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In this paper, a series of Li 2 Zn[Ti 1- x (Co 1/3 Nb 2/3) x ] 3 O 8 (0.0 ≤ x ≤ 0.4) ceramics were prepared via the conventional solid-state method. The influences of (Co 1/3 Nb 2/3)4+ complex ions on the phase composition, spectral characteristics, microstructure, and microwave dielectric properties of Li 2 Zn[Ti 1- x (Co 1/3 Nb 2/3) x ] 3 O 8 ceramics were studied systematically. XRD analysis accompanied with Rietveld refinements showed that pure Li 2 ZnTi 3 O 8 solid solution ceramics with the cubic spinel structure were obtained at x = 0.2–0.4. New Raman-active mode of about 858 cm−1 should be attributed to the vibrations of NbO 6 due to the high bond energy of Nb–O bonds, exerting a certain impact on the structure and performance of Li 2 Zn[Ti 1- x (Co 1/3 Nb 2/3) x ] 3 O 8 ceramics. XPS results indicated that Nb5+ ion donor suppressed the deoxidation process and therefore resulted in the disappearance of Ti3+ ion and oxygen vacancy. The downward trend variation in the ε r value with the increase of (Co 1/3 Nb 2/3)4+ content could be explained by the presence of "compressed" cations and "rattling" cations effect. In addition, the Q × f of the current ceramics was closely dependent on relative density, grain size, FWHM, and oxygen vacancy. Good combined microwave dielectric properties of ε r = 24.5, Q × f = 91,250 GHz, and τ f = −16.8 ppm/°C were achieved for the Li 2 Zn[Ti 0.8 (Co 1/3 Nb 2/3) 0.2 ] 3 O 8 ceramic sintered at 1120 °C. High quality factor gives evidence that the Li 2 Zn[Ti 0.8 (Co 1/3 Nb 2/3) 0.2 ] 3 O 8 ceramic is an appealing candidate for highly selective microwave devices. [ABSTRACT FROM AUTHOR]

In this study, LiF was utilized to decrease sintering temperature, improve microstructure, enhance Q × f , and regulate τ f of Li 2 Ti 0.9 (Zn 1/3 Ta 2/3) 0.1 O 3 (abbreviated as LTZT) ceramics. A complete solid solution together with a phase transition from monoclinic to cubic rock salt structure occurred. The cell volume of LTZT ceramics decreased as the LiF content increased. Relatively dense and uniform microstructures were observed for the ceramics as the LiF content was not less than 2 wt%. The dielectric constant of LTZT ceramics initially increased and then decreased with the increasing LiF content. The FWHM of the Raman band at about 808 cm−1 was closely related to the Q × f value. Notably, the samples with 3 wt% LiF exhibited the highest relative density of 97.4 % and satisfactory microwave dielectric properties of ε r = 23.14 ± 0.16, Q × f = 110,090 ± 1100 GHz, and τ f = +3.25 ± 1.45 ppm/°C when sintered at 950 °C. Good chemical compatibility with silver indicated the ceramic is a promising candidate in LTCC applications. [ABSTRACT FROM AUTHOR]

We report a successful fabrication of 0.6Ca0.61Nd0.26TiO3–0.4Nd(Zn0.5Ti0.5)O3 (hereinafter abbreviated as 6CNT–4NCT) microwave ceramics with good sintering activity and desired dielectric properties from EDTA-gel combustion synthesized powders in this paper. The as-synthesized nanopowders have been characterized by X–ray diffraction (XRD), Fourier transformation infrared (FT–IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques, respectively. The sintering behavior and dielectric performance have been evaluated on the sintered ceramics. The as-obtained product with amorphous structure could be directly crystallized and produced pure 6CNT–4NCT solid solution phase with orthorhombic perovskite structure at a relatively low temperature of 700 °C, without formation of any intermediate phase. TEM images revealed that homogeneous and well dispersed spherical-shaped nanostructure with an average particle size of 23.8 nm was formed at 800 °C. Well-dense 6CNT–4NCT bulk ceramics with 98.8% relative density were obtained at a relatively low sintering temperature of 1225 °C due to high sintering activity of nanopowders. Moreover, the bulk ceramics exhibited a higher quality factor (Q × f) value than those prepared via the conventional solid-state reaction method. Desired microwave dielectric properties were achieved at 1200 °C: dielectric constant εr = 57.2, Q × f = 59,360 GHz, and temperature coefficient of resonant frequency τf = + 1.95 ppm/°C. This study indicates that the EDTA-gel combustion route is a convenient, low-cost, and interesting route to fabricate high-quality microwave ceramics for practical applications. [ABSTRACT FROM AUTHOR]