Nowadays, the prevailing of 5G communication era has greatly stimulated a tremendous progress in microwave devices and has also made a demand of more stringent dielectric characteristics. Therefore, it is important to develop ceramics with excellent microwave dielectric properties.
Vanadate dielectrics are attracting attention due to their relatively low sintering temperatures. But their large and negative τf values still limit practical applications, just as most of low εr ceramics. Adding those materials with positive τf values into low εr ceramics is an effective method to adjust τf to the near-zero value. However, this method will inevitably pose the decline in the Q×f value. Consequently, one key challenge facing low εr ceramics is how to adjust τf to the near-zero value without deteriorating Q×f.
Based on the analysis of the ionic polarizability and crystal structure, Ca3Co2SiV2O12 (CCSV) should be a low εr material. Moreover, it has a lower synthesis temperature compared with other garnet-structured microwave dielectric ceramics, such as germanates, aluminates, and gallates. Consequently, exploring the microwave dielectric properties of CCSV ceramics is necessary. Researchers have introduced Zn2+, Mg2+ and Cu2+ to the Co-site in CCSV to produce Ca3(Co0.25Zn0.25Mg0.25Cu0.25)2SiV2O12 (CZMC) medium-entropy ceramics. The smaller ionic radius difference maintains the structural stability of medium-entropy ceramics and promotes the formation of single-phase solid solutions. In addition, this strategy not only lowers the sintering temperature but also preserves a high Q×f value while adjusting τf to nearly zero, leading to enhanced overall performance of the ceramics.
The team published their work in Journal of Advanced Ceramics on June 10, 2025.
"The increase in the ΔSconfig can effectively reduce the sintering temperature of ceramics and promote the densification. The reason is that the multicomponent occupied the same lattice site causes the compositional disorder and leads to severe lattice distortion. The lattice distortion produced by the medium–entropy effect will introduce defects (e.g., vacancies, dislocations) that act as diffusion pathways. These defects can reduce the energy barrier for atomic movement and allow atoms to diffuse more easily, thus reducing the sintering temperature." said Jiamao Li, senior author of the study.
The researchers found that the B-site of the CZMC ceramics has a higher bond energy relative to CCSV ceramics based on the calculation of bond energy (Eb). Therefore, the B-site bonding energy is improved by the medium–entropy strategy. "Larger Eb makes CZMC ceramics have a more stable structure, hence resulting in a near-zero τf." said Jiamao Li.
In addition, the researchers performed AC impedance spectral analysis in order to investigate the correlation between dielectric properties and applied electrical signals. The good linear relationship between lnσ and 1000/T is consistent with the Arrhenius relationship for thermally activated processes and the Ea value of 1.16 eV corresponds to the typical activation energy for oxygen vacancy migration. Thus, the conductivity of CZMC ceramic can be attributed to the diffusion of thermally activated oxygen vacancies.
This work was supported by the Natural Science Foundation of Anhui Provincial Education Department (KJ2019A0054) and the Anhui Provincial Natural Science Foundation (1608085ME92)
About Author
Junxian Wang is a master's degree student in the School of Materials Science and Engineering, Anhui University of Technology, China. His main research interest is microwave dielectric ceramic materials.
Jiamao Li is an associate professor and master's tutor in the School of Materials Science and Engineering, Anhui University of Technology. His main research interests are microwave dielectric ceramics and energy storage ceramics. In recent years, he has published more than 40 SCI papers as the first author or corresponding author, and participated in the writing of 2 textbooks. He has served as a reviewer for Journal of Advanced Ceramics, Ceramics International, Journal of the European Ceramic Society and Journal of Alloys and Compounds. He is a senior member of the key materials and technology committee of electronic components of the Chinese society of instrumentation and functional materials.
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen . JAC's 2024 IF is 16.6, ranking in Top 1 (1/33, Q1) among all journals in "Materials Science, Ceramics" category, and its 2024 CiteScore is 25.9 (5/130) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
