Effects of Ag+ substitution on the enhanced microwave dielectric properties of Na4Co(MoO4)3 ceramics

Abstract

Novel Na4-xAgxCo(MoO4)3 (x = 0–0.09) compounds were prepared using a solid state ceramic route. The investigation focused on the impact of intrinsic and extrinsic factors on the microwave dielectric properties of the samples. All samples were identified as belonging to the monoclinic structure with the C2/c space group. An optimal combination of microwave dielectric properties (εr = 8.55, Q × f = 30,300 GHz and τf = –30 ppm/°C) can be obtained for pure Na4Co(MoO4)3 specimen fired at 660 °C. Partially replacing Na+ with Ag+ in Na4-xAgxCo(MoO4)3 ceramics resulted in a more stable structure and significantly increased the Q × f value to 64,000 GHz at x = 0.03. Additionally, the study suggested that Na3.95Ag0.05Co(MoO4)3, sintered at 600 °C, could be a very promising candidate for ULTCC applications at microwave and millimeter wave frequencies due to its high thermal stability. This compound exhibited tremendous microwave dielectric properties (εr = 9.2, Q × f = 53,000 GHz and τf = –9.8 ppm/°C), which fit well within the criteria for today's 5G/6G applications, and demonstrated good compatibility with Al pastes. The designed and fabricated hairpin filter on the Na3.95Ag0.05Co(MoO4)3 substrate also demonstrated an excellent frequency response for 5G/6G applications.