Entropy engineering for advanced microwave ceramics

Relative dielectric constant (ε_r), quality factor (Q×f), and temperature coefficient of resonant frequency (τ_f) are pivotal parameters for microwave dielectrics. A common strategy for tuning these parameters involves modifying the cation-oxygen octahedral geometry. However, conventional approaches, such as foreign-element doping or solid-solution, narrow the designable compositional space, resulting in insufficient tunability of octahedral structural attributes, which limits the synergistic properties modulation. Here, we introduce configurational entropy as a structural index to simultaneously regulate central-cation displacement, octahedral distortion, and M-O bond covalency, enabling synergistic improvement of microwave properties. Our results show that cation displacement, and octahedral distortion are positively correlated with configurational entropy, whereas M-O bond covalency shows a non‑monotonic trend, consistent with the systematic modulation of ε_r, τ_f, and Q×f. The optimized composition exhibits ε_r ~ 22.3, high Q×f (~ 140,000 GHz), and near-zero τ_f (-14.8 ppm/°C) in NiNb₂O₆-based medium-entropy ceramics. Furthermore, we fabricate a prototype dielectric antenna that achieves broad frequency selectivity within the 5-8.5 GHz range and high energy conversion efficiency (>99.98 %), demonstrating its potential applications.