Novel Method to Achieve Temperature-Stable Microwave Dielectric Ceramics: A Case in the Fergusonite-Structured NdNbO4 System

• Published in: ACS applied materials & interfaces 2023-04, Vol.15 (15), p.19129-19136
• Main Authors: Zhou, Di, Zhang, Ling, Xu, Di-Ming, Qiao, Feng, Yao, Xiaogang, Lin, Huixing, Liu, Wenfeng, Pang, Li-Xia, Hussain, Fayaz, Darwish, Moustafa Adel, Zhou, Tao, Chen, Yawei, Liang, Qixin, Zhang, Meirong, Reaney, Ian M.
• Format: Article
• Language: English
• Subjects: Functional Inorganic Materials and Devices
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.2c23180

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 V5+ ions (r V = 0.355 Å, with coordination number (CN) = 4) were substituted for Nb5+ (r Nb = 0.48 Å with CN = 4) in the Nd­(Nb1–x V x )­O4 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 (αL) of the high-temperature scheelite phase was +11 ppm/°C, whereas for the low-temperature fergusonite phase, it was + 14 < αL < + 15 ppm/°C. The abrupt change in αL, the associated negative temperature coefficient of permittivity (τε), and the minimum value of ε r at T F‑S resulted in a near-zero TCF ∼ (+7.8 ppm/°C) for Nd­(Nb0.8V0.2)­O4 (ε r ∼ 18.6 and Qf ∼ 70,100 GHz). A method to design near-zero TCF compositions based on modulation of τε and αL at T F‑S is thus demonstrated that may also be extended to other fergusonite systems.