Morphotropic‐Like Phase Boundary Enables Continuous τ ƒ Regulation in ZnNb 2 O 6
Zhiqiang Zhang, Simin Wang, Bangxi Xie, Guangzhao Shi, Haiyi Peng, Shaohu Jiang, Xiaogang Yao, Kaixin Song, Di Zhou, Huixing LinABSTRACT
Low‐loss and high‐performance microwave dielectric ceramics are essential for emerging fifth‐generation (5G) and sixth‐generation (6G) communication systems. However, conventional composite strategies rely on fixed phase fractions to compensate the temperature coefficient of resonant frequency (TCF) ( τ ƒ ), often at the expense of quality factor (Q × ƒ) and without enabling continuous τ ƒ regulation. Here, a morphotropic‐like phase boundary (MPB‐like) is constructed in ZnNb 2 O 6 ‐based ceramics through synergistic control of composition and sintering temperature. Near the orthorhombic‐tetragonal phase boundary, the competing phases possess comparable formation energetics, making the phase fraction highly sensitive to sintering temperature. This enables a continuous τ ƒ tuning from −65 to +50 ppm/°C within a narrow composition‐temperature window through temperature‐driven phase evolution. At the phase boundary, the optimized ceramic exhibits dielectric constant ( ε r ) = 46, Q × ƒ = 37 000 GHz, and τ ƒ = −0.22 ppm/°C. Raman and terahertz spectroscopies reveal that an optimal local cation configuration contributes to the low dielectric loss. A cylindrical dielectric resonator antenna (DRA) fabricated from this ceramic delivered an experimentally measured reflection coefficient of −42.79 dB at 9.6 GHz and a simulated radiation efficiency of 88%. This work establishes a temperature‐sensitive phase‐boundary regulation mechanism, providing a new strategy for precise τ ƒ control in microwave dielectric ceramics.