With 5G/6G communication technologies evolving toward space-air-ground-sea integrated networks (SAGSIN), the bottleneck for traditional functional ceramics is how to simultaneously achieve the stable microwave signal transmission and precise temperature sensing over a wide temperature range. Especially under the demand of expanding millimeter-wave communication bands to Ku/Ka bands, microwave dielectric ceramics need to simultaneously possess three key characteristics: (1) tunable dielectric constant (ε_r) to meet the requirement of device miniaturization; (2) high Q·f value to enhance frequency selectivity; (3) near-zero resonant frequency temperature coefficient (τ_f) to ensure thermal stability. Meanwhile, as “thermal managers” of system, negative temperature coefficient (NTC) thermistor ceramics need to exhibit high linearity and high B-value over a wide temperature range to calibrate temperature drift in real time.

Although spinel ceramics exhibit outstanding performance in single-functional domains, such as the excellent microwave properties of MgAl₂O₄ and the NTC characteristics of MnFe₂O₄, they have inherent defects: the former cannot realize thermistor functionality due to ultra-high resistivity, while the latter causes high-temperature electrical instability due to Fe³⁺/Fe²⁺ valence change. The B-value  of the Mg_0.8Mn_0.2Al_1.6Fe_0.4O₄ ceramics prepared via solid-solution design has increased to 8056 K, but they are still limited by oxygen vacancy-induced charge imbalance and non-Arrhenius behavior, leading to difficulty in reconciling microwave performance and thermistor linearity.

Recently, researchers from the Laboratory of Materials Physics and Chemistry at the Xinjiang Technical Institute of Physics and Chemistry, CAS, addressed issues concerning the nonlinear electrical properties and microwave loss of Mg-Al-Mn-Fe-O spinel ceramics at elevated temperatures. They proposed a strategy based on regulating the valence equilibrium through the Sc³⁺ lattice anchoring effect, simultaneously suppressing oxygen vacancy diffusion and strengthening octahedral bond valences.

Experimental results show that highly linear thermistor characteristics (B_{200℃/1000℃} = 8367-9758 K) are achieved within an ultra-wide temperature range of 200-1000°C, meeting the linearity requirements for wide-temperature-range temperature sensing. Meanwhile, a balance among low ε_r (10.08), ultra-high Q·f (149,000 GHz), and near-zero τ_f (-10.2×10^-6/°C) is realized in these ceramics. The cylindrical dielectric resonant antenna fabricated using this material achieves a radiation efficiency of 92% and a gain of 6.28 dBi in the 12 GHz satellite communication band, fully validating its engineering application potential in satellite communication front-end modules.

The study entitled “Sc³⁺-modified Mg-Al-Mn-Fe-O spinel ceramics with co-enhanced microwave dielectric and thermosensitive properties for multifunctional applications” has been published in Journal of Advanced Ceramics. The Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences served as the primary contributing institution. Doctoral candidate Wenyuan Li is the first author, with his supervisor, Professor BoZhang, acting as corresponding author. This work was supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region, Xinjiang Tianshan Talent Training Program, National Natural Science Foundation of China, and the Youth Innovation Promotion Association of CAS.

Figure. Structure, performance and application prospects of the prepared ceramics. (Image by Prof. ZHANG Bo's group)