Comparative study of thermal stability and crystallization kinetics of 70B2O3-30Bi2O3 and 70B2O3-30PbO glasses

Glasses with compositions 70B₂O₃-30Bi₂O₃ and 70B₂O₃-30PbO have been prepared and studied by differential thermal analysis (DTA). The crystallization kinetics of the glasses were investigated under non-isothermal conditions. From the dependence of glass-transition temperature (T_g) on heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined. Thermal stability of these glasses were achieved in terms of the characteristic temperatures, such as glass-transition temperature, T_g, onset temperature of crystallization, T_in, temperature corresponding to the maximum crystallization rate, T_p, beside the kinetic parameters, K(T_g) and K(T_p). The results revealed that 70B₂O₃-30PbO is more stable than 70B₂O₃-30Bi₂O₃. The crystallization mechanism is characterized for both 70B₂O₃-30Bi₂O₃ and 70B₂O₃-30PbO glasses (kinetic exponent n=2.06 for 70B₂O₃-30Bi₂O₃, and n=3.03 for 70B₂O₃-30PbO). The phases at which the glass crystallizes after the thermal process were identified by X-ray diffraction.     

Crystallization kinetics of Li2O-PbO-V2O5 glasses

Lead vanadate glasses of the system 5Li₂O−(45−x) PbO−(50+x) V₂O₅, with x=0, 5, 10, and 15 mol% have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC using continuous-heating techniques. In addition, from dependence of the glass-transition temperature (T_g) on the heating rate, the activation energy for the glass transition was derived. Similarly the activation energy of the crystallization process was determined and the crystallization mechanism was characterized. The results reveal the increase of the activation energy for glass transition which was attributed to the increase in the rigidity, the cross-link density and the packing density of these glasses. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of Li_0.30V₂O₅, Li_0.67O₅V₂, LiV₆O₁₅, Li₄O₄Pb, and O₇Pb₂V₂ in a remaining amorphous matrix.     

Control of Crystallization Kinetics and Study of the Thermal, Structural and Morphological Properties of an Li2O–B2O3–Al2O3 Vitreous System

A glass matrix with nominal composition 50Li₂O·45B₂O₃·5Al₂O₃ (mol%) was synthesized, and its physical properties were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and atomic force microscopy (AFM). The glass transition temperature T _g, the crystallization-onset temperature T _x,, the crystallization peak temperatures T _c1 and T _c2, and the fusion peak temperatures T _m1 and T _m2 were determined from at least two glass matrix phases to be approximately 382, 457, 486, 574, 761, and 787?°C, respectively, at 5?°C/min heating rate. Heat treatments at 450?°C for an increasing sequence of time intervals allowed control over the amount of crystallization. Additional information on the crystallization kinetics for the LBA glass matrix was gathered from AFM images, DTA thermograms, and XRD diffractograms. The latter technique showed that LiBO₂ (ICDD-16568) and Li₃AlB₂O₆ (ICDD-51754) phases are formed in the glass?Cceramic system. Debye?CScherrer analysis of the XRD peaks revealed a competition between the evolutions of crystal phases during heat treatment. Activation energies for crystallization, obtained from theoretical models applied to the DTA data showed that the crystallization is heterogeneous. The AFM images demonstrated that this heterogeneous crystallization starts at the surface of the LBA glass matrix and identified crystal sizes in agreement with the results of the Debye?CScherrer analysis. Our study shows that thermal and structural characterization techniques can be combined with theoretical results drawn from well-tested models to offer a unified view of crystallization in a glass?Cceramics system.     

Study of PbO-SrO-TiO2-B2O3 glass and glass ceramics

The glasses with composition (50−X)PbO–XSrO-25TiO₂-25B₂O₃ (where X=0, 5, 10 and 15 mol%) were prepared using conventional quenching technique. The T_g, T_c, density and CTE of the glass samples were measured. The T_g observed to increase with increasing concentration of SrO, while the T_c first decreased and then increased. The glass samples were converted to glass ceramics by following two stage heat treatment schedule. The glass ceramic samples were characterized by XRD, SEM and dielectric measurements. The XRD results revealed the formation of ferroelectric lead titanate as a major crystalline phase in glass ceramics. Additional phases observed include Sr₂B₂O₅ and PbB₂O₄. The room temperature (RT) dielectric constant of glass and glass ceramics are in the range of 100–120 which is promising for capacitor application.     

Effect of iron doping on the characterization and transport properties of calcium phosphate glassy semiconductors

X-ray diffraction (XRD), differential scanning calorimeter (DSC), density (d) and dc conductivity (σ) of the glasses in Fe₂O₃-CaO-P₂O₅ system were reported. The dc conductivity in the temperature range 303-453 K was measured. The overall features of these XRD curves confirm the amorphous nature of the present samples. The density of glasses increases from 2.750 to 2.892 g/cm³ with increasing Fe₂O₃ content as a result of a strengthening of cross-linking within glass network. The glass temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The glasses had conductivities ranging from 10⁻⁹ to 10⁻⁵ Sm⁻¹ at temperatures from 303 to 453 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

NaBO2-B2O3体系玻璃的形成和晶化机制

本文用热学分析、高温和室温X射线衍射分析、红外吸收光谱等方法研究了NaBO₂-B₂O₃体系玻璃的形成、热稳定性和晶化机制。这一体系十分容易形成稳定的非晶玻璃,晶化过程与非晶的宏观状态有关。块状玻璃的晶化温度比非晶粉末高。部分成份晶化后形成不同的物相,熔点也不同。晶化产物的晶体结构类似于玻璃的结构。NaBO₂-B₂O₃体系的电导率用交流阻抗直接测量法测定。玻璃态的电导率比晶态试 关键词：     

New alkali antimonate glasses

Glass formation has been investigated in ternary systems Sb₂O₃-PbO-M₂O in which M is alkali Li, Na and K and antimony oxide is the glass former. Alkali elements were introduced as carbonates. The size of the glass forming region is enlarged as alkali ionic radius increases. Binary Sb₂O₃-M₂O glasses were obtained: (100−x) Sb₂O₃-xLi₂O, (10<x<30), (100−x) Sb₂O₃-xNa₂O, (10<x<70), and (100−x) Sb₂O₃-xK₂O, (10<x<90). In ternary systems, PbO content could reach 60 mol%. Temperatures of glass transition, T_g, onset of crystallization, T_x, and maximum of crystallization, T_p, have been measured using differential scanning calorimetry. Depending on composition, glass transition temperature ranges from 240 to 330 °C. The incorporation of alkali oxide increases T_g while lead oxide has the reverse effect. Thermal stability range (T_x-T_g) was usually between 65 and 266 °C, while no crystallization exotherm was observed in some cases. Density and thermal expansion increases as lead concentration increases. Optical transmission has been measured. The UV cut-off depends on alkali content: samples are yellow and turn green for large K and Na content. These glasses have potential applications as low phonon energy glasses for infrared transmission or active devices.     

Controlled crystallization a ionic conductivity of nanostructured LiNbFePO 4 glass ceramic

Glass sample with a composition of Li_1.3Nb_0.3Fe_1.7(PO₄)₃, prepared by a conventional melt-quenching method, was heat treated to obtain glass ceramics of NASICON type. Glass transition (T _g) and crystallization (T _c) 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 T _c, precipitation of crystalline particles with NASICON-type structure was confirmed by XRD. Valency and local structure of Fe atoms were investigated by Mössbauer spectroscopy at room temperature. DC-conductivity and impedance measurements of the glass ceramics proved the increased electrical conduction caused by heat treatment.     

Thermal features and physical properties of sulfur modified barium vanadate glasses

Differential scanning calorimetry (DSC) and XRD were used to investigate the role of sulfur in the network of V₂O₅–Fe₂O₃–BaO glasses. The crystallization kinetics of the glasses were investigated under non-isothermal conditions applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC. The activation energy for the glass transition (E _g) was derived from dependence of the glass-transition temperature (T _g) on the heating rate. Similarly the activation energy of the crystallization (E _c) and the frequency factor (K ₀) were determined. The results reveal the increase of the activation energy for glass transition was attributed to the increase in the rigidity and the cross-link density of these composites. The evaluated thermal stability decreases with increasing sulfur content. The phases of BaFe₂O₄, V₂O₅ and FeVO₄ micro-crystallites in the remaining amorphous matrix have been identified by X-ray diffraction.     

Thermal analysis and infrared study of Nb2O5–TeO2 glasses

Tellurite glasses of the xNb₂O₅–(100–x) TeO₂, (3 ≤ x ≤ 20 mol%) system have been prepared and studied by IR spectroscopy and differential thermal analysis to explore the role of Nb₂O₅ on their structure. IR analysis indicates that NbO₆ transforms TeO₄ units into tellurite structural TeO₃ units, with a shift of lattice vibrations towards higher wavenumbers. The stretching force constant of the tellurite structural units increases with Nb₂O₅ content, a feature that is attributed to the higher bond strength and higher coordination number of Nb₂O₅ relative to TeO₂. The crystallization kinetics has been studied under non-isothermal conditions using the formal theory of transformations for heterogeneous nucleation. The crystallization results are analyzed, and both the activation energy of the crystallization process and the crystallization mechanism are characterized. The thermal stability of these glasses are characterized in terms of characteristic temperatures, such as the glass-transition temperature, T _g, the temperature of onset of crystallization, T _in, the temperature corresponding to the maximum crystallization rate, T _p, and two kinetic parameters, K(T _g) and K(T _p). The results reveal that thermal stability increases with increasing Nb₂O₅ content. XRD diffraction of the studied glasses indicates the presence of microcrystallites of α-tellurite, γ-telluride, Nb₂Te₄O₁₃ and an amorphous matrix.     

Structure and electrical properties of SrO-borovanadate (V2O5)0.5(SrO)0.5−y(B2O3)y glassses

SrO-borovanadate glasses with nominal composition (V₂O₅)_0.5(SrO)_0.5−y(B₂O₃)_y, 0.0≤y≤0.4 were prepared by a normal quench technique and investigated by direct current (DC) electrical conductivity, inductively coupled plasma (ICP) spectroscopy, infrared (IR) spectroscopy and X-ray powder diffraction (XRD) studies in an attempt to understand the nature of mechanism governing the DC electrical conductivity and the effect of addition of B₂O₃ on the structure and electrical properties of these glasses. XRD patterns confirm the amorphous nature of the present glasses and actual compositions of the glasses were determined by ICP spectroscopy. The temperature dependence of DC electrical conductivity of these glasses has been studied in terms of different hopping models. The IR results agree with previous investigations on similar glasses and it has been concluded that similar to SrO-vanadate glasses, metavandate chain-like structures of SrV₂O₆ and individual VO₄ units also occur in SrO-borovanadate glasses. The SrV₂O₆ and VO_n polyhedra predominate in the low B₂O₃-containing SrO-borovanadate glasses as B substitutes into the V sites of the various VO_n polyhedra and only when the concentration of B₂O₃ exceeds the SrO content do BO_n structures appear. This qualitative picture of three distinct structural groupings for Sr-vanadate and Sr-borovanadate glasses is consistent with the proposed glass structure on previous IR and extended X-ray absorption fine structure (EXAFS) studies on these types of glasses. The conductivity results were analyzed with reference to theoretical models existing in the literature and the analysis shows that the conductivity data are consistent with Mott's nearest neighbor hopping model. Analysis of the conductivity data shows that they are consistent with Mott's nearest neighbor hopping model. However, both Mott VRH and Greaves models are suitable to explain the data. Schnakenberg's generalized polaron hopping model is also consistent with temperature dependence of activation energy. However, various model parameters such as density of states, hopping energy, etc. obtained from the best fits were not found to be in accordance with the prediction of the Mott model.     

Study of glasses and glass ceramics in Bi2O3-GeO2-Fe2O3 and Bi2O3-GeO2-Cr2O3 systems by optical spectroscopy

The ferroelectric Bi₂GeO₅ crystalline phase is synthesized by heat treatment of 1Bi₂O₃-1GeO₂-xFe₂O₃ and 1Bi₂O₃-1GeO₂-yCr₂O₃ glasses. The obtained glass ceramics and initial glasses are studied using X-ray diffraction analysis and optical spectroscopy. The dielectric characteristics are measured, and the Curie temperature is determined. The effect of chromium and iron ions on the absorption spectra and dielectric properties of glasses and glass ceramics is determined.     

NIR luminescence from Er/Yb, Tm/Yb, Er/Tm and Nd ions-doped zincborotellurite glasses for optical amplification

In this paper, we report the near-infrared luminescence from the Er³⁺/Yb³⁺, Tm³⁺/Yb³⁺, Er³⁺/Tm³⁺ and Nd³⁺ ions-doped TeO₂-ZnO-B₂O₃-Li₂O-Na₂O glasses for optical amplification. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) profiles of the host glass matrix have been carried out. From the DSC thermogram, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The near-infrared spectra of Er³⁺/Yb³⁺, Tm³⁺/Yb³⁺, Er³⁺/Tm³⁺ and Nd³⁺ ions-doped glasses have shown full-width at half-maxima (FWHM) around 58, 127, 87 and 35 nm, respectively. These glasses with better thermal stability and broad near-infrared emissions should have potential applications in broadly tunable laser sources and broadband optical amplification at low-loss telecommunication windows.     

An anomalous enhancement in the electrical conductivity of Li2O : B2O3 : Al2O3 glasses

The study of electrical conductivity of 27.5 Li₂O : (72.5 − x) B₂O₃ : x Al₂O₃ glass samples has been carried out. It has been observed that the conductivity exhibits Arrhenius behavior for all samples up to glass transition temperature T_g. Beyond T_g, an anomalous enhancement followed by decrease in conductivity has been observed. The results have been explained by dividing the temperature range into two regions. In region-I, it has been observed that the conductivity variation exhibits a maximum at 2.5 mol% Al₂O₃, which has been explained on the basis of Mixed Glass Former Effect (MGFE). An anomalous enhancement in the conductivity observed in region-II has been attributed to the nucleation in the glass. The subsequent decrease in the conductivity has been attributed to the crystallization of the glass samples.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

Raman spectra of soda-lime-silicate glass doped with rare earth

Soda-lime-silicate glasses doped with different rare earth oxides (La₂O₃, CeO₂, Nd₂O₃, Gd₂O₃ and Y₂O₃) of 1 mol% content were prepared by the traditional melting-quenching methods. In order to reveal the effects of rare earth elements on the behavior of soda-lime-silicate glass the structures of soda-lime-silicate glasses doped with different rare earth oxides were determined using an INVIA confocal microRaman spectrometer equipped with a CCD detector, and viscosities of glass melts were measured using a rotating crucible viscometer; the melting temperature of the studied glasses was derived on the basis of the Arrhenius equation. Three expressions of the fraction of non-bridging oxygen (NBO/NBO+BO), average number of non-bridging oxygen (NBO) per tetrahedron (NBO/tetrahedron) and average number of bridging corners per tetrahedron (bridges/tetrahedron) for investigated soda-lime-silicate glasses were given, and the effect of rare earth dopants on the structure of soda-lime-silicate was characterized by the Raman shift, variation of the [SiO₄] tetrahedron structural unit Qⁿ (n=1,2,3,4), fraction of non-bridging oxygen and the average number of bridging corners per tetrahedron. The effect of doping rare earth oxides into glass on the viscosity and melting temperature was interpreted by changes in structure of soda-lime-silicate glasses doped with rare earth oxides.     

Electrical and thermal properties of lead titanate glass ceramics

Glass samples with composition of (50−X)PbO-(25+X)TiO₂-25B₂O₃ (where X=0, 5, 10 and 12.5 mol%) were prepared using conventional quenching technique. The glass transition temperature, T_g and crystallization temperature T_c were determined from the DTA. These glass samples were converted to glass ceramics by following two stage heat treatment schedule. The glass ceramic samples were characterized by XRD, SEM and dielectric constant measurements. The XRD results revealed the formation of ferroelectric lead titanate (PT) as a major crystalline phase in the glass ceramics. The density increases and the CTE decreases for all glass ceramics with increase in X (mol%). This may be attributed to increase in PT phase. The SEM results which show rounded crystallites of lead titanate, also supports other results. Hysteresis loops observed at room temperature confirms the ferroelectric nature of glass ceramics. The optimized glass ceramic sample exhibits high dielectric constant which is of technical importance.     

Mixed alkali effect in boroarsenate glasses

We report, for the first time the study of mixed alkali effect (MAE) in boroarsenate glasses. Density, DSC, DC electrical conductivity and IR studies have been carried out for xK₂O-(40−x)Na₂O-50B₂O₃-10As₂O₃ glasses. The DC electrical conductivity was measured in the temperature range 100 °C to below the glass transition temperature. The strength of the MAE in T_g, DC electrical conductivity and activation energy has been determined. It is observed that the strength of MAE in DC electrical conductivity is less pronounced with increase in temperature. The results are explained by the structural model recently proposed by Swenson and coworkers, supporting molecular dynamic results. The IR studies show that the glass system contains BO₃ and BO₄ units in the disordered manner.     

Crystallization kinetics and thermal stability in Se85-xTe15Sbx chalcogenide glasses

Crystallization process of Se_85-xTe₁₅Sb_x (x = 2.7, 7.5, 10 and 15 at %) chalcogenide glasses has been studied by using differential scanning calorimetry (DSC) with different heating rates. These glasses are found to have a double glasses transition and overlapped crystalline phases for Se₇₀Te₁₅Sb₁₅ glass while single glasses transition and single crystallization stage for other glasses. Glass transition temperature, T_g, onset crystallization temperature, T_c, and peak crystallization temperature, T_p, are found to be dependent on composition and heating rates. Values of various kinetic parameters such as activation energy of glass transition, E_g, activation energy of crystallization, E_c, Hurby number, H_r, thermal stability, S_p, rate constant, K_p, and Avrami exponent, n, are determined for the present systems. Results indicate that rate of crystallization is dependent on thermal stability and glass-forming ability. Crystallization mechanism occurs in two dimensions for studied compositions. Crystalline phases resulting from DSC and scanning electron microscopy have been identified by using X-ray diffraction.     

Nickel ion—A structural probe in BaO-Al2O3-P2O5 glass system by means of dielectric, spectroscopic and magnetic studies

BaO-Al₂O₃-P₂O₅ glasses containing different concentrations of NiO (ranging from 0 to 1.0 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption spectra), magnetic susceptibility and dielectric properties (constant ε′, loss tan δ, AC conductivity σ_AC over a range of frequency and temperature) of these glasses have been carried out. The studies on chemical durability indicate that there is a significant increase in the corrosion resistance of the glasses; where as the results of differential thermal analysis suggests that there is a substantial improvement in the glass forming ability, with increase in the concentration of NiO up to 0.6 mol% in the glass matrix. The optical absorption, magnetic susceptibility and IR spectral studies point out nickel ions occupy both tetrahedral and octahedral positions in the glass network; the later positions seems to be dominant when the concentration of NiO is beyond 0.6 mol% in the glass matrix. The studies of dielectric properties reveal that the presence of nickel oxide in the glass network causes a considerable improvement in the insulating strength of the se glasses when the concentration of NiO?0.6 mol%.