Using niobium crucibles for melting phosphate and silicate glasses of various modifier oxide contents, and therefore varying optical basicity (Lambda), was found to result in varying dissolution rates of niobate during melting. Because of their high electronic polarizability, even small concentrations of niobates are detectable in the Raman spectra of glasses. Even <1 mol% Nb2O5 can be identified, as independently confirmed by SEM-EDX analysis. Silica-rich glasses (similar to 60% SiO2, Lambda similar to 0.6) did not show significant Nb dissolution from the crucible, while higher basicity metasilicate glasses (similar to 50% SiO2, Lambda similar to 0.65) and pyrophosphate glasses (similar to 30% P2O5, Lambda similar to 0.7) did show the typical niobate signature in the Raman spectra at 810-840 cm(-1), depending on composition. While niobium is well-dissolved throughout the pyrophosphate glass, metasilicate glasses showed a much more intense Raman signature of niobate units near the outer surface of the glass. Measurements along the cross-section of a fractured metasilicate glass showed a steady decrease of the strength of the niobate signature from the surface toward the bulk of the material. Besides correlation with optical basicity, the tendency of melts to dissolve Nb crucible was discussed in terms of the connectivity or polymerization of the network and the corresponding melt viscosity.

In this work, glass-ceramics in the xBeO–20Fe₂O₃–(80-x)TeO₂ system with x = 0–25 mol% were synthesized by the traditional melt quenching route and studied by inductively coupled plasma optical emission spectroscopy, X-ray diffraction, confocal microscopy, infrared and Raman spectroscopy. BeO addition was found to support the crystallization process of Fe2O3 during melting, and an increased BeO content was associated with an increased fraction of the crystalline Fe₂O₃ phase and an increased size of these crystallites. Furthermore, samples doped with BeO exhibit an increasing polymerization of the residual tellurite glass network compared to the undoped sample. The magnetic properties and specific heat of all synthesized materials were measured, and the results show that all studied samples behave as spin-glasses. Also, the Morin transition of hematite was observed at 260 K with intensity depending on the material content in Fe₂O₃ crystalline phase, the formation of which correlates with the amount of added BeO.

Inspired by the work of John Duffy on optical basicity of oxyfluoride glasses, we apply here the conceptof optical basicity to oxynitride systems. While in the original work of Duffy and Ingram the basicity of amedium could be probed by s2 ions like Pb2+, the low energy intrinsic absorption edge of nitridecontainingsystems does not allow the use of such probe ions. This study uses therefore experimentaldata on refractive index and density of alkaline earth and rare earth containing silicate oxynitride glasses,prepared by the authors or taken from the literature. In addition, literature reports on experimental orcalculated refractive index, density and polarizability data are used to compare pure nitride systems, e.g.bulk or thin film materials that are either crystalline or glassy. We compare simple and complex nitridesystems with their oxygen counterparts, by calculating their optical basicity using the chemicalcomposition as well as the established relationship between optical basicity, L, and electronicpolarizability in oxide systems. Our results on oxynitride systems are in good agreement with Duffy’sprevious work on oxyfluoride glasses and indicate that the optical basicity varies for the isoelectronicanions in nitrides, oxides and fluorides (N3:O2:F) of a cation Mm+ as follows: L(MFm) = 1/2L(M2Om) =1/3L(M3Nm). Using this relation for CaO, for which the optical basicity was set as unity by Duffy andIngram, one has L(CaF2) = 0.50, L(CaO) = 1.00 and L(Ca3N2) = 1.50. The optical basicity of complexnitrides can therefore be calculated by the same method established for oxides using the equivalentfractions and the basicity of the constituent nitrides. The relationship between nitride polarizability aNand basicity L(nitride) was found to be linear, with L(nitride) = 0.39aN 0.14 where aN is given in Å3.

Laser melting techniques have been used in the preparation of unconventional glasscompositions with high melting temperatures. Thus, we wanted to test the feasibilityof using a CO2 laser in the preparation of nitrogen-rich oxynitride glasses and nitridesilicate glasses. Melting from oxides and metallic raw materials, we wanted to studyfirst glass formation and possible evaporation losses of the glass components. Twoglass series were prepared and studied for their structure and thermal properties, onewith Ca2+- and a higher melting La3+-doped soda-lime-silicate (SLS) series. In lessthan 3 minutes of laser melting, spheres of up to 6 mm diameter were successfullyfabricated. The obtained glass samples were homogeneous and transparent in thevisible region. X-ray diffraction and Raman spectroscopic analysis confirmed theamorphous nature of the synthesized samples. Sodium losses increase as calcium isadded to the soda-lime-silicate glass. As expected, increasing Ca2+ or La3+ additionlead to increased depolymerization of the silicate network. Moreover, the increasesin Tg with the addition of Ca2+ or La3+ ions indicating strengthening of the sodalime-silicate glass by increasing strength of the M-O bonds of divalent and trivalentions over monovalent sodium ions, weak Na-O bonds also resulting in significantevaporation loss during the short laser melting times. The thermal stability decreasesupon addition of Ca2+ or La3+ ions to the soda-lime-silicate glasses.

In this article, we investigate the correlation of selected physical properties with structural changes in quaternary mixed modifier alkali/alkaline earth oxide silicate glass systems, focusing either on the mixed alkali effect [(20−x)Na₂O–xK₂O–10CaO–70SiO₂ (x = 0, 5, 10, 15, 20)] or on the mixed alkaline earth effect [20Na₂O–(10−y)CaO–yBaO–70SiO₂ (y = 0, 5, 10)]. A maximum microhardness and packing density, as well as a minimum glass transition temperature were observed for mixed alkali glasses. The mixed alkaline earth glasses do not exhibit any clear extrema in any of the properties studied. The hardness and glass transition temperature decreases, while the density and molar volume increases with increasing BaO content. Raman spectroscopy showed an increase in the Q³ group compared to the Q² and Q⁴ groups as the high field strength ions Na⁺ or Ca²⁺ are substituted by their low field strength analogs K⁺ or Ba²⁺. In the mixed alkali series, the high field strength ion Na⁺, seems to push the low field strength ion K⁺ into lower energy sites when present simultaneously, while such an effect is not apparent for the mixed alkaline earth glasses, where the far IR spectra of mixed glasses are equivalent to the weighted averages of the pure glasses.

Two oxynitride glass series with the composition of 35Na₂O-5BeO-(60-x)SiO₂-xSi₃N₄ and 9Li₂O- 27Na₂O-5BeO-(59-x)SiO₂-xSi₃N₄, were prepared. The glasses' topography and structure were studied by Scanning Electron Microscopy and Raman spectroscopy. The composition was analyzed by Inductively Coupled Plasma Optical Emission Spectrometer, SEM-EDS and nitrogen and oxygen elemental analyzer. Na-(Li)-Be-silicate glasses were found to contain up to approximately 3.4 (or 5.2 for EDS measurements) at.% of N, respectively. The samples were homogenous in their topography and compositions of their cross-sections.

The presence of three-fold coordinated nitrogen atoms in Na-Be-Si-O-N glasses results in higher degree of polymerization as was observed by Raman spectroscopy. The spectrum of analogous glasses with lithium did not show a significant decrease in Q² units but exhibit the presence of Q⁴ units which also indicates a polymerization of the network. The incorporation of nitrogen in these glasses leads to the increase of the glass transition temperature and thermal stability.

Be-Na-(Li)-Si oxide glasses containing up to 15 mol% of BeO were prepared. Their structure was characterized by X-ray powder diffraction and Raman as well as infrared spectroscopic techniques, while their chemical compositions were examined by Inductively Coupled Plasma Optical Emission Spectrometry. All materials were found to be amorphous and contain Al contaminations from minor dissolution of the alumina crucibles. The results of Raman and IR spectroscopies showed that BeO addition to Na-(Li)-Si glass systems resulted in the formation of [BeO_4/2]²⁻ tetrahedra which are inserted into the silicate glass network, demonstrating the intermediate glass-forming role of BeO. In parallel, the effective destruction of Si-O-Si bridges was observed by vibrational spectroscopy. The glass transition temperature was studied by Differential Thermal Analysis and found to range from about 431 °C to 551 °C. A significant increase in T_g by 70 °C was found as SiO₂ was substituted by up to 15 mol% BeO.

Opaque mosaic glass tesserae containing calcium antimonates from Ancient Messene, Greece (1st-4th century CE) were investigated by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. Both trigonal CaSb2O6 and cubic Ca2Sb2O2, with crystallite diameters below 1 pm, were identified as opacifying agents. To better understand ancient technologies, we prepared model glasses that were opacified by crystallisation via a secondary heat treatment, by direct crystallisation during the melting process, or by the addition of pre-reacted calcium antimonate to a base glass. We found that direct crystallisation replicated the antique glass artefacts most accurately. We demonstrated that 0.2 wt% of nucleating agents like TiO2 and SnO2 already exert significant influence on the crystallisation behaviour of calcium antimonates. Secondary scattering centres such as silica and carbonates contribute to the optical appearance. Concurrently, we reproduced opaque white glass ceramics in a reconstructed, wood-fired, Roman-type glass furnace built by Wiesenberg (2014).

Red opaque glasses of two different sites in central Germany, a medieval glassworks in Glashutten, Taunus Mountains, and an early modern glassworks in Wieda, Harz Mountains, were analysed with regard to their optical appearance. By scanning electron microscopy and X-ray diffraction, metallic copper nanoparticles were identified as a conspicuous constituent in these glasses. In addition, similar opaque red glasses were reproduced in the laboratory in order to better understand the manufacturing process. Detailed analysis of the optical scattering was conducted in order to evaluate the role of Cu-0 nanoparticles in the colouring mechanism relative to other possible reasons of colouration. We find clear differences between the possible contributions of Cu2O (cuprite) particles and metallic copper (Cu-0) nanoparticles. Through simulated backscattering spectra we were able to calculate an average copper particle radius in the archaeological glass samples resulting in a value of up to 95 nm, which matches well the results of SEM investigation (minimum 65 nm). Using the methods we applied in this study, it becomes possible to reconstruct various processing conditions as they were applied in medieval manufacture of these particular materials. (C) 2018 Elsevier B.V. All rights reserved.

We report X-ray diffraction, resonance Raman, and infrared (IR) results on pristine ultra-low expansion (ULE) glass, a binary titanosilicate glass with 5.67 mol. % TiO2. ULE processing by femtosecond (fs) laser radiation leads to nanograting writing and photo-darkening for imaging and data storage. We investigate here the vibrational/structural changes induced by fs laser irradiation of ULE at 515 nm. Optical imaging revealed the formation of micro-cavities, and Raman mapping showed molecular oxygen trapped in such cavities of laser-irradiated ULE glass. While titanium in the pristine glass was found predominantly in tetrahedral Ti4+ sites highly dispersed in the silicate matrix, Raman and IR reflectance spectroscopy on laser-irradiated ULE indicated the formation of Ti3+ sites; Ti3+ octahedral sites are formed in the shells of cavities and aggregate in amorphous Ti2O3-type clusters, while the glass around and below cavities contains Ti3+ tetrahedral sites dispersed in the silicate network. Laser-processed ULE glass was found to also exhibit local restructuring of the silicate matrix. Shifts of the strong IR band at about 1080-1100 cm(-1) were translated into changes of the average Si-O-Si bond angle in the laser-transformed areas and found to reflect local density variations; the average local density increases relative to silica glass up to about 8% in the shells of micro-cavities and decreases by about 0.5% in the surrounding material. Chemical processes were proposed to account for photo-darkening and the local structural transformation effect in the probed areas of the fs laser-processed ULE glasses. Published by AIP Publishing.