钡镧钛系高介低损耗微波介质陶瓷研究进展

Research Progress of BaO-Ln2O3-TiO2 System Microwave Dielectric Ceramics with High Permittivity and Low Loss

微波介质陶瓷是指用于微波频段电路中作为介质材料并能实现一种或几种功能的陶瓷,是近几十年来发展起来的一类新型电子陶瓷材料,主要用于制作片式天线、双工器、稳频振荡器、微波电容器、滤波器、谐振器等微波元器件。这些元器件可广泛应用于4G/5G移动通信系统、全球卫星定位系统、卫星通信系统、无线互联网、军事雷达等领域。随着5G移动通信系统产业的快速发展,作为通信设备中的重要器件,微波元器件特别是滤波器、谐振器受到研发人员广泛的关注。为了进一步提升微波元器件的性能、缩小微波元器件的尺寸以及降低制造成本,对微波介电材料的要求主要有以下几点:(1)较高的介电常数(ε r);(2)尽可能高的品质因数( Q f);(3)近零的谐振频率温度系数(TCF);(4)所选材料价格便宜且无毒环保。从介电常数的角度划分,高介电常数微波介质陶瓷通常是指介电常数在70及70以上的微波介电材料,主要材料体系通常包括钡镧钛体系、ABO 3型钙钛矿结构体系、钙锂镧钛体系、铋基体系、锂基体系及铅基钙钛矿体系等。目前在高介电常数微波介电材料体系中,关于钡镧钛体系的研究比较多,它属于类钙钛矿钨青铜结构,结构单元中具有形状各异、大小不一的几类空隙,能够填充不同价态、不同半径的离子,不同离子的填充会引起结构发生对应的变化,从而使钡镧钛体系微波介电材料具备性能各异的微波介电性能。众多研究人员针对这一特性,将各种不同价态、不同半径的离子掺入该材料体系中,期望将离子填充到晶体结构中的某个空隙,从而获得更好的微波介电性能。钡镧钛系微波介质陶瓷具有温度稳定性好、介电常数高、损耗低等优点,是移动通信领域所使用的主要介质材料,随着5G通信技术的快速发展,其相关的研究具有非常重要的理论意义和应用价值,也是微波介电材料的研究热点之一。本文综合介绍了钡镧钛系微波介质陶瓷的晶体结构以及固溶极限,从A位置换、B位置换、A/B位协同置换、复合改性、抗还原研究及低温烧结几个方面综述了近年来钡镧钛系微波介质陶瓷的研究进展,并探讨了目前其研究中所存在的主要问题及未来的研究重点。

Microwave dielectric ceramics is a kind of functional ceramics which can be used in microwave frequency circuits as dielectric materials. It is also a new type of electronic ceramic materials developed in recent decades, and mainly used in microwave devices such as antennas duplexers, frequency stabilized oscillators, microwave capacitors , filters and resonators. These components have a wide range of applications in many fields such as 4G/5G mobile com muni cati on systems, global satellite positi oning systems, satellite com muni catio n systems, wireless In ter net and military radar. With the rapid development of the 5G mobile communication system industry, microwave components especially filters and resonators, act ing as importa nt devices in com muni catio n equipme nt, have received exte nsive atte ntio n from researchers all over the world. In order to make a further improvement in the performance of microwave components, decrease the size of microwave components and reduce manufacturing costs, the requirements for microwave dielectric materials are shown as follows:(1) high dielectric constant(εr);(2) high quality factor (Qf);(3)near zero temperature coefficient of resonance frequency(TCF);(4) cheap, non-toxic and environmentally friendly raw materials. From the perspective of dielectric constant, high dielectric constant microwave dielectric ceramics generally refer to the materials with dielectric constants above 70. The main material systems of high dielectric constant microwave dielectric ceramics usually include barium lanthanum titanium system( BaO-Ln2O3-TiO2), ABO3 perovskite structure system, calcium lithium Ianthanum titanium system, bismuth based system, lithium based system and lead based perovskite system .In the high dielectric con sta nt microwave dielectric material system studied in rece nt years, the barium lanthanum titanium system has got the most attention. This system belongs to the perovskite-like tungsten bronze structure, and there are several types of voids in the structural unit with different shapes and sizes, which can be filled by ions with different valence states and radii. The filling of different ions would cause corresponding changes in the structure, and would influence the microwave dielectric properties at the same time. Based on the property above, many researchers have incorporated ions of different valences and radii into the Ba-Ln-Ti system, and desired to fill the ions into a certain space in the crystal structure, in order to obtain better microwave dielectric properties. BaO-L n2O3-TiO2 system microwave dielectric ceramics is widely used in mobile com muni cati on for its good temperature stability, high permittivity and low loss. With the rapid development of 5G communication, the research on this system exhibits great theoretical significance and application value, therefore becoming one of the hottest research topics in microwave dielectric area. This article first introduces the crystal structure and solid solubility limit of BaO-Ln2O3-TiO2 ceramics, and then provides an overview of the progress on BaO-Ln2O3-TiO2 system in recent years from several aspects including A-site substitution, B-site substitution, A/B-site collaborative substitution, combined modification, anti-reduction and low-temperature sintering. Current existed problems and future research priorities are also discussed in the end of the article.