Novel ultralow-permittivity BaMg2Al6Si9O30-based microwave dielectric ceramics with self near-zero temperature coefficient of resonant frequency and thermal expansion

• Published in: Journal of the European Ceramic Society 2023-12, Vol.43 (16), p.7485-7492
• Main Authors: Du, Kang, Zhou, Mengdie, Liu, Zheyu, Wen, Tailai, Yin, Changzhi, Cai, Yiyang, Li, Xiaoxiao, Zhu, Wei, Guo, Jianyong, Wang, Shengxiang, Lei, Wen
• Format: Article
• Language: English
• Subjects: BaMg2Al6Si9O30 ceramic; Microwave dielectric property; Near-zero thermal expansion; Phase composition
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2023.07.078

Novel BaMg2Al6Si9O30-based ceramics were prepared using the traditional solid-phase reaction method, and this paper presents the fabrication procedure, crystal structure, microstructure, microwave dielectric properties and temperature coefficient of thermal expansion of BaMg2Al6Si9O30-based ceramics. BaMg2Al6Si9O30-based ceramics were found to possess a hexagonal crystal structure with the P6/mcc space group. The BaAl2Si2O8 and BaMg2Al6Si9O30 phases coexisted in BaMg2Al6Si9O30 ceramic given that raw MgO material reacted easily with water vapour in the air, and the BaMg2Al6Si9O30 single-phase ceramic could be synthesized with calcined raw MgO material. The BaMg2Al6Si9O30 single-phase ceramic exhibited ultralow εr (5.68 at 14.05 GHz), moderate Q×f value (28534 GHz at 14.05 GHz), a self near-zero τf value (7.35 ppm/°C), a near-zero average temperature coefficient of thermal expansion (+1.89 ppm/°C) at 30 °C1000 °C and a rare negative temperature coefficient of thermal expansion (9.43 ppm/°C) at 655 °C710 °C. The rare near-zero and negative thermal expansions of the BaMg2Al6Si9O30 single-phase ceramic were mainly related to the strong Si/Al-O bonds with high relative covalency and 2 coordinate O(1) allowing longitudinal vibrations.