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1.
K. Park J.-G. Kim W.-S. Cho 《Journal of Materials Science: Materials in Electronics》2002,13(1):13-19
Rutile TiO2 (a=4.594 å and c=2.958 å) phase was formed on the outer region of Ti powders after oxidation at 600 °C for 1–300 h. Porous (Ba,Sr)TiO3 ceramics were fabricated by adding partially oxidized Ti powders (4–8 vol %) into (Ba,Sr)TiO3 powders, and showed excellent positive temperature coefficient of resistivity (PTCR) characteristics after paste-baking treatment at 580 °C in air. The PTCR characteristics of the porous ceramics were mainly attributed to the adsorption of oxygen at the grain boundaries. The microstructure and electrical properties of the porous (Ba,Sr)TiO3 ceramics containing the partially oxidized Ti powders oxidized at 600 °C for different oxidation times (1–300 h) were investigated. 相似文献
2.
J.-G. Kim W.-P. Tai J.-M. Lee J.-G. Ha S.-M. Lim 《Journal of Materials Science: Materials in Electronics》2004,15(4):241-245
We fabricated porous (Ba,Sr)(Ti,Sb)O3 ceramics by adding potato-starch (1–20 wt %) and investigated the effects of sintering temperature (1300–1450 °C) and time (0.5–10 h) on the positive temperature coefficient of resistivity characteristics of the porous ceramics. The room-temperature electrical resistivity of the (Ba,Sr)(Ti,Sb)O3 ceramics decreased with increasing sintering temperature, while that of the ceramics increased with increasing sintering time. For example, the room-temperature electrical resistivity of the (Ba,Sr)(Ti,Sb)O3 ceramics for the samples sintered at 1300 °C and 1450 °C for 1 h is 6.8×103 and 5.7×102 cm, respectively, while that of the ceramics is 6.5×102 and 1.3×107 cm, respectively, for the samples sintered at 1350 °C for 0.5 h and 10 h. In order to investigate the reason for the decrease and increase of room-temperature electrical resistivity of the samples with increasing sintering temperature and time, the average grain size, porosity, donor concentration of grains (N
d), and electrical barrier height of grain boundaries () of the samples are discussed. 相似文献
3.
J.-G. Kim W.-S. Cho J.-H. Sim 《Journal of Materials Science: Materials in Electronics》2002,13(8):497-501
Porous semiconducting (Ba, Sr)TiO3 ceramics were fabricated by the addition of potato-starch to the (Ba, Sr)TiO3 powders. The effects of potato-starch on the microstructure and PTCR characteristics of the porous (Ba, Sr)TiO3 ceramics have been investigated. The porosity largely increased and the grain size slightly decreased with increasing potato-starch content. The crystalline structure of (Ba, Sr)TiO3 ceramics was independent of the potato-starch content. The (Ba, Sr)TiO3 ceramics containing potato-starch showed higher PTCR (106) characteristics than that of the (Ba, Sr)TiO3 ceramics without potato-starch. It was found that the development of PTCR characteristic in the porous (Ba, Sr)TiO3 ceramics containing various amounts of potato-starch, in the same way as normal BaTiO3 ceramics without potato-starch, is associated with grain boundaries, from the impedance analysis. 相似文献
4.
Venkata Ramana Mudinepalli Shenhua Song B. S. Murty 《Journal of Materials Science: Materials in Electronics》2013,24(6):2141-2150
Microwave sintering has emerged in recent years as a new method for sintering a variety of materials that has shown significant advantages against conventional sintering procedures. Sr and Pb doped BaTiO3 ceramics has been prepared by the high energy ball milling followed by conventional and microwave sintering. The phase formation was confirmed by X-ray diffractometer followed by Scanning electron microscopy, atomic force microscopy and Transmission electron microscopy. Dielectric constant was measured on both the samples and it is observed that, in Ba0.8Pb0.2TiO3 (abbreviated as BPT), it increased more than one order of magnitude and in Ba0.8Sr0.2TiO3 (abbreviated as BST), it increased two orders of magnitudes at room temperature and Curie transition temperature by microwave sintering. Interestingly the Curie transition temperature of BPT value decreased from 224 to 210 °C, where as in BST ferroelectric ceramics, no variation of transition temperature by conventional sintering and microwave sintering respectively. This promising technique has distinguished characteristics of energy saving, rapid processing and uniform temperature distribution throughout the samples. 相似文献
5.
《Materials Letters》2006,60(25-26):3027-3030
Perovskite barium–strontium titanate, (Ba,Sr)TiO3 was prepared and effects of Sb2O3 additives on its PTCR properties were investigated. The (Ba,Sr)TiO3 with 0.05∼0.25 mol% Sb2O3 showed semiconducting PTCR behavior and anomalous grain growth was also observed when sintered at 1360 °C. It was considered that charge compensation by doping Sb2O3 as well as anomalous grain growth by sintering leads to resistivity reduction from insulating to semiconducting transition. 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.
D.S. Jung 《Materials Research Bulletin》2008,43(7):1789-1799
Nano-sized Ba1−xSrxTiO3 (BST) powder was prepared by flame spray pyrolysis using “CA-assisted” spray solution. The effects of the mole ratios of Ba to Sr components on the mean sizes, morphologies, and crystal structures of the BST powder prepared by flame spray pyrolysis were investigated. The precursor powders obtained by flame spray pyrolysis had large size, fractured and hollow structures irrespective of the mole ratios of Ba to Sr components. The post-treated BST powders had slightly aggregated morphology of the primary particles with nanometer sizes. The slightly aggregated BST powders turned to nano-sized primary particles by a simple milling process. The milled BaTiO3 particles post-treated at temperature of 1000 °C had spherical-like shape. On the other hand, the milled Ba0.5Sr0.5TiO3 and SrTiO3 particles had square shape. The mean sizes of the milled BaTiO3, Ba0.5Sr0.5TiO3 and SrTiO3 particles were each 110, 32, and 48 nm. Phase pure BST powder was obtained at a post-treatment temperature of 1000 °C irrespective of the mole ratios of Ba to Sr components. The BaTiO3 powder had tetragonal crystal structure. On the other hand, the BST except for the BaTiO3 composition had cubic crystal structures at post-treatment temperature of 1000 °C. The mean crystallite sizes of the milled Ba1−xSrxTiO3 primary particles were changed from 29 to 37 nm according to the mole ratios of Ba to Sr components. 相似文献
8.
A. B. Antipov A. A. Bosak E. M. Dedlovskaya N. P. Kuz'mina A. N. Grigor'ev A. R. Kaul' 《Inorganic Materials》2003,39(7):741-744
La0.7Sr0.3MnO3 ceramics are prepared from powders produced via gelation and/or microwave processing of solutions of polynuclear chelates (La, Sr, and Mn diethylenetriaminepentaacetates), and their electrical resistivity is measured as a function of temperature. As the sintering temperature is raised from 800 to 1100°C, the average grain size of the ceramics, evaluated by the Debye–Scherrer method, increases by about a factor of 2.5 and their resistivity drops by about two orders of magnitude. The effect of the sintering temperature on the average grain size depends very little on the preparation procedure. For some of the samples, the room-temperature weak-field magnetoresistance is determined. 相似文献
9.
Composite ceramics of Ba0.6Sr0.4TiO3 + 60 wt.% MgO were prepared from fine constituent powders by sintering at 1200–1280 °C. The composite specimens sintered at the relatively low temperatures showed satisfactory densification due to fine morphology of the constituent powders. The elevation of sintering temperature promoted the incorporation of Mg2+ into the lattice of the Ba0.6Sr0.4TiO3 phase and grain growth of the two constituent phases. The dependence of the dielectric properties on sintering temperature was explained in relation to the structural evolution. Controlling the sintering temperature of the composite was found to be important to achieve the desired nonlinear dielectric properties. Sintering at 1230 °C was determined to be preferred for the composite in terms of the nonlinear dielectric properties. The specimen sintered at the temperature attained a tunability of 17.3% and a figure of merit of 127 at 10 kHz and 20 kV/cm. 相似文献
10.
Jun LiangWen-Zhong Lu Jia-Min WuJian-Guo Guan 《Materials Science and Engineering: B》2011,176(2):99-102
Li2TiO3 ceramics were prepared at the sintering temperatures from 1050 to 1250 °C. The optimal microwave dielectric properties were ?r = 23.29, Q × f = 15,525 GHz (5.9 GHz), and τf = 35.05 ppm/ °C for the sample sintered at 1200 °C. The microwave dielectric properties were improved obviously when the Li2TiO3 ceramics were sintered at low temperatures with small additions of H3BO3 (B2O3 in the form of H3BO3). Only monoclinic Li2TiO3 was found in the pure or H3BO3-doped Li2TiO3 ceramics. About 1.0 wt.% H3BO3 addition aided the sintering of Li2TiO3 ceramics effectively while excessive H3BO3 (≥2.5 wt.%) was not favorable. Typically the best microwave dielectric properties were ?r = 23.28, Q × f = 37,110 GHz (6.3 GHz), and τf = 30.43 ppm/ °C for the 1.0 wt.% H3BO3-doped Li2TiO3 ceramic sintered at 920 for 3 h, which is promising for LTCC applications. 相似文献
11.
(5 − x)BaO-xMgO-2Nb2O5 (x = 0.5 and 1; 5MBN and 10MBN) microwave ceramics prepared using a reaction-sintering process were investigated. Without any calcinations involved, the mixture of BaCO3, MgO, and Nb2O5 was pressed and sintered directly. MBN ceramics were produced after 2-6 h of sintering at 1350-1500 °C. The formation of (BaMg)5Nb4O15 was a major phase in producing 5MBN ceramics, and the formation of Ba(Mg1/3Nb2/3)O3 was a major phase in producing 10MBN ceramics. As CuO (1 wt%) was added, the sintering temperature dropped by more than 150 °C. We produced 5MBN ceramics with these dielectric properties: ?r = 36.69, Qf = 20,097 GHz, and τf = 61.1 ppm/°C, and 10MBN ceramics with these dielectric properties: ?r = 39.2, Qf = 43,878 GHz, and τf = 37.6 ppm/°C. The reaction-sintering process is a simple and effective method for producing (5 − x)BaO-xMgO-2Nb2O5 ceramics for applications in microwave dielectric resonators. 相似文献
12.
Jiao Li Wu Songping Ding Xiaohong Ni Jing 《Journal of Materials Science: Materials in Electronics》2009,20(12):1186-1192
Mixture of zinc metatitanate and rutile (ZnTiO3 + 0.2TiO2), had been prepared via the conventional solid-state reaction method. The sintering behavior and microwave dielectric properties of ZnO–TiO2 system were investigated. The composition and microstructure of ceramics were discussed with XRD and SEM. It was found that ZnO–TiO2 ceramics, which was sintered at 900°C using 1.0 wt% B2O3 as sintering additive, had homogeneously fine microstructures and high densification. Samples possessed excellent microwave dielectric properties: ε r = 26, Q × f = 34,890 GHz, and τ f = ?11 ppm/°C. The above- mentioned material was suitable for the tape casting process and compatible with Ag electrodes, therefore, was an excellent candidate for multilayer ceramic capacitor applications. 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.
Z. Z. Huang S. U. Adikary H. L. W. Chan 《Journal of Materials Science: Materials in Electronics》2002,13(10):605-608
The processing behavior of PTCR ceramics of (Ba,Sr,Ca,Pb)TiO3 solid solution composition with additives of lanthanum oxide (La2O3) and boron nitride (BN) was studied. The ceramics can be sintered at temperatures as low as 1100 °C and possess rather low room-temperature resistivity with good PTCR effect. The sample ball milled with de-ionized water exhibits a more uniform microstructure compared to the sample ball-milled with alcohol. Particle size of less than 1 m was found to be adequate for preparing the ceramics and the finer particles (0.45 m) do not significantly improve the PTCR behavior. The performance of the PTCR sample is not sensitive to the sintering parameters such as the sintering time and cooling rate. This may be ascribed to the presence of excess BaO in the sample and the low sintering temperature, thereby eliminating the effect of Ba ion vacancies on the properties of the PTCR sample. 相似文献
15.
Radhapiyari Laishram O. P. Thakur 《Journal of Materials Science: Materials in Electronics》2013,24(9):3504-3507
Improved density (>98 %) has been realized in Zr0.8Sn0.2TiO4 (ZST) composition using nano-powder as precursor obtained from high energy milling process. Sintering has been performed at 1,325 °C for 4 h without using any sintering aids. XRD pattern shows single phase formation with orthorhombic structure. The microwave dielectric properties of ZST ceramics derived from precursor nano powder (obtained by high energy milling for 4 h) gives an optimum value of permittivity (ε′ ~ 38) and quality factor (Q × f ~ 1,03,300). However, precursor nanopowder obtained from extended milling (12 h) renders fine particle size (~20 nm) with meager change in permittivity within experimental error, whereas quality factor gets drastically reduced. 相似文献
16.
K.P. Surendran 《Materials Research Bulletin》2007,42(10):1831-1844
Ba(Mg1/3Ta2/3)O3 [BMT] dielectric ceramics are prepared by solid state (one step, two step and molten salt synthesis) and wet chemical methods (precipitation, citrate gel and sol-gel). The formation mechanism of BMT in each synthesis technique is discussed. The formation temperature and particle size of the formed BMT were found to be much lesser (in nanometer range) for solution synthesized powders. It is found that synthesis by sol-gel method resulted in the formation of ultra pure nanopowders of BMT at about 600 °C with average crystallite size of about 18 nm where as in solid state synthesis the formation of BMT was formed at about 1100 °C with average crystallite size of 220 nm. On sintering these powders, densification and grain growth of the chemically derived powders were found to be lower than that of solid state synthesized BMT powder. This has resulted in a slight decrease in density and microwave dielectric properties of the solution synthesized BMT samples. It is found that the microwave dielectric properties improved with increase in the average grain diameter of the sintered BMT ceramics. 相似文献
17.
Cheng-Shing HsuCheng-Liang Huang Jing-Fang TsengChi-Yuen Huang 《Materials Research Bulletin》2003,38(6):1091-1099
The microwave dielectric properties and the microstructures of MgNb2O6 ceramics with CuO additions (1-4 wt.%) prepared with conventional solid-state route have been investigated. The sintered samples exhibit excellent microwave dielectric properties, which depend upon the liquid phase and the sintering temperature. It is found that MgNb2O6 ceramics can be sintered at 1140 °C due to the liquid phase effect of CuO addition. At 1170 °C, MgNb2O6 ceramics with 2 wt.% CuO addition possesses a dielectric constant (εr) of 19.9, a Q×f value of 110,000 (at 10 GHz) and a temperature coefficient of resonant frequency (τf) of −44 ppm/°C. The CuO-doped MgNb2O6 ceramics can find applications in microwave devices requiring low sintering temperature. 相似文献
18.
Jingdong Guo Weibing Ma Minjie Ma Huaidang Zhao Yixuan Yang Jifeng Gao 《Journal of Materials Science: Materials in Electronics》2018,29(5):3640-3647
Microwave dielectric properties and microstructures of ultra-low loss Li2Mg3TiO6 ceramic prepared by reaction-sintering method (RS) and conventional solid-state reaction method (CS) have been investigated. The XRD patterns and SEM images revealed that the single phase of Li2Mg3TiO6 and uniform morphology are obtained by both RS and CS methods at the optimal sintering temperatures. In order to further investigate the effects of different sintering methods on the microwave dielectric properties of Li2Mg3TiO6 ceramics, the oxide polarizabilities and packing fraction were calculated based on the Rietveld refinement. The calculation results revealed that the RS method was more beneficial to the microwave dielectric properties of Li2Mg3TiO6 ceramics in comparison with CS method. Excellent microwave dielectric properties for Li2Mg3TiO6 ceramics with enhanced Q?×?f value of 157,036 GHz could be obtained using RS method sintered at 1250 °C for 6 h. 相似文献
19.
Porous n-BaTiO3 ceramics are synthesized by the addition of pore-forming agent into the (Ba,Sr)TiO3 powder. From the DTA-TGA analysis for samples containing the PEG and corn-starch, it was found that an exotherm occurred at 262 and 315°C, respectively, weight loss commenced at 165 and 252°C, and was virtually complete by 265 and 472°C, respectively. The porosity of n-BaTiO3 ceramics increased and the grain size decreased with increasing the pore-forming agent. From the XRD analysis at high angles, all the samples with and without the pore-forming agent at room-temperature exhibit the tetragonal structure. PTCR jump of the samples containing pore-forming agent is 1-2 orders higher than that of sample without the pore-forming agent. It is also found that the development of PTCR characteristic in the porous n-BaTiO3 ceramics containing pore-forming agent is related to grain boundaries, which basically equals that in ordinary BaTiO3 without pore-forming agent, from the complex impedance results. 相似文献
20.
L. NedelcuA. Ioachim M. ToacsanM.G. Banciu I. PasukC. Berbecaru H.V. Alexandru 《Thin solid films》2011,519(17):5811-5815
Ferroelectric ceramics Ba0.6Sr0.4TiO3 (BST 40) were prepared, by solid-state reaction in the temperature range 1210-1450 °C. Maximum values of the ceramic densities were around 94% of their theoretical value. X-ray diffraction techniques (XRD) and scanning electron spectroscopy (SEM) were used to analyze the structure and the surface morphology of ceramics. Rounded, well defined or abnormal granular growth was observed in the SEM images, vs. sintering conditions and purity of the raw materials. In all samples, BST 40 ceramic is the major phase, but there are also present small amounts of secondary phases, as revealed in XRD diffraction patterns. Permittivity and dielectric loss measurements were performed in the temperature range − 150 to + 150 °C, and 150 Hz-5 MHz frequency values. Permittivity values rising from 1200 to 12,500, with increasing sintering temperatures, were recorded. Narrow and well defined transition peaks were noticed at higher sintering temperatures. Curie temperature was around 2 °C, for samples with the mentioned composition. Permittivity and losses vs. frequency show different behavior whether BST ceramics are in polar or non-polar state and with the distance toward phase transition. Microwave measurements performed at room temperature have shown lower values of permittivity, compared with similar data at low frequency, and dielectric losses lower than 1% at 0.7 GHz. The sintering conditions (temperatures, sintering time, etc.) and purity of the raw materials lead to important changes of transition temperatures in the polymorphic diagram, which we have built—for the other Ba1−xSrxTiO3 compositions (x = 0.25-0.90) sintered at 1260 °C for 2 h. 相似文献