Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO<sub>4</sub> System
Di Zhou, Ling Zhang, Diming Xu, Feng Qiao, Xiaogang Yao, Huixing Lin, Wenfeng Liu, Li‐Xia Pang, Fayaz Hussain, Moustafa A. Darwish, Tao Zhou, Yawei Chen, Qi‐Xin Liang, Meirong Zhang, Ian M. Reaney
Abstract
Microwave dielectric ceramics with permittivity (ε r ) ∼ 20 play an important role in massive multiple-input multiple-output (MIMO) technology in 5G. Although fergusonite-structured materials with low dielectric loss are good candidates for 5G application, tuning the temperature coefficient of resonant frequency (TCF) remains a problem. In the present work, smaller V 5+ ions ( r V = 0.355 Å, with coordination number (CN) = 4) were substituted for Nb 5+ ( r Nb = 0.48 Å with CN = 4) in the Nd(Nb 1– x V x )O 4 ceramics, which, according to in situ X-ray diffraction data, lowered the fergusonite-to-scheelite phase transition ( T F-S ) to 400 °C for x = 0.2. The thermal expansion coefficient (α L ) of the high-temperature scheelite phase was +11 ppm/°C, whereas for the low-temperature fergusonite phase, it was + 14 < α L < + 15 ppm/°C. The abrupt change in α L, the associated negative temperature coefficient of permittivity (τ ε ), and the minimum value of ε r at T F-S resulted in a near-zero TCF ∼ (+7.8 ppm/°C) for Nd(Nb 0.8 V 0.2 )O 4 (ε r ∼ 18.6 and Qf ∼ 70,100 GHz). A method to design near-zero TCF compositions based on modulation of τ ε and α L at T F-S is thus demonstrated that may also be extended to other fergusonite systems.