δ T ) decreases. The activation energy of crystallization and the Avrami exponent were also obtained using the modified Ozawa equation.     

Toughening and Strengthening of NiAl with Al2O3 by the Addition of ZrO2(3Y)

NiAl/10-mol%-ZrO₂(3Y) composites of almost full density have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The former intermetallic compound, which contains a trace amount of Al₂O₃, has been prepared via self-propagating high-temperature synthesis. The composite microstructures are such that tetragonal ZrO₂ (∼0.2 μm) and Al₂O₃ (∼0.5 μm) particles are located at the grain boundaries of the NiAl (∼46 μm) matrix. Improved mechanical properties are obtained: the fracture toughness and bending strength are 8.8 MPa·m^1/2 and 1045 MPa, respectively, and high strength (>800 MPa) can be retained up to 800°C.     

Red Color GeSe2-Based Chalcohalide Glasses for Infrared Optics

GeSe₂–Ga₂Se₃–CsI chalcohalide glasses are synthesized, and their optical properties and thermo-mechanical properties are studied. A typical characteristic of the glasses is their excellent transparency in the red-light region in addition to the 8–14 μm atmospheric window, which is of vital importance to the quality control of infrared systems. The short-wavelength absorption edge λ_s of the glass system has a distinct blue shift with increasing CsI content, and the physicochemical interpretations are suggested and formulated. These glasses present a glass transition temperature ( T _g) around 300°C and good thermal stability. Consequently, they can be promising candidate materials for infrared optics, although their hardness is relatively weak.     

Glass Formation and Properties of Chalcogenides in a GeSe2–As2Se3–PbSe System

The glass-forming region in a GeSe₂–As₂Se₃–PbSe system was determined, and the dependence of properties on the composition as a formula of 20 GeSe₂–(80− x )As₂Se₃− x PbSe ( x =0–30) was investigated. Measurements include density, differential scanning calorimetry, X-ray diffraction, Vis-NIR, and IR transmission spectra. A fairly large glass-forming region was obtained where the higher lead content could be introduced into the system in the As₂Se₃-rich region than in the GeSe₂-rich region. With the introduction of PbSe, the density of glass increased and the calculated molar volume decreased while the crystallization tendency increased, which was indicated by the decreasing Δ T ( T _x− T _g). The activation energy of crystallization and the Avrami exponents were also obtained using the modified Ozawa equation. Under proper annealing conditions, suitable IR transmittance glass–ceramics were obtained.     

Influence of ZrO2 Grain Size and Content on the Transformation Response in the Al2O3─ZrO2 (12 mol% CeO2) System

Based on experimental and modeling studies, the rate of increase in the martensite start temperature M _s for the tetragonal-to-monoclinic transformation with increase in zirconia grain size is found to rise with decrease in ZrO₂ content in the zirconia-toughened alumina ZTA system. The observed grain size dependence of M _s can be related to the thermal expansion mismatch tensile (internal) stresses which increase with decrease in zirconia content. The result is that finer zirconia grain sizes are required to retain the tetragonal phase as less zirconia is incorporated into the alumina, in agreement with the experimental observations. At the same time, both the predicted and observed applied stress required to induce the transformation are reduced with increase in the ZrO₂ grain size. In addition, the transformation-toughening contribution at temperature T increases with increase in the M _s temperature brought about by the increase in the ZrO₂ grain size, when T > M _s. In alumina containing 20 vol% ZrO₂ (12 mol% CeO₂), a toughness of ∼10 MPa. √m can be achieved for a ZrO₂ grain size of ∼2 μm ( M _s∼ 225 K). However, at a grain size of ∼2 μm, the alumina–40 vol% ZrO₂ (12 mol% CeO₂) has a toughness of only 8.5 MPa. √m ( M _s∼ 150 K) but reaches 12.3 MPa. ∼m ( M _s∼ 260 K) at a grain size of ∼3 μm. These findings show that composition (and matrix properties) play critical roles in determining the ZrO₂ grain size to optimize the transformation toughening in ZrO₂-toughened ceramics.     

Infrared Spectra of a Water-Containing Glass

Infrared absorption was measured on an NajO-K₂O-ZnO-Al₂O₃-SiO₂ glass with up to ∼11 wt% water. Fundamental and overtone-combination bands were observed at 1.41, 1.91, 2.22, 2.87, and 6.1 μm. Molar absorptivities were determined for the hydrated glass for H₂O and OH levels using the molar absorptivity calculated for the 2.22-μm band in the as-melted glass. By this procedure the concentration of molecular water and OH groups could be determined separately. These results show that the OH content of the hydrated glass, as determined from the 2.22-μm band, is constant at >7 wt% H₂O; additional H₂O is attributed to molecular water only. Good agreement was found between these data and H₂O/OH molecular ratios obtained from NMR.