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

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 duple-xers, frequency stabilized oscillators, microwave capacitors, filters and resonators. These components have a wide range of applications in many fields such as 4G/5G mobile communication systems, global satellite positioning systems, satellite communication systems, wireless Internet and military radar. With the rapid development of the 5G mobile communication system industry, microwave components especially filters and resonators, acting as important devices in communication equipment, have received extensive attention 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 manufactu-ring 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 lanthanum titanium system, bismuth based system, lithium based system and lead based perovskite system. In the high dielectric constant microwave dielectric material system studied in recent 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-Ln2O3-TiO2 system microwave dielectric ceramics is widely used in mobile communication for its good temperature stability, high permitti-vity 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. © 2019, Materials Review Magazine. All right reserved.