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Thermal poling is a widely used method for creating glass surfaces with modified structure and altered properties by application of DC voltage. The mechanism of structural change has remained controversial, especially as poling is performed well below the glass transition temperature. Specifically, the role of Joule heating in facilitating structural transformation has remained an open question, conceivably through local heating to temperatures approaching Tg. Here, we investigate this possibility directly by in situ measurements of the local glass temperature during poling using infrared imaging. Examination near the anode region reveals only a slight temperature increase (~10°C) above the furnace temperature at the start of poling, and remains a few hundred degrees below Tg throughout. SIMS analysis revealed a ~1‐µm thick alkali depletion layer next to the anode. XPS analysis of the anode, cathode, and unpoled regions shows complex changes in structure and composition including migration of alkali ions, injection of hydrogen at the anode interface, removal of non‐bridging oxygen, and polymerization of the network via electrolysis. All these changes arise as a result of high electric field (~106 V/cm) produced across the highly resistive depletion layer, and refutes any significant increase in the temperature by Joule heating as the cause of their creation. [ABSTRACT FROM AUTHOR]

Single‐crystal architectures in glass, formed by a solid‐solid transformation via laser heating, are novel solids with a rotating lattice. To understand the process of lattice formation that proceeds via crystal growth, we have observed in situ Sb2S3 crystal formation under X‐ray irradiation with simultaneous Laue micro X‐ray diffraction (μXRD) pattern collection. By translating the sample with respect to the beam, we form rotating lattice single (RLS) crystal lines with a consistently linear relationship between the rotation angle and distance from nucleation site. The lines begin with a seed crystal, followed by a transition region comprising of sub‐grain or very similarly oriented grains, followed by the presence of a rotating lattice single crystal of unrestricted length. The results demonstrate that the primary cause of lattice rotation within RLS crystals is the densification accompanying the glass → crystal transformation, rather than stresses produced from the difference in thermal expansion coefficient of the two phases or paraelectric → ferroelectric transition during cooling to ambient temperature. [ABSTRACT FROM AUTHOR]

Abstract: Electric field‐induced softening (EFIS) is a recently discovered phenomenon leading to significant reduction in the furnace temperature at which glass softens under the application of DC voltage. Unfortunately, it is accompanied by local compositional changes due to migration of ions that could limit its usefulness. To overcome this drawback, we have investigated the same phenomenon using AC voltage, that is, AC‐EFIS on a sodium disilicate glass and a 50/50 mixed lithium‐sodium disilicate glass of very different ionic resistivity yet similar network structure. The results show that the magnitude of EFIS temperature reduction is significantly greater for AC compared to DC for both glass compositions. The enhancement of EFIS under AC voltage appears to be due to a more uniform power dissipation and self‐healing of changes than under DC voltage. This uniformity allows for the overall sample temperature to increase throughout the bulk and provides a better technique for practical applications than the DC case which produces potentially undesirable changes, especially in the anode region. [ABSTRACT FROM AUTHOR]

We have investigated the role of charge state of Ti in the electronic properties and structure of electrically conductive CMAS-TiO2-Pd glass and glass-ceramics by X-ray photoelectron spectroscopy, electron paramagnetic resonance, positron annihilation lifetime spectroscopy, and fluorescence spectroscopy. These studies suggest the concentration of Ti3+ ions was, at most, ~0.1 wt% in glass-ceramics devitrified in the reducing atmosphere of forming gas; no other glass or glass-ceramic samples exhibited measurable levels of Ti3+. The observed fluorescence at liquid nitrogen temperature in parent glasses and glass-ceramics obtained in air is explained by UV-induced charge-transfer processes involving Ti4+ ions and oxygen surroundings. The X-ray photoelectron spectroscopy data are correlated with rutile, anorthite, diopside, and titanite crystalline phases identified in Pd-free and Pd-doped Ti: CMAS glass-ceramics earlier. [ABSTRACT FROM AUTHOR]

Low-Energy Ion-Scattering ( LEIS) spectroscopy is a technique with a unique sensitivity to the elemental composition of the top atomic layer of a solid surface. LEIS measurements of ternary silicate glasses modified with Na2O, Cs2O, CaO, and BaO show that the compositions of the as-cast (melt) surface and the in-vacuum fracture surface often differ. While the as-cast surface is usually depleted of alkali ions (Na+ or Cs+) compared to the nominal (batch) glass composition, there is often strong accumulation of the same mobile cations on the fresh fracture surface. Depth profiles obtained by sputter etching reveal elemental concentration gradients normal to the glass surface. The final concentrations often fail to reach the nominal glass composition, suggesting the likely presence of preferential sputtering effects and thereby the distortion of the measured concentration gradient. At present, the lack of reliable standards and preferential sputtering effects in the LEIS of multicomponent glasses limit somewhat the absolute chemical composition and structural information that can be obtained with this otherwise unique and powerful method of surface analysis. [ABSTRACT FROM AUTHOR]

We have investigated devitrification of glasses within infrared transmitting x SbSI-(100 − x) Sb2 S3 pseudo-binary series, which forms SbSI and Sb2 S3 ferroelectric crystal phases. Differential scanning calorimetry ( DSC) and X-ray powder diffraction results show unusual behavior for the formation of the SbSI phase, which occurs by two parallel processes: one-dimensional crystallization at low temperature which starts from the sample surface, and three-dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The ratio of the intensities of the high-temperature exothermal peak to the low-temperature peak in DSC scans increases as the particle size and heating rate are increased. In contrast to the SbSI phase, the temperature of crystallization for the Sb2 S3 phase does not depend on the particle size. Models are proposed for the origin of the various crystallization mechanisms. [ABSTRACT FROM AUTHOR]

The structure of electrically conductive CMAS-TiO2-Pd glass and ceramics was investigated by transmission electron microscopy ( TEM), scanning transmission electron microscopy ( STEM), X-ray photoelectron spectroscopy ( XPS), X-ray absorption near-edge spectroscopy ( XANES), and extended X-ray absorption fine structure spectroscopy ( EXAFS). The XANES spectra of Ti do not show any significant difference between the glasses ceramized in air or in a reducing 'forming' gas, as well as between Pd-containing versus Pd-free samples, nor between surface versus bulk of the glass-ceramic samples. However, EXAFS and XANES data recorded at the Pd K-edge show significant dependences on whether the glass-ceramic was ceramized in air or in 'forming' gas. The XPS spectra of Ti 2 p core-level electrons for glasses ceramized in air or 'forming' gas also show a strong difference depending on whether the samples did or did not contain Pd. STEM mapping confirms the existence of grains in the form of main crystalline phases identified with XRD, and also reveals the existence of Pd nanoparticles in glasses ceramized in both air and in 'forming' gas. [ABSTRACT FROM AUTHOR]

Very few studies have been directed at the compositional dependence of the intrinsic photostability of the Ge x Se1− x binary ChG films especially for the Ge-rich films with the mean coordination number ( MCN) larger than 2.67. Here, by measuring the in-situ transmission changes, it shows that the photosensitivity (e.g., photobleaching, PB) of the Ge-rich films (as compared to the GeSe2 film) is attenuated, in fact almost completely eliminated in the film with the largest MCN. A straightforward technique, in-situ Raman spectroscopy, is used to record the time-resolved intrinsic structural changes during the irradiation of the films. The result indicates a transition from PB towards photostability occurs at the critical composition of GeSe2 corresponding to the structural phase transition. The stressed rigid structures of the Ge-rich films inhibit any significant photo-structural changes. [ABSTRACT FROM AUTHOR]

Congruent crystallization of antimony sulphoiodide ( SbSI) glass of stoichiometric composition, which is prepared successfully for the first time using rapid melt-quenching, has been investigated using differential scanning calorimetry ( DSC). The results for glass powder show a glass transition at 127°C and two separate exothermal peaks with maxima around 140°C and 190°C. The ratio of the intensities of the exothermal peak at ~190°C to the peak at ~140°C increases as the particle size and heating rate are increased, but their total enthalpy remains constant at 62 ± 2 J/g for all DSC runs. Surface heating of the glass induced by a 520 nm CW laser shows two contracted regions: needle-like crystalline formations at low temperature and bulk crystallization at high temperature. The observed phenomena and DSC results suggest two different kinds of crystallization of the SbSI phase: one-dimensional crystallization at low temperature which starts from the sample surface and three-dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The origin of the two different crystallizations can be traced to the strong anisotropy of the SbSI crystal structure due to the weak van der Waals interaction between covalent-ionic chains (Sb2S2I2) n. [ABSTRACT FROM AUTHOR]

A key requirement for the use of bio scaffold is that its degradation rate matches the growth rate of target tissue. Therefore, the degradation of recently developed tailored amorphous multiporous ( TAMP) scaffold of 70 SiO2·30 CaO (mol%) in simulated body fluid ( SBF) was studied under both static and quasi-dynamic conditions. The degradation was assessed through the dissolution of silica from the glass into SBF, while the in-vitro bioactivity was characterized by precipitation of calcium phosphate ( CaP) on and inside the scaffold. Under static conditions, the degradation stopped due to the saturation of solution with silica in 3 days, whereas the precipitation of CaP continued. Rapid degradation and better in-vitro bioactivity was found under quasi-dynamic conditions, where the concentration gradient across the sample was maintained. The degradation followed exponential dependence on time with a half-life of 15.4 days and initial degradation rate 4.5% day−1. The remaining samples maintained their integrity and pore structure during degradation. The degradation occurred in three distinct stages: (a) wetting stage, (b) initial degradation stage when CaP precipitation dominates, and (c) intensive degradation stage when the nanopores rupture and network dissolves. By varying the sintering parameters the nanopore structure, and hence the degradation rate, can be tailored to suit the anticipated tissue regeneration rate. With demonstrated rapid and controllable degradation and good in-vitro bioactivity, the TAMP scaffold shows promise as candidate for bone regeneration application under various conditions in the body. [ABSTRACT FROM AUTHOR]

Formation of sufficiently large three-dimensional (3D) nanomacroporosity in bone scaffolds remains a challenge in spite of several methods reported in literature. It is required for tissue ingrowth and for the concurrent degradation of implanted structure. We report a new technique for fabricating superior high surface area, nanomacroporous bioactive glass scaffold, which combines the sol-gel process and polymer sponge replication method. The formation of 3D structure is demonstrated in 70 mol% SiO2-30 mol% CaO glass composition as an example, which is uniform across the sample. It consists of open, interconnected macropores with size from 300 to 600 μm, as desired for tissue ingrowth. At the same time, coexisting nanopores provide high-specific surface area (∼184 m2/g), which is needed for enhancing the structure's degradation rate. These bioscaffolds hold promise for applications in hard tissue engineering. [ABSTRACT FROM AUTHOR]

Sol–gel-derived SiO2–CaO–P2O5 porous glass monoliths with a dual hierarchical pore structure including both macropores of ∼20–200 micrometers and mesopores ∼5–20 nanometers in size are prepared in the presence of the drying control chemical additive formamide, for a possible application as scaffolds in bone tissue regeneration. While the mesopores are intrinsic to the sol–gel processing, the interconnected macropores are achieved through a polymer-induced phase separation together with the sol–gel transition, by adding a water-soluble polymer, poly(ethylene oxide), to the precursor sol. The textural nanopore structure is controlled through solvent exchange procedures and the addition of urea. The overall pore size distribution obtained by mercury intrusion porosimetry was found to shift to larger pore sizes when formamide is added. In vitro tests are used to evaluate the bioactivity. The cell-support function of the resultant scaffolds is also assessed in vitro using osteoblast-like cells cultured for 2 days. The results show that the scaffold has a significant bioactivity and a good ability to support the attachment of MC3T3 preosteoblast cells. [ABSTRACT FROM AUTHOR]

We have investigated the evolution of the structure of nano–macro porous CaO–Na2O–P2O5–SiO2 bioactive glass–ceramics by Fourier transform infrared (FTIR) and Raman spectroscopies, and X-ray diffraction (XRD). A controlled devitrification, followed by a chemical leaching treatment is used to produce a multimodal distribution of nano/macro pores that are expected to improve cell attachment. Data show that the leaching process removes the sodium- and calcium-containing crystalline phases that are formed during the ceramming heat treatment. The primary Si–O peaks in the infrared spectra blue shift with leaching, indicating that the sample becomes SiO2 rich. In parallel, the fraction of nonbridging oxygen decreases. These results suggest a restructuring of the glass network far below the glass transition temperature. The stresses from leaching, capillary forces, and subsequent restructuring develop and grow, eventually producing cracks in the sample. [ABSTRACT FROM AUTHOR]

High-resolution X-ray photoelectron spectroscopy is used to identify the mechanism of X-ray-induced Ag diffusion into Ge30Se70 chalcogenide glass thin films, which are prepared in situ to avoid oxygen contamination. From the analysis of Ge 3d, Se 3d, and Ag 3d core levels, and valence band spectra, changes in the electronic structure are determined as Ag diffuses gradually with increasing irradiation. The ternary phase based on Ge2Se6 units, which contains homopolar Ge–Ge bonds, forms when diffusion approaches equilibrium where Ag content ∼30 at.%. The formation of a Se-rich composition is indicated in the near-surface region at the initial stage of the process, but the previously assumed Ag2Se phase is not detected. [ABSTRACT FROM AUTHOR]

Using a novel, selective heating by Nd:YAG laser, a single-crystal architecture is created in a model glass system, Sm0.5La0.5BGeO5, which devitrifies congruently into a ferroelectric phase of the same composition as the parent glass. The Sm3+ ions in glass absorb the light and heat the matrix locally resulting in devitrification. Initially, a polycrystalline spot is formed. However, with optimum laser power, scanning speed, and the depth of focus, one of the grains acts as the seed for further growth as a single crystal. By programming the relative displacement of the glass with respect to laser spot, desired single ferroelectric crystal architecture is created. The optical functionalities (guiding of light and second harmonic generation) of the architectures are shown, which demonstrate the viability of this method for constructing active elements in optical integrated circuits. The single-crystal nature of the architecture is confirmed from the electron backscattered diffraction results. [ABSTRACT FROM AUTHOR]

The reaction of soda-lime-silicate glassware with model cleaning solutions gives rise to a systematic pattern of inhomogeneous corrosion. This corrosion is not uniform on the entire surface, but is localized only to certain regions of the glassware. The surface composition, as determined by X-ray photoelectron spectroscopy, and the microstructure, as characterized by optical and scanning electron microscopy, vary considerably in different regions of the glassware. The visibly heterogeneous corrosion pattern, which correlates with the compositional and structural inhomogeneities, is explained in terms of surface conditions that exist during different stages of glass manufacturing. The role of sodium disilicate in solution is also explored for promoting inhomogeneous glass corrosion. [ABSTRACT FROM AUTHOR]

We demonstrate that suitable thermal treatment of biocompatible CaO–Na2O–P2O5–SiO2 glasses prepared by the usual melt-quench results in spinodal phase separation and crystallization of phases at very different length scales. Selective chemical leaching of these phases allows the formation of interconnected multi-modal porosity, with pore size ranging from several nanometers to tens of micrometers. Such novel nano–macroporous glasses have potential applications as superior bioscaffolds. [ABSTRACT FROM AUTHOR]