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1.
Effect of Ga3+ substitution on the microwave dielectric properties of 0.67CaTiO3–0.33LaAlO3 ceramics
《Ceramics International》2016,42(6):6743-6748
0.67CaTiO3–0.33La(Al1−xGax)O3 (0≤x≤0.4) (CTLAG) ceramics with pure perovskite structure were prepared by a conventional two-step solid-state reaction process. The effect of Ga3+ substitution for Al3+ on the microwave dielectric properties of the ceramics was subsequently investigated. As Ga content increased, the ionic polarizability increased and led to an increase of the dielectric constant (εr). Meanwhile, both the tolerance factor (t) of CTLAG ceramics and A-site bond valence were considered to have effect on the temperature coefficient of the resonant frequency (τf) with the increase of Ga content. Results also showed that the quality factor (Q×f ) varied with increasing Ga3+ content because of not only intrinsic factor but also extrinsic factors such as the bimodal grain size distribution, the variation of relative density, and the packing fraction. Excellent microwave dielectric properties with εr≈45.81, Q×f≈34,152 GHz, and τf≈3.09 ppm/°C were achieved for 0.67CaTiO3–0.33La(Al0.9Ga0.1)O3 ceramics sintered at 1420 °C for 4 h. 相似文献
2.
《Journal of the European Ceramic Society》2000,20(2):195-199
We investigated the sintering behavior of Cr2O3–Al2O3 ceramic materials. In our observation of the isothermal shrinkage behavior of Cr2O3–Al2O3 ceramic, the activation energy of sintering reaction was measured to be 102 kJ/mol, that is, the near value of the activation energy of diffusion of Al ions in Al2O3 single crystal. Therefore the diffusion of cations is believed to control the sintering behavior of this material. With the addition of TiO2, (the compound chosen to accelerate the diffusion of cations) to Cr2O3–Al2O3, the sintering behavior was accelerated. 相似文献
3.
(1–x)SiO2–xBPO4 (x?=?23–70?wt%) glass-fluxed ceramics have been prepared by a traditional ceramic process. The phase assemblage, sintering, crystallization behavior, microwave dielectric properties and chemical compatibility with Ag/Cu have been studied. The SiO2-rich compositions (x?=?23–50?wt%) could be well densified at ~975?°C/2?h, while the BPO4-rich compositions demonstrated poor sinterability and porous microstructure. The SiO2-rich compositions sintered at 975?°C/2?h contained BPO4, low temperature cristobalite and glassy phases. Crystallization of BPO4 occurred at lower temperature than that of SiO2. Good combined microwave dielectric properties with ?r?=?~5, Q?×?f?=?25,000?GHz and τf value of –7.3?ppm/°C could be obtained when 10?wt% TiO2 was added after sintering at 975?°C/2?h. The x?=?23?wt% composition chemically reacted with Ag, but exhibited good chemical compatibility with Cu after sintering at 975?°C/2?h. 相似文献
4.
《Ceramics International》2016,42(7):7943-7949
This paper reports the investigation of the performance of Li2O–B2O3–SiO2 (LBS) glass as a sintering aid to lower the sintering temperature of BaO–0.15ZnO–4TiO2 (BZT) ceramics, as well as the detailed study on the sintering behavior, phase evolution, microstructure and microwave dielectric properties of the resulting BZT ceramics. The addition of LBS glass significantly lowers the sintering temperature of the BZT ceramics from 1150 °C to 875–925 °C. Small amount of LBS glass promotes the densification of BZT ceramic and improves the dielectric properties. However, excessive LBS addition leads to the precipitation of glass phase and growth of abnormal grain, deteriorating the dielectric properties of the BZT ceramic. The BZT ceramic with 5 wt% LBS addition sintered at 900 °C shows excellent microwave dielectric properties: εr=27.88, Q×f=14,795 GHz. 相似文献
5.
This study investigates the bulk density, sintering behaviour, and microwave dielectric properties of the MgO–2B2O3 series ceramics synthesised by solid-state r... 相似文献
6.
《应用陶瓷进展》2013,112(4):227-231
AbstractGlass ceramics in the Li2O–Al2O3–SiO2 system have been synthesised to produce bulk materials grown in a glass phase via quenching followed by controlled crystallisation. The crystallisation and microstructure of Li2O–Al2O3–SiO2 (LAS) glass–ceramic with nucleating agents (B2O3 and/or P2O5) are investigated by differential thermal analysis, X-ray diffraction and scanning electron microscopy and the effects of B2O3 and P2O5 on the crystallisation of LAS glass are also analysed. The introduction of both B2O3 and P2O5 promotes the crystallisation of LAS glass by decreasing the crystallisation temperature and adjusting the crystallisation kinetic parameters, allows a direct formation of β spodumene phase and as a result, increases the crystallinity of the LAS glass ceramic. Microstructural observations show that the randomly oriented, nanometre sized crystalline is found with residual glass concentrated at crystallite boundaries. Furthermore, it is interesting that codoping of B2O3 and P2O5 creates not much effect on the crystallisation temperature. The dielectric properties of the glass–ceramics formed through controlled crystallisation have a strong dependence on the phases that are developed during heat treatment. The dielectric constant is continuously increased and the dielectric loss is decreased with addition of additives where mobile alkali metal ions (e.g. Li+) are incorporated in a crystal phase and minimise the residual glass phase. 相似文献
7.
《Ceramics International》2017,43(4):3688-3692
Li2O-3MgO-mTiO2 (1≤m≤6) ceramics were prepared by the solid state reaction method. X-ray diffraction, energy dispersive spectrometer and scanning electron microscopy techniques were used to investigate the phase composition and crystal structure. With increasing m values, the phase structures of ceramics changed as: (Li2Mg3TiO6, m=1)→(Li2Mg3Ti4O12 and Mg2TiO4, m=2,3)→(Li2Mg3Ti4O12, m=4)→(Li2Mg3Ti4O12, MgTiO3 and Li2MgTi3O8, m=5)→(Li2Mg3Ti4O12, MgTiO3, Li2MgTi3O8 and MgTi2O5, m=6). The optimized sintering temperature was lowered from 1275 °C to 1050 °C. When m=5, Li2O-3MgO-5TiO2 ceramics showed good microwave dielectric properties at a wide sintering temperature range of 1000–1200 °C, and the best microwave dielectric properties of Q×f=71,726 GHz, εr=21.9 and τf=−20.9 ppm/°C were obtained at a relatively low sintering temperature of 1050 °C. 相似文献
8.
Xiao-Qiang Song Wen-Zhong Lu Xiao-Chuan Wang Xiao-Hong Wang Gui-Fen Fan Raz Muhammad Wen Lei 《Journal of the European Ceramic Society》2018,38(4):1529-1534
BaAl2?2x(ZnSi)xSi2O8 (x = 0.2–1.0) ceramics were prepared using the conventional solid-state reaction method. The sintering behaviour, phase composition and microwave dielectric properties of the prepared compositions were then investigated. All compositions showed a single phase except for x = 0.8. By substituting (Zn0.5Si0.5)3+ for Al3+ ions, the optimal sintering temperatures of the compositions decreased from 1475 °C (x = 0) to 1000 °C (x = 0.8), which then slightly increased to 1100 °C (x = 1.0). Moreover, the phase stability of BaAl2Si2O8 was improved. A novel BaZnSi3O8 microwave dielectric ceramic was obtained at the sintering temperature of 1100 °C. This ceramic possesses good microwave dielectric properties with εr = 6.60, Q × f = 52401 GHz (at 15.4 GHz) and τf = ?24.5 ppm/°C. 相似文献
9.
Trirutile-structure MgTa2O6 ceramics were prepared by aqueous sol–gel method and microwave dielectric properties were investigated. Highly reactive nanosized MgTa2O6 powders were successfully synthesized at 500 °C in oxygen atmosphere with particle sizes of 20–40 nm. The evolution of phase formation was detected by DTA–TG and XRD. Sintering characteristic and microwave dielectric properties of MgTa2O6 ceramics were studied at different temperatures ranging from 1100 to 1300 °C. With the increase of sintering temperature, density, ?r and Q · f values increased and saturated at 1200 °C with excellent microwave properties of ?r ~ 30.1, Q · f ~ 57,300 GHz and τf ~ 29 ppm/°C. The sintering temperature of MgTa2O6 ceramics was significantly reduced by aqueous sol–gel process compared to conventional solid-state method. 相似文献
10.
《Journal of the European Ceramic Society》2003,23(14):2403-2408
(1−x)La(Mg0.5Ti0.5)O3 (LMT)–xCaTiO3 (CT) [0<x<1] ceramics were prepared from powder obtained by a nonconventional chemical route based on the Pechini method. The crystal structure of the microwave dielectric ceramics has been refined by Rietveld method using X-ray powder diffraction data. LMT and CT were found to form a solid solution over the whole compositional range. The 0.9LMT–0.1CT composition was refined using P21/n space group, which allows taking into account B-site ordering. The compounds having x⩾0.3 were found to be disordered and were refined using Pbnm space group. Microstructure evolution was also analysed. Dielectric characterization at microwave frequencies was performed on the LMT–CT ceramics. The permittivity and the temperature coefficient of resonant frequency of the solid solutions showed a non-linear variation with composition. The quality factor demonstrates a considerable decrease with the increase of CT content. 相似文献
11.
ZnO-doped Mg2TiO4–MgTiO3–CaTiO3 microwave dielectric ceramics were successfully prepared by the reaction sintering route. The compact samples consisted of MgTiO3, Mg2TiO4 and CaTiO3, which was confirmed by X-ray diffraction and energy-dispersive spectra. ZnO efficiently lowered the sintering temperature and promoted the densification, as well as the improvements in the dielectric constant and the quality factor. At the level of ZnO?=?1 wt-%, the ceramics exhibited optimum microwave dielectric properties: a dielectric constant of 20.3, a high quality factor of 64,740 GHz (at 9.9 GHz) and a near-zero temperature coefficient of resonant frequency (–1.3 ppm/oC) after sintering at 1320oC for 4 h. 相似文献
12.
《Ceramics International》2020,46(6):7050-7054
Phase evolution and microwave dielectric properties of SrTiO3 added ZnAl2O4–3Zn2SiO4–2SiO2 ceramics system were investigated. With the addition of SrTiO3, the sintering temperature for dense ceramic is reduced from 1320 °C to 1180–1200 °C. According to the nominal composition ZnAl2O4–3Zn2SiO4–2SiO2-ySrTiO3, phase evolution is revealed by XRD patterns and Back Scattering Electron images: Zn2SiO4, ZnAl2O4 and SiO2 phases coexist at y = 0; SrTiO3 reacts with ZnAl2O4 and SiO2 to form SrAl2Si2O8, TiO2 and Zn2SiO4 at y = 0.2 to 0.8, and SiO2 phase disappears at y = 0.8; new phase of Zn2TiO4 is obtained at y = 1. The existence of TiO2 has important effect on the dielectric properties. The optimized microwave dielectric properties are obtained at y = 0.6 and the ceramics show low dielectric constant (7.16), high-quality factor (57, 837 GHz), and low temperature coefficient of resonant frequency (−30 ppm °C−1). 相似文献
13.
《Ceramics International》2016,42(9):10801-10807
The Ba1−xSrxMg2V2O8 (0≤x≤0.4) microwave dielectric ceramics were fabricated by a standard solid-state reaction method. The formation of a continuous solid solution within the whole composition range was identified. The ceramic samples could be well densified in the temperature range of 885–975 °C in air for 4 h. The permittivity εr was found to increase with increasing ionic polarizabilities. The Q×f values were believed to be closely related with packing fraction and grain refinement. The Sr2+ substitution contributed to a monotonous increase of the A-site bond valence, such that the τf value experienced a considerable variation from negative to positive values. The optimum microwave dielectric properties of an εr of 13.3, a high Qxf of 86,640 GHz (9.6 Hz) and a near-zero τf of −6 ppm/°C could be yielded in the x=0.15 sample when sintered at 915 °C for 4 h. 相似文献
14.
Fine-sized La2O3–B2O3–TiO2 glass powders with spherical shape were directly prepared by spray pyrolysis at a temperature of 1500 °C. The optimum flow rate of the carrier gas to prepare the glass powders with dense inner structure and fine size by complete melting was 10 L/min. The ratio of La/Ti was identified to be 2.06:1, which was close to the original starting ratio of La/Ti in mixture of the spray solution. The Tg and Tc of the powders were 614 and 718 °C. The crystal structures within the powders were observed from the sintered disc at 630 °C. The mean sizes of the powders changed from 0.24 to 0.71 μm when the concentrations of the spray solution were changed from 0.025 to 0.5 M. The BET surface areas of the powders changed from 4.4 to 1.6 m2/g. The grain sizes of the sintered discs increased with increasing the sintering temperatures. The main crystal structure of the sintered discs was LaBO3. 相似文献
15.
Xiaohua Zhou Enzhu Li Shilin Yang Bo Li Bin Tang Ying Yuan Shuren Zhang 《Ceramics International》2012,38(7):5551-5555
The La2O3–B2O3 (LB) addition, synthesized using the traditional solid-state reaction process, was chosen as a novel sintering aid of the low temperature co-fired CaO–B2O3–SiO2 (CBS) glass–ceramic. The effects of LB on the flexural strength and microwave dielectric properties have been investigated. The LB addition promotes the crystallization of the CaSiO3 but high amount of the LB addition leads to the formation of more pores. The CBS sample with 4 wt% LB addition sintered at 850 °C for 15 min shows good properties: flexural strength = 193 MPa, ?r = 6.26 and loss = 9.96 × 10?4 (10 GHz). 相似文献
16.
Amanda L. Snashall Lasse Norén Yun Liu Toru Yamashita Frank Brink Raymond L. Withers 《Ceramics International》2012
There are significant inconsistencies in published literature surrounding the phase analysis and physical properties of ceramics with the nominal composition BaO–Nd2O3–5TiO2 (BNT125). A careful phase analysis investigation of BNT125 ceramics using variable size TiO2 reagents was therefore undertaken using XRD, FESEM and EPMA with corresponding dielectric properties characterised over 2–3 GHz. Three distinct phases were consistently formed: Ba6?3xNd8+2xTi18O54 (x ~ 0.67), Ba2Ti9O20 and TiO2. The use of nano-scale TiO2 reagents significantly reduced porosity and improved the dielectric properties of the composite ceramics, while markedly reducing processing times. Structural and crystal chemical indications as to the origin of this system's physical properties are discussed, with these results providing new insights into optimisation paths for microwave dielectric materials of this type. 相似文献
17.
A novel low-temperature sinterable (1 ? x)Li2TiO3-xLi2CeO3 (x = 0.08 ? 0.16 in molar) microwave dielectric ceramic was successfully prepared by a conventional solid-state reaction method. The X-ray diffraction and scanning electron microscopy analysis revealed the coexistence of two phases with different structures owing to their good chemical stability. Their relative content was easily adjusted to achieve near-zero temperature coefficient of the resonant frequency (τf) according to the mixing rule of dielectrics. The low-temperature sintering and desirable microwave dielectric properties can be simultaneously achieved by adding Li2CeO3 to the Li2TiO3 matrix owing to its low-firing characteristic and opposite-sign τf. The composite ceramics with x = 0.14 could be well sintered at 850 °C and exhibited excellent microwave dielectric properties of εr ~ 21.2, Qxf~ 59,039 GHz and τf ~?7.4 ppm/°C. In addition, no chemical reaction was identified between the matrix phase and Ag, suggesting that the Li2TiO3-Li2CeO3 ceramics might be promising candidates for low-temperature co-fired ceramic applications. 相似文献
18.
《Ceramics International》2017,43(18):16167-16173
In this work, a series of low-temperature-firing (1−x)Mg2SiO4–xLi2TiO3–8 wt% LiF (x = 35–85 wt%) microwave dielectric ceramics was prepared through conventional solid state reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that the Li2TiO3 phase was transformed into cubic phase LiTiO2 phase and secondary phase Li2TiSiO5. Partial substitution of Mg2+ ions for Ti3+ ions or Li+Ti3+ ions increased the cell volume of the LiTiO2 phase. The dense microstructures were obtained in low Li2TiO3 content (x ≤ 65 wt%) samples sintered at 900 °C, whereas the small quantity of pores presented in high Li2TiO3 content (x ≥ 75 wt%) samples sintered at 900 °C and low Li2TiO3 content (x = 45 wt%) sintered at 850 and 950 °C. Samples at x = 45 wt% under sintering at 900 °C for 4 h showed excellent microwave dielectric properties of εr = 10.7, high Q × f = 237,400 GHz and near-zero τf = − 3.0 ppm/°C. The ceramic also exhibited excellent chemical compatibility with Ag. Thus, the fabricated material could be a possible candidate for low temperature co-fired ceramic (LTCC) applications. 相似文献
19.
《Ceramics International》2016,42(5):6005-6009
Li2MnO3 ceramics co-doped with 2 wt% LiF and x wt% TiO2 (x=0, 3, 5, 7, 10) were prepared by solid-state reaction for low-temperature co-fired ceramics (LTCC) applications. The sintering temperatures of Li2MnO3 ceramics were successfully lowered to 925°C due to the formation of a LiF liquid phase. Their temperature stability was improved by doping with TiO2. A typical Li2MnO3-2 wt% LiF-5 wt% TiO2 sample with well-densified microstructures displayed optimum dielectric properties (εr=13.8, Q×f= 23,270 GHz, τf=1.2 ppm/°C). Such sample was compatible with Ag electrodes, which suggests suitability of the developed material for LTCC applications in wireless communication systems. 相似文献
20.
Pseudobrookite-type Mg5Nb4O15 ceramics were prepared by aqueous sol–gel process and microwave dielectric properties were investigated. Highly reactive nanosized Mg5Nb4O15 powders were successfully synthesized at 600 °C in oxygen atmosphere with particle sizes of 20–40 nm firstly and then phase evolution was detected by DTA-TG and XRD. Sintering characteristics and microwave dielectric properties of Mg5Nb4O15 ceramics were studied at different temperatures ranging from 1200 °C to 1400 °C. With the increase of sintering temperature, density, ?r and Q·f values increased, and then saturated at 1300 °C. Excellent microwave properties of ?r ~11.3, Q·f ~43,300 GHz and τf ~?58 ppm/°C, were obtained finally. The sintering temperature of Mg5Nb4O15 ceramics was significantly reduced by aqueous sol–gel process compared to conventional solid-state methods. 相似文献