Studies in Germanium Oxide Systems: II, Phase Equilibria in the System Na2O—GeO2

Phase equilibrium relations in the system Na₂O-GeO₂ have been determined using standard quenching techniques supplemented by differential thermal analysis. Two congruently melting compounds, Na₂O·GeO₂ and 2Na₂O·9GeO₂, exist; the melting points are 1103°± 15°C and 1073°± 3°C, respectively. The eutectic temperature between GeO₂ and 2Na₂O·9GeO₂ is 950°±f 10°C at 94.5 wt GeO₂. The eutectic temperature between 2Na₂O · 9GeO₂ and Na₂O·GeO₂ is 790° f 10°C at about 75 wt% GeO₂. Both the refractive index and the density of glasses in the system Na₂O-GeO₂ exhibit maximum values at about 16 to 18 mole % Na₂O. The Ge-O-Ge absorption band at 890 cm⁻¹ shifts toward lower wave numbers with the addition of Na₂O.     

Quantitative Identification of Phonon Modes Controlling the Multiphonon Relaxation in Heavy-Metal Oxide Glasses

The phonon mode(s) controlling the multiphonon relaxation (MPR) in PbO–Bi₂O₃–Ga₂O₃ glass was analyzed, and the effect of GeO₂ addition on the MPR process was investigated. MPR rates were obtained from the lifetimes of the Tm³⁺:³ H ₄ level in glasses over the temperature range 20–280 K. In PbO–Bi₂O₃–Ga₂O₃ glass, phonons from the bending vibration between GaO₄ tetrahedra (∼550 cm⁻¹) controlled the MPR process. On the addition of GeO₂, the phonon mode at ∼770 cm⁻¹ due to the stretching vibration of GeO₄ tetrahedra started to affect the MPR process. Phonon modes controlling the MPR process in PbO–Bi₂O₃–Ga₂O₃–GeO₂ glass were both 550 cm⁻¹ and 770 cm⁻¹.     

Spectroscopic Properties and Thermal Stability of Er3+-Doped Germanotellurite Glasses for Broadband Fiber Amplifiers

The thermal stability and spectroscopic properties of Er₂O₃-doped TeO₂–GeO₂–ZnO–Na₂O–Y₂O₃ glasses for 1.5 μm fiber amplifiers were investigated. The thermal stability of the 75TeO₂·20ZnO· 5Na₂O glass was improved by introducing GeO₂ and Y₂O₃. The radiative transition and the nonradiative transition have a dominant influence on the ⁴I_13/2 level lifetime of Er³⁺ in high- and low-GeO₂ regions, respectively. Adding Y₂O₃ increases the ⁴I_13/2 level lifetime of Er³⁺ significantly. The Judd–Ofelt (J-O) parameter Ω₆ shows a strong correlation with the 1.5 μm emission bandwidth; and the larger the Ω₆, the wider the bandwidth.     

Oxidation-Reduction Equilibria in Iron-Containing Glass

The oxidation-reduction equilibrium between ferrous and ferric iron in Na₂O · 2Si0₂ glass melts was studied by equilibrating melts with various oxygen partial pressures. Exceedingly long equilibration times were required to obtain meaningful results. The reaction appears to be diffusion-controlled and may be expressed as 20^2-+ 4Fe³⁺$4 4Fe²⁺+ O₂. Data are presented in which the valence of iron varies from predominantly +3 to predominantly +2.     

Transparent, Conducting, Amorphous Oxides: Effect of Chemical Composition on Electrical and Optical Properties of Cadmium Germanates

Amorphous cadmium germanate thin films with the chemical composition x CdO·(100 — x)GeO₂ (}20, x , }80 mol%) were prepared by a radio-frequency sputtering method in an ArO₂ atmosphere. The electrical and optical properties of the as-sputtered films and films after proton (H⁺) implantation were measured in the temperature range 300–6 K. The optical band gaps of the as-sputtered films were 3.1 eV for all specimens; therefore, they were transparent to visible radiation. Direct-current conductivities of all the films prepared were 10⁻⁹ S·cm⁻¹ at room temperature. Upon proton implantation to a fluence of 2 × 10¹⁶cm⁻², the conductivity of the film with x 78 at room temperature was enhanced to 210 S·cm⁻¹, 11 orders of magnitude greater than the conductivity of the as-sputtered film, and the conductivities remained almost constant to }6 K, whereas those of films with x , }55 remained at 10⁻⁹ S·cm⁻¹. The carrier electron density and the mobility of carriers in the former films, both of which were evaluated from the Hall measurements, were }1 × 10²⁰ cm⁻³ and 12 cm²V⁻¹·s⁻¹, respectively. Effects of the chemical composition on persistent photocurrents also were examined. Significant photocurrents were observed in the films with x · }50, and they were greatly enhanced in the films with x · }75. This result indicated that the bottom part of the conduction band, which was composed mainly of 5s orbitals of cadmium cations, was extended for the films with x · }75.     

Ultraviolet Absorption of Pentavalent Vanadium in Binary Alkali Borate Classes

The ultraviolet absorption of vanadium(V) in R₂O-B₂O₃ glasses (R represents Li, Na, or K) and in aqueous buffer solutions was investigated. In glasses of variable R₂O:B₂O₃ ratio, a change in the absorption spectra similar to the [VO₄]³- → [VO₃(OH)]^2- change in aqueous solution was observed. It is suggested that vanadium(V) in these glasses may be present as either [VO₄]^3- or [VO₃O_1/2]^2- (O_1/2 indicates a bridging oxygen ion), depending on the basicity of the melt. The critical R₂O concentration, above which this change in vanadium(V) environment occurs with increasing alkalinity, is 24, 26, and ≅30 mol%, for K₂O, Na₂O, and Li₂O, respectively.     

Gamma-Ray Induced Coloring of Some Phosphate Glasses

The changes in gamma-ray induced optical absorption in phosphate glasses resulting from changes in composition, conditions during melting, and additions of small amounts of some oxides are discussed. A resolution of the induced spectra showed that the observed absorption is due to the superposition of three bands at 2.3, 2.9, and 5.5 e.v. (540, 425, and 225 mü) and to a fourth band whose absorption peak is beyond 6 e.v. The ultraviolet induced absorption increases, whereas the visible absorption decreases in glasses melted under reducing conditions as opposed to those melted under normal conditions in air and on replacement of K⁺ by Na⁺ or Li⁺. A similar effect is produced on replacement of Ba⁺⁺ by Pb++ and on the addition of T1₂O to a CaO-P₂O₅ glass or the addition of As₂O₃ to a CaOP₂O₅, GeO₂ glass. Additions of large amounts of GeO₂ are accompanied by a decrease in the number of nonbridging oxygens and a decrease in the visible induced absorption. Replacement of Ca ⁺⁺ by Ba⁺⁺ ions showed an over-all decrease in the induced absorption. The addition of small amounts of the oxides of germanium, titanium, iron, thallium, niobium, and arsenic showed an appreciable effect in inhibiting the visible induced coloration.     

Sodium Transport in the Na2O-H2O-SiO2 Glass System

The variation with water content of dc conductivity and Na diffusion coefficient for the Na₂O · 4siO₂ and Na₂O · 2SiO₂ glass systems was found to be similar to that of the Na₂O.3SiO₂ series reported earlier. The conductivity was estimated for the ternary system Na₂O-H₂O-SiO₂ by combining the present results with the previous data on the Na₂O · 3SiO₂ system. When the conductivity of those glasses with a constant [Na₂O] + [H₂O] content was plotted against water content, a pronounced mixed "alkali" effect was demonstrated. The Haven ratio, calculated by comparison of the dc conductivity to the Na diffusion coefficient at 100°C for each of the three glass systems, was found to increase toward unity with increasing water content. This suggests that the addition of water reduces the number of sodium charge carriers. The subsequent increase in conductivity beyond the minimum with the introduction of larger amounts of water is, probably, due to an increase in the mobility of the Na⁺ ions.     

High-Temperature Hydroxylation of Mullite

A plane-parallel, polished, 0.9 mm thick, single-crystal (001) plate of 2:1 mullite was treated for 6 h at 1600°C in an Ar/H₂O (90/10) gas mixture at 100 kPa. Optical microscopy studies and infrared (IR) reflection spectroscopy studies of the lattice vibrations yielded no evidence for change with respect to the untreated reference crystal. However, IR absorption spectroscopy showed that structurally bound OH groups were formed by the heat treatment in the Ar/H₂O gas mixture. IR absorption depth profile analysis showed a rather homogeneous OH distribution through the crystal. Five different hydroxyl groups were separated according to dipole orientations and peak positions: E ‖ a , ω _{a 1}= 3447 cm⁻¹, ω _{a 2}= 3579 cm⁻¹; E ‖ b , ω _{b 1}= 3456 cm⁻¹, ω _{b 2}= 3544 cm⁻¹; and E ‖ c , ω _{c 1}= 3498 cm⁻¹. All IR peaks were strongly broadened (between 90 and 150 cm⁻¹) because of a distribution in O-H binding distances caused by the real structure of mullite.     

Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er³⁺-doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO₂·0.3Al₂O₃)· x Na₂O·8.2La₂O₃· 0.6Er₂O₃·0.2Yb₂O₃·1Sb₂O₃ (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω _t ( t = 2, 4, 6) decreases with increasing Na₂O. Ω₂ decreases rapidly with increasing Na₂O while Ω₄ and Ω₆ decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na₂O. Fluorescence spectra of the ⁴ I _13/2 to ⁴ I _15/2 transition have been measured and the change with Na₂O content is discussed. It is found that the full width at half-maximum decreases with increasing Na₂O.     

Photochemical Hole Burning and Local Structural Change in Sm2+-Doped Borate Glasses

Photochemical hole burning (PHB) not only can be applied for data storage systems but also serves as a powerful method for studying the local structure around optical centers. The present work investigated the effects of aluminum, magnesium, and silicon ions on hole burning and the phonon sideband for borate glasses that exhibit PHB at room temperature. Hole burning was measured for the ⁵ D ₀₋₇ F ₀ transition of Sm²⁺ and the phonon sideband spectrum for the ⁵ D ₀-⁷ F ₀ transition of Eu³⁺. The hole width was closely related to local structural change, especially as it seemed to decrease with decreases in the number of nonbridging oxygens produced around the rare-earth ions. In the case of sodium aluminoborate glasses, the hole width decreased considerably with increasing alumina content. The ratio Γ_ih/Γ_h for 85B₂O3·10Al₂O₃·5Na₂O·1Sm₂O₃ glass, then, was 80 at room temperature, the largest value ever reported.     

States of Sulfur in Alkali Borate Glasses

Simple binary alkali borate glasses of differing alkali content (alkali = Li, Na, or K) containing sulfur were prepared and their absorption spectra were measured in the range of 200 to 700 nm. The absorption bands obtained were used to determine the stable states of sulfur in these glasses by directly comparing them with published data. The following states of sulfur were identified and their ranges of stability were determined: the S₂ molecule in glasses containing at least 15 mol% alkali oxide, the S₃⁻ and S₂⁻ in glasses containing 20 to 30 mol% Na₂O or K₂O, and the polysulfide ion (S x ²⁻) in glasses of 30 to 35 mol% Na₂O or K₂O.     

Infrared Absorption Spectra of Sodium Silicate Glasses from 4 to 30μ

The infrared absorption spectra of sodium silicate glasses of molar composition Na₂O·xSiO₂ (where = 5, 4, 3, and 2) were determined with unpolarized radiation in the 4 to 30μ region. The glass spectra showed a definite similarity to the spectra of α-quartz, with lattice vibrational bands around 1066,786, and 464 cm⁻¹. As x decreased, some bands shifted toward lower frequencies indicating a decrease in the force constant. No new frequencies were found in the silicate glasses which did not have counterparts in α-quartz.     

Visible Spectroscopy of Irradiated High-Alkali Borate and Mixed-Alkali Phosphate Glasses

Expectations of increased stability for trapped electrons in high-alkali glasses, based on extrapolations from observations on low-alkali borate glasses, are not borne out. In 69Na₂O-31B₂O₃ glass, electron centers have approximately the same thermal stability as in Na₂O·2B₂O₃ glass. In Na₂Oplus;P₂O₅ glasses the lifetimes, 3 · 0.5 μS, of transiently trapped electrons as well as their absorption spectra prove to be independent of increase of Na₂O content from 50 to 60 mol%. The same composition change destabilizes "permanent" hole centers. Exchange of Na₂O with K₂O in the metaphosphate glass also has no effect on the trapped electron lifetime. Small linear shifts in the trapped-hole absorption peak wavelengths are observed in the latter case. The most important positive finding in the phosphate glasses is a pronounced mixed-alkali effect on the yield of transiently trapped electrons and holes and of permanently trapped holes. The yield is a minimum at Na:K=1:1, due either to the elimination of trap sites or to the reduction of alkali ion mobilities which play a role in trap formation.     

Polymer Mixtures in Na2O.Sb2O3.GeO2 Glasses

Ternary Na₂O.Sb₂O₃.GeO₂ glasses (with various [Na]/[Na + Sb] ratios) that contained ≥65 mol% GeO₂ were prepared. Their densities (volumes), refractive indices, and infrared spectra were determined and their colors noted. The ternary glasses with ≥88 mol% GeO₂ exhibit nearly additive volumes, refractivities, and frequencies for the main Ge-O vibration. Ternary glasses with lesser amounts of GeO₂ exhibit a variety of behaviors, depending on the [Na]/[Na + Sb] ratio. Small amounts of Sb₂O₃ cause significant volume and refraction deviations, as well as changes in ν_Ge-O, that can be associated with gradual elimination of GeO₆ octahedra. All the information supports a model for the glasses with 65 to 88 mol% GeO₂ that involves a degree of depolymerization that is greater when Na₂O and Sb₂O₃ are present together than when either is present alone.     

Phase Formation in the System Na2O · Al2O3-CaO · A12O3-Al2O3 at 1200°C in Air

Phase relations in the system Na₂O_· Al₂O₃-CaO· Al₂O₃-Al₂O₃ at 1200°C in air were determined using the quenching method and high-temperature X-ray diffraction. The compound 2Na₂O · 3CaO · 5Al₂O₃, known from the literature, was reformulated as Na₂O · CaO · 2Al₂O₃. A new compound with the probable composition Na₂O · 3CaO · 8Al₂O₃ was found. Cell parameters of both compounds were determined. The compound Na₂O · CaO-2Al₂O₃ is tetragonal with a = 1.04348(24) and c = 0.72539(31) nm; it forms solid solutions with Na₂O · Al₂O₃ up to 38 mol% Na₂O at 1200°C. The compound Na₂O · 3CaO · 8Al₂O₃ is hexagonal with) a = 0.98436(4) and c = 0.69415(4) nm. The compound CaO · 6Al₂O₃ is not initially formed from oxide components at 1200°C but behaves as an equilibrium phase when it is formed separately at higher temperatures. The very slow transformation kinetics between β and β "-Al₂O₃ make it very difficult to determine equilibrium phase relations in the high-Al₂O₃ part of the diagram. Conclusions as to lifetime processes in high-pressure sodium discharge lamps can be drawn from the phase diagram.     

Optical Spectra of the Various Valence States of Vanadium in Na2 O.2SiO2 Glass

Optical absorption data are presented for Na₂O₂SiO₂ glass containing vanadium equilibrated in various states of oxidation. Spectra of 5⁺, 4⁺, and 3⁺ vanadium were derived. The variation in amounts of the three species is in accord with mass action considerations. The spectra are related to crystal field assignments.     

Influence of Pseudo-Alkali Cations on Network Depolymerization in Mixed-Cation Germanate Glasses

Mixed-cation germanate glasses that contained ≥69 mol% GeO₂ and equimolar amounts of Na₂O/K₂O, Ag₂O/Tl₂O, Tl₂O/K₂O, or Ag₂O/K₂O were prepared. Densities, refractive indices, and infrared absorptions were measured and colors noted. In all glasses, the expected shift of the ir absorption to longer wavelengths is enhanced by the presence of the second cation. The mixed-alkali glasses are less voluminous and the mixed-cation glasses more voluminous than predicted. The mixed-cation glasses in some cases also exhibit more intense colors than anticipated and deviations of the refractive index from additivity. These results are interpreted in terms of slight differences in the mode of network depolymerization which appear to be caused by the polarizing nature of Tl⁺ and Ag⁺     

Effect of Poling Temperature on Optical Second-Harmonic Intensity of Lithium Sodium Tellurite Glass

Second-harmonic generation has been observed in poled 10Li₂O10Na₂O80TeO₂ glass. The effect of poling temperature on the second-harmonic intensity has been examined. The second-harmonic intensity increases, attains a maximum, and then decreases as the poling temperature increases. In other words, an optimum poling temperature that results in a maximum second-harmonic intensity exists. The optimum poling temperature linearly increases as the glass-transition temperature increases for several types of tellurite glasses, including the present 10Li₂O10Na₂O80TeO₂ glass. This fact suggests that the process to create a polarization that results in the second-harmonic generation is affected by the structural relaxation at the glass-transition range. The thermal stability of 10Li₂O10Na₂O80TeO₂ glass is higher than that of 18Na₂O82TeO₂ (30NaO_1/270TeO₂) glass, as revealed via differential scanning calorimetry. As a result, the temperature range within which the poling is effective is wider for the former glass.     

Structure of Glasses and Melts in the Na2O·GeO2·B2O3 System

Density and viscosity results are presented for ternary Na₂O·GeO₂·B₂O₃ melts (∼600° to 1300°C) and glasses containing as much as 35 mole % Na₂O. Synthetic partial molar volume models indicate a fairly broad stability region for BO₄ tetrahedra in the B₂O₃-rich melts. Similar models for GeO₂-rich melts reveal a more limited stability region for GeO₆ octahedra. The expansion coefficient contours and viscosity isotherms confirm the volume-based conclusions for the liquid state. The high-temperature volume models were used to develop glass volume models that agree to within several percent of experiment. It has been concluded that the melts and glasses possess similar structures. The relatively greater compositional stability of GeO₆ octahedra in the presence of B₂O₃ (compared to Al₂O₃) can be related to the smaller average number of oxygens around boron (III), at a fixed O/Ge ratio, compared to aluminum (III). Evidence is presented for a slight decrease of the thermal stability of GeO₆ octahedra in the GeO₂-rich melts above about 1000°C.