The structure of borate glasses studied by Raman scattering

Raman spectra of alkali and alkaline-earth borate glasses are reported. These spectra are used to discuss the molecular structure of the glasses. The influence of additions of Al₂O₃ on the structure of alkali borate glasses is also presented. The experimental evidence indicates that the same type of groups are present in borate glasses as in crystalline borates. The presence of tetraborate, metaborate, pyroborate and orthoborate groups in borate glasses is strongly suggested by the Raman spectra.     

Physical properties of glasses containing several glass-forming oxides

Physical properties, such as dielectric loss, acoustic velocity and electrical conductivity of glasses containing several glass-forming oxides were measured at temperatures in the range from −200°C to 200°C. The relationships between the structure and properties of the glasses, and the change in coordination number of individual glass-forming cations in alkali-containing glasses were analysed. It is shown that the glasses containing several glass-forming oxides are characterized by an inhomogeneous structure.     

Structural properties of lithium metaphosphate glasses by ab initio molecular electronic structure calculations

Following a theoretical determination of cluster-models for lithium metaphosphate glass, a theoretical method for the prediction of structural data such as radial and bond distribution functions is presented. These are calculated and compared to experimental data for this particular glass. Useful conclusions are drawn regarding the general use of molecular electronic structure methods for the determination of the structure of glasses.     

Structural study of sol-gel silicate glasses by IR and Raman spectroscopies

A study of the structure and bonding configuration of sol-gel silicate glasses by Raman and infrared spectroscopies is presented. Moreover, a review of the Raman lines and infrared bands assignment, the identification of the non-bridging silicon-oxygen groups and the ring structures are also demonstrated. The evolution of the changes of the bonding configuration in the composition and the stabilization temperature of the bioactive glasses is discussed in terms of the structural and textural characteristics of the glasses. Raman and infrared analyses contribute to the improvement in understanding of the local symmetry for sol-gel silicate glasses. infrared spectroscopy has allowed to identify the vibration bands of the hydroxyl groups associated with various configurations of the terminal silanol bonds on the glass surface and the free molecular water in the glass matrix. Raman analysis has provided an alternative method of quantifying the network connectivity grade and predicting the textural properties of the sol-gel silicate glasses.     

Structure,chemical durability and crystallization behavior of incinerator-based glassy systems

Vitrification by melting is being proposed as a convenient method to solidify different kinds of silicate and other oxide-based inorganic wastes. Incinerator bottom and fly ashes have been mixed with glass cullet, feldspar and clay by-products as melting fluxing agents. Washing, drying, and grinding pre-treatments followed by melting at 1450 °C lead to the formation of glasses and glass-ceramics, depending on the starting materials composition and thermal treatment. The obtained glasses have been studied by SEM, chemical durability tests in aqueous and alkaline environment, leaching test (UNI 10802), and by differential thermal analysis. The glass-ceramics morphology was investigated by XRD and SEM. The results were explained by the structure of the glasses caused by the presence of different amount of modifiers in the glassy lattice. The obtained glasses show good chemical resistance, in particular in alkaline environment and thermal characterization highlighted that the materials are also suitable to obtain glass-ceramics.     

The structure of borosilicate glasses studied by Raman scattering

Raman spectra of alkali and alkaline earth borosilicate glasses are reported. These spectra are used to discuss the molecular structure of the glasses. The influence of Al₂O₃ additions on the structure of borosilicate glass is also discussed. It is shown that the same type of groups are present in borosilicate glasses as in borate and silicate glasses. The presence of large borate groups such as tetraborate and metaborate groups is strongly suggested by the Raman spectra. It appears that boron ions are hardly taken up in the silicon-oxygen network. Our results suggest that the region of phase separation is larger than the region presently acknowledged.     

Adequacy test of the fictive temperatures of silica glasses determined by IR spectroscopy

Adequacy of the fictive temperature determined by the IR spectroscopy method was examined for various silica glasses by measuring the extent of the memory effect. The IR method of fictive temperature measurement of silica glasses relies upon the assumption that a silica glass has a silica structural band with a unique wavenumber when it has a particular fictive temperature. Silica glasses with various impurities or added components such as Cl, F, and OH were given a cross-over heat-treatment and the extent of the resulting deviation of the wavenumber during the second stage heat-treatment at a constant temperature corresponding to the apparent fictive temperature of the sample was determined. Silica glasses containing high concentrations of water or fluorine exhibited distinct memory effects while glasses with low water concentration or Cl did not. These results seem to indicate that the main source of the memory effect in silica glasses is the composition fluctuation rather than density fluctuation. Thus, the IR method of determining the fictive temperature is adequate for high purity silica glasses even when the glass samples have unknown thermal history.     

Vibrational spectra and structure of chloro-fluorozirconate glasses

A series of barium chloro-fluorozirconate glasses have been prepared. Their IR absorption, IR reflectivity and Raman spectra have been measured down to 33 cm^?1. The glass transition and crystallization temperatures have also been measured. The high frequency IR absorption and Raman modes of the chloro-fluorozirconate glasses have been assigned as in fluorozirconate glasses. The IR reflection spectra of chloride-containing glasses differed from the fluorozirconates in that one band was clearly related to Cl atom motions. The structure of the glasses probably consists of zig-zag chains of ZrCl₂F₄ mixed halide octahedra plus a pure fluoride matrix whose structure is similar to that of a ZrF₄BaF₂ glass with the same composition.     

Chemical ordering of interstitial voids: the origin of the first sharp diffraction peak for covalent glasses

The first sharp diffraction peak (FSDP) in the structure factor of covalent glasses and liquids is ascribed to a chemical-order pre-peak in the partial structure factor, S_CC(Q), associated with the ordering of interstitial voids around cation-centred clusters in the structure. The deposition of the FSDP of AX₂-type glasses can be predicted quantitatively. The anomalous behaviour of the FSDP as a function of temperature, pressure and modifier-ion content can all be understood in this interpretation.     

REDOR NMR: approaching structural elucidation of hydrated layers in silicate electrode glasses

Rotational echo double resonance (REDOR) is proposed as an alternative method for the structural determination of hydrated glasses, in particular of the incorporation of protons into the structure. First ²³N---¹H and ²⁷Al---¹H REDOR nuclear magnetic resonance data are presented for hydrated layers of electrode glasses of the system Na₂O---Al₂O₃---SiO₂ showing distinct differences of both the equilibrium amplitudes of the REDOR signals and the heteronuclear dipole couplings. The potential of this approach is demonstrated for kaolinite in terms of quantitative results.     

A structural study of sol–gel and melt-quenched phosphate-based glasses

Phosphate-based glasses have recently attracted much interest as a new generation of biomaterials because of their ability to react and dissolve in the physiological environment and eventually to be replaced by regenerated hard or soft tissue. A series of phosphate-based glasses containing 45 mol% P₂O₅ and various amounts of CaO and Na₂O were synthesized by sol–gel and melt-quenching techniques. A comparison between the structure of the sol–gel glass and the structure of the analogous melt-quenched glasses has been undertaken. A broad-based characterization approach combining different techniques has been used to investigate the short-range structure of the glasses and the effect of adding modifier oxides to the network structure (conventional and high energy X-ray diffraction, infra-red spectroscopy, ³¹P solid state magic angle spinning NMR spectroscopy). Sol–gel and melt-quenched glasses appear to have a similar structure, showing similar Qⁿ distributions and atomic correlations.     

Local structure around lead,barium and strontium in waste cathode-ray tube glasses

Cathode-ray tubes (CRTs) are made of two different kinds of glasses. The front part, panel, or screen, is made of barium- and strontium-containing glasses, while the rear part, the funnel, is made of lead-containing glasses. The structure and the role of these elements in the glasses are different: lead oxide is generally considered as a network intermediate whereas barium and strontium oxides as network modifiers. To study the local structure around the three aforementioned heavy elements we have used X-ray absorption spectroscopy (XAFS) on Pb and Ba L_III-edges and Sr K-edge as well as X-ray photoemission spectroscopy (XPS) analyzing the Pb 4f, Sr 3p, Ba 3d, Si 2p and O 1s core peaks. Due to the complex formulation of these glasses the coordination of lead and strontium could be affected compared with the local structure of binary glassy systems. We demonstrate that the average coordination number of lead is close to three (Pb–O distances being 2.24 Å) as in other lead silicate glasses. In case of strontium, the coordination number is found close to five (Sr–O distances being 2.52 Å) similar to that in Sr-containing glasses.     

Structural investigation of SnO-B2O3 glasses by solid-state NMR and X-ray photoelectron spectroscopy

Local structure of the SnO-B₂O₃ glasses was investigated using several spectroscopic techniques. ¹¹B MAS-NMR spectra suggested that BO₄ tetrahedral units maximized at around the composition with 50 mol% SnO. The BO₄ units were still present at compositions with high SnO content (67 mol% SnO), suggesting that SnO acted not only as a network modifier but also as a network former. O1s photoelectron spectra revealed that the addition of small amounts of SnO formed non-bridging oxygens (NBO) (B-O?Sn) and the amounts of NBO increased with an increase in SnO content. ¹¹⁹Sn Mössbauer spectra indicated that Sn was present only as Sn(II) in the glasses. The structure of the SnO-B₂O₃ glasses was compared with that of conventional alkali borate glasses and lead borate glasses. The thermal and viscous properties of these glasses were discussed on the basis of the glass structure revealed in the present study.     

Structure and properties of glasses in the MI + M2S + (0.1Ga2S3 + 0.9GeS2), M = Li, Na, K and Cs, system

The structure and properties of glasses in the MI + M₂S + (0.1Ga₂S₃ + 0.9GeS₂), M = Li, Na, K and Cs, system were studied using Raman, IR spectroscopy, DSC and density measurements to help better understand the ionic transport in these glasses. The glass forming ranges of these ternary glasses were compared to those of the binary alkali sulfide and germanium sulfide systems. The more extensive glass forming range in the Na₂S system was used to examine the more extensive changes of structure and properties of these glasses as a function of Na₂S content. As expected, non-bridging sulfurs (NBS) form with the addition of alkali sulfide. Unlike their oxide counterparts, however, the alkali sulfide doped glasses appear to support longer-range super-structural units. For example, evidence that the adamantine-like structure exists in the K₂S and Cs₂S modified glasses is found in the Raman spectra of the glasses. The structural role of the alkali iodide addition was also explored since the addition of alkali iodide helps to improve the conductivity. For most of these glasses, as observed in many other oxide glasses, the added MI dissolves interstitially into the glass structure network without changing the alkali sulfide network structure. In 0.6Na₂S + 0.4(0.1Ga₂S₃ + 0.9GeS₂) glasses, however, the added NaI may affect the glass structure as it causes systematic changes in the frequency of the Ge-S network mode as seen in the Raman spectra.     

Raman and optical reflection spectra of germanate and silicate glasses

Germanate and phosphosilicate glasses made in oxygen surplus conditions were studied by Raman and optical reflection methods. We found that the optical reflection spectra of the germanate glasses are quite similar to the one those of a GeO₂ crystal with the α-quartz structure. The reflection of phosphosilicate glasses is very close to silica glass-related spectra. Hence, the determining influence of the tetrahedral structure on reflection spectra is revealed. The Raman spectra of germanate samples are similar to those reported the one known in the literature. Octahedral entities, namely bands similar to stishovite vibration modes, were difficult to detect in phosphosilicate glasses through Raman spectroscopy.     

EPR and UV–Vis characterization of multicomponent germano-silicate glasses for photonics

Photosensitive, germanium-doped multicomponent silicate glasses with different amount of boron oxide and sodium oxide were prepared and investigated by means of electron paramagnetic resonance (EPR) and ultraviolet–visible (UV–Vis) spectroscopy in order to investigate the structural changes occurring in the glasses under UV laser irradiation at 248 nm (KrF excimer UV laser). Spectral data were recorded before and after UV laser irradiation: all the glasses showed EPR signals only after UV laser irradiation, independently from the presence of a UV–Vis absorption band on the as prepared glasses. The main results showed that the presence or the absence of boron and sodium and their amount play a role in the type and the number of defects, their time and thermal decay, under the same UV laser exposure conditions. A clear correlation between the EPR signal and the UV–Vis absorption is observed only for the 240 nm band. It is also demonstrated that the sodium ions decrease the number of paramagnetic defects in these glasses and deeply change the germano-silicate glass structure. The presence, the absence and the co-presence of sodium and boron ions has a role in the structure, the number, the nature and the stability of the paramagnetic defects. It is important to understand the role of sodium and boron in order to increase the photosensitivity of germano-silicate glasses, for their interest in the field of ion-exchangeable glasses for photonic waveguides and Bragg-grating based devices.     

Properties and structure of glasses in the system AsS

In obtaining the glass, at first, the raw materials were mixed up and melted by using porcelain crucible, but in this case it was found by infra-red absorption method that the glass contains some oxygen impurities. Then a range of glasses was prepared by melting elementary pure As and S in definite proportions in a sealed vacuum tube. The infra-red absorption, molecular volume, molecular refraction, hardness, thermal expansion and viscosity of sample glasses with various compositions were investigated and, additionally, solubility of these glasses into CS₂ was measured. The structure of glasses in the system AsS was studied by X-ray diffraction and a structural model was set up. From the measurements the following conclusions were made. The structure of As₂S₃ glass is a distorted form of the crystalline orpiment structure. With increasing S content above As₂S₃, S is likely to exist in the chain-like form, but when the S content is greater than that in As₂S_8–10, both chain-like and ring type forms co-exist. With decreasing S content below As₂S₃, S between As and As is eliminated and AsAs bonds are formed. Consequently a deformation of layer occurs and an expansion of the layer distance was observed.     

Structure of single and mixed alkali Li–Rb borate glasses by neutron diffraction

We have compared the local structure of Li–, Rb– and Li–Rb diborate glasses using neutron diffraction and reverse Monte Carlo simulations. The fraction of tetrahedral boron decreases as the Rb content increases, but is similar in the single and mixed alkali glasses at diborate compositions. Rb borate glasses exhibit an extensive cation ordering with Rb–Rb correlations at 4.7 and 7 Å. The environment of alkalis is slightly modified between the single and mixed glasses while their relative distribution is essentially random. This indicates that the alkali environment is affected by the presence of a different alkali and this cation–cation interaction could be a fundamental mechanism, together with the site mismatch, to explain the mixed alkali effect.     

Structure and lithium ion diffusion in lithium silicate glasses and at their interfaces with lithium lanthanum titanate crystals

Solid state lithium ion electrolytes are important to the development of next generation safer and high power density lithium ion batteries. Lithium containing glasses such as lithium silicate glasses have been widely studied due to their high ionic conductivity. Recently, lithium silicate glasses were introduced in polycrystalline lithium lanthanum titanate (LLT) ceramics as intergranular thin films between the crystalline grains to achieve higher lithium ion conductivities in these solid state electrolytes. In this work, we present investigations of the structure and diffusion behavior of lithium silicate glasses and their interfaces with LLT crystals using molecular dynamics simulations. The short and medium range structures of the lithium silicate glasses were characterized and the ceramic/glass interface models were obtained using MD simulations. Lithium ion diffusion behaviors in the glass and across the glass/ceramic interfaces, as well as the effect of atomic structure on diffusion behaviors, were investigated. It was found that there existed a minor segregation of lithium ions at the glass/crystal interface. The interface lithium ion diffusion energy barrier was found to be dominated by the glass phase.     

Spectroscopy of transition metal ions in inorganic glasses

Transition metal (TM) ions have been used as colouring agents in the glass industry for a long time. Recently, great attention has been paid to the TM ion doped glasses for the development of new lasers or luminescence materials. The absorption spectra of TM ions in different kinds of glasses have been studied extensively, but little work has been done for fluorescence and relaxation spectra. In this paper emphasis is laid on analysing the influence of chemical bond characteristics of the base glass on the spectra and the site structure of transition metal ions in glasses. Recent experimental results about the luminescence characteristics of low valence ions (such as Ti³⁺, Cr³⁺, V²⁺, Mn²⁺, Cu⁺, Mo³⁺) in glasses are also reported.