共查询到20条相似文献,搜索用时 11 毫秒
1.
《Ceramics International》2019,45(11):13859-13864
BaFe12-xCoxO19 (BFCO, x ≤ 0.4) ceramics with superior magnetic and electromagnetic (EM) properties were prepared using Co3+ substituted BaFe12O19 (BFO) in 2.6–18 GHz. Compared with the ceramics without Co3+, the incorporation of 40 mol% Co3+ enhances magnetic properties; the saturation magnetization (MS) is improved by about 55.6 emu·g−1 due to the variety of magnetocrystalline anisotropy. The resonance behaviors of complex permeability are observed and resonance frequency shifts to lower frequency range from 6 to 3 GHz. The minimum reflection loss (RL) of −32.1 dB (<−10 dB) is obtained at 11.2 GHz in 8.5–13.5 GHz at 2.0 mm thickness in the sample with x = 0.4, which suggests that such ceramics is highly promising as effective microwave absorbers for EM applications. 相似文献
2.
Haonan Gong Shujuan Tan Jing Zheng Kangsen Peng Yanting Zhang Yunjia Hu Songhan Duan Guoyue Xu 《Ceramics International》2021,47(9):12389-12396
In this work, flake-shaped FeCo/BaFe12O19 composites were successfully prepared via a facile two-step process involving ball milling and sol-gel treatment. Compared with commonly used FeCo alloys, FeCo/BaFe12O19 composite material can achieve remarkable microwave absorption performance, and this is largely because of the flake-shaped structure and dielectric relaxation processes. Furthermore, changing mass fractions of BaFe12O19 enable flexible control of applicable frequency ranges of FeCo/BaFe12O19 composites. It was found that when the BaFe12O19 mass fraction is as high as 20%, minimum reflection loss can reach ?51.22 dB with effective loss of < –10 dB and effective bandwidth of 6.24 GHz even at a thin thickness of 1.45 mm. It is highly believed that these significant achievements will arouse interest from researchers for further practical exploration of microwave absorbers. 相似文献
3.
《Ceramics International》2019,45(13):16512-16520
Zinc-substituted cobalt oxide nanoparticles (ZnxCo3-xO4, 0 ≤ x ≤ 0.5) were produced by microwave refluxing technique. The structural, microstructural and magnetic properties of these samples were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and magnetic property measurement system (MPMS) respectively. XRD and TEM analyses confirmed the single phase nature for all the samples. Rietveld analysis of the samples further confirmed the substitution of Zn-ions into the Co3O4 lattice. The chemical states of the elements were studied using X-ray photoelectron spectroscopy (XPS), which suggest the presence of Zn2+, Co2+, and Co3+ ions in the samples. The maximum saturation magnetization (MS) values of 0.33 Am2/kg was obtained for x = 0.01 sample, and then it continuously reduced with increased Zn content. The dielectric property of the samples was studied in the frequency range of 40 Hz–110 MHz. The samples x = 0.05 and 0.5 displayed the lowest conductivity due to the narrow size distribution of grains. 相似文献
4.
Commercial lead zirconate titanate (PZT) perovskite powders were used to fabricate ceramic tape and then sintered by microwave and conventional methods. Both dielectric and piezoelectric properties of PZT ceramic tapes were studied in terms of sintering process. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) show the PZT perovskite phase with smaller grain size and dense microstructure can be obtained at a lower sintering temperature by microwave process. It was also observed that shrinkage ratio and bulk density of the tapes sintered at 800 °C were obtained about 19% and 7.46 g/cm3 by the microwave heating method, respectively, that is corresponding to those values of sintered PZT tapes at 950 °C by conventional process. Moreover, the dielectric constant and maximum permittivity are increased about 30% as compared with conventional processing method. The experimental results demonstrated that the characteristics of the PZT tapes could be significantly improved by microwave heating method. These results demonstrate that such a simple approach can upswing the piezoelectric and dielectric properties of these tapes by using microwave process with a short heating time. 相似文献
5.
《Ceramics International》2016,42(10):11780-11795
Both Y-La-Bi substituted and non-substituted Sr-hexaferrites (SrM) were synthesized by sol-gel auto combustion technique and the influences of Y, La and Bi ions on ac/dc conductivities, dielectric constant/loss properties as well as complex dielectric modulus were investigated extensively for a variety of substitutions. It was observed that ac conductivity of SrM increases slightly with increasing Y3+ La3, and Bi3+ substitutions at first, and then decreases with its further increments. Furthermore, ac conductivity increased with increasing frequency which could be regarded as an origin indication of both electronic and polaron hopping mechanism. It is also worthy to note that the activation energy, which is an indication of both mechanisms depicted in the Arrhenius plot, is increased as the enhanced contributions of substitutions in SrM with the illustration of a better stability and tunability of electrical bonds among substituted ions and ferrous and ferric ions. The dielectric constant, dielectric loss and dielectric modulus represent a very interesting tunability and optimised consequences regarding to the variation of frequencies, temperatures and substitutions of SrM. 相似文献
6.
《Ceramics International》2017,43(9):7346-7350
In this work, ultrapure hexagonal BaFe12O19 nanoferrite was synthesized by a facile co-precipitation method. Formation of single phase was analyzed by using wide angle X-ray diffraction. Crystallite size was found to increase from 50 nm to 78 nm when annealing temperature increased from 800 °C to 1000 °C, respectively. Ferrimagnetic behavior with moderate value of saturation magnetization and coercivity were studied at room temperature with the help of vibrating sample magnetometer (VSM). The electromagnetic radiation (EMR) absorption properties were studied in the frequency range of 2–18 GHz by using Vector Network analyzer (VNA). The maximum EMR absorption of −26.52 dB was observed at a frequency of 5.79 GHz. The FTIR spectra confirm tetrahedral and octahedral sites in BaFe12O19 structure. The surface morphology was analyzed by scanning electron microscopy (SEM), which reveals that the particles are agglomerated into irregular shapes. Particle size was measured with transmission electron microscopy (TEM), which was in correlation with the already calculated size from x-ray diffraction (XRD) spectra. 相似文献
7.
《Ceramics International》2016,42(9):10565-10571
Zinc substituted magnesium (Mg–Zn) ferrites with the general formula Mg1−xZnxFe2O4 (x=0.00, 0.25, 0.50, 0.75, and 1.00) were prepared using the solution combustion route. The dried powder after calcination (700 °C for 2 h) was compacted and sintered at 1050 °C for 3 h. The structural, morphological, dielectric and magnetic properties of the sintered ferrites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), impedance spectroscopy, and vibration sample magnetometry (VSM). The XRD analysis of sintered samples confirmed that the expected spinel cubic phase was formed for all samples. The crystallite sizes evaluated using Scherre's formula were found to be in the range of 47–80 nm. SEM analysis showed homogeneous grains with a polyhedral structure. The electrical conductivity increased with increasing frequency, which is normal dielectric behavior for such materials. The dielectric constant, dielectric loss tangent, and AC conductivity were found to be lowest for x=0.50. The VSM results showed that the zinc concentration had a significant influence on the saturation magnetization and coercivity. 相似文献
8.
《Ceramics International》2016,42(9):10682-10689
A ternary nanocomposite of Fe3O4@SnO2/reduced graphene oxide (RGO) with different contents of SnO2 nanoparticles was synthesized by a simple and efficient three-step method. The transmission electron microscopy and field emission scanning electron microscopy characterization display that plenty of Fe3O4@SnO2 core–shell structure nanoparticles are well distributed on the surface of RGO sheets. The X-ray diffractograms show that the products consist of highly crystallized cubic Fe3O4, tetragonal SnO2 and disorderedly stacked RGO sheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the products at room temperature. The microwave absorption properties of paraffin containing 50 wt% products were investigated at room temperature in the frequency range of 2–18 GHz by a vector network analyzer. The electromagnetic data show that the maximum reflection loss is −45.5 dB and −29.5 dB for Fe3O4@SnO2/RGO-1 and Fe3O4@SnO2/RGO-2 nanocomposite, respectively. Meanwhile, the reflection loss less than −10 dB is up to 14.4 GHz and 13.8 GHz for Fe3O4@SnO2/RGO-1 and Fe3O4@SnO2/RGO-2 nanocomposite, respectively. It is believed that such nanocomposite could be used as promising microwave absorbers. 相似文献
9.
10.
AC susceptibility and hyperfine interactions of Mg-Ca ions co-substituted BaFe12O19 nanohexaferrites
M.A. Almessiere Y. Slimani H. Güngüneş S. Ali A. Baykal I. Ercan 《Ceramics International》2019,45(8):10048-10055
Magnesium and calcium co-substituted Ba M-type nanohexaferrite (NHFs) is fabricated via sol-gel auto-combustion technique. The phase formation was proved by XRD powder pattern, FESEM and HR-TEM. Magnetic properties of Ba1-2xCaxMgxFe12O19 (x?≤?0.1) NHFs investigated by Mossbauer Spectroscopy. The variations in line width, quadrupole splitting, isomer shift, the cation distribution of Ca2+ and Mg2+ ions and hyperfine magnetic field values were estimated. The AC magnetic susceptibility and ZFC-FC measurements were also performed for the Ba1-2xCaxMgxFe12O19 (x?=?0.02 and 0.08) NHFs. The MFC-MZFC results do not show blocking temperature peak, indicating the ferrimagnetic (FM) behavior of prepared products. Different models including Neel-Arhenius (N-A), Vogel-Fulcher (V-F) and critical slowing down (CSD) were tested to evaluate the AC-magnetic susceptibility behaviors. It is demonstrated that the magnetic interactions are important for x?=?0.02 NHFs. 相似文献
11.
12.
A novel low-loss microwave dielectric material MgZrNb2O8 was reported for the first time. Single-phase MgZrNb2O8 was prepared by a conventional mixed-oxide route and sintered in the temperature range of 1280–1360 °C. The microstructure and microwave dielectric properties were investigated systematically. The X-ray diffraction results showed that all samples exhibit a single wolframite structure. When the sintering temperature was lower than 1340 °C, the Q×f value mainly depended on the relative density. However, when the sintering temperature was above 1340 °C, the Q×f value mainly relied on the grain morphology in addition to the density. The MgZrNb2O8 ceramic sintered at 1340 °C for 4 h exhibited excellent microwave dielectric of εr=26, Q×f=120,816 GHz (where f=6.85 GHz), and τf=?50.2 ppm/°C. These results demonstrate that MgZrNb2O8 could be a promising candidate material for the application of highly selective microwave ceramic resonators and filters. 相似文献
13.
《Ceramics International》2023,49(3):4599-4606
The impact of La substitution has been explored systematically in the present work, it covers a rough scan of the range of solubility of Lanthanum in the Sr3Co2Fe24O41 (SCFO) structure. The La substituted Z-type hexaferrites Sr3-xLaxCo2Fe24O41, with x = 0.00, 0.15, 0.30, and 0.45, have been prepared via solid-state reaction route and named as SCFO, SLCFO5, SLCFO10 and SLCFO15 respectively. The structure and particle morphology of the samples have been investigated via variety of structural characterization methods like X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). A substantial change in structural properties beyond x ≥ 0.45 suggests that their exists a limit of Lanthanum solubility in the Sr3-xLaxCo2Fe24O41 which is x = 0.45. The dielectric properties (ε′ & ε′′) of SCFO, SLCFO5, SLCFO10 and SLCFO15 were examined by varying temperature from 313 to 613 K in the frequency range of 500 Hz to 10 MHz. The dielectric responses of all the samples are frequency-dependent and thermally stimulated, with relaxation-type dielectric behavior. From M-H loops, it has been observed that with increasing La substitution, the saturation magnetization value reduces from 63.85 to 59.17 emu/g, whereas coercivity increases from 109.74 to 450.51 oersted, indicating an increase in magnetic hardness. The saturation magnetization (Ms) and Magneto crystalline anisotropy constant (K1) were calculated by fitting the experimental data. A weak signature of magneto-electric coupling is observed by employing an indirect method in the SCFO sample. 相似文献
14.
《Ceramics International》2017,43(5):4229-4234
The M-type SrFe12O19 hexaferrite has been synthesized by a microwave solid state reaction process – a fast heating process – in a home-made 2.45 GHz single-mode microwave cavity. Starting from SrCO3 and Fe2O3 mixtures (1:6 ratio), cold pressed samples have been heated up in the microwave electric field without needing any susceptor, demonstrating the good coupling of the precursors with this microwave mode in our experimental setup.After optimization of the experimental conditions, the properties of the obtained ceramics, including structure, microstructure and magnetic properties, are compared with those of ceramics synthesized by conventional solid state reaction. With that microwave process, it is found that SrFe12O19 ceramics prepared in less than 30 min exhibit magnetic properties similar to those of the same compound produced by a conventional process. This highlights the potentialities of the technique to synthesize hexaferrite ceramics. 相似文献
15.
《Ceramics International》2022,48(4):4658-4664
Two garnet-structured Ca3MgBGe3O12 (B = Zr, Sn) ceramics with tetravalent cations at B-site were prepared by conventional solid state reaction. The crystal structure, microstructure evolution, and microwave dielectric performance were investigated using X-ray powder diffraction, Rietveld refinement, scanning electron microscopy, Raman spectroscopy, and infrared spectroscopy techniques. Dense Ca3MgZrGe3O12 and Ca3MgSnGe3O12 ceramics were obtained at sintering temperatures of 1420 and 1400 °C, respectively. The dielectric constant, unloaded quality factor, and temperature coefficient of resonance frequency of Ca3MgZrGe3O12 were 10.80 ± 0.2; 79,600 ± 1000 GHz (f = 12.61 GHz); and ?66.8 ± 1 ppm/°C, respectively, and the corresponding values for Ca3MgSnGe3O12 were 9.68 ± 0.2; 83,400 ± 1000 GHz (f = 14.19 GHz); and ?57.9 ± 1 ppm/°C, respectively. The dielectric performances of the two ceramics were compared by analyzing the ionic polarizability, packing fraction, and bond valence. The intrinsic dielectric properties were predicted by fitting the infrared reflectivity spectra. 相似文献
16.
《Journal of the European Ceramic Society》2017,37(13):3951-3957
A parallel preparation method was developed using dry powders as starting materials to synthesize multi-compositional microwave dielectric ceramics. The Li2O-Nb2O5-TiO2 ternary system was investigated as a model material. The validity of the parallel ceramic preparation process was confirmed by synthesizing a group of LiNb0.6Ti0.5O3 ceramics in parallel, which showed the same crystalline structure and close dielectric properties. The ceramic libraries with M-phase-rich samples and Li2TiO3-rich samples were prepared using the parallel process, and the microwave dielectric properties and crystal phases were investigated systematically. An excellent microwave ceramic with a composition of 0.55Li2O-0.05Nb2O5-0.40TiO2 was obtained, which has a dielectric constant of 18.4 and a high quality value (Q × f) of 79000 GHz. This parallel process can be applied extensively to explore a variety of bulk ceramic libraries for discovering new functional materials with high performances. 相似文献
17.
X. Huang Y.T. Liu G.S. Luo C. Lin X. Wu X.H. Zheng D.P. Tang 《Ceramics International》2021,47(15):21024-21028
High density Ba4Sm2Fe2Nb8O30 (BSFN) multiferroics ceramics with tetragonal tungsten bronze structure had been prepared by microwave sintering (MS) for 30min and conventional sintering (CS) methods for 4 h at 1275 °C. Single tungsten bronze phase and equiaxial grains are obtained for the MS BSFN ceramics, while a small amount secondary phase of SmNbO4 is observed in the CS BSFN ceramics with columnar grains. Compared to Ba4Sm2Fe2Nb8O30 ceramics prepared by CS method, enhanced dielectric, ferroelectric and magnetic properties are achieved for the MS BSFN ceramics. The values of electric polarization Pr and coercive electric field Ec are 2.11 μC/cm2 and 7.14 kV/cm for the MS BSFN ceramics, respectively. Meantime, the magnetic polarization Mr of 0.410emu/g and coercive magnetic field Hc of 2930Oe are also obtained for the MS BSFN ceramics. Based on the density, crystal structure, point defect and grain, the reasons of enhanced dielectric, ferroelectric and magnetic properties are discussed for the MS BSFN ceramics It is indicated that Ba4Sm2Fe2Nb8O30 is an intrinsic room temperature multiferroic materials. 相似文献
18.
In the present study, magnetic properties of barium ferrite foams were investigated. We especially examine the effects of porosity on interparticle interactions and remanence properties of these materials. It was observed that magnets become harder with porosity. On the other hand, saturation magnetization decreases slightly. Existence of porosities increases the strength of demagnetising-like interactions of neighboring particles. 相似文献
19.
《Ceramics International》2017,43(9):7065-7072
Aeschynite-type La1−xLnxTiNbO6 (Ln=Ce, Sm, x=0–1) ceramics were prepared via a conventional solid state method. Analysis of X-ray diffraction, Raman, infrared reflectivity spectra and the microstructures revealed a series of composition-induced phase evolution in sequence: monoclinic→coexistence of monoclinic and orthorhombic→orthorhombic structure, i.e. M→M+O→O. The critical compositions of distinguishing the dominant M or O phase were x=0.15 in La1−xCexTiNbO6 and x=0.10 in La1−xSmxTiNbO6 ceramics, exactly corresponding to the average ionic radius of rare earth ions (IR) ~1.027 Å. The crystal structure and microwave dielectric properties of RETiNbO6 (RE=rare earth) ceramics strongly depended on IR. Near-zero τf was achieved in the Ce-sample with x=0.153 (εr=28.9, Q×f=17,275 GHz@6.54 GHz) as well as in the Sm-sample with x=0.098 (εr=28.2, Q×f=19,186 GHz@6.78 GHz). Eventually, RETiNbO6 would form O euxenite (-τf), O aeschynite (+τf), and M aeschynite (-τf), as IR<0.945 Å, 0.945 Å <IR<1.027 Å, and 1.027 Å<IR<1.032 Å, respectively. The infrared reflectivity study also confirmed that the structural phonon oscillations in the infrared region dominated the dielectric performance in the microwave region for this system. 相似文献
20.
Dy substituted CCTO ceramics were synthesized using solid state reaction method. Effect of Dy on structural, microstructural, dielectric and electrical properties has been studied over a wide temperature (300–500 K) and frequency range (100 Hz–1 MHz). Rietveld refinement, carried out on the samples, confirmed single phase formation and indicated overall decrease in lattice constant. Microstructure showed bimodal distribution of grains in CCTO with bigger grains surrounded by smaller grains. Dy substitution reduced grain size. Dy substitution in CCTO reduces the dielectric constant which may be attributed to increase of the Schottky potential barrier. The dielectric constant remains nearly constant in temperature range 300–400 K. The AC conductivity obeys a power law, σac=A fn, where n is the temperature dependent frequency exponent. The AC conductivity behaviour can be divided into three regions, over entire temperature range, depending on conduction processes. The relevant charge transport mechanisms have been discussed. 相似文献