共查询到20条相似文献,搜索用时 411 毫秒
1.
P. Thomas L. N. Sathapathy K. Dwarakanath K. B. R. Varma 《Bulletin of Materials Science》2007,30(6):567-570
CaCu3Ti4O12 (CCTO) was synthesized and sintered by microwave processing at 2·45 GHz, 1·1 kW. The optimum calcination temperature using
microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were
sintered to 94% density at 1000°C/60 min. The microstructural studies carried out on these ceramics revealed the grain size
to be in the range 1–7 μm. The dielectric constants for the microwave sintered (1000°C/60 min) ceramics were found to vary
from 11000–7700 in the 100 Hz–00 kHz frequency range. Interestingly the dielectric loss had lower values than those sintered
by conventional sintering routes and decreases with increase in frequency. 相似文献
2.
Huanfu Zhou Xiuli Chen Liang Fang Changzheng Hu Hong Wang 《Journal of Materials Science: Materials in Electronics》2010,21(9):939-942
Ba5Nb4O15 powders were synthesized by molten-salt method in NaCl–KCl flux at a low temperature of 650–900 °C for 2 h, which is lower
than that of the conventional solid-state reaction. This simple process involved mixing of the raw materials and salts in
a certain proportion. Subsequent calcination of the mixtures led to Ba5Nb4O15 powders at 650–900 °C. XRD and SEM techniques were used to characterize the phase and morphology of the fabricated Ba5Nb4O15 powders, respectively. After sintering at 1,300 °C for 2 h, the densified Ba5Nb4O15 ceramics with good microwave dielectric properties of εr = 39.2, Q × f approximated as 27,200 GHz and τ
f
= 72 ppm/°C have been obtained. 相似文献
3.
Roberto Köferstein Florian Oehler Stefan G. Ebbinghaus 《Journal of Materials Science》2018,53(2):1024-1034
A one-pot polymerization method using citric acid and glucose for the synthesis of nano-crystalline BaFe0.5Nb0.5O3 is described. Phase evolution and the development of the crystallite size during decomposition of the (Ba,Fe,Nb)-gel were examined up to 1100 °C. Calcination at 850 °C of the gel leads to a phase-pure nano-crystalline BaFe0.5Nb0.5O3 powder with a crystallite size of 28 nm. The shrinkage of compacted powders starts at 900 °C. Dense ceramic bodies (relative density ≥ 90%) can be obtained either after conventional sintering above 1250 °C for 1 h or after two-step sintering at 1200 °C. Depending on the sintering regime, the ceramics have average grain sizes between 0.3 and 52 µm. The optical band gap of the nano-sized powder is 2.75(4) eV and decreases to 2.59(2) eV after sintering. Magnetic measurements of ceramics reveal a Néel temperature of about 23 K. A weak spontaneous magnetization might be due to the presence of a secondary phase not detectable by XRD. Dielectric measurements show that the permittivity values increase with decreasing frequency and rising temperature. The highest permittivity values of 10.6 × 104 (RT, 1 kHz) were reached after sintering at 1350 °C for 1 h. Tan δ values of all samples show a maximum at 1–2 MHz at RT. The frequency dependence of the impedance can be well described using a single RC-circuit. 相似文献
4.
E. Borsari B. G. G. Freire F. G. Garcia M. S. Silva C. C. Silva A. Z. Simões 《Journal of Materials Science: Materials in Electronics》2018,29(21):18020-18029
Crystalline aluminum substituted yttrium iron garnet nanoparticles Y3Fe3.35Al1.65O12 (YIG) was synthesized by hydrothermal microwave synthesis at 140 °C with soaking times ranging from 15 to 60 min. X-ray diffraction confirmed the single-phase YIG nanoparticles excluding the presence of any other phases in the reaction products. The Raman spectra revealed that the largest soaking time provides greater energy crystallization causing changes of lattice vibration and a certain degree of disorder in the crystal lattice. Field emission gun-scanning electron microscopy and high resolution transmission electronic microscopic revealed a homogeneous size distribution of nanometric YIG powders with agglomerated particles. Magnetic measurements were achieved by using a vibrating-sample magnetometer unit. YIG nanoparticles have great potential in magneto-hyperthermia application once in vivo applications magnetic induction heating ferromagnetic compounds generate heat in AC magnetic fields. 相似文献
5.
In this paper, the effects of doping with GeO2 on the synthesis temperature, phase structure and morphology of (K0.5Na0.5)NbO3 (KNN) ceramic powders were studied using XRD and SEM. The results show that KNN powders with good crystallinity and compositional homogeneity can be obtained after calcination at up to 900°C for 2 h. Introducing 0.5 mol.% GeO2 into the starting mixture improved the synthesis of the KNN powders and allowed the calcination temperature to be decreased to 800°C, which can be ascribed to the formation of the liquid phase during the synthesis. 相似文献
6.
Srimala Sreekantan Ahmad Fauzi Mohd Noor Zainal Arifin Ahmad Radzali Othman Anthony West Derek Sinclair 《Journal of Materials Science》2007,42(7):2492-2498
Ba0.9Sr0.1TiO3 powder was processed at 80°C by reacting Ti sol in aqueous solutions that contained BaCl2, SrCl2 and NaOH at atmospheric pressure. Well-crystallized, spherical, nanosizes powders were formed by this method. The powders
were found to have a cubic structure, which was retained even after heating at 900°C. Sintering at 1400°C, led to the formation
of a tetragonal structure with a secondary phase of Ba6Ti17O40. Abrupt grain growth was observed at 1400°C. The electrical response of the sample sintered at 1400°C has three electrically
different regions. Each region of the sample is represented by different RC element. Element 1 (R
1
C
1) is the most resistive and its capacitance ishigh (0.5 nFcm−1) indicating a thin region, probably the grain boundary. Element 2 (R
2
C
2) shows a smaller resistance value compared to element 1. The capacitance value of element 2 is temperature-dependent and
displays a Curie–Weiss behaviour, indicative of a ferroelectric material above T
c. The lower capacitance of C
2 (15 pFcm−1) indicates that it is a much thicker region than element 1 and can be assigned as a ferroelectric bulk region. Element 3
is probably an electrode effect. 相似文献
7.
Based on the principle of stability of geopolymer gel as refractory binder, a geopolymeric paste in the K2O–Al2O3–SiO2 system was developed and used to produce refractory concretes by adding various amount of α-quartz sand (grain size in the
range 0.1 μm to 1 mm) and fine powder alumina (grain size in the range 0.1–100 μm). The consolidated samples were characterized
before and after sintering using optical dilatometer, DSC, XRD and SEM. The total shrinkage in the range of 25–900 °C was
less than 3%, reduced with respect to the most diffused potassium or sodium based geopolymer systems, which generally records
a >5% shrinkage. The maximum shrinkage of the basic geopolymer composition was recorded at 1000 °C with a 17% shrinkage which
is reduced to 12% by alumina addition. The temperature of maximum densification was shifted from 1000 °C to 1150 or 1200 °C
by adding 75 wt% α-quartz sand or fine powder alumina respectively. The sequences of sintering of geopolymer concretes could
be resumed as dehydration, dehydroxylation, densification and finally plastic deformation due to the importance of liquid
phase. The geopolymer formulations developed in this study appeared as promising candidates for high-temperature applications:
refractory, fire resistant or insulating materials. 相似文献
8.
Alok Kumar Rai N. K. Singh Sang-Kwon Lee K. D. Mandal D. Kumar Om Parkash 《Journal of Materials Science: Materials in Electronics》2011,22(9):1286-1289
Dielectric properties of iron doped CaCu3Ti4O12 (CCTO), viz. CaCu3Ti3.9Fe0.1O12 (CCTFO) prepared by a novel semi-wet route have been investigated. X-ray diffraction of powder sintered at 900 °C show formation
of single phase solid solution. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of CuO rich phase at grain
boundaries of CCTFO. Nature of dielectric relaxation observed above room temperature is studied using complex plane impedance
analysis and modulus spectroscopy. It has been found that out of the two relaxations reported earlier above room temperature,
one occurring at lower temperature is due to grainboundaries interfacial polarization. 相似文献
9.
YAG:Ce nanosized spherical precursors were synthesized by coprecipitation using ammonium hydrogen carbonate as precipitant. Composition, phase transition, morphologies, and luminescence properties of the powders during calcination were studied. The precursors directly convert to pure YAG structure at about 900°C. The mean size of precursors is about 100 nm, and the grain size increases with increase of calcination temperature. When calcined above 1400°C, the grain size comes into a micrometer. With increase of calcination temperature, the luminescent intensity increases, and the emission band shows a redshift, while the lifetime increases. 相似文献
10.
J. Yu H. Wang J. Q. Li X. K. Cheng C. L. Chen Z. L. Huang 《Inorganic Materials》2010,46(11):1212-1219
Apatite-type La9.33(SiO4)6O2 powders have been prepared by urea-nitrates combustion at low temperature. Process parameters of combustion and characteristics
of electrolyte were studied and optimized. Gelation time of precursor has been shortened distinctly by introducing an appropriate
solvent system. Molar ratio of nitric acid to lanthanum oxide dependence of the nature of the phases has first been characterized.
Well-crystallized La9.33(SiO4)6O2 powders with an average size of 30.5 nm were obtained at a calcining temperature as low as 800°C for 12h. Dense ceramic with
a relative density of 96% was prepared by sintering the green compact of these nanopowders at 1400°C for 3 h. The sintering
body exhibited a high ionic conductivity of 4.38 × 10−3 S/cm at 700°C. 相似文献
11.
Guo-hua Chen Jun-tao Liu Hua-rui Xu Chang-rong Zhou Min-hong Jiang Xin-yu Liu 《Journal of Materials Science: Materials in Electronics》2011,22(8):915-919
Ultrafine strontium barium niobate (Sr0.3Ba0.7Nb2O6, SBN30) powders were prepared by urea method starting from a precursor solution constituting of Sr (NO3)2, Ba (NO3)2, NbF5, urea and polyvinyl alcohol (PVA) as surfactant. Their structural behavior and morphology were examined by means of X-ray
diffractometry (XRD) and Scanning electron microscopy (SEM). The results showed that the SBN30 powders crystallized to a pure
tetragonal phase at annealing temperatures as low as 750 °C. The average particle size of SBN powders subjected to 750 °C
was of the order of 150–300 nm. With increasing calcination temperature,however, the average particle size of the calcined
powders increased. The SBN30 ceramic prepared from urea method can be sintered at temperature as low as 1,225 °C. The transition
temperature from the ferroelectric phase to the paraelectric phase and the relative dielectric permittivity of the SBN30 powder
were less than the corresponding values of the bulk ceramic. The permittivity and loss tangent (tan δ) at room temperature
(1 kHz) was found to be 930 and below 0.025. 相似文献
12.
Synthesis and dielectric properties of BiFeO<Subscript>3</Subscript> derived from molten salt method
X. H. Zheng P. J. Chen N. Ma Z. H. Ma D. P. Tang 《Journal of Materials Science: Materials in Electronics》2012,23(5):990-994
BiFeO3 powder was synthesized in NaCl media at temperature range from 700 to 800 °C, using Bi2O3 and Fe2O3 as raw materials. Effects of calcining temperature and salt ratios on the synthesis of BiFeO3 powder had been investigated. It was found that NaCl effectively promoted the formation of BiFeO3. Almost pure BiFeO3 phase with a very small amount of Bi2Fe4O9 phase was synthesized at 750 °C with salt weight ratios of 1:1. A large amount of BiFeO3 phase decomposed to Bi2Fe4O9 and Bi25FeO39 phase when the temperature was up to 800 °C. In the present method, the calcining temperature played an important role in
the formation of BiFeO3 phase. BiFeO3 ceramics derived from molten salt method were prepared and exhibited the higher dielectric constant. 相似文献
13.
Chunchun Li Wangxi Wen Huaicheng Xiang Liang Fang Yihua Sun 《Journal of Materials Science: Materials in Electronics》2018,29(3):1907-1913
Crystal structure and dielectric properties of Zn3Mo2O9 ceramics prepared through a conventional solid-state reaction method were characterized. XRD and Raman analysis revealed that the Zn3Mo2O9 crystallized in a monoclinic crystal structure and reminded stable up to1020 °C. Dense ceramics with high relative density (~ 92.3%) were obtained when sintered at 1000 °C and possessed good microwave dielectric properties with a relative permittivity (ε r ) of 8.7, a quality factor (Q?×?f) of 23,400 GHz, and a negative temperature coefficient of resonance frequency (τ f ) of around ??79 ppm/°C. With 5 wt% B2O3 addition, the sintering temperature of Zn3Mo2O9 ceramic was successfully lowered to 900 °C and microwave dielectric properties with ε r ?=?11.8, Q?×?f?=?20,000 GHz, and τ f = ??79.5 ppm/°C were achieved. 相似文献
14.
Biao Dong Hua Yang Lianxiang Yu Yuming Cui Weiqun Jin Shouhua Feng 《Journal of Materials Science》2007,42(13):5003-5006
Sm
x
BiY2–x
Fe5O12 (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8) nanocrystals were fabricated by sol–gel method. Samples were characterized by powder X-ray
diffraction (XRD), thermal gravity analysis (TGA) and differential thermal analysis (DTA), transmission electron microscopy
(TEM), vibrating sample magnetometer(VSM). The samples were calcined at 850 °C and 1000 °C and the average size of the particles
were determined by Scherrer’s formula . In this paper, we discussed the effect of Sm3+ substitution for Y3+ on magnetic properties of BiY2Fe5O12. The magnetic properties of Sm
x
BiY2−x Fe5O12 are decreased with increasing content of Sm ion. 相似文献
15.
X. H. Zheng J. Xiao X. Huang D. P. Tang X. L. Liu 《Journal of Materials Science: Materials in Electronics》2011,22(8):1116-1119
The formation behavior of CaCu3Ti4O12 (CCTO) had been investigated via solid state reaction from CaTiO3, CuO and TiO2 powders. In the temperature range from 750 to 1,200 °C, the reaction sequence was traced by XRD, and the microstructure evolution
of calcined powders was also investigated by SEM. CCTO began to form owing to the reaction between CaTiO3, CuO and TiO2 at around 850 °C, and became the major phase at 1,000 °C. Finally, the single phase CCTO was obtained at 1,150 °C. However,
CCTO was decomposed at CaTiO3, CuO and TiO2 when the temperature increased to 1,200 °C. In addition, no other intermediate phases occurred in the synthesized process.
The formation behaviors indicated that CaTiO3 prevented the formation and growth of CCTO. 相似文献
16.
Xiuli Chen Huanfu Zhou Liang Fang Dongjin Chu Changda Li Ruili Guo Hong Wang 《Journal of Materials Science: Materials in Electronics》2011,22(4):371-375
The influences of B2O3 and CuO (BCu, B2O3: CuO = 1:1) additions on the sintering behavior and microwave dielectric properties of LiNb0.6Ti0.5O3 (LNT) ceramics were investigated. LNT ceramics were prepared with conventional solid-state method and sintered at temperatures
about 1,100 °C. The sintering temperature of LNT ceramics with BCu addition could be effectively reduced to 900 °C due to
the liquid phase effects resulting from the additives. The addition of BCu does not induce much degradation in the microwave
dielectric properties. Typically, the excellent microwave dielectric properties of εr = 66, Q × f = 6,210 GHz, and τ
f
= 25 ppm/oC were obtained for the 2 wt% BCu-doped sample sintered at 900 °C. Chemical compatibility of silver electrodes and low-fired
samples has also been investigated. 相似文献
17.
We have studied the effect of hot-pressing conditions (different pressure rise rates and isothermal holding temperatures in the range 1450–1550°C) on the microstructure of ceramics produced from nanopowder with the composition Ce0.09Zr0.91O2/MgAl6O10/γ-Al2O3 (20.6, 37.4, and 42.0 wt %, respectively). Firing at 1450°C for 1 h made it possible to obtain fine-grained ceramics with less than 3 μm in grain size. The compaction pressure rise rate was shown to be a key parameter under such thermal conditions (20 + 10°C/min → 1450°C). Grain growth was prevented most effectively when the maximum load, 30 MPa, was reached at a temperature of 1000°C. Under such conditions, the grain size was 0.4–0.8 μm and the relative density reached 98.8%. 相似文献
18.
A. N. Hapishah M. M. Syazwan M. N. Hamidon 《Journal of Materials Science: Materials in Electronics》2018,29(24):20573-20579
In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co0.5Zn0.5Fe2O4 was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co0.5Zn0.5Fe2O4 provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material. 相似文献
19.
Kalpana Parida Sujit Kumar Dehury R. N. P. Choudhary 《Journal of Materials Science: Materials in Electronics》2016,27(11):11211-11219
The polycrystalline sample of bismuth based-complex multiferroic of a composition Bi0.5Pb0.5Fe0.5Ce0.5O3 was prepared by a high-temperature solid-state reaction technique (calcinations temperature = 900 °C, sintering temperature = 960 °C, time = 4 h). Preliminary structural analysis using XRD data exhibits the formation of a single-phase compound. Studies of surface morphology of the ceramic sample of the compound, recorded at room temperature using a scanning electron microscope, show uniform distribution of grains of different size with few voids. Detailed studies of dielectric properties (εr, tan δ) supported the existence of multiferroic properties in the above complex system. The analysis of impedance parameters, recorded in a wide frequency (1 kHz–1 MHz) and temperature (room temperature to 450 °C) range of the material provide better understanding of (a) role of grains and grain boundaries in resistive and capacitative characteristics, (c) structure-properties relationship and (b) type of relaxation process occurred in the material. Study of temperature dependence of dc conductivity of the compound shows the existence of negative temperature coefficient of resistance in it. The nature of variation of ac conductivity with temperature of the material follows the Josher’s universal power law. Study of magneto-electric characteristics of the sample at room temperature has provided many useful and new data on magneto-electric coupling coefficient of different orders. 相似文献
20.
Strontium aluminates are important compounds with interesting properties such as long-duration phosphorescence and elastico-deformation luminescence. They have potential application in flexible light emitting panels. Since there are serious discrepancies in available thermodynamic data for these compounds, a redetermination of their Gibbs energies of formation was undertaken using solid-state electrochemical cells incorporating single-crystal SrF2 as the electrolyte in the temperature range from 1000 to 1300 K. However, the measurements were restricted to SrAl12O19 and SrAl4O7 because of the formation of strontium oxyfluoride phase between SrAl2O4 and SrF2. For the reactions, SrO + 6 Al2O3 → SrAl12O19, ΔG o/J mol?1 (± 280) = ?83386 ? 25.744 (T/K), and SrO + 2Al2O3 → SrAl4O7, ΔG o/J mol?1 (± 240) = ?80187 ? 25.376 (T/K). The high entropy of SrAl4O7 and SrAl12O19 can be partly related to their complex structures. The results of this study are consistent with calorimetric data on enthalpy of formation of other Sr-rich aluminates and indicate only marginal stability for SrAl4O7 relative to its neighbours, SrAl12O19 and SrAl2O4. The thermodynamic data explain the difficulty in direct synthesis of phase pure SrAl4O7 and the formation of SrAl2O4 as the initial ternary phase when reacting SrO and Al2O3 or crystallizing from amorphous state, irrespective of composition. 相似文献