Bilayer co-fired microwave dielectric ceramics in Sm0.5Na0.5TiO3-Sm0.5Li0.5TiO3 system

To compensate for the large positive temperature coefficient of resonant frequency (τ f ) in a typical ABO 3 -type perovskite-structured Sm 0.5 Na 0.5 TiO 3 ceramic material, the laminated Sm 0.5 Na 0.5 TiO 3 -Sm 0.5 Li 0.5 TiO 3 (SNT-SLT) microwave dielectric ceramic system is designed with the tunable layer mass fractions. Among all the compositions of x gSm 0.5 Na 0.5 TiO 3 -(2– x )gSm 0.5 Li 0.5 TiO 3 ( x  = 0.8, 0.9, 1.0, 1.1, and 1.2) and the sintered temperatures (1200–1400 °C), the sample with 0.9 g SNT and 1.1g SLT sintered at 1200 °C exhibits a near-zero τ f  ≈ −1.1 ppm/°C, while maintaining a relatively higher ε r  ≈ 69.6 and Q×f  ≈ 3043 GHz in these SNT-SLT ceramics. Wherein, the most noteworthy characteristic results show that the interfacial diffusion of A-site cations leads to the formation of an inhomogeneous solid-solution region, which becomes more pronounced at the higher sintering temperatures. Additionally, the relatively higher sintered temperatures (1250–1400 °C) can intensify the interfacial diffusion and solid-solution formation, which ultimately results in a decrease in the Q×f values. The microwave dielectric measurements in the 3–4 GHz band reveal that the τ f values vary approximately linearly with the increasing SNT content. This study presents a promising strategy for the development of the advanced bilayer ceramic systems and highlights their potential in the next-generation 5G/6G communication devices.