Search

The short-range order of binary zinc borate glasses, xZnO–(1 − x)B2O3, has been quantitatively described as a function of ZnO content over the entire glass forming range for the first time, to the best of our knowledge.

OVERVIEWIn theory, any molten material can form a glass when quenched fast enough. Most natural glasses are based on silicates and for thousands of years only alkali/alkaline earth silicate and lead-silicate glasses were prepared by humankind. After exploratory glass experiments by Lomonosov (18th ct) and Harcourt (19th ct), who introduced 20 more elements into glasses, it was Otto Schott who, in the years 1879–1881, melted his way through the periodic table of the elements so that Ernst Abbe could study all types of borate and phosphate glasses for their optical properties. This research also led to the development of the laboratory ware, low alkali borosilicate glasses. Today, not only can the glass former silicate be replaced, partially or fully, by other glass formers such as oxides of boron, phosphorous, tellurium or antimony, but also the oxygen anions can be substituted by fluorine or nitrogen. Chalcogens, the heavier ions in the group of oxygen in the periodic table (S, Se, Te), on their own or when paired with arsenic or germanium, can function as glass formers. Sulfate, nitrate, tungstate and acetate glasses lack the conventional anion and cation classification, as do metallic or organic glasses. The latter can occur naturally—amber predates anthropogenic glass manufacture by more than 200 million years.In this chapter, we are going to provide an overview of the different glass families, how the structure and properties of these different glass types differ from silicate glasses but also what similarities are dictated by the glassy state. Applications and technological aspects are discussed briefly for each glass family.

Electrical properties of beryllium-alumino-tellurite glasses and glass–ceramics doped with iron ions were studied using impedance spectroscopy. The conductivity was measured over a wide frequency range from 10 mHz to 1 MHz and the temperature range from 213 to 473 K. The D.C. conductivity values showed a correlation with the Fe-ion concentration and ratio of iron ions on different valence states in the samples. On the basis of Jonscher universal dielectric response the temperature dependence of conductivity parameters were determined and compared to theoretical models collected by Elliott. In glasses, the conduction process was found to be due to the overlap polaron tunneling while in glass–ceramics the quantum mechanical tunneling between semiconducting crystallites of iron oxides is proposed. The D.C. conductivity was found not to follow Arrhenius relation. The Schnakenberg model was used to analyze the conductivity behavior and the polaron hopping energy and disorder energy were estimated. Additionally, the correlation between alumina dissolution and basicity of the melts was observed.

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.

Ultralow expansion (ULE) glass, a binary TiO2–SiO2 glass with 5.67 mol % TiO2, was exposed to microindentation. Vitreous silica was similarly treated and used as a reference material, including the...

The role of boron oxide in glass science is broad, spanning from borate glasses used as bioactive materials, sealing agents, dosimeters, and radiation shielding glasses, to an additive in chemically durable or nuclear-waste-immobilizing borosilicate glasses. The structure of borate glasses from pure boron oxide glass up to highly modified compositions is discussed in this chapter, covering the full range of borate chemical structures in glasses and melts. The boron anomaly, the conversion of trigonal borate units to tetrahedral borate units is introduced, and we outline the impact this has on the structure and properties of modified borate glasses. The factors influencing the equilibrium between three- and four-coordinated boron, such as modifier type and quantity, synthesis temperature, and the number of non-oxygen anions, are looked at to demonstrate the highly tuneable nature of borate glasses for diverse applications.

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 pre ...

Inspired by the work of John Duffy on optical basicity of oxyfluoride glasses, we apply here the concept of optical basicity to oxynitride systems. While in the original work of Duffy and Ingram the basicity of a medium could be probed by s2 ions like Pb2+, the low energy intrinsic absorption edge of nitride-containing systems does not allow the use of such probe ions. This study uses therefore experimental data 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 or calculated 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 nitride systems with their oxygen counterparts, by calculating their optical basicity using the chemical composition as well as the established relationship between optical basicity, Λ, and electronic polarizability in oxide systems. Our results on oxynitride systems are in good agreement with Duffy's previous work on oxyfluoride glasses and indicate that the optical basicity varies for the isoelectronic anions in nitrides, oxides and fluorides (N3-:O2-:F-) of a cation Mm+ as follows: Λ(MFm) = 1/2Λ(M2Om) = 1/3Λ(M3Nm). Using this relation for CaO, for which the optical basicity was set as unity by Duffy and Ingram, one has Λ(CaF2) = 0.50, Λ(CaO) = 1.00 and Λ(Ca3N2) = 1.50. The optical basicity of complex nitrides can therefore be calculated by the same method established for oxides using the equivalent fractions and the basicity of the constituent nitrides. The relationship between nitride polarizability αN and basicity Λ(nitride) was found to be linear, with Λ(nitride) = 0.39αN- 0.14 where αN is given in A3.

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 de-creases, 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.

A systematic investigation of the luminescence properties of Dy3+ doped alkali-alkaline earth orthoborates of the stoichiometric composition XZBO3 with X = Li, Na, K and Z = Mg, Ca, Ba was conducted. XRD diffractograms show that the compounds LiMgBO3, LiCaBO3, LiBaBO3, NaMgBO3, NaCaBO3, NaBaBO3, and KMgBO3 could be produced in high purity. Relatively intense luminescence was observed only for the phases LiCaBO3, NaMgBO3, NaCaBO3 and NaBaBO3. Micro Raman investigations show that the Dy3+ luminesence mainly originates from the orthoborate phase in these samples. Photo-luminescence spectroscopy of LiCaBO3, NaCaBO3 and NaBaBO3 shows the typical Dy3+ emission with the prominent emission peak in the yellow spectral range around 575 nm. A second, but much less intense peak is observed at around 485 nm (cyan). The luminescence emission spectrum of Dy3+:NaMgBO3 is much different: here, the highest emission intensity is observed at about 485 nm. It is proposed that the Dy3+ ions occupy the Na positions in this crystal phase which has a much higher symmetry than the alkaline earth positions in the other examined crystal phases. This is supported by broadened and more split up peaks in the excitation and emission spectra of Dy3+:NaMgBO3 suggesting a much stronger local crystal field at the rare earth position in this compound. The results are additionally compared to spectroscopic data of different well known Dy3+ doped crystalline compounds and Dy3+ and Eu3+ doped alkali-alkaline earth orthoborates from other publications, which offer further insight into the relation between the crystallographic sites of the doped rare earth ions and their luminescence.

Glass formation and structure-property relations were explored in highly modified borate glasses containing high loads of rare-earth elements, whose crystalline analogues display a trigonal to tetrahedral borate phase transition (BO33− → BO2O23−, where O and O− indicate bridging and non-bridging oxygen atoms). The resulting borate networks are completely depolymerized, where borate anions are crosslinked to rare-earth and modifier cations via ionic bonds. The borate structure was found to be based on a single structural unit, BO33− triangles, whose fundamental vibrations are all active in both the Raman and infrared. The local environment of the rare-earth ions in orthoborate glasses was studied with far infrared spectroscopy and, in some cases, by using terbium as a probe ion. A linear correlation was obtained between the effective force constant in the far infrared and the field strength of the rare-earth cation.

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 Ca2Sb2O7, with crystallite diameters below 1 μm, 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).

Sodium-calcium-phosphate glasses doped with SiO2 or Si3N4 having similar sodium ion concentrations were prepared by melt quenching. The conductivity was measured by impedance spectroscopy under nitrogen atmosphere in a wide frequency range (10 mHz–1 MHz) and wide temperature range (153–473 K). At 36.6 °C, DC conductivities of all glasses vary between 1.1 ∗ 10−12 and 8.9 ∗ 10−12 S cm−1 and have similar activation energies (between 0.87 and 0.91 eV), which are characteristic for an ionic conduction mechanism. The analysis of AC conductivities showed that the spectra are governed by one dynamic process – hopping of the mobile charge carriers - which may be described i.e., by the ‘concept of mismatch and relaxation’ or by the ‘random barrier’ model. The obtained results confirmed a higher influence of nitrogen incorporation on the various glass conductivity parameters than shown for silicon doping alone. However, the influence of fundamental structural changes on the glass conductivity is less relevant as is the overall sodium ion concentration, which remains the decisive factor for a high ion conduction.

Laser-induced defects in glasses are of considerable interest for many applications from optics to photonics. The importance of low-level impurities of polyvalent ions in aiding defect formation has been identified early on. (Fluoride-)phosphate glasses are used today as laser materials, waveguides, amplifiers and luminescing materials, all sensitive to a change of the materials transmission by the interaction with light during application. To better understand the processes of defect generation and recovery, a systematic comparison of defect formation in various glasses and for various radiation sources and dopants has been conducted over the last decades. Here we will focus on (fluoride-) phosphate glasses doped with 50 to 5000 ppm of the 4d and 5d ions Zr, Nb, Ta, Mo and W. Glasses were melted under air or under reducing conditions in order to shift the redox equilibrium of the dopants before irradiation with either the 193 nm or 248 nm excimer laser. Only for W, Mo and Nb reduced ion species were confirmed by optical and/or ESR spectroscopy in the pre-irradiated glasses. However, irradiation showed for all metaphosphates the presence of reduced dopant species (W5+, Mo5+, Ta4+, Nb4+, Zr3+), acting as extrinsic hole centers (HC) after being photo-oxidized by laser irradiation to the fully oxidized d0 ions (Mn+)+–HC. Only for Ta5+ with its (Ta5+)− -electron center (EC), photo-reduction to the tetravalent ion was observed. Defect recovery was followed up to 16 years after the irradiation experiments, showing that most (Mn+)+–HC were very stable, while intrinsic HC either recombined with EC or converted into extrinsic (Mn+)+–HC. Due to ubiquitous iron impurities, even these high purity glasses with iron levels of 5–10 ppm or less, showed the formation of (Fe2+)+-HC.

Oxynitride phosphate glasses and glass-ceramics were prepared using new synthesis routes for phosphate glasses. Materials were melted from pre-prepared glass samples in the system Na-Ca-P-O with addition of Mg and/or Si3N4 powders under different preparation conditions. The melting process was conducted at 1000–1500 °C either under air or nitrogen atmosphere to obtain materials with different nitrogen content. Their topography and structure were characterized by Confocal Microscopy, Scanning Electron Microscopy, X-ray powder diffraction and Raman and infrared spectroscopy techniques, while their chemical compositions were examined by Energy Dispersive X-ray spectroscopy (EDS). All materials prepared under nitrogen atmosphere were found to contain a relative low quantity of nitrogen and high amount of Nb leached from the crucible. The reaction with the Nb crucible was not previously observed for silicon-based oxynitride glasses. The synthesized materials form two groups: glasses and glass-ceramics. The first ones, were prepared under air and nitrogen atmospheres at temperatures up to 1400 °C, and were found to be amorphous and homogeneous. Raman and infrared spectroscopy measurements confirm the presence of amorphous phosphates in the synthesized materials. The samples of the second group were prepared at temperatures above 1400 °C and were found to be translucent and partially crystallized. They contain nanocrystallites of calcium and sodium phosphates including hydroxyapatite (HAp). The thermal properties of samples were studied by Differential Scanning Calorimetry (DSC). The obtained glass transition temperatures range from about 360 °C to 640 °C and exhibit high values for glass-ceramic materials. Stability is improved in the studied glass-ceramics because of the increased degree of network polymerization of the remaining glassy matrix. The approximate fragility index decreases two times for oxynitride materials compared to the primary glass. The synthesized new materials may be competitive to well-known bioactive phosphate glasses thanks to their improved stability by Mg, Si, N and Nb doping.

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 Cu0 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 (Cu0) 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.

Alkali germanotellurite glasses of composition 0.3M2O–0.7[(1-x)GeO2–xTeO2], M=Li, Na and 0 ≤ x ≤ 1, were investigated by Raman and infrared vibrational spectroscopic techniques to search for the origins of the alkali ion-dependent network former mixing (NFM) effect in these ion-conducting glasses. The vibrational spectra measured on mixed network-former glasses, and the spectral comparison between equimolar-mixed glasses (x = 0.5) and pellet-mixtures of the endmember glasses, 0.3M2O–0.7GeO2 and 0.3M2O–0.7TeO2, provided evidence for the formation of hetero-atomic Ge–O–Te linkages and structural rearrangements in the germanate and tellurite components of the glass. The mixing-induced structural rearrangements were expressed in terms of chemical equilibria between the network-building units and were used to make qualitative predictions for changes in the network cross-linking density and the related network-strain energy, as well as in the binding energy part of the activation energy for ion conduction. Thus, it is proposed that the mixing-induced structural modifications in the germanate and tellurite parts of glass cause the cancelation of changes in the binding energy and the network-strain energy contributions to the activation energy for ion transport. These qualitative predictions were discussed in the context of the previously found absence of an NFM effect in ionic conductivity for M=Na and the presence of a weak positive NFM effect for M=Li.

An alkali niobate-silicate veneer ceramic for ZrO2-based dental restoration was developed and characterized for its physical properties and structure. The properties were adjusted for dental applications. The new lithium disilicate glass-ceramic VBK (sold as cerafusion or LiSi) can easily be applied by spray coating to any individually formed ZrO2-matrix and needs only one final tempering treatment. The surface of the glass-ceramic is very smooth. The color of the already translucent glass-ceramic can be adjusted to that of individual natural teeth. The structure of the glass-ceramicwas studied by XRD and Ramanspectroscopy as a function of heat-treatment and of spatial variations within the material and at its interfaces. ToF SIMS, SEM and thermal analysis techniques were applied to investigate the crystallization behavior and surface-interface reactions. XRD and Raman spectroscopy identified different crystalline phases in the amorphous glass matrix including Li2Si2O5, Li2SiO3, NaxLi(1−x)NbO3 and Na3NbO4. The Raman spectrum of the amorphous matrix is dominated by the vibrational activity of the highly polarizable niobate units with a prominent feature at 865 cm−1, assigned to Nb-O stretching in NbO6 octahedra, which have non-bridging oxygen atoms and are connected to the silicate matrix rather than to other niobate polyhedra.

Thermal poling, i.e., exposure of a glass to a DC electrical field at moderate temperature, enables the generation of an anisotropic surface layer. Cation motion on the anode side results in the formation of an internal gradient in the electrical potential which can be frozen-in upon cooling. This is accompanied with a change in the polarity of the anode surface and, hence, a change in surface wettability. In this article, we study the effect of thermal poling on the wettability of soda-lime silicate glasses. We confirm a poling-induced increase in surface hydrophobicity on the air-side of commercial float glass, with a water wetting angle increase of around 20° for poling at 210 °C and 1.5 kV. The effect is persistent after storage for three months under ambient conditions. Significant variation between air and tin-side of the float glass indicates strong compositional dependence and offers a route for tailoring the surface chemical properties of functional glass substrates.

Modifier-mixing provides a well-established tool for generating non-linear trends in physical properties of multi-component glasses. While typically, mixtures of alkali or alkaline earth ions are considered, here, we report on the structural incorporation of Co 2 + and Mn 2 + , respectively, in strontium metaphosphate glasses, and on the associated Co-Sr/Mn-Sr mixed-modifier effect. Structural variations in the short and intermediate range were investigated with vibrational spectroscopy and synchrotron X-ray diffraction, elucidating the coordination states of the two transition metals as a function of mixing ratio. For the join of Co-Sr, we find that the octahedral coordination dominates for lower contents of cobalt, whereas the tetrahedral state is predominantly found at higher cobalt concentration. The analogue decrease in the coordination number is weaker when mixing manganese and strontium ions. Coordination numbers are shown to correlate clearly with vibrational spectroscopic data and macroscopic physical properties.

A previous report (Möncke et al., PCG 2013) discussed the possible formation of a borosilicate layer on the surface of Late Bronze Age glass samples (Mycenaean period, excavated in Palaia Epidavros, Greece). Now, we investigate potential mechanisms for such suggested borate incorporation into the surface of alkali-lime silicate glasses. Since former studies reported that glass relief fragments have been found alongside gold foils featuring identical reliefs, we tested the hypothesis that borates could have been introduced through gold working via the reaction of a borax-treated gold foil with the silicate glass surface at elevated temperature. A borosilicate layer was successfully generated on replica soda lime silicate glass samples and identified by vibrational spectroscopy. Different approaches were used in order to merge gold sheets to the glass samples. At temperatures above 800 °C, borax could have been used either as a solder in the fusion process between a gold sheet and the glass surface, or borate was transferred from the gold sheet previously in contact with a borax melt, presumably for cleaning gold or during ore extraction. The depth of the borosilicate layer on the thus treated glasses extents from the surface several μm into the bulk glass as probed by micro-Raman and IR spectroscopy, while the dimensions of the spread across the glass surface can be visualized by neutron radiography. Keywords: Mycenaean glass, Gold processing, Borosilicate layer, FT-IR spectroscopy, Raman spectroscopy, Neutron radiography, Borax

In this article, a synthesis of the compound In2O3–TiO2–Al2O3 (molar relation 3:4:1 and 5:8:1) at 1350 °C by solid-state reactions is described. The compounds were obtained after heat treatment at 1350 °C for two days. X-ray diffraction patterns indicate that the synthesized samples belong to the monoclinic crystal system with the space group C 2/m. An agglomeration of the crystals was observed by scanning electron microscopy for the heat-treated samples of either composition (S1HT and S2HT). Atomic quantitative analysis showed variations of the two compositions presented and TEM analyses confirmed that In3Ti2AlO10 crystals were formed. Partial nanocrystallization and irregularities can be observed in the micrographs. Both samples were polymorphic and presented chain discontinuities attributed to oxygen vacancies and/or distortions in the structure. UV–vis measurements were performed obtaining a band gap ~ 3.2 eV for all the samples analyzed. XPS analysis for S1HT and S2HT confirmed the expected oxidation of the compounds.

Fluoride phosphate/fluorophosphate (FP) glasses form an intriguing material's basis for diverse applications in optics, photonics and energy storage. The optimization of the materials' properties with regard to the application envisioned demands an understanding of the key concepts describing their local structures on different distance regimes. Because of the inevitable losses of fluoride during melting or annealing, the synthesis and elemental analytical characterization present important and critical challenges. In this contribution we summarize the current state of the literature regarding the structural characterization of these glasses. Foci are the detailed analysis of vibrational spectra with special emphasis on Raman scattering results and multinuclear solid-state NMR spectroscopy. While vibrational spectra give important information about the local environments (short range order) advanced multi-dimensional and multi-resonance methodology can extend the informational content of solid-state NMR into the sub-nanometer distance range, including second and third coordination spheres. Exemplary results will be presented for (a) aluminum fluoride based simple model systems, (b) fluoride phosphate glasses containing heavy transition metals or post-transition metal elements, and (c) rare-earth doped fluoride phosphate glasses for laser applications. The latter application field documents the utility of correlated spectroscopic studies using both methods in understanding the structural foundations of photophysical properties. Keywords: Fluoride phosphate and fluoro-phosphate glasses, Analysis, NMR spectroscopy, ESR spectroscopy, Raman and IR, Spectroscopy, Structure

Glass is a fascinating material, not only because of its transparency and for its formability, but also because of the manifold facets of bright colors it can display. Just remember how the colored glasses of cathedral windows made us dream in our childhood, and how much we could quarrel in the schoolyard over a marble or a bead necklace.

Undoped, singly Sm doped, Ce doped, and Sm/Ce co-doped lithium alumino-phosphate glasses with different alkaline earth modifiers were prepared by melt quenching. The structure of the prepared glasses was investigated by FT-IR and Raman, as well as by optical spectroscopy. The effect of the optical basicity of the host glass matrix on the added active dopants was studied, as was the effect doping had on the phosphate structural units. The optical edge shifts toward higher wavelengths with an increase in the optical basicity due to the increased polarizability of the glass matrix, but also with increasing CeO2 concentration as a result of Ce3+/Ce4+ inter valence charge transfer (IV-CT) absorption. The optical band gap for direct and indirect allowed transitions was calculated for the undoped glasses. The glass sample containing Mg2+ modifier ions is found to have the highest value (4.16 eV) for the optical band gap while Ba2+ has the lowest value (3.61 eV). The change in the optical band gap arises from the structural changes and the overall polarizability (optical basicity). Refractive index, molar refractivity Rm and molar polarizability αm values increase with increasing optical basicity of the glasses. The characteristic absorption peaks of Sm3+ were also investigated. For Sm/Ce co-doped glasses, especially at high concentration of CeO2, the absorption of Ce3+ hinders the high energy absorption of Sm3+ and this effect becomes more obvious with increasing optical basicity.

The effect of alkaline earth ions on the structure and properties of borate glasses near the metaborate composition was studied for two glass series, 30MO-10Li2O-10Al2O3-50B2O3 with M=Mg, Ca, Sr or Ba and xMgO-(30-x)BaO-10Li2O-10Al2O3-50B2O3 series, for undoped and doped (0.5 mol% MnO or CuO) glasses. Thermal and optical properties, including the optical basicity, were correlated with structural variations. IR and Raman spectra showed the highest N4 fraction for the high basicity glasses, decreasing for higher field strength ions (Ba>Sr>Ca>Mg). As determined from far IR bands the mixing of dissimilar cations affects M-O interactions. The glass transition temperature Tg correlates well to the average bond strength of the compared alkaline earth ions. The redox ratio of Mn2+/Mn3+ or Cu2+/Cu+ shifted to lower valences in low basicity glasses. The optical basicity probe ion Mn2+ gives consistently higher values compared to the average optical basicity, suggesting that Mn2+ ions seek out high basicity ligands.

The local structure of the model glasses (NaPO3)1–x-(AlF3)x (0 ≤ x ≤ 0.4), prepared by standard melt-cooling, was extensively investigated by high-resolution solid-state nuclear magnetic resonance (NMR) including advanced double-resonance techniques. This glass system offers the opportunity of studying five different heteronuclear distance correlations (Na–F, Na–P, P–F, Al–F, and P–Al) by 10 distinct double-resonance experiments, involving all of the constituent elements present. 27Al MAS-NMR data indicate that aluminum is predominantly six-coordinated. According to 27Al{31P} and 27Al{19F} rotational-echo double-resonance (REDOR) spectroscopic results, two to three Al–F and three to four Al–O–P linkages occur in these glasses, independent of composition x. 19F MAS-NMR spectra show the presence of terminal P-bound and Al-bound fluorine species. A small amount of fluorine bridging to two aluminum octahedra, which could be assigned based on 19F{27Al} and 19F{31P} REDOR experiments, was also detected. 19F{23N...

Journal of applied physics 123(23), 233105 (2018). doi:10.1063/1.5030687, 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. % TiO$_2$. 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 Ti$^{4+}$ sites highly dispersed in the silicate matrix, Raman and IR reflectance spectroscopy on laser-irradiated ULE indicated the formation of Ti$^{3+}$ sites; Ti$^{3+}$ octahedral sites are formed in the shells of cavities and aggregate in amorphous Ti$_2$O$_3$-type clusters, while the glass around and below cavities contains Ti$^{3+}$ 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 American Inst. of Physics, Melville, NY

Fluoride–phosphate (FP) glasses have been developed (in terms of glass forming ability) as a more stable alternative to fluoride glasses. Benefitting from the low polarizability of the fluoride anion, high electronic band-gap and low phonon energy, they present one of the most important host species for the inclusion of rare-earth and other optically active dopants into fiber and bulk glass. A major limitation, however, has been the mechanical performance of these glasses and their susceptibility to damage and fracture. Here, we provide comprehensive data on elasticity, plasticity and fracture of a series of mixed fluoride–phosphate glasses with strongly ionic bonding character, spanning the compositional join of strontium metaphosphate and alkaline earth aluminum fluoride. Simplistic models such as that of Makishima and Mackenzie can reproduce the mechanical properties of these glasses within a limited compositional range. This break-down is explained in the context of glass structure, in particular, the role of intermediate VIAl3 + species which act as bridges between the fluoride and the phosphate sub-networks. A simple binominal model is implemented to estimate the atomic fractions of aluminum as well as of magnesium cations, which are linked to two or more phosphate units, and used as an indicator for the connectivity between the anion sub-networks. Such adjustment of the Makishima–Mackenzie model provides an unambiguous rational for the elastic properties, but also for the susceptibility to inelastic deformation and fracture of FP glasses.

Interaction of radiation with glasses often modifies their properties (e.g., the refractive index). Most noticeable is a loss in transmission. Such phenomena can be exploited in photo-sensitive materials, but have to be avoided in other applications. To improve the understanding of defect generation processes, a systematic comparison of defect formation in (fluoride-)phosphate glasses doped with low concentrations of 3d ions was attempted. Samples doped with 10–5000 ppm of Ti, V, Cr, Mn, Fe, Co, or Ni were irradiated in the UV range by excimer lasers. Defects, which generally form in the levels of several ppm, were characterized by optical and by electron spin resonance spectroscopy. V4+ was photo-oxidized to the empty valence shell d0 ion. Co2+, Mn2+, and Fe2+ were all photo-oxidized to the trivalent state while Ni2+ was photo-reduced. The fully oxidized Ti4+ was also photo-reduced. Cr3+ showed photo-disproportionation into Cr2+ and Cr6+. Qualitative and quantitative changes in defect formation rates depend not only on the ion, but also on the radiation parameters, for example, the wavelength of the excimer lasers used (193, 248, 351 nm) or the initial transmission of the glass samples at the chosen laser wavelength. Defect recovery was followed up to 10 years after the irradiation experiments.

Plastic deformation, densification, and cracking of sodium borosilicate (NBS) glasses were examined during indentation with a three-sided pyramidal indenter. Compositions of 74.0SiO 2 –10.0B 2 O 3 –16.0Na 2 O (NBS1), and 74.0SiO 2 –20.7B 2 O 3 –4.3Na 2 O–1.0Al 2 O 3 (NBS2) (mol%) were investigated. The effect of thermal history was additionally considered for the NBS2 composition, which lies near the boron anomaly line. Hardness, elastic modulus, and fracture toughness were estimated with instrumented indentation techniques. Atomic force microscopy (AFM), Raman micro-spectroscopy, and post-indent annealing experiments were used to analyze surface topographies, densification, and recovery of deformed material. The results indicate that NBS1 exhibits a greater hardness and elastic modulus, and undergoes less densification than the NBS2 glasses. Different casting conditions influenced the plastic deformation and onset of crack initiation in NBS2. Interpretation of fracture toughness measured by indentation is complicated by residual stresses, densification during contact, and model assumptions. However, distinct differences in elastic modulus, plastic deformation and cracking between the glasses were noticeable. Such results and observations are discussed in terms of structural changes in the glass.

Frontiers in Materials 4, 5 (2017). doi:10.3389/fmats.2017.00005, Published by Frontiers Media, Lausanne

International audience; In an earlier review we discussed the connectivity in borosilicate glasses and compared our experimental findings by NMR, infrared and Raman spectroscopies with older structural models. We could show, contrary to the often cited reedmergnerite type model, that a significant preference exists in low alkali borosilicate glasses for trigonal rather than tetrahedral borate groups to link to silicate entities. Another often cited misconception is the application of the Loewenstein rule to borate tetrahedra. While linking of two "[AlØ4]– tetrahedra is disadvantageous compared to higher coordinated aluminate polyhedra, the borate tetrahedral units represents already the alternate higher coordination state and accordingly, many examples of linked [BØ4]– tetrahedra are known to exist in glasses as well as in crystalline compounds of boron at normal pressure conditions. We now present more NMR data on three different low alkali borosilicate glasses with Na2O:B2O3=0·2 to 0·35 and decreasing SiO2 fractions (74 to 43 mol% SiO2), for which we compare variations in the near and intermediate range structure of quenched and slowly annealed samples. None of the studied glasses showed a significantly higher fraction of trigonal BØ3 groups in the quenched than in the annealed samples, even though borate in the three-coordinated state is the preferred metaborate unit in the melt. However, for the two silicate rich glasses (including NBS 2), we observe at low temperatures a deviation of the viscosity–temperature plot from the ideal VFT-fit, that is from Tg at circa 440 to the expected 600°C. For samples prepared at any annealing temperature below 600°C, structural variations with thermal history are apparent, and are also reflected in many glass properties including density, fracture probability, or refractive index. Even though the glass NBS 2 shows no visible phase separation, DSC measurements indicate the presence of two different Tg values corresponding to the borate and the silica rich subnetworks. The values of the two Tg events shift with different cooling rates: for fast quenched glasses the two Tg values are closer together than for slowly annealed glasses. The study of these low alkali borosilicate glasses is ongoing, as we understand better how structural variations with changing thermal history impact the glasses' properties. Analogously, we can apply the same techniques to follow structural variations under external forces, such as irradiation, laser modification, pressure and mechanical impact.

We report on the deformation behavior of a series of glasses in the ternary alkali-borosilicate system. Vickers indentation was applied to different samples and structural changes were studied by micro-Raman spectroscopy. Selected sodium- and potassium-borosilicate glasses, a soda-lime silicate glass and pure vitreous SiO 2 were chosen as models for technical glasses, as their varying content of non-bridging oxygen atoms affects the connectivity of the silicate and borate sub-networks. Indentation experiments were performed with different loads and two different load times in order to analyze the response of the two sub-networks in the studied glasses. The measured Raman spectra show distinct indentation-induced changes in the glass structure. These changes depend not only on the borate concentration, but also on the silicate sub-network's connectivity and reflect anomalous (densification-driven) and normal (shear-driven) deformation mechanisms. Using vitreous SiO 2 as reference material, indentation-induced structural changes were also correlated to hydrostatic compression experiments from the literature in order to develop a more detailed picture of the apparent evolution of the local compaction in and around the indent.

We report on the effect of micro-indentation on the local structure of glasses in the ternary borosilicate glass system Na2O–B2O3–SiO2. Indentation experiments were performed with loads ranging from 0.49 to 4.91 N and for loading times of 10–30 s in order to analyze the impact on the silicate and borate sub-networks in glasses ranging from pure SiO2 to binary Na2O–4B2O3, with a ratio of R = Na2O/B2O3