Low dielectric loss in vanadium-based zircon ceramics via high-entropy strategy

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. Researchers have concentrated on vanadium-based zircon ceramics due to their low ε_r (9.9–32.5), low sintering temperature (950–1240 °C), and ability to change τ_f from negative to positive (-52.9– +80.0 ppm/°C) through ion substitution regulation. The structure of AVO₄ zircon is composed of distorted [AO₈] dodecahedron and regular [VO₄] tetrahedron, and its high dielectric loss (Q×f = 20,000–50,000 GHz) is mainly affected by the non-harmonic vibration of cations in the dodecahedron.

To reduce the dielectric loss of zircon ceramic, a research team led by Fang Liang from Guilin University of Technology in China introduced rare earth ions with the same valence but different ionic radii and ionic polarizabilities into the A-site of vanadium-based zircon AVO₄, designing a high-entropy ceramic: (Nd_0.2Eu_0.2Y_0.2Ho_0.2Yb_0.2)VO₄. Optimal microwave dielectric properties were achieved at 1060°C: ε_r = 11.55, Q×f = 76,400 GHz (at f = 12.31 GHz), and τ_f = -37.3 ppm/°C. This Q×f value is more than twice that of most traditional zircon ceramics and represents the highest Q×f reported for zircon ceramics to date. The research strategy and conclusions of this study can provide new insights for the development of novel microwave dielectric ceramics with ultra-low dielectric loss.

The team published their work in Journal of Advanced Ceramics on December 2, 2024.

“In this report, (Nd_0.2Eu_0.2Y_0.2Ho_0.2Yb_0.2)VO₄ ceramics were synthesized through solid-state reaction. X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) analyses indicate that the (Nd_0.2Eu_0.2Y_0.2Ho_0.2Yb_0.2)VO₄ high-entropy ceramics exhibit a pure tetragonal zircon-type structure. When sintered at 1060 °C, it possessed the optimal microwave dielectric properties of low ε_r of 11.55, high Q×f of 76,400 GHz, and exceptional positive τ_f of -37.3 ppm/°C, along with a low linear thermal expansion coefficient (α_L) of 7.9 ppm/°C. The Q×f value is more than double that of most traditional zircon ceramics, which can be attributed to the high chemical bond strength and structural stability induced by the high-entropy effect in the dodecahedral A-sites of the zircon structure.” said Huaicheng Xiang, associate professor at College of Physics and Electronic Information Engineering, Guilin University of Technology. (China).

“TEM and activation energy results confirm that high-entropy ceramics exhibit lower defect densities. Raman spectroscopy confirms the narrowest FWHM in high-entropy ceramics, corresponding to higher Q×f values. The total lattice energy (U_total) of high-entropy ceramics significantly exceeds that of traditional zircon ceramics, and the average lattice energy at the A-site greatly surpasses that of traditional zircon ceramics, indicating that the high-entropy effect enhances binding forces and the structural integrity of dodecahedral units. The ε₀ value fitted from the infrared reflectivity spectrum (13.6) is slightly higher than the measured value (11.5), and the fitted Q×f value (117,500 GHz) is also slightly higher than the measured value, suggesting that further optimization of the synthesis process can improve the microwave dielectric properties of (Nd_0.2Eu_0.2Y_0.2Ho_0.2Yb_0.2)VO₄ ceramics. Therefore, (Nd_0.2Eu_0.2Y_0.2Ho_0.2Yb_0.2)VO₄ holds considerable potential for application in high-performance, high-power microwave devices. The research strategies and conclusions can provide new insights for the development of novel microwave dielectric ceramics with ultra-low dielectric loss.” 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, exploring microwave dielectric ceramics with an improved tetragonal zircon structure still requires more meticulous research efforts. In this work, compositing with TiO₂ can yield a tf value closer to zero (τ_f = -2.4 ppm/°C), but this leads to a significant deterioration in the Q×f value (only 37,500 GHz). Therefore, based on the high inclusivity of A-site dodecahedra, we can design solid solutions with superior performance by selectively substituting or combining a wider variety of different ions.

This work was funded by the Natural Science Foundation of Guangxi Zhuang Autonomous Region (Grant No. 2023GXNSFBA026076), and the Science and Technology Plan of Guangxi (Grant No. ZY22096019).

About Author

Dr. Huaicheng Xiang is an associate professor in the College of Physics and Electronic Information Engineering, Guilin University of Technology. He obtained his Ph.D. in Materials Science and Engineering from Guilin University of Technology in 2019, during which time he was jointly trained at the University of Oulu in Finland for one year. From 2019 to 2021, he conducted postdoctoral research at Shenzhen University. His research work covers the fields of low-dielectric microwave dielectric ceramics, electronic information functional materials, high-entropy ceramics, and solid-state electrolytes. He has hosted one project funded by the National Natural Science Foundation of China, two by the Natural Science Foundation of Guangxi, and one by the Natural Science Foundation of Shenzhen. He has published over 80 academic papers, including more than 40 as the first or corresponding author in journals such as Journal of Advanced Ceramics, Applied Materials Today, ACS Sustainable Chemistry & Engineering, Journal of Materials Science & Technology, and Journal of the European Ceramics Society. He holds 7 authorized national invention patents.

Dr. Liang Fang is a professor in the College of Materials Science and Engineering, Guilin University of Technology. He is an expert who enjoys special government allowance from the State Council, a talent under the "New Century Excellent Talents in University" program of the Ministry of Education, a specially-appointed "Chutian Scholar" professor in Hubei Province, a specially-appointed expert in Guangxi (both the first and sixth batches), and one of the top hundred talents in the 'National Intellectual Property Talents Program for Hundreds, Thousands, and Tens of Thousands Initiatives' of the National Intellectual Property Administration. He graduated from Wuhan University of Technology with a major in Materials Science and Engineering, and his research primarily focuses on the preparation, structure, and properties of novel inorganic non-metallic functional materials. He has hosted over 30 projects, including nine projects funded by the National Natural Science Foundation of China, key national defense technology projects, major science and technology projects of the Ministry of Education, and the "New Century Excellent Talents in University" support plan fund of the Ministry of Education. He has published more than 350 SCI-indexed papers in domestic and international academic journals, which have been cited over 5000 times. He holds 205 authorized Chinese invention patents and has won two first-prize and three second-prize awards for science and technology at the provincial and ministerial levels.

Mr. Yuheng Zhang is a master degree candidate at the College of Physics and Electronic Information Engineering, Guilin University of Technology. His research focused on new electronic information functional ceramic materials. He has Currently published articles in journals such as Journal of Advanced Ceramics, Journal of Materials Science & Technology, and Ceramics International.

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