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     

Dc Conductivity of Ge-S-Ag and As-S-Ag Glasses

The dc conductivity in GeS₂-GeS-Ag₂S and As₂S₃-Ag₂S glasses was measured over the range – 20° to 80°C using an electrode of 1 at.% Ag amalgam to avoid polarization. The room-temperature conductivity varies with increasing Ag₂S content from 10⁻¹⁵ to 10⁻⁴Ω⁻¹ cm⁻¹ for GeS₂-GeS-Ag₂S glasses and from 10⁻¹⁶ to 10⁻⁵Ω⁻¹ for As₂S₃-Ag₂S glasses. Also, the transport numbers of Ag ions in the glasses were measured by the Hittorf and emf methods. The results show that all glasses in both systems, except for compositions with low Ag₂S contents, are purely ionic conductors because of the presence of Ag ions, so that they may be regarded as solid electrolytes.     

Prediction of Fracture Energy and Flaw Size in Glasses from Measurements of Mirror Size

Fracture strengths (δ), fracture-initiating flaw sizes, and mirror radii ( r ), as outlined by either the mist or the hackle boundary, were measured for silicate and nonsilicate glasses (e.g. As₂S₃ and glassy carbon). For all glasses, δr^1/2= constant. The average ratios of inner and outer mirror radii to flaw size were ∼10:1 and ∼13:1, respectively, for most of the glasses. Critical fracture energies calculated from either flaw or mirror size agreed very well with those obtained by double-cantilever-beam measurements.     

Infrared Spectroscopy of Wide Composition Range xNa2S + (1 –x)B2S3 Glasses

Wide composition range studies of the IR spectra of x Na₂S + (1 – x )B₂S₃ glasses are reported for the first time. Glasses can be prepared in two composition regions: 0 x 0.33 in a low-alkali region and 0.55 x 0.80 in a highalkali region. The structures of glasses in the former region are dominated by the creation of tetrahedral boron units similar to those observed in the alkali borate glasses. For pure B₂S₃, a large fraction of six-membered rings is found, as in glassy B₂O₃. As alkali is added, the vibrational frequency of the six-membered ring mode decreases, but not the intensity, and a new band grows in which is used to propose, by analogy with the alkali borate glasses, that the fraction of tetrahedral borons increases with alkali sulfide content. These observations suggest that isolated six-membered rings persist even in the presence of tetrahedral borons. For the high-alkali glasses, both the six-membered rings and tetrahedral boron structures are destroyed in preference to the formation of isolated orthothioborate groups, Na₃BS₃. The IR spectra of the high-alkali glasses show a monotonic increase in symmetry and simplicity, indicating an increase in structural simplicity as the orthothioborate composition is approached. For the orthothioborate composition, both glass and polycrystal can be prepared. The IR spectra of the two phases are very similar, with the glass exhibiting a broadened absorption envelope.     

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.     

Crystallization of Gallium Lanthanum Sulfide Glasses

The crystallization of gallium lanthanum sulfide (GLS) glasses of composition (100 - x )Ga₂S₃ x La₂S₃ (mol%) has been analyzed using X-ray diffraction, and optical and transmission electron microscopy. The major crystalline phase, X, was found to be different from the La_3.33Ga₆S₁₄ phase reported previously in similar compositions. X was the primary phase present and was observed in all samples, forming on quenching as well as on subsequent heat treatment. The phase occurred as spherulites composed of lamellae, approximately 1 µm wide and all of the same orientation. A small quantity of crystals of Ga₂S₃ (20 nm) were observed to grow discontinuously between the lamellae. Electron diffraction and energy dispersive X-ray analysis suggested that phase X was monoclinic and had approximately a 2:1 Ga₂S₃:La₂S₃ ratio.     

Structural Changes in Stressed As2S3 Glass Fibers Determined by Raman Spectroscopy

Raman spectra were measured transverse to As₂S₃ glass fibers which were stressed to various levels up to their breaking strength of 200 MPa. The spectra consisted of a single intense band near 340 cm-¹, several weak bands, and a scattering tail at low wavenumbers. The intense band exhibited a decrease in intensity and a small wavenumber shift but retained the same half-width in the stressed fibers. A new band appeared as a shoulder at 320 cm-¹ with an intensity that could be related to the stress level. The stress-related band is postulated to arise from local broken-bond defect centers containing nonbridging sulfur atoms.     

Properties of As40S(60–x) Sex Glasses for IR Fiber Optics

The physical and optical properties of glasses in the As₄₀S₍₍₆₀-_x:)Se_x system where x = 0, 5,10,15, and 20 at. % Se have been investigated. The changes in the glass transition temperature, density, hardness, IR edge, and refractive index can be attributed to the presence of Se, which simply replaces S in these glasses. The glasses do not exhibit crystallization under the conditions used in this study, which is a desirable property from the viewpoint of flberization. Appropriate core and cladding glass compositions have been identified for fabrication of optical fibers with known numerical apertures. Furthermore, it has been shown that these glasses will not impart additional thermal or mechanical stresses in optical fibers made from these compositions.     

Gamma-Induced Absorption and Structural Studies of Arsenic Borate Glasses

Gamma-induced coloration in borate glasses containing arsenic was studied to secure information on: ( a ) the effect of addition of As₂O₃ on the induced coloration of the alkali borate base glass, and ( b ) the possibility of using radiation-induced coloration in studying structural changes. At concentrations of less than 10 mole % As₂O₃, arsenic takes network-modifying positions and at concentrations greater than 10.0 mole % As₂O₃, it takes network-forming positions. Between 15.0 and 25.0 mole % As₂O₃, an additional change in the structure was detected. This change may be confined to the mode of arrangement of the structural units associated with the formation of groups or compounds. Additional studies based on infrared absorption, ultraviolet absorption edge, and density measurements, as well as the chemical analysis of the glasses, confirmed the structural changes suggested from irradiation studies.     

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.     

Raman Study of Glasses of Ba2TiSi2O8 and Ba2TiGe2O8

Raman spectra are reported for fresnoite (Ba₂Ti(Si,Ge)₂O₈ glasses, and comparison is made between the Raman spectra of the corresponding crystalline powders and glasses of Ba₂TiSi₂O₈ and Ba₂TiGe₂O₈. The Ba₂TiGe₂O₈ glass spectra show correspondence with the Ba₂TiGe₂O₈ crystalline Raman spectra; the v _s(Ge–O–Ge) mode occurs at 518 cm⁻¹ in the glass and at 521 cm⁻¹ in the crystalline material. Five-fold coordinated titanium is the majority species present in the Ba₂TiGe₂O₈ glass as revealed by a strong band at 824 cm⁻¹ in the I glass spectrum. The Ba₂TiSi₂O₈ glass spectra are similar to the Ba₂TiSi₂O₈ crystalline spectrum; the strongest band is found at 836 cm⁻¹ in the I glass spectrum. Through comparison with the previous Raman data of other titania silicate glasses, we conclude that the Ba₂TiSi₂O₈ glass has a structure similar to the crystalline phase.     

Influence of As2O3 on the Optical Properties of Ultrapure Multicomponent Silicate Glasses and Optical Fibers

To obtain low transmission loss optical fibers from ultrapure multicomponent silicate glasses, it is necessary to add small quantities of As₂O₃ (or Sb₂O₃). In optical fibers prepared from glasses without these agents, a significant increase in loss is observed. To investigate this effect, the influence of As₂O₃ (added to the batch and present in the glass as As₂O₅) on the optical properties of ultrapure silicate glasses was studied. These properties are the Rayleigh scattering loss coefficient, transition metal absorption, and position of the uv absorption edge. This study showed that the increase in loss of As₂O₃-free glass cannot be assigned to any of these contributions and was attributed to absorption by electrons, trapped in relatively shallow traps in the glass network. The As⁵⁺ ions serve as deep traps and therefore remove the additional absorption. The same phenomenon, although much more pronounced, was observed in optical fibers prepared from alkali borosilicate glasses.     

Pressure-Temperature Study of Sulfospinels

Several new compounds with the formula AB₂S₄ were synthesized. Pressure-induced polymorphism of the sulfospinels was investigated. The only spinels which transformed to the NiAs derivatives were those in which the A and B cations had unfilled d orbitals. Pressure-temperature phase relations were investigated for a series of sulfochromites. At 600°C the transformation pressure decreased in the order MnCr₂S₄, FeCr₂S₄= CoCr₂S₄, NiCr₂S₄ (an NiAs structure at P = 1 atm). Sulfospinels which produced new high-pressure phases were NiRh₂S₄, FeYb₂S₄, CrIn₂, NiIn₂S₄, CoIn₂S₄, and MnIn₂S₄.     

29Si and 31P MAS-NMR Spectra of Li2S-SiS2-Li3PO4 Rapidly Quenched Glasses

²⁹Si and ³¹P MAS-NMR spectra were measured for the Li₂S-SiS₂-Li₃PO₄ glasses. ²⁹Si MAS-NMR spectra revealed that a large number of silicon atoms in the glasses were coordinated with both sulfur and oxygen atoms. ³¹P MAS-NMR spectra showed that some phosphorus atoms were also coordinated with both sulfur and oxygen atoms. Such structural units resulted in the improvement of the conductivity and the glass stability against crystallization by the doping of Li₃PO₄ to the Li₂S-SiS₂ glasses.     

Preparation of Li2S–P2S5 Amorphous Solid Electrolytes by Mechanical Milling

Amorphous solid electrolytes in the Li₂S–P₂S₅ system were prepared successfully from a mixture of crystalline Li₂S and P₂S₅, using a mechanical milling technique. The amorphous-forming region was extended to higher Li₂S compositions by mechanical milling, compared with melt quenching. The pelletized samples of the 75Li₂S·25P₂S₅ (on a mole-percent basis) amorphous powders obtained by mechanical milling for 20 h exhibited high conductivity (2 × 10⁻⁴ S/cm at room temperature) and an activation energy for conduction of 34 kJ/mol. The lithium-ion transport number of the amorphous powders was almost unity.     

Synthesis of BaAl2S4:Eu2+ Electroluminescent Material by the Polymerizable Complex Method Combined with CS2 Sulfurization

Eu-activated BaAl₂S₄ (BaAl₂S₄:Eu) blue light emission phosphor has attracted considerable attention recently as a prospective material for full color electroluminescent display applications. Although BaAl₂S₄:Eu was discovered over 30 years ago, the solid-state reaction between metal sulfides in sealed quartz ampoules remains the main method for the synthesis of this material. In this work, a homogeneous single-phase Ba_0.95Eu_0.05Al₂S₄ (BaAl₂S₄:Eu) phosphor was obtained by the sulfurization–reduction of the multicomponent oxide precursor in a CS₂ atmosphere at 1050°C. The oxide precursor containing barium, aluminum, and europium for this process was prepared by the polymerizable complex method, which ensures a high degree of homogeneity in the final product. The BaAl₂S₄:Eu material thus obtained exhibited a single emission line at 475 nm and a fluorescence intensity of 35% compared with one of the best commercially available (Ba,Eu)MgAl₁₀O₁₇ phosphors.     

Hydrothermal Synthesis of Bismuth Sulfide Whiskers by a Template-Free Approach

Uniform Bi₂S₃ whiskers were synthesized via a template-free hydrothermal route using bismuth nitrate (Bi(NO₃)₃·5H₂O), thiourea (CS(NH₂)₂), and lithium hydroxide (LiOH) as starting materials. The resultant powders were characterized in detail by X-ray diffraction, scanning electron microscopy, and photoluminescent spectra techniques (PL), respectively. It was found that Bi₂S₃ whiskers could be easily synthesized in the presence of LiOH, whereas only irregular and aggregated particles were obtained without adding LiOH, and that elevating hydrothermal reaction temperature in a certain range would promote the preferred orientation growth of Bi₂S₃ crystallites. The PL spectra results evidenced that the optical properties of Bi₂S₃ crystallites were obviously influenced by their size and morphology.     

Preparation and Infrared Characterization of Thioborate Compounds and Polycrystals

Polycrystals and compounds in the series x Na₂S + (1 − x )B₂S₃ have been prepared for the first time in the range 0 x 0.75. Infrared spectroscopy has been used to examine the extent to which the structures of the thioborate systems are similar or dissimilar to their oxide analogues. The complexity of the IR spectra systematically increases and then decreases as the composition is changed away from and then up to another compound. This behavior is used to propose the existence of a new compound in the series, 2Na₂S · B₂S₃, sodium dithioborate. The other known compounds in this series, Na₂S · B₂S₃ and Na₂S · 3B₂S₃, were isolated in this same way. the IR spectra do not suggest the compound Na₂S · 2B₂S₃ forms. Evidence is found, however, for the formation of tetrahedral borons, isolated thioboroxyl rings, and orthoborate triangles. These results are used to conclude that there are significant similarities between the structures and compounds that form in the alkali thioborate and borate systems.     

Density Measurements of Glasses in the Series xNa2S + (1 −x)B2S3

Measurements of the densities of glasses in the series x Na₂S + (1 − x )B₂S₃ are reported for the first time. As has been found in the corresponding oxyborate series x Na₂O + (1 − x )B₂O₃, the addition of Na₂S to B₂S₃ causes the density to increase, from 1.80 g/mL for pure B₂S₃ to 1.99 g/mL at the limit of the low-alkali sulfide glass-forming range of x = 0.25. These data provide evidence for the formation of tetrahedral boron units (BS₄⁻) as alkali is added. Volumes for the trigonal BS₃ and tetrahedral BS₄⁻ groups of 57.55 and 51.79 ų, respectively, were determined. As has also been found in the oxyborates, the tetrahedral boron group occupies a smaller volume than the trigonal boron group and causes the increase in density with added Na₂S.     

Synthesis and Sintering of Cerium(III) Sulfide Powders

Cerium(III) sulfide (Ce₂S₃) powder was synthesized via the sulfurization of ceria (CeO₂) powder using carbon disulfide gas. Single-phase α-Ce₂S₃ could be formed via sulfurization at 973 K for 28.8 ks. The preparation of α-Ce₂S₃ became feasible at low temperature, in comparison to sulfurization using hydrogen sulfide gas. According to the fact that the formation of α-Ce₂S₃ was accelerated by the addition of carbon black to the CeO₂ powder, carbothermic reduction was considered to become a dominant reaction, as the temperature increased. To obtain the activation energy for the densification of β-Ce₂S₃ powder, which was prepared by vacuum heating α-Ce₂S₃, the data of densification by hot pressing was analyzed by a kinetic equation that was proposed by other researchers. As a result, the sintering behavior could be best explained by a grain-boundary-diffusion mechanism that had an apparent activation energy of 382 kJ/mol.