Structure–property correlations in lead silicate glasses and crystalline phases

Lead silicate glasses containing 40–65?mol% of PbO were prepared at two melt-quenching rates and characterized by X-ray diffraction, UV-Visible absorption spectroscopy, density, microhardness, thermo-mechanical analysis, differential scanning calorimetry and Raman scattering studies. On increasing the PbO concentration, density increases, glass transition temperature decreases and the optical absorption edge shifts towards longer wavelength. An intense optical absorption band was observed just below the absorption edge in glasses with 55?mol% and higher concentration of PbO. Dilatometric measurements show an unusual property that glasses do not show any abrupt increase in volume near the glass transition temperature but transform directly into the liquid state. Raman spectroscopy confirmed that the concentration of SiO₄ tetrahedra containing one or more NBOs increase with PbO mol%. Devitrification studies on lead silicate glasses found that samples with 40–45?mol% of PbO do not crystallize, whereas samples with higher PbO concentration produce multiple crystalline phases like PbSiO₃, Pb₃₃Si₂₄O₈₁, Pb₂SiO₄ and Pb₃Si₂O₇ on heat treatment.     

Physical, optical, structural and gamma-ray shielding properties of lead sodium borate glasses

Lead sodium borate glasses with compositions xPbO:20Na₂O:(80−x)B₂O₃ (where x=5, 10, 15, 20, 25, 30, 35, 40, 45, 50 and 55 mol%) have been prepared using melt-quenching method and investigated on their optical, physical, structural and gamma-rays shielding properties. The densities of these glass samples were increased with increase in PbO concentration. The FTIR spectra and molar volumes indicate that PbO acts differently on this glass structures over their compositions. For the PbO composition less than 20 mol%, Pb²⁺ is incorporated as network former, while it acts as network modifier for the composition from 20-55 mol%. For gamma-ray shielding properties, parameters such as mass attenuation coefficients, effective atomic number and half value layer were increased with increase in PbO concentration. Our results showed relative difference between theory and experiment of less than 1% between experimental and theoretical values. Moreover half value layers of the glass systems have been compared with some standard radiation shielding materials and they exhibited better shielding properties than barite concrete and ferrite concrete at 15 and 25 mol% of PbO, respectively.     

Glass formation in the system Li2B4O7–Pb3O4–CuO using X-ray diffraction

X-ray diffraction was performed to construct the phase diagram for the ternary Li₂B₄O₇–Pb₃O₄–CuO glass system. Three principal regions were identified: (1) a glass-forming region observed at the composition (75 < Li₂B₄O₇ < 100) mol%, (0 < CuO < 35) mol% and (0 < Pb₃O₄ < 70) mol% in the ternary system, and (100 ? x) mol% Li₂B₄O₇–x mol% Pb₃O₄ where x = 0 up to 70, (100 ? y) mol% Li₂B₄O₇–y mol% CuO where y = 0 up to 25 in the binary system;. (2) a crystalline region: all compositions prepared from the binary system Pb₃O₄–CuO and the ternary system containing Li₂B₄O₇ up to 60 mol%; (3) a partially crystalline region formed between the glass and crystalline regions.     

Compositional-dependent lead borate based glasses doped with Eu ions: Synthesis and spectroscopic properties

New multicomponent lead borate based glasses with various PbO/B₂O₃ weight ratio were prepared. The glass samples were analyzed in detail by using Raman and IR absorption spectroscopy. Optical properties of Eu³⁺ ions have been investigated in lead borate based systems, in which PbO/B₂O₃ weight ratios were changed from 1:2 to 8:1 in glass composition. The values of the phonon energy of the host and ⁵D₀ lifetime of Eu³⁺ decrease, whereas absorption and emission intensities, as well as bonding parameter increase with increasing PbO concentration. Additionally, spectral lines are shifted in direction to the lower frequency region. Non-monotonic dependence of the fluorescence intensity ratio R (⁵D₀-⁷F₂/⁵D₀-⁷F₁) upon PbO/B₂O₃ content has been observed in contrast to bonding parameter that is also non-linear but monotonic. Some structural and spectroscopic aspects for Eu-doped lead borate based glasses are presented.     

Lead−barium fluoroborate glass ceramics doped with Nd<Superscript>3+</Superscript> or Er<Superscript>3+</Superscript>

Lead?barium fluoroborate glasses in the PbF₂–BaF₂–B₂O₃, PbF₂–BaO–B₂O₃, and PbO_– BaF₂–B₂O₃ systems doped with rare-earth ions (Nd³⁺ or Er³⁺) are synthesized and studied. It is shown that, based on these glasses, it is possible to produce transparent glass ceramics with fluoride crystalline phases, including ceramics with one crystalline phase of the fluorite structure. The spectral and luminescent properties of the doped glasses, glass ceramics, and polycrystalline complex fluorides containing Pb, Ba, and rare ions are studied.     

Effect of copper addition on BO<Subscript>4</Subscript>, H<Subscript>2</Subscript>O groups and optical properties of lithium lead borate glass

Lead lithium borate glass samples composition 50Li₂B₄O₇–(50?x)Pb₃O₄–x CuO, where x = 0–35 mol% were prepared by melt quenching method. The density of the prepared samples was measured and molar volume was calculated. IR spectra were measured for the prepared samples at room temperature to investigate the glass structure. The IR spectra were deconvoluted using curves of Gaussian shape at approximately the same frequencies. The deconvoluted data were used to study the effect of CuO content on all the structural borate and water groups. The optical band gap obtained directly from absorption coefficient, refractive index and extinction coefficient, also by using the Tauc model. The type of transition is determined by the simple and accurate method.     

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.     

Novel photosensitive properties of gadolinium–lead germanate glasses

Glasses of the system xGd₂O₃ · (100 ? x)[7GeO₂ · 3PbO] with 0 ≤ x ≤ 40 mol% were prepared using the melt quenching method. Lead germanate glasses are particularly interesting in the context of the germanate anomaly. In this paper, we investigate changes in the coordination number of germanium in gadolinium–lead germanate glasses using molar volume analysis, density measurements, FTIR and UV–VIS spectroscopy, and density functional theory (DFT). Despite some inconsistencies, the coordination change model remains the currently accepted model for the anomalous behaviour of lead germanate glasses. Based on these experimental results, we propose the following mechanism for the germanate anomaly. (i) The low thermodynamic stability of the [GeO₆] structural unit and the occupation of interstices of larger dimensions (the six-coordinated interstices of the [PbO₆] structural units) in the lead germanate network yield [GeO₅] structural units with higher thermodynamic stability and larger ionic radii. (ii) Not linked to the terminal oxygens of the [GeO₅] structural units and with the formation of smaller network cavities of the lead germanate glass, links are required with [GeO₄] tetrahedra for stabilization, generating the formation of three-membered rings of [GeO₄] tetrahedral structural units.     

Ultrasonic and FT-IR studies on Bi2O3–Er2O3–PbO glasses

Glasses in the 90Bi₂O₃–(10?x)Er₂O₃?xPbO (x = 3, 5, 7, 9 and 10 mol%) system have been prepared by the melt-quenching technique. Elastic properties and FT-IR spectroscopic studies have been employed to study the role of PbO in the structure of the investigated system. Elastic properties and Debye temperature were recorded using sound wave velocity measurements at 4 MHz at room temperature. The results showed that density increased and molar volume decreased, while both sound velocities increased with an increase in x. Infrared spectra of the glasses revealed that the bismuthate network is affected by an increase in PbO content. The results are interpreted in terms of the conversion of [BiO₆] into [BiO₃] structural units, indicating that Pb ions have been substituted for erbium ions as tetrahedral network formers. The elastic moduli increased with increasing PbO content due to the increased average bond strength and degree of connectivity, as a direct effect of the increase in [BiO₃] structural units.     

Influence of heat treatment on structure and some physical properties of lithium boro-niobate glass

The glass composition (90?mol% Li₂B₄O₇–10?mol% Nb₂O₅) was prepared by the melt quenching technique. The quenched sample was heat treated at 480°C, 545°C and 630°C for 5?h and heat treated at 780°C with different time. The times were 5, 10, 15, 20, 28, and 36?h. The glass and glass ceramics were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and dc conductivity as a function of temperature. Lithium niobate (LiNbO₃) and lithium diborate (Li₂B₄O₇) were the main phases in glass ceramic addition to traces from LiNb₃O₈. Crystallite size of the main phases determined from the X-ray diffraction peaks are in the range <100?nm. The fraction of crystalline (LiNbO₃) phase increases with increase the heat treatment temperature and time. The relation between physical properties and structure were studied.     

Cobalt ion as a structural probe in PbO–As2O3 glass ceramics

PbO–As₂O₃ glasses mixed with different concentrations of CoO (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy, EDS and differential scanning calorimetric techniques. The X-ray diffraction studies have indicated the presence of Pb(As₂O₆), Pb₃(AsO₄)₂, Co₆As₂O₁₁, Co₃O₄ crystalline phases in these samples. Optical absorption, IR and photoluminescence studies of these samples have been carried out. The analysis of the results of these studies has indicated that the cobalt ions exist in Co²⁺ and Co³⁺ states in the glass matrix. The studies have further revealed that as the concentration of the CoO is increased, there is a gradual transformation of cobalt ions from tetrahedral to octahedral positions.     

The influence of CdSe and ZnSe nanoparticles on the optical properties of Sm<Superscript>3+</Superscript> ions in lead borate glasses

The effect of glass composition and the presence of CdSe/ZnSe nanoparticles (NPs) on the optical absorption and fluorescence of Sm-doped lead borate glasses are studied. Three sets of glass samples xPbO:(99.5-x) B₂O₃:0.5Sm₂O₃, x = 29.5–69.5 mol%, xPbO:(96.5-x) B₂O₃:0.5Sm₂O₃: 3CdSe/ZnSe, x = 36.5, and 56.5 mol% are prepared. NPs are grown by annealing these glasses just below the glass transition temperature. Average size of both types of NPs increases with annealing time; however, CdSe NPs grew to a larger size range (2 to 20 nm) compared to ZnSe NPs (1 to 16 nm). We analyzed the hypersensitive transition, intensity parameters, radiative transition probability, stimulated emission cross section (σ_p), and the area ratio of the electric dipole/magnetic dipole transitions of Sm³⁺. The intensity parameters show a minimum at 11 h annealing for 36.5 mol% and a maximum for the same annealing duration in 56.5 mol% PbO containing CdSe NPs. The σ_p for 56.5 mol% of PbO with CdSe NPs is found to be a maximum when the average NP size is around 14 nm. ZnSe NPs containing glasses also show significant changes in σ_p when the average particle size is ~16 nm, for 36.5 mol% PbO. Our results suggest that the optical properties of Sm³⁺ in lead borate glasses are sensitive to its electronic environment which can be modified by varying the base glass composition and/or incorporating large NPs of CdSe/ZnSe. The large σ_p values that we observe for some of the glass compositions make them attractive materials for photonic devices and photovoltaic applications.

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Induced crystallization and the physical properties of PbO–Sb2O3–As2O3: MoO3 glass system

PbO–Sb₂O₃–As₂O₃ glasses mixed with different concentrations of MoO₃ (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy and differential thermal analysis techniques. The X-ray diffraction and the scanning electron microscopic studies have revealed the presence of Pb₅Sb₂O₈, PbSb₂O₆, SbAsO₄, Sb₂MoO₆, Sb₄Mo₁₀O₃₁, As₄Mo₃O₁₅, Pb₅Sb₄O₁₁ crystalline phases in these samples. The differential thermal analysis indicated that the surface crystallization prevails over the bulk crystallization as the concentration of the crystallizing agent is increased. The infrared (IR) spectral studies exhibit bands due to MoO₄ structural units in addition to the conventional bands due to various antimonate and arsenate structural groups. The studies on PbO–Sb₂O₃–As₂O₃: MoO₃ glass-ceramics with respect to various physical properties viz., dielectric properties over a range of frequency and temperature, optical absorption, electron spin resonance (ESR) and magnetic susceptibility at room temperature have also been reported. The optical absorption, ESR and magnetic susceptibility studies indicated that the molybdenum ions exist in Mo⁵⁺ state in addition to Mo⁶⁺ state in these samples. The redox ratio found to increase as the concentration of the MoO₃ is increased. The variations observed in all these properties with the concentration of the crystallizing agent have been analyzed in the light of different oxidation states and environment of molybdenum ions in the glass ceramic network.     

Li2O-B2O3-SiO2系统玻璃的Raman光谱研究

在Li₂O≥30mol％的Li₂O-B₂O₃-SiO₂系统玻璃中,以Li₂O代B₂O₃或SiO₂都导致玻璃网络中带非桥氧的硼酸盐和硅酸盐基团的量的增加;以B₂O₃代SiO₂则使玻璃网络中带和不带非桥氧的硼酸盐基团以及带非桥氧的硅酸盐基团的量都增加。 关键词：     

Surface modifications of crystalline SiO2 and Al2O3 induced by energetic heavy ions

Abstract

Glasses with composition × CoO.(0.25-x) CaO.0.75 B₂O₃ have been prepared over the range 0 ≤ x ≤ 0.25 containing 2 mol% of V₂O₅. Electron paramagnetic Resonance spectra of VO²⁺ of these glasses has been measured at X-band (ν ≈ 9.15 GHz) at room temperature and at liquid nitrogen temperature. Spin Hamiltonian parameters of the VO²⁺ ions have been calculated. It is found that for x ≤ 0.12 the octahedral symmetry of the V⁴⁺ site is improved. A part of these glasses were annealed at 473 K for 24 hours and EPR spectra were recorded and analysed.     

Magnetic properties of x • MnO • (1−x)[19TeO2 • PbO] glasses

The results of magnetic studies on x ? MnO ? (1 ? x)[19TeO₂ ? PbO] glasses are reported. The magnetic properties of these glasses are function of MnO content. For glasses with x > 5 mol% MnO, an antiferromagnetic behaviour is evidenced.     

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.     

Mixed polaronic-ionic conduction in lithium borate glasses and glass-ceramics containing copper oxide

The effect of electric field strength on conduction in lithium borate glasses doped with CuO with different concentration was studied and the value of the jump distance of charge carrier was calculated. The conductivity measurements indicate that the conduction is due to non-adiabatic hopping of polarons and the activation energies are found to be temperature and concentration dependent. Lithium borate glasses are subjected to carefully-programmed thermal treatments which cause the nucleation and growth of crystalline phases. X-ray diffraction analysis confirmed the amorphous nature for the investigated glass sample and the formation of crystalline phase for annealed samples at 650 °C. The main separated crystalline phase is Li₂B₈O₁₃. The scanning electron micrographs of some selected glasses showed a significant change in the morphology of the films investigated due to heat treatment of the glass samples. It was found that the dc-conductivity decreases with an increase of the HT temperature. The decrease of dc conductivity, with an increase of the HT temperature, can be related to the decrease in the number of free ions in the glass matrix. There is deviation from linearity at high temperature regions in the logσ-1/T plots for all investigated doped samples at a certain temperature at which the transition from polaronic to ionic conduction occurs. The hopping of small polarons is dominant at low temperatures, whereas the hopping of Li⁺ ions dominates at high temperatures. PACS 71.55.Jv; 72.60.+g; 72.80.Ng     

Barium borate glass and transparent glass ceramics doped with Pb4Lu2YbF17

Barium borate glasses doped with complex Pb₄Lu₂YbF₁₇ fluoride have been synthesized and investigated. Heat treatment produced glass ceramics containing the crystalline BaF₂:Yb³⁺ phase. The changes in the structural and optical properties of the glass ceramics were revealed by X-ray diffraction, Raman spectroscopy, and luminescence spectroscopy of Yb³⁺ ions in polycrystalline Pb₄Lu₂YbF₁₇, initial glass, and glass ceramics.     

Structural and optical properties of lithium borobismuthate glasses

Glasses with compositions 25Li₂O-(75−x)Bi₂O₃-x B₂O₃, with 0?x?30 mol%, have been prepared using the melt quenching technique. The density and the molar volume have been determined. IR spectroscopy is used as a structural probe of the nearest neighbor environment in the glass network. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400-1100 nm. The values of the optical band gap E_g^opt for indirect transition and refractive index have been determined for 0?x?30 mol%. The average electronic polarizability of the oxide ion α_o²⁻ and the optical basicity have been estimated from the calculated values of the refractive indices. Variations in the different physical parameters such as the density, molar volume, optical band gap, refractive index, average electronic polarizability of the oxide ion and optical basicity with B₂O₃ content have been analyzed and discussed in terms of the changes in the glass structure.