Complex ion substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics. In this work, Li₂Zn[Ti_1−x(Ni_1/3Nb_2/3)_x]₃O₈ (LZTNNx, 0 ≤ x ≤ 0.3) ceramics were designed based on the complex ion substitution strategy, following the substitution rule of radius and valence to investigate the relationship among phase compositions (containing oxygen vacancies and Ti³⁺ ions), microstructures, and microwave dielectric characteristics of the LZTNNx ceramics. The samples maintained a single Li₂ZnTi₃O₈ solid solution phase as x ≤ 0.2, whereas the sample of x = 0.3 produced a second phase with the LiNbO₃ structure. The appropriate amount of (Ni_1/3Nb_2/3)⁴⁺ substitution could slightly improve the densification of the LZTNNx ceramics due to the formation of the Li₂ZnTi₃O₈ solid solution accompanied by a decrease in the average grain size. The presence of a new A_1g Raman active band at about 848 cm⁻¹ indicated that local symmetry changed, affecting atomic interactions of the LZTNNx ceramics. The variation of the relative dielectric constant (ε_r) was closely related to the molar volume ionic polarizability ( ${\alpha }_{\text{D}}^{\text{T}}$), and the temperature coefficient of the resonant frequency (τ_f) was related to the bond valence (V_i) of Ti. The increase in density, the absence of the Ti³⁺ ions and oxygen vacancies, and the reduction in damping behavior were responsible for the decreased dielectric loss. The LZTNN0.2 ceramics sintered at 1120 ℃ exhibited favorable microwave dielectric properties: ε_r = 22.13, quality factor (Q×f) = 97,350 GHz, and τ_f = −18.60 ppm/℃, which might be a promising candidate for wireless communication applications in highly selective electronics.

A rapid and facile approach was developed for the synthesis of ultrafine SmAlO₃ powders through the combustion of stearic acid precursors. The obtained products were characterized by typical techniques including X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to analyze the phase composition and microstructure. The dielectric characteristics of SmAlO₃ microwave ceramics, using the as-obtained products as original materials, were also studied. Compared with the conventional solid-state reaction method, the synthesis temperature was dramatically reduced to 750 ℃. The large-size sheet structure was composed of a number of micro/nano-scale crystallites, which were mostly irregular in shape due to the mutual growth and overlapping shapes of adjacent grains. The SmAlO₃ ceramics with high density and uniform microstructure were obtained after sintering at 1500 ℃ for 4 h due to the favorable sintering activity of the as-synthesized powders. In addition, desired dielectric properties at microwave frequencies (dielectric constant ε_r = 20.22, quality factor Q·f = 74110 GHz, and a temperature coefficient of resonant frequency τ_f = -74.6 ppm/℃) were achieved.