Abstract: During the co-firing of Sm_0.5Na_0.5TiO₃-Sm_0.5Li_0.5TiO₃ (SNT-SLT) isostructural perovskite bilayer ceramics, interfacial residual stress arises from mismatches in lattice parameters and thermal expansion coefficients between the dissimilar layers, which in turn induces extrinsic dielectric loss at the interfaces. Although the isostructural perovskite bilayer design can partially alleviate this stress, the improvement in dielectric loss remains limited. In order to further suppress this interfacial extrinsic dielectric loss, this study designed and fabricated a trilayer ceramic by introducing an SNT-SLT solid-solution intermediate layer. The phase composition, microstructure, and interfacial characteristics of SNT+xg(SNT-SLT)+SLT (x=0.0~0.20) samples were systematically investigated by XRD, SEM-EDS, Raman spectroscopy, TEM, and their microwave dielectric properties were evaluated. XRD results indicate that all trilayer ceramics retain a single orthorhombic perovskite structure without detectable secondary phases. In the Raman spectra, the red shifts of the Ti-O stretching mode and the A-site cation vibration mode indicate local lattice relaxation, confirming that the introduction of the solid-solution interlayer effectively relieves interfacial stress concentration. TEM observations reveal that the intermediate layer exhibits uniform lattice fringes with spacings falling between those of SNT and SLT, reflecting the formation of a solid solution. Meanwhile, EDS analysis shows directional diffusion of Na⁺ from the SNT side to the SLT side, corroborating that an appropriate amount of the intermediate layer facilitates the formation of a smooth compositional transition zone. When the intermediate-layer addition is 0.10 g and sintering is carried out at 1200 ℃ for 4 h, the trilayer ceramic preserves a dielectric constant (ε_r ≈ 69.5) and temperature stability (τ_f ≈ +2.1×10^-6 ℃^-1) comparable to those of the SNT-SLT bilayer system, while showing markedly reduced dielectric loss, as reflected by an improved Q×f value of about 3413 GHz. These results demonstrate that introducing an SNT-SLT solid-solution intermediate layer enables a smooth compositional transition across the interface, effectively relieves interfacial stress, and suppresses extrinsic dielectric loss, thereby providing an effective strategy for tailoring the microwave dielectric properties of multilayer isostructural ceramics.

Key words: microwave dielectric properties, dielectric loss, multilayer ceramics, isostructural perovskite, microstructural characteristics