Structure–property correlations in lead borate and borosilicate glasses doped with aluminum oxide

Glass samples from four systems: xPbO–(100?x)B₂O₃ (x = 30, 40, 50 and 60 mol%), 50PbO–yAl₂O₃–(50?y)B₂O₃ (y = 2, 4, 6, 8 mol%), 50PbO–ySiO₂–(50?y)B₂O₃ (y = 5, 10, 20, 30 mol%) and 50PbO–5SiO₂–yAl₂O₃–(45?y)B₂O₃ (y = 2, 4, 6, 8 mol%) were prepared by a melt-quench technique. Characterization of these systems was carried out using density measurements, UV–visible spectroscopy, differential scanning calorimetry (DSC), and ¹¹B and ²⁷Al magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR). Our studies reveal an increase in glass density with increasing lead(II) oxide concentration in pure lead borates and also with addition of silica into 50PbO–50B₂O₃ glass. ¹¹B MAS NMR measurements determine that the fraction of tetrahedral borons (N₄) reaches a maximum for the glass containing 50 mol% of PbO in the PbO–B₂O₃ glass series and that N₄ is sharply reduced upon adding small amounts of Al₂O₃ into lead borate and lead borosilicate systems. ²⁷Al MAS NMR experiments performed on glasses doped with aluminum oxide show that the Al³⁺ are tetra-, penta- and hexa-coordinated with oxygen, even without any excess concentration of Al³⁺ over charge-balancing Pb²⁺ cations. ^[5]Al and ^[6]Al concentrations are found to have unusually high values of up to 30%. The results of UV–visible absorption spectroscopy, DSC and density measurements support the conclusions drawn from the NMR studies, providing a consistent picture of structure–property relations in these glass systems.     

Ionic conductivity of sodium–strontium germanate Na4SrGe6O15

Crystallography Reports - The electrical conductivity of sodium–strontium germanate Na4SrGe6O15 (sp. gr. P63/m) has been studied by impedance spectroscopy in the frequency range of...     

X-ray absorption near edge structure investigation of iron–sodium silicate glasses

X-ray absorption near edge structure spectroscopy has been used at the O K and Fe L_2,3 edges to investigate the electronic and atomic structure of (Fe₂O₃)_x(Na₂O)_0.30(SiO₂)_0.70 ? x (x < 0.2) obtained by melt-quench technique. The Fe L_2,3 edge spectra show that the Fe atoms are in octahedral coordination. The O K edge spectra reveal no change in coordination of Fe and increased degree of hybridization between O 2p and Fe 3d orbitals with iron doping. It is estimated that about 10% Fe²⁺ and 90% Fe³⁺ are in these glasses by peak fitting analysis of Fe L₃ edge. The ligand-field splitting of Fe 3d orbital is about 1.6 eV.     

FTIR and UV–VIS spectroscopy investigations on the structure of the europium–lead–tellurate glasses

Glasses in the xEu₂O₃·(100-x)[4TeO₂·PbO₂] system where 0 ≤ x ≤ 50 mol% have been prepared using the melt quenching method. The influence of europium ions on the structure of lead–tellurate glasses has been investigated using density measurements, FTIR and UV–VIS spectroscopy. Structural changes produced by increasing the rare earth concentration were followed.The europium and lead ions show a preference towards [TeO₃] structural units causing a deformation of the TeOTe linkages. Structural changes inferred by analyzing the band shapes of IR spectra revealed that the increase of the Eu^+ 3 content causes the intercalation of [EuO_n] entities in the [TeO₄] chain network. The excess of oxygen can be supported into the glass network by the formation of [PbO_n] and [EuO_n] structural units.The UV–VIS spectroscopy data show that europium ions enter the glass matrix in the Eu²⁺ and Eu³⁺ valence states, the last being predominant in the studied glasses. The Pb^+ 2 ions produce strong absorption in the ultraviolet domain.     

UV–visible and infrared absorption spectra of transition metals-doped lead phosphate glasses and the effect of gamma irradiation

Undoped and transition metals (TM 3d)-doped lead phosphate glasses were prepared. Ultraviolet–visible absorption spectra were measured in the range 200–1100 nm before and after successive gamma irradiation. Experimental results indicate that the undoped lead phosphate glass reveals before irradiation strong and broad ultraviolet absorption which is related to the co-sharing of absorption due to both trace iron impurities and lead ions (Pb²⁺). In the TM-doped glasses, characteristic absorption bands are obtained in both the UV and/or visible regions due to each respective TM ion in addition to that observed by the base undoped UV absorption. Gamma irradiation produces with the undoped glass a prominent induced ultraviolet broad band centered at about 300 nm originating mostly from the contribution of trace iron impurities and the visible spectra reveal markedly high shielding behavior towards successive gamma irradiation, due to the presence of both high content of heavy Pb²⁺ ions and the sharing of phosphate as a partner. With TM-doped samples, the observed induced bands are virtually varying and related to the type of the sharing TM ions. Infrared absorption spectra reveal in the undoped and TM-doped glasses characteristic structural phosphate groups mainly consisting of metaphosphate and pyrophosphate units. Transition metals are assumed to cause depolymerization of the phosphate glass network with different ratios but the changes in IR spectral data are limited due to the low doping level. Gamma irradiation of the samples is assumed to cause changes in the bond angles or bond lengths of the structural phosphate units within network as evident in the variation of the intensities of the IR bands.     

FTIR and UV–VIS optical absorption spectra of gamma-irradiated MoO3-doped lead borate glasses

Structure and optical properties of MoO₃-doped lead borate glasses which contain high PbO content (60, 70 and 80%) have been studied using Fourier transform infrared (FTIR) and ultraviolet–visible (UV–VIS) spectroscopic tools. FTIR spectra reveal absorption bands which are characteristic for various structural units of borate network, mainly BO₃ triangles and BO₄ tetrahedra, in addition to the PbO_n (where n = 3 and/or 4) structural units. UV–VIS optical absorption spectra reveal broad intense charge transfer UV bands due to Pb^2 + ions in the range 320–385 nm. Within this range, molybdenum ions, preferably Mo^3 + and Mo^5 +, can interfere at about 360–385 nm. Additionally, molybdenum ions give a weak visible band at about 850–860 nm. The optical absorption spectra of the studied glasses show marked resistance to successive gamma irradiation up to 5 Mrad. This shielding behavior can be related to the present high content of the high atomic mass Pb^2 + ions. Changes in the atomic structure before and after gamma irradiation are described and explained.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

Dielectric properties,conductivity, UV–visible and infrared spectroscopy of PbO P2O5 NaF glasses containing WO3

Homogeneous (50P₂O₅–(30 ? x)PbO–20NaF–xWO₃ where x = 0.0, 5, 10 and 15 mol%) glasses were synthesized using a melt-quenching method. The short range structures of the phosphate samples were examined by Fourier transform infrared spectroscopy. The infrared spectral studies have pointed out the existence of conventional PO₄, WO₄ and WO₆ structural units in the glass network, the number of WO₄ tetrahedra decreases as WO₃ concentration increases. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range of 190–1100 nm. The values of the optical band gap E_op for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of the dielectric constant have been determined. The type of electronic transitions in the present glass system is indirectly allowed and the high values for the refractive index and dispersion are recorded due to the high polarizability of tungsten ions. The results of refractive indices as determined reveal the homogeneity of samples and were found to depend on the glass composition. The electrical properties of the glasses were investigated by ac conductivity from 0.12 to 100 kHz for temperatures ranging from room temperature to 600 K. The study of dielectric properties suggested increase in the insulating character of the glass system with increase in the content of WO₃. The ac conductivity in the high temperature region seems to be connected mainly with the polarons involved in the process of transfer from W⁴⁺ to W⁵⁺ ions.     

Structural modifications induced by addition of copper oxide to lead–phosphate glasses

xCuO(1-x)[P₂O₅·PbO] glass system with 0 ≤ x ≤ 50 mol% was prepared and investigated by means of EPR and IR spectroscopy in order to evidence the structural changes induced by different amounts of copper ions. EPR spectra analysis together with EPR parameters has indicated a distorted tetragonal symmetry – named tetrahedral local symmetry – for Cu^2 + ions in the studied glasses. A change in the shape of EPR spectra was also observed as for small CuO concentration (x < 20 mol%) these glasses present an asymmetrical line typical for isolated ions and for high CuO content this line is replaced by a symmetrical one characteristic of clustered ions through dipole–dipole interactions. IR spectra of the studied glasses put in evidence a strong depolymerization effect with a gradual increase of CuO. The shift of PO asymmetric stretching vibration band to lower wave number can be explained by the increase of PO₄ tetrahedra charge density leading a more ionic and less covalent bonding.     

Influence of thermal and thermoelectric treatments on structure and electric properties of B2O3–Li2O–Nb2O5 glasses

A transparent glass with the composition 60B₂O₃–30Li₂O–10Nb₂O₅ (mol%) was prepared by the melt quenching technique. The glass was heat-treated with and without the application of an external electric field. The as-prepared sample was heat-treated (HT) at 450, 500 and 550 °C and thermoelectric treated (TET) at 500 °C. The following electric fields were used: 50 kV/m and 100 kV/m. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, dc and ac conductivity, as a function of temperature, were used to investigate the glass and glass-ceramics properties. LiNbO₃ crystals were detected, by XRD, in the 500 °C HT, 550 °C HT and 500 °C TET samples. The presence of an external electric field, during the heat-treatment process, improves the formation of LiNbO₃ nanocrystals at lower temperatures. However, in the 550 °C HT and in the TET samples, Li₂B₄O₇ was also detected. The value of the σ_dc decreases with the rise of the applied field, during the heat-treatment. This behavior can indicate an increase in the fraction of the LiNbO₃ crystallites present in these glass samples. The dc and ac conduction processes show dependence on the number of the ions inserted in the glass as network modifiers.The Raman analysis suggests that the niobium ions are, probably, inserted in the glass matrix as network formers.These results reflect the decisive effect of temperature and electric field applied during the thermoelectric treatment in the structure and electric properties of glass-ceramics.     

Thermal,structure and morphological properties of lithium disilicate glasses doped with copper oxide and their glass–ceramic derivatives

This research aims to investigate and compare the structural and the morphological properties of both lithium disilicate glasses doped with copper oxide and their glass–ceramic derivatives. Density measurements were measured for all samples by Archimedes method at room temperature. Differential scanning calorimetric analysis was used to determine the glass transition temperature (T_g) and crystallization temperature (T_c) for all glasses. The glass transition temperature was observed to decrease with increasing CuO concentration indicating the formation of non-bridging oxygen bonds in the glass network. X-ray analysis patterns reveal the appearance of crystalline lithium metasilicate phase as the main phase within the glass–ceramic derivatives, and their crystallite sizes were observed to decrease as the CuO increased. Experimental infrared absorption data indicate the existence of characteristic vibrational bands due to structural building SiO₄ units in resemblance to the same vibrations observed from traditional crystalline silicates. Scanning electron microscopic investigations show the vitreous nature for lithium disilicate glasses and the distinct crystalline morphological features for the corresponding glass–ceramic derivatives.     

Structure of V2O5–P2O5 glasses by X-ray and neutron diffraction

The atomic structures of two V₂O₅–P₂O₅ glasses and vitreous (v-) V₂O₅ were investigated by X-ray and neutron diffraction. The V=O double bond is a common characteristic of the VO_n units that constitute the structures of the glasses. VO₅ square pyramids with elongated bonds of ~ 0.190 nm to the pyramidal base are found for the 50V₂O₅–50P₂O₅ glass. These weaker V–O bonds are balanced in V–O–P bridges by overbonded P–O bonds. The V^(IV) sites, which account for 19.7% and 35.2% of the total V sites in the 73V₂O₅–27P₂O₅ and 50V₂O₅–50P₂O₅ glasses, respectively, form similar pyramids in agreement with the structure of crystalline (VO)₂P₂O₇. The short-range structure of v-V₂O₅ and the 73V₂O₅-27P₂O₅ glass is formed of mixtures of VO₅ and VO₄ pyramids. A significant amount of V···O distances > 0.22 nm found for all glasses belong either to linkages V=O···V or to three-coordinated O sites.     

Hardness and refractive index of Ca–Si–O–N glasses

Vickers hardness and refractive index was determined for Ca–Si–O–N glasses with 14.6–58 e/o N and 19–42 e/o Ca. By applying slow cooling rates, transparent glasses were obtained for compositions near Ca_9.94Si₁₀O_17.73N_8.14, while the majority of the glasses were opaque due to small inclusions of elemental Si and/or Ca-silicide. Determined glass densities varied between 2.80 and 3.25 g/cm³. Hardness was found to vary from 7.3 to 10.1 GPa at a load of 500 g and, respectively increase and decrease linearly with N and Ca content. The refractive index was found to increase linearly with N content from 1.62 to 1.95 and showed no significant dependence on Ca content.     

Thermal and optical properties of TeO2–ZnO–BaO glasses

We report the results of a systematic study of the thermal and optical properties of a new family of tellurite glasses, TeO₂–ZnO–BaO (TZBa), as a function of the barium oxide mole fraction and compare them with those of TeO₂–ZnO–Na₂O (TZN). The characteristic temperatures of this new glass family (glass transition, T_g, crystallization, T_x, and melting, T_m) increase significantly with BaO content and the glasses are more thermally stable (greater ΔT = T_x ? T_g) than TZN glasses. Relative to these, Raman gain coefficient of the TZBa glasses also increases by approximately 40% as well as the Raman shift from ~ 680 cm^? 1 to ~ 770 cm^? 1. The latter shift is due to the modification of the glass with the creation of non-bridging oxygen ions in the glass network. Raman spectroscopy allows us to monitor the changes in the glass network resulting from the introduction of BaO.     

Emissions of 1.20 and 1.38 μm from Ho3+-doped lithium–barium–bismuth–lead oxide glass for optical amplifications

Efficient infrared emissions at 1.20 μm [⁵I₆ → ⁵I₈ transition] and 1.38 μm [(⁵ F₄, ⁵ S₂) → ⁵I₅ transition] from Ho³⁺-doped lithium–barium–bismuth–lead (LBBP) glass were observed. The stimulated emission cross-sections were calculated to be 0.29 × 10^?20 and 0.25 × 10^?20 cm² for 1.20 and 1.38 μm emissions, respectively. Judd-Ofelt characteristic parameters Ω₂, Ω₄ and Ω₆ for Ho³⁺ in LBBP glass were calculated to be 6.72 × 10^?20, 2.35 × 10^?20 and 0.61 × 10^?20 cm², respectively, which indicates a strong asymmetry and a covalent environment between the Ho³⁺ ions and the ligands in this glass. The optical amplifications operating at these relatively unexplored wavelength regions were evaluated and discussed.     

Free volume and viscosity of Fe–Co–Cr–Mo–C–B–Y bulk metallic glasses and their correlation with glass-forming ability

In this work, the variation of the glass-forming ability (GFA) in Fe–Co–Cr–Mo–C–B–Y alloy system with Co addition has been investigated from the viewpoints of non-isothermal viscosity and free volume. The best GFA for the alloy containing 7% Co is found to closely relate with its highest viscosity, and the minimum sizes and lowest concentrations of the intermediate and largest open volumes. The results may provide more insights into the formation mechanism of metallic glasses.     

Growth from Solutions,Structure, and Spectral–Luminescent Properties of Crystalline Films of Di-n-hexyl-para-quaterphenyl

Crystallography Reports - The results of studying the growth and structure of crystalline films of para-quaterphenyl derivative with terminal n-hexyl...     

Structure and properties of self-assembled fluorocarbon–silica nanocomposites

The formation of fluorocarbon–silica nanocomposites by the self-assembly of a fluorinated surfactant and aminoalkoxysilane coupling agents was studied by X-ray diffraction, electron microscopy, NMR spectroscopy and thermal analysis. The prepared materials posses a lamellar nanostructure consisting of non-crystalline fluorinated and condensed silica layers, the latter being very thin. The prepared materials show interesting properties for applications, such as hydrophobicity, thermal stability, high content of aminopropyl groups and low dielectric constant (≈2.8), which is almost independent on frequency. Moreover, the dielectric response can be interpreted in the framework of the Maxwell–Wagner model.     

Electrical and dielectric properties of MnF2–ZnF2–NaPO3 glasses

Direct electrical conductivity and dependencies of complex electrical modulus vs. temperature and frequency have been measured on glasses from the MnF₂–ZnF₂–NaPO₃ system. These glasses are sensitive to atmospheric humidity and as a consequence, the electrical conductivity increases up to temperature of 50 °C. A hydrated layer is created by the effect of water and leads to the significant increase of the electrical conductivity in the case of 0MnF₂–20ZnF₂–80NaPO₃ glass. This behavior is governed by Arrhenius relation where the values of activation energy are increasing and values of the electrical conductivity are decreasing with the amount of MnF₂. Dielectric measurements show that a heterogeneous phase is formed in the bulk of glasses. This may be seen when plotting complex electrical modulus in the complex plane. The records made by the light microscope confirmed the occurrence of the other phase in the bulk of glasses.