Processing Effects on the Microstructure and Dielectric Properties of Barium Strontium Titanate (BST) Ceramics

Barium Strontium Titanate (BST) ferroelectric thick films have been investigated as potential candidates for use in frequency agile microwave circuit devices. Powder processing techniques such as screen-printing have been used to make BST thick films. However, due to the interactions between the BST and substrates such as alumina, the sintering temperatures for the BST thick films are limited and the resultant films are difficult to achieve full densification. In this paper, the effects of different powder processing conditions (calcination, sintering temperature and time) on the sintering behaviour and dielectric properties of the BST ceramics have been investigated. The dielectric behaviour of the ceramics has been correlated with composition and microstructural features such as chemical homogeneity, grain size and domain wall movements.     

Secondary electron emission and surface charging evaluation of alumina ceramics and sapphire

The breakdown of alumina rf windows is mostly caused by multipactor, as well as by material defects and contamination. Since multipator induces localized surface heating, leading to surface melting, it is necessary to observe secondary electron emission (SEE) coefficients of alumina ceramics under high temperature conditions. The SEE coefficients of commercial alumina ceramics and sapphire were measured by a scanning electron microscopy (SEM) with a single short-pulsed electron beam (100 pA, 1 ms) at room temperature and at 650degC. Additive materials used for sintering alumina, such as SiO ₂ and MgO, were also investigated. Surface charging evaluations have also become important because the accumulated charges are discharged at the threshold Held, resulting in surface discharge. The surface charging evaluations were carried out by multi-pulse measurements with the injection of successive pulses on the sample. As a result, reductions in the SEE coefficients with temperature were confirmed, except for sapphire. The multi-pulse measurement results indicated that surface charging of the sapphire was higher than that of other samples. This may be one of the factors that causes sapphire not to be durable for rf window applications, compared with alumina ceramics. Although there are few exceptions, it was found that the SEE coefficients of alumina ceramics increased with the purity and the average grain size     

烧结温度对氧化铝陶瓷介质陷阱分布的影响

论文采用等温衰减电流法研究了在不同烧结温度下制备的陶瓷试样的陷阱分布，试验结果表明，烧结温度能够影响到氧化铝陶瓷介质的陷阱分布，微观结构分析表明，不同的烧结温度会导致陶瓷介质不同数量的结构缺陷，从而造成了它们陷阱分布的不同。     

Development of epoxy resin composites with high thermal conductivity

High-performance central processing units (CPUs) and power devices such as IGBTs have high electrical power dissipation, which causes substantial heating. As a result, efficient cooling is essential for insulating materials within such devices. Although polymers such as epoxy resins are good insulating materials, they have quite low thermal conductivities, usually 1 to 3 orders of magnitude lower than those of ceramics and metals. Thus, the development of insulating resin with high thermal conductivity is mandatory if operating temperatures are to be increased.     

The fabrication of lead titanate ceramics by a two-stage sintering technique

In this work, a two-stage sintering technique, which began with an initial heating at lower temperature and followed by higher temperature sintering, was employed in the production of PbTiO₃ ceramics. Effects of designed sintering conditions on phase formation, densification, microstructure and dielectric properties of the ceramics were characterized via X-ray diffraction (XRD), Archimedes method, scanning electron microscopy (SEM) and dielectric measurement, respectively. The potentiality of a two-stage sintering technique as a low-cost and simple ceramic fabrication to obtain highly dense and pure lead titanate ceramics was demonstrated. It has been found that, under suitable conditions, the perovskite phase of densified PT ceramics with reasonable dielectric properties may be achieved with equivalent to those obtained from a single-stage sintering technique.     

钛酸锶陶瓷烧结的研究进展

钛酸锶陶瓷电容具有高储能、低损耗、高稳定性等优点,但烧结温度高,烧成密度低.依据国内外钛酸锶陶瓷烧结的研究情况,综述了影响钛酸锶陶瓷烧结中的两大因素,即烧结工艺和烧结助剂等方面的研究进展,并对其进行了展望.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

THE ELECTRICAL AND STRUCTURAL PROPERTIES OF Li2CO3 DOPED 0.7(Ba,Sr)TiO3-0.3MgO CERAMICS

ABSTRACT

We have studied the formation and characterization of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃-0.3MgO ceramics for the low temperature sintering and microwave applications. In this study 1 ～ 5 wt% of Li₂CO₃ was added to the 0.7(Ba,Sr)TiO₃-0.3MgO ceramic materials to reduce the sintering temperature. The MgO contents, which added in this experiment, play a role of improving dielectric permittivity such as low frequency dispersion and low loss tangent.

In this paper, we will discuss the crystalline properties, dielectric properties, and the microstructures of Li₂CO₃ doped 0.7(Ba,Sr)TiO₃- 0.3MgO ceramics. No pyro phase was observed in the X-ray diffraction method. Very weak frequency dispersion of dielectric permittivity was observed from the 1 kHz to 1 MHz range. Different grain sizes of Li₂CO₃ doped 0.7(Ba_0.5Sr_0.5)TiO₃-0.3MgO ceramics were observed through the SEM methods.     

Advances in electronic ceramic materials in Japan

A survey is provided of Japanese research on ceramic materials for substrates, microwave dielectric ceramics, piezoelectric ceramics, semiconducting ceramics, and superconducting ceramics. Novel processing technologies are described, covering the use of amorphous materials, superfine powders, lamination, multilayer thin films, porous ceramics, and superlattices     

Energy Conservation in Urban Areas

This article outlines the energy conservation measures in the civilian sector from a few different viewpoint regarding energy conservation in cities. First, the energy consumption trends in the business and residential sectors are discussed, focusing the importance of energy conservation measures in applications such as home heating, water heating and specific power demand. Second, as a measure to reduce energy demand itself, energy conservation by way of applying heat insulating materials to buildings and changing the life style of residents is considered. And from the viewpoint of improving the energy system efficiency, additionally discussed here are the measures to improve the efficiency of each energy equipment such as air‐conditioners and co‐generation equipment, and the characteristics of District heating and cooling systems such as the local energy infrastructures. Lastly, from the knowledge obtained through model analyses by the authors, a scheme is recommended that would be one of the most efficient city‐energy schemes where the energy systems including heat pumps, co‐generators or equipment using solar power are utilized for their best‐suited applications for business and residential customers. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An Investigation Demonstrating the Feasibility of Microwave Sintering of Base-Metal-Electrode Multilayer Capacitors

A microwave sintering technique has been developed for base-metal electrode (BME) multilayer ceramic capacitors (MLCCs). Commercial green chips of size 0603 MLC with nickel electrodes were sintered in a microwave field. With a specially designed susceptor/insulation package to optimize coupling and uniformity of heating, a number of sintering experiments were conducted in the temperature range of 1200 to 1250∘C in a multimode microwave cavity operating at 2.45 GHz under a partially reducing atmosphere. Microstructure of the microwave processed MLCCs was investigated with both SEM and TEM techniques. The dielectric properties of the microwave sintered MLCCs were measured and compared with those sintered using conventional process at 1320∘C and lower pO₂’s ≈ 10^{− 9} atms. The results demonstrate that nickel electrodes remain metallic after microwave sintering even though the pO₂’s were relatively high and would thermodynamically favor NiO. The microwave sintered samples showed a dense, fine and uniform microstructure. The properties of the microwave-sintered samples were comparable to the conventionally sintered samples. The microwave processing was found to have enhanced sintering kinetics of the BME MLCCs, lowering sintering temperature by about 100∘C and also the processing time by about 90%.     

Control of shrinkage on the behavior of co-firing of ferrite and varistor multi-layers composite with organic content

When make multi-layer ceramics device such as EMI filter, there are a lot of process problems. Specially, crack, camber and delamination should be controlled surely by different sinter shrinkage rate of interface of two materials. The purpose of this work was to co-fire defect-free ferrite/varistor ceramic multi-layers fabricated via a calcination temperature and organic vehicle contents of ferrite. Sintering shrinkage of both calcined ferrite and varistor materials were measured using dilatometer. X-ray diffraction analysis indicated that no significant phase change occurred in the materials under investigation as a result of the sintering process. Crack and delamination of each interface were observed by scanning electron microscopy and optical microscope. We obtained the defect-free and co-fired ferrite/varistor ceramic multi-layer by controlling calcinations temperature.     

Microvaristors: Functional Fillers for Novel Electroceramic Composites

Microvaristors are tiny electroceramic particles, which have highly nonlinear, voltage controlled electrical transport properties and can be used as active fillers in a variety of insulating matrix materials for functional composites. Due to the internal grain boundary structure, each individual microvaristor particle shows an IV-characteristics similar to the one known from bulk ceramics, except for the scaled down switching voltage. By controlling the material formulation, the particle morphology and the sintering conditions the switching characteristics of microvaristors can be tailored for specific applications.In the present paper the basic properties of ZnO microvaristors are described and it is shown how they impart their nonlinearity to the composite. A single microvaristor can withstand surprisingly high current loadings, without major changes in their electrical properties. Combined with the high manufacturing flexibility known from polymer processing, the varistor composites can be used for new solutions in overvoltage protection or control of electrical fields.     

CuO基多金属氧化物复合陶瓷的制备及电性质

用硝酸盐热分解方法制备的以ＣｕＯ为主体含１３种金属氧化物的系列复合陶瓷，室温下的电阻率与组成及烧结时间有明显的相关性．当组成（ＣＵ：Ｃａ：Ｓｒ：Ｂａ：Ｂｉ：Ｐｂ：Ｃｅ：Ｌａ：Ｓｂ：Ｆｅ：Ｚｎ：Ｔｉ：Ｃｒ）为３：２：２：２：１：１：０．２０：０．６０：０．２５：０．５０：０．５０：０．２５：０．７５（ｍｏｌ：ｍｏｌ）时，陶瓷具有良好的绝缘性能．     

微波烧结Ni-Zn铁氧体软磁材料的初步研究

采用微波高温烧结炉对Ni-Zn铁氧体软磁材料进行公斤级烧结工艺研究.结果表明,运用微波烧结可以实现Ni-Zn铁氧体材料烧结过程中的快速升温,短时保温,不仅大大降低能源消耗,缩短工艺周期,而且提高了Ni-Zn铁氧体软磁材料物理及机械性能.     

Synthesis and properties of multiferroic BiFeO3 ceramics

BiFeO₃ was synthesized using a modified sol–gel process, i.e., so-called Pechini method, as evidenced by X-ray diffraction pattern. Optimal conditions for the synthesis of single-phase BiFeO3 ceramics were obtained. This Pechini technique developed in this work is expected to be useful in synthesis of doped BiFeO₃ or BiFeO₃-based solid solution. Conventional sintering and spark plasma sintering processes were used to fabricate BiFeO₃ ceramics. Ferroelectric and magnetic loops were measured at room temperature. The ceramic sample shows a stable dielectric constant and low loss tangent between 100 Hz and 10 MHz.     

多晶透明氧化铝陶瓷晶相结构及光谱特性的研究

以不同形貌的高纯氧化铝粉体及典型的氧化镁添加剂为原料,采用固相反应烧结法制备多晶透明氧化铝产品。运用SEM、能谱分析仪、光谱分析仪等手段,研究了多晶透明氧化铝晶体结构的影响因素和光谱特性。结果表明,组成球形状态的粒子,在后期烧结过程中更容易形成六面形晶体结构;低比表面积的粉体在后期加工中容易分散,晶体形状和结构更稳定,工艺易于控制;外加剂氧化镁在小于1 700℃时在晶界能比较高的非{0001}面生成镁铝尖晶石,从而对六边形晶体形状起到钉扎作用,有利于形成均匀的晶相结构;对于有定量添加剂的透明氧化铝陶瓷,380～780nm的可见光谱范围为透光率最高区,780～1 000nm为近红外次透过区。     

弯曲电极结构对真空中氧化铝陶瓷沿面闪络耐压的影响

氧化铝陶瓷以其良好的绝缘性能广泛应用于高压真空器件,起到绝缘和支撑作用,但氧化铝陶瓷的沿面闪络现象严重制约了其耐压性能。分析了阴极金属-陶瓷-真空三结合处电场局部增强的原因,对阴极金属电极结构对柱状氧化铝陶瓷三结合处电场分布影响进行了仿真和单次脉冲耐压试验研究,给出了不同电极情况下,氧化铝陶瓷的耐压结果。结果表明,弯曲电极结构能有效减弱氧化铝陶瓷三结合处的电场强度,并且随着金属电极弯曲长度的增加而明显减小;相对于平板电极,弯曲电极的平均最高耐压提高了45%。     

High dielectric constant in (1 − x)SrTiO3/xCuO composite ceramics

Semiconductive secondary phase CuO was introduced into SrTiO₃ ceramic matrix to yield dielectric composite ceramics with high dielectric constant. The dense composite ceramics could be obtained by sintering at 1050°C in air for 3 h, in which the co-presence of SrTiO₃ and CuO/Cu₂O was confirmed. The dielectric constant of the present composite ceramics increased firstly and then decreased with increasing the content of CuO, and the highest dielectric constant was obtained at x?=?0.4. There were steps and peaks on the curves of dielectric constant vs temperature and dielectric loss vs temperature, respectively, and the peak temperatures of dielectric loss indicated the Debye-type relaxation.     

Microwave Dielectric Mechanism Studied by Microwave Near-Field Microscopy and Raman Spectroscopy

Microwave dielectric ceramics such as Ba(Mg_1/3Ta_2/3)O₃ and Ba₂Ti₉O₂₀ possess high dielectric constant and low dielectric loss in microwave frequency regime and have tremendous potential for device applications. In these materials, the presence of extrinsic defects, such as secondary phases, usually altered the microwave dielectric properties of the materials markedly, but the correlation of the microwave dielectric response of the materials with their microstructure has not been fully understood due to the lack of dielectric response in the local area. In this article, microwave near-field microscopy and Raman spectroscopy were used to investigate the microwave dielectric mechanism, viz. we measured the microwave dielectric properties of the materials in micron region by using a evanescent microwave probe (EMP) and, at the same time, examined the lattice vibration characteristics of the region by using a micro-Raman spectrum. How the presence of the secondary phase affects the microwave dielectric properties of the materials is thus systematically investigated. The causes of intrinsic or extrinsic dielectric loss were explored by comparing the dielectric images in SEMP at microwave frequencies and the corresponding Raman Spectra.