Preparation of the LTCC composite ceramics with low permittivity

In this work, the LTCC composite ceramics containing ??-alumina and quartz based on the binary system BaO?CB₂O₃ were prepared by traditional solid-state preparation process at a sintering temperature of 900 °C. Sintering mechanism and physical properties of the LTCC composite ceramics are investigated and discussed in detail in terms of their mineral phase composition. The results indicate that, by the chemical combination of barium hydroxide octahydrate and an aqueous solution of boric acid, a barium borate phase can be formed form the binary system BaO?CB₂O₃ and consequently supply a liquid sintering aid for the fabrication of LTCC composite ceramics at a sintering temperature of 900 °C. The introduction of ??-alumina to the binary system BaO?CB₂O₃ can improve the sintering behavior whereas the presence of quartz in the composite ceramics is important to achieve low permittivity. By the combination of ??-alumina, quartz and BaO?CB₂O₃ composition, the dense LTCC composite ceramics, which is characterized by excellent dielectric properties (permittivity: 3.56; 4.83; dielectric loss: 3 × 10^?4; 4 × 10^?4), can be fabricated availably.     

Preparation and characterization of magnesium-aluminium-silicate glass ceramics

Synthesis of machinable quality magnesium aluminium silicate (MgO-Al₂O₃-SiO₂) for fabrication of insulators/spacers usable in high voltage applications under high vacuum conditions has been carried out following two different routes i.e. (i) sintering route, and (ii) glass route. A three-stage heating schedule involving calcination, nucleation and crystallization, has been evolved for the preparation of magnesium aluminium silicate (MAS) glass ceramic with MgF₂ as a nucleating agent. The effect of sintering temperature on the density of compacted material was studied. Microstructure and machinability of samples obtained from both routes were investigated. They were also characterized for microhardness. Initial studies on material obtained by glass route reveal that these samples are superior to those obtained from sintered route in respect of their high voltage breakdown strength and outgassing behaviour. Outgassing rate of 10⁻⁹ Torr l·s⁻¹ cm⁻² and breakdown strength of 160 kV/cm were obtained. Different types of spacers, lugs, nuts and bolts have been prepared by direct machining of the indigenously developed glass ceramic.     

Radiation dosimetry by potassium feldspar

The thermoluminescence (TL) properties of raw and annealed feldspar have been studied for their use in gamma dosimetry. The raw gamma exposed feldspar shows glow peaks at 120°C and 319°C. Gamma dose beyond 500 cGy can be measured without any significant fading even after 40 days of termination of exposure. The annealed feldspar shows a glow peak at 120°C after gamma exposure. This peak can be used to measure gamma doses beyond 25 cGy when the TL is measured after 24 h from termination of exposure.     

Tape casting of AlN/glass composites for LTCC substrate

AlN/glass composite is low-fired substrate material for microelectronic packaging material. In this work, AlN/glass sheets were prepared by tape casting process. The dispersion, stabilization and the rheological properties of the slurry were studied. The optimum drying condition and mechanisms of debinding were also investigated. The results showed that powder size influenced the optimum content of dispersant and the viscosity of slurry. The slurry for tape casting exhibited a typical shear-thinning behavior. Smooth green tape without cracking was acquired after it was dried at solvent atmosphere. The binder was fully burned out at 600°C at low heating speed. The lamination with uniform microstructure was achieved by hot-pressed at 900°C.     

Fatigue strength testing of LTCC and alumina ceramics bonds

In this paper the results of fatigue strength tests of ceramic joints are presented. These tests have been performed on the samples subjected to thermal and vibration fatigue as well as on the reference samples without any additional loads. The main goal of the investigation was to determine the strength of hybrid ceramics joints using tensile testing machine. The experiment enabled evaluation of fatigue effects in the mentioned joints. Geometry of test samples has been designed according to FEM simulations, performed in ANSYS FEM environment. Thermal stress as well as the stress induced by vibrations have been analyzed in the designed model. In the experiments two types of ceramics have been used ?? LTCC green tape DP951 (DuPont) and alumina ceramic tape. The samples have been prepared by joining two sintered ceramic beams made of different types of material. The bonds have been realized utilizing low temperature glass or a layer of LTCC green tape.     

Production and characterization of glass ceramics from steelwork slag

Glass and glass ceramics were obtained using steelwork slag as a raw material. Glass was melted at 1500°C and heat treatments were performed at 720°C for nucleation and at 883°C for crystallization. Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM), with energy dispersive X-ray spectrometer (EDX) were used to investigate glass and glass ceramics. The crystalline phases developed were diopside and augite. The final microstructure was made up of crystals uniformly distributed, with a size of 1 to 3.5 m.     

Preparation and doping modification of cerium oxide photosensitizers applied to photosensitive glass ceramics

CeO₂ nanoparticles doped with different types of Pr, Y, W and CaF₂ are prepared via a facile one-pot combustion method. Their crystallinity, particle size and absorption spectrum are investigated by X-ray diffraction (XRD), grading analysis and ultraviolet–visible spectroscopy (UV–Vis) absorption spectrum. Among the doped samples, W-doped CeO₂ (Ce_0.9W_0.1O₂) is selected out, which exhibits obvious red-shift of the absorption band as compared with the undoped CeO₂, achieving good match between the ceria absorption peak and the industrial 365 nm light source. Consequently, under the 365 nm exposure, the W-doped CeO₂ show more efficient reduction ability for Ag⁺ to Ag. The results indicate that W-doped CeO₂ is a very promising photosensitizer for photosensitive glass ceramics under industrial 365 nm light exposure, which can better absorb photons under UV light and then reduce Ag⁺ to elemental Ag.

     

Preparation and photoluminescence properties of fluorosilicate glass ceramics containing CeOF: Dy nanocrystals

The Ce³⁺ and Dy³⁺ co-doped oxyfluoride glasses and glass ceramics containing CeOF or CeF₃ nanocrystals have been prepared in the reducing atmosphere. The crystallinity increased significantly with the Ce³⁺ concentration, while the crystal size of nanocrystals is mainly influenced by the annealing temperatures. The glasses and glass ceramics emitted white light, deriving from a combination of the Ce³⁺ blue and the Dy³⁺ yellow light. The emission intensity and CIE chromaticity coordinates of the Ce³⁺ and Dy³⁺ co-doped glasses can be tuned by adjusting the ratio of Ce³⁺/Dy³⁺ concentration or the annealing temperature.     

低温烧结Al2O3-硅酸盐玻璃系玻璃陶瓷的制备和性能研究

采用Al2O3-硅酸盐玻璃复合体系制备低温烧结玻璃陶瓷，通过TG-DTA、XRD、SEM等分析方法对样品进行表征，随着玻璃含量的增加玻璃陶瓷的烧结温度逐渐降低，在玻璃含量约为50％（质量分数）时玻璃陶瓷的热导率达到最大值2．70W/m·K，此时的玻璃陶瓷具有低的烧结温度（800℃）、高的相对密度（≥95％）、低的电容率（8～10）、低的介电损耗（1．5％～0．7％），有望成为LED封装用基板材料。     

New heat treatment methods for glass removal from silicon nitride and sialon ceramics

Sialon ceramics were discovered simultaneously (but independently) in late 1971 at Newcastle University and also at the Toyota Research Laboratories in Japan. During the 30 years since their original discovery, the Newcastle laboratory has made a significant contribution to current understanding of the science and technology of these materials. Sialons are of interest as engineering materials for high temperature (>1000°C) applications because they can be pressureless-sintered to high density and be designed to retain good mechanical properties even up to 1350°C, whereas competing metallic materials are weaker and prone to corrosion. A characteristic disadvantage of all nitrogen ceramics is that an oxide additive is always included in the starting mix to promote densification, and this remains in the final product as a glassy phase distributed throughout the grain boundaries of the final microstructure. Since the glass melts at 1000°C, the high temperature properties of the final ceramic are in fact determined by the properties of the grain-boundary glass. The most common method of improving high-temperature performance is to heat-treat the material at temperatures of 1100–1350°C in order to devitrify the glass into a mixture of crystalline phases. More specifically it is desirable to convert the glass into a sialon phase plus only one other crystalline phase, the latter having a high melting point and also displaying a high eutectic temperature (max 1400°C) in contact with the matrix sialon phase. Previous studies have shown that there are a limited number of possible metal-silicon-aluminium-oxygen-nitrogen compounds which satisfy these requirements. The present paper gives an overall review of this subject area and then summarises recent work at Newcastle aimed at total removal of residual grain boundary glass. This has been achieved by: (1) a post-preparative vacuum heat treatment process to remove the grain boundary glass from silicon nitride based ceramics in gaseous form, (2) above-eutectic heat-treatment (AET) of sialon-based ceramics to crystallize grain-boundary liquid into five-component crystalline sialon phases.     

A new microwave dielectric ceramics for LTCC applications: Li2Mg2(WO4)3 ceramics

A novel microwave dielectric ceramics Li₂Mg₂(WO₄)₃ (LMW) for low-temperature co-fired ceramics (LTCC) application were prepared by the conventional solid-state sintering method. Densification, phases, microstructure and microwave dielectric properties of the Li₂Mg₂(WO₄)₃ ceramics were investigated. The optimal sintering temperature of dense Li₂Mg₂(WO₄)₃ ceramic approximately ranges from 825 to 875 °C for 3 h. The ceramic specimens fired at 875 °C for 3 h exhibits excellent microwave dielectric properties: ε _r  = 7.72, Q × f = 29,600 GHz (f = 6.0 GHz), and τ _f  = ?15.5 ppm/°C. Moreover, the Li₂Mg₂(WO₄)₃ ceramics has a chemical compatibility with Ag during cofiring, which makes it a promising ceramic for LTCC technology application.     

Lead-free piezoelectric ceramics manufactured from tantalum-substituted potassium sodium niobate nanopowders

Nanopowders of lead-free (K_0.5Na_0.5)(Nb_0.9Ta_0.1)O₃ (KNNT) system were prepared by high-energy ball milling at different milling times keeping the milling speed fixed at 250 rpm. The particle size first decreases from 35 nm to 3 nm and then increases to 98 nm as the milling time increases in steps of 5 h from 10 h to 30 h. Without using any sintering aid, dense ceramics were formed by sintering the powders at 1050 °C for 1 h. With decreasing particle size of the starting nanopowders, the ceramics exhibit gradual increase in density from 93.1% to 95.8%, coercive field (E_c) from 10.9 kV/cm to 15.1 kV/cm, electromechanical coupling factor (k_p) from 35% to 48%, and piezoelectric charge constant (d₃₃) from 80 pC/N to 128 pC/N. The systematic changes observed in these parameters corroborate the observed increase in particle size as the milling time increases from 25 h to 30 h.     

Dielectric behavior of perovskite glass ceramics

The recent developments of energy storage devices are concerned with larger energy storage ability, low loss and good temperature stability. It has a great technological importance in engineering science. The dielectric materials like ceramics and glass ceramics have great interest in electronic ceramic industry due to above concern. The ceramic dielectrics are used as a capacitive element in electronic circuits. The perovskite glass ceramics have very high dielectric constant and low dielectric loss. The high dielectric constant in glass ceramics is attributed to space charge polarization. In order to produce glass ceramics of high dielectric constant, barium titanate glass ceramics is the first discovered ferroelectric perovskite. In this review article, we are summarizing the dielectric behavior of perovskite glass ceramics such as BaTiO₃, SrTiO₃, PbTiO₃, (Ba,Sr)TiO₃ and (Pb,Sr)TiO₃.     

Structure and electromagnetic properties of LBBS glass added M-type Sr ferrites for LTCC technology

Journal of Materials Science: Materials in Electronics - Sr ferrites with x wt% Li2O–B2O3–Bi2O3–SiO2 glass (x for 0–2 wt%) calcined at 850 °C and...     

Preparation and dielectric properties of ceramics based on mixed potassium titanates with the hollandite structure

We have studied the crystallization of potassium polytitanates (PPTs) modified in aqueous solutions of salts of various transition metals. The results demonstrate that the modified materials crystallize in the form of solid solutions with the hollandite structure. Ceramic materials obtained using the PPT/Fe, PPT/Ni, and PPT/Co systems have high dielectric permittivity in the low-frequency region (ε ~ 10⁵), whereas PPT/Cu ceramics have lower ε (~10³), retaining it to a frequency of 1 MHz, and very low dielectric losses (tanδ ~ 10^–2).