Glass formation in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

New glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system have been prepared and characterized. The glass-forming regions have been explored and the stability of the glasses against crystallization studied. Results show that the PbBr₂–PbCl₂–P₂O₅ ternary system has a broad glass-forming region which extends to 30 mol% P₂O₅. Most of the glasses in this system show strong stability against crystallization and some have glass transition temperatures as low as 146°C. When 5% PbO or 5% PbF₂ is introduced into the PbBr₂–PbCl₂–P₂O₅ system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF₂ and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF₂ alone improves the glass-forming ability of the system while the introduction of PbO alone lowers the glass-forming ability.     

Glass formation, properties and structure of glasses in the P2O5---WO3---K2O---Al2O3 system

Glass formation in the P₂O₅---WO₃---K₂O---Al₂O₃ system was investigated and the glass-forming regions are presented.

the properties of the glasses in the P₂O₅---WO₃---K₂O---Al₂O₃ system (Al₂O₃ 8 mol.%) are reported.

The colouration of glass was studied. It was found that W⁵⁺ ions make glass blue.

Infrared spectra were measured by means of making KBr pills. Results of the investigation suggest that P---O---P, P---O---W, and W---O---W bonds form a continuous network in the phosphate glasses. So we suggest that tungsten trioxide is a glass former.     

Glass formation and optical properties of glasses in the systems (R2O or R''O)-Ta2O5---Ga2O3

Gallate glasses containing no conventional glass formers were obtained in the systems (Na₂O, K₂O or Cs₂O)-Ta₂O₅---Ga₂O₃ and (Sr or BaO)-Ta₂O₅---Ga₂O₃ by an ordinary crucible-melting technique. The glasses showed high optical transmission in the infrared as well as in the visible region. Infrared spectroscopic analysis suggested that the Ga³⁺ ions are tetrahedrally coordinated in the glasses. The glass-forming tendency of the melt and the infrared transmission of the glasses are discussed in terms of the glass structure.     

Structure and properties of the pure and Pr-doped Ge25Ga5Se70 and Ge30Ga5Se65 glasses

The Ge₂₅Ga₅Se₇₀ and Ge₃₀Ga₅Se₆₅ pure and Pr³⁺-doped glasses were prepared by direct synthesis from elements and PrCl₃. It was found that up to 1 mol% PrCl₃ can be introduced in the Ge₂₅Ga₅Se₇₀ and Ge₃₀Ga₅Se₆₅ glasses. Both types of glasses with overstoichiometric and substoichiometric content of Se were homogeneous and of black color. The optical energy gap is E^opt_g=2.10 eV, and the glass transition temperature is T_g=543 K for Ge₂₅Ga₅Se₇₀ and T_g=633 K for Ge₃₀Ga₅Se₆₅. The long-wavelength absorption edge is near 14 μm and it corresponds to multiphonon processes. Doping by Pr³⁺ ions creates absorption bands in transmission spectra, which can be assigned to the electron transitions from the ground ³H₄ level to the higher energy levels of Pr³⁺ ions ³H₅, ³H₆, ³F₂, ³F₃ and ³F₄, respectively. By excitation with YAG:Nd laser line (1064 nm), two intense luminescence bands (1343 and 1601 nm) were excited. The first band can be ascribed to electron transitions between ¹G₄ and ³H₅ energy levels of Pr³⁺ ions. Full width at half of maximum (FWHM) of the intensity of luminescence was found to be 70 nm for (Ge₂₅Ga₅Se₇₀)_1 − x(PrCl₃)_x and (Ge₃₀Ga₅Se₆₅)_1 − x(PrCl₃)_x glasses. The FWHM in selenide glasses is lower than in halide and sulphide glasses. The second luminescence band (1601 nm) can be probably ascribed to the transitions between ³F₃ and ³H₄ energy levels of Pr³⁺ ions. The absorption and luminescence spectra of Pr³⁺ ions in studied glasses are slightly influenced by stoichiometry of glassy matrix. The Raman spectra of studied glasses were deconvoluted and assignment of Raman bands to individual vibration modes of basic structural units was suggested. The structure of studied glasses is mainly formed by corner-sharing and edge-sharing GeSe₄ tetrahedra. The vibration modes of Ga-containing structural units were not found, they are apparently overlapping with Ge-containing structural units due to small difference between atomic weights of Ge and Ga. In the glasses with substoichiometry of Se, the Ge–Ge bonds of Ge₂Se₆ structural units were found. In Se-rich glasses the Se–Se vibration modes were found. In all studied glasses also ‘wrong' bonds between like atoms were found in small amounts. Maximum phonon energy of studied glasses is 320 cm⁻¹.     

Influence of the mixed alkali effect on the chemical durability of Na2O---TiO2---SiO2 glasses

The influence of the mixed alkali effect on the chemical durability of Na₂O---TiO₂---SiO₂ glasses during substitution of K₂O for Na₂O in 21Na₂O---26TiO₂---53SiO₂ glasses was investigated. The best chemical durability was found at K₂O/Na₂O = 2.5 where the minimum was close to K⁺ ions of larger size. It was shown that the water corrosion process of the system was predominantly controlled by both the mobility and the exchange function of K⁺ ions resulting in the generation of a titanium-rich and silicon-rich layer at the surface. The mixed alkali effect can therefore be applied to lower the rate of water corrosion and increase chemical durability so that optical glasses with higher chemical durability can be obtained.     

Properties and structure of RO---Na2O---Al2O3---P2O5 (R = Mg, Ca, Sr, Ba) glasses

The properties and structure of (45 - x)RO · xNa₂O · 2.5Al₂O₃ · 52.5P₂O₅ (R = Mg, Ca, Sr, Ba, 0 x 31 mol%) glasses were investigated. The variation in the molar volumes of glasses in the MgO series is closely related to the formation of the end groups in the glasses with the substitution of Na⁺ ions for Mg²⁺ ions, resulting in a variation of the density and refractive index of the glasses. The properties of glasses containing CaO in terms of Na₂O substitution depend mainly on the low field strength of Na⁺ ions substituting for CaO even though the end groups occurring in the glasses increased. The variation in properties of the glasses containing SrO and BaO, some of which were substituted by Na₂O, could be explained by differences in masses, field strength and polarizability between the Na⁺ ions and the alkaline-earth ions due to a small variation in the structure of the glasses despite Na₂O substitution.     

Ionic conduction in As2S3---Ag2S, GeS2---GeS---Ag2S and P2S5---Ag2S glasses

The glass-forming region in the system P---S---Ag was determined and density, thermal expansion, dc conductivity and the transport number of Ag ions were measured for P₂S₅---Ag₂S glasses found in the P---S---Ag system. The results for the transport number measurement show that P₂S₅---Ag₂S glasses are purely ionic conductors owing to the Ag ion migration, like most of the As₂S₃---Ag₂S and GeS₂---GeS---Ag₂S glasses reported previously. Glass structure and ionic conduction processes in As₂S₃---Ag₂S, GeS₂---GeS---Ag₂S and P₂S₅---Ag₂S glasses are discussed, based on their ionic conductivity and density data. The structural concept of -Ag₂S was applied to these glasses, which suggests that the Ag ions in the glasses are distributed in the available Ag ion sites in the non-conducting framework composed of both S anions and As, Ge or P cations. In each system the ionic conductivity increases linearly with increasing Ag⁺/total cation (%) in glass composition, the determining factor being the activation energy for ionic conduction alone. Thus, the activation energy in these glasses depends predominantly upon the molar ratio of Ag ions to total cation in the glass, irrespective of the kind of system. Small differences in the activation energy among the three systems can be interpreted as arising from differences in the field strength of As, Ge and P cations.     

Raman spectra of rapidly quenched glasses and melts containing large amounts of Li2O

Raman spectra were measured of rapidly quenched glasses and the corresponding liquids in binary and ternary (pseudobinary) systems composed of Li₂O and several glass-forming oxides such as B₂O₃, P₂O₅, and/or SiO₂. The fractions of the various structural units present were determined from the deconvoluted Raman peaks. Glasses with large amounts of Li₂O were composed of discrete structural units such as ortho-oxoanions and pyro-oxoanions. Based on these data the structural units in the glasses and the corresponding liquids were identical, although in some cases those in the corresponding crystals were different. In the pseudobinary systems combining pyro-oxosalts of lithium borate, phosphate and silicate, non-bridging oxygens were preferentially formed at the phosphate structural units rather than at the borate or silicate structural units. This order of preference was consistent with that of the acidity of the glass-forming oxides in the liquids.     

Formation and structure of titanate glasses

The formation of high titanium oxide (30–60 wt%) containing glasses was studied. Stable titanate glasses with high content of TiO₂ and BaO could be obtained even without other glass-forming oxides. It is demonstrated that the coloration of titanate glasses with high content of TiO₂ is due to oxygen loss during the melting. A systematic study of controlling melting and heat treatment conditions led to the successful decoloration of titanium oxide containing glasses. Infrared spectra and X-ray diffraction studies showed that Ti⁴⁺ in titanate glasses is in sixfold coordination. Phase separation was observed by electron microscopy when the titanate glasses were heat-treated at the temperature above T_g. The crystallization of titanate glasses is generally preceded by phase separation. The obtained crystalline phases are mainly different titanates.     

Cation site occupation by Ag/Na ion-exchange in R2O–Al2O3–SiO2 glasses

Ag⁺/Na⁺ ion-exchanged R₂O–Al₂O₃–SiO₂ glasses with uniform concentration profile of Ag⁺ and Na⁺ were prepared by heat treatment in molten silver salt followed by holding at the same temperature in an ambient atmosphere. Their glass transition temperature (T_g) and thermal expansion coefficient (TEC) were measured and structures were investigated using ²⁹Si-MAS NMR, ²⁷Al-MAS NMR, IR and Raman spectroscopies. Both T_g and TEC decreased with increase of the exchange ratio, but T_g was still above the ion-exchange temperature of 400°C even for the fully exchanged sample. The ²⁹Si- and ²⁷Al-MAS NMR spectra were mostly unchanged and no sign of the structural alteration of the glass network was observed. On the other hand, the vibrational spectra showed remarkable peak shifts depending on the exchange ratio. From these structural results, it was found that when the exchange ratio was low, the introduced Ag⁺ ions were stabilized at the non-bridging oxygen (NBO) site, and then Na⁺ ions in AlØ₄ site were exchanged by Ag⁺ ions after full replacement of NBO sites, where Ø represents the bridging oxygen.     

The vanadyl ion as a spectroscopic probe:: Measurement of optical basicity in the visible / near-infrared region

Previously optical basicity was always measured using s-p absorption spectra of Tl⁺, Pb²⁺ and Bi³⁺, but since these spectra are in the UV region, media containing oxides of transition metal aons have been excluded from such measurements. The present work shows that for VO²⁺ the d-d transition ²B₂ → ²E red-shifts with increasing optical basicity, and a study in the Na₂O---P₂O₅ glass system allows comparison with results obtained previously with Tl⁺ and other probe ions. It is shown that under controlled conditions determination of optical basicity with VO²⁺ is viable, and since the ²B₂ → ²E spectral band occurs in the visible / near-IR region, UV transparency of the medium is no longer necessary. The VO²⁺ probe therefore offers a means of obtaining optical basicities of glasses containing e.g. PbO, or of metallurgica slags containing e.g. Fe₂O₃ or MnO.     

Raman spectroscopic study on the structure of ZnCl2---ZnX2 and ZnCl2---KX (X = Br, I) glasses

Raman spectra have been measured for ZnCl₂---ZnX₂ and ZnCl₂---KX (X = Br, I) glasses to investigate the structure of the glasses with varying composition. The assignment of each band was made, and the change of the spectra with composition was explained in terms of the bridging and non-bridging states of halide ions and the change of the tetrahedral units, ZnX_nCl_4−n²⁻ (n = 0–4), formed in the glasses. As the content of ZnX₂ in ZnCl₂---ZnX₂ glasses increases (20 → 80 mol%), the peak frequency of the Zn---Cl stretching mode increases (238 → 248 cm⁻¹ in X = I glasses, 238 → 259 cm⁻¹ in X = Br glasses) while the Zn---I and Zn---Br stretching frequencies decrease (173 → 120 cm⁻¹ for Zn---I, 196 → 157 cm⁻¹ for Zn---Br). The decrease of the Zn---I and Zn---Br band frequencies was attributed to the increase of the number n of the ZnX_nCl_4−n²⁻ tetrahedra. The increase of the Zn---Cl frequency suggests the existence of the bonding state of Cl⁻ ions which is intermediate between the bridging and the non-bridging states. In ZnCl₂---KX glasses, the Zn---Cl_non-bridging band at about 300 cm⁻¹ was observed in addition to the bands observed in ZnCl₂---ZnX₂ glasses. The addition of KX produces non-bridging anions while the tetrahedral units, ZnX_nCl_4−n²⁻ are also formed.     

New solvents for the growth of substituted BaFe12O19 single crystals from high-temperature solutions

The solubility of a series of hexaferrite derivatives of BaFe₁₂O₁₉ in solvents of the system Na₂O-B₂O₃ with oxide ratios of 7:3 and 3:2 has been investigated. The temperature dependences of the saturation concentration in these solvents are determined for ferrites with the nominal compositions Ba_0.8Pb_0.2Fe₁₂O₁₉, BaFe₁₀Ga₂O₁₉, BaFe₁₀Al₂O₁₉ and BaFe₈Mn₂ Ti₂O₁₉. Single crystals of BaFe₁₂O₁₉, in which part of the metal ions are replaced by various amounts of Pb²⁺, Ga³⁺, Al³⁺ and Mn²⁺ + Ti⁴⁺ ions, are g rown from the solutions by the slow cooling technique. The distribution coefficients of the substituting ions and the compositions of the crystals obtained are established by microprobe analysis (EPMA). Information on the position of substitution is obtained from the Mössbauer spectra.     

Glass formation and crystallization in the ZrO2---Al2O3---P2O5 system

The glass formation of the ZrO₂---Al₂O₃---P₂O₅ system in the high phosphate region is determined. The crystallization process and the crystal types formed during heat treatment have been studied. The structure of these glasses is discussed.     

Formation of oxygen-deficient type structural defects and state of ions in SiO2 glasses implanted with transition metal ions

The properties and concentrations of oxygen-deficient type structural defects in type III SiO₂ glasses implanted with Ti⁺, Cr⁺, Mn⁺, Fe⁺, or Cu⁺ to doses from 0.5×10¹⁶ to 6×100¹⁶ ions/cm² at an energy of 160 keV have been measured by using vacuum UV and EPR spectroscopies. An intense absorption band centered around 7.5 eV is observed in all the samples except for Cu-implanted ones and is attributed primarily to Si---Si homo-bonds with the bond distance close to that of the Si₂H₆ molecule. The homo-bond and implanted ion concentrations are of the same order of magnitude in the implanted layers. An E′ type center associated with the homo-bond is observed in all the samples except for Cu-implanted ones. Anomalous behaviors of the Cu-implanted samples are attributed to the formation of Cu-colloids. An enhanced formation of metallic particles or colloids is suggested for the samples implanted with Cr, Mn or Fe to doses higher than 3×10¹⁶ ions/cm².     

Mössbauer studies on some glasses and crystals in the Na2O---Fe2O3---SiO2 system

Mössbauer absorption measurements have been made at room temperature on ⁵⁷Fe in iron sodium silicate glasses containing 3–15 mol% Fe₂O₃ and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s⁻¹, while those of Na₂O · Fe₂O₃ · 4 SiO₂ and 5 Na₂O · Fe₂O₃ · 8 SiO₂ crystals showed much smaller quadrupole splitting, 0.28 mm s⁻¹ and 0.10 mm s⁻¹, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi₂O₆ and MFeSi₃O₈ crystals, the quadrupole splitting became wider and approached to 0.73 mm s⁻¹. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals.     

Structural and thermal properties of some tellurite glasses

Tellurium oxide glasses were prepared by the hammer and anvil technique. The glass systems are (0.85TeO₂ + 0.15Z), where Z = K₂O, TiO₂, V₂O₅, MnO, Fe₂O₃, CoO, NiO or CuO. A second group is a ternary system 0.85TeO₂+(0.15 − x)TiO₂ + xFe₂O₃) with x=0.0, 0.05, 0.1, 0.15 mol. X-ray diffraction, infrared spectroscopy and differential thermal analysis measurements were carried out. The present study showed the different glass-forming groups, the glass transition and crystallization temperatures as well as the crystallization processes.     

Migration of Cu ions in Cu2O---Al2O3---SiO2 glasses on heating in air

The behavior of copper ions in the Cu₂O·Al₂O₃·4SiO₂ (in moles) glass on heating in air at temperatures up to 500°C was studied. When the glass, in which about 90% of Cu was present as Cu⁺ ions, was heated in air above 300°C, a CuO layer was formed on the surface. The amount of CuO was increased with heating temperature and time, corresponding to the decrease in weight of the glass. Furthermore, the fraction of Cu²⁺ ions in the glass increased. These observations suggest that oxygens do not diffuse into the glass, but Cu⁺ ions migrate to the surface from the interior to balance the surplus positive charge produced by the oxidation of Cu⁺ to Cu²⁺ ions inside the glass. The following reaction scheme for the formation of the CuO layer was proposed; 2Cu⁺(interior) + ₂¹O₂(surface) → Cu²⁺(interior) + CuO(surface).     

Molecular dynamics simulation of the mixed anion glasses Li4SiO4---Li3BO3

The structure and the mixed anion effect in the conductivity have been examined for the mixed anion glasses Li₄SiO₄---Li₃BO₃ by molecular dynamics (MD) simulation and X-ray diffraction (XRD) analysis. Structure factors derived from the MD simulation are in good agreement with those from derived from the XRD analysis of the actual glasses, showing that the MD simulation successfully reproduces the actual glass structure. Moreover, the enhancement of the diffusion coefficients of the Li⁺ ions in the middle of the composition range in the system Li₄SiO₄---Li₃BO₃ is simulated by the MD calculation. Structural analysis of the glasses derived from the MD simulation revealed that the increase in the halfwidth of the modified radial distribution function of the Li---O pairs due to the mixing of two ortho-oxoanions is one of the factors in the origin of the mixed anion effect in the conductivity.     

Study of electrical properties of MoO3–Fe2O3–P2O5 and SrO–Fe2O3–P2O5 glasses by impedance spectroscopy. II

The electrical and dielectric properties for three series of MoO₃–Fe₂O₃–P₂O₅ and one series of SrO–Fe₂O₃–P₂O₅ glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO₃ is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe₂O₃ content and Fe(II)/Fe_tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe₂O₃ content in MoO₃–Fe₂O₃–P₂O₅ glasses with O/P at 3.5 the dc conductivity, σ_dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe₂O₃ and is independent of the MoO₃ content. Also, the dielectric properties such as ^′(ω), ^″(ω) and σ_ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO₃. On the other hand, the dc conductivity for MoO₃–Fe₂O₃–P₂O₅ glasses with O/P > 3.5 increases with the substitution of MoO₃ which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ^′(ω) with increasing MoO₃ content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe₂O₃–P₂O₅ glasses the conductivity and dielectric permittivity remained constant with increasing SrO.