Influences of substituting of (Ni_1/3Nb_2/3)⁴⁺ for Ti⁴⁺ on the phase compositions, microstructures, and dielectric properties of Li₂Zn[Ti_1−x(Ni_1/3Nb_2/3)_x]₃O₈ (0 ≤ x ≤ 0.3) microwave ceramics

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.