Influences of substituting of (Ni1/3Nb2/3)4+for Ti4+on the phase compositions, microstructures, and dielectric properties of Li2Zn[Ti1−x(Ni1/3Nb2/3)x]3O8(0 ≤x≤ 0.3) microwave ceramics

Abstract

Complex ions substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics. In this work, Li₂Zn[Ti_1-<em>x</em>(Ni_1/3Nb_2/3)<em>_x</em>]₃O₈ (LZTNN<em>x</em>, 0 ≤ <em>x</em> ≤ 0.3) ceramics were designed based on complex ions substitution strategy, following the substitution rule of radius and valence to investigate the relationships between phase composition (containing oxygen vacancies and Ti³⁺ ions), microstructure, and microwave dielectric characteristics of LZTNN<em>x</em> ceramics. The samples maintained a single Li₂ZnTi₃O₈ solid solution phase as <em>x</em> ≤ 0.2 whereas the <em>x</em> = 0.3 sample produced a secondary phase with LiNbO₃ structure. The appropriate amount of (Ni_1/3Nb_2/3)⁴⁺ substitution could slightly improve the densification of LZTNN<em>x</em> ceramics due to the formation of Li₂ZnTi₃O₈ solid solution accompanied by a decrease in average grain size. The presence of a new <em>A</em>_1g Raman active band at about 848 cm^-1 indicated that the local symmetry changed, affecting the atomic interactions of LZTNN<em>x</em> ceramics. The variation in dielectric constant (ε<em>_r</em>) was closely related to molar volume ionic polarizability, and the temperature coefficient of resonant frequency (τ<em>_f</em>) was related to the bond valence of Ti. The increase in density, the absences of Ti³⁺ ions and oxygen vacancies, and the reduction in damping behavior were responsible for decreased dielectric loss. The LZTNN0.2 ceramic sintered at 1120 ^oC exhibited favorable microwave dielectric properties: ε<em>_r</em> = 22.13, quality factor (<em>Q</em>×<em>f)</em> = 97350 GHz, and τ<em>_f</em> = −18.6 ppm/^oC, which might be a promising candidate for wireless communication applications in highly selective electronics.