Crystallization of bismuth oxide nano-crystallites in a SiO2–PbO–Bi2O3 glass matrix

SiO₂–PbO–Bi₂O₃ glasses having the composition of 35SiO₂–xPbO–(65 ? x)Bi₂O₃ (where x = 5, 20 and 45; in mol%) have been prepared using the conventional melting and annealing method. Differential scanning calorimetry (DSC) was employed to characterize the thermal behavior of the prepared glasses in order to determine their crystallization temperatures (T_cr). It has been found that T_cr decreases with the decrease of Bi₂O₃ content. The amorphous nature of the prepared glasses as well as the crystallinity of the produced glass–ceramics were confirmed by X-ray powder diffraction (XRD) analysis. SiPbBi₂O₆ glass nano-composites, comprising bismuth oxides nano-crystallites, were obtained by controlled heat-treatment of the glasses at their (T_cr) for 10 h. Transmission electron microscopy (TEM) of the glass nano-crystal composites demonstrates the presence of cubic Bi₂O₃ nano-crystallites in the SiPbBi₂O₆ glass matrix. Nano-crystallites mean size has been determined from XRD line width analysis using Scherrer's equation as well as from TEM; and the sizes obtained from both analyses are in good agreement. These sizes varied from about 15 to 170 nm depending on the chemical compositions of parent glasses and, consequently, their structure. Interestingly, replacement of the Bi₂O₃ by PbO in the glass compositions has pronounced effect on the nature, morphology and size of the formed nano-crystallites. Decrease of the Bi₂O₃ content increases the size of the nano-crystallites, and at the lowest Bi₂O₃ extreme, namely 20 mol%, introduces minority of the monoclinic Bi₂O₄ in addition to the cubic Bi₂O₃. The crystallization mechanism is suggested to involve a diffusion controlled growth of the bismuth oxide nano-crystallites in the SiPbBi₂O₆ glass matrix with the zero nucleation rate.     

Influence of Bi2O3 content on the crystallization behavior of TeO2–Bi2O3–ZnO glass system

Glass ceramic materials with composition 75TeO₂–xBi₂O₃–(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi₂O₃ content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi₂O₃ content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi_0.864Te_0.136O_1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass.     

Phase transformation and crystallization kinetics of melt-spun Ni60Nb20Zr20 amorphous alloy

The glass transition and crystallization kinetics of melt-spun Ni₆₀Nb₂₀Zr₂₀ amorphous alloy ribbons have been studied under non-isothermal and isothermal conditions using differential scanning calorimetry (DSC). The dependence of glass transition and crystallization temperatures on heating rates was analyzed by Lasocka's relationship. The activation energies of crystallization, E_x, were determined to be 499.5 kJ/mol and 488.6 kJ/mol using the Kissinger and Ozawa equations, respectively. The Johnson–Mehl–Avrami equation has also been applied to the isothermal kinetics and the Avrami exponents are in the range of 1.92–2.47 indicating a diffusion-controlled three-dimensional growth mechanism. The activation energy obtained from the Arrhenius equation in the isothermal process was calculated to be E_x = 419.5 kJ/mol. The corresponding three dimensional (3D) time–temperature–transformation (TTT) diagram of crystallization for the alloy has been drawn which provides the information about transformation at a particular temperature. In addition, the intermetallic phases and morphology after thermal treatment have been identified by X-ray diffraction (XRD) and scanning electron microscope (SEM).     

Electrical properties of SrBi2(Nb0.7V0.3)2O9−δ in the SrO–Bi2O3–0.7Nb2O5–0.3V2O5–Li2B4O7 glass system

Glasses in the system (100 − x)Li₂B₄O₇–x(SrO–Bi₂O₃–0.7Nb₂O₅–0.3V₂O₅) (where x = 10, 30 and 50, in molar ratio) were fabricated via melt quenching technique. The compositional dependence of the glass transition (T_g) and crystallization (T_cr) temperatures was determined by differential thermal analysis. The as-quenched glasses on heat-treatment at 783 K for 6 h yielded monophasic crystalline strontium bismuth niobate doped with vanadium (SrBi₂(Nb_0.7V_0.3)₂O_9−δ (SBVN)) in lithium borate (Li₂B₄O₇ (LBO)) glass matrix. The formation of nanocrystalline layered perovskite SBVN phase was preceded by the fluorite phase as established by both the X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The dielectric constants for both the as-quenched glass and glass–nanocrystal composite increased with increasing temperature in the 300–873 K range, exhibiting a maximum in the vicinity of the crystallization temperature of the host glass matrix. The electrical behavior of the glasses and glass–nanocrystal composites was characterized using impedance spectroscopy.     

Crystallization of amorphous Al2O3–SiO2 precursors doped with nickel

The crystallization of amorphous diphasic Al₂O₃–SiO₂ precursors doped with nickel has been studied by differential scanning calorimetry (DSC), XRD diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Diphasic gels with constant atomic ratio (Al + Ni)/Si = 3:1, where 0, 1, 2 and 3 at.% of aluminum were replaced by nickel, have been prepared by hydrolyzing of TEOS in aqueous solution of aluminum nitrate. Crystallization of Ni-containing γ-Al₂O₃ preceded the crystallization of Al–Si spinel. Activation energy of 603 ± 16 kJ mol⁻¹ for crystallization of Ni-containing γ-Al₂O₃ was obtained in non-isothermal conditions. Ni-incorporated γ-Al₂O₃ transforms gradually with the temperature increase into Ni aluminate spinel, while Al–Si spinel reacts with amorphous silica forming mullite at about 1200 °C. Rietveld structure refinement of phases present in the samples annealed at 1600 °C and SEM-EDS and TEM-EDS analyses of related phases have shown that nickel predominantly crystallizes as NiAl₂O₄, but small amount of nickel is incorporated in mullite structure, as well as, dissolved in the glassy phase of the system.     

Thermal properties and glass formation in the SiO2–B2O3–Bi2O3–ZnO quaternary system

Lead-free glasses in the SiO₂–B₂O₃–Bi₂O₃–ZnO quaternary system were studied. The glass formation region, as determined by XRD patterns of bulk samples, was limited to glasses having more than 40 mol% of the glass-forming oxides SiO₂ and B₂O₃. Crystalline phases of Zn₂SiO₄ (willemite) were detected in compositions of 30SiO₂ · 10B₂O₃ · 20Bi₂O₃ · 40ZnO and 20SiO₂ · 10B₂O₃ · 25Bi₂O₃ · 45ZnO. Glass transition temperatures (T_g), dilatometric softening points (T_d) and linear coefficients of expansion in the temperatures range of 25–300 °C (α_25–300) were measured for subsystems along the B₂O₃ join of 10, 20 and 30 mol%. For these subsystems, T_g ranged from 411 to 522 °C, and T_d ranged from 453 to 563 °C, both decreasing with increasing Bi₂O₃ content. The measured α_25–300 ranged from 53 to 95 × 10⁻⁷ °C⁻¹, with values increasing with increasing Bi₂O₃ content. The ZnO content had the opposite effect to the Bi₂O₃ content. It appears that Bi³⁺ acts as a glass-modifier in this quaternary system.     

Nano-crystals precipitation and upconversion luminescence properties in Er3+/Yb3+ co-doped fluoride phosphate glass-ceramics

Er³⁺/Yb³⁺ co-doped transparent glass-ceramics containing Ca₅(PO₄)₃F nano-crystals were prepared and their upconversion properties were investigated. Transparent glass-ceramics were obtained after heat treatment at the first crystallization temperature, TEM images showed that Ca₅(PO₄)₃F nano-crystals of 10–20 nm in diameter precipitated uniformly in the glass matrix, which is similar to the result of those calculated by Scherrer equation. Comparing with the samples before heat treatment, high efficiency upconversion luminescence of Er³⁺ at 547 nm and 667 nm was observed in the glass-ceramics under 980 nm excitation, and the intensity of red emission showed different tendency to that of green emission after nano-crystals precipitation. The reasons for the highly efficient upconversion luminescence in glass-ceramics were discussed.     

Non-isothermal crystallization kinetic studies on MgO–Al2O3–SiO2–TiO2 glass

Thermal stability and crystallization kinetics of the glass 21% MgO, 21.36% Al₂O₃, 53.32% SiO₂ and 4.11% TiO₂ (mol%) has been studied using differential thermal analysis (DTA), dilatometry and X-ray diffraction (XRD). Glass in both bulk and frit forms were produced by melting in platinum crucible at 1600 °C for 1–2 h. From variation of DTA peak maximum temperature with heating rate, the activation energies of crystallization were calculated to be 340 kJ mol⁻¹ and 498 kJ mol⁻¹ for first and second crystallization exotherms, respectively. Crystallization of bulk glass was carried out at various temperatures and for different time durations in the range of 850–1000 °C. The influence of the addition of TiO₂ on the crystallization sequence of the glass was experimentally determined and discussed.     

Preparation and characterization of CuO doped Bi2O3–B2O3–BaO–ZnO glass system for transparent dielectric layer

The electrical, thermal, optical, and morphological properties of CUO doped Bi₂O₃–B₂O₃–BaO–ZnO glasses were studied as a PbO-free, low firing transparent dielectric layer for plasma display panels (PDP). CuO improved the transmittance of Bi₂O₃–B₂O₃–BaO–ZnO by up to 84% in the visible region, eliminating a yellowish color typical of Bi₂O₃–B₂O₃–BaO–ZnO. A slight absorption within the near infrared (NIR) region was also observed. The glass transition temperature (T_g), thermal coefficient of expansion (TCE), and root-mean square (rms) roughness of 0.005 wt% CuO doped Bi₂O₃–B₂O₃–BaO–ZnO were found to be 455 °C, 81.4 × 10⁻⁷/K, respectively, and 162 ± 14 Å, which satisfied the requirements for a transparent dielectric layer for PDP application.     

27Al NMR structural study on aluminum coordination state in bismuth doped silica glass

The aluminum coordination state in bismuth doped silica glass, which has new broad infrared emission at 1.3 μm regions, was investigated by using ²⁷Al NMR, and it is demonstrated that 6-fold coordinated aluminum ions with corundum structure are dominant in bismuth doped silica glass until Bi₂O₃ concentrations of 1.0 mol% with Al₂O₃. The aluminum ion efficiently affects the creation of a Bi luminescent center at an intensity of Bi₂O₃ (1.0 mol%)–Al₂O₃ (2.3 mol%)–SiO₂ (96.7 mol%); the sample is three orders of magnitude larger than the Bi₂O₃ (1.0 mol%)–SiO₂ (99.0 mol%) sample. Aluminum ions with corundum structure in silica glass have a very important role for the configuration of peculiar Bi luminescent centers.     

Effect of TiO2 addition on the chemical durability of Bi2O3–SiO2–ZnO–B2O3 glass system

The effect of the substitution of ZnO for TiO₂ on the chemical durability of Bi₂O₃–SiO₂–ZnO–B₂O₃ glass coatings in hot acidic medium (0.1 N H₂SO₄ at 80 °C) for different times was studied. The thick films produced by a screen-printing method and heat treated at 700 °C/5 min were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The glass from the Bi₂O₃–SiO₂–ZnO–B₂O₃ system developed Zn₂SiO₄ and a glassy phase that were readily attacked by hot 0.1 N sulfuric acid, whereas the heat treated coating from the Bi₂O₃–SiO₂–TiO₂–ZnO–B₂O₃ system presented a finer microstructure with thin interconnected Bi₄Ti₃O₁₂ crystals and a glassy phase more resistant to hot 0.1 N sulfuric acid attack etching.     

Laser spectroscopy of Nd3+-doped PbO–Bi2O3–Ga2O3–BaO glasses

We present spectroscopic results of PbO–Bi₂O₃–Ga₂O₃–BaO glass doped with different concentration of Nd₂O₃. These glasses have high refractive index (∼2.4) and large spectral transmission window. Measurements of absorption, emission and fluorescence lifetime are presented. From the calculations of the Judd–Ofelt parameters the radiative lifetimes, branching ratios and quantum efficiency of ⁴F_3/2 level are calculated. The highest emission intensity was measured for the sample doped with 0.5 wt% of Nd₂O₃ with emission cross-section of 2.6 × 10⁻²⁰ cm², at 1069 nm, fluorescence lifetime of 110 μs, quantum efficiency of 82% and effective linewidth of 34 nm. The results point out this glass system as good candidate to be used in the development of photonic devices operating in the near infrared spectral range.     

Structural characterization and phase transformation kinetics of Se58Ge42−xPbx (x = 9, 12) chalcogenide glasses

The glass transition behavior and crystallization kinetics of Se₅₈Ge_42?xPb_x (x = 9, 12) have been investigated using Differential Scanning Calorimetry (DSC) at five different heating rates under non-isothermal conditions. It has been observed that these glassy systems exhibit single glass transition and double crystallization on heating. The XRD pattern revealed that the considered glasses get crystallized into GeSe₂ and PbSe/Se phases after annealing at 633–643 K for 2 h. The GeSe₂ and Se phases were found to crystallize in monoclinic structure while, PbSe phase crystallizes in cubic structure. Besides this, a mixed phase was also observed in DSC thermograms after annealing. The kinetic studies include determination of various parameters such as Avrami exponent (n), frequency factor (K_o), dimensionality of growth (m), the activation energy for glass transition (E_t) and for crystallization (E_c). The values of E_t increases while that of E_c decreases after annealing. Also, dimensionality of growth decreases to one dimension from two and three dimensions after annealing.     

Effect of B2O3 addition on the thermal properties and density of barium phosphate glasses

Variations in glass transition temperature, onset of crystallization, thermal expansion coefficient, density and molar volume with B₂O₃ concentration were studied in a series of xB₂O₃–(100 − x)Ba(PO₃)₂ glasses with 0–10 mol% B₂O₃. DTA analysis and isothermal treatments for powdered glass samples reveal that ⩾7.5 mol% B₂O₃ addition suppresses surface crystallization during softening process. Raman spectroscopy suggests that the properties are related to the glass structure consisting of PO₄ Q² units with diborate and PO₄–BO₄ groups.     

Crystallization of bismuth titanate and bismuth silicate grown as thin films by atomic layer deposition

Bismuth silicate and bismuth titanate thin films were deposited by atomic layer deposition (ALD). A novel approach with pulsing of two Bi-precursors was studied to control the Si/Bi atomic ratio in bismuth silicate thin films. The crystallization of compounds formed in the Bi₂O₃–SiO₂ and Bi₂O₃–TiO₂ systems was investigated. Control of the stoichiometry of Bi–Si–O thin films was studied when deposited on Si(1 0 0) and crystallization was studied for films on sapphire and MgO-, ZrO₂- and YSZ-buffered Si(1 0 0). The Bi–Ti–O thin films were deposited on Si(1 0 0) substrate. Both Bi–Si–O and Bi–Ti–O thin films were amorphous after deposition. Highly a-axis oriented Bi₂SiO₅ thin films were obtained when the Bi–Si–O thin films deposited on MgO-buffered Si(1 0 0) were annealed at 800 °C in nitrogen. The full-width half-maximum values for 200 peak were also studied. An excess of bismuth was found to improve the crystallization of Bi–Ti–O thin films and the best crystallinity was observed with Ti/Bi atomic ratio of 0.28 for films annealed at nitrogen at 1000 °C. Roughness of the thin films as well as the concentration depth distribution were also examined.     

Mechanism of crystallization of fast fired mullite-based glass–ceramic glazes for floor-tiles

The mechanism of crystallization from a B₂O₃-containing glass, with composition based in the CaO–MgO–Al₂O₃–SiO₂ system, to a glass–ceramic glaze was studied by different techniques. Glass powder pellets were fast heated, simulating current industrial tile processing methods, at several temperatures from 700 to 1200 °C with a 5 min hold. Microstructural study by field emission scanning electron microscopy revealed that a phase separation phenomenon occurred in the glass, which promoted the onset of mullite crystallization at 900 °C. The amount of mullite in the glass heated between 1100 and 1200 °C was around 20 wt%, as determined by Rietveld refinement. The microstructure of the glass–ceramic glaze heated at 1160 °C consisted of interlocked, well-shaped, acicular mullite crystals longer than 4 μm, immersed in a residual glassy phase.     

The effect of TiO2 on phase separation and crystallization of glass-ceramics in CaO–MgO–Al2O3–SiO2–Na2O system

The experiments were carried out on studying the effect of phase separation on nucleation and crystallization in the glass based on the system of CaO–MgO–Al₂O₃–SiO₂–Na₂O. In the experiments, TiO₂ was chosen as nucleating agent. Three batches of 5, 8 and 10 wt% TiO₂ substitution were investigated by the techniques of DSC, XRD, FTIR and FESEM equipped with EDS. XRD and FTIR analysis indicated that the super cooled glasses were all amorphous, the heat treatment leading to nucleation would cause a disruption of silica network which followed phase separation. The phase separation followed the generation of crystal seeds Mg(Ti, Al)₂O₆. FESEM observation and EDS analysis revealed that the more TiO₂ content of glass, the more droplet separated phase and crystal seeds after nucleation heat treatment. The main crystal phase is clinopyroxene, Ca(Ti, Mg, Al)(Al, Si)O₆, of crystallized glass.     

EPR and magnetic susceptibility studies of B2O3–Bi2O3–Gd2O3 glasses

Glasses of the xGd₂O₃ · (100 − x)[B₂O₃ · Bi₂O₃] system with 0.5 ⩽ x ⩽ 10 mol% were studied by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Data obtained show that for low gadolinium oxide contents of the samples (x ⩽ 3 mol%) the Gd³⁺ ions are randomly distributed in the host glass matrix and are present as isolated and dipole–dipole coupled species. For higher gadolinium oxide contents of the samples (x > 3 mol%) the Gd³⁺ ions appear as both isolated and antiferromagnetically coupled species. The EPR spectra of the glasses reveal resonance sites with an unexpected high crystalline field in addition to the ‘U’ spectrum, typical for Gd³⁺ ions in disordered systems. This absorption line is due to Gd³⁺ ions that replace Bi³⁺ ions from the host glass matrix and could play the network unconventional former role in the studied glasses.     

Influence of rare-earth impurities on the Ge and Ga local structure in the Ca3Ga2Ge3O12 glass

The present contribution presents X-ray absorption fine structure (XAFS) measurements and analysis of the Ge and Ga local structure in glass of Ca₃Ga₂Ge₃O₁₂ composition, doped with rare-earth metals (Ce, Eu, Ho, Er in the amount of 0.7 wt% and Nd in the amount of 1.0 wt%). The Ge and Ga ion neighborhoods in the considered glass samples have been compared with data obtained for undoped glass. The results have shown that introduction of rare-earth ions modifies the local structure around the Ga ions in the glass network, leaving the same occurrence ratio of the GaO₄ and GaO₆ structural units as in undoped Ca₃Ga₂Ge₃O₁₂ glass. At the same time, the GeO₂ subsystem remains completely unaffected by the presence of rare-earth dopants.