As one of the key materials of modern microwave communication technology, microwave dielectric ceramics are widely used in many core components of microwave circuits. In recent years, with the rapid development of microwave communication technology marked by mobile communication, in order to meet the requirements of the development of mobile communication technology, including 5G/6G, new requirements have been put forward for the performance parameters of microwave dielectric ceramics: low dielectric constant to reduce signal delay, low dielectric loss or high quality factor, and near-zero resonance frequency temperature coefficient. The three parameters are mutually restricted, the common materials with low medium and high Q×f value τf is negative, and the materials with positive τf are generally high medium and low Q×f value, among which the microwave dielectric ceramics containing rare earth are the focus and hot spot of microwave dielectric materials research and development at home and abroad. However, the reported Ga-based microwave dielectric ceramic materials τf are all negative, which can not meet the practical application requirements of the device.
To address these problems, a research team led by Liang Fang from Guilin University of Technology, China has developed the first gallium based microwave dielectric ceramic with positive τf: SrGa12O19 ceramic. Unlike the reported Ga-based microwave dielectric ceramics with negative τf, gallium-based SrGa12O19 microwave dielectric ceramics possessed great properties (εr = 14.46, Q×f = 64,705 GHz, τf = +55.7 ppm/°C) at 1430 °C. This is the first low dielectric gallium based microwave dielectric ceramic with positive τf and can be used as a good temperature compensator for low-dielectric microwave dielectric ceramics. The causes of abnormal positive τf, intrinsic polarization and loss mechanism are studied systematically, which provides a new idea for exploring microwave dielectric ceramics with excellent comprehensive properties.
The team published their work in Journal of Advanced Ceramics on August 1, 2024.
"In this report, SrGa12O19 ceramics were synthesized by the solid-state reaction between SrCO3 and Ga2O3. According to XRD and TEM, SrGa12O19 ceramic formed a pure hexagonal magnetoplumbite structure with the spinel block and the rock-salt block stacking along the crystallographic c-axis." said Jie Li, associate professor at College of Materials Science and Engineering, Guilin University of Technology (China).
"When sintered at 1430 °C, it possessed the optimal microwave dielectric properties of low εr of 14.46, high Q×f of 64,705 GHz, and exceptional positive τf of +55.7 ppm/°C, along with a low linear thermal expansion coefficient (αL) of 11.617 ppm/°C. The large positive deviation between εr and εr(C-M) of 45.31% resulted from the rattling effect of atoms in a rock-salt block. The unique positive τf (+55.7 ppm/°C) was governed by the rattling effect, resulting in a positive ταm of 8.489 ppm/℃ and a large negative τε of −132.864 ppm/℃." said Ying Tang, professor in the College of Physics and Electronic Information Engineering, Guilin University of Technology..
Investigated by the P-V-L chemical bond theory, "S2+" block made the greater contribution to fi (52.95%), ε (55.15%), E (56.87%) and U (74.88%) than those in "R2-" block of SrGa12O19. Raman spectroscopy confirmed the SrGa12O19 ceramic possessed the narrowest FWHM of 10.23 cm−1 at 503 cm−1 corresponding to the largest Q×f of 64,705 GHz. The fitted ε0 value by infrared reflectivity spectra (11.33) was lower than the measured εr value (14.46) and the fitted Q×f value (131,591 GHz) was twice the measured Q×f value (64,705 GHz) of SrGa12O19 ceramics, indicating the microwave dielectric property can be improved by further optimizing the synthesis process. "Therefore, SrGa12O19 was a novel example of τf compensator in low-εr ceramics, broadening the thought train of exploring and discovering new materials in microwave dielectric ceramics."said Liang Fang, professor at College of Materials Science and Engineering, Guilin University of Technology (China), a senior expert whose research interests focus on the field of electronic functional ceramic materials.
However, more delicate research works are still needed to explore the series of hexagonal magnetoplumbite compounds. The AB12O19-type hexagonal magnetoplumbite is composed of A-site dodecahedron, B-site octahedron, B-site trigonal bipyramid and B-site tetrahedron. The species of cations that can occupy the A and B sites are rich, and even the same cation can enter multiple polyhedral. Therefore, according to the ionic radius ratio rules for A-site and B-site ions, bond energy, and the spatial distribution of covalent bonds, selectively substitute or combine different ionic charges and radii in SrGa12O19 can be investigated, thereby a series of magnetoplumbite-structured compounds and solid solutions can be designed.
Other contributors include Weishuang Fang, Huixing Lin from the Key Laboratory of Inorganic Functional Material and Device, Shanghai Institute of Ceramics, Chinese Academy of Sciences in Shanghai, China; Huaicheng Xiang, Liang Fang from Guangxi Universities Key Laboratory of Non-ferrous Metal Oxide Electronic Functional Materials and Devices, Guangxi Key Laboratory of Optical and Electronic Materials and Devices, College of Materials Science and Engineering at Guilin University of Technology in Guilin, China; Lei Li from the Laboratory of Dielectric Materials, School of Materials Science and Engineering at Zhejiang University in Hangzhou, China.
This work was funded by the Natural Science Foundation of Guangxi Zhuang Autonomous Region (No. 2024GXNSFFA010013), Project of Scientific Research and Technical Exploitation Program of the Guangxi Zhuang Autonomous Region (No. AD24010021), the Guilin University of Technology Research Startup Project (No. GUTQDJJ2019183), and Guangxi BaGui Scholars Special Funding.
About Author
Dr. Jie Li is an associate professor in the College of Materials Science and Engineering, Guilin University of Technology. She received her Ph.D degree in microelectronics and solid-state electronics from Huazhong University of Science and Technology. Her research focused on electronic information ceramics, encompassing the investigation of microwave dielectric materials' mechanisms and their application in the field of communication, as well as the preparation and utilization of C0G multilayer ceramic capacitors. In recent years, her current interests and fields of research are on the design of compositions, structural analysis, and dielectric properties of low dielectric constant materials derived from colored metal oxides such as tridymite, spinel, and melilite.
She served as reviewer in J. Adv. Ceram., J. Eur. Ceram. Soc. and other journals. She has published more than 40 papers in SCI journals as the first author or corresponding author. In addition, she has presided a project of National Natural Science Foundation, 2 projects of Guangxi Natural Science Foundation, a project of China Postdoctoral Science Foundation, as well as been selected as the 2020 Guangxi Postdoctoral Innovative Talent Support Program. As the first inventor, she has obtained 11 authorized Chinese invention patents and completed 2 patent transfer projects.
Dr. Ying Tang is a professor in the College of Physics and Electronic Information Engineering, Guilin University of Technology. She received her Ph.D degree in metallurgical engineering from University of Science and Technology Beijing. Her research focused on new electronic information functional ceramic materials. In recent years, her current interests and fields of research are on the study of composition design, structure and dielectric properties of microwave dielectric ceramic materials, such as garnet, spinel and olivine.
She was supported by the Outstanding Youth Fund of Guangxi Natural Science Foundation in 2023. So far, she has published more than 30 papers as the first author or corresponding author, including more than 30 papers in SCI top journals. She has presided 2 National Natural Science Foundation projects (one for youth and one for regions), obtained 25 authorized Chinese invention patents as the first inventor, and completed 2 patent transfer projects (1.284 million yuan).
Miss Yang Yang is a Ph.D candidate at the College of Materials Science and Engineering, Guilin University of Technology. Her research focused on new electronic information functional ceramic materials. She has currently published 5 papers in J. Adv. Ceram., J. Eur. Ceram. Soc., Ceram. Int., etc as the first author.
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