Sodium Borophosphate Glasses Research Articles

Impact of CdO on optical, physical, and radiation resistance of sodium borophosphate glasses

This article focuses on exploring the effects of CdO on the optical, radiation, and physical characteristics of sodium borophosphate glass with different compositions. The glass compositions included B2O3, Na2O, P2O5, and varying content of CdO from 0 to 12 mol %. One of the observed effects of adding CdO to the glass composition is a substantial increase in glass density. The density increased from 3.42 g/cm³ to 4.87 g/cm³ as the CdO increased. UV–visible spectroscopy was utilized to determine the optical bandgap and other correlated physical parameters. Bandgap values increased from 2.39 to 2.74 eV for Eoptind and from 2.51 to 2.82 eV for Eoptdi. Connections between the optical and physical characteristics of CdNaBP glasses are discussed. Moreover, different shielding parameters were assessed using Phy-X simulation software. This study explores the importance of radiation shielding efficiency and the positive impact of higher CdO content on photon blocking in sodium borophosphate glasses. The addition of CdO enhances the radiation shielding capabilities of this glass. Additionally, the study explored the gamma shielding properties. Hence, all these observations infer that the CdNaBP-12 glass sample is the most suitable for transparent radiation shielding applications.

Impact of copper oxide on the structural, optical, and dielectric properties of sodium borophosphate glass

Sodium borophosphate glasses containing copper oxide (CuO) have produced by melt annealing technique. Phosphate units are presented in Q2, whereas the borate groups are presented as trigonal and tetraborate units. The addition of CuO in the network former modifies the characteristic mid region of infrared bands or peaks. The base glass sample has a density of 2.57 g/cm3 raising to 2.71 g/cm3 after doping with 0.1 CuO. The absorption edges of such glass shifted towards lower photon energy due to the formation of non-bridging oxygens (NBOs). With the increase in the copper content from 0 to 0.1 mole fraction, the optical transition values decreased from 3.682 to 1.672 eV. The real and imaginary part of dielectric constants decreased as the applied frequency increase due to the dipolar, interfacial, and dielectric polarization effects. The relaxation process has observed at high frequency and 0.1 CuO sample correlated to the formation of NBOs.

The effect of the sodium content on the structure and the optical properties of thermally poled sodium and niobium borophosphate glasses

Six niobium rich glasses presenting different sodium contents were synthetized. On the basis of complementary infrared and Raman analysis, the influence of the sodium content and its role on the structure of the glasses prior to and following poling was examined. Correlative second harmonic generation (SHG)/Raman microscopy on the poled glasses cross section has shown a co-localization of the SHG signal and the structural variations. It also evidenced similar structural rearrangements whether sodium is removed through poling (230–300 °C) or through the alkali content defined by the starting glass compositions (melted at 1300–1500 °C). The effect of the sodium content on the optical properties, prior to and after thermal poling, is also discussed. It was found that refractive index variations induced by poling (ranging between 10−3 and 3 × 10−2) are mainly the result of a density decrease in the poled region rather than compositional and structural changes. The electro-optic origin of the poling-induced second order nonlinear response is confirmed by the Maker Fringe SHG analysis, and the evolution of χ(2) (2–2.5 pm/V) with the sodium content is discussed based on a selection of parameters influencing either the third order susceptibility [χ(3)] or the internal electric field strength of the poled layer.

The internal friction of lithium and sodium borophosphate glasses

Alkali borophosphate glasses have recently gained strong interest, not only for their fundamental importance due to the mixed glass former effect but also because of their potential applicability as solid state electrolytes in energy harvesting devices. In the present work, internal friction measurements of lithium and sodium borophosphate glasses have been performed in order to look for further insights on the relationships between the ionic conduction mechanism and the structure of the glasses that has been previously determined. Absorption of acoustic waves shows two marked internal friction peaks with activation energy in the range of the activation energy for the ionic conduction of the glasses between 0.5 and 0.7 eV. Furthermore, the substitution of phosphorus by boron network former results in the decrease of the activation energy associated to both processes in parallel to the Ea of the ionic conduction of alkali cations; and the relationship between the areas of both peaks suggests a change of the distribution of alkali ions between positions energetically different in agreement with the structural changes of the glass network.

Dielectric Study of Lithium and Sodium Borophosphate Glasses

Ionic conductivity and dielectric properties such as dielectric permittivity and loss tangent for the samples of lithium and sodium borophosphate glasses were investigated using the electrical conductivity measurements in the range of frequency from 10 Hz to 2 MHz and various temperatures below Tg. The measured data of ac conductivity were described according Jonscher's power law and experimental values of imaginary part of electric modulus were fitted by KWW function. From the fitted parameters, the activation energies for conduction and relaxation time were found which characterize the hopping processes and transport mechanism in these ion conducting glasses.

Positive and Negative Mixed Glass Former Effects in Sodium Borosilicate and Borophosphate Glasses Studied by (23)Na NMR.

Glasses with varying compositions of constituent network formers but constant mobile ion content can display minima or maxima in their ion transport which are known as the negative or the positive mixed glass former effect, MGFE, respectively. Various nuclear magnetic resonance (NMR) techniques are used to probe the ion hopping dynamics via the (23)Na nucleus on the microscopic level, and the results are compared with those from conductivity spectroscopy, which are more sensitive to the macroscopic charge carrier mobility. In this way, the current work examines two series of sodium borosilicate and sodium borophosphate glasses that display positive and negative MGFEs, respectively, in the composition dependence of their Na(+) ion conductivities at intermediate compositions of boron oxide substitution for silicon oxide and phosphorus oxide, respectively. A coherent theoretical analysis is performed for these glasses which jointly captures the results from measurements of spin relaxation and central-transition line shapes. On this basis and including new information from (11)B magic-angle spinning NMR regarding the speciation in the sodium borosilicate glasses, a comparison is carried out with predictions from theoretical approaches, notably from the network unit trap model. This comparison yields detailed insights into how a variation of the boron oxide content and thus of either the population of silicon or phosphorus containing network-forming units with different charge-trapping capabilities leads to nonlinear changes of the microscopic transport properties.

Charge Compensation in Sodium Borophosphate Glasses Studied by 11B{23Na} and 31P{23Na} Rotational Echo Double Resonance Spectroscopy

Network former–network modifier interactions in three sodium borophosphate glasses have been probed by 11B{23Na} and 31P{23Na} rotational echo double resonance (REDOR) experiments. For the compositions chosen essentially all of the boron atoms in these glasses are four-coordinated and, thus, of formally anionic character, whereas the majority of the phosphorus species are of the (nominally charge-neutral) P(3) type. Despite this fact, the dipolar second moments M2(11B{23Na}) and M2(31P{23Na}) extracted from these REDOR data indicate that the sodium cations interact significantly more strongly with the phosphate than with the borate species. As a matter of fact, the distance sums ∑rP–Na–6 calculated from these second moments are close to those measured in sodium ultraphosphate glasses with similar sodium concentrations, whereas the corresponding ∑rB–Na–6 values are significantly smaller than those measured in sodium borate glasses with comparable sodium concentrations. These results are corroborated by com...

Ionic Conductivity of Mixed Glass Former 0.35Na2O + 0.65[xB2O3 + (1 – x)P2O5] Glasses

The mixed glass former effect (MGFE) is defined as a nonlinear and nonadditive change in the ionic conductivity with changing glass former fraction at constant modifier composition between two binary glass forming compositions. In this study, mixed glass former (MGF) sodium borophosphate glasses, 0.35Na2O + 0.65[xB2O3 + (1 - x)P2O5], 0 ≤ x ≤ 1, have been prepared, and their sodium ionic conductivity has been studied. The ionic conductivity exhibits a strong, positive MGFE that is caused by a corresponding strongly negative nonlinear, nonadditive change in the conductivity activation energy with changing glass former content, x. We describe a successful model of the MGFE in the conductivity activation energy terms of the underlying short-range order (SRO) phosphate and borate glass former structures present in these glasses. To do this, we have developed a modified Anderson-Stuart (A-S) model to explain the decrease in the activation energy in terms of the atomic level composition dependence (x) of the borate and phosphate SRO structural groups, the Na(+) ion concentration, and the Na(+) mobility. In our revision of the A-S model, we carefully improve the treatment of the cation jump distance and incorporate an effective Madelung constant to account for many body coulomb potential effects. Using our model, we are able to accurately reproduce the composition dependence of the activation energy with a single adjustable parameter, the effective Madelung constant, that changes systematically with composition, x, and varies by no more than 10% from values typical of oxide ceramics. Our model suggests that the decreasing columbic binding energies that govern the concentration of the mobile cations are sufficiently strong in these glasses to overcome the increasing volumetric strain energies (mobility) caused by strongly increasing glass-transition temperatures combined with strongly decreasing molar volumes of these glasses. The dependence of the columbic binding energy term on the relative high-frequency dielectric permittivity suggests that the increased polarizability of the bridging oxygens connecting SRO tetrahedral boron units to phosphorus units causes further charge delocalization away from the negatively charged tetrahedral boron units, leading to a lowering of the charge density, and is the underlying cause of the MGFE.

Glass transition temperature and topological constraints of sodium borophosphate glass-forming liquids

Sodium borophosphate glasses exhibit intriguing mixed network former effect, with the nonlinear compositional dependence of their glass transition temperature as one of the most typical examples. In this paper, we establish the widely applicable topological constraint model of sodium borophosphate mixed network former glasses to explain the relationship between the internal structure and nonlinear changes of glass transition temperature. The application of glass topology network was discussed in detail in terms of the unified methodology for the quantitative distribution of each coordinated boron and phosphorus units and glass transition temperature dependence of atomic constraints. An accurate prediction of composition scaling of the glass transition temperature was obtained based on topological constraint model.

Structure and Ionic Conductivity in the Mixed-Network Former Chalcogenide Glass System [Na2S]2/3[(B2S3)x(P2S5)1–x]1/3

Glasses in the system [Na2S]2/3[(B2S3)x(P2S5)1–x]1/3 (0.0 ≤ x ≤ 1.0) were prepared by the melt quenching technique, and their properties were characterized by thermal analysis and impedance spectroscopy. Their atomic-level structures were comprehensively characterized by Raman spectroscopy and 11B, 31P, and 23Na high resolution solid state magic-angle spinning (MAS) NMR techniques. 31P MAS NMR peak assignments were made by the presence or absence of homonuclear indirect 31P–31P spin–spin interactions as detected using homonuclear J-resolved and refocused INADEQUATE techniques. The extent of B–S–P connectivity in the glassy network was quantified by 31P{11B} and 11B{31P} rotational echo double resonance spectroscopy. The results clearly illustrate that the network modifier alkali sulfide, Na2S, is not proportionally shared between the two network former components, B and P. Rather, the thiophosphate (P) component tends to attract a larger concentration of network modifier species than predicted by the bulk composition, and this results in the conversion of P2S74–, pyrothiophosphate, Na/P = 2:1, units into PS43–, orthothiophosphate, Na/P = 3:1, groups. Charge balance is maintained by increasing the net degree of polymerization of the thioborate (B) units through the formation of covalent bridging sulfur (BS) units, B–S–B. Detailed inspection of the 11B MAS NMR spectra reveals that multiple thioborate units are formed, ranging from neutral BS3/2 groups all the way to the fully depolymerized orthothioborate (BS33–) species. On the basis of these results, a comprehensive and quantitative structural model is developed for these glasses, on the basis of which the compositional trends in the glass transition temperatures (Tg) and ionic conductivities can be rationalized. Up to x = 0.4, the dominant process can be described in a simplified way by the net reaction equation P1 + B1 ⇆ P0 + B4, where the superscripts denote the number of BS atoms for the respective network former species. Above x = 0.4, all of the thiophosphate units are of the P0 type and both pyro- (B1) and orthothioborate (B0) species make increasing contributions to the network structure with increasing x. In sharp contrast to the situation in sodium borophosphate glasses, four-coordinated thioborate species are generally less abundant and heteroatomic B–S–P linkages appear to not exist. On the basis of this structural information, compositional trends in the ionic conductivities are discussed in relation to the nature of the charge-compensating anionic species and the spatial distribution of the charge carriers.

Optical and infrared absorption spectra of 3d transition metal ions-doped sodium borophosphate glasses and effect of gamma irradiation

Undoped and transition metals (3d TM) doped sodium borophosphate glasses were prepared. UV–visible absorption spectra were measured in the region 200–900nm before and after gamma irradiation. Experimental optical data indicate that the undoped sodium borophosphate glass reveals before irradiation strong and broad UV absorption and no visible bands could be identified. Such UV absorption is related to the presence of unavoidable trace iron impurities within the raw materials used for preparation of this base borophosphate glass. The TMs-doped glasses show absorption bands within the UV and/or visible regions which are characteristic to each respective TM ion in addition to the UV absorption observed from the host base glass.Infrared absorption spectra of the undoped and TMs-doped glasses reveal complex FTIR consisting of extended characteristic vibrational bands which are specific for phosphate groups as a main constituent but with the sharing of some vibrations due to the borate groups. This criterion was investigated and approved using DAT (deconvolution analysis technique). The effects of different TMs ions on the FTIR spectra are very limited due to the low doping level (0.2%) introduced in the glass composition. Gamma irradiation causes minor effect on the FTIR spectra specifically the decrease of intensities of some bands. Such behavior is related to the change of bond angles and/or bond lengths of some structural building units upon gamma irradiation.

The glass transition temperature of mixed glass former 0.35Na2O + 0.65[xB2O3 + (1 − x)P2O5] glasses

The mixed glass former effect (MGFE) is defined as the non-linear and non-additive change in the ionic conductivity with changing glass former fraction at constant modifier composition between two binary glass former compositions. In this study, sodium borophosphate glasses, 0.35Na2O+0.65[xB2O3+(1−x)P2O5] with 0≤x≤1, have been prepared and their glass transition temperatures (Tg) have been examined as an alternative indicator of the MGFE and as an indicator of changes in the short range order (SRO) structural network units that could cause or contribute to the MGFE. The changes in Tg show a positive non-additive and non-linear trend over the changing glass former fraction, x. The increase in Tg is related to the increasing number of bridging oxygens (BO) in the glass samples, which is caused by the increase in the number of tetrahedral boron, B4, units in the SRO structure.

Investigation of the Structures of Sodium Borophosphate Glasses by Reverse Monte Carlo Modeling to Examine the Origins of the Mixed Glass Former Effect

We present new results for the Reverse Monte Carlo modeling of 0.35Na2O + 0.65[xB2O3 + (1 – x)P2O5] glasses based on previously reported X-ray diffraction (XRD) data. Structural models have been generated that accurately reproduce the pair correlation functions and structure factors determined by XRD while maintaining nearly perfect charge neutrality between the positively charged cations and the negatively charged phosphate and borate oxyanion groups and while maintaining appropriate bond distances between the various atom pairs. These models, however, are not successful in accounting for the concentrations of network forming units (NFUs), as predicted by recent theoretical modeling and by magic-angle spinning nuclear magnetic resonance (MAS NMR) data for sodium borate glasses with similar stoichiometry. By a further refinement of the modeling, the NFU concentrations can be successfully reproduced as well. For the optimized structures, we investigate the question if the conductivity activation energy cor...

Effect of titanium on structure of sodium borophosphate glasses

Glasses in the system 30P2O5-30B2O3-40Na2O-xTiO2 (0 ≤ x ≤ 25 mol %) have been prepared by the melt-quenching technique. Increasing the TiO2 content of the glass structure results in a decrease in the molar volume and an increase in the glass transition/softening temperatures. Structural changes were studied by Raman spectroscopy, and 11B and 31P solid-state NMR. The observed changes in the spectra and the properties of the studied glasses can be ascribed to several reasons, such as the addition of TiO2 that results in the formation of distorted Ti octahedral linked to pyrophosphate unit through P-O-Ti bonds. In these glass series, the overall glass network was enhanced by TiO2 addition, although a depolymerization in the original P-O-P network occurred.

The densities of mixed glass former 0.35 Na2O + 0.65 [xB2O3 + (1 − x)P2O5] glasses related to the atomic fractions and volumes of short range structures

The mixed glass former effect (MGFE) is defined as a non-linear and non-additive change in the ionic conductivity with changing glass former fraction at constant modifier composition between two binary glass forming compositions. In this study, mixed glass former (MGF) sodium borophosphate glasses, 0.35 Na2O+0.65 [xB2O3+(1−x)P2O5], 0≤x≤1, which have been shown to have a strong positive MGFE, have been prepared and their physical properties, density and molar volume, have been examined as predictors of structural change. The density exhibits a strong positive non-linear and non-additive change in the density with x and a corresponding negative non-linear and non-additive change in the molar volume. In order to understand the structural origins of these changes, a model of the molar volume was created and best-fit to the experimentally determined molar volumes in order to determine the volumes of the short range order (SRO) structural units in these glasses, how these volume change from the molar volumes of the binary glasses, and how these volumes change across the range of x in the ternary glasses. The best-fit model was defined as the model that required the smallest changes in the volumes of the ternary phosphate and borate SRO structural groups from their values determined by the densities of the binary sodium phosphate and sodium borate glasses. In this best-fit molar volume model, it was found that the volumes of the various phosphate and borate SRO structural groups decreased by values ranging from a minimum value of ~1% for x=0.1 and 0.9 to a maximum value of ~6% for the phosphate and ~9% for the borate SRO groups at the minimum in molar volume at x=0.4. The free volume was found to have a negative deviation from linear which is unexpected given the positive deviation in ionic conductivity.

The mixed network former effect in glasses: solid state NMR and XPS structural studies of the glass system (Na2O)x(BPO4)1−x

The structural organization of sodium borophosphate glasses with composition (Na(2)O)(x)(BPO(4))(1-x) (0.25 ≤x≤ 0.55) has been investigated by differential scanning calorimetry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), as well as single- and double resonance (11)B and (31)P magic-angle spinning (MAS) NMR. (11)B MAS-NMR data indicate the dominance of anionic four-coordinated boron units, and (31)P MAS NMR reveals the successive transformation of neutral P(3) into singly charged P(2) units and their further transformation into doubly charged P(1) units at high Na(2)O contents. The quantification of these units provides detailed insight into the competition of the network formers borate and phosphate for the network modifier oxide. At low modifier content (x < 0.35), the anionic species are almost exclusively borate (B(4)) units, whereas at higher sodium concentrations, large numbers of anionic phosphate (P(2) and P(1)) species are formed. O-1s XPS data provide a quantitative distinction between B-O-B, B-O-P, and P-O-P linkages as well as non-bridging oxygen atoms, and comparable numbers can be extracted from (11)B and (31)P MAS-NMR experiments. Both XPS as well as (31)P{(11)B} and (11)B{(31)P} rotational echo double resonance (REDOR) NMR results reveal strong interactions between the two network formers boron oxide and phosphorus oxide, resulting in a preferred formation of B-O-P linkages. For higher Na(2)O contents, however, the successive network modification diminishes this preference, resulting in close-to-statistical network connectivities. Compositional trends of T(g) in the Na(2)O-B(2)O(3)-P(2)O(5) glass forming system can be correlated with the overall network connectedness, expressed by the total number of bridging oxygen atoms per network former species. However, separate linear correlations are observed for different compositional lines, indicating also the relevance of the type of network former linkages present.

EPR and optical absorption studies of Fe 3+ ions in sodium borophosphate glasses

Electron paramagnetic resonance (EPR) and optical absorption spectral investigations have been carried out on Fe 3+ ions doped sodium borophosphate glasses (NaH 2PO 4–B 2O 3–Fe 2O 3). The EPR spectra exhibit resonance signals with effective g values at g=2.02, g=4.2 and g=6.4. The resonance signal at g=4.2 is due to isolated Fe 3+ ions in site with rhombic symmetry whereas the g=2.02 resonance is due to Fe 3+ ions coupled by exchange interaction in a distorted octahedral environment. The EPR spectra at different temperatures (123–295 K) have also been studied. The intensity of the resonance signals decreases with increase in temperature whereas linewidth is found to be independent of temperature. The paramagnetic susceptibility ( χ) was calculated from the EPR data at various temperatures and the Curie constant (C) and paramagnetic Curie temperature ( θ p ) have been evaluated from the 1/ χ versus T graph. The optical absorption spectrum exhibits bands characteristic of Fe 3+ ions in octahedral symmetry. The crystal field parameter ( Dq) and the Racah interelectronic repulsion parameters ( B and C) have also been evaluated and discussed.

Effect of silver on phase separation and crystallization of niobium oxide containing glasses

Effect of silver introduction in sodium phosphate and sodium borophosphate glasses containing large amount of niobium oxide have been investigated using differential scanning calorimetry and XRD. Same sodium niobate phase in the Nb 2O 5–NaNbO 3 based solid solution have been observed following two heat treatments designed for nucleation and growth of the crystalline phase. Silver introduction in the glass composition is clearly responsible for increasing the crystallization rate. Its effect after nucleation and crystallization treatments has been shown. Phase metastable separation is occurring during heat treatment with formation of a phosphate rich and niobium rich phase. Crystallization effect on optical transparency of glasses and on Raman scattering response have been investigated.

Viscosity properties of sodium borophosphate glasses

The viscosity behavior of (1 − x)NaPO 3− xNa 2B 4O 7 glasses ( x = 0.05–0.20) have been measured as a function of temperature using beam-bending and parallel-plate viscometry. The viscosity was found to shift to higher temperatures with increasing sodium borate content. The kinetic fragility parameter, m, estimated from the viscosity curve, decreases from 52 to 33 when x increases from 0.05 to 0.20 indicating that the glass network transforms from fragile to strong with the addition of Na 2B 4O 7. The decrease in fragility with increasing x is due to the progressive depolymerization of the phosphate network by the preferred four-coordinated boron atoms present in the low alkali borate glasses. As confirmed by Raman spectroscopy increasing alkali borate leads to enhanced B–O–P linkages realized with the accompanying transition from solely four-coordinated boron (in BO 4 units) to mixed BO 4/BO 3 structures. The glass viscosity characteristics of the investigated glasses were compared to those of P-SF67 and N-FK5 commercial glasses from SCHOTT. We showed that the dependence of the viscosity of P-SF67 was similar to the investigated glasses due to similar phosphate network organization confirmed by Raman spectroscopy, whereas N-FK5 exhibited a very different viscosity curve and fragility parameter due to its highly coordinated silicate network.

Second-harmonic generation in sodium and niobium borophosphate glasses after poling under field-assisted silver ions anodic injection

Monovalent silver ions, resulting from a thin silver layer initially deposited at the anode surface, have been introduced using the field-assisted ion-exchange technique in sodium niobium borophosphate glasses. A reproducible susceptibility χ(2) could be gained after this poling treatment, although a drop in the nonlinearity is observed due to the introduction of silver ions. From energy dispersive x-ray spectroscopy, it has been found that the nonlinear layer is characterized by a strong migration of sodium ions 4 μm deep inside the anode side, which have been partially replaced by silver ions. These results indicate a complex space-charge-migration process during the poling treatment, which is involved in the decrease in the mean second-harmonic generation signal.