Microwave Dielectric Properties of LiKSm2(MoO4)4 Ceramics with Ultralow Sintering Temperatures

In this work, a novel low‐temperature firing microwave dielectric ceramic LiKSm₂(MoO₄)₄ was prepared via solid‐state reaction method. Ceramic samples with relative densities about 94.6% were obtained at sintering temperature 640°C–680°C. The best microwave dielectric properties was obtained in ceramic sample sintered at 620°C with a permittivity about 11.5, a Q × f value about 39 000 GHz and a temperature coefficient of frequency about ?15.9 ppm/°C. According to XRD patterns and backscattered electron micrograph, combined with Energy Dispersive Spectra analysis, of cofired samples with 30 wt% aluminum sintered at 620°C/4 h, the LiKSm₂(MoO₄)₄ ceramic was found to be chemically compatible with Al but react seriously with Ag, forming AgSmMo₂O₈ phase, at its sintering temperature.     

固有烧结温度低的微波介质陶瓷

微波介质陶瓷是现代通讯技术中的关键基础材料。在制备多层微波介质片时,为了使用Cu、Ni等低熔点电极,必须降低微波介质陶瓷的烧结温度。开发固有烧结温度低(<1060℃)同时具有良好性能的微波介质材料成为必然的选择。本文简要介绍了7类固有烧结温度低的微波介质陶瓷的烧结特性与微波介电性能,同时也指出了研究中存在的一些问题。     

Low‐Temperature Sintering and Microwave Dielectric Properties of CaMoO4‐Based Temperature Stable LTCC Material

The CaMoO₄–xY₂O₃–xLi₂O ceramics were prepared by the solid‐state reaction method. The sintering behavior, phase evolution, microstructure, and microwave dielectric properties were investigated. CaMoO₄ solid solution was obtained when x = 0.030, and two‐phase system including tetragonal CaMoO₄ phase and cubic Y₂O₃ phase formed when 0.066 ≤ x ≤ 1.417. A temperature stable CaMoO₄‐based microwave dielectric ceramic with ultralow sintering temperature (775°C) was obtained in the CaMoO₄–xY₂O₃–xLi₂O system when x = 0.306, which showed good microwave dielectric properties with a low permittivity of 9.5, a high Q_f value of 63 240 GHz, and a near‐zero temperature coefficient of resonant frequency of +7.2 ppm/°C.     

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.     

掺杂玻璃助剂的Ba5Nb4O15陶瓷烧结特性及介电性能

引入玻璃烧结助剂,采用液相烧结手段制备了低温烧结Ba5Nb4O15微波介质陶瓷.采用X射线衍射和扫描电子显微技术分析了陶瓷的物相组成和微观形貌.研究表明:陶瓷主晶相为Ba5Nb4O15,铋硅酸盐玻璃在陶瓷中以液相形式存在,促使陶瓷烧结温度从1300℃降至1100℃.添加4wt.％铋硅酸盐玻璃的Ba5Nb4O15陶瓷在1100℃烧结,具有良好的微波性能:相对介电常数εr=39.01,品质因子Q × f=12214GHz.     

CaTiO3添加剂对氧化铝陶瓷烧结、显微结构及微波介电性能的影响

CaTiO3添加剂通过湿法球磨与Al2O3粉料混合,并通过无压烧结制备了氧化铝陶瓷,研究了CaTiO3添加剂对氧化铝陶瓷烧结性能、相组成、显微结构和微波介电性能的影响.CaTiO3可以使Al2O3的烧结温度降低至1450℃,但在该温度下烧结的样品由于CaTiO3的加入会产生CaAl12O19第二相.样品中存在大、小两种晶粒,根据EDS能谱分析,大晶粒主要是CaAl12O19,而小晶粒为Al2O3和CaAl12O19的混合相.添加CaTiO3有利于Al2O3陶瓷介电常数的提高,1450℃下掺杂2.5wt％ CaTiO3的氧化铝陶瓷具有较好的烧结性能和微波介电性能,相对密度可达到97.74％,εr～10.86,Q×f～ 8061 GHz.     

B2O3-CuO掺杂CSLST微波介质陶瓷介电性能研究

选用B2O3-CuO(BC)低熔点复合氧化物作为烧结助剂,采用固相法制备(Ca0.9375Sr0.0625)0.25(Li0.5Sm0.5)0.75TiO3(CSLST)陶瓷,研究了不同含量的BC对CSLST陶瓷的晶相组成、烧结性能及微波介电性能的影响.研究结果表明:随BC添加量的增多,CSLST陶瓷的烧结温度降低,陶瓷的微波介电常数εr和谐振频率温度系数(Τ)f下降,品质因素Qf明显降低.当BC添加量为5wt％时,在1000℃保温5h可烧结,此时陶瓷具有较佳的微波介电性能:εr=80.4,Q×f=1380 GHz,(Τ)f=- 32.89×10-6/℃.     

Effects of the Susceptor Dielectric Properties on the Microwave Sintering of Alumina

Microwave sintering of alumina has been carried out using SiC and Y‐ZrO₂ based susceptors. The microstructure of the sintered samples has been rigorously compared and correlated to the heating behaviour of the susceptor used. It was found that the nature of the susceptor highly influences the sintering behaviour of alumina. The results show that at high temperatures, the electrical conductivity of the SiC susceptor tends to screen the incident electric field, thus resulting in a surface heating of the alumina sample material. When using ZrO₂ susceptor, the microstructure analysis of the sintered alumina samples reveals a volumetric heating, which is a signature of the microwave dielectric loss mechanism. This could be explained by the lower ZrO₂ electrical conductivity compared to the SiC one. The simulation results confirm this behaviour, particularly showing that in the presence of ZrO₂, the intensity of the electric field within the sample is higher than the one when SiC susceptor is used. Basically, the results of the simulation data are in good agreement with our experimental results. Although the SiC based susceptor is usually used in the microwave heating of materials, the ZrO₂ based susceptor presents numerous advantages over the SiC one, especially in term of direct microwave heating contributions.     

Low-Temperature Sintering and Microwave Dielectric Properties of Zinc Metatitanate-Rutile Mixtures Using Boron

Mixtures of zinc metatitanate and rutile (ZnTiO₃+ x TiO₂, where x = 0-0.5) have been prepared via the conventional mixed-oxide method. Centrifugal planetary milling with zirconia beads 1 mm in diameter produced very fine powders (mean particle size of 0.2 µm), which allowed the synthesis of ZnTiO₃ and sintering at temperatures <945°C, which is the decomposition temperature of ZnTiO₃. Sintering of the mixtures was enhanced further by the addition of B₂O₃. Densities of >94% of the theoretical density have been attained for the specimens that were sintered at 875°C for 4 h with B₂O₃ additions of <1 wt%. Microwave dielectric properties of the aforementioned compositions were as follows: dielectric constant of 29-31, normalized quality factor of 56000-69000 GHz, and a temperature coefficient of resonance frequency between -10 and +10 ppm/°C. Sintering was enhanced by the formation of a ZnO-B₂O₃ liquid phase, which affected the microwave properties, because of variation in the phase composition.     

Dielectric Properties of Lithium Molybdate Ceramic Fabricated at Room Temperature

Lithium molybdate disks were fabricated by moistening water‐soluble Li₂MoO₄ powder with deionized water and compressing it under a pressure of 130 MPa. Disks were postprocessed at room temperature, at 120°C, and at 540°C, which is a common sintering temperature for Li₂MoO₄. Regardless of the postprocessing temperature, densities as high as 87%–93% of the theoretical value were achieved. The X‐ray diffraction patterns of processed disks were all the same with no signs of hydrates or constitutional water. The samples also exhibited very similar microstructures and microwave dielectric properties with a relative permittivity of 4.6–5.2 and a Q × f value of 10 200–18 500 at 9.6 GHz, depending on the postprocessing temperature.     

Sintering Mechanism and Microwave Dielectric Properties of Bi12TiO20 Ceramics

A homogeneous Bi₁₂TiO₂₀ phase was developed in a specimen that was calcined at 700°C without the formation of a secondary phase. A small amount of the Bi₁₂TiO₂₀ phase melted during sintering and assisted the densification of the specimen. The Bi₂O₃ and Bi₈TiO₁₄ secondary phases were found in all specimens. All the specimens that were sintered at temperatures ≥775°C exhibited high relative densities above 98% of the theoretical density. The Q × f value of the Bi₁₂TiO₂₀ ceramics was influenced by the grain size. The Bi₁₂TiO₂₀ ceramics sintered at 800°C for 5 h showed promising microwave dielectric properties of ε_r = 41, Q × f = 10 400 GHz, and τ_f = ?10.8 ppm/°C.     

Sintering Process and Microwave Dielectric Properties of Bi8TiO14 Ceramics

The formation of a homogeneous Bi₈TiO₁₄ phase was successfully achieved in a specimen calcined at 600°C. However, a Bi₄Ti₃O₁₂ secondary phase also developed in specimens calcined at temperatures higher than 600°C, probably because of Bi₂O₃ evaporation. For specimens sintered above 800°C, a small amount of the Bi₈TiO₁₄ phase melted during sintering, with the liquid phase contributing to the densification of the specimens; however, Bi₄Ti₃O₁₂ and Bi₁₂TiO₂₀ secondary phases were still formed in these specimens. The microwave dielectric properties of the Bi₈TiO₁₄ phase were considerably affected by variations in the microstructure of the specimens. When the sintering temperature exceeded 825°C, the amount of secondary phases increased, and this decreased the density and Q×f values of the specimens. Bi₈TiO₁₄ ceramics sintered at 825°C exhibited promising microwave dielectric properties, with ε_r = 47.4, Q×f = 5370 GHz, and τ_f = ?16.01 ppm/°C.     

集成电路封装用低温低介陶瓷材料的研制

简要地叙述了国家八五攻关项目“85-705”中“低温低介电常数陶瓷材料”这一课题的研制过程及关键工艺技术问题     

烧成温度对多孔SiC陶瓷管性能的影响

以SiC为骨料,添加低共熔混合物烧结促进剂,煤粉作为造孔剂,在不同的温度下烧成制备多孔陶瓷管.考察了烧成温度对多孔SiC陶瓷管的孔隙率、气体渗透通量、孔径分布以及抗弯强度等性能的影响,并通过SEM对其结构形貌进行了表征.结果表明:随着烧成温度的提高,孔隙率、气体通量及抗弯强度下降,孔径分布变宽.     

烧结温度对黄土陶瓷膜支撑体性能的影响

实验以洛川黄土为骨料,十二烷基苯磺酸钠(SDBS)为烧结助剂.利用滚压成型法、固态离子烧结法来制备黄土陶瓷膜支撑体,并对制备的支撑体的性能影响因素进行了探究.通过压汞法、三点弯曲法、X-射线衍射(XRD)、扫描电镜(SEM)以及自制装置对支撑体试样进行测试.分别研究孔径分布、孔隙率、抗折强度、晶相变化、表面形貌、酸碱腐蚀率以及纯水通量等对黄土陶瓷膜支撑体性能的影响.研究结果表明:十二烷基苯磺酸钠能显著降低黄土陶瓷膜烧结时候的温度.当烧结温度小于1000℃时,支撑体中没有新物质生成;当烧结温度大于1090℃时,纯水通量随烧结温度的升高呈现出下降趋势;当烧结温度恰好达到1070℃,此时制得的支撑体性能良好,中值孔径为6975.9 nm、抗折强度37.83 MPa、孔隙率20.65％、纯水通量1943.70 L/(m2·h·MPa)、酸/碱腐蚀率0.340％/0.195％.     

低温烧结Mg4Nb2O9微波介质陶瓷

研究了V2O5对Mg4Nb2O9陶瓷的烧结温度、相结构和微波介电性能的影响.结果表明,添加1％～8％的V2O5,能使该陶瓷的烧结温度降低到1000～1050℃而对其微波介电性能的影响很小,材料的主晶相为有序型刚玉结构的Mg4 Nb2O9,存在Mg4Nb2O6和Mg5Nb4O15杂相而没有检测到V2O5的存在.陶瓷的密度对微波介电性能起着决定性作用,介电常数e1与密度成线性关系(在99.99％的置信限内,其相关系数为0.98252),Q·f值与密度的关系较复杂.添加1％的v2O5,将Mg4Nb2O9陶瓷的烧结温度降低到了1050℃,得到了εr=12.72,Q·f=151040GHz的优异性能.     

Influence of Copper(II) Oxide Additions to Zinc Niobate Microwave Ceramics on Sintering Temperature and Dielectric Properties

The effect of CuO additions on the firing temperature of ZnNb₂O₆ ceramics was investigated using dilatometry, transmission electron microscopy, and X-ray diffractometry. A 5 wt% CuO addition to ZnNb₂O₆ ceramics significantly lowered the firing temperature from 1150° to ∼900°C. The presence of a CuO-rich intergranular phase in the specimen was observed and was evidence of the formation of a liquid phase during sintering. The composition of the liquid phase was (ZnCu₂)Nb₂O₈. In particular, the low-fired ZnNb₂O₆ ceramics had good microwave dielectric characteristics— Q × f = 59 500, ɛ_r= 22.1, τ_f=–66 ppm/^oC. These properties were correlated with the formation of a second phase, (ZnCu₂)Nb₂O₈.     

微波介质瓷粉的湿化学合成

湿化法是合成微波介质陶瓷行之有效的方法，其中，共沉淀法、水热法、溶胶-凝胶法以及柠檬酸盐法都能制得纯度高、粒径小、均匀度高具有良好微波性能的材料。本文综述了湿化学法制备微波介质陶瓷粉体的研究进展，并对存在的问题进行了分析。     

Simulation of Microwave Sintering of Ceramic Bodies with Complex Geometry

Microwave sintering, an emerging technology in which the energy is applied directly to the material, enabling rapid sintering, shows potential for the synthesis of advanced ceramic materials with superior properties. The process is complex, combining the propagation and absorption of electromagnetic waves in the ceramic material, heat transport within the geometric body, and densification. The densification changes both macroscopic shape and microstructural morphology. A dynamic balance between the rate of electromagnetic energy absorbed within the bulk of the sample and the rate of energy loss from its surface generally results in temperature gradients. These temperature gradients may be especially important during the microwave sintering of bodies with a complex geometry, because neither the diffusion distance nor the electromagnetic penetration depth scale with sample dimensions. The gradients generated in a ZnO green body of a complex geometry were studied theoretically using various microwave-sintering approaches, and it was found that (1) dual-frequency (2.45 and 30 GHz) microwave processing leads to a decrease in the duration of the temperature gradients, and (2) an increase in the heating rate from 5°C/min to 1400°C/min at 2.45 GHz decreases the total required microwave energy by a factor of 55, while at the same time the internal temperature gradients are maintained over a substantially shorter time.