Sc³⁺-modified Mg–Al–Mn–Fe–O spinel ceramics with co-enhanced microwave dielectric and thermosensitive properties for multifunctional applications

With the rapid development of communication technology, multifunctional ceramics that integrate microwave dielectric and negative temperature coefficient (NTC) thermistor properties have met the evolving needs of electronic components. Although conventional spinel oxides excel in single functionalities, they struggle to simultaneously achieve linear NTC behavior and stable microwave dielectric performance over a wide temperature range. To address this, the role of Sc³⁺ substitution in modifying Mg_0.8Mn_0.2Al_1.6Fe_0.4O₄ ceramics was systematically investigated. The results demonstrate that Sc³⁺ substitution effectively inhibits oxygen vacancy formation and achieves the ratio regulation of the Mn²⁺/Mn³⁺ and Fe³⁺/Fe²⁺ bimetallic redox pairs, which significantly improves the material constant B (B_200/1000°C = 8367–9758 K) and enables linear resistance–temperature curves (lnρ–1000/T) within a broad temperature range (200–1000 °C). Additionally, the ceramics exhibit optimal microwave dielectric properties: low dielectric constants (ε_r = 8.86–10.55), ultrahigh quality factors (Q∙f = 96,000–149,000 GHz), and near-zero temperature coefficients of resonant frequency (τ_f = −33.2×10⁻⁶ to −10.2×10⁻⁶ °C⁻¹), resulting from Sc³⁺-induced lattice stabilization and octahedral bond-valence strengthening effects. A cylindrical dielectric resonator antenna (CDRA) fabricated from Mg_0.8Mn_0.2Al_1.3Sc_0.3Fe_0.4O₄ achieves 92% radiation efficiency and 6.28 dBi gain at 12 GHz, validating its potential for Ku-band satellite communication. This work reveals that Sc³⁺ substitution synergistically enhances both the microwave dielectric and thermosensitive functionalities of Mg–Al–Mn–Fe–O spinel ceramics, offering a breakthrough in material design for next-generation multifunctional communication devices.