Effect of BaO substitution for CaO on the structural and thermal properties of SiO2–B2O3–Al2O3–CaO–Na2O–P2O5 bioactive glass system used for implant coating applications

The present study replaced 3.30 and 9.00 mol.% BaO for CaO in a SiO₂–B₂O₃–Al₂O₃–CaO–Na₂O–P₂O₅ bioactive glass system used for implant coating applications. Variations of the glass structure, thermal properties, cytotoxicity, and radiopacity of glasses were studied. As demonstrated by the results, upon adding barium oxide to the glass structure, the weight density increased significantly, while a slight decrease in oxygen density was determined. Introducing barium oxide into glass composition did not cause any considerable change in the spectra of FTIR and Raman. It was demonstrated that the amount of bridging oxygen in the glass structure remained quite unaffected. The hot stage microscopy evaluations revealed further shrinkage of barium-containing frits due to lower viscosity and hence, higher viscous flow of these glasses. By substituting barium oxide for calcium oxide and increasing its concentration, the glass transition temperature (T_g) and the dilatometric softening temperature (T_d) decreased, while the thermal expansion coefficient increased. Moreover, upon substituting 9 mol.% barium oxide for calcium oxide, a 30 °C reduction in maximum sintering temperature (T_ms) of the glass was obtained, whereas the shrinkage rate was increased 1.7 times. It was indicated that the sintering process of barium-incorporated glasses would easily proceed without any phase crystallization. The barium-incorporated glasses exhibited more radiopacity. Additionally, no cytotoxic effect was caused by the substitution, and the Ba-containing glasses could be used for biomedical applications and implant coating as well.     

Effect of properties and crystallization behavior of BaO–ZnO–B2O3–SiO2 glass on the electrical conductivity of Cu paste

The extensive application of multilayer ceramic capacitors provides an attractive development for terminal electrode pastes. However, the growing requirement for advanced glass materials used in terminal electrode pastes is substantiated. Therefore, to advance the development of electrode pastes, better development and deeper exploration of glass powder are required. Here, a series of BaO–ZnO–B₂O₃–SiO₂ (BZBS) glasses were prepared by melt-quenching technique, which are used to investigate the effect of the introduction of BaO on structure and properties of the ZnO–B₂O₃–SiO₂ (ZBS) glass. With the introduction of BaO, the relative amount of [BO₄] was much less, which made the glass network structure loosen, decreased the glass transition temperature (T_g) and increased the coefficient of thermal expansion of the glass. The decreasing contact angle was observed on the surface of a barium titanate (BaTiO₃) substrate. When the BaO content was around 3–7 mol%, the stability of ZBS glass frit could be strengthened by inhibiting the precipitation of Zn₂SiO₄ crystal. In addition, to further characterize the effect of glass on terminal electrode paste, BZBS glass powder was adopted to prepare copper electrode paste, which was printed on the BaTiO₃ substrate and subsequently fired at 800°C for 10 min. With the related copper paste containing ZBS glass doped with 7 mol% BaO, the optimum value of acid resistance and sheet resistance (1.99 mΩ) were exhibited, at which the coated copper paste formed a dense conducting layer.     

Structure and viscosity of phase‐separated BaO–SiO2 glasses

Barium silicate glasses with 0‐40 mol% BaO were synthesized either by aerodynamical levitation and laser heating (at low barium content) or by conventional melting and quenching process. Characterization by means of Raman scattering spectroscopy and scanning transmission electron microscopy reveals a structural transition between glasses with low BaO content (<10 mol%) showing an atomic network resembling the one of amorphous silica, and glasses with a BaO content larger than 10 mol%, which exhibit the typical signature of a binary silicate glass with Q₂ and Q₃ units. Viscosity curves show a marked increase of the viscosity as the BaO content decreases below 20 mol%. Barium is found to easily diffuse and promote phase separation while silicon remains homogeneously distributed. A dramatic increase in the viscosity is observed as phase separation proceeds, resulting in the formation of Ba‐rich nodules in a percolating SiO₂‐rich matrix at low barium content, or in Ba‐poor nodules in a BaO‐rich matrix at large barium content.     

Elucidating the role of AlO6‐octahedra in aluminum silicophosphate glasses through topological constraint theory

The local structures of sodium aluminum silicophosphate glasses containing unique AlO₆‐octahedra were characterized through nuclear magnetic resonance (NMR) and modeled by topological constraint theory (TCT). Subsequent calculation results of the glass‐transition temperature (T_g) and Vickers hardness (H_v) obtained using TCT were verified by the experimental data, which provided us evidence of the glass former role of the AlO₆‐octahedra and their behavior in the aluminum‐containing glass systems. The glass‐forming behavior of the AlO₆‐octahedra was identified by their displacement of SiO₆‐octahedra based on their corresponding NMR spectrum. The structure featured a constant total amount of AlO₆ and SiO₆‐octahedra (AlO₆‐octahedra increased whereas SiO₆‐octahedra decreased) with an increasing aluminum content, which was caused by the mutual replacement between them. The glass former role of the AlO₆‐octahedra was further supported by the theoretical computation of T_g and H_v through application of TCT. Specifically, the model of the aluminum‐containing glasses reported here is an extension of the conventional TCT that only incorporates the constraints of the glass formers.     

Preparation and sealing effects of Mg–Al–Si–Ba–O-based glass-ceramic coatings on NTC thermistors

Herein, Mg–Al–Si–Ba–O-based glass ceramics were studied as potential candidates to protect Mn–Co–Ni–O-based negative temperature coefficient (NTC) thermistors at high temperatures such as 900 °C. The ceramics were prepared in three glass formulations (1#: 15MgO–15Al₂O₃-44.7SiO₂–25BaO, 2#: 17MgO–17Al₂O₃–41SiO₂–25BaO and 3#: 17MgO–17Al₂O₃–41SiO₂–20BaO–5Y₂O₃ (in mol%)) and their glass-transition temperatures (T_g) were determined using the differential scanning calorimetry (DSC) method. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the parent glasses and glass-ceramic coatings. The sealing effects of the glass ceramics were examined by conducting an insulation test. The glass-ceramic sealing structures were subjected to 1000 thermal shock cycles at temperatures varying from room temperature to 900 °C. Notably, the sealing structure of glass-ceramic coating 1# was compact at a T_g of 760.9 °C. The glass-ceramic coatings effectively maintained the NTC properties of the sensitive ceramics in all three formulations. Interestingly, the glass-ceramic coating 3# containing Y₂O₃ demonstrated an increase in electrical resistance. Both the NTC thermistors coated with 1# and 2# glass formulations successfully passed 1000 thermal shock cycles without visible failures, and their resistance change ratios were well below the requisite 20%.     

Structure and physical properties of Ge15Sb20Se65‐xSx glasses

We explored the structure and physical properties of Ge₁₅Sb₂₀Se_65‐xS_x (with x = 0, 16.25, 32.5, 48.75, and 65) glasses in order to screen the best compositions for the applications in photonics, since the laser damage thresholds in Se‐based glasses are too low although their optical nonlinearities are high. We found that, linear and nonlinear refractive index of the glasses decreased, but glass transition temperature T_g, optical bandgap E_g and the laser damage threshold increased with increasing S content. We further employed Raman scattering and high‐resolution X‐ray photoelectron spectra to probe the structure of the glasses. Through the analysis of the evolution of the different structural units in the glasses, it was concluded that, the heteropolar bonds (Ge–Se/S, Sb–Se/S) were dominated in these glasses. With the increase in chalcogen Se/S ratio, the number of the Se‐related chemical bonds (Ge–Se, Sb–Se and Se–Se) increased and that of S‐related chemical bond (Ge–S, Sb–S and S–S) decreased gradually, and Ge was prior to bond with S rather than Se. The elemental substitution thus had negligible effect on the glass structure. The change of the physical properties was mainly due to the difference of the strength of the chemical bonds between S–Ge(Sb) and Se–Ge(Sb).     

Understanding the structural origin of intermediate glasses

Intermediate glasses show nearly constant elastic moduli with temperature and/or pressure. These glasses would prove useful in designing a-thermal optical fibers for enhanced telecommunication, fiber sensing applications, and in designing glass products for applications where a broad range of thermal and mechanical stimulation is expected. In this study, intermediate glasses belonging to the Na₂O–SiO₂, Na₂O–Al₂O₃–SiO₂, and Na₂O–TiO₂–SiO₂ glass systems were identified from in situ high-temperature Brillouin light scattering (BLS) experiments. Glasses important for engineering applications like the international simple glass (ISG) and the less brittle glass (LBG) were also found to exhibit intermediate behaviors. In situ Raman spectroscopy was used to investigate their structural evolution from room temperature to temperatures beyond T_g. Raman spectra along with molecular dynamics simulations revealed common structural signatures that intermediate glasses with different compositions possess. Our study showed that the intermediate elastic behaviors come from a delicate balance between the stiffening effect associated with conformation changes in the medium-range flexible rings and the softening effect due to the weakening of short-range chemical bonds with temperature.     

Structural and emission properties of Eu3+‐doped alkaline earth zinc‐phosphate glasses for white LED applications

Quaternary alkaline earth zinc‐phosphate glasses in molar composition (40 ? x)ZnO – 35P₂O₅ – 20RO – 5TiO₂ – xEu₂O₃ (where x=1 and R=Mg, Ca, Sr, and Ba) were prepared by melt quenching technique. These glasses were studied with respect to their thermal, structural, and photoluminescent properties. The maximum value of the glass transition temperature (T_g) was observed for BaO network modifier mixed glass and minimum was observed for MgO network modifier glass. All the glasses were found to be amorphous in nature. The FT‐IR suggested the glasses to be in pyrophosphate structure, which matches with the theoretical estimation of O/P atomic ratio and the maximum depolymerization was observed for glass mixed with BaO network modifier. The intense emission peak was observed at 613 nm (⁵D₀→⁷F₂) under excitation of 392 nm, which matches well with excitation of commercial n‐UV LED chips. The highest emission intensity and quantum efficiency was observed for the glass mixed with BaO network modifier. Based on these results, another set of glass samples was prepared with molar composition (40 ? x)ZnO – 35P₂O₅ – 20BaO – 5TiO₂ – xEu₂O₃ (x=3, 5, 7, and 9) to investigate the optimized emission intensity in these glasses. The glasses exhibited crystalline features along with amorphous nature and a drastic variation in asymmetric ratio at higher concentration (7 and 9 mol%) of Eu₂O₃. The color of emission also shifted from red to reddish orange with increase in the concentration of Eu₂O₃. These glasses are potential candidates to use as a red photoluminsecent component in the field of solid‐state lighting devices.     

Phase evolution and electrical properties of copper-electroded BaTi4O9 materials with BaO–ZnO–B2O3–SiO2 glass system in reducing atmosphere

BaTi₄O₉ (BT4) microwave dielectric ceramics using a copper electrode and containing 10 wt% BaO–ZnO–B₂O₃–SiO₂ (BZBS) glass frit were sintered under reducing atmosphere at 950 °C and were investigated on the phase evolutions, microstructures and dielectric properties of BT4 with various BaO/SiO₂ and ZnO/SiO₂ ratios of BZBS glasses. Experimental results show that the BaO/SiO₂ ratio contributes to wettability of glass with BaTi₄O₉ ceramics, and ZnO/SiO₂ ratio determines the densification of BaTi₄O₉ ceramics. The different Ba–Ti–O and Ba–Cu–O phases with various Ba/Ti and Ba/Cu ratios can be attributed to the contents of BaO in glass. Ba₄Ti₁₃O₃₀ and Ba₂Cu₃O_5+X may form when BaO contents are too high, and inducing copper diffusion due to the reactions of BaO and Cu, accompanying with degrading of the dielectric characteristics. If the ZnO contents of BZBS glasses were raised, a little bit of ZnSiO₃ and Ba₂Cu₃O_5+X phases appear without Cu diffusion due to non-reaction of ZnO and CuO. The high ZnO/SiO₂ ratio of glass reveals the lower softening point, indicating that the high ZnO glass could enhance the density and therefore increase the dielectric constant and quality factor.     

Quantitative prediction of the glass-forming region and luminescence properties in Tm3+-doped germanate laser glasses

Germanate laser glasses have received much attention as a promising host materials for mid-infrared fiber lasers in recent years because of the outstanding infrared transparency, low phonon energy, and high rare earth solubility of such glasses. However, the development of high-performance germanate laser glasses is usually based on intuition and a trial-and-error method, which can involve long experimental periods and high costs, and thus, this approach is highly inefficient. Recently, with proposals for materials genome engineering, the concept of the “glass genome” has grown of interest to us. Herein, the structures of Tm³⁺-doped germanate laser glasses (BaO–GeO₂ and BaO–La₂O₃–GeO₂) were investigated by Fourier transform infrared spectra (FTIR) and Raman spectra analyses, which revealed that the resulting glass contains similar structural groups to the neighboring congruently melted glassy compounds (NCMGCs) in the composition diagram. What is more, the structure and properties of the resulting laser glasses largely depend on NCMGCs. Then, the glass-forming region, physical properties, and luminescence properties were calculated via the use of NCMGCs in Tm³⁺-doped BaO–GeO₂ binary and BaO–La₂O₃–GeO₂ ternary laser glass systems. The calculated results were in good agreement with the experimental results, thus demonstrating that our approach is practical for predicting the glass-forming region, physical properties, and luminescence properties in Tm³⁺-doped BaO–GeO₂ binary and BaO–La₂O₃–GeO₂ ternary laser glass systems. This work may provide an effective method to develop Tm³⁺-doped germanate laser glasses rapidly and at low cost.     

Suppression of phosphor‐glass reactions in YAG:Ce phosphor‐embedded glasses

For high‐power white LED applications, YAG:Ce‐based yellow phosphors were embedded in a low‐T_g Bi₂O₃–B₂O₅–ZnO–Sb₂O₅ glass (BiG) by sintering route. A high‐T_g silicate glass (SiG) was also used for comparison. Dense (porosity<2%) phosphor‐glass composites were obtained after sintered at 800°C (for SiG) and 325°C (for BiG). XRD quantitative analysis indicates that the loss of phosphor content is in the range of 2.5%‐22%, caused by partial dissolution of phosphor particles into the glass matrix during sintering. The element distribution across the interface and within the reaction zone between phosphor and glass was analyzed by TEM/SEM‐EDS. The intrinsic emission characteristic of YAG:Ce is nearly not altered, possibly resulted from the slight modification of the YAG phase during sintering. Thus the final emission intensity of the sintered body is mainly determined by the residual amount of the YAG:Ce phase. Replace the high‐T_g SiG glass by the low‐T_g BiG glass, prenitridize the YAG:Ce phosphor, and change the sintering atmosphere from air to N₂ suppress the loss of phosphor during sintering. Therefore, the resulting loss of emission intensity of the phosphor‐embedded glass material can be reduced to only about 1.8%.     

Characterization of the low temperature firing BaO–B2O3–SiO2 glass: The effect of BaO content

In the low temperature sinterable glass system of BaO–B₂O₃–SiO₂, the structural changes of the glasses and the resultant changes in the properties of the glasses were examined as a function of BaO content. ¹¹B MAS-NMR analysis was conducted in order to examine the coordination number of borons in the glass. It showed that the amount of O₄ was greatest at 35 mol% of BaO. The glass transition temperature, hardness, thermal expansion coefficient and dielectric constant of the glasses were examined and the results were explained on the basis of the structural change.     

Thermal Stability,Optical Transmittance,and Refractive Index Dispersion of La2O3–Nb2O5–Al2O3 Glasses

La₂O₃–Nb₂O₅–Al₂O₃ high‐refractive‐index glasses were fabricated by containerless processing, and the glass‐forming region was determined. The thermal stability, density, optical transmittance, and the refractive index dispersion of these glasses were investigated. All the glasses were colorless and transparent in the visible to near infrared (NIR) region and had high refractive index with low wavelength dispersion. Some of these glasses were found to have significantly high glass‐forming ability. These results indicate that the ternary glasses are suitable for optical applications in the visible to NIR region. The effects of the substitution of Al₂O₃ for Nb₂O₅ on optical properties were discussed on the basis of the Drude–Voigt equation. It was suggested that the substitution of Al₂O₃ for Nb₂O₅ increased the molecular density and suppressed a decrease in the refractive index, even when both the average oscillator strength and inherent absorption wavelength decreased in La₂O₃–Nb₂O₅–Al₂O₃ glasses. These results are helpful for designing new optical glasses controlled to have a higher refractive index and lower wavelength dispersion.     

Enhanced Thermostability,Thermo‐Optics,and Thermomechanical Properties of Barium Gallo‐Germanium Oxyfluoride Glasses and Glass‐Ceramics

Serial substitutions of BaF₂ for BaO in BaO–Ga₂O₃–GeO₂ glasses were performed, and the effects of the substitutions on the glass properties were investigated. The glass transition temperature, density, refractive index, thermo‐optics coefficient, and figure of merit for thermal shock decreased with the replacement of oxygen by fluorine. On the other hand, the glass‐forming ability increased. Fluorine substitution removed the absorption band of hydroxyl near 2.9 μm. Raman scattering spectroscopy was used to characterize the fluorogermanate glasses. The crystallization process of the glass‐ceramics under different heat‐treatment conditions was also investigated using differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, and atomic force microscopy. The thermal and mechanical properties were improved by controlling the crystal size of the near‐ and middle‐infrared transparent glass‐ceramics.     

Glass‐Ceramics in the System BaO–SrO–ZnO–SiO2 with Adjustable Coefficients of Thermal Expansion

Glasses from the system BaO–SrO–ZnO–SiO₂ with different Ba/Sr ratios were characterized regarding crystallization behavior as well as the thermal expansion of almost fully crystallized glasses. Depending on the SrO concentration, different crystalline phases precipitate from the glasses. Those with low SrO concentrations precipitate crystals with the structure of low‐temperature BaZn₂Si₂O₇ as one of the major phases. Higher SrO concentrations cause the formation of Ba_1?xSr_xZn₂Si₂O₇ solid solutions with the structure of high‐temperature BaZn₂Si₂O₇. Both, the low‐ as well as the high‐temperature phase exhibit very different thermal expansion behaviors ranging from a very high coefficient of thermal expansion in the case of the low‐temperature phase to a very low coefficient of thermal expansion in the case of the high‐temperature phase. The glass‐ceramics with the highest and that with the lowest coefficient of thermal expansion measured between 100°C and 800°C show a difference of 7.9 × 10^?6 K^?1, which is caused solely by a substitution of BaO with SrO. In contrast, the maximum variation in the thermal expansion of the glasses was only 1.5 × 10^?6 K^?1. The microstructure of sintered and afterward crystallized glass powders was analyzed via scanning electron microscopy and showed crack‐free samples with low porosity.     

Barium Borosilicate Sealing Glasses Synthesized by a Sol–Gel Process: Chemical Interactions with a Stainless Steel and Gas‐Tightness of a SOFC

Several glasses synthesized by sol–gel route and based on the BaO–B₂O₃–X–Al₂O₃–SiO₂ (X = CaO, MgO) glass system have been investigated to evaluate their applicability as sealant for solid oxide fuel cell (SOFC). Chemical interactions with K41X stainless steel and hydrogen‐tightness of these materials were evaluated after operations at high temperatures over 1,000 h in air atmosphere. Formation of a new phase at the steel–glass interface and formation of porosity in the glass were observed and determined as critical problems over mid‐term operations. The role of MgO is important to obtain a gas‐tight sealing. Application of the glass paste without binder addition was performed in order to avoid possible residual porosity related problems. The best glass was finally used as sealant between anodic and cathodic compartments in complete SOFCs operated at 760 and at 800 °C. Open circuit voltages and power densities of the cells were recorded during the first hours of operation.     

On the structure of glasses in the BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

The structure of single-phase glasses in the BaO-B₂O₃-SiO₂ system has been studied by the large- and small-angle X-ray scattering techniques. The glasses containing 40 mol % BaO upon equimolar replacement of B₂O₃ by SiO₂ have been investigated. It has been demonstrated that the incorporation of barium ions into structural groupings fixes their position and provides ordering in the distribution of barium ions at interatomic distances up to at least 5 Å. The glasses under investigation are homogeneous, and their inhomogeneity is determined by thermal density fluctuations and fluctuations of the concentration of a part of barium ions distributed in a statistically random manner in the volume of the glass. The observed ordering in the distribution of barium ions is not reduced to the formation of local clusters with an increased concentration of barium ions but is most likely a characteristic feature of the bulk glass structure. The glass structure is consistent with the model of ideal associated solutions.     

Mechanical properties,bioactivity and cell behavior of barium-containing calcium-phospho-alumino-borosilicate glass

In this study, the effect of replacing CaO by BaO on mechanical properties, bioactivity, and cell adhesion of SiO₂–B₂O₃–Al₂O₃–P₂O₅–CaO–Na₂O based glass was investigated. Mechanical characterization, depth-sensing nano-indentation, and surface micro-indentation techniques were employed to determine the fracture toughness (K_IC). The surface was photographed after micro-indentation effect using scanning electron microscopy. In vitro responses of the compounds of tris-buffered SBF solution were studied from different points of view: (i) morphology and elemental surface analysis using field emission electron microscopy equipped with energy dispersive spectroscopy; (ii) change in bonds using Raman spectroscopy; and (iii) ICP method for detecting the change in ion chemistry of SBF solution. The cell adhesion behavior was qualitatively evaluated by examining the morphology and attachment of mouse fibroblastic cells to the surface of the glasses. The results demonstrated that with the replacement of barium oxide, the hardness of the base glass increased, while the level of fracture toughness was maintained. In addition, in vitro bioactivity of barium oxide-containing glass was reduced compared to the base glass. However, structural dissolution and formation of calcium phosphate layers on their surfaces were also confirmed. The results showed that BaO-incorporated glasses had adequate cell propagation and proliferation, hence enjoying appropriate biocompatibility for use in coating applications.     

Optical properties,thermal stability,and forming region of high refractive index La2O3–TiO2–Nb2O5 glasses

The high refractive index La₂O₃–TiO₂–Nb₂O₅ glasses were prepared by containerless processing, and the glass‐forming region was determined. The refractive index showed the range from 2.20 to 2.32, and the values were much higher than those of most optical glasses. The completely miscible 30LaO_3/2–(70?x)TiO₂–xNbO_5/2 (0 ≤ x ≤70) system was fabricated to study the compositional dependence of refractive index and optical transmittance. The crucial determinants of the refractive index of oxide glasses, oxygen molar volume, and electronic polarizability of oxygen ions were calculated. The principle of additivity of glass properties was suitable for the calculation of refractive index between glass and compositional oxides. All the glasses were colorless and transparent in the visible to 6.5 μm middle infrared (MIR) region. These results are useful for designing new optical glasses with high refractive index and low wavelength dispersion in wide optical window.     

Ionic conductivity behavior by activated hopping conductivity (AHC) of barium aluminoborosilicate glass–ceramic system designed for SOFC sealing

Non-conducting BaO-B₂O₃-Al₂O₃-SiO₂ parent glasses designed for solid oxide fuel cell (SOFC) sealing applications were prepared using the melt-quenching technique. The glass formation region was determined according to phase equilibrium relations and was found to be in the composition range 70BaO-(x)Al₂O₃-(10−x)B₂O₃-20SiO₂ where 3.0 < x < 6.0 wt%. The conductivity values obtained conductivity ranged from 10⁻⁵ to 10⁻¹⁰ S/cm at temperatures between 600 and 850 °C. The batch compositions presented a threshold of dc conductivity near 70BaO wt% with a quasi linear behavior with the decrease of the BaO content. Different values of conduction activation energy were observed at temperatures above the glass transition temperature (T_g) (up to 700 °C), which were attributed to the thermal bond-breaking of non-bridging oxygen (NBO) defects. The experimental results of the electrochemical characterization by impedance spectroscopy of glass–ceramic interfaces with yttria-stabilized zirconia (YSZ) acting as solid ionic conductor electrolyte are presented and discussed.