BaO B2O3 Research Articles

High-temperature Raman spectroscopy of microstructure around the growing β-BaB2O4crystal in the BaO–B2O3–Na2O system

High-temperature Raman spectroscopy has been applied to studyin situthe microstructure of the solution near the β-BaB2O4crystal–solution interface in the BaO–B2O3–Na2O growth system. A boundary layer near the crystal–solution interface was observed. In accordance with the high-temperature Raman spectroscopy and first principles calculations, a boron–oxygen structural model is proposed to explain the microstructure of the solution and growth habit. The results show that the growth solution contains a special group, [BO2ØBOØB=O]3−(Ø = bridging oxygen), which transformed to the growth unit [B3O6]3−near the interface.

Investigation on the Li, Ba//BO2, F ternary reciprocal system and growth of bulk β-BaB2O4 crystals

Methods of spontaneous crystallization on a platinum loop, modified VPA method, solid phase synthesis, X-ray powder diffraction analysis and chemical analyses were used to study phase formation in the Li, Ba//BO2, F ternary reciprocal system and the base of the BaO–B2O3–Li2O prism of quaternary reciprocal system Ba, B, Li//O, F. In these systems the fields of primary crystallization of β-BaB2O4 were determined and a promising solvent for crystal growth was found. A series of experiments were carried out on the growth of bulk barium borate crystals in the system BaB2O4–LiF.

Effects of BaO–B2O3–SiO2 glass additive on dielectric properties of Ba(Fe0.5Nb0.5)O3 ceramics

Ba(Fe0.5Nb0.5)O3 (BFN) ceramics doped with BaO–B2O3–SiO2 (BBS) glass were prepared by the conventional solid-state ceramic route. The effects of glass content on the sintering temperature, phase composition, microstructure, dielectric properties and breakdown strength of Ba(Fe0.5Nb0.5)O3 ceramics were investigated. The sintering temperature of the BaO–B2O3–SiO2 glass added Ba(Fe0.5Nb0.5)O3 ceramics decreased by 150–330°C than that of the pure Ba(Fe0.5Nb0.5)O3. The addition of 5wt% BaO–B2O3–SiO2 glass reduces the dielectric loss at 1kHz from 1.5 to 0.019. Glass addition as high as 5wt% shows the highest breakdown strength of 27.12kV/cm, which is approximate 30 times higher than that of pure Ba(Fe0.5Nb0.5)O3.

Subsolidus phase relations and crystallisation region of rutile in TiO2–BaO–B2O3

Subsolidus phase relations in the ternary system TiO2–BaO–B2O3 were analysed with X-ray diffraction. According to the constructed phase relations, 15 ternary phase regions were identified in the subsolid phase, in which 11 binary compounds and 2 ternary compounds were investigated in detail. Additionally, the crystallisation region of rutile was identified, and it was found that rutile crystal with dimension of 10×4×2 mm was grown through spontaneous nucleation from a new flux BaO–B2O3.

Photoluminescence properties of Dy3+-doped oxyfluoride germanosilicate optical glass-ceramics

Dy3+-doped oxyfluoride germanosilicate glass and glass-ceramics were fabricated using a GeO2–SiO2–Al2O3–B2O3–BaO–BaF–Dy2O3 system. Differential thermal analysis, X-ray diffraction, and photoluminescence spectra were carried out to study the effects of the concentration of F− ions and the heat treatment on structure and optical properties of the samples. The results showed that the glass has the strongest luminescence intensity when BaF2 totally substitutes BaO. Moreover, Ba3AlF9 nanocrystal was formed in the glass matrix after being heat treated at 560–600°C for 2–8h. The glass after heat treatment had stronger intensity of luminescence than the precursor glass. The intensity of luminescence reaches an optimum when it was heat treated at 580°C for 4h.

Glasses for laser joining of zirconia ceramics

Abstract Laser joining of ZrO2 ceramics using glasses and glass ceramics as sealing components requires optimized systems. The ternary systems SiO2–BaO–B2O3 and BaO–SrO–SiO2 were selected as a basis for development of suitable glass compositions for the laser joining process. Additives such as CaO, TiO2, Al2O3, and MgO were used to control the crystallization processes and hence the thermal expansion coefficients during glass synthesis. The glass viscosity, the strength of the ceramic-glass-ceramic joint, and the joint tightness are other important glass properties which were optimized for the laser process. For glass G018-345, this yielded strengths of up to 225 MPa (Weibull modulus of m = 8.6) and He leak rates of up to 4.3 × 10−5 mbar l s−1. Because of the varying viscosities obtained, the optimized glass systems could be used selectively in a temperature range of 700–900 °C.

Creep rupture of the joint of a solid oxide fuel cell glass–ceramic sealant with metallic interconnect

Creep properties of sandwich joint specimens made of a newly developed BaO–B2O3–Al2O3–SiO2 glass–ceramic sealant (GC-9) and a ferritic-stainless-steel interconnect (Crofer 22 H) for planar solid oxide fuel cells (pSOFCs) are investigated at 800 °C under constant shear and tensile loadings. The creep rupture time of Crofer 22 H/GC-9/Crofer 22 H joint specimens is increased with a decrease in applied load for both shear and tensile loading modes. The given metal/sealant/metal joint has a greater degradation of joint strength at 800 °C under prolonged, constant tensile loading as compared to shear loading. The tensile creep strength at a rupture time of 1000 h is about 9% of the average tensile joint strength, while the shear creep strength at 1000 h is about 23% of the average shear joint strength. Failure patterns of both shear and tensile joint specimens are similar regardless of the creep rupture time. In general, creep cracks initiate at the interface between the (Cr,Mn)3O4 spinel layer and the BaCrO4 chromate layer, penetrate through the BaCrO4 layer, and propagate along the interface between the chromate layer and glass–ceramic substrate until final fracture. Final, fast fracture occasionally takes place within the glass–ceramic layer.

Structure, phase formation, and wetting behavior of BaO–SiO2–B2O3 based glass–ceramics as sealants for solid oxide fuel cells

In the present study, glasses from the three different compositional triangles in the BaO–B2O3–SiO2 system with fixed B2O3/SiO2 ratio and different BaO/SiO2 molar ratios (designated as Ba32, Ba37, and Ba42) were prepared, and suitability of them as sealant in solid oxide fuel cells were investigated. Structure of the glasses was characterized with Raman spectroscopy. According to the results, the structure of the glass with 32 % molar BaO (Ba32) predominantly consisted of Q2 structural species. In glasses with 37 and 42 % molar BaO (Ba37 and Ba42), with the substitution of SiO2 by BaO, distribution of Qn units widened, silicate glass network depolymerized, and concentration of Q1 structural units increased at the expense of Q2 units. X-ray diffraction analyses revealed that in samples Ba32 and Ba37, initially, Ba3Si5O13 and Ba5Si8O21 phases were crystallized, respectively, and it seemed they acted as the sites for the subsequent growth of BaSi2O5 phase. In contrast, the dominant phase in sample Ba42 was Ba2Si3O8. Sintering, wetting, and crystallization behavior of the glasses were studied using hot-stage microscopy and differential thermal analysis, respectively. Delay in the crystallization accompanied by depolymerization of the structure led into deformation at lower temperatures and greater wettability on the steel for Ba37 glass. All the glasses wetted AISI430 alloy at temperatures higher than 1,000 °C.

Microstructure and energy-storage performance of BaO–B2O3–SiO2 glass added (Na0.5Bi0.5)TiO3 thick films

(Na0.5Bi0.5)TiO3 lead-free thick films were successfully fabricated on alumina substrates via a screen printing method with 0–10 wt% BaO–B2O3–SiO2 glass addition. Microstructure, dielectric properties and energy-storage performance of the thick films were systematically investigated. The results show that the denser thick films were obtained by addition of glass. Thus, the breakdown strength, the energy-storage density and efficiency were greatly improved. The maximum recoverable energy-storage density and efficiency of sample with 1 wt% glass were 2.0 J/cm3 and 44.1 %, respectively. Meanwhile, a low leakage current density of about 10−6 A/cm2 was obtained for all samples at 100 kV/cm.

Microstructures, phases, and properties of low melting BaO–B2O3–ZnO glass films prepared by pulsed laser deposition

With the motivation to employ BaO–B2O3–ZnO for high performance capacitors by using viscous flow/liquid phase sintering, the microstructures, phases, and dielectric properties of BaO–B2O3–ZnO films prepared by pulsed laser deposition were examined as a function of heat-treatment. The glass transition temperature (Tg) and crystallization temperature of the films are ~536°C and 640°C, respectively. The phases in the films are quite complicated after heat-treated above 700°C until 900°C where the film is dominated by a single phase. Zn concentration is reduced after heat-treatment at high temperature due to segregation and evaporation. The dielectric constant of the film decreases with the increasing heat-treatment temperature, probably due to Zn reduction, Si diffusion, and crystallization of the film. Experimental data shows that ~700°C is the optimal temperature to use the low melting glass BaO–B2O3–ZnO to make high performance capacitors by viscous flow/liquid phase sintering.

Aging effects on high-temperature creep properties of a solid oxide fuel cell glass-ceramic sealant

Creep properties at 800 °C are investigated for a newly developed solid oxide fuel cell BaO–B2O3–Al2O3–SiO2 glass-ceramic sealant (GC-9) in variously aged conditions using a ring-on-ring test technique. GC-9 specimens are thermally aged at 750 °C for 4 h (designated as non-aged), 100 h, or 1000 h after sintering at 850 °C. Results show a longer thermal aging treatment leads to a higher crystallinity and greater creep resistance for the given glass-ceramic sealant. When subjected to an applied constant load at 800 °C, the 1000 h-aged GC-9 lasts much longer than the non-aged and 100 h-aged ones before rupture. The 1000 h-aged GC-9 also exhibits a creep strain rate much smaller than that in the non-aged and 100 h-aged samples. The value of creep stress exponent increases from 6 to 29 as the aging treatment time is increased from 4 h to 1000 h. The creep strength at a rupture time of 1000 h for the non-aged, 100 h-aged, and 1000 h-aged GC-9 is about 21%, 28%, and 39%, respectively, of the corresponding Weibull characteristic strength at 800 °C.

Growth and luminescent properties of (Lu–Y)AlO3:Ce single crystalline films

The work is dedicated to the development of scintillating screens based on single crystalline films (SCF) of Ce doped Lu–Y–Al perovskites grown by the liquid phase epitaxy method. We show in this work that Lu1−xYxAP:Ce SCF with very good structural and optical perfection can be grown from the PbO-based flux onto YAP substrates in all range of x-values. We also found the Lu1−xYxAP:Ce SCF can be crystallized by LPE method from the lead free BaO–B2O3–BaF2 flux onto YAP substrates in the range of x values up to 0.4 formula units.

Effect of borosilicate glasses on the microwave dielectric properties of ZnO–Nb2O5–Ta2O5 system

(1 − y)[0.5ZnNb2O6–0.5Zn3Nb2O8]–yZnTa2O6 with y = 0.91 (ZNT) ceramic have been prepared by conventional solid state ceramic route. The effect of glass additives on the microstructure, densification, and microwave dielectric properties of the ZNT ceramic for low temperature co-fired ceramic applications was investigated. Different weight percentages of quenched glass such as ZnO–B2O3–SiO2, BaO–B2O3–SiO2, LiO–B2O3–SiO2 and MgO–B2O3–SiO2 were added to ZNT powder. The crystal structure of the ceramic–glass composites was studied by X-ray diffraction and microstructure by scanning electron microscopy. The microwave dielectric properties such as relative permittivity (er), quality factor (Quxf) and co-efficient of temperature variation of resonant frequency (τf) of the ceramics have been measured in the frequency range 4–6 GHz. The 5 wt% ZnO–B2O3–SiO2 added ZNT ceramic sintered at 900 °C showed: er = 28.1, Quxf = 32820 GHz (at 4.92 GHz), and τf = −7.7 ppm/oC respectively.

Evaluation on Properties of CaO–BaO–B2O3–Al2O3–SiO2 Glass–Ceramic Sealants for Intermediate Temperature Solid Oxide Fuel Cells

To develop suitable sealants for intermediate temperature solid oxide fuel cells (IT-SOFC), glass–ceramics based on the CaO–BaO–B2O3–Al2O3–SiO2 system were studied. Coefficient of thermal expansion (CTE), glass transition temperature (Tg) and dilatometric softening point temperature (Td) of specimens were determined by means of dilatometer analysis and crystallization temperature was measured by differential thermal analysis (DTA). Also, crystallization behavior during prolonged heat-treatment and microstructure properties were studied by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Electrical properties were measured at different temperatures, and the results showed a high resistance (>104 Ω) at the SOFC operation temperature (600–800 °C). Moreover, mechanical properties of heat-treated specimens (1, 10, 30, 50 h) were measured. Microstructure investigation revealed a well-adhered bonding between the sealant glass–ceramic electrolyte and glass.

Phosphate glasses for optical fibers: Synthesis, characterization and mechanical properties

Phosphate glasses (P2O5–Al2O3–Li2O–B2O3–BaO–La2O3) are studied in the present work for the fabrication of passive optical fiber for amplifier and laser applications. Innovative phosphate glasses with large stability toward crystallization (more than 200°C), low transition temperatures (477°C) and low thermal expansion coefficient (10×10−6°C−1) have been successfully produced. Thermo-mechanical and optical properties of the glasses are presented and discussed with respect to the glass composition. Specific care was used to the design and fabrication of two glasses with adequate thermo-mechanical properties to be suitable in the fiber drawing process. Due to the inner surface quality of the tubes manufactured by the rotational casting, the fiber presents very high quality interface between the core and the cladding. Mechanical characterization of the obtained fibers allowed the evaluation of tensile strengths of the order of 200–500MPa and a Weibull modulus of about 10.

Effect of BBS‐Based Frit on the Low Temperature Sintering and Electrical Properties of KNN Lead‐Free Piezoceramics

Using BaO–B2O3–SiO2 (BBS)‐based frit as sintering aid, the K0.49Na0.51NbO3 (KNN) + x wt% BBS (x = 1.0, 1.5, 2.0 and 2.5) lead‐free piezoelectric ceramics were successfully fabricated by solid‐state reaction method under low‐sintering temperature of 1000°C. The effect of BBS frit doping amount on the structure and electrical properties of the ceramics was investigated. The KNN ceramics with 1.5 wt% BBS frit showed optimal properties as follows: piezoelectric constant d33 = 108 pC/N, planar electromechanical coupling coefficient kp = 41%, mechanical quality factor Qm = 225, relative dielectric constant εr = 410, dielectric loss tanδ = 0.57% and Curie temperature Tc = 400°C. This ceramic sample should be a good lead‐free candidate for actuators or high temperature sensors application due to its ultra‐low tanδ, relatively high Qm and Tc.

Erratum to: Structure and dielectric properties of BaO–B2O3–ZnO–[(BaZr0.2Ti0.80)O3]0.85 − [(Ba0.70Ca0.30)TiO3]0.15 glass–ceramics for energy storage

Alkali-free [0.10 BaO + 0.4 B2O3 + 0.5 ZnO], [0.3 BaO + 0.6 B2O3 + 0.1 ZnO] glass powder materials were mixed with [(BaZr0.2Ti0.80)O3]0.85 − [(Ba0.70Ca0.30)TiO3]0.1—BZT–BCT ceramic materials for energy density storage capacitor applications. Calcined (1,250 °C/10 h) BZT–BCT ceramic powder materials were mixed with (15 wt. %) two different glass compositions of [0.10 BaO + 0.4 B2O3 + 0.5 ZnO], [0.3 BaO + 0.6 B2O3 + 0.1 ZnO] separately and were ground using low energy ball milling for 2 h at 400 rpm. The ball milled powders were made into discs having 13 mm diameter and 0.5 mm thickness using hydraulic press (2 ton) and sintered at 900 °C for 2 h. Both the compositions have shown dielectric breakdown field strength ~260, 280 kV/cm and energy density values ~1.118 and 0.50 J/cm3.

Phase formation and properties of the BaO–B2O3–SiO2 and –Al2O3 ceramics prepared via an aqueous suspension route

The low-temperature sintering ceramics based on the eutectic systems BaO–B2O3–SiO2 and –Al2O3 are fabricated by an aqueous suspension process at a sintering temperature of 900–940oC. Sintering mechanism and physical properties, e.g., dielectric and thermal properties, of the low-temperature sintering ceramics have been investigated and discussed in detail in terms of their mineral phase compositions. The results indicate that the barium borate compounds with low melting characteristics can be easily obtained by the chemical combination of Ba(OH)2·8H2O and an aqueous solution of H3BO3. In turn, the presence of the BaO–B2O3 composition in the low-temperature sintering ceramics can supply a liquid phase sintering aid for the mineral phase formation and the achievement of densification sintering. The addition of a SiO2 component to the BaO–B2O3 composition can cause the emergence of barium silicate phases and consequently achieves high coefficients of thermal expansion (11–17ppmoC−1), whereas the introduction of an Al2O3 component to the BaO–B2O3–SiO2 composition can result in the formation of a hexacelsian phase, which can achieve a low permittivity and loss (permittivity: 7.1–7.4; loss: 5–7×10−4). The work may be referenced for the fabrication of LTCC materials with tailored physical properties.

Structure and dielectric properties of BaO–B2O3–ZnO–[(BaZr0.2Ti0.80)O3]0.85 − [(Ba0.70Ca0.30)TiO3]0.15 glass–ceramics for energy storage

Structure and dielectric properties of BaO–B2O3–ZnO–[(BaZr0.2Ti0.80)O3]0.85 − [(Ba0.70Ca0.30)TiO3]0.15 glass–ceramics for energy storage

Modification in structural and optical properties of CeO2 doped BaO–B2O3 glasses

Abstract BaO–B2O3 glasses containing different concentrations of CeO2 (ranging from 0 to 10 mol%) is prepared. It has been shown from X-ray diffraction that these samples have amorphous nature. UV–Visible spectroscopic studies reveal the presence of Ce4+ groups of cerium. Infrared spectroscopic measurements are carried out for the undoped and CeO2 doped samples which confirm the conversion of three fold borate BO3 to tetrahedral BO4 groups. The density of the glasses increases (2.81–3.43 g/cm3) with the addition of CeO2 in these glasses. The changes caused by the addition of CeO2 on the structure and optical properties of these glasses have been observed.