Sc3+-modified Mg-Al-Mn-Fe-O spinel ceramics enable synergistically enhanced microwave dielectric and thermosensitive properties for 6G multifunctional front-ends

The paradigm shift from Internet of Everything (IoE) to Space-Air-Ground-Sea-Integrated Networks (SAGSIN) necessitates multifunctional ceramics capable of overcoming critical bottlenecks in next-generation communication systems. While significant progress has been achieved in multi-category composites (e.g., magnetic-microwave, ferroelectric-luminescent), the synergistic integration of microwave dielectric and NTC thermosensitive functionalities remains unexplored. Microwave dielectric ceramics are prioritized for communication applications due to three essential characteristics: tunable ε_r enabling device miniaturization, high Q·f ensuring frequency selectivity, and near-zero τ_f guaranteeing thermal stability. Concurrently, NTC thermistors serve as indispensable thermal managers with precision temperature sensing across broad operational ranges. The development of ceramics concurrently exhibiting these dual functionalities presents a viable pathway for advanced communication front-ends.

Recently, a team of material scientists led by Bo Zhang from the Xinjiang Technical Institute of Physics and Chemistry, CAS, developed Sc³⁺-modified Mg-Al-Mn-Fe-O spinel ceramics, achieving a synergistic breakthrough in microwave dielectric and thermosensitive properties. The results demonstrate that Mg_0.8Mn_0.2Al_1.3Sc_0.3Fe_0.4O₄ ceramic displays NTC thermistor properties across an extended temperature range (200-1000 ℃), with a B-value of 9754 K ensuring measurement accuracy and temperature sensitivity. In addition, the optimized Mg_0.8Mn_0.2Al_1.3Sc_0.3Fe_0.4O₄ ceramic simultaneously achieves superior microwave dielectric properties with ε_r = 10.08, Q·f = 149,000 GHz, and τ_f = -10.2×10^-6/°C. Significantly, the developed Mg_0.8Mn_0.2Al_1.3Sc_0.3Fe_0.4O₄-based resonant antenna demonstrates practical applicability in millimeter-wave systems, operating at 11-12.8 GHz with 92% radiation efficiency and 6.28 dBi realized gain. Ultimately, these comprehensive functional properties establish Mg_0.8Mn_0.2Al_1.3Sc_0.3Fe_0.4O₄ ceramic as a promising dual-functional material for microwave-thermosensitive integrated devices.

The team published their work in Journal of Advanced Ceramics on August 17, 2025.

“Rare-earth ion doping plays a pivotal role in tailoring microstructural evolution, stabilizing crystal lattices, and optimizing dielectric behavior. While conventional rare-earth dopants such as Nd, Y, Sm, and Ce are widely studied, Sc³⁺ is particularly significant for its ability to stabilize the crystal structure of solid oxide electrolytes and modulate ion mobility. Guided by this mechanism, we designed a series of B-site-substituted Mg_0.8Mn_0.2Al_1.6-xSc_xFe_0.4O₄ spinels. As anticipated, Sc³⁺ substitution effectively resolved the longstanding challenge of inferior NTC linearity at elevated temperatures, while simultaneously achieving exceptional microwave dielectric performance.” said Bo Zhang, a senior researcher at the Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences (CAS), specializing in the design and application of high-temperature thermosensitive ceramic materials and devices.

The research team employed the solid-phase reaction method to prepare a series of ceramic samples, which were sintered at 1510°C to achieve near-full-density ceramics(> 98%).“This implies that density, porosity, and grain size may have a negligible effect on the quality.”said Bo Zhang. Resistance-temperature (R-T) test results demonstrated that the Mg_0.8Mn_0.2Al_1.4Sc_0.2Fe_0.4O₄ ceramic exhibits typical NTC thermistive behavior over an ultra-wide temperature range of 200-1000°C, with a B-value as high as 9758 K. Moreover, the R-T curve displays near-ideal linearity (Pearson's r = 0.9995). Zhang further elucidated the mechanism underlying this exceptional property: “Sc³⁺ substitution effectively inhibits oxygen vacancy formation and regulates the valence ratio of Mn²⁺/Mn³⁺ and Fe³⁺/Fe²⁺ redox couples.” These conclusions were validated by experimental data obtained from XPS and EPR.

Additionally, the ceramics exhibit optimal microwave dielectric properties: low ε_r = 8.86-10.55, ultrahigh Q·f = 96,000-149,000 GHz, and near-zero τ_f = -33.2 to -10.2×10^-6/°C. “This is attributed to the lattice stabilisation induced by Sc³⁺ ions and the octahedral bond strength enhancement effect.” said Bo Zhang.

Although this study has successfully integrated microwave dielectric and NTC thermosensitive functions in Sc³⁺-modified spinel ceramics, several key challenges remain to be overcome for practical application in 6G systems. Future work should focus on the following areas: Conduct ageing performance studies to assess the long-term stability of the material, combine extreme environment adaptability testing to clarify its application boundaries, utilise far-infrared (FIR) reflectance spectroscopy to elucidate the intrinsic mechanisms underlying microwave dielectric properties, apply chemical bond theory (P-V-L) to reveal the intrinsic correlation mechanisms between crystal structure and functional properties, and focus on overcoming technical bottlenecks in the integration process of multifunctional devices.

Other contributors include Wenyuan Li, Yue Xian, Jianan Xu, and Aimin Chang from the Xinjiang Institute of Physics and Chemistry, Chinese Academy of Sciences; Hanao Deng and Yaxin Wei from Xinjiang University.

This work was supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region (Grant No. 2024D01E32), Xinjiang Tianshan Talent Training Program (Grant No. 2023TSYCCX0092), National Natural Science Foundation of China (Grant No. 62471468), and the Youth Innovation Promotion Association of CAS (Grant No. Y2023117).

About the Author

Professor Bo Zhang currently serves as a Research Fellow and PhD Supervisor at the Xinjiang Technical Institute of Physics and Chemistry, CAS, and has long been dedicated to research and application of high-temperature thermistor ceramic materials and devices. As an Outstanding Member of the Youth Innovation Promotion Association, Chinese Academy of Sciences; Winner of the 10th Xinjiang Youth Science and Technology Award; Xinjiang Tianshan Talent-Young Top-notch Talent; Xinjiang Tianshan Cedar - Leading Talent in Scientific and Technological Innovation; Recipient of the Xinjiang Outstanding Youth Fund; with visiting scholar experience at Alfred University, USA; and recipient of the President’s Award of the Chinese Academy of Sciences, he has achieved remarkable academic results: As the first author/corresponding author, he has published 67 SCI papers in journals such as J. Adv. Ceram., Small, J. Mater. Chem. A (3 ), Appl. Phys. Lett. (4 papers), J. Eur. Ceram. Soc. (5 papers), J. Am. Ceram. Soc. (10 papers), and ACS Appl. Mater. Interfaces (2 papers). As the first inventor, he has obtained 13 national invention patents (3 of which have been commercialized). Additionally, he has presided more than 20 national and provincial/ministerial-level scientific research projects, including 3 projects funded by the National Natural Science Foundation of China. He has successively received several awards such as the First Prize of Xinjiang Science and Technology Progress, the Final Winner of the 1st CAS "Pioneer Cup", the Second Prize of Science and Technology Progress of the China Electronic Components Industry Association, and the Second Prize of the "UCAS Cup" Innovation and Entrepreneurship Competition.

Dr. Li Wenyuan is a doctoral candidate at the Xinjiang Institute of Physics and Chemistry, CAS, where he primarily conducts research on microwave dielectric ceramics and resonator antenna substrates. As the first author, he has published five papers in journals such as J. Adv. Ceram., J. Am. Ceram. Soc., and J. Mater. Chem. A.