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Li 2 TiO 3 -based materials are gaining momentum in the field of microwave dielectric ceramics for their moderate dielectric constant and high-quality factor. Herein, a novel oxyfluoride ceramic Li 3 TiO 3 F in the Li 2 TiO 3 –LiF system was successfully prepared by a traditional ceramic method. The synthesis process of Li 3 TiO 3 F ceramic was optimized to obtain improved microstructure and desired microwave dielectric properties (MDP) by means of material characterization techniques, such as thermogravimetric-differential thermal analysis, X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. A cubic rock salt structure for Li 3 TiO 3 F ceramic was confirmed by Rietveld refinement results. The ceramic sintered at 900 °C showed the most favorable MDP of ε r = 17.28, quality factor (Q × f) = 96,280 GHz, and τ f = −32.7 ppm/°C, obtaining a microstructure superior to that of Li 2 TiO 3. Moreover, the ceramic exhibited favorable chemical compatibility with Ag at 900 °C, indicating a great potential for the use of Li 3 TiO 3 F ceramic as substrates in low temperature cofired ceramic (LTCC) technology. More importantly, the results of this work offered the option of using low temperature firing of ceramic by forming a solid solution between the oxide and the fluoride. [ABSTRACT FROM AUTHOR]

Nowadays, low-temperature co-fired ceramic (LTCC) technology has become one of the main forms of manufacturing electronic devices. However, a majority of microwave dielectric ceramics are not suitable as LTCC materials due to their high sintering temperatures. Developing novel LTCC materials with good microwave dielectric properties is extremely urgent. In this paper, an LiF sintering aid was added to Li2Ti0.8(Co1/3Nb2/3)0.2O3 (LTCN) ceramics to explore new LTCC materials. The sintering behavior, microstructure and microwave dielectric properties of LTCN + x wt% LiF ceramics were investigated in detail. The results indicated that the addition of LiF increased the degree of disorder in the LTCN matrix, transforming it from a monoclinic to a cubic crystal system. The ceramics exhibited relatively dense and homogeneous microstructures at the sintering temperature of 950 °C as the LiF doping amount was not less than 2 wt%. By LiF doping, the quality factor (Q × f) value was significantly enhanced due to the improved microstructure. Meanwhile, the temperature coefficient of resonant frequency (τf) of LTCN ceramics was successfully regulated to the near zero value owing to the negative τf characteristic of LiF. Excellent microwave dielectric properties of dielectric constant (εr) = 19.01, Q × f = 144,890 GHz, τf = −1.52 ppm/°C were obtained when the sample doped 3 wt% LiF was sintered at 950 °C for 3 h. Furthermore, the good chemical compatibility of the LTCN-3 wt% LiF ceramic with silver electrodes suggested that the ceramic was a potential material for LTCC applications. [ABSTRACT FROM AUTHOR]

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 paper, nanocrystalline Nd[(Zn0.925Co0.075)1/2Ti1/2]O3 (NZCT75) powders were synthesized through glycine–nitrate combustion method with the intent of reducing the sintering temperature and improving the microwave dielectric properties of NZCT75 ceramics. Phase composition, structure, and morphology of the powders were analyzed by thermogravimetric analysis–differential thermal analysis (TG–DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRD results showed that the as-synthesized powder after rapid self-propagating combustion was highly crystallized and was mainly composed of NZCT75 phase and small amount of unknown phase. The unknown phase could be vanished through the calcination process of 600 °C. Compared to solid-state reaction route, a reduction of about 600 °C in the synthesis temperature for pure phase NZCT75 was realized. A large amount of pores with inhomogeneous distribution in size and shape was found from the SEM image of the as-synthesized powder due to the rapid combustion reaction between glycine and nitrates. The TEM study revealed that the average particle size of the calcined powder is around 31.9 nm. The bulk sample prepared by the nanosized powder could be sintered to 98.8% of the theoretical density at 1250 °C, reducing about 160 °C more than the solid-state reaction method. Meanwhile, excellent microwave dielectric properties of NZCT75 ceramics presented a dielectric constant of 37.17, a quality factor of 257,600 GHz, and a temperature coefficient of resonant frequency of – 29.48 ppm/oC. This study develops a facile approach to synthesize nanocrystalline powder for a promising application in microwave dielectric ceramics. [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]