Doping of iron phosphate glasses with Al2O3, SiO2 or B2O3 for improved thermal stability

The effects of doping 60 P₂O₅–40 Fe₂O₃ (mol%) glasses with 5–10 mol% SiO₂, Al₂O₃ or B₂O₃ on their thermal stability, iron environments and redox were investigated. Thermal stability improved markedly with 5% dopant addition in the order Al₂O₃ > SiO₂ > B₂O₃ ≫ base glass. Solubility of pro rata additions when melted at 1150 °C was 5–10% SiO₂, <5% Al₂O₃, and >10% B₂O₃. It was possible to dissolve 5% Al₂O₃ by replacing Fe₂O₃. These additions generally had little effect on dilatometric measurements and iron environments, however the Fe²⁺/ΣFe redox ratio increased in the order base glass < Al₂O₃ < SiO₂ < B₂O₃. This behaviour was broadly consistent with the effects of glass basicity. The increased thermal stability of these glasses may improve their suitability for applications such as waste immobilisation or sealing.     

Electrical and dielectric analysis of phosphate based glasses doped with alkali oxides

In this work, new phosphate glasses with the molar composition 20.7P₂O₅–17.2Nb₂O₅–13.8WO₃–34.5A₂O–13.8B₂O₃ where A = Li, Na and K were prepared using the melt quenching technique. These types of glasses have potential to absorb hydrogen in its structure, which makes them promising materials to be used as electrolytes in intermediate temperature fuel cells. Additionally, niobium phosphate glasses can also have applications such as glass fibers, optical lenses, hermetic sealing and electrodes. The structure of the obtained samples was analyzed using Differential Thermal Analysis (DTA), X-ray powder diffraction (XRD), and Raman spectroscopy and the morphology by Scanning Electron Microscopy (SEM). The DTA measurements revealed values of glass transition temperature around 415 °C, and the Raman analysis showed that the amount of alkali and niobium oxides included on the studied compositions, successfully disrupted the P–O–P chains characteristic of the phosphate glasses. Dc (σ_dc) and ac (σ_ac) conductivities and dielectric spectroscopy measurements were performed as function of the temperature (200–370 K) which presented conductivity predominantly ionic (σ_electronic/σ_ionic of about 10^− 4). The dielectric spectroscopy was measured in the frequency range 100–1 MHz.     

Sintering and crystallisation of vanadium doped CaO–ZrO2–SiO2 glass-ceramics

The effect of addition of V₂O₅ on densification and crystallisation of glass powder compacts in the system CaO–ZrO₂–SiO₂ has been investigated. A well crystallized material of relatively high density (95% of theoretical density) was obtained after sintering at 900 °C for 1 h by adding 5 mol% V₂O₅. Crystalline phases identified were wollastonite, calcium zirconium silicate and calcium zirconium oxide. The addition of V₂O₅ was shown to reduce the sintering temperature and also to enhance the electrical conductivity of the base CaO–ZrO₂–SiO₂ glass-ceramic. Possible applications of the present vanadium containing glass-ceramics are the production of coloured glazes and in coatings and enamels with “anti-static” behaviour.     

Low temperature sintering and microwave dielectric properties of zinc silicate ceramics

Effects of ZnO–B₂O₃–SiO₂ glass on the sintering behavior, the microstructure, and the microwave dielectric properties of Zn₂SiO₄ ceramics have been investigated. The ZnO–B₂O₃–SiO₂ glass lowered the sintering temperature of Zn₂SiO₄ ceramics effectively from 1300 to 900 °C. The X-ray diffraction results showed that the secondary phase of SiO₂ in the Zn₂SiO₄ ceramics could be dissolved in the glass. The dielectric constant decreased slightly, and the quality factor decreased with increasing glass content. Especially, when the glass content was chosen as 20 wt%, the ceramics sintered at 900 °C for 2 h exhibited a low dielectric constant of 6.85, a high quality factor of 31,690 and the temperature coefficient of the resonant frequency of −28 ppm/°C, which demonstrated a good potential for use in low temperature co-fired ceramics field.     

Preparation,phase structure and microwave dielectric properties of CoLi2/3Ti4/3O4 ceramic

A new low loss microwave dielectric ceramic with composition of CoLi_2/3Ti_4/3O₄ was prepared by a conventional solid-state reaction method. The compound has a cubic spinel structure [Fd-3m (227)] similar to MgFe₂O₄ with lattice parameters of a = 8.3939 Å, V = 591.42 Å³, Z = 8 and ρ = 4.30 g/cm³. This ceramic has a low sintering temperature (～1050 °C) and good microwave dielectric properties with relative permittivity of 21.4, Q × f value of 35,000 GHz and τ_f value of ?22 ppm/°C. Furthermore, the addition of BaCu(B₂O₅) (BCB) can effectively lower the sintering temperature from 1050 °C to 900 °C and does not induce much degradation of the microwave dielectric properties. Compatibility with Ag electrode indicates that the BCB added CoLi_2/3Ti_4/3O₄ ceramics are good candidates for LTCC applications.     

Microwave dielectric properties of Ba2Ti3Nb4O18 ceramic doped with ZnO–B2O3–SiO2 glass and its compatibility with silver electrode

The effects of ZnO–B₂O₃–SiO₂ glass (ZBS) additions on the sintering behavior and microwave dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramic have been investigated. Due to the liquid phase effects resulting from the additives, the addition of ZBS glass can reduce the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramic from 1,250 to 925 °C and induce no obvious degradation of the microwave dielectric properties. Typically, when 3wt% ZBS is added, a dense ceramic can be sintered at 925 °C with a ε_r of 33.2, a high of Q × f of 13,600 GHz and a low τ _f of −5.9 ppm/°C. Moreover, ZBS glass-added Ba₂Ti₃Nb₄O₁₈ ceramic has a chemical compatibility with silver electrode, which suggests that the ceramic could be applied to LTCC devices application.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Zirconia nucleating agent on microstructural and electrical properties of a CaMgSi2O6 diopside glass–ceramic for microwave dielectrics

Addition of different amount of zirconia (ZrO₂) nucleating agent into MgO–CaO–SiO₂ system to enhance the quality factor (Q × f) of CaMgSi₂O₆ diopside glass–ceramic for low sintering temperature process (from 850 to 950 °C) was carried out in this work. The microstructures, microwave dielectric properties and nucleating/growth mechanism of m-ZrO₂ added CaMgSi₂O₆ system were analyzed using transmission electron microscopy (TEM) and electrical property measurements. Experimental results demonstrate that a solid solution of an amorphous phase MgO–CaO–SiO₂ and ZrO₂ forms after melted at 1500 °C. The t-ZrO₂ appears in the amorphous matrix first and then crystalline CaMgSi₂O₆ particle grows up at around the boundary of t-ZrO₂ after thermal treatment at 850 °C due to heterogeneous nucleating. Formation of t-ZrO₂ is attributed to diffusion of Ca²⁺ to stabilize the m-ZrO₂. The quality factor of CaMgSi₂O₆ was significantly enhanced by adding 3 wt.% m-ZrO₂, indicating that the ZrO₂ nucleating agent could enhance crystallization and therefore increase the quality factor.     

Low-temperature sintering and microwave dielectric properties of CaTi1−x(Fe0.5Nb0.5)xO3 ceramics with B2O3 addition

CaTi_1−x(Fe_0.5Nb_0.5)_xO₃ (0 ≤ x ≤ 1) dielectrics were synthesized via the solid state reaction route and structure analysis was performed together with the dielectric characterization. The substitution of Ti⁴⁺ by Fe³⁺/Nb⁵⁺ and developed phase were studied by X-ray diffraction. The dielectric constant and temperature coefficient of resonant frequency decrease rapidly with an increase of x. The influence of 1–5 wt.% B₂O₃ as a sintering additive investigated at CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ solid solutions. The dielectric properties were found to strongly depend on the sintering conditions and contents of B₂O₃ additions. ɛ_r = 52.3, Q × f_o = 2930 GHz and T_f = 13 ppm/°C were obtained for CaTi_0.5(Fe_0.5Nb_0.5)_0.5O₃ specimen 3 wt.% B₂O₃ sintered at 900 °C for 2 h.     

Low temperature sintering and dielectric properties of Ba2Ti3Nb4O18 ceramics for silver co-sintering application

Low temperature sintering and dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with ZnO–B₂O₃–SiO₂ (ZBS) frit and lithium salts addition were investigated for silver co-sintering application. The sintering temperature of dense Ba₂Ti₃Nb₄O₁₈ ceramics with ZBS frit or LiNO₃ addition was effectively lowered to 950 or 1,000 °C, respectively. LiNO₃ is found to be more efficient than LiF or Li₂CO₃ to lower the sintering temperature of Ba₂Ti₃Nb₄O₁₈ ceramics. The sintering temperature of 900 °C was obtained for the Ba₂Ti₃Nb₄O₁₈ ceramics with a combination of ZBS frit and LiNO₃ addition. The dielectric properties of Ba₂Ti₃Nb₄O₁₈ ceramics with 1 wt.% ZBS and 0.5 wt.% LiNO₃ sintered at 900 °C are as follows: ε_r ~ 37.8, tan δ ~ 0.0003, τ_ε ~ 4.6 ppm/°C.     

Effect of B2O3 on the densification and magnetic properties of Li–Zn ferrite

Densification, grain growth and magnetic properties of Li–Zn ferrite (Li_.30Zn_.4Fe_2.30O₄) doped with B₂O₃ as a sintering aid were investigated. B₂O₃ is a low melting point (460 °C) oxide and forms a liquid phase during sintering which affects the densification and grain growth of ferrites. Results showed that density and grain growth rate were sensitive to the B₂O₃ content and sintering temperature. At low amounts of B₂O₃ (<1 wt.%), an increase in the B₂O₃ content increased density and grain growth rate. The highest density and the maximum magnetization were obtained for the sample containing 1.0 wt.% B₂O₃ which was sintered at a lower temperature (1000 °C) for 1.5 h, in comparison with undoped samples. Higher B₂O₃ contents than 1.0 wt.% caused a decrease in density of samples due to secondary phases formation and evaporation of B₂O₃. The sample with the highest grain size showed the highest permeability and the lowest magnetic loss.     

Linear and non-linear optics and FTIR characteristics of borosilicate glasses doped with gadolinium ions

Borosilicate glasses have been prepared using the high-temperature melt components of ingredients Gd₂O₃ doped borosilicate glasses. FTIR spectra were measured in the wavenumber range (4000–400 cm⁻¹) to explore the state and influence of Gd³⁺ ions in the structure of the glasses. Data indicated that B₂O₃ is acting as dual network formers (BO₃) and (BO₄) structural units whereas the gadolinium ions playing the role of network modifier in these glasses. Optical transmission spectra were recorded in the range 190–2500 nm and different optical parameters such as the direct and the indirect optical band gap, Urbach energy, refractive index and optical dielectric constant, have been determined. The molar refraction, electronic polarizability and the optical basicity results have been determined using the measured glass refractive indices. Gadolinium-doped borosilicate glasses are found to be characterized by different optical parameters.     

Thermal and structural characterization of erbium-doped borosilicate fibers with low silica content containing various amounts of P2O5 and Al2O3

We report results on the processing and characterization of different glass preforms and single core fibers within the SiO₂–Na₂O–B₂O₃–Er₂O₃–P₂O₅–Al₂O₃ system. Micro-Raman spectroscopy was used to identify post-draw structural modification. The differences in the micro-Raman spectra recorded on the preform and on the fiber glass were attributed to a change in the structure induced by the drawing process. Changes in the silicate network organization and small scale molecular orientation within the glass matrix are suspected to occur during the fiber drawing process. We found that the extent in the changes between the preform and fiber properties depend on the glass composition. The glass network of the Al-containing fiber is expected to be less sensitive to the drawing process than that of the fiber matrix as the network of this Al-containing fiber is formed by a larger number of Si-BO units in the network and neutral three-coordinated boron compared to the network of the fiber matrix. From the micro-Raman spectra, formation of small crystals is suspected to occur in the P-containing glasses during the fiber drawing process. The resulting fibers were found to have propagation losses at 1330 nm and Er³⁺ absorption between (7 ± 1) and (25 ± 1) dB/m and (36 ± 1) and (47 ± 1) dB/m, respectively, depending on the glass composition.     

CaAlSiN3:Eu2+ phosphors bonding with bismuth borate glass for high power light excitation

The CaAlSiN₃:Eu²⁺ red phosphor-in-glass was prepared using bismuth borate glass as the binder for high power light excitation. B₂O₃–Bi₂O₃–Al₂O₃–ZnO glass powder showed good sintering behavior with CaAlSiN₃:Eu²⁺ phosphors at around 550 °C. The phosphor-in-glass has flat surface with a thickness of about 100 μm. From the images of FE-SEM and confocal laser scanning microscope, the uniform distribution of phosphor particles inside the phosphor-in-glass was vividly and clearly observed. And the luminescent property of phosphors was not greatly affected by glasses, as shown in fluorescence spectra. When the volume radio of CaAlSiN₃:Eu²⁺ phosphors was 50%, the sample exhibited low thermal quenching and high flexural strength of 28.5 MPa. Compared YAG:Ce³⁺ phosphor-in-glass with CaAlSiN₃:Eu²⁺ phosphor-in-glass, we found bismuth borate glass had better wettability on YAG:Ce³⁺ particles, which caused a higher flexural strength of the YAG:Ce³⁺ phosphor-in-glass.     

New phospho-tellurite glasses with optimization of transition temperature and refractive index for hybrid microstructured optical fibers

The glass formation and compositional dependences of glass thermal properties and optical properties were investigated in TeO₂–ZnO–Na₂O–P₂O₅ system. The refractive index at 1.55 μm and glass transition temperature varied in a wide range from 1.513 to 2.036 and from 265 °C to 376 °C by controlling of the TeO₂/P₂O₅ and ZnO/Na₂O content, respectively. These properties enable phospho-tellurite glasses with large freedom in designing and fabrication of hybrid microstructured optical fiber. The structures of glasses were investigated by Raman spectra to understand their dependence of structure on composition. Using the present glasses, some hybrid microstructured optical fibers with various dispersion profiles were designed.     

Perovskite phase stabilization and dielectric properties of Pb(Zn1/3Ta2/3)O3–BaTiO3 ceramics

The phase structure and dielectric properties of (1 − x)Pb(Zn_1/3Ta_2/3)O₃–xBaTiO₃ (x = 0.00–0.40) ceramics were investigated. Pure perovskite is obtained when x ≥ 0.24. With increasing BT content, the diffuse phase transition and frequency dissipation of the dielectric constant increase and the dielectric maxima temperature decreases. It is related to the existing of Ba(Zn_1/3Ta_2/3)O₃ paraelectric microregions and the incomplete solid solution reaction between Pb(Zn_1/3Ta_2/3)O₃ and BaTiO₃.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.     

Low-firing of BiSbO4 microwave dielectric ceramic with V2O5–CuO addition

Effects of 1.0 wt.% V₂O₅–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO₄ ceramics have been investigated. BiSbO₄ ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V₂O₅–CuO mixtures addition with different ratios of CuO to V₂O₅. The formation of BiVO₄ phase and substitution of Cu²⁺ can explain the decrease of sintering temperature. Dense BiSbO₄ ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C^?1 and ?77.8 ppm °C^?1. BiSbO₄ ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.     

Influence of CuO addition to BaSm2Ti4O12 microwave ceramics on sintering behavior and dielectric properties

Microwave dielectric ceramics of tungsten–bronze-type BaSm₂Ti₄O₁₂ were prepared by doping CuO (up to 2 wt.%) as the liquid-phase sintering aid. The effects of CuO additive on the densification, micro structure and dielectric properties were investigated. Due to the liquid-phase effect, the sintering temperature of BaSm₂Ti₄O₁₂ ceramics with 1 wt.% CuO addition can be effectively reduced to 1160 °C, about 200 °C lower than that of pure BaSm₂Ti₄O₁₂ ceramics, while good microwave dielectric properties of ɛ_r = 75.8, Q*f = 4914.6 GHz and τ_f = −7.65 ppm/°C were still achieved.     

Characterization and electrochemical properties of P2O5–ZrO2–SiO2 glasses as proton conducting electrolyte

The H₂/O₂ fuel cell based on the proton conducting P₂O₅–ZrO₂–SiO₂ glasses was prepared by sol–gel technique. Structural characterization were carried out using X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (³¹P MAS NMR), N₂ adsorption–desorption analysis, differential thermal analysis (DTA) and thermal gravimetric analysis (TGA) and impedance measurements. The absorption bonds of Si–O–Si, Si–O–P and Si–O–Zr were observed in the P₂O₅–ZrO₂–SiO₂ glasses which were heat treated at 600 °C. A sample (5P₂O₅–4ZrO₂–91SiO₂, mol%) was selected as the electrolyte for the H₂/O₂ fuel cell test and yielded the maximum power density value of 8.5 mW/cm² using electrochemical measurements at 30 °C under relative humidity atmosphere.