Structure and electrical properties of ZnO doped barium-metaphosphate glasses

The zinc–barium–metaphosphate glasses (ZBP) with composition of (50 − x)BaO–xZnO–50P₂O₅; (0 ≤ x ≤ 50 mol %), have been successfully prepared. The influences of the amount of ZnO on the structure, physical and chemical properties, and crystallization behavior of the glasses were investigated using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction and energy dispersive X-ray techniques (XRD/EDX). The density and the glass transition temperature (T_g) of glass were measured using Archimedes' method and differential thermal analysis (DTA). The FTIR analysis revealed a shortening of the phosphate chains by the shift of (P–O–P)_as band to higher wave number owing to the substitution ZnO of BaO. The amount of ZnO was further increased, [ZnO4] tetrahedra were formed and ZnO acted as a glass network former, integrating the phosphate glass network. The density, chemical stability and the activation energy of crystallization of the glasses increased with the amount of ZnO, whereas the glass transition temperature decreased. The dc- and ac-conductivity were measured. The results obtained from ac-conductivity reveals that the values of σ(ω) increases on increasing frequency and it is also increases on increasing the ZnO content level. The dc-conductivity of all the glasses increases with an increase in temperature. The dielectric permittivity (?′) and loss factor (?″) were calculated in the frequency range of 50 Hz–1 MHz. The dipolar relaxation occurred between 10⁵–10⁶ Hz. Finally, the dielectric strength (Δ?) and the relaxation time (τ) were estimated.     

Effect of the introduction of vanadium pentaoxide in phospho-tellurite glasses containing gadolinium ions

A range of phospho-tellurite glasses containing gadolinium was prepared and infrared absorption spectra were measured. Structural changes, as recognized by analyzing band shapes of IR spectra, revealed that Gd₂O₃ causes a higher extent of network polymerization as far as x ≤ 15 mol% because the conversion of [TeO₄] to [TeO₃] structural units is supported by the increase of metaphosphate structural groups. While for x between 20 and 30 mol% Gd₂O₃ show some drastic structural modifications which lead to the increase in the glass fragility. Thus the addition of V₂O₅ resulted in gradual depolymerization of the phosphate chains and formation of short phosphate units, which are linked to vanadium through P–O–V bonds. The formation of P–O–V bonds increases the cross-link between the phosphate chains and the bending mode of Te–O–Te or O–Te–O linkages.     

Highlighting of structural units of B2O3–Li2O–P2O5 system under heat treatment

As technology evolves towards the design of small size – high efficiency devices there is a necessity for the development of solid, stable electrolytes that can be fabricated in various shapes. Accordingly, a glass system of xB₂O₃·0.4Li₂O·(0.6 − x)P₂O₅ with 0 ≤ x ≤ 0.6 mol%, was prepared by melting the raw materials at 1200 °C and rapidly cooling the melts at room temperature. The samples were afterwards heat treated to develop crystalline structures, for better identification of the units that build up the network.     

Structural characterizations and optical properties of new Li–Sr–Nb-phosphate glasses

A new Li₂O–SrO–Nb₂O₅–P₂O₅ glass system was prepared by a high-temperature alumina crucible, and structural characterization and optical properties were investigated. Proper content of Li₂O and Nb₂O₅ was employed to replace partial SrO and P₂O₅ to improve the optical properties. It was observed that the enhancement of the refractive index from 1.75 to 1.85 is mainly due to the Nb₂O₅ content. An addition of Li₂O significantly increases the optical transmittance; optical transparency can be enhanced from 60% to higher than 85% in the UV–visible region with addition of 20–40 mol% Li₂O species. However, optical transmittance is monotonically decreased from about 90% to 80% under 10–30 mol% Nb₂O₅ addition. The 40P₂O₅–20Nb₂O₅–20SrO–20Li₂O glasses demonstrate the optimum refractive index (n > 1.75) and high optical transparency (>80%) in the UV–visible region.     

Spectroscopic properties of Sm-containing yttrium-aluminoborate glasses and analogous huntite-like polycrystals

Sm_xY_1–xAl₃(BO₃)₄ polycrystals with huntite structure and glasses of system (mol %) 12.5 (Sm_xY_1–x)₂O₃–37.5Al₂O₃–50B₂O₃ with identical composition have been synthesized by solid state reaction and by melting process, respectively in order to compare light-emission and nonradiative energy transfer mechanisms in the two systems. The data have been analyzed to determine the concentration-dependent quantum yield of the Sm³⁺ luminescence as well as multipolarity and macro- and microparameters of the Sm–Sm interaction. The results show that the structure of the huntite cation lattice is preserved by passing from polycrystals to glasses, with an increase in the Sm–Sm minimum distance from 0.59 to 0.67 nm. At activator concentration ≤1 × 10²⁰ cm⁻³, the luminescence quantum yield in glass is higher than in polycrystals. The result turns out to be related to the partial substitution in glass by BO₄ groups of the trigonal BO₃ groups, which are responsible in crystalline Sm_xY_1–xAl₃(BO₃)₄ for efficient intracenter non-radiative energy exchange from the metastable excited ⁴G_5/2 state to phonon excitations.     

Study of lithium–zinc borophosphate glasses

Mixed lithium–zinc borophosphate glasses were prepared and studied in three compositional series xLi₂O–(50−x)ZnO–50P₂O₅, xLi₂O–(50−x)ZnO–10B₂O₃–40P₂O₅ and xLi₂O–(50−x)ZnO–20B₂O₃–30P₂O₅ with x = 0, 10, 20, 30, 40 and 50 mol% Li₂O. The obtained glasses were characterized by the measurements of the density (ρ), molar volume (V _M), glass transition temperature (T _g) and thermal expansion coefficient (α). For the investigation of structural changes ¹¹B and ³¹P MAS NMR and Raman spectroscopy were applied. The replacement of zinc by lithium in borophosphate glasses slightly decreases V _M and T _g, while α increases. In Li–Zn metaphosphate glasses the compositional dependence of T _g reveals a minimum, while at the borophosphate series T _g decreases monotonously with increasing Li₂O content. Chemical stability of Li–Zn borophosphate glasses is very good for glasses with x = 0–30 mol% Li₂O. Spectral studies showed in the glass series with 10 mol% B₂O₃ only the presence of BO₄ sites. In the glasses with 20 mol% B₂O₃ the presence of BO₃ and two BO₄ sites was revealed in ZnO-rich glasses and only one BO₄ site in Li₂O-rich glasses; the number of BO₃ groups decreases with increasing Li₂O content which is ascribed to the formation of P–O–Zn covalent bonds in ZnO-rich glasses.     

Relaxation process in PbI2–Ag2O–V2O5–B2O3 system: Dielectric,AC conductivity and modulus studies

Silver ion conducting super-ionic glass system xPbI₂–(100 − x) [Ag₂O–2(V₂O₅–B₂O₃)], where, 5 ≤ x ≤ 25, were prepared via melt quenching route and -characterized by XRD and DSC. Their electrical properties were measured by impedance spectroscopy in the frequency range of 2 MHz to 20 Hz from 30 to 120 °C. The electrical relaxation mechanism has been studied using AC conductivity, dielectric modulus function and frequency dependent dielectric permittivity over a wide range of frequency and temperature. Two different scaling approaches for AC conductivity as well as dielectric permittivity spectra were used to understand the nature of relaxation processes.     

Properties of (0.5−x)Zn-xFe2O3-0.5P2O5 glasses

Experimental determination of the properties of less studied zinc-iron-phosphate glasses was investigated. Glasses of the general composition (50−x)ZnO-xFe₂O₃-50P₂O₅, mol%, with x=0, 10, 20, 30 and 40, was chosen for these investigations. These studies included, glass forming, glass density, thermal expansion coefficient, dilatometric softening temperature, an initial test of chemical durability and vibrational properties. It is shown that an Fe/P ratio of the compositions at about 0.6 and 0.8 and the O/P ratio at 3.4 and 3.8 could be considered as chemically durable phosphate candidates.     

Structural and other physical properties of barium vanadate glasses

XRD, IR spectra, DTA, density, oxygen molar volume and dc conductivity of barium vanadate glasses of compositions xBaO(100 − x)V₂O₅, where x = 30, 35, 40, 45 and 50 mol%, are reported. The IR studies of the glasses suggest the glass network is built up of mainly VO₄ polyhedra. The glass transition temperatures are observed to increase with an increase of BaO content in the compositions. The cross-linking density decrease with increasing BaO content in the compositions. Introduction of BaO into the V₂O₅ matrix changes the 2D layer structure of the crystalline V₂O₅ into a more complicated 3D structure. Analysis of the electrical properties has been made in the light of small polaron hopping model. The parameters obtained from the fits of the experimental data to this model are reasonable and consistent with glass composition. The conduction is attributed to non-adiabatic hopping of small polaron.     

Structural and optical properties of high refractive indices lead vanadate thin films

Glasses with the chemical formula xWO₃–50PbO–(50 − x)V₂O₅, (0 ≤ x ≤ 10 mol%) were prepared by the usual melt quenching technique. FTIR analysis revealed that, the incorporation of WO₃ into the lead-vanadate network increases the number of bridging oxygens, and replaces low-coordinated structural units such as PbO₄, and VO₄ with higher coordinated structural units WO₆ and VO₅ which increases the number of bonds and the average cross-link density. Thin films of these glasses onto quartz substrates have been obtained by thermal evaporation technique. Based only on the measured transmittance spectra in the wavelength range 200–2500 nm, both the film thickness and the complex index of refraction have been calculated precisely. The absorption edge was shifted toward the long wavelength side (i.e. red shift of the optical band gap) as the WO₃ content increases. The dispersion of the refractive index was discussed in terms of the single oscillator model. The allowed non-direct transitions successfully describe the absorption mechanism in these films. Based on generalized Miller's rule, the third-order non-linear optical susceptibility χ⁽³⁾ has been investigated. The obtained values of χ⁽³⁾ values are rather large, indicating that the films under study are interesting materials for non-linear optical devices.     

Optical absorption,P NMR,and photoluminescence spectroscopy study of copper and tin co-doped barium–phosphate glasses

The optical and structural properties of 50P₂O₅:50BaO glasses prepared by melting have been investigated for additive concentrations of 10 and 1 mol% of CuO and SnO dopants. Absorption and photoluminescence spectroscopies were employed in the optical characterization, whereas structural properties were assessed by ³¹P nuclear magnetic resonance (NMR) spectroscopy. Residual Cu²⁺ was detectable by absorption spectroscopy for the highest concentration of CuO and SnO. More prominently, the optical data suggests contributions from both twofold-coordinated Sn centers and Cu⁺ ions to light absorption and emission in the glasses. The luminescence depends strongly on excitation wavelength for the highest concentration of dopants where a blue–white emission is observed under short-wavelength excitation (e.g., 260 nm) largely due to tin, while an orange luminescence is exhibited for longer excitation wavelengths (e.g., 360 nm) essentially due to Cu⁺ ions. On the other hand, dissimilar luminescent properties were observed in connection to Cu⁺ ions for the lowest concentration studied, as the copper ions were preferentially excited in a narrower range at shorter wavelengths near tin centers absorption. The structural analyses revealed the glass matrix to be composed essentially of Q² (two bridging oxygens) and Q¹ (one bridging oxygen) phosphate tetrahedra. A slight increase in the Q¹/Q² ratio reflected upon SnO doping alone suggests a major incorporation of tin into the glass network via P–O–Sn bonds, compatible with the 2-coordinated state attributed to the luminescent Sn centers. However, a significant increase in the Q¹/Q² ratio was indicated with the incorporation of copper at the highest concentration, consistent with a key role of the metal ions as network modifiers. Thus, the change in Cu⁺ optical properties concurs with different distributions of local environments around the ions induced by variation in metal ion concentration. Luminescence decay curve analyses were found in agreement with the presence of Cu⁺ ions in the glasses suggesting their existence in tetragonally-distorted octahedral sites.     

Ultrasonic studies of (TeO2)50–(V2O5)50−x(TiO2)x glasses

New ternary tellurite glasses in the form (TeO₂)₅₀–(V₂O₅)_50−x(TiO₂)_x have been prepared. Both longitudinal and shear ultrasonic velocities were measured in different compositions of the glass system by using the pulse-echo method at 5 MHz frequency and at room temperature. The elastic properties of ternary telluirte glasses (TeO₂)₅₀–(V₂O₅)_50−x(TiO₂)_x were measured as a function of composition. The ultrasonic velocity data, the density, the calculated elastic moduli, micro-hardness, softening temperature, and Debye temperature depend on the glass composition. By calculating the number of network bonds per unit volume, the average stretching force constant, and the average ring size, information about the structure of the glass can be deduced. Comparison between the calculated and the experimental elastic moduli and Poisson's ratio have been carried out.     

Structural investigation of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–K<Subscript>2</Subscript>O glass system with antibacterial potential

The xV₂O(1?x)[0.8 P₂O₅ ? 0.2 K₂O] glass system with 0 ≤ x ≤ 50 mol% was prepared and the structural changes induced in these glasses by increasing the vanadium oxide content were investigated by IR and ESR spectroscopies. The dual behaviour role of V₂O₅ oxide, as network modifier (for x ≤ 10 mol%) and the network former (x ≥ 20 mol%), as a consequence of phosphate network depolymerization and P–O–V and V–O–V linkages appearance was also highlighted. The antibacterial effect of the glasses with x ≤ 20 mol% V₂O₅ content was tested by optical density (OD) measurements. A linear correlation between the amount of vanadium and the antibacterial effect was evidenced.     

Effect of some VA group modifiers on R2O3 (R = Sb,Bi)–ZnF2–GeO2 glasses doped with CuO by means of spectroscopic and dielectric investigations

Transparent glasses 40Sb₂O₃–20ZnF₂–(40 − x)GeO₂:xCuO, and 40Bi₂O₃–20ZnF₂–(40 − y)GeO₂:yCuO with x = 0, 0.6 and 0 ≤ y ≤ 1 wt% were prepared by melt quenching technique and were characterized by XRD and differential thermal analysis. Spectroscopic studies like optical absorption, FTIR, Raman, EPR and dielectric parameters (such as ?′, loss(tan δ), and σ_ac) were carried out to examine the modifier and dopant effect on zinc germanate glass network. Optical absorption and EPR data have revealed that the environment of Cu²⁺ ions is more ionic in bismuth series rather than antimony glasses. Reduced bismuth ions have been found in pure and at lower concentration of dopant in Bi₂O₃ mixed glasses, which are useful for IR amplifications. FTIR and Raman spectra have indicated the conversion of GeO₄ to GeO₆ structural units by forming cross linking bonds like Bi–O–Ge, Ge–O–Cu, etc., and open the glass network with integration of Bi₂O₃ and CuO doping. It is also confirmed by decreasing T_g and E_g values. The temperature dependence of dielectric parameters at different frequencies was interpreted in terms of structural changes in the glass network.     

Novel structural properties of the lead–vanadate–tellurate glass ceramics

In this paper, we have examined and analyzed the effects of systematic intercalation of the lead ions on vanadate–tellurate glass ceramics with interesting results. The structural properties of the lead–vanadate–tellurate glass ceramics of compositions xPbO·(100 − x)[6TeO₂·4V₂O₅], x = 0 − 100 mol%, are reported for the first time. It has been shown by X-ray diffraction that single-phase homogeneous glasses with a random network structure can be obtained in this system. Among these unconventional lead–vanadate–tellurate glass ceramics, we found that network formers are good host material for lead ions and are capable to intercalate a variety of species such as Te₂V₂ ⁵⁺O₉, Pb₃(V⁵⁺O₄)₂, Pb₂V₂ ⁵⁺O₇, and V₂O₅-rich amorphous phase. On the other hand, these glass ceramics contain V⁴⁺ and V⁵⁺ ions necessary for the electrical conduction. Based on these experimental results, we propose that the V⁴⁺=O bonds are created by two different mechanisms: the first of reduction of V⁵⁺ ions to V⁴⁺ ions and thus of creation of V⁴⁺=O bonds.     

The effect of P2O5 on the structure,sintering and sealing properties of barium calcium aluminum boro-silicate (BCABS) glasses

The effect of P₂O₅ incorporation on the sintering, flow and crystallization characteristics of BCABS glasses of composition (mol%) 35BaO–15CaO–5Al₂O₃–(37 − x)SiO₂–8B₂O₃–xP₂O₅ (0 ≤ x ≤5) is investigated. It is observed that addition of P₂O₅, removes cations (Ba²⁺ and Ca²⁺) from the silicate network, resulting in an increase in polymerization. This is reflected by a reduction in TEC and an increase in sealing temperature. In addition, the removal of cations for charge compensation causes a change in major crystalline phases formed, from BaSiO₃ to Ba(Al₂Si₂O₈). In addition, beyond 3 mol% P₂O₅, crystallization of phosphate phases is evident. Based upon the flow temperature, glasses with 0, 1 and 2 mol% P₂O₅ are selected for sealing. In these glasses, conversion of Cr to Cr₂O₃ is observed_, yielding improved adhesion. However, the 2 mol% P₂O₅ glass showed an increased crystallization tendency, resulting in incomplete sintering. Therefore, 1 mol% P₂O₅ seems a good compromise for sealing with improved adhesion.     

Structural investigations of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–CaO glass system by FT-IR and EPR spectroscopies

xV₂O₅·(100 − x)[0.7P₂O₅·0.3CaO] glass system was obtained for 0 ≤ x ≤ 35 mol% V₂O₅. In order to obtain information regarding their structure, several techniques such as X-Ray diffraction, FT-IR, and EPR spectroscopies were used. X-Ray diffraction patterns of investigated samples are characteristic of vitreous solids. FT-IR spectra of 0.7P₂O₅·0.3CaO glass matrix and its deconvolution show the presence in the glass structure of all structural units characteristic to P₂O₅. Their number are increasing for x ≤ 3 mol% V₂O₅ then, for higher content of vanadium ions, the number of phosphate structural units are decreasing leading to a depolymerization of the structure. The structural units characteristic to V₂O₅ were not evidenced but their contribution to the glass structure can be clearly observed. EPR revealed a well resolved hyperfine structure (hfs) typical for vanadyl ions in a C_4v symmetry for x ≤ 3 mol% V₂O₅. For 5 < x < 20 mol% V₂O₅ the spectra show a superposition of two EPR signals one due to a hfs structure and another consisting of a broad line typical for associated V⁴⁺–V⁴⁺ ions. For x ≥ 20 mol% V₂O₅ only the broad line can be observed. The composition dependence of the line-width suggests the presence of dipole–dipole interaction between vanadium ions up to x ≤ 5 mol% V₂O₅ and superexchange interactions between vanadium ions for x > 5 mol% V₂O₅.     

Volume and thermal studies for tellurite glasses

Binary tellurite glass systems of the forms TeO₂(100 − x) − xA _n O _m where A _n O _m  = La₂O₃ or V₂O₅ and x = 5, 7.5, 10, 12.5, 15, 17.5, and 20 mol% for La₂O₃ and 10, 20, 25, 30, 35, 40, 45, and 50 mol% for V₂O₅ were prepared. Density and molar volume of each glass were measured and calculated. The compressibility model has been used to find the difference volume V _d due to the exchange of one formula unit between Te and both of La and V in the binary glass system and the mean volume V _A per formula unit in the present binary glass in order to check whether or not it is independent of the percentage of the modifier for a glass series and also different from series to another. Differential scanning calorimetric at different heating rates was used to gain some insight into the thermal stability and calorimetric behavior of the present binary transition metal and rare-earth tellurite glasses. The glass transformation temperature T _g and glass crystallization temperature T _c were recorded at different heating rates to calculate both of the glass transition activation and the glass crystallization activation energies by using different methods.     

Physical properties and MAS-NMR studies of titanium phosphate-based glasses

In this study, for a series phosphate-based glasses ((P₂O₅)_0.45(CaO)_0.3(Na₂O)_0.25−x(TiO₂)_x, 0 ≤ x ≤ 0.15), their degradation, ion release, surface and thermal properties have been determined. The results show that adding TiO₂ was associated with a significant increase in density and glass transition temperature, but a decrease in degradation rate and ion release. ³¹P solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR) showed that the local structure of the glasses changes with increasing TiO₂ content. As TiO₂ is incorporated into the glass, the phosphate connectivity increases as Q¹ units transform to Q², confirming that an increase in the nominal TiO₂ content correlates unequivocally with an increase in glass stability. As reported for titania–silica gels, Ti⁴⁺ is clearly adopting a network former role in these phosphate-based glasses. ²³Na MAS-NMR results corroborate this phenomenon with a marked upfield trend of the ²³Na isotropic chemical shift suggesting that the local Na–O bond distances are decreasing within a more condensed glass network upon increased incorporation of TiO₂.     

Low-temperature sintered ZnNb2O6–CaTiO3 ceramics with near-zero τf

The phases, microstructure and microwave dielectric properties of ZnNb₂O₆–xCaTiO₃ ceramics with BaCu(B₂O₅) glass additions prepared by solid state reaction method were charactered by using X-ray diffraction, Scanning electron microscopy and Advantest network analyzer. The τ_f of ZnNb₂O₆ was modified to near 0 ppm °C⁻¹ by incorporating CaTiO₃ with opposite τ_f values on the basis of Lichtenecker empirical rule. The microwave dielectric properties of ZnNb₂O₆–xCaTiO₃ (x = 8.0 wt.%) samples with BaCu(B₂O₅) glass additives sintered in 900–1000 °C were investigated, and the results indicated that the behaviors of the ε_r and Q × f were associated with the sintering temperature and the amount of BaCu(B₂O₅) glass. The sintering temperature of the ceramics was reduced to 950 °C from 1175 °C. Addition of 5.0 wt.% BaCu(B₂O₅) glass in ZnNb₂O₆–xCaTiO₃ (x = 8.0 wt.%) ceramics sintered at 950 °C showed excellent dielectric properties of ε_r = 20.2, Q × f = 14,100 GHz (f = 7.3 GHz) and τ_f = 0 ppm °C⁻¹. Moreover, the material had a chemical compatibility with silver, which represented a promising candidate materials for low-temperature-co-fired ceramics applications.