共查询到20条相似文献,搜索用时 15 毫秒
1.
Liang Fang Hui Zhang T.H Huang Richard Dronskowski 《Materials Research Bulletin》2004,39(11):1649-1654
Two new cation-deficient hexagonal perovskites Ba4LaMNb3O15 (M = Ti, Sn) ceramics were prepared by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction, scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The Ba4LaTiNb3O15 has high dielectric constant of 52, high quality factors (Q) 3500 (at 4.472 GHz), and temperature variation of resonant frequency (τf) +93 ppm °C−1 at room temperature; Ba4LaSnNb3O15 has dielectric constant of 39 with high Q value of 2510 (at 5.924 GHz), and τf −29 ppm °C−1. 相似文献
2.
The effects of CuO-V2O5 addition on the sintering temperature and microwave dielectric properties of ZnO-Nb2O5-TiO2-SnO2 were investigated. The CuO-V2O5 addition lowered the sintering temperature of ZnO-Nb2O5-TiO2-SnO2 ceramics effectively from 1150 to 860 °C due to the liquid-phase effect of Cu2V2O7 and Cu3(VO4)2, as observed by XRD. The microwave dielectric properties were found to strongly correlate with the sintering temperature and the amount of CuO-V2O5 addition. The maximum Qf values decreased with increasing CuO-V2O5 content, due to the formation of the second phase, Cu3(VO4)2 and CuNbO3. Zero τf value can be obtained by properly adjusting the sintering temperature. At 860 °C, ZnO-Nb2O5-TiO2-SnO2 ceramics with 1.5 wt.% CuO-V2O5 gave excellent microwave dielectric properties: ?r = 42.3, Qf = 9000 GHz and τf = 8 ppm/°C. 相似文献
3.
Hang-Won Lee Jeong-Hyun Park Sahn Nahm Jae-Gwan Park 《Materials Research Bulletin》2010,45(1):21-6912
We demonstrate the correlation between sintering behavior and microstructural observations in low-temperature sintered, LaNbO4 microwave ceramics. Small CuO additions to LaNbO4 significantly lowered the sintering temperature from 1250 to 950 °C. To elucidate the sintering mechanism, the internal microstructure of the sample manipulated by a focused ion beam (FIB) was investigated using transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). LaNbO4 with 3 wt% CuO sintered at 950 °C for 2 h possessed the following excellent microwave dielectric properties: a quality factor (Qxf) of 49,000 GHz, relative dielectric constant (?r) of 19.5, and temperature coefficient of resonant frequency (τf) of 1 ppm/°C. The ferroelastic phase transformation was also investigated using in situ X-ray diffraction (XRD) to explain the variation of τf in low-temperature sintered LaNbO4 as a function of CuO content. 相似文献
4.
In this study, we tried to lower the sintering temperature of Ba0.6Sr0.4TiO3 (BST) ceramics by several kinds of adding methods of Bi2O3, CuO and CuBi2O4 additives. The effects of different adding methods on the microstructures and the dielectric properties of BST ceramics have been studied. In the all additive systems, the single addition of CuBi2O4 was the most effective way for lowering the sintering temperature of BST. When CuBi2O4 of 0.6 mol% was mixed with starting BST powders and sintered at 1100 °C, the derived ceramics demonstrated dense microstructure with a low dielectric constant (? = 4240), low dielectric loss (tan δ = 0.0058), high tunability (Tun = 38.3%) and high Q value (Q = 251). It was noteworthy that the sintering temperature was significantly lowered by 350 °C compared with no-additive system, and the derived ceramics maintained the excellent microwave dielectric properties corresponding to pure BST. 相似文献
5.
Polycrystalline BaTi2O5 (BT2) was prepared by pressureless sintering in air using BaCO3 and TiO2 as starting materials. XRD results of the calcined powder showed BaCO3 and TiO2 reacted completely after being calcined above 950 °C, showing a mixture of BaTiO3 (BT), BT2, BaTi4O9 and Ba4Ti13O30. A small amount of ZrO2 (less than 0.1 wt%) was effective to prepare BT2 in a single phase and the second phase of BT and B6T17 increased with ZrO2 content. BT2 sintered body in a single phase was obtained at 1175-1300 °C when ZrO2 content was 0.08 wt%. The maximum permittivity of BT2 sintered body was 340 at the Curie temperature (Tc) of 463 °C and the frequency of 100 kHz. 相似文献
6.
The effects of B2O3 addition, as a sintering agent, on the sintering behavior, microstructure and microwave dielectric properties of the 11Li2O-3Nb2O5-12TiO2 (LNT) ceramics have been investigated. With the low-level doping of B2O3 (≤2 wt.%), the sintering temperature of the LNT ceramic could be effectively reduced to 900 °C. The B2O3-doped LNT ceramics are also composed of Li2TiO3ss and “M-phase” phases. No other phase could be observed in the 0.5-2 wt.% B2O3-doped ceramics sintered at 840-920 °C. The addition of B2O3 induced no obvious degradation in the microwave dielectric properties but increased the τf values. Typically, the 0.5 wt.% B2O3-doped ceramics sintered at 900 °C have better microwave dielectric properties of ?r = 49.2, Q × f = 8839 GHz, τf = 57.6 ppm/°C, which suggest that the ceramics could be applied in multilayer microwave devices requiring low sintering temperatures. 相似文献
7.
Meganathan ThirumalIsuhak N. Jawahar Kuzhichalil P. SurendiranPezholil Mohanan Ashok K. Ganguli 《Materials Research Bulletin》2002,37(1):185-191
Oxides of the type, Sr3Zn1−xMgxNb2O9 (0≤x≤1) have been obtained by the ceramic method. These oxides crystallize in the hexagonal cell corresponding to ordered triple perovskites. Sintered disks show nearly frequency-independent dielectric constant for all the compositions. Compositions sintered at 1425°C yield dielectric constant of 20-22 at ∼6 GHz, with quality factor ranging from 1300 to 1500. Sr3Zn0.5Mg0.5Nb2O9 shows a very low temperature coefficient of resonant frequency (τf) of +4 ppm/°C. 相似文献
8.
The effects of sintering aids on the microstructures and microwave dielectric properties of SmAlO3 ceramics were investigated. CuO and ZnO were selected as sintering aids to lower the sintering temperature of SmAlO3 ceramics. With the additions, the sintering temperature of SmAlO3 can be effectively reduced from 1650 to 1430°C. The crystalline phase exhibited no phase differences at low addition level while Sm4Al2O9 appeared as a second phase as the doping level was over 0.5 wt.%. In spite of the additions, the dielectric constants showed no significant change and ranged 19-21. However, the quality factor Q×f was strongly dependent upon the type and amount of additions. The Q×f values of 51,000 and 41,000 GHz could be obtained at 1430°C with 0.25 wt.% CuO and ZnO additions, respectively. The temperature coefficients depended on the additions and varied from −40 to −65 ppm/°C. Results of X-ray diffractions, EDS analysis and scanning electron microscopy were also presented. 相似文献
9.
Min-Han KimChang-Soo Woo Sahn Nahm Chang-Hack ChoiHwack-Joo Lee Hyun-Min Park 《Materials Research Bulletin》2002,37(3):605-615
Crystal structure and microwave dielectric properties of (1−x)NdAlO3-xCaTiO3 ceramics have been investigated. Crystal structure of the specimens changed with the composition. Rhombohedral structure was found for the specimens with x≤0.1. When 0.3≤x≤0.7, the specimens had the tetragonal structure and it changed to the orthorhombic structure as x exceeded 0.7. Two types of the second phases were observed in (1−x)NdAlO3-xCaTiO3 ceramics. For the specimens with x≤0.5, Nd4Al2O9 phase was observed and Al-rich phase was found in the specimens with x≥0.7. The dielectric constant (εr) and the temperature coefficient of the resonant frequency (τf) increased with the increase of x. The Q×f value of the specimen increased with x and exhibited the maximum value when x=0.5. The microwave dielectric properties of Q×f=45,000 GHz, εr=45 and τf=−1.5 ppm/°C were obtained for 0.3NdAlO3-0.7CaTiO3 ceramics. 相似文献
10.
La2O3 and Nd2O3 were used to substitute Bi2O3 and the effects of complex substitution on the sintering behavior and the microwave dielectric properties of BiNbO4 ceramics were studied. With 0.5 wt.% CuO-V2O5 mixtures addition, all of the Bi1−x(La0.38Nd0.62)xNbO4 ceramics could be densified below 920 °C. The triclinic phases are identified in Bi1−x(La0.38Nd0.62)xNbO4 ceramics with x=0.01 sintered at 820 °C and the triclinic intensities increase with increasing the x value and sintering temperature. The saturated bulk density slightly decreases from 7.17 to 7.13 g/cm3 and the εr value from 44.24 to 42.76 with increasing x from 0 to 0.07 for Bi1−x(La0.38Nd0.62)xNbO4 ceramics. The saturated Q×f value is between 10,300 and 12,400 GHz depending on the x value. The τf values of dense Bi1−x(La0.38Nd0.62)xNbO4 ceramics decrease from 28.32 to 12.79 ppm/°C with x varying from 0 to 0.01 and remain almost unchanged with further increasing x. 相似文献
11.
Hongmei Ren 《Materials Research Bulletin》2010,45(11):1608-1613
Na0.5Bi0.5Cu3Ti4O12 (NBCTO) ceramics were prepared by conventional solid-state reaction method. The phase structure, microstructure and dielectric properties of NBCTO ceramics sintered at various temperatures with different soaking time were investigated. Pure NBCTO phase could be obtained with increasing the temperature and prolonging the soaking time. High dielectric permittivity (13,495) and low dielectric loss (0.031) could be obtained when the ceramics were sintered at 1000 °C for 7.5 h. The ceramics sintered at 1000 °C for 7.5 h also showed good temperature stability (−4.00 to −0.69%) over a large temperature range from −50 to 150 °C. Complex impedances results revealed that the grain was semiconducting and the grain boundaries was insulating. The grain resistance (Rg) was 12.10 Ω cm and the grain boundary resistance (Rgb) was 2.009 × 105 Ω cm when the ceramics were sintered at 1000 °C for 7.5 h. 相似文献
12.
S. Bala Murali Krishna 《Materials Research Bulletin》2010,45(12):1783-1791
ZnO-Sb2O3-As2O3 transparent glasses containing small concentrations of chromium ions (introduced as Cr2O3) ranging from 0 to 0.2 mol% is prepared. A number of studies viz., XRD, SEM, DTA, optical absorption, FT-IR, Raman, ESR spectra, magnetic susceptibility and dielectric properties (constant ?′, loss tan δ, ac. conductivity σac over a wide range of frequency and temperature as well as dielectric breakdown strength at room temperature) of these glasses have been carried out as a function of chromium ion concentration. The results have been analysed in the light of different oxidation states of chromium ions. The analyses indicates that when the concentration of chromium ions is low, these ions mostly exist in Cr6+ and Cr5+ states, occupy network forming positions with CrO42− and CrO43− structural units respectively and increase the rigidity of the glass network. When the concentration of chromium ions is gradually increased, these ions seem to be existing mostly in Cr3+ state. 相似文献
13.
Wen-Cheng Tzou Sang-Li ChangCheng-Fu Yang Ying-Chung Chen 《Materials Research Bulletin》2003,38(6):981-989
The microwave characteristics and the microstructures of 0.88Al2O3-0.12TiO2 with various amounts of MgO-CaO-SiO2-Al2O3 (MCAS) glass sintered at different temperatures have been investigated. The sintering temperature can be lowered to 1300 °C by the addition of MCAS glass. The densities, dielectric constants (εr) and quality values (Q×f) of the MCAS-added 0.88Al2O3-0.12TiO2 ceramics decrease with the increase of MCAS glass content. The temperature coefficients of the resonant frequency (τf) are shifted to more negative values as the MCAS content or the sintering temperatures increase. The change of the crystalline phases of Al2TiO5 phase and rutile-TiO2 phase has profound effects on the microwave dielectric properties of the MCAS-added Al2O3-TiO2 ceramics. As sintered at 1250 °C, 0.88Al2O3-0.12TiO2 ceramics with 2 wt.% MCAS glass addition exists a εr value of 8.63, a Q×f value of 9578 and a τf value of +5 ppm/°C. 相似文献
14.
Microstructure and microwave dielectric characteristics of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics
Wen-Cheng Tzou Yao-Sheng Yang Ho-Hua Chung Chien-Chen Diao 《Materials Research Bulletin》2007,42(11):1897-1904
(1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 (0.1 ≤ x ≤ 0.85) composites are prepared by mixing 1150 °C-calcined BaTi4O9 with 1150 °C-calcined Ba(Zn1/3Ta2/3)O3 powders. The crystal structure, microwave dielectric properties and sinterabilites of the (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics have been investigated. X-ray diffraction patterns reveal that BaTi4O9, ordered and disordered Ba(Zn1/3Ta2/3)O3 phases exist independently over the whole compositional range. The sintering temperatures of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics are about 1240 - 1320 °C and obviously lower than those of Ba(Zn1/3Ta2/3)O3 ceramics. The dielectric constants (?r) and the temperature coefficient of resonant frequency (τf) of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics increase with the increase of BaTi4O9 content. Nevertheless, the bulk densities and the quality values (Q × f) of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics increase with the increase of Ba(Zn1/3Ta2/3)O3 content. The results are attributed to the higher density and quality value of Ba(Zn1/3Ta2/3)O3 ceramics, the better grain growth, and the densification of sintered specimens added a small BaTi4O9 content. The (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramic with x = 0.1 sintered at 1320 °C exhibits a ?r value of 31.5, a maximum Q × f value of 68500 GHz and a minimum τf value of 4.1 ppm/°C. 相似文献
15.
Sherin Thomas 《Materials Research Bulletin》2008,43(4):843-851
The 0.83ZnAl2O4-0.17TiO2 (ZAT) ceramics were synthesized by solid state ceramic route. The effect of 27B2O3-35Bi2O3-6SiO2-32ZnO (BBSZ) glass on the microwave dielectric properties of ZAT was investigated. The crystal structure and the microstructure of the ceramic-glass composites were studied by X-ray diffraction and scanning electron microscopic techniques. The low frequency dielectric loss was measured at 1 MHz. The dielectric properties of the sintered samples were measured in the microwave frequency range by the resonance method. Addition of 0.2 wt% of BBSZ improved the dielectric properties with quality factor (Qu × f) > 120,000 GHz, temperature coefficient of resonant frequency (τf) = −7.3 ppm/°C and dielectric constant (?r) = 11.7. Addition of 10 wt% of BBSZ lowered the sintering temperature to about 950 °C with Qu × f > 10,000 GHz, ?r = 10 and τf = −23 ppm/°C. The reactivity of 10 wt% BBSZ added ZAT with silver was also studied. The results show that ZAT doped with suitable amount of BBSZ glass is a possible material for low-temperature co-fired ceramic (LTCC) application. 相似文献
16.
Shuo Jin 《Materials Research Bulletin》2011,46(3):432-437
Sr2−xCaxBi4Ti5O18(x = 0, 0.05) powders synthesized by solid state route were uniaxially pressed and sintered at 1225 °C for 2 h. The obtained dense ceramics exhibited crystallographic anisotropy with a dominant c axis parallel to the uniaxial pressing direction which was quantified in terms of the Lotgering factor. Microstructure anisotropy of both compositions (x = 0, 0.05) consisted of plate like grains exhibiting their larger surfaces mostly perpendicular to the uniaxial pressing direction. Dielectric and ferroelectric properties of Sr2−xCaxBi4Ti5O18 ceramics were measured under an electric field (E) applied parallel and perpendicularly to uniaxial pressing direction. The obtained dielectric ?R(T) and polarization (P-E) curves depended strongly on E direction thus denoting a significant effect from microstructure and crystallographic texture. Sr2−xCaxBi4Ti5O18 properties were also significantly affected by Ca content (x): Curie temperature increased from 280 °C (x = 0) to 310 °C (x = 0.05) while ?R and remnant polarization decreased for x = 0.05. The present results are discussed within the framework of the processing and crystal structure-properties relationships of Aurivillius oxides ceramics. 相似文献
17.
The microwave dielectric properties and the microstructures of Nd(Co1/2Ti1/2)O3 ceramics prepared by conventional solid-state route have been studied. The prepared Nd(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. It is found that low-level doping of B2O3 (up to 0.75 wt.%) can significantly improve the density and dielectric properties of Nd(Co1/2Ti1/2)O3 ceramics. Nd(Co1/2Ti1/2)O3 ceramics with additives could be sintered to a theoretical density higher than 98.5% at 1320 °C. Second phases were not observed at the level of 0.25-0.75 wt.% B2O3 addition. The temperature coefficient of resonant frequency (τf) was not significantly affected, while the dielectric constants (?r) and the unloaded quality factors Q were effectively promoted by B2O3 addition. At 1320 °C/4 h, Nd(Co1/2Ti1/2)O3 ceramics with 0.75 wt.% B2O3 addition possesses a dielectric constant (?r) of 27.2, a Q × f value of 153,000 GHz (at 9 GHz) and a temperature coefficient of resonant frequency (τf) of 0 ppm/°C. The B2O3-doped Nd(Co1/2Ti1/2)O3 ceramics can find applications in microwave devices requiring low sintering temperature. 相似文献
18.
M.K. Suresh 《Materials Research Bulletin》2010,45(10):1389-1395
Ba8Zn(Nb6−xSbx)O24 (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 and 2.4) ceramics were prepared through the conventional solid-state route. The materials were calcined at 1250 °C and sintered in the range 1400-1425 °C. The structure of the system was analyzed by X-ray diffraction, Fourier transform infrared and Raman spectroscopic methods. The theoretical and experimental densities were calculated. The microstructure of the sintered pellets was analyzed using scanning electron microscopy. The low frequency dielectric properties were studied in the frequency range 50 Hz-2 MHz. The dielectric constant (?r), temperature coefficient of resonant frequency (τf) and the unloaded quality factor (Qu) are measured in the microwave frequency region using cavity resonator method. The τf values of the samples reduced considerably with the increase in Sb concentration. The materials have intense emission lines in the visible region. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications. 相似文献
19.
Prasun Ganguly 《Materials Research Bulletin》2011,46(5):692-697
In the present work, structural, dielectric, ferroelectric, piezoelectric and pyroelectric properties of tungsten-bronze structured Ba5SmTi3Nb7O30 ceramics, synthesized by mechanical activation and conventional solid-state reaction processes, have been studied with an objective of comparing the properties of the specimens synthesized by the two processes. X-ray diffraction analysis shows the formation of the compound in an orthorhombic structure by both the processes. Scanning electron microscopy reveals the formation of a fine granular microstructure in the specimen synthesized by mechanical activation process compared to the specimen synthesized by conventional solid-state method. The specimen prepared using mechanical activation process exhibits improved electrical properties with higher dielectric constant, lower dielectric loss and higher resistivity. The effective remanent polarization () value, d33 value and pyroelectric coefficients are also observed to be higher in the sample synthesized by the mechanical activation process. 相似文献
20.
Co2O3 doped BaWO4-Ba0.5Sr0.5TiO3 composite ceramics, prepared by solid-state route, were characterized systematically, in terms of their phase compositions, microstructure and microwave dielectric properties. Doping of Co2O3 promoted grain growth, reduced Curie temperature and broadened phase-transition temperature range of BaWO4-Ba0.5Sr0.5TiO3, which were attributed mainly to the substitution of Co3+ for Ti4+ at B site in the perovskite lattice. Dielectric diffusion behaviors of the composite ceramics were discussed. The composite ceramics all had dielectric tunability of higher than 10% at 30 kV/cm and 10 kHz, with promising microwave dielectric properties. Specifically, the sample doped with 0.2 wt.% Co2O3 exhibited a tunability of 20%, permittivity of 225 and Q of 292 (at 1.986 GHz), making it a suitable candidate for applications in electrically tunable microwave devices. 相似文献