As-quenched Glass Research Articles

Evolution of Nanocrystalline Ba2NaNb5O15 in 2BaO–0.5Na2O–2.5Nb2O5–4.5B2O3 Glass System and Its Refractive Index and Band Gap Tunability

Monophasic Ba2NaNb5O15 was crystallized at nanometer scale (12-36 nm) in 2BaO-0.5Na(2)O-2.5Nb(2)O(5)- 4.5B(2)O(3) glass system. To begin with, optically transparent glasses, in this system, were fabricated via the conventional melt. quenching technique. The amorphous and glassy characteristics of the as-quenched samples were respectively confirmed by X-ray powder diffraction and differential thermal analyses. Nearly homogeneous distribution of Ba2NaNb5O15 (BNN) nanocrystals associated with tungsten bronze structure akin to their bulk parent structure was accomplished by subjecting the as-fabricated glasses to appropriate heat-treatment temperatures. Indeed transmission electron microscopy (TEM) carried out on these samples corroborated the presence of Ba2NaNb5O15 nanocrystals dispersed in a continuous glass matrix. The as-quenched glasses were similar to 75% transparent in the visible range of the electromagnetic spectrum. The optical band gap and refractive index were found to have crystallite size (at nanoscale) dependence. The optical band gap increased with the decrease in crystallite size. The refractive indices of the glass nanocrystal composites as determined by Brewster angle method were rationalized using different empirical models. The refractive index dispersion with wavelength of light was analyzed on the basis of the Sellmeier relations. At room temperature under UV excitation (355 nm) these glass nanocrystal composites displayed violet-blue emission which was ascribed to the defects states.

Controlled crystallization a ionic conductivity of nanostructured LiNbFePO 4 glass ceramic

Glass sample with a composition of Li1.3Nb0.3Fe1.7(PO4)3, prepared by a conventional melt-quenching method, was heat treated to obtain glass ceramics of NASICON type. Glass transition (Tg) and crystallization (Tc) temperatures of as-quenched glass sample were determined by differential thermal analysis (DTA). X-ray diffraction (XRD) patterns also confirmed the formation of glass sample. After heat treatment above Tc, precipitation of crystalline particles with NASICON-type structure was confirmed by XRD. Valency and local structure of Fe atoms were investigated by Mossbauer spectroscopy at room temperature. DC-conductivity and impedance measurements of the glass ceramics proved the increased electrical conduction caused by heat treatment.

Mechanical properties of glasses and TiO2 nanocrystal glass composites in BaO–TiO2–B2O3 system

Glasses and glass-nanocrystal (anatase TiO2) composites in BaO–TiO2–B2O3 system were fabricated by conventional melt-quenching technique and controlled heat treatment respectively. Poisson's ratio and Young's moduli were predicted through Makishima–Mackenzie theoretical equation for the as-quenched glasses by taking the four and three coordinated borons into account. Mechanical properties of the glasses and glass-nanocrystal composites were investigated in detail through nanoindentation and microindentation studies. Predicted Young's moduli of glasses were found to be in reasonable agreement with nanoindentation measurements. Hardness and Young's modulus were enhanced with increasing volume fraction of nanocrystallites of TiO2 in glass matrix whereas fracture toughness was found susceptible to the surface features. The results were correlated to the structural units and nanocrystals present in the glasses.

Thermal behaviour of zircon/zirconia-added chemically durable borosilicate porous glass

Macroporous alkali resistant glass has been developed by making additions of zirconia (ZrO2) and zircon (ZrSiO4) to the sodium borosilicate glass system SiO2–B2O3–Na2O. The glass was made using a traditional high temperature fusion process. Differential thermal analysis (DTA) was carried out to identify the glass transition temperature (Tg) and crystallisation temperature (Tx). Based on these findings, controlled heat-treatments were implemented to separate the glass into two-phases; a silica-rich phase, and an alkali-rich borate phase. X-ray diffraction (XRD) was used to identify any crystal phases present in the as-quenched and heat-treated glasses. Fourier transform infrared (FTIR) spectroscopy also proved effective in investigating phase separation and crystallisation behaviour. After leaching, a silica-rich skeleton with an interconnected pore structure and a uniform pore distribution was observed. Pore characterisation was carried out using mercury porosimetry. The size and shape of the pores largely depended on the heat-treatment temperature and time. ZrO2/ZrSiO4 additions increased the alkali resistance of the porous glass 3–4 times.

Native amorphous nanoheterogeneity in gallium germanosilicates as a tool for driving Ga2O3nanocrystal formation in glass for optical devices

Nanoparticles in amorphous oxides are a powerful tool for embedding a wide range of functions in optical glasses, which are still the best solutions in several applications in the ever growing field of photonics. However, the control of the nanoparticle size inside the host material is often a challenging task, even more challenging when detrimental effects on light transmittance have to be avoided. Here we show how the process of phase separation and subsequent nanocrystallization of a Ga-oxide phase can be controlled in germanosilicates - prototypal systems in optical telecommunications - starting from a Ga-modified glass composition designed to favour uniform liquid-liquid phase separation in the melt. Small angle neutron scattering data demonstrate that nanosized structuring occurs in the amorphous as-quenched glass and gives rise to initially smaller nanoparticles, by heating, as in a secondary phase separation. By further heating, the nanophase evolves with an increase of nanoparticle gyration radius, from a few nm to a saturation value of about 10 nm, through an initial growing process followed by an Ostwald ripening mechanism. Nanoparticles finally crystallize, as indicated by transmission electron microscopy and X-ray diffraction, as γ-Ga(2)O(3)- a metastable gallium oxide polymorph. Infrared reflectance and photoluminescence, together with the optical absorption of Ni ions used as a probe, give an indication of the underlying interrelated processes of the structural change in the glass and in the segregated phase. As a result, our data give for the first time a rationale for designing Ga-modified germanosilicates at the nanoscale, with the perspective of a detailed nanostructuring control.

Nanocomposite Dielectrics in PbO–BaO–Na2O–Nb2O5–SiO2 System with High Breakdown Strength for High Voltage Capacitor Applications

Nanocomposite dielectrics in 6PbO-4BaO-20Na2O-40Nb2O5-30SiO2 system were prepared via melt-quenching followed by controlled crystallization. X-ray diffraction studies reveal that Pb2Nb2O7, Ba,NaNb5O15, NaNbO3 and PbNb2O6 phases are formed from the as-quenched glass annealed in temperature range from 700 degrees C to 850 degrees C. Ba2NaNb5O15, Pb2Nb2O7 crystallizes at 700 degrees C and then Pb2Nb2O7 disappears at 850 degrees C, while PbNb2O6 and NaNbO3 are formed at 850 degrees C. Microstructural observation shows that the crystallized particles are nanometer-sized and randomly distributed with glass matrix being often found at grain boundaries. The dielectric constant of the nanocomposites formed at different crystallization temperatures shows good frequency and electric field stability. The breakdown strength is slightly decreased when the glass-ceramics thickness is varied from 1 mm to 4 mm. The corresponding energy density could reach 2.96 J/cm3 with a breakdown strength of 58 kV/mm for thickness of 1 mm.

Fabrication of Transparent BaNaB9O15 Glass–Microcrystal Composites

Transparent glasses in the BaO-Na2O-B2O3 (BNBO) system were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were confirmed by x-ray powder diffraction (XRD) and differential thermal analysis (DTA), respectively. Cyclic heat treatment of the as-quenched glasses yielded transparent glass–microcrystal composites. The volume fraction of the crystallites and their sizes could be easily controlled by this process. Heat-treated samples were highly transparent owing to the minimum mismatch between the refractive indices of the crystallites and the glass residual matrix. BNBO samples that were heat treated at 540°C for 4 h for 10 cycles were found to be 60% to 70% transparent in the 500 nm to 900 nm wavelength range.

Microstructure and Electrochemical Behavior of Pd–Cu–Ni–P Bulk Metallic Glass and Its Crystallized Alloys

The microstructure and electrochemical behavior of the Pd42.5Cu30Ni7.5P20 as-quenched bulk metallic glass and its crystallized alloys after heat-treatment at 623 and 723K were investigated. The results revealed that the Pd42.5Cu30Ni7.5P20 bulk metallic glass and its crystallized alloys were spontaneously passivated in 0.144M NaCl and Hanks’ solution with a low passive current density and a wide passive region. The transpassive potential of the fully crystallized alloy heat-treated at a higher temperature was lower than those of the as-quenched bulk metallic glass and partially crystallized alloy. The difference in the microstructure of the as-quenched bulk metallic glass, the partially crystallized alloy and the fully crystallized alloy was responsible for their different transpassive potentials. The wider passive region of the alloys in Hanks’ solution is attributed to the presence of HCO3 ¹ , HPO4 2¹ ,S O4 2¹ and H2PO4 ¹ ions in the solution, which act as corrosive inhibitors.

Conversion of sandy tailing from banded iron formation exploitation into glass-ceramic materials

Glass-ceramic materials made of 40.0 wt. (%) of sandy tailing from banded iron formation exploitation and 60 wt. (%) of slag from steelwork were analyzed. Vitrification was obtained by heating the batch samples up to 1400 °C for 1 hour and quenching the melt on a stainless steel plate. Devitrification was obtained by heat-treating the as-quenched glass samples in isothermal conditions at 750 and 1000 °C for 2 hours. FTIR spectroscopy analysis on the devitrified samples indicates a peak shift towards higher wave number with respect to the as-quenched glass because of the crystallization. XRD analysis revealed the presence of crystalline diopside CaMgSi2O6 as the major phase in the glass samples isothermally heat-treated at 1000 °C. Results also indicated that the devitrification at 1000 °C and an incipient devitrification at 750 °C resulted into harder glass-ceramic materials.

Effect of nanocrystallization on the electrical conduction of silver lithium phosphate glasses containing iron and vanadium

xLi2O·(20-x)Ag2O·20Fe2O3·60P2O5 glasses (x = 0, 5, 10, 15 and 20 mol%) and 5Ag2O·15Li2O·5V2O5·15Fe2O3·60P2O5 glass were prepared by melt-quenching of the reagent mixture at 1000 °C. Glass transition temperature (T g) and crystallization temperature (T c) of these samples were determined by differential thermal analysis (DTA). It proved that T g increased with Li2O content. XRD of as-quenched glasses confirmed their amorphous nature. XRD of samples heat treated for one hour at temperature near their T c, indicated nanocrystals precipitated in the glassy matrix with an average particle size of 35 nm. Mossbauer results revealed that the relative fraction of Fe2 + was decreased with an increasing Li2O content. The isomer shift values of Fe3 + lie in a range of 0.38–0.45 mm s − 1, while those for Fe2 + were 1.10–1.31 mm s − 1. Heat-treated sample of 5Ag2O·15Li2O·5V2O5·15Fe2O3·60P2O5 glass exhibit an enhancement of the electrical conductivity by three orders of magnitude due to the 3d-electron (polaron) hopping from V4 + to V5 + in the “vanadate glass” units.

Nano-heterogeneous structure of (1-x)KNbO 3–xSiO 2 glasses in the low glass-forming oxide content range 0.05 ≤ x ≤ 0.3

Glasses with a high content of niobium oxide are of significant interest for electro-optics and nonlinear optics. In the present paper we report the results of the investigation of the submicroscopic structure and nonlinear optical properties of (1- x)KNbO 3– xSiO 2 (KNS) glasses (x = 0.05–0.30) by XRD, SANS, electron microscopy and second harmonic generation (SHG) technique. Vitreous samples were fabricated by rapid melt cooling, via pressing the melt by steel plates, quenching between rotating metal rolls or splat cooling in air or nitrogen flow. Glasses with x < 0.15 are shown to possess a micro-inhomogeneous structure with regions enriched by SiO 2. On the contrary, as-quenched glasses with x > 0.15 are found by SANS to be homogeneous, but form nanostructures enriched by SiO 2 after heat-treatment. At temperatures below ~( T g + 50 °C), SiO 2-enriched regions grow slightly, whereas their chemical composition shifts considerably closer to SiO 2. The data on the nano-inhomogeneous structure enables clarifying the complicated T g ( x) dependence of KNS glasses. SHG-active KNbO 3 phase precipitates at later stages of crystallization when the glass starts to lose its transparency, and crystallization of perovskite-like KNbO 3 is accompanied by the enhancement of SHG efficiency by several orders of magnitude.

Electrical relaxation and transport in 0.5Cs2O-0.5Li2O-3B2O3 glasses

The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the transparent glasses in the composition 0.5Cs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O-0.5Li <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O-3B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (CLBO) were investigated in the 100 Hz - 10 MHz frequency range. The dielectric constant for the as-quenched glass increased with increasing temperature, exhibiting anomalies in the vicinity of the glass transition and crystallization temperatures. The temperature coefficient of dielectric constant was estimated (35 ± 2 ppm.K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) using Havinga's formula. The dielectric loss at 313 K is 0.005 ± 0.0005 at all the frequencies understudy. The activation energy associated with the electrical relaxation determined from the electric modulus spectra was found to be 1.73 ± 0.05 eV, close to that of the activation energy obtained for DC conductivity (1.6 ± 0.06 eV). The frequency dependent electrical conductivity was analyzed using Jonscher's power law. The combination of these dielectric characteristics suggests that these are good candidates for electrical energy storage device applications.

Linear optical properties of BaNaB 9O 15, BaLiB 9O 15 and SrLiB 9O 15 glasses

Transparent BaNaB 9O 15 (BNBO), BaLiB 9O 15 (BLBO) and SrLiB 9O 15 (SLBO) glasses were fabricated via the conventional melt-quenching technique. X-ray diffraction (XRD) and Differential thermal analysis (DTA) studies carried out on the as-quenched glasses confirmed their amorphous and glassy nature, respectively. The optical properties for these as-quenched glasses were investigated. The refractive index, optical band gap, Urbach energy and Fermi energy were determined. The average electronic polarizability calculated from the refractive index expression.

Phase separation in Cu 46Zr 47− xAl 7Gd x metallic glasses

The influence of Gd addition on phase separation of rapidly quenched Cu 46Zr 47− x Al 7Gd x metallic glasses ( x = 2,5,7) was studied. For low Gd content ( x = 2), a homogeneous glass is obtained for the as-quenched state. Annealing leads to cluster formation by nucleation and growth prior to crystallization. For the Gd contents x = 5 and 7, early stages of spinodal decomposition are observed in the as-quenched glasses. Further annealing increases the amplitude of the compositional fluctuations prior to crystallization. Atom probe tomography gives evidence of the presence of Gd-enriched clusters of 2–5 nm size for the Cu 46Zr 42Al 7Gd 5 glass. The structure formation as a function of the Gd content is essentially determined by the composition dependence of the miscibility gap of the metastable undercooled melt. Early stages of spinodal decomposition or almost homogeneous glassy states are obtained if the critical temperature of liquid–liquid phase separation is close or below to the glass transition temperature.

Ferroelectricity in the glassy material of the composition Bi 2O 3–Pb 3O 4–CuO–K 2O

Glass sample of the composition 31.4 Bi 2O 3–2.33 Pb 3O 4–64.53 CuO–1.74 K 2O in mol% was prepared by the conventional quenching melt technique. The as-quenched single phase glass shows interesting ferroelectric properties which is not known in the field of glass science. If the as-quenched glass is heat treated above the glass transition temperature all signs of ferroelectricity disappears completely. X-ray diffraction and transmission electron microscopy as well as differential thermal analysis were used to recognize the glassy nature of the as-quenched sample. Ac dielectric measurements were performed as a function of temperature and frequency and showing ferroelectric to paraelectric phase transition at Curie's temperature of 540 K. Non-linear polarization as a function of temperature and applied electric field as well as pyroelectricity were also studied. The conduction mechanism was confirmed to obey the adiabatic small polaron hopping (SPH) and was mainly due to electronic transport between Cu ions. The dominant factor determining conductivity was the hopping carrier mobility in this glass. From the best fits, reasonable values of various SPH and VRH parameters are obtained.

Effect of nanocrystallization on the electrical conductivity enhancement and Mössbauer hyperfine parameters of iron based glasses

Selected glasses of Fe2O3–PbO2–Bi2O3 system have been transformed into nanomaterials by annealing at temperature close to crystallization temperature (Tc) for 1 h. The effects of the annealing of the present samples on its structural and electrical properties were studied by Mössbauer spectroscopy, transmission electron micrograph (TEM), differential scanning calorimeter (DSC) and dc conductivity (σ). Mössbauer spectroscopy was used in order to determine the states of iron and its hyperfine structure. The effect of nanocrystalization on the Mössbauer hyperfine parameters did not exhibit significant modifications in present glasses. However, in case of glass ceramic nanocrystals show a distinct decrease in the quadrupole splitting (Δ) is observed, reflecting an evident decrease in the distortion of structural units like FeO4 units. In general, the Mössbauer parameters of the nano-crystalline phase exhibit tendency to increase with PbO2 content. TEM of as-quenched glasses confirm the homogeneous and essentially featureless morphology. TEM of the corresponding glass ceramic nanocrystals indicates nanocrystals embedded in the glassy matrix with average particle size of about 32 nm. The crystallization temperature (Tc) was observed to decrease with PbO2 content. The glass ceramic nanocrystals obtained by annealing at Tc exhibit improvement of electrical conductivity up to four orders of magnitude than the starting glasses. This considerable improvement of electrical conductivity after nanocrystallization is attributed to formation of defective, well-conducting phases “easy conduction paths” along the glass–crystallites interfaces.

Dielectric and Electrical Conductivity Relaxation in 0.5Li2O-0.5Na2O-2B2O3 Glasses

The frequency and temperature dependence of the dielectric constant, electric modulus and electrical conductivity of the transparent glasses in the composition 0.5Li2O-0.5Na2O-2B2O3 (LNBO) were investigated in the 100 Hz - 10 MHz frequency range. The dielectric data have been analyzed using Cole-Cole equation with an addition of the conductivity term. The electrical conductivity was found to be obeying Jonscher's universal law. The dielectric constant and the loss for the as-quenched glasses increased with increasing temperature, exhibiting anomalies in the vicinity of the glass transition and crystallization temperatures. The bulk DC conductivity at various temperatures was extracted from the electrical relaxation data. Conductivity plots were not found to follow Summerfield scaling due to mixed alkali effect. The imaginary part of electric modulus spectra was modeled using an approximate solution of Kohlrausch-Williams-Watts (KWW) relation. The stretching exponent, {\beta}, was found to be 0.56 and temperature independent.

Dielectric properties of (100−x)Li2B4O7–x(Ba5Li2Ti2Nb8O30) glasses and glass nanocrystal composites

Transparent glasses of various compositions in the system (100 -x)(Li2B4O7)-x(Ba5Li2Ti2Nb8O30) (5 <= x <= 20, in molar ratio) were fabricated by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). X-ray powder diffraction studies confirmed the as-quenched glasses to be amorphous and the heat-treated to be nanocrystalline. Controlled heat-treatment of the as-quenched glasses at 500 degrees C for 8 h yielded nanocrystallites embedded in the glass matrix. High Resolution Transmission Electron Microscopy (HRTEM) of these samples established the size of the crystallites to be in the nano-range and confirmed the phase to be that of Ba5Li2Ti2Nb8O30 (BLTN) which was, initially, identified by X-ray powder diffraction. The frequency, temperature and compositional dependence of the dielectric constant and the electrical conductivity of the glasses and glass nanocrystal composites were investigated in the 100 Hz to 10 MHz frequency range. Electrical relaxations were analyzed using the electric modulus formalisms. The imaginary part of electric modulus spectra was modeled using an approximate solution of Kohlrausch-Williams-Watts relation. The frequency dependent electrical conductivity was rationalized using Jonscher's power law. The activation energy associated with the dc conductivity was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. (C) 2010 Elsevier B.V. All rights reserved.

Optical and dielectric properties of transparent glasses and nanocrystals of lithium niobate and lithium diborate in borate glasses

The glass composition 92.5 Li 2 B 4 O 7 –7.5Nb 2 O 5 (mol%) was prepared by the conventional melt quenching technique. The as-quenched sample, blue and transparent, was heat-treated at 550 and 650 °C (HT). The glassy nature of the as-quenched sample was established by Differential scanning calorimetry (DSC). Lithium niobate LiNbO 3 and Li 2 B 4 O 7 nanocrystals were produced within the glass by heat-treating it at 550 and 650 °C/3. The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Various optical parameters such as optical band gap ( E opt ) and Urbach energy (Δ E ) of these transparent glass–ceramics have been found to be crystallite size dependent. The volume ratio of the particles increases with increase in heat-treatment temperature. The behavior of the σ ac , with the increase in the heat-treatment (HT) temperature, was related with the decrease in the free ions number in the glass matrix and consequent increase in the fraction of the crystallites LiNbO 3 phase to the crystallites Li 2 B 4 O 7 phase and the glass matrix. The dielectric constants of the glass–ceramics decrease with increase in the HT temperature and with increase in frequency (0.12–100 kHz).

Structural and optical properties of (100−x)Li2B4O7·x(Ba5Li2Ti2Nb8O30) glasses and glass nanocrystal composites

Optically clear glasses of various compositions in the system (100-x)(Li₂B₄O₇)·x(Ba₅Li₂Ti₂Nb₈O₃₀) (5 ≤ x ≤ 20, in molar ratio) were fabricated by splat quenching technique. Controlled heat-treatment of the as-quenched glasses at 500 °C for 8 h yielded nanocrystallites embedded in the glass matrix. High Resolution Transmission Electron Microscopy (HRTEM) of these samples established the composition of the nano-crystallites to be that of Ba₅Li₂Ti₂Nb₈O₃₀. ¹¹B NMR studies revealed the transformation of BO₄ structural units into BO₃ units owing to the increase in TiO₆ and NbO₆ structural units as the composition of Ba₅Li₂Ti₂Nb₈O₃₀ increased in the glass. This, in turn, resulted in an increase in the density of the glasses. The influence of the nominal composition of the glasses and glass nanocrystal composites on optical band gap (E(opt)), Urbach energy (ΔE), refractive index (n), molar refraction (R(m)), optical polarizability (α(m)) and third order non-linear optical susceptibility (χ³) were studied.