Papers by Keyword: Microwave Dielectric Ceramics

Abstract: The 0.85(Mg_0.7Zn_0.3)TiO₃-0.15(Ca_0.61La_0.26)TiO₃(referred to as 85M₇Z₃CLT) ceramics were fabricated by microwave sintering(MWS) and conventional sintering(CS) techniques. The effects of MWS and CS on the sintering property, crystal phase structure and dielectric properties of 85M₇Z₃CLT were discussed. Compared with CS, MWS had a short sintering period and a high volume density. The results indicated that the phase composition of 85M₇Z₃CLT ceramics were not changed after MWS, with (Mg_0.7Zn_0.3)TiO₃ and (Ca_0.61La_0.26)TiO₃ structure as the main crystal phase were also obtained by MWS. However, the grain growth was significantly inhibited due to the rapid sintering speed of MWS, which resulted in a fine, uniform microstructure. Furthermore, microwave-sintered ceramics had excellent dielectric properties due to the miscellaneous phase (Mg_0.7Zn_0.3)Ti₂O₅ being suppressed. As a result, excellent dielectric properties of 27.11 for ε_r, 103,500GHz for Q·f and +2ppm/°C for τ_f were obtained by microwave sintering at 1275°C for 20 min. Therefore, the ceramic quality factor was increased by 22% compared with the conventional sintering.Key words: microwave technique; (Mg,Zn)TiO₃; dielectric ceramics

Abstract: A low temperature sintering method was used to avoid the relatively high sintering temperatures typically required to prepare 0.67CaTiO₃-0.33LaAlO₃ (CTLA) ceramics. 0.67CaTiO₃-0.33LaAlO₃ ceramics doped with Li₂O-B₂O₃-SiO₂ (LBS) were prepared by a conventional two-step solid-state reaction process. The sintering behavior, crystal structure, surface morphology, and microwave dielectric proprieties of the prepared ceramics were studied. As the small amount of LBS content increased, the small amount of liquid phase formed in an amorphous state around the surface of the grain boundaries. With the increase the content of LBS glass, the quality factor (Q×f) value decreased. CTLA+0.05 wt.% LBS ceramics sintered at 1320°C for 4h exhibited the optimal microwave dielectric properties of dielectric permittivity (ε_r) = 45.02, quality factor (Q×f) = 37400 GHz, and temperature coefficient of resonant frequency (τ_f) = 9.84 ppm/°C. .

Abstract: The effects of B₂O₃ on the sinterability and microwave dielectric properties of Ca [(Li_1/3Nb_2/3)_0.95Zr_0.05]O_3−δ ceramics were investigated. B₂O₃ doping can effectively reduce sintering temperatue by 150~200oC. The temperature coefficient of resonator frequency τ_f increased with an increase of B₂O₃ content and sintering temperatue. When B₂O₃ of 2wt% were added, the optimum microwave dielectric properties: ε_r =28.7,Qf =13580GHz and τ_f = − 7.8×10⁻⁶/oC were obtained at the sintering temperature of 950oC.

Abstract: (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O₇ (BZN) ceramic samples were prepared by solid state reaction. B₂O₃ was introduced by liquid coating technology with H₃BO₃ solution in the BZN ceramic specimen to reduce its sintering temperature. The sintering behavior, phase composition and dielectric properties of ceramics were investigated by X-ray diffraction, scanning electron microscopy and vector network analyzer. The (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O₇ ceramic composite could be sintered well at 900°C for 3h when 0.9M/l H₃BO₃ was added and showed good dielectric properties of ε_r=150,Q×f=228,τ_f=-362ppm/°C.

Abstract: The (Mg_0.8Zn_0.2)TiO₃(MZT) as the foundation is mainly studied to join high dielectric material Ba₄Nd_28/3Ti₁₈O₅₄·zBi₂O₃(BNT) to preparation microwave dielectric ceramic 0.7(Mg_0.8Zn_0.2)TiO₃·0.3{Ba₄Nd_28/3Ti₁₈O₅₄·zBi₂O₃}(z=0.15, 0.18, 0.2) to improve dielectric properties of MZT. While Bi³⁺ could reduce the sintering temperature to make MZT and BNT composite in a lower sintering temperature (1200~1230 °C). According to the results of the dielectric properties, density, XRD and SEM tests of the obtained ceramics, we can find out that the amount of doped Bi³⁺ and the sintering temperature affected the structure and properties of the ceramics. The results show that when z=0.18, 0.7(Mg_0.8Zn_0.2)TiO₃·0.3{Ba₄Nd_28/3Ti₁₈O₅₄·zBi₂O₃}

Abstract: Ba [Zn_1/3(Nb_1-xTa_x)_2/3]O₃ (BZNT, x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solutions were synthesized by conventional solid-state sintering technique. Fourier transform far-infrared reflection spectroscopy (FTIR) and X-ray diffraction (XRD) were employed to evaluate the correlation between crystal structures and vibration modes of these solid solutions as a function of Nb⁵⁺ ions replaced by Ta⁵⁺ ions. Spectroscopic and structural data show sensitivity to the sample structural evolution with Ta⁵⁺ concentration. XRD result shows that the peaks shift to lower angle, i.e. higher d-spacing, with the increase in Ta⁵⁺content, and the lattice structures have changed from cubic structure to hexagonal structure gradually with the increase in the unit cell volume due to the substitution of Ta⁵⁺ to Nb⁵⁺. The phase transition is also verified by the FTIR spectra. The phonon modes of the vibration spectra were assigned, the position and width were determined, and the correlation of phonon vibrations with the crystal structures for the different atoms substituted in the-site was found.

Abstract: The effects of B2O3 on the sinterability and microwave dielectric properties of Ca[(Li1/3Nb2/3)0.95Zr0.05]O3−δ−0.04TiO2 (CLNZ−0.04TiO2) ceramics were investigated . B2O3 doping can effectively reduce sintering temperatue by 150~200°C. The temperature coefficient of resonator frequency τf increased with an increase of B2O3 content and sintering temperatue. When B2O3 of 2wt% were added, the optimum microwave dielectric properties: εr =31.8,Qf =17240GHz and τf = − 5.9×10−6/°C were obtained at the sintering temperature of 950°C.

Abstract: Ba₂Ti₉O₂0 ceramics were prepared with different additives of B₂O₃ by liquid coating method and solid phase mix method. The sintering behavior, phase structure and dielectric properties of ceramics were investigated by X-ray diffraction, scanning electron microscopy and inductance-capacitance resistance analysis. The liquid coating method can reduce the amount of sintering aid and minimized the negative impact of sintering aid on dielectric properties. A ceramic composite which could be sintered well at 900°C for 3h and showed good dielectric properties of εr=42,tanδ=0.002 and TCF=-4ppm/°C（1MHz）was obtained when 1.0mol/l H₃BO₃ was added to the Ba₂Ti₉O₂₀ ceramic.

Abstract: MgTa₂O₆ powders with the tetragonal phase have been synthesized by mixed oxide method at 1100 °C when the molar ratios of MgO and Ta₂O₅ increase from 1:1 to 1.2:1. The microwave dielectric properties of sintered MgTa₂O₆ ceramics without additives at 1400°C for 6h, which consists of tetragonal and orthorhombic phases have been investigated. The results show that the ceramic possesses a dielectric constant of 27.5, a high Q×f value of 156000 GHz and a temperature coefficient of resonant frequency of 21.6 ppm/°C at 6-10 GHz. Different amounts of CuO has been used as sintering additives to lower the sintering temperature of MgTa₂O₆ ceramics. The effect of the CuO doping agent on the microstructure, densification and the microwave dielectric properties of MgTa₂O₆ ceramics has been studied using X-ray diffraction, scanning electron microscope and HP8720ES network analyzer. The results indicate that the 1-5 wt. % CuO dopant can lower the sintering temperatures of this materials dramatically. The second phase of CuTa₂O₆ was found in MgTa₂O₆ ceramics, which caused the deterioration of Q×f value of the ceramics.

Abstract: Aluminum Oxide microwave dielectric ceramics exhibit good microwave dielectric characteristics and suitable be used in the microwave devices. In this letter, using screen-printing technique and Ag/Pd paste, a novel dual-mode 2.4 GHz microstrip bandpass filter with U-shaped defected ground structure is screen printed on the Aluminum Oxide (Al₂O₃, relative dielectric constant=9.8) microwave dielectric ceramic substrate. In addition, a pair of input/output microstrip lines are designed to be 50 Ω and coupled to a λ/4×λ/4 square loop resonator. And in the ground plane, a U-shaped defected ground structure is used toλ excite the degenerate modes, which can be considered as a perturbation element to control the odd-mode frequency and -3 dB bandwidth of the bandpass filter. Finally, the coupling effects between these degenerate modes are presented and detailed investigated.