Evolution Of Glass Structure Research Articles

Evolution of glass structure during femtosecond laser assisted crystallization of LaBGeO5 in glass

Single crystal LaBGeO5 architecture formed in La2O3-B2O3-2GeO2 glass serves as a model system for understanding of the transformation from glass to single crystal under fs laser irradiation. This transformation is highly sensitive to glass composition, raising the need to understand how the glass structure and composition evolve during crystallization. In this work, micro X-ray absorption spectroscopy and X-ray fluorescence mapping were used to study the glass structure and composition preceding LaBGeO5 crystallization in the region surrounding the single crystal growth front. The results show precipitation of germanium nanoparticles, as well as anisotropic segregation of Ge and La prior to LaBGeO5 crystallization, which are explained assuming electromigration in high fields within the plasma formed by the fs laser irradiation. However, these nanoparticles do not serve as sites for heterogeneous nucleation. The similarity of local structure around Ge in the starting glass and the ultimate crystal appears to enhance the crystallization process.

Statistical Mechanical Modeling of Borate Glass Structure and Topology: Prediction of Superstructural Units and Glass Transition Temperature.

Predicting the compositional evolution of the atomic-scale structure and properties of oxide glasses is important for designing new materials for advanced applications. A statistical mechanics-based approach has recently been applied to predict the composition-structure evolution in binary phosphate glasses, while topological constraint theory (TCT) has been applied in the last decade to predict the structure-property evolution in various oxide and nonoxide glass systems. In this work, we couple these two approaches to enable quantitative predictions of the compositional dependence of glass transition temperature and the population of superstructural units. The object of the study is the lithium borate glass system because they feature interesting structural characteristics (e.g., boron anomaly), and ample structure and property data are available. In these glasses, the average coordination number of boron first increases when lithium modifiers are added and then later decreases accompanied by network depolymerization. First, on the basis of 10B nuclear magnetic resonance spectroscopy data from literature, we present a statistical description of the structural evolution in lithium borate glasses by accounting for the relative enthalpic and entropic contributions to the bonding preferences. We show that the entire glass structure evolution (both short- and intermediate-range) can be predicted based on experimental structural information for only a few glass compositions. We then show that the developed structural model can be combined with a previously established TCT model to predict the compositional evolution of the glass transition temperature. This work thus opens a new avenue for the computational design of glasses with tailored properties.

Predicting Q-Speciation in Binary Phosphate Glasses Using Statistical Mechanics.

Predicting the compositional evolution of the atomic-scale structure of oxide glasses is important for developing quantitative composition-property models. In binary phosphate glasses, the addition of network modifiers generally leads to depolymerization of the networks as described by the Q-speciation, where Q n denotes PO4 tetrahedra with n number (between 0 and 3) of bridging P-O-P linkages per tetrahedron. Upon the initial creation of nonbridging oxygens and thus partly depolymerized Q species, a variety of network former-modifier interactions exist. Here, on the basis of 31P magic angle spinning nuclear magnetic resonance spectroscopy data from the literature, we present a statistical description of the compositional evolution of Q-speciation in these glasses by accounting for the relative enthalpic and entropic contributions to the bonding preferences. We show that the entire glass structure evolution can be predicted based on experimental structural information for only a few glass compositions in each series. The model also captures the differences in bonding preferences in glasses with different field strengths (charge-to-size ratio) of the modifier cations.

Spectroscopic properties in Er3+-doped germanotellurite glasses and glass ceramics for mid-infrared laser materials

Transparent Er3+-doped germanotellurite glass ceramics (GCs) with variable Te/Ge ratio were prepared by controllable heat-treated process. X-ray diffraction (XRD) and transmission electron microscope (TEM) confirmed the formation of nanocrystals in glass matrix. Raman spectra were used to investigate the evolution of glass structure and photon energy. Fourier transform infrared (FTIR) spectra were introduced to characterize the change of hydroxyl group (OH−) content. Enhanced 2.7 μm emission was achieved from Er3+-doped GCs upon excitation with a 980 nm laser diode (LD), and the influence of GeO2 concentration and heat-treated temperature on the spectroscopic properties were also discussed in detail. It is found that the present Er3+-doped GC possesses large stimulated emission cross section at around 2.7 μm (0.85 × 10−20 cm2). The advantageous spectroscopic characteristics suggest that the obtained GC may be a promising material for mid-infrared fiber lasers.

The Effect of Electron Irradiation on the Structure of Sodium Aluminum-Iron Phosphate Glasses

ABSTRACTGlasses of the series (mol.%) 40 Na2O, (20-x) Al2O3, x Fe2O3, 40 P2O5 were irradiated with 8 MeV electrons to doses equivalent of 0.1, 0.5, and 1.0 MGy and characterized by FTIR spectroscopy and ESR at room temperature. FTIR spectra of all the glasses consist of strong bands due to O-P-O stretching modes in (PO4)3- and (P2O7)4- units at 1000-1200 cm-1, P-O-P stretching modes at 900-950 cm-1 (νas) and 700-750 cm-1 (νs), and bending modes in the PO4 units. The wavenumber range lower 800 cm-1 has some contribution due to stretching modes in MO4 and MO6 (M = Al, Fe) units. Moreover the bands at 3300-3700 cm-1 and 1550-1650 cm-1 due to stretching and bending modes in both absorbed and structurally bound H2O molecules were present. As irradiation dose increases the bands due to stretching and bending modes in water molecules and M-O-H bonds become stronger and are split. No essential changes with increasing dose were observed within the spectral range of stretching modes of the O-P-O and P-O-P bonds. Irradiation yields phosphorus-oxygen hole centers - PO42- (D5) and PO42- (D6), and PO32- ion-radicals (D2) observable in ESR spectra of low-Fe glasses. At x>5 their responses are overlapped with strong broad line due to Fe(III). On the whole, with the increase in iron content the glass structural evolution decrease.

Effect of the Glass Structure on Emission of Rare‐Earth‐Doped Borate Glasses

A series of glasses composed of xB2O3–8Al2O3‐(90−x)Na2O–R2O3 (x = 65, 70, 75, 80, 85; R = Dy3+, Tb3+, Sm3+) were prepared through melt‐quenching. Structural evolution was induced by varying the glass composition. Increasing the glass network former B2O3 enhanced the luminescence of rare‐earth ions, as observed in the emission spectra. The mechanism of the glass structural evolution was investigated by the NMR spectra analysis. The dispersant effect of the glass structure was believed to promote the better distribution of the rare‐earth ions in the matrix and reduced the concentration quenching between them. The relationship between the glass structure and its optical properties was established.

Ionic transport of alkali in borosilicate glass. Role of alkali nature on glass structure and on ionic conductivity at the glassy state

Ionic transport of alkali was investigated in the SiO2–B2O3–R2O glass system (with R=Li, Na, K or Cs) by using impedance spectroscopy measurements at the glassy state. Transport mechanisms are also understood on the basis of glass structural analysis, such as X-ray total scattering and Raman spectroscopy, which helped to describe the alkali distribution and the network structure of borosilicate glasses.It was shown that an alkali size increase induces a glass network expansion, with weaker binding forces between alkali and non-bridging oxygens (NBO) and a change in network polymerization, with a Q3 unit increase and a “quasi-absence” of borosilicate unit in the case of lithium glass. The glass structure evolution with alkali size leads to a change in its macroscopic properties, especially glass transition temperature and electrical conductivity.The alkali conduction mechanism is described by an interstitial pair migration based on Frenkel defects in ionic crystals, which is thermally activated. Based on electrical conductivity data, activation energy of conductivity and alkali jump distances were calculated. The latter were linked to the values of bond lengths as determined by X-ray total scattering experiments, which pointed out a likely heterogeneous distribution of alkali in the borosilicate glasses studied.

Oxide glass structure evolution under swift heavy ion irradiation

The effects of ion tracks on the structure of oxide glasses were examined by irradiating a silica glass and two borosilicate glass specimens containing 3 and 6 oxides with krypton ions (74MeV) and xenon ions (92MeV). Structural changes in the glass were observed by Raman and nuclear magnetic resonance spectroscopy using a multinuclear approach (11B, 23Na, 27Al and 29Si). The structure of irradiated silica glass resembles a structure quenched at very high temperature. Both borosilicate glass specimens exhibited depolymerization of the borosilicate network, a lower boron coordination number, and a change in the role of a fraction of the sodium atoms after irradiation, suggesting that the final borosilicate glass structures were quenched from a high temperature state. In addition, a sharp increase in the concentration of three membered silica rings and the presence of large amounts of penta- and hexacoordinate aluminum in the irradiated 6-oxide glass suggest that the irradiated glass is different from a liquid quenched at equilibrium, but it is rather obtained from a nonequilibrium liquid that is partially relaxed by very rapid quenching within the ion tracks.

XRD and FTIR studies the effect of heat treatment and doping the transition metal oxide on LiNbO3 and LiNb3O8 nano-crystallite phases in lithium borate glass system

Glasses of various compositions in the system 90 Li2B4O710 Nb2O5 mixed with T.M ions (where T.M is the transition metal) were prepared by quenching technique. Heat-treatment of the parent glasses was performed at 540, 570 and 620°C, for 5 and 16h. The glass structure evolution during the controlled crystallization was examined by XRD and FT-IR spectroscopy analysis. The crystalline phases present in the glass ceramics were identified via X-ray diffraction as a function of heat treatment. The FT-IR data propose for these glasses and heat-treated glass network structures mainly built by: di-, tri-, tetra-, penta-and ortho-borate groups. It was found that the quantitative evolution of these various borate species in the glass structures is influenced by the transition metal. A detailed discussion relating to the N4 evolution with the T.M content was made.

Direct visualization of Ni-Nb bulk metallic glasses surface: From initial nucleation to full crystallization

This article is devoted to in situ investigation of the Ni-based bulk metallic glass structural evolution and crystallization behavior by scanning tunneling microscopy/spectroscopy. The possibility of different surface nanostructures formation is shown by annealing of an original bulk glassy alloy in ultra high vacuum. Atomic locations in these surface nanostructures are completely different from those formed according to Ni-Nb binary phase diagram in the bulk area of the sample. The validity of the results is also verified by transmission electron microscopy and nano-beam diffraction measurements.

Effects of nickel on network structure and thermal properties of a new solid oxide cell seal glass

Successful seal design relies on good understanding of glass network structure and the corresponding impact on glass thermophysical properties. This study is focused on effects of nickel replacement of glass formers SiO 2 and B 2O 3 and glass modifier SrO on SrO La 2O 3 Al 2O 3 B 2O 3 SiO 2 glass network structure and thermal properties. Glass structure local ordering was studied by Raman spectroscopy. Glass network connectivity was formulated to compare glass structure evolution with nickel addition for different compositions. Glass transition temperature and dilatometric softening temperature were evaluated by dilatometry. Glass thermal stability was studied by X-ray diffraction. Nickel behaves as a glass modifier in the studied glass system and decreases glass network connectivity. However, nickel can increase or decrease glass transition temperature and dilatometric softening temperature depending on the specific composition. Overall, nickel addition degrades glass thermal stability by increasing the amount of non-bridging oxygen atoms and devitrification.

Preparation and properties of GeSe 2-Ga 2Se 3-KBr new chalcohalide glasses

A series of novel GeSe 2-Ga 2Se 3-KBr chalcohalide glasses were prepared and the glass-forming region was determined. The evolution of glass structure was studied by Raman spectra. The optical and the thermal properties of glasses were investigated. The results show that these chalcohalide glasses have a broad transparent region in the entire 0.6–16 μm spectral region. At least 35 mol% KBr can be dissolved into the glasses and the absorption edge of the glass shifts towards short-wavelength direction with increasing amount of KBr. The glasses have relatively high glass transition temperatures ( T g = 290–350 °C) and good thermal stability. These properties make them promising candidate materials for infrared optics.

Influence of Al2O3 addition on thermal and structural properties of erbium doped glasses

Changes in the structural properties of Er3+ doped soda-lime silicate glasses were investigated as a function of Al2O3 content. A combined approach of experimental techniques and molecular dynamic simulations (MD) was used to evaluate the structural features directly correlated to the glass properties. The experimental results in term of density, thermal properties as well as microstructural and mineralogical data showed a significant variation when increasing the alumina content from 10 mol% to 15 mol%. These results were compared to the MD information and discussed: changes in erbium and aluminium local configuration, due to the glass structural evolution as a function of the alumina concentration, have been investigated.

Crystal field spectroscopy of Cr 3+ in glasses: Compositional dependence and thermal site expansion

Optical absorption (= crystal field) spectra of Cr 3+ in silicate glasses have been investigated as a function of chemical composition and temperature. In a large range of glass compositions, most spectra show a variation of Crystal Field Stabilization Energy (CFSE) as a function of glass chemistry. Cr 3+ CFSE ranges between 215 and 234 kJ/mol-Cr 3+ and it increases with the theoretical glass basicity. Alkali-bearing glasses make a noticeable exception, as CFSE only varies with the nature of the alkali and not with its concentration. In glasses representing simplified magmatic compositions, CFSE varies by 7 kJ/mol-Cr 3+ and the lowest CFSE values are observed in silica-rich compositions. This CFSE variation may contribute to the compositional dependence of mineral/liquid Cr-partition coefficients. Near UV–visible absorption spectra have been recorded up to 800 K, using a homemade diode array spectrometer fitted with a furnace. The modification of the optical spectra at high-temperature is characterized by a red shift of the Cr 3+ absorption bands. CFSE shows a nearly linear negative dependence on temperature, with an overall variation of about 7 kJ/mol-Cr 3+ over 500 K, a value similar to that characterizing the CFSE chemical dependence. This systematic red shift is related to the local thermal expansion of the Cr site and may be treated in glasses using a polyhedral approach. The Cr–O linear thermal expansion coefficient is 15–20 × 10 − 6 K − 1 in alkali-bearing silicate and borosilicate glasses and is similar to those determined in silicate minerals. The local thermal expansion coefficient exhibits a weak compositional dependence and is larger than the bulk thermal expansion coefficient of the glasses. The compositional and thermal dependence of the Cr 3+ crystal field spectra shows that this ion is a sensitive probe of the evolution of glass structure as a function of composition or temperature. These data are consistent with the location of Cr 3+ ions in cationic domains in glasses.

Nanostructured sodium lithium niobate and lithium niobium tantalate solid solutions obtained by controlled crystallization of glass

Transparent, nanostructured glass ceramics based on ferroelectric solid solutions of the type Na 1− x Li x NbO 3 (in very narrow composition regions for x = 0.12 and 0.93) and LiNb 1− y Ta y O 3 ( y = 0.5 unlimited solid solubility), can be obtained by controlled crystallization of glass. The parent glass samples were prepared by conventional melt-quenching technique. Heat-treatment of the parent glasses was performed at the various temperatures, for the same time. The glass structure evolution during the controlled crystallization was examined by FT-IR spectroscopy analysis. Crystalline phases were identified by X-ray diffraction analysis and SEM was used for microstructure characterization. Densities of the crystallized glasses were measured by Archimedean principle. The capacitance and dielectric loss tangent were measured at a frequency of 1 kHz, at the room temperature. It was found that in the all investigated systems crystallize solid solutions Na 1− x Li x NbO 3 and LiNb 1− y Ta y O 3 in the glassy matrix, have crystal size on nanoscale (less than 100 nm), which is one of requirements to get a transparent glass ceramic that could be a good ferroelectric material regarding to the measured properties.

Synthesis and characterization of GeS 2[sbnd]Ga 2S 3[sbnd]MCl 2 ( [formula omitted], Cd) chalcohalide glasses

New chalcohalide glasses in the GeS 2 Ga 2S 3 MCl 2 (M = Ba, Cd) systems have been prepared. Physical properties have been characterized in terms of glass transition temperature, T g ( T g = 295 – 430 °C ), thermal stability Δ T ( Δ T = 50 – 180 °C ), thermal expansion coefficient, microhardness H v and density d. Optical properties such as indices of refraction and optical bandgap are studied as a function of halide content. The Ge Ga-based chalcohalide glasses show optical bandgap extended towards shorter wavelengths. The evolution of glass structure due to MCl 2 addition has been studied by Raman spectroscopy in the range 175–550 cm −1. Structural variations are related to those of physical properties.

Structure of zinc polyphosphate glasses studied by two-dimensional solid and liquid state NMR

A series of 10 binary zinc phosphate glasses with composition xZnO+(1− x)P 2O 5 (0.35≤ x≤0.80) is studied by means of two-dimensional (2D) solid and liquid state 31P nuclear magnetic resonance (NMR). Double quantum (DQ) filtering method is used to probe 31P– 31P connectivities through dipolar interactions in solid samples. Similar information is obtained using the correlation spectroscopy (COSY) experiment in solution. It is shown that these 2D NMR methods are capable of scrutinizing the evolution of glass structure versus x with improved precision. Varied relative concentrations of dimers, short or long branched chains and ring structures are found in glasses with different composition. Average chain length in the glasses is determined from the NMR results and compared with HPLC data and theoretical predictions. Finally, the evolution of glass structure is studied as a function of the synthesis temperature.

Electrical properties of Cr 2O 3-containing glasses

Glass compositions of SiO 2MgOLi 2OCr 2O 3 and SiO 2CaOLi 2OCr 2O 3 systems have been prepared by melting in a platinum crucible and induction heating at 1500°C. The glass transition and crystallization temperatures were estimated by D.T.A. and electrical d.c. conductivity, dynamic measurements at a heating rate of 10°C/min. The electrical conductivity data have been used to describe the thermal evolution of glass structure. It can also be correlated with the conduction mechanism probably governed by the Cr 2O 3 content of the glass compositions. Thermally stimulated polarization techniques have been applied to elucidate the nature of the charge carrier and conduction process. The influence of the modifier ion, MO, on the crystallization and electrical properties of the glasses is discussed also.