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1.
Microwave dielectric properties of (Zn1/3Nb2/3)0.40(Ti1−xSnx)0.60O2 ceramics were investigated as a function of SnO2 content (0.15 ≤ x ≤ 0.30). A single phase with tetragonal rutile structure was obtained through the entire composition. The unit-cell volume of the specimens was increased with SnO2 content, due to the larger ionic radius of Sn4+ (0.69 Å) than that of Ti4+ (0.605 Å) for octahedral site. Dielectric constant (K) of the sintered specimens was affected by the dielectric polarizability. Quality factor (Qf) was dependent on the degree of reduction of Ti4+ ion. With an increase of SnO2 content, the temperature coefficient of resonant frequency (TCF) of the specimens decreased due to the decrease of the octahedral distortion of rutile structure. 相似文献
2.
It is known that Curie temperature of barium titanate system can be altered by the substitution of dopants into either A- or B-site. Dopants could pinch transition temperature, lower Curie temperature, and raise the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transition close to room temperature. This isovalent substitution could improve the ferroelectric properties of the BaTiO3-based system. In this study, barium zirconate titanate Ba(ZrxTi1−x)O3 (BZT; x = 0, 0.02, 0.05 and 0.08) ceramics were prepared by conventionally mixed-oxide method. The ferroelectric properties of BZT ceramics were investigated. Increasing Zr content in the BaTiO3-based compositions caused a decrease in Curie temperature (Tc). At Tc, the highest relative permittivity of BZT with an addition of 0.08 mol% of Zr was 12,780. The BZT specimens with the additions of 0.05 mol% and 0.08 mol% of Zr presented the remanent polarization at 25 μC/cm2 and 30 μC/cm2, respectively. 相似文献
3.
The sintering behavior and dielectric properties of the monoclinic zirconolite-like structure compound Bi2(Zn1/3Nb2/3)2O7 (BZN) and Bi2(Zn1/3Nb2/3−xVx)2O7 (BZNV, x = 0.001) sintered under air and N2 atmosphere were investigated. The pure phase were obtained between 810 and 990 °C both for BZN and BZNV ceramics. The substitution of V2O5 and N2 atmosphere accelerated the densification of ceramics slightly. The influences on microwave dielectric properties from different atmosphere were discussed in this work. The best microwave properties of BZN ceramics were obtained at 900 °C under N2 atmosphere with r = 76.1, Q = 850 and Qf = 3260 GHz while the best properties of BZNV ceramics were got at 930 °C under air atmosphere with r = 76.7, Q = 890 and Qf = 3580 GHz. The temperature coefficient of resonant frequency τf was not obviously influenced by the different atmospheres. For BZN ceramics the τf was −79.8 ppm/°C while τf is −87.5 ppm/°C for BZNV ceramics. 相似文献
4.
Dependence of microwave dielectric properties on the crystal structure of (Zn1/3B2/35+)xTi1 − xO2 (B5+ = Nb, Ta) ceramics was investigated as a function of Zn1/3B2/35+O2 (B5+ = Nb, Ta) content (0.4 ≤ x ≤ 0.7). Dielectric constant (K) and the temperature coefficient of resonant frequency (TCF) of sintered specimens were strongly dependent on the structural characteristics of oxygen octahedra in rutile structure. Cation rattling and the distortion of oxygen octahedra were dependent on the bond length ratio of apical (dapical)/equatorial (dequatorial) of oxygen octahedra. The quality factor (Qf) was dependent on the reduction of Ti ion as well as the microstructure of the sintered specimens. 相似文献
5.
Bi2O3–ZnO–Nb2O5-based pyrochlore ceramics are receiving increasing attention due to their excellent dielectric properties in the microwave frequency range. Site disorder at the pyrochlore A-site is well known for lone pair active cations like Bi3+ and is attributed as the reason for this material's high dielectric constant and tunability. Bismuth zinc niobate ((Bi1.5Zn0.5)(Nb1.5Zn0.5)O7) [BZN] ceramics are prepared by the conventional solid-state reactions. The relative permittivity (r) and the dielectric loss tangent (tan δ) of the BZN ceramics sintered at 1000 °C are found to be around 130 and 0.0004, respectively at a frequency of 1 MHz measured at room temperature. The impedance spectroscopy measurements are conducted at different temperatures to separate grain and grain boundary contributions to the dielectric constant. The tunability of these ceramics is studied under a constant dc bias voltage. 相似文献
6.
Lead free piezoelectric Bi0.5(Na0.5K0.5)0.5TiO3 (pure and 1 wt.%, 2 wt.%, 4 wt.% Sb-doped) ceramics were synthesized away from its MPB. The crystalline nature of the BNKT ceramic was studied by XRD and SEM. Depolarization temperature (Td) and transition temperature (Tc) were observed through phase transitions in dielectric studies which were found to increase after Sb-doping, thus increasing its usable temperature range. In the study of relaxation behavior, the activation energy for relaxation was found to be 0.33, 0.43, 0.57 and 0.56 eV for pure and Sb-doped samples, respectively. All samples were found to exhibit normal Curie-Weiss law above their Tc. Doping of Sb was found to restrain the diffused character of the pure sample. In P-E loop, Sb-doping was found to increase the ferroelectric properties.Pure and Sb-doped BNKT ceramics exhibited high values of piezoelectric charge coefficient (d33) as 115, 121, 129 and 100 pC/N, respectively. 相似文献
7.
M. Unruan N. Vittayakorn R. Wongmaneerung A. Prasatkhetragarn S. Ananta R. Yimnirun 《Ceramics International》2009
Pb(Co1/3Nb2/3)O3 (PCN) ceramics have been produced by sintering PCN powders synthesized from lead oxide (PbO) and cobalt niobate (CoNb2O6) with an effective method developed for minimizing the level of PbO loss during sintering. Attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development, dielectric and ferroelectric properties of the sintered ceramics. From X-ray diffraction analysis, the optimum sintering temperature for the high purity PCN phase was found at approximately 1050 and 1100 °C. The densities of sintered PCN ceramics increased with increasing sintering temperature. However, it is also observed that at very high temperature the density began to decrease. PCN ceramic sintered at 1050 °C has small grain size with variation in grain shape. There is insignificant change of dielectric properties with sintering temperature. The P–E hysteresis loops observed at −70 °C are of slim-loop type with small remanent polarization values, which confirmed relaxor ferroelectric behavior of PCN ceramics. 相似文献
8.
New ternary compositions in the Pb(Mg1/3Nb2/3)O3-Pb(Yb1/2Nb1/2)O3–PbTiO3 (PMN-PYbN-PT) system were prepared using 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 (PYbNT) and (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (x = 0.26; PMNT26 or x = 0.325; PMNT32.5) powders synthesized via the columbite method. Dense (≥ 96% of theoretical density) ceramics with PMN/PYbN mole ratios of 25/75 (R-25), 50/50 (R-50) and 75/25 (R-75T and R-75R) were fabricated by reactive sintering at 1000 °C for 4 h. Therefore, incorporation of PYbNT to PMNT successfully decreased sintering temperature of PMNT from 1200 °C-1250 °C to 1000 °C. Samples with higher density and perovskite ratio together with lower weight loss possessed higher dielectric and piezoelectric values in each composition. The R-75 samples had remanent polarization (Pr) values of 34-36 μC/cm2 and piezoelectric charge coefficient (d33) of 560 pC/N. The sharp phase transition PMNT as a function of temperature became broader or more diffuse with increasing PYbNT content. However, PYbNT addition to PMNT increased Curie temperature (Tc) from 183 °C (for PMNT32.5) to 220-242 °C (for R-75T and R-75R) to 336 °C (for R-25). Therefore, these ternary compositions can be tailored for various high temperature applications due to the relatively higher Tc with enhanced piezoelectric and dielectric properties as compared to PMNT. 相似文献
9.
Wei LiZhijun Xu Ruiqing ChuPeng Fu Guozhong Zang 《Journal of the European Ceramic Society》2012,32(3):517-520
Lead-free (Ba1−xCax)(Ti0.94Sn0.06)O3 (BCST) (x = 0.01-0.04) ceramics were prepared using a solid-state reaction technique. The effects of Ca content on the phase structure and electrical properties of the BCST ceramics were investigated. High piezoelectric coefficient of d33 = 440 pC/N, planar electromechanical coupling factor of kp = 45% and dielectric constant ?r = 6900 were obtained for the samples at x = 0.03. At room temperature, a polymorphic phase transition (PPT) from orthorhombic phase to tetragonal phase was identified in the composition range of 0.02 < x < 0.04. 相似文献
10.
Preparation, microstructure and microwave dielectric properties of ZrxTi1−xO4 (x=0.40–0.60) ceramics
S. X. Zhang J. B. Li J. Cao H. Z. Zhai B. Zhang 《Journal of the European Ceramic Society》2001,21(16):2931-2936
ZrxTi1−xO4 (x=0.40–0.60) ceramics sintered without additives were prepared from powders made by the coprecipitation of metal salts from aqueous solutions in order to investigate the existence range of a homogeneous phase and the relationships between composition, microstructure and the dielectric properties. XRD, TEM, SEM, EDS, and the dielectric measurements were used to characterize the products. A homogeneous solid solution was obtained. Its crystal structure was isomorphous with ZrTiO4. The variation of the lattice parameters with TiO2 content was discussed. The optimum sintering temperature of samples was dependent of composition. TiO2 suppressed the densification and acted as a grain growth enhancer during the sintering process. With the increase in TiO2 content the relative densities of the sintered bodies decrease, while the grain sizes increase. The dielectric properties at microwave frequency (1.8 GHz) in this system, especially Q value, were poor, due to low densification, impurities and lattice defects. The dielectric constant r and Q value exhibited a significant dependence on the relative density and composition. Both r and Q increased with the increase in relative density, but they were primarily influenced by the composition and the effect of the relative density could be ignored when the relative density was greater than 90% theoretical. r increased slightly with increasing TiO2 content, while Q value decreased. 相似文献
11.
The compositionally graded and homogeneous Ba(ZrxTi1−x)O3 (BZT) thin films were fabricated on LaNiO3 (LNO) buffered Pt/Ti/SiO2/Si and Pt/Ti/SiO2/Si substrates by a sol–gel deposition method, respectively. These films crystallized into a single perovskite phase. The BZT thin films deposited on LaNiO3/Pt/Ti/SiO2/Si substrates had a highly (1 0 0) preferred orientation and exhibited a preferred (1 1 0) orientation when the thin films were deposited on Pt/Ti/SiO2/Si substrates. The LNO and Ba(Zr0.30Ti0.70) served as seed layer on Pt/Ti/SiO2/Si substrates and analyze the relationship of seed layer, microstructure and dielectric behavior of the thin films. The compositionally graded thin films from BaTiO3 to BaZr0.35Ti0.65O3 were fabricated on LNO/Pt/Ti/SiO2/Si substrates. The tunability behavior of compositionally graded films was analyzed in order to produce optimum effective dielectric properties. The dielectric constant of BaZrxTi1−xO3 compositionally graded thin films showed weak temperature dependence. This kind of thin films has a potential in a fabrication of a temperature stable tunable device. 相似文献
12.
Bi2O3 was selected as liquid phase sintering aid to lower the sintering temperature of La(Mg0.5Ti0.5)O3 ceramics. The sintering temperature of La(Mg0.5Ti0.5)O3 ceramics is generally high, about 1600 °C. However, the sintering temperature was significantly lowered about 275 °C from 1600 °C to 1325 °C by incorporating in 15 mol% Bi2O3 and revealed the optimum microwave dielectric properties of dielectric constant (?r) value of 40.1, a quality factor (Q × f) value of 60,231 GHz, and the temperature coefficient (τf) value of 70.1 ppm/°C. During all addition ranges, the relative dielectric constants (?r) were different and ranged from 32.0 to 41.9, the quality factors (Q × f) were distributed in the range of 928–60,231 GHz, and the temperature coefficient (τf) varies from 0.3 ppm/°C to 70.3 ppm/°C. Noticeably, a nearly zero τf can be found for doping 5 mol% Bi2O3 sintering at 1325 °C. It implies that nearly zero τf can be achieved by appropriately adjusting the amount of Bi2O3 additions and sintering temperature for La(Mg0.5Ti0.5)O3 ceramics. 相似文献
13.
The influence of various sintering aids on the microwave dielectric properties and the structure of Nd(Mg0.5Ti0.5)O3 ceramics were investigated systematically. B2O3, Bi2O3, and V2O5 were selected as liquid-phase sintering aids to lower the sintering temperature. The sintered Nd(Mg0.5Ti0.5)O3 ceramics are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and microwave dielectric properties. The sintering temperature of Nd(Mg0.5Ti0.5)O3 microwave dielectric ceramics is generally high, about 1500 °C. However, the sintering temperature was significantly lowered about 175 °C from 1500 °C to 1325 °C by incorporating in 10 mol% B2O3 and revealed the optimum microwave dielectric properties of dielectric constant (r) value of 26.2, a quality factor (Q × f) value of 61,307 (at 9.63 GHz), and τf value of −45.5 ppm/°C. NdVO4 secondary phase was observed at 10 mol% V2O5 addition in the sintering temperature range of 1300–1325 °C, which led the degradation in microwave dielectric properties. The microwave dielectric properties as well as grain sizes, grain morphology, and bulk density were greatly dependent on sintering temperature and various sintering aids. In this study, it is found that Nd(Mg0.5Ti0.5)O3 incorporated with 10 mol% B2O3 with lower sintering temperature and excellent dielectric microwave properties may be suggested for application in microwave communication devices. The use of liquid-phase sintering, the liquid formed during firing normally remains as a grain boundary phase on cooling. This grain boundary phase can cause a deterioration of the microwave properties. Therefore, the selection of a suitable sintering aid is extremely important. 相似文献
14.
(Mg1−xZnx)2SiO4 ceramics were prepared and characterized. The densification temperatures of the present ceramics are much lower than those for Mg2SiO4 and Zn2SiO4 end-members. Small solid solution limits of Zn in Mg2SiO4 and Mg in Zn2SiO4 are observed, and the bi-phase structure is confirmed in (Mg1−xZnx)2SiO4 ceramics with x = 0.1–0.9. Even though, it is clear that the Qf value of Zn2SiO4 ceramics can be significantly improved together with a suppressed temperature coefficient of resonant frequency τf by substituting Mg for Zn. (Mg0.4Zn0.6)2SiO4 ceramics indicate a good combination of microwave dielectric characteristics: r = 6.6 Qf = 95,650 GHz, and τf = −60 ppm/°C. 相似文献
15.
Single-phase dielectric ceramics Li2CuxZn1−xTi3O8 (x=0–1) were synthesized by the conventional solid-state ceramic route. All the solid solutions adopted Li2MTi3O8 cubic spinel structure in which Li/M and Ti show 1:3 order in octahedral sites whereas Li and M are distributed randomly in tetrahedral sites with the degree of Li/M cation mixing varying from 0.5 to 0.3. The substitution of Cu for Zn effectively lowered the sintering temperatures of the ceramics from 1050 to 850 °C and significantly affected the dielectric properties. As x increased from 0 to 0.5, τf gradually increased while the dielectric constant (εr) and quality factor value (Q×f) gradually decreased, and a near-zero τf of 1.6 ppm/°C with εr of 25.2, Q×f of 32,100 GHz could be achieved for Li2Cu0.1Zn0.9Ti3O8 ceramic sintered at 950 °C, which make it become an attractive promising candidate for LTCC application. As x increases from 0.5 to 1, the dielectric loss significantly increases with AC conductivity increasing up to 2.3×10−4 S/cm (at 1 MHz). 相似文献
16.
In this study, Ba(Zn1/3Ta2/3)O3-based complex perovskite compounds, including Ba(Zn1/3Ta2/3)O3, Ba(Zn1/3Ta1/3Nb1/3)O3, Ba(Zn1/6Co1/6Ta2/9Nb2/9Sb2/9)O3, and Ba1/2Sr1/2(Zn1/6Co1/6Ta2/9Nb2/9Sb2/9)O3, were prepared and characterized. There was no second phase formation shown in the XRD patterns. Though it has been suggested that substitutions of multiple ions over A-site or B-site of the Ba(Zn1/3Ta2/3)O3 ceramics may not be beneficial to their microwave dielectric properties, the Ba(Zn1/6Co1/6Ta2/9Nb2/9Sb2/9)O3 and Ba1/2Sr1/2(Zn1/6Co1/6Ta2/9Nb2/9Sb2/9)O3 ceramics in this study were found to perform in a fairly acceptable manner. The Ba(Zn1/6Co1/6Ta2/9Nb2/9Sb2/9)O3 ceramic (sintered at 1575 °C for 6 h) and the Ba1/2Sr1/2(Zn1/6Co1/6Ta2/9Nb2/9Sb2/9)O3 ceramic (sintered at 1550 °C for 6 h) reported the following characteristics after annealing at 1400 °C for 10 h: 24.9 and 27.0 for dielectric constants (?r), 83,000 and 32,100 GHz for quality factors (Q × f) values and −12.8 and −22.6 ppm/°C for temperature coefficients of resonance frequency (τf). 相似文献
17.
Synthesis,structural analysis and dielectric properties of Ba8(Mg1−xZnx)Nb6O24 hexagonal perovskites
Ba8(Mg1−xZnx)Nb6O24 (x=0, 0.2, 0.4, 0.6, 0.8 and 1) ceramics were prepared through the conventional solid-state route. The materials were calcined at 1250 °C and sintered at 1375–1425 °C. The structure of the system was analyzed using X-ray diffraction and vibrational spectroscopic studies. The microstructure of the sintered pellet was analyzed using scanning electron microscopy. The dielectric constant (εr), temperature coefficient of resonant frequency (τf) and the unloaded quality factor (Qu) were measured in the microwave frequency region. The τf values of the compositions were reduced by varying the value of x from 0 to 1. The dielectric responses to frequency were also studied in the radio frequency region. The compositions have good microwave dielectric properties and hence are suitable for dielectric resonator applications. 相似文献
18.
Shengquan Yu Shuren ZhangBin Tang Xiaohua ZhouYouwei Fang 《Ceramics International》2012,38(1):613-618
Microwave dielectric properties of (1 − x)BaZn2Ti4O11-xBaNd2Ti4O12 (x = 0-1.0) ceramics were investigated by the solid-state reaction with the purpose of finding a microwave ceramics with high dielectric constant (?r), high quality factor (Q × f) and low temperature coefficient of resonant frequency (τf). A two phase system BaZn2Ti4O11-BaNd2Ti4O12 was formed and SEM photographs show equiaxed BaZn2Ti4O11 grains and columnar BaNd2Ti4O12 grains. The microwave dielectric properties were strongly determined by the chemical composition. As increasing x from 0 to 1.0, the phase composition varied from pure BaZn2Ti4O11, to the two phase system BaZn2Ti4O11-BaNd2Ti4O12 and then to pure BaNd2Ti4O12. Therefore, the ?r raised from 29.1 to 82.0 and the Q × f values decreased from 54,630 GHz to 8110 GHz, and the τf values increased from −29 ppm/°C to 94 ppm/°C. 0.8BaZn2Ti4O11-0.2BaNd2Ti4O12 ceramics sintered at 1250 °C for 2.5 h had ?r = 39.1, Q × f = 37,850 GHz and τf = −9 ppm/ °C. 相似文献
19.
A novel low-loss microwave dielectric material MgZrNb2O8 was reported for the first time. Single-phase MgZrNb2O8 was prepared by a conventional mixed-oxide route and sintered in the temperature range of 1280–1360 °C. The microstructure and microwave dielectric properties were investigated systematically. The X-ray diffraction results showed that all samples exhibit a single wolframite structure. When the sintering temperature was lower than 1340 °C, the Q×f value mainly depended on the relative density. However, when the sintering temperature was above 1340 °C, the Q×f value mainly relied on the grain morphology in addition to the density. The MgZrNb2O8 ceramic sintered at 1340 °C for 4 h exhibited excellent microwave dielectric of εr=26, Q×f=120,816 GHz (where f=6.85 GHz), and τf=?50.2 ppm/°C. These results demonstrate that MgZrNb2O8 could be a promising candidate material for the application of highly selective microwave ceramic resonators and filters. 相似文献
20.
The microwave dielectric properties of Sm(Mg0.5Ti0.5)O3 incorporated with various amount of Bi2O3 and B2O3 additives have been investigated systematically. In this study, both Bi2O3 and B2O3 additives acting as a sintering aid can effectively lower the sintering temperature from 1550 °C to 1300 °C. The ionic radius of Bi3+ for a coordination number of 6 is 0.103 nm, whereas the ionic radius of B3+ is 0.027 nm. Clearly, the ionic radius of Bi3+ is greatly larger than one of B3+, which resulted in the specimens incorporated with Bi2O3 having larger lattice parameters and cell volume than those incorporated with B2O3. The experimental results show that no second phase was observed throughout the entire experiments. Depending on the interfacial tension, the liquid phase may penetrate the grain boundaries completely, in which case the grains will be separated from one another by a thin layer as shown in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with Bi2O3. Whereas, in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with B2O3, the volume fraction of liquid is high, the grains may dissolve into the liquid phase, and rapidly rearrange, in which case contact points between agglomerates will be dissolved due to their higher solubility in the liquid, leading plate-like shape microstructure.A dielectric constant (?r) of 29.3, a high Q × f value of 26,335 GHz (at 8.84 GHz), and a τf of −32.5 ppm/°C can be obtained for Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 10 mol% Bi2O3 sintered at 1300 °C. While Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 5 mol% B2O3 can effectively lower temperature coefficient of resonant frequency, which value is −21.6 ppm/°C. The Sm(Mg0.5Ti0.5)O3 ceramic incorporated with heavily Bi2O3 and B2O3 additives exhibits a substantial reduction in temperature (∼250 °C) and compatible dielectric properties in comparison with that of an un-doped one. This implied that this ceramic is suitable for miniaturization in the application of dielectric resonators and filters by being appropriately incorporated with a sintering aid. 相似文献