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1.
Hong Xia Yuan Xiang Ming Chen Min Min Mao 《Journal of the American Ceramic Society》2009,92(10):2286-2290
CaNdAlO4 microwave dielectric ceramics were modified by Ca/Ti co-substitution, and their dielectric characteristics were evaluated along with their structure and microstructures. Ca1+ x Nd1− x Al1− x Ti x O4 ( x =0, 0.025, 0.05, 0.10, 0.15, 0.20) ceramics with the relative density of over 95% theoretical density were obtained by sintering at 1400°–1450°C in air for 3 h, where the K2 NiF4 -type solid solution single phase was determined from the compositions of x <0.20, while a small amount of CaTiO3 secondary phase was detected for x =0.20. With Ca/Ti co-substitution in CaNdAlO4 ceramics, the dielectric constant (ɛr ) increased with increasing x , and the temperature coefficient of resonant frequency (τf ) was adjusted from negative to positive, while the Q × f 0 value increased significantly at first and reached an extreme value at x =0.025 and the maximum at x =0.15. The best combination of microwave dielectric characteristics were achieved at x =0.15 (ɛr =19.5, Q × f 0 =93 400 GHz, τf =−2 ppm/°C). The improvement of the Q × f 0 value primarily originated from the reduced interlayer polarization with Ca/Ti co-substitution, while the decreased tolerance factor, the subsequent increased interlayer stress, and the appearance of CaTiO3 secondary phase brought negative effects upon the Q × f 0 value. 相似文献
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Chang Wei Zheng Xie Cheng Fan Xiang Ming Chen 《Journal of the American Ceramic Society》2008,91(2):490-493
Infrared reflection spectra of (Mg1− x Zn x )Al2 O4 ceramics were analyzed by Kramers–Kroning analysis and classical oscillator model simulation. The dielectric properties were extrapolated down to the microwave range using the classical oscillator model for fitting the dielectric function. According to structure analysis, the losses originating from bend vibration and stretch vibration of the bond between A-site cation and oxygen anion dominated the whole dielectric losses of the spinel ceramics. The coexistence of Mg and Zn deteriorated the intrinsic dielectric properties due to the bond asymmetry thus introduced. The calculated Qf (∼105 GHz) was much higher than the measured ones (∼104 GHz), suggesting that the extrinsic loss was significant. Therefore, the microwave dielectric properties of MgAl2 O4 and ZnAl2 O4 could be improved much by microstructure modification, and the little superiority in their solution compared with the end-members was due to microstructure improvement. 相似文献
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Fei Zhao Zhenxing Yue Jing Pei Hao Zhuang Zhilun Gui Longtu Li 《Journal of the American Ceramic Society》2007,90(8):2461-2466
Microwave dielectric ceramics with the composition of Ba[Ti1− x (Ni1/2 W1/2 ) x ]O3 ( x =0.4–0.6) were prepared by a solid-state reaction method. The evolution of the crystalline phases was investigated by X-ray powder diffraction analysis. A cubic-to-hexagonal phase transition occurred between 1000° and 1300°C. The phase transition is irreversible; thus, the hexagonal phase remains stable at room temperature. The X-ray powder diffraction data for x =0.5 were refined using the Rietveld method. It was identified as a h -BaTiO3 -type hexagonal perovksite with the space group of P 63 / mmc . It also reveals that random occupancy of Ti4+ and W6+ ions occurs in the B-site substructures, whereas Ni2+ ions exclusively occupy the octahedral site in the corner-sharing octahedron. The dielectric properties of dense-sintered ceramics were characterized at microwave frequencies. With an increase in x from 0.4 to 0.6, the Q × f value increased from 26 700 to 42 000 GHz, whereas ɛr decreased from 29.8 to 20.0, and τf from +6.5 to −9.9 ppm/°C. 相似文献
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Modification of the microwave dielectric properties in Ba6−3 x Nd8+2 x Ti18 O54 ( x = 0.5) solid solutions by Bi/Sm cosubstitution for Nd was investigated. A large increase in the dielectric constant and near-zero temperature coefficient combined with high Qf values were obtained in modified Ba6−3 x Nd8+2 x Ti18 O54 solid solutions where an enlarged solid solution limit of Bi in Ba6−3 x Nd8+2 x Ti18 O54 was observed. Excellent microwave dielectric characteristics (ɛ= 105, Qf = 4110 GHz, and very low τf ) were achieved in the composition Ba6−3 x (Nd0.7 Bi0.18 Sm0.12 )8+2 x Ti18 O54 . 相似文献
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Xiuying Guo Ning Zhu Mi Xiao Xiawan Wu 《Journal of the American Ceramic Society》2007,90(8):2467-2471
Sb2 O5 were selected to substitute (Nb0.8 Ta0.2 )2 O5 and the effects of Sb substitution on the dielectric properties of Ag(Nb0.8 Ta0.2 )O3 ceramics were studied. The perovskite Ag(Nb0.8 Ta0.2 )1− x Sb x O3 ceramics showed no obvious change with x value being no more than 0.08, and the pseudoperovskite unit cell parameters a = c , b and monoclinic angle β decrease with Sb concentration increasing. The dielectric properties of Ag(Nb0.8 Ta0.2 )1− x Sb x O3 ceramics were found to be affected greatly by the substitution of Sb for Nb/Ta. The ɛ value of Ag(Nb0.8 Ta0.2 )1− x Sb x O3 ceramics sintered at their densified temperature increased from 480 to 825 with x from 0 to 0.08, the tan δ value decreased sharply from 0.0065 to 0.0023 (at 1 MHz) with x increasing from 0 to 0.04, and then kept a stable lower tan δ value ∼0.0024 with x to 0.08. The temperature coefficient of capacitance values continuously decreased from a positive value of 1450 ppm/°C for x =0 to a negative value of −38.52 ppm/°C for x =0.08. 相似文献
6.
Yi Li Xiang Ming Chen † Ni Qin YaoWu Zeng 《Journal of the American Ceramic Society》2005,88(2):481-484
Tin (Sn) substitution for titanium (Ti) was investigated in Ba6−3 x Nd8+2 x Ti18 O54 ( x =1/2, 2/3, and 3/4) ceramics. A small amount ( z <0.1) of Sn substitution resulted in Ba6−3 x Nd8+2 x (Ti1− z Sn z )18 O54 solid solutions, and some secondary phases were observed with increasing Sn content. A small amount of Sn substitution improved the Q f value significantly, while, due to the formation of secondary phases, the Q f value degraded sharply for larger Sn content. The relative dielectric constant (ɛr ) decreased with increasing Sn-content, while the temperature coefficient of resonant frequency (τf ) generally decreased, although an obvious fluctuation was observed for x =3/4. 相似文献
7.
Hui Zhang Liang Fang Heping Su Qian Yu Bolin Wu 《Journal of the American Ceramic Society》2009,92(1):238-240
Single-phase polycrystalline microwave dielectric ceramics Ba6 Ti1− x Sn x Nb4 O18 , with x changing from 0 to 1, were synthesized by the solid-state reaction method. All the solid solutions fitted well with A6 B5 O18 cation-deficient hexagonal perovskite structure. The substitution of Sn for Ti effectively enhanced the quality factor and controlled τf . With increasing Sn content, the dielectric constant decreased from ∼47 to ∼32, and the Q × f value increased significantly from 11 530 to 28 496 GHz, with τf varying from 64 to 0 ppm/°C. A zero τf was realized when Sn was fully replaced by Ti with the composition Ba6 SnNb4 O18 . 相似文献
8.
Dielectric ceramics in the system (Zn1− x Co x )TiO3 ( x = 0–1) were synthesized by the solid-state reaction route. The phase distribution, microstructure, and dielectric properties were characterized by using powder X-ray diffraction analysis, electron microscopy, and microwave measurement techniques. Three phase composition regions were identified in the specimens sintered at 1150°C; [spinel + rutile] at 0 ≤ x ≤ 0.5, [spinel + ilmenite + rutile] at 0.5 < x ≤ 0.7, and [ilmenite] phase at 0.7 < x ≤ 1. For the 0 ≤ x ≤ 0.5 region, the amount of Ti-rich precipitates incorporated into the spinel phase decreased with the Co content at 0 ≤ x ≤ 0.5, with a concomitant increase of the rutile phase. The ilmenite phase appeared for high Co content. The microwave dielectric properties depended on the phase composition and volume according to the three phase regions, where the relative amount of rutile to the spinel or ilmenite determined the dielectric properties. The dielectric constant as a function of Co addition was modeled with a Maxwell mixing rule. An optimum phase distribution was determined in this system with dielectric constant of 25, a Q * f 70 000 GHz, and a low temperature coefficient of the resonant frequency. 相似文献
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Ni Qin Marjeta Maek Krmanc Danilo Suvorov 《Journal of the American Ceramic Society》2008,91(8):2593-2600
K x Ba1− x Ga2− x Ge2+ x O8 (0.6≤ x ≤1) polycrystalline ceramics are potential materials for glass-free low-temperature cofired ceramics (LTCC) substrates. We have made a comprehensive study of the kinetics of the monoclinic-to-monoclinic P 21 / a ⇔ C 2/ m phase transition. The low-temperature-stable P 21 / a phase with a high Q × f value was synthesized using a subsolidus method and was well sintered at the LTCC temperature with a H3 BO3 additive. A good combination of low sintering temperature (910°–920°C), high Q × f values (96 700–104 500 GHz), low permittivities (5.6–6.0), and a small temperature coefficient of resonant frequency (∼−20 ppm/°C) was obtained for ceramics with x =0.67 and 0.9 and with 0.1 wt% of H3 BO3 . 相似文献
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Effects of La on Dielectric and Piezoelectric Properties of Pb1−x La2x/3 (Nb0.95 Ti0.0625 )2 O6 Ceramics
Gao-li Men Peng Liu Ruo-xi Zhang Hong Chen Bo Wang Jian-ping Zhou Gang-qiang Zhu 《Journal of the American Ceramic Society》2009,92(8):1753-1757
Ceramics with the chemical compositions of Pb1− x La2 x /3 (Nb0.95 Ti0.0625 )2 O6 (0≤ x ≤0.060) (PLTN) were prepared by the conventional solid-state reaction method. X-ray diffraction analysis indicated that Ti and La doping not only decreased the rhombohedral–tetragonal phase transformation temperature, but also stabilized the orthorhombic phase of PLTN ceramics. All ceramics sintered at 1190°–1250°C had shown the pure orthorhombic ferroelectric phase. La doping suppresses grain growth and inhibits the formation of pores and cracks, resulting in an increase in relative density up to 97%. The amount of La doping to PLTN ceramics obviously affect ceramics' piezoelectric constant ( d 33 ) and dielectric loss (tanδ). The sample with x =0.015 possesses high Curie temperature ( T c =560°C), low dielectric loss (tanδ=0.0054), and excellent piezoelectric constant ( d 33 =92 pC/N), presenting a high potential to be used in high-temperature applications as piezoelectric transducers. 相似文献
14.
Qun Zeng Wei Li Jian-lin Shi Xian-lin Dong Jing-kun Guo 《Journal of the American Ceramic Society》2008,91(2):644-647
A group of new y M-phase/(1− y ) Li2+ x Ti1−4 x Nb3 x O3 composite ceramics with adjustable permittivities for low-temperature co-fired ceramic applications was initially investigated in the study. The 0.5 M-phase/0.5 Li2+ x Ti1−4 x Nb3 x O3 ( x =0.01, 0.02, 0.04, 0.06, 0.081) composite ceramics were first investigated to find the appropriate "Li2 TiO3 ss" composition ( x value). The best dielectric properties of ɛr =40.1, Q × f values up to 9318 GHz, τf =25 ppm/°C, were obtained for the ceramics composites at x =0.02. Based on the good dielectric properties, the suitable "Li2 TiO3 ss" composition with x =0.02 was mixed with the Li1.0 Nb0.6 Ti0.5 O3 powder as the ratio of y "M-phase"/(1− y ) "Li2 TiO3 ss" ( y =0.2, 0.4, 0.5, 0.6, 0.8). By adjusting the y values, the group of composite ceramics could exhibit largely are adjustable permittivities varying from ∼20 to ∼60, while Q × f and τf values relatively good. Nevertheless, in this study, because there are interactions between the M-phase and Li2 TiO3 ss during sintering process, their microwave dielectric properties could not be predicted precisely by the empirical model. 相似文献
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Qun Zeng Wei Li Jian-lin Shi Jing-kun Guo 《Journal of the American Ceramic Society》2006,89(10):3305-3307
The effects of V2 O5 addition on the sintering behavior, microstructure, and the microwave dielectric properties of 5Li2 O–0.583Nb2 O5 –3.248TiO2 (LNT) ceramics have been investigated. With addition of low-level doping of V2 O5 (≤2 wt%), the sintering temperature of the LNT ceramics could be lowered down to around 920°C due to the liquid phase effect. A secondary phase was observed at the level of 2 wt% V2 O5 addition. The addition of V2 O5 does not induce much degradation in the microwave dielectric properties but lowers the τf value to near zero. Typically, the excellent microwave dielectric properties of ɛr =21.5, Q × f =32 938 GHz, and τf =6.1 ppm/°C could be obtained for the 1 wt% V2 O5 -doped sample sintered at 920°C, which is promising for application of the multilayer microwave devices using Ag as an internal electrode. 相似文献
17.
The microwave dielectric properties and the microstructures of (Mg1− x Co x )2 TiO4 ceramics prepared by the conventional solid-state route were investigated. Lattice parameters were also measured for specimens with different x . The formation of solid solution (Mg1− x Co x )2 TiO4 ( x =0.02–0.1) was confirmed by the X-ray diffraction patterns, energy dispersive X-ray analysis, and the lattice parameters measured. By increasing x from 0 to 0.05, the Q × f of the specimen can be tremendously boosted from 150 000 GHz to a maximum of 286 000 GHz. A fine combination of microwave dielectric properties (ɛr ∼15.7, Q × f ∼286 000 GHz at 10.4 GHz, τf ∼−52.5 ppm/°C) was achieved for (Mg0.95 Co0.05 )2 TiO4 ceramics sintered at 1390°C for 4 h. Ilmenite-structured (Mg0.95 Co0.05 )TiO3 was detected as a second phase. The presence of the second phase would cause no significant variation in the dielectric properties of the specimen because it possesses compatible properties compared with that of the main phase. In addition, only a small deviation in the dielectric properties was monitored for specimens with x =0.04–0.05 at 1360°–1420°C. It not only provides a wide process window but also ensures an extremely reliable material proposed as a very promising dielectric for low-loss microwave and millimeter wave applications. 相似文献
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The (YBa2 Cu3 )1−x Nax O7–δ system in the range of x = 0–0.8 was investigated. Experimental data suggest that the sodium doping with x 0.26 does not affect the critical transition temperature Tc , and the crystal structure maintains the orthorhombic lattice with a slightly smaller unit cell. However, sodium doping increases the sintering and grain growth kinetics, resulting in a higher superconducting phase volume and an enhanced Meissner effect. It also lowers the processing temperaturel. The experimental data also suggest that the sodium atoms diffuse into the superconducting YBa2 Cu3 O7−δ crystallites, which stabilizes the orthorhombic phase. The transition temperature (ortho-rhombic to tetragonal) in sodium-doped materials increases with the increasing concentration of sodium. 相似文献
20.
Hariharan Padma Kumar Shyla Joseph Sam Solomon Manoj Raama Varma Jijimon Kumpukkatu Thomas 《International Journal of Applied Ceramic Technology》2008,5(4):347-352
LnTiSb x Ta1− x O6 ceramics were prepared by the conventional solid-state ceramic route for x =0, 0.05, 0.1, 0.15, and 0.2. The structures of the materials were analyzed using X-ray diffraction techniques. The cell parameters and the theoretical densities of the samples were calculated using least square methods. The materials are sintered to >94% of theoretical density at 1480°C. The microwave dielectric properties were measured using the cavity resonator method. The surface morphology of the sintered samples was analyzed using scanning electron microscopy. All the materials have good microwave dielectric properties and are suitable for dielectric resonator applications. 相似文献