Open Access Research Article Issue
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
Journal of Advanced Ceramics 2023, 12 (4): 760-777
Published: 15 March 2023
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Complex ion substitution is gaining more attention as an appealing method of modifying the structure and performance of microwave ceramics. In this work, Li2Zn[Ti1−x(Ni1/3Nb2/3)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 (Ni1/3Nb2/3)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 A1g 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 (εr) was closely related to the molar volume ionic polarizability ( αDT), and the temperature coefficient of the resonant frequency (τf) was related to the bond valence (Vi) 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: εr = 22.13, quality factor (Q×f) = 97,350 GHz, and τf = −18.60 ppm/℃, which might be a promising candidate for wireless communication applications in highly selective electronics.

Open Access Research Article Issue
Structure, morphology, and microwave dielectric properties of SmAlO3 synthesized by stearic acid route
Journal of Advanced Ceramics 2020, 9 (5): 558-566
Published: 22 June 2020
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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 εr = 20.22, quality factor Q·f = 74110 GHz, and a temperature coefficient of resonant frequency τf = -74.6 ppm/℃) were achieved.

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