Effects of the Addition of Different Types of Fillers on the Properties of BaO–ZnO–B2O3–SiO2 Glass Composites for Application to Barrier Ribs of Plasma Display Panels

Various types of crystalline ceramic fillers (TiO₂, ZrO₂, Al₂O₃, MgO, and cordierite) were added to BaO–ZnO–B₂O₃–SiO₂ (BZBS) glass (5–20 wt%), and the resultant dielectric constant, coefficient of thermal expansion (CTE), and optical reflectance were investigated for the application of the composites to the barrier ribs in plasma display panels. All the investigated fillers were partially dissolved into the glass at the fabrication temperature (575°C), and the residual fillers were aligned along the boundaries of sintered glass frits. By considering all aspects of the properties, the addition of TiO₂ fillers of about 10 wt% to BZBS glass was the most desirable of the types of fillers investigated. The addition of TiO₂ filler (10 wt%) yielded 61% in optical reflectance, 8.3 × 10⁻⁶ K^–1 in coefficient of thermal expansion, and 15.5 in dielectric constant, which were properties comparable with the currently used Pb-based barrier ribs.     

Low-Temperature Sintering and Microwave Dielectric Properties of Anorthite-Based Glass-Ceramics

TiO₂ nucleated anorthite-based glass-ceramics were fabricated from glass powders. After sintering and crystallization heat treatment, various physical properties, including apparent bulk density and water absorption, were examined to evaluate the sintering behavior of anorthite-based glass-ceramic. Results showed that the complete-densification temperature for specimens was as low as 900°C. Sufficient crystallization was achieved by subsequently raising the firing temperature to 950°C, and the dielectric quality factor was promoted to the maximum value. Contents of nucleating agent (TiO₂) played an important role in the dielectric constants. The crystallinity was controlled by raising the firing temperature at a constant heating rate. The degree of crystallization affected the dielectric properties of sintered glass-ceramics. At the resonant frequency of 10 GHz, anorthite glass-ceramics with 5 wt% TiO₂ possessed the lowest permittivity of 8 and exhibited appropriate dielectric properties as compared with those with B₂O₃ and 10 wt% TiO₂.     

Synthesis of Pb(Mg1/3Nb2/3)O3 in Excess Lead Oxide by Mechanical Activation

Twenty hours of mechanical activation of mixed oxides at room temperature led to the formation of Pb(Mg_1/3Nb_2/3)O₃ (PMN) in excess PbO. The crystallinity of the activation-derived perovskite PMN phase was further established when the activated PMN–PbO phase mixture was subjected to calcination at 800°C. Pyrochlores, such as Pb₃Nb₄O₁₃ and Pb₂Nb₂O₇, were not observed as transitional phases on mechanical activation and subsequent calcination, although 50% excess PbO was deliberately added. The perovskite PMN phase was recovered by washing off excess PbO using acetic acid solution at room temperature. It was sintered to a relative density of 98.9% of theoretical at 1200°C for 1 h and the sintered PMN exhibited a dielectric constant of ∼14 000 at 100 Hz and a Curie temperature of −11°C.     

Co-Additions of TiO2 and SiO2 Crystalline Fillers to Tailor the Properties of BaO–ZnO–B2O3–SiO2 Glass for Application to Barrier Ribs of Plasma Display Panels

The influence of co-additions of crystalline TiO₂ and SiO₂ fillers (10 wt% addition in total) to BaO–ZnO–B₂O₃–SiO₂ glass on resultant properties was investigated from the viewpoint of applying the material to the barrier ribs of plasma display panels. The substitution of SiO₂ for TiO₂ reduced the dielectric constant significantly, while it maintained high optical reflectance and appropriate coefficient of thermal expansion (CTE) in the case when TiO₂ alone was used. A 5–7.5 wt% SiO₂ addition with 2.5–5 wt% TiO₂ under the constraint of 10 wt% total fillers demonstrated an optical reflectance of about 55%, a CTE of about 8.3 × 10⁻⁶ K⁻¹ (compatible with glass panels), and a dielectric constant of about 7.5, which are promising properties for the barrier rib application.     

Effect of Glass Additions on BaO–TiO2–WO3 Microwave Ceramics

The effect of glass addition on the properties of BaO–TiO₂-WO₃ microwave dielectric material N-35, which has Q = 5900 and K = 35 at 7.2 GHz for samples sintered at 1360°C, was investigated. Several glasses including B₂O₃, SiO₂, 5ZnO–2B₂O₃, and nine other commercial glasses were selected for this study. Among these glasses, one with a 5 wt% addition of B₂O₃ to N-35, when sintered at 1200°C, had the best dielectric properties: Q = 8300 and K = 34 at 8.5 GHz. Both Q and K increased with firing temperature as well as with density. The Q of N-35, when sintered with a ZnO–B₂O₃ glass system, showed a sudden drop in the sintering temperature to about 1000°C. The results of XRD, thermal analysis, and scanning electron microscopy indicated that the chemical reaction between the dielectric ceramics and glass had a greater effect on Q than on the density. The effects of the glass content and the mixing process on the densification and microwave dielectric properties are also presented. Ball milling improved the densification and dielectric properties of the N-35 sintered with ZnO–B₂O₃.     

Effect of Alkali Metal Oxide Addition on the Sinterability of MgO–B2O3–Al2O3 Glass–Al2O3 Filler Composites

The sintering of a composite of MgO–B₂O₃–Al₂O₃ glass and Al₂O₃ filler is terminated due to the crystallization of Al₄B₂O₉ in the glass. The densification of a composite of MgO–B₂O₃–Al₂O₃ glass and Al₂O₃ filler using pressureless sintering was accomplished by lowering the sintering temperature of the composite. The sintering temperature was lowered by the addition of small amounts of alkali metal oxides to the MgO–B₂O₃–Al₂O₃ glass system. The resultant composite has a four-point bending strength of 280 MPa, a coefficient of thermal expansion (RT—200°C) of 4.4 × 10⁻⁶ K⁻¹, a dielectric constant of 6.0 at 1 MHz, porosity of approximately 1%, and moisture resistance.     

Thermal, Dielectric, and Optical Properties of Neodymium Borosilicate Glasses for Thick Films

Because of their thermal, dielectric, and optical properties, new glass compositions and thick-filmed transparent dielectrics containing neodymium oxide (Nd₂O₃) were studied as a source of purer images in plasma display panels. In the present study, PbO–B₂O₃–SiO₂ and PbO–B₂O₃–SiO₂–ZnO–Al₂O₃ were used as starting glass compositions, to which up to 25 wt% of Nd₂O₃ then was added. Increased amounts of Nd₂O₃ increased the glass transition temperature and dielectric constant of the bulk glasses and decreased the coefficient of thermal expansion. The fired thick films (around 30 μm) allowed selectively visible light to penetrate and showed deep absorption properties at 585 nm that were related to an extraneous gas from neon discharge.     

Refiring Performance of Calcium Aluminoborosilicate-Based Dielectrics

Two dielectric materials consisting of a zinc calcium aluminoborosilicate glass with either an Al₂O₃ or a CaTiO₃ filler were selected to investigate the sensitivity of refirings at a fixed temperature of 850°C to the final physical and dielectric performance. The property changes with refirings depended on the type of filler material and the number of refirings. For example, crystallization of the unexpected ZnAl₂O₄ phase was found to progress further on increasing the number of refirings in the case of the Al₂O₃ filler sample. The five refirings of the sample resulted in a decrease of the dielectric constant from 8.46 to 8.06 at 1 MHz. The case of the CaTiO₃ filler can be highlighted with the opposite increasing effect of the dielectric constant as the crystalline CaTiSiO₅ phase evolved further with refirings.     

Effects of La2O3/ZnO Additives on Microstructure And Microwave Dielectric Properties of Zr0.8Sn0.2TiO4 Ceramics

Dielectric ceramics of Zr_0.8Sn_0.2TiO₄ containing La₂O₃ and ZnO as sintering aids were prepared and investigated for microstructure and microwave dielectric properties. Low-level doping with La₂O₃ and ZnO (up to 0.30 wt%) is good for densification and dielectric properties. These additives do not affect the dielectric constant and the temperature coefficient. Dielectric losses increase significantly at additive levels higher than 0.15 wt%. The combined additives La₂O₃ and ZnO act as grain growth enhancers. With 0.15 wt% additives, a ceramic having a dielectric constant, a quality factor, and a temperature coefficient of frequency at 4.2 GHz of 37.6, 12 800, and –2.9 ppm/°C, respectively, was obtained. The quality factor was considerably improved by prolonged sintering.     

Characterization and Crystallization of Y-Si-Al-O-N Glass

Glasses were prepared from sintered powders ofSi₃N₄, Al₂O₃, Y₂O₃ AlN, andSiO₂ to study their crystallization on subsequent heat treatment. Appreciable crystallization was efected only after the glasses were doped with up to 5 wt% ZrO₂. Electron microscopy and microanalysis showed that the crystalline phase was Y₂O₃·2SiO₂ without detectable Zr. The sofening temperature is in the range 850° to 1020°C. In-situ heating in a high-voltage electron microscope at ∼12OO°C produced renucleation and growth of the crystalline phase; at higher temperatures, however, the glass phase volatilized.     

Crystallization of Bismuth Borosilicate-Based Dielectric Thick Films on a LiZn Ferrite Substrate

The compatibility and crystallization of dielectric thick films, consisting of a bismuth borosilicate glass and crystalline cordierite, on a LiZn ferrite substrate were investigated by focusing on phase development and microstructural changes. Significant diffusion of Li and Fe from the substrate to the dielectric was confirmed as unexpected crystalline phases such as Li₂Al₂Si₃O₁₀ and Fe₂O₃ were found in the thick films fired at 850°C. The crystallization was believed to be initiated from the film interface and developed further toward the film surface as evidenced from cross-sectional microstructures of the films with additional firings. The degree of crystallization and the relative contents of the observed phases were dependent on the ratio between the glass and cordierite and the number of refirings.     

Nucleation and Crystallization of a Lead Halide Phosphate Glass by Differential Thermal Analysis

The nucleation and crystallization mechanisms of a lead halide phosphate glass [40P₂O₅·30PbBr₂·30PbF₂ (mol%)] were investigated by differential thermal analysis (DTA) and X-ray diffraction analysis. There were two crystalline phases in the crystallized samples: the major phase was PbP₂O₄, and the minor phase was PbP₂O₆. The average activation energy for crystallization, E , for two different particle sizes of this glass was determined to be 119 ± 4 kJ/mol by the Kissinger method and 124 ± 4 kJ/mol by the Augis–Bennett method. The Avrami constants were determined to be 1.6 and 2.5 for particle sizes of 203 and 1040 μm, respectively, by the Ozawa equation, and 1.7 and 2.4 for particle sizes of 203 and 1040 μm, respectively, by the Augis–Bennett equation. The decrease in the crystallization peak height in the DTA curve with increasing particle size suggested that the particles crystallize primarily by surface crystallization. A nucleation-rate type curve was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/ T _p, or the height of the crystallization peak, (δ T )_p, as a function of nucleation temperature, T _n. The temperature where nucleation can occur for this glass ranges from 360°–450°C and the maximum nucleation rate is at 420°± 10°C.     

Dielectric Studies of Some Borate and Phosphate Glasses

Some borate glasses, with sag points of 350° to 500°C., of high specific resistance and low power factor have been prepared. The power factor of the glasses has been measured to 250° C., and the resistivity has been measured up to temperatures approaching the transformation region. Borate glasses have higher resistivities and power factors than phosphate glasses. An increase in sag point of lead borate glasses by substitution of PbO with BaO, Al₂O₃, or SiO₂ improves their dielectric properties. Depending on the type of glass, the dielectric constant varies linearly with the density of the glass.     

Effect of P2O5 on the Crystallization of Lead Silicate Glasses

The effect of P₂O_S on the devitrification of binary lead silicate glasses containing 64 and 59 mol% PbO was studied. Glasses underwent isothermal crystallization treatments at 400°, 450°, 500°, and 550°C. A polymorph of 3PbO₂SiO₂ was the major product of crystallization for all compositions of glasses. Secondary products of crystallization were found to be a polymorph of PbOSiO₂ in the 59 mol% and a low-temperature polymorph of 2PbOSiO₂ in the 64 mol% PbO glasses. Dominant mode of crystallization in both binary glasses was surface devitrification at all temperatures studied. Addition of P₂O₅ promoted internal crystallization in the form of spherulites. 400°C was found to be the most effective temperature for nucleating spherulitic growth. Crystallization at 400°C led to high concentrations of spherulites in all glasses containing at least 0.5 mol% P₂O₅. Concentrations of 0.5 mol% P₂O₅ were needed to produce detectable levels of spherulitic nucleation at r<400°C.     

Effect of Silicon Carbide Additions on the Crystallization Behavior of a Magnesia-Lithia-Alumina-Silica Glass

Glass in the MgO-Li₂O-A1₂O₃-SiO₂ system was observed to crystallize readily at temperatures from 700° to 900°C. The primary crystalline phase evolved was Li₂Si₂O₅, and the secondary phase evolved was Li₂SiO₃. The glass was amorphous after heating in air at 1050°C for 30 min. The addition of 0.5 wt% SiC powder resulted in the crystallization of Li₂SiO₃ during heating in air at 1050°C for 30 min. It was suggested that the difference in crystallization behavior with Sic addition was due to dissolution of Sic into the oxide glass.     

Phase Evolution and Microwave Dielectric Properties of Lanthanum Borate-Based Low-Temperature Co-Fired Ceramics Materials

A new potential low-temperature co-fired ceramics (LTCC) system based on a simple lanthanum borate (La₂O₃–B₂O₃) glass was investigated with regard to phase development and microwave dielectric properties as functions of alumina filler content less than 50 wt% and firing temperature up to 1050°C. Unexpected crystalline phases, such as La(BO₂)₃, LaAl_2.03(B₄O₁₀)O_0.54, LaBO₃, and Al₂₀B₄O₃₆, developed during the firing process are likely responsible for substantial resultant changes in physical and microwave dielectric properties. As a specific example, a high-quality factor of 785 at 15.8 GHz obtained for a composition containing 30 wt% alumina supports the hypothesis that the phase-dielectric property relation exists in this LTCC system. On a practical basis, two phases of LaAl_2.03(B₄O₁₀)O_0.54 and LaBO₃ must be important in determining the final dielectric performance by manipulating the ratios of glass and filler and by selecting a desirable temperature.     

Single-Calcination Synthesis of Pyrochlore-Free 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 and Pb(Mg1/3Nb2/3)O3 Ceramics Using a Coating Method

A coating approach for synthesizing 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (0.9PMN–0.1PT) and PMN using a single calcination step was demonstrated. The pyrochlore phase was prevented by coating Mg(OH)₂ on Nb₂O₅ particles. Coating of Mg(OH)₂ on Nb₂O₅ was done by precipitating Mg(OH)₂ in an aqueous Nb₂O₅ suspension at pH 10. The coating was confirmed using optical micrographs and zeta-potential measurements. A single calcination treatment of the Mg(OH)₂-coated Nb₂O₅ particles mixed with appropriate amounts of PbO and PbTiO₃ powders at 900°C for 2 h produced pyrochlore-free perovskite 0.9PMN–0.1PT and PMN powders. The elimination of the pyrochlore phase was attributed to the separation of PbO and Nb₂O₅ by the Mg(OH)₂ coating. The Mg(OH)₂ coating on the Nb₂O₅ improved the mixing of Mg(OH)₂ and Nb₂O₅ and decreased the temperature for complete columbite conversion to ∼850°C. The pyrochlore-free perovskite 0.9PMN–0.1PT powders were sintered to 97% density at 1150°C. The sintered 0.9PMN–0.1PT ceramics exhibited a dielectric constant maximum of ∼24 660 at 45°C at a frequency of 1 kHz.     

Reactions and Microstructure Development in Mullite Fibers

Microstructural and compositional changes during heat treatment of sol–gel-derived mullite fibers with additions of 2 wt% B₂O₃, 2 wt% P₂O₅, 2 wt% Cr₂O₃, and (1 wt% P₂O₅+ 1 wt% Cr₂O₃) were compared with those of undoped mullite fibers. For all compositions the sequence of phase development was the crystallization of a spinel phase (†-Al₂O₃ or Al–Si spinel) from amorphous material, followed by the formation of mullite at higher temperatures. Differential thermal analysis showed that additions of B₂O₃ and P₂O₅ increased the temperature of spinel formation and that B₂O₃ significantly decreased the temperature of mullite formation. After 1 h at 1200°C, the size of mullite grains in fibers that contained B₂O₃ was less than 1000 Å the grains in fibers of other compositions were 6000 to 12000 Å. After 60 h at 1400°C, fibers modified with B₂O₃ had a grain size less than 2000 to 3000 Å the grains in fibers of other compositions were 6000 to 12000 Å. B₂O₃ was the most volatile additive.     

Crystallization of MgO-CaO-SiO2-P2O5 Glass

The crystallization behavior of a glass with a composition of 40 wt% 3CaO · P₂O₅−60 wt% CaO · MgO · 2SiO₂ was investigated. The primary crystalline phase was apatite with a dendritic form and ellipsoidal shape. β-(3CaO · P₂O₅) and CaO · MgO · 2SiO₂ were crystallized as samples heated to 990°C, and a three-layer structure was obtained. The development and morphology of this construction were explained by both the surface crystallization of the apatite and CaO · MgO · 2SiO₂ and the bulk crystallization of apatite and the CaO · MgO · 2SiO₂-β-(3CaO · P₂O₅) composite.     

Crystallization of Anorthite-Seeded Albite Glass by Solid-State Epitaxy

Stoichiometric albite glass (NaAlSi₃O₈) was seeded with 5 wt% crystalline anorthite (CaAl₂Si₂O₈) to make albite glass-ceramics. The epitaxial crystallization of the albite glass to the glass-ceramics was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). High albite was observed as the major crystallization product over the temperature range of 800–1200°C. No crystalline albite could be crystallized from pure albite glass without seeds. Small amounts of nepheline (NaAlSiO₄), however, crystallized along with albite after heat treatments at temperatures lower than 1000°C. The platelike microstructure of albite crystals was revealed in the seeded glasses. The albite blades grew epitaxially from the anorthite seeds, and the Ca content decreased in the direction away from the seeds. The degree of crystallization and the grain size were dependent upon the heat treatment conditions. By increasing the particle size of the seed, the crystallization process was retarded and the resultant microstructure was degraded. The seeding efficiency was also lowered by adding nonisostructural hexagonal anorthite seeds which produced less albite but more nepheline crystals. Crystallization of albite glass by seeding with 5 wt% anorthite is much greater than with the surface nucleation which takes place in a homogeneous 95 wt% albite + 5 wt% anorthite glass.