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1.
Effect of Ca substitution on structure and dielectric properties of bismuth-based microwave ceramics
The effect of the chemical substitution of Ca cation on the microstructure and microwave dielectric properties of bismuth-based pyrochlores has been investigated. Broad ranges of solid solutions based on (Bi3x Zn2?3x )(Zn x Nb2?x )O7 (x?=?0.56–0.64) were obtained with Ca cation substitution of Zn at A site. The XRD patterns revealed that the substitution of Ca for Zn led to the α–β pyrochlore phase transformation and pure β pyrochlore structure were obtained. The dielectric constants (? r ) varied slightly with x increasing. The quality factor Q was significantly improved by Ca substitution. The temperature coefficient of resonant frequency (τ f ) was negative and increased with x increasing. (Bi3x Ca2?3x )(Zn x Nb2?x )O7(x?=?0.58) ceramic, sintered at 960 °C, exhibits the optimal microwave dielectric properties of ? r ?~?74, Qf value ~6,457 (at 4.8 GHz), and τ f ?~??143 ppm/°C. 相似文献
2.
Effect of Gd amphoteric substitution on structure and dielectric properties of BaTiO3-based ceramics
Lingxia Li Mingjing Wang Dong Guo Ruixue Fu Qinglei Meng 《Journal of Electroceramics》2013,30(3):129-132
BaTiO3-based ceramics (doped with a small amount of Ni2+, Mn2+, Nb5+, Ca2+ and Zr4+) with various Gd2O3 concentrations were prepared by the conventional solid-state reaction method. Effects of Gd2O3 doping concentrations on the structure and dielectric properties were investigated. It was deduced from XRD patterns that different substitution sites of Gd3+ ions could be affected by Gd2O3 doping amount. Gd3+ tended to occupy Ba-site when Gd2O3 concentration was less than 0.25 mol%. With increasing Gd2O3 doping amount to 0.3 mol%, Gd3+ substituted into both Ba- and Ti-site which contributed to an obvious improvement on dielectric constant of BaTiO3-based ceramics. Influences of the Gd3+ amphoteric substitution on the improvement of the dielectric constant were discussed based on the self-compensation mechanism. 相似文献
3.
Jianzhang Shi Hong Wang Tingwei Yao Feng Xiang Xi Yao 《Journal of Electroceramics》2008,21(1-4):452-456
Two-dimensional electromagnetic bandgap structures (2D EBGs) are designed and fabricated by moulding/demoulding. A high permittivity and low dielectric loss microwave material, Bi2O3-ZnO-Nb2O5 (BZN) was used. The impacts of high permittivity on the 2D EBGs’ properties are investigated. As the experiments showed, wide electromagnetic band gap is found in the frequency ranges from 5.6 to 10.6 GHz, and 12.6 to 16.6 GHz. The first gap is greater than 60% of the gap center frequency, while the second gap is 25% of the center frequency. The interval between the two gaps is larger than 2 GHz, and the return loss of both gaps is as large as ?40 dB. This interesting phenomenon of multi band gaps is very useful for diplexers, multi-mode tunable dielectric antennas and resonators. Based on these, expansive applications may be exploited in the future. The experimental results are in good agreement with the simulations’. 相似文献
4.
In this paper we try to do systematic investigation on the structure and dielectric properties of low temperature sintered barium titanate based X7R ceramics, which are doped with rare earth oxide, Nb2O5, Co3O4 using ZnO–B2O3 as the sintering aids. The dielectric ceramic powder can be sintered at the temperature below 950°C to satisfy X7R requirement and also with good permittivity and low dielectric loss. The research strongly suggest that this doped BaTiO3 based ceramic, which can be sintered at a rather low temperature, may be used in the production of MLCC with low content of Pd in the Ag–Pd electrode, and for sure, the production cost would be greatly reduced. 相似文献
5.
In the present work, BaLaAlO4 ceramics with orthorhombic structure similar to K2SO4 in space group P212121 were prepared by a solid state sintering process. The dense BaLaAlO4 ceramics with minor amount of secondary phase have a low dielectric loss and a temperature stable dielectric constant with obvious frequency dependence. A dielectric constant around 15 was obtained at 12 GHz in the present ceramics together with a Qf value over 5,000 GHz. 相似文献
6.
A new patterning method combining electron beam (EB) lithography and electrophoretic deposition (EPD) for fabricating micropatterned barium titanate (BaTiO3) thin films was investigated. At first, resist molds with high resolution were prepared using EB lithography on Pt/Ti/Si substrates. Then BaTiO3 nanoparticles were deposited on the substrates by EPD from a transparent suspension of monodispersed BaTiO3 nanoparticles; a mixed solvent of 2-methoxyethonal and acetylacetone with a 9:1 volumetric ratio was used as a dispersion medium. The nanoparticles with an average size of about 10 nm were synthesized at a low temperature of 90 °C by a high concentration sol-gel process. EPD layers superfluously deposited on the resist molds were mechanically polished away, followed by chemically removing the molds in a resist remover to leave micropatterns of BaTiO3 nanoparticles on the substrates, which were finally sintered to yield micropatterned BaTiO3 ceramic thin films. The method developed may be used to fabricate other micropatterned electroceramic thin films. 相似文献
7.
Hu Qi Tang Jiayuan Teng Yuancheng Zhao Xiaofeng Arslanov Temirlan Ahuja Rajeev 《Journal of Electroceramics》2022,48(3):117-126
Journal of Electroceramics - CaCu3Ti4O12 ceramics have great dielectric constant, excellent temperature stability and good frequency stability. However, due to high dielectric loss, its practical... 相似文献
8.
Ba x Sr1-x TiO3, nanoparticles with different Ba compositions were synthesized by a hydrothermal method. The mechanism of hydrothermal reactions was discussed based on DTA/TG, XRD and TEM characterizations. The result showed that perovskite structure was developed through the mutual diffusion between the intermediate phases and TiO2 phase. The grain size of the Ba0.77Sr0.23TiO3 (BST77) powders was about 20–40 nm. BST ceramics were made from the hydrothermal-derived BST powders and the dielectric properties of the BST ceramics were measured. Due to the small grain size and active surface energy of the BST powders prepared by hydrothermal method, the BST ceramics showed low sintering temperature. It was found that the BST77 ceramics sintered at 1280 °C showed dielectric constant peak dispersion which was believed to be caused by dimension domino effect. 相似文献
9.
Z. Valdez-Nava S. Guillemet-Fritsch Ch. Tenailleau T. Lebey B. Durand J. Y. Chane-Ching 《Journal of Electroceramics》2009,22(1-3):238-244
In pursuit of high permittivity materials for electronic application, there has been a considerable interest recently in the dielectric properties of various perovskite oxides like calcium copper titanate or lanthanum doped barium titanate. When processed in a particular way, this later material present at ambient temperature and at f?=?1 kHz unusual interesting dielectric properties, a so called “colossal” permittivity value up to several 106 with relatively low dielectric losses. Moreover and contrary to what is classically expected and evidenced for this type of materials, no temperature dependence is observed. This behavior is observed in nanopowders based ceramics. An assumption to explain the observed properties is proposed. These results have important technological applications, since these nanoceramics open a new route to the fabrication of very thin dielectric films. 相似文献
10.
Nanocrystalline yttria powders have been successfully synthesized by using yttrium nitrate as starting salt and ammonium hydrogen
carbonate as precipitant. It was found that a small amount of ammonia sulfate in the yttrium nitrate solution can effectively
reduce the agglomeration and the resultant powders display good dispersion. Pure cubic phase yttria powders were prepared
by calcining the precipitate at 1100 °C for 4 h. The size of the as-prepared yttria powders was about 60 nm in diameter and
showed excellent sintering activity. The as-prepared yttria nanopowders and commercial ultrafine alumina powders were used
to fabricate YAG ceramics by solid-state reaction method and transparent YAG ceramics have been obtained by vacuum sintering
at 1760 °C for 6 h. 相似文献
11.
Monazite-type compounds, BiPO4 polymorphs were prepared by the solid-state reaction method. The phase transformation and microwave dielectric properties
of sintered ceramics were investigated using the X-ray powder diffraction (XRD) and a network analyzer, respectively. The
low-temperature phase of BiPO4 has monoclinic structure, and was transformed into the high-temperature phase with a slight distortion of monoclinic when
it is heated above 600∘C. The effect of the transformation on the microwave dielectric properties was examined. It was found that the dielectric
properties of each phase were significantly different. In particular, the high-temperature phase sintered at 950∘C has good microwave dielectric properties; the relative dielectric constant (ε
r
) = 22, the quality factor (Q× f) = 32,500 GHz and the temperature coefficient of resonant frequency (τ
f
) = − 79 ppm/ ∘C. 相似文献
12.
The effect of V2O5 substitution on the sintering behavior and the microwave dielectric properties of BiNbO4 ceramics were studied. The sintering temperatures of Bi(V x Nb1?x )O4 ceramics decrease from 990 to 810°C with x value increasing from 0.002 to 0.064. The size of grains increased with the sintering temperature increasing and decreased with the substitution amount increasing. The dielectric properties are affected by the microstructures very much. The quality factor Q value is from 2500 to 4000 at about frequency?=?5 GHz and reach to the maximum when x?=?0.032. With the different x value, the Q f values change between 15000 to 20000 GHz; the τ f values changes between 0 and +20 ppm/°C between temperature range 25~85°C and decreased with the increasing of x value. 相似文献
13.
ABSTRACTIn this paper, we prepare silver nanowires circuit graphics by UV-curing technology. The optimal condition of preparation of the silver nanowires circuit graphics are examined. Experiment results show that the UV-curing technology is a kind of individual, low-cost and environment-friendly method to prepare silver nanowires circuit graphics. The main influence factors on the lines' width are the UV beam power and scanning speed. And we also study the influence of the hot pressing temperature on the resistivity of the circuit graphics. In the experiments, the optimal condition is that the UV beam power is 190 mW and the scanning rate is 6 cm/s, then we get the minimum line width, which is 0.25 mm. The thickness of silver nanowires layer is 100 µm and the hot pressing temperature is 100°C, we will get the sample whose resistivity is 21× 10?5 Ω·cm. 相似文献
14.
Mg4Nb2O9 ceramics have been prepared by a hydrothermal synthesis in order to reduce the sintering temperature. The sintering and microwave dielectric properties of the hydrothermally processed Mg4Nb2O9 were studied under various sintering temperatures ranging from 900 to 1300°C. The highest Q×f o value of 26,069 GHz was obtained at the sintering temperature of 1300°C and is attributed to the increased density and appropriate grain growth. τ f value of ?17.1 ppm/°C was improved by the addition of TiO2 and τ f value of 6.7 ppm/°C was obtained at 20 wt% TiO2. Chemical compatibility of Mg4Nb2O9 with Ag was tested to identity the possibility of using Mg4Nb2O9 for an LTCC application. Since any secondary phase was not observed in the XRD pattern of the mixtures of Mg4Nb2O9 and Ag powder heat treated at 900°C, it was considered that the Mg4Nb2O9 system is applicable to the multilayer microwave devices using Ag as an electrode. 相似文献
15.
16.
The effects of CuO and TiO2 additives on the microstructure and microwave dielectric properties of Al2O3 ceramics were investigated. Al2O3 ceramics with CuO and TiO2 additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti4Cu2O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO2 content, due to the formation of the second phase Ti4Cu2O. However, the varying behaviors of the dielectric constant (ɛ
r
) and temperature coefficients (τ
f
) were associated with phase constitutions, as a result of the change of CuO and TiO2content. The τ
f
can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO2. The specimens with 0.5 wt.% CuO and 7 wt.% TiO2 sintered at 1,360 °C for 4 h showed ɛ
r
of 11.8, Qf value of 30,000 GHz, and τ
f
of −7 ppm/°C. 相似文献
17.
18.
Atomic force microscopy (AFM) has become an attractive technique to fabricate nano devices since the observing mechanism is different from fabricating one. We have fabricated the superconducting flux flow transistor (SFFT) with a serial-channel structure using the AFM lithography analyzed the modified surface by the AFM image. We investigated the induced voltage in a serial-channel terminals dependence on the gate current by the I–V measurement system. We performed the numerical simulation to get the theoretical characteristics of the SFFT controlled by the gate current via the modified channel. The transresistance was 0.006 Ω for Id=51 mA at Ig=5 mA. It is very low transresistance in comparison with SFFTs fabricated by the other processes, however our results show that the SFFT with a serial-channel structure is effectively fabricated by an AFM lithography method. 相似文献
19.
F. Levassort J. Holc E. Ringgaard T. Bove M. Kosec M. Lethiecq 《Journal of Electroceramics》2007,19(1):127-139
Porous ceramics are of interest for ultrasonic transducer applications. Porosity allows to decrease acoustical impedance,
thus improving transfer of acoustical energy to water or biological tissues. For underwater applications, the dhgh figure of merit can also be improved as compared to dense materials. In the case of high frequency transducers, namely for
high resolution medical imaging, thick film technology can be used. The active films are generally porous and this porosity
must be controlled. An unpoled porous PZT substrate is also shown to be an interesting solution since it can be used in a
screen-printing process and as a backing for the transducer. This paper describes the fabrication process to obtain such materials,
presents microstructure analysis as well as functional properties of materials. Modelling is also performed and results are
compared to measurements. Finally, transducer issues are addressed through modelling and design of several configurations.
The key parameters are identified and their effect on transducer performance is discussed. A comparison with dense materials
is performed and results are discussed to highlight in which cases porous piezoceramics can improve transducer performance,
and improvements are quantified. 相似文献