共查询到20条相似文献,搜索用时 15 毫秒
1.
M. AirimioaeiC.E. Ciomaga N. ApostolescuL. Leontie A.R. IordanL. Mitoseriu M.N. Palamaru 《Journal of Alloys and Compounds》2011,509(31):8065-8072
Nanocrystalline Ni1−xMnxFe2O4 (x = 0; 0.17; 0.34; 0.5) ferrite powders were successfully synthesized using the sol-gel combustion method, by using nitrates as cations source and citric acid (C6H8O7) as combustion/chelating agent. The reaction advancement was observed by means of IR absorption spectroscopy, by monitoring two characteristic bands for the spinel compounds at about 600 cm−1 and 400 cm−1, respectively. The as-synthesized powders were characterized by IR spectroscopy, X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The magnetic study shows that the saturation magnetization decreases with increasing the Mn addition, as result of the particle size reduction. The dielectric properties were measured as a function of frequency in the range of 10 Hz to 1 MHz. The real part of permittivity has values of ∼88 at 1 kHz and ∼7 at 1 Hz for x = 0. An increasing dielectric permittivity with increasing the amount of Mn is observed. For all the investigated compositions, both the real and imaginary parts of permittivity decrease with frequency. 相似文献
2.
Yuan-Bin Chen 《Journal of Alloys and Compounds》2011,509(37):9226-9229
Solid solutions of (1 − x)La(Co1/2Ti1/2)O3-xLa(Mg1/2Ti1/2)O3 were used to prepare La(Mg1−xCox)1/2Ti1/2O3 using solid-state synthesis. X-ray diffraction patterns of the sintered samples revealed single phase formation. A maximum density of 6.01 g/cm3 was obtained for La(Mg1−xCox)1/2Ti1/2O3 (x = 1) ceramics sintered at 1375 °C for 4 h. The maximum values of the dielectric constant (?r = 29.13) and the quality factor (Q × f = 80,000 GHz) were obtained for La(Mg1−xCox)1/2Ti1/2O3 with 1 wt% ZnO additive sintered at 1375 °C for 4 h. The temperature coefficient of resonant frequency τf was −59 ppm/°C for x = 0.3. 相似文献
3.
G. Murtaza Rai Faiza aenMisbah-ul-Islam M.U. Rana 《Journal of Alloys and Compounds》2011,509(14):4793-4796
We have prepared BaCd2−xSrxFe16O27 (x = 0, 0.5, 1, 1.5 and 2.0) W-type hexagonal ferrites by standard ceramic method. In this work, the structural, dielectric and magnetic properties have been studied of the prepared samples. The XRD analysis of the samples reveals single phase behavior sintered at 1400 °C for 6 h. The saturation magnetization (Ms) shows increasing behavior with the increasing concentration of Sr2+. While the coercivity (Hc) decreases rapidly up to 409 G for x = 1.5 and then increases for (x > 1.5) due to the preference of Cd2+ for tetrahedral sites and the number of spin-down magnetic ions. The real and imaginary parts of the dielectric constant (?′,?″) and dielectric loss tangent (tan δ) are determined in the frequency range 0.1-107 Hz. It is observed that both the real and imaginary parts of the dielectric constant and tan δ decrease with the increasing concentration of Sr2+, which is due to the contribution of Cd2+ ions in addition to Fe3+ and Fe2+ ions to interfacial polarization. 相似文献
4.
Jijing XuGuijuan Ji Haifeng ZouYuan Zhou Shucai Gan 《Journal of Alloys and Compounds》2011,509(11):4290-4294
Z-type hexaferrites doped with Nd3+, Ba3−xNdxCo2Fe24O41 (x = 0, 0.05, 0.10, 0.15, and 0.25), were prepared by solid-state reaction. The effect of the Nd3+ ions substitution for Ba2+ ions on the microstructure and electromagnetic properties of the samples was investigated. The results reveal that an important modification of microstructure, complex permeability, complex permittivity, and static magnetic properties can be obtained by introducing a relatively small amount of Nd3+ instead of Ba2+. SEM image shows that the grains of the ferrites doped with Nd3+ were smaller, more perfect and homogeneous than that of the pure ferrite. The real part (?′) of complex permittivity and imaginary part (?″) increase at first, and then decrease with increasing Nd content. At low frequency, the imaginary part μ″ of complex permeability decreases with Nd content and then increases when frequency is above 7.0 GHz. The magnetization (Ms) and the coercivity (Hc) are 79.38 emu g−1 and 36.94 Oe for Ba2.75Nd0.25Co2Fe24O41. The data of magnetism show that the ferrite doped with Nd3+ ions is a better soft magnetic material due to the higher magnetization and lower coercivity. 相似文献
5.
We present the structural, microstructural, dielectric and impedance behavior of Pb0.7Sr0.3[(Fe2/3Ce1/3)0.012Ti0.988]O3 (PSFCT) and Pb0.7Sr0.3[(Fe2/3La1/3)0.012Ti0.988]O3 (PSFLT) nanoparticles. These nanoparticles were prepared by a chemical synthesis route using polyvinyl alcohol as surfactant. The X-ray diffraction pattern shows polycrystalline nature with coexistence of tetragonal and cubic phase in both PSFCT and PSFLT nanoparticles. The average particle size has been measured using Scherer's relation. The average particle sizes also measured by TEM are 10 and 11 nm, and by SEM 9 and 12 nm, respectively, of PSFCT and PSFLT nanoparticles. By measuring the value of relative permittivity (?′) and loss (tan δ) at lower frequency, the dielectric properties show Maxwell-Wagner type interfacial polarization. However, due to nano size effect of PSFCT and PSFLT, dispersionless dielectric response has been observed up to higher frequency of 15 MHz. The frequency dependent real (Z′) and imaginary (Z″) parts of impedance confirmed the variation which was observed in dielectric properties. The values of resistance of grain boundaries, Rgb is higher than grains, Rg indicates that the effect of grain boundaries is dominant on electrical properties when the size of nanoparticles is quite small. 相似文献
6.
A.K. SinghAkhilesh Kumar Singh 《Journal of Alloys and Compounds》2011,509(16):5167-5172
We present here the results of comprehensive X-ray diffraction and dielectric studies on several compositions of (1 − x)[Pb(Mg0.5W0.5)O3]-xPbTiO3 (PMW-xPT) solid solution across the morphotropic phase boundary. Rietveld analysis of the powder X-ray diffraction data reveals cubic (space group Fm3m) structure of PMW-xPT ceramics for the compositions with x ≤ 0.42, tetragonal (space group P4mm) structure for the compositions with x ≥ 0.72 and coexistence of the tetragonal and cubic phases for the intermediate compositions (0.46 ≤ x ≤ 0.68). Temperature dependence of the dielectric permittivity above room temperature exhibits diffuse nature of phase transitions for the compositions in the cubic and two phase region while the compositions with tetragonal structure at room temperature exhibit sharp ferroelectric to paraelectric phase transition. The PMW-xPT compositions with coexistence of tetragonal and cubic phases at room temperature exhibit two anomalies in the temperature dependence of the dielectric permittivity above room temperature. Using results of structural and dielectric studies a partial phase diagram of PMW-xPT ceramics is also presented. 相似文献
7.
Composite ceramics in the solid solution of Zrx(Zn1/3Nb2/3)1−xTiO4 (x = 0.1-0.4) have been prepared by the mixed oxide route. Formation of solid solution was confirmed by the X-ray diffraction patterns. The microwave dielectric properties, such as dielectric constant (?r), Q × f value and temperature coefficient of resonant frequency (τf) have been investigated as a function of composition and sintering temperature. With x increasing from 0.1 to 0.4, the dielectric constant decreases from 70.9 to 43.2, and the τf decreases from 105 to 55 ppm/°C. The Q × f value, however, increases with increasing x value to a maximum 26,600 GHz (at 6 GHz) at x = 0.3, and then decreases thereafter. For low-loss microwave applications, a new microwave dielectric material Zr0.3(Zn1/3Nb2/3)0.7TiO4, possessing a fine combination of microwave dielectric properties with a high ?r of 51, a high Q × f of 26,600 GHz (at 6 GHz) and a τf of 70 ppm/°C, is suggested. 相似文献
8.
Liang FangDongjin Chu Huanfu Zhou Xiuli ChenHui zhang Baocheng ChangChunchun Li Yuandong QinXi Huang 《Journal of Alloys and Compounds》2011,509(35):8840-8844
The Li2ZnxCo1−xTi3O8 (x = 0.2-0.8) solid solution system has been synthesized by the conventional solid-state ceramic route and the effect of Zn substitution for Co on microwave dielectric properties of Li2CoTi3O8 ceramics has also been investigated. The microwave dielectric properties of these ceramics show a linear variation between the end members for all compositions. The optimized sintering temperatures of Li2ZnxCo1−xTi3O8 ceramics increase with increasing content of Zn. The specimen with x = 0.4 sintered at 1050 °C/2 h exhibits an excellent combination of microwave dielectric properties with ?r = 27.7, Qu × f = 57,100 GHz and τf = −1.0 ppm/°C. 相似文献
9.
Phase evolution and microwave dielectric properties of (1 − x)(Mg0.95Co0.05)2TiO4-xTiO2 (x = 0-1) ceramics prepared by the conventional mixed oxide route have been investigated. Increasing the TiO2 content would lead to a main phase transformation from (Mg0.95Co0.05)2TiO4 to (Mg0.95Co0.05)TiO3, (Mg0.95Co0.05)Ti2O5 and then TiO2. Not only did the TiO2 addition compensate the τf, it also lowered the sintering temperature of specimen. A huge drop of Q × f occurs at a 40-60 mol% TiO2 addition was attributed to the formation of (Mg0.95Co0.05)Ti2O5 phase. Specimen with x = 0.78 can possess an excellent combination of microwave dielectric properties: ?r ∼ 24.77, Q × f ∼ 38,500 GHz and τf ∼ −1.3 ppm/°C. 相似文献
10.
Zupei Yang Lijuan ZhangXiaolian Chao Lirong XiongJie Liu 《Journal of Alloys and Compounds》2011,509(35):8716-8719
The Ca1−xSrxCu3Ti4O12 (CSCTO) giant dielectric ceramics were prepared by conventional solid-state method. X-ray diffraction patterns revealed that a small amount of Sr2+ (x < 0.2) had no obvious effect on the phase structure of the CSCTO ceramics, while with increasing the Sr2+ content, a second phase of SrTiO3 appeared. Electrical properties of CSCTO ceramics greatly depended on the Sr2+ content. The Ca0.9Sr0.1Cu3Ti4O12 ceramics exhibited a higher permittivity (71,153) and lower dielectric loss (0.022) when measured at 1 kHz at room temperature. The ceramics also performed good temperature stability in the temperature range from −50 °C to 100 °C at 1 kHz. By impedance spectroscopy analysis, all compounds were found to be electrically heterogeneous, showing semiconducting grains and insulating grain boundaries. The grain resistance was 1.28 Ω and the grain boundary resistance was 1.31 × 105 Ω. All the results indicated that the Ca0.9Sr0.1Cu3Ti4O12 ceramics were very promising materials with higher permittivity for practical applications. 相似文献
11.
Yuan-Bin Chen 《Journal of Alloys and Compounds》2011,509(3):1050-1053
Ceramics in the system La(Mg1−xZnx)1/2Ti1/2O3 with B2O3 additions (1 wt.%) have been investigated by the conventional solid-state route. The XRD patterns of the sintered samples (0.3 ≤ x ≤ 1.0) revealed single phase formation with a structure. The unit cell volume slightly increased with increasing Zn content (x). La(Mg1−xZnx)1/2Ti1/2O3 were found to form perovskite solid solutions in the whole compositional range. The maximum values of the dielectric constant and the quality factor multiples resonant frequency (Q × f) can be obtained when the La(Mg0.7Zn0.3)1/2Ti1/2O3 with 0.5 wt.% B2O3 additive were sintered at 1475 °C for 4 h. The temperature coefficient of resonant frequency τf (−63 ppm/°C) was measured for x = 0.7. 相似文献
12.
Uche G. NwokekeAlan V. Chadwick Ricardo AlcántaraMaria Alfredsson José L. Tirado 《Journal of Alloys and Compounds》2011,509(6):3074-3079
In an effort to improve the electrochemical performance of tin intermetallic phases as electrode active material for lithium-ion batteries, Fe1−xCoxSn2 solid solutions with x = 0.0, 0.25, 0.3, 0.5, 0.6 and 0.8 were prepared by chemical reduction in tetraethylene glycol. Precise control of the synthesis conditions allowed single-phase nanocrystalline materials to be prepared, with particle diameters of about 20 nm and cubic, nanorods, and U-shaped morphologies. The substitution of iron by cobalt induced a contraction of the unit cell volume. The hyperfine parameters of the 57Fe Mössbauer spectra were sensitive to the Co/Fe substitution and revealed a superparamagnetic behaviour. In lithium cells nanocrystalline Fe1−xCoxSn2 active materials delivered reversible capacities above 500 mAh g−1 that depended on the composition and cycling conditions. The intermediate compositions exhibit better electrochemical performance than the end compositions CoSn2 and FeSn2. 相似文献
13.
Polycrystalline samples of Ho doped BiFeO3 were prepared by solid state reaction method and effect of partial substitution of Ho on dielectric, magnetic and ferroelectric properties was studied. High temperature dielectric results show two dielectric anomalies both in ? and tan δ, out of which, anomaly at higher temperature (∼400 °C) could be ascribed to antiferromagnetic Néel temperature which, is a signature of magnetoelectric coupling. The magnetic moment is greatly improved and the maximum magnetization was found to be 0.736 emu/g. Saturated ferroelectric hysteresis loops were observed for Bi0.95Ho0.05FeO3 with remnant polarization (Pr) = 1.59 μC/cm2, maximum polarization (Pmax) = 2.56 μC/cm2 and coercivity (Ec) = 5.45 kV/cm. We have conducted comprehensive magnetoelectric and magnetodielectric properties at room temperature. Magnetic field induced ferroelectric hysteresis loop observed in Bi0.95Ho0.05FeO3 is of prime importance. 相似文献
14.
Lead-free piezoelectric ceramics Sr2−xCaxNaNb5O15 + y wt% MnO2have been prepared by the conventional solid state reaction method. Our results reveal that Ca2+and Mn ions have entered into the Sr2NaNb5O15 lattices to form a solid solution with tungsten-bronze structure. The substitution of Ca2+ induces a decrease in piezoelectric coefficient d33, electromechanical coupling factors kp and kt, while, the addition of Mn ions decreases the sintering temperature and effectively promotes the densification of the ceramics. The effect of substitution of Ca2+and Mn ions on the structure, electrical properties and diffused phase changing were investigated systematically. For the ceramic with x = 0.05 and y = 0.5, the piezoelectric, dielectric and ferroelectric properties become optimum, giving a piezoelectric coefficient d33 = 190 pC/N, electromechanical coupling factors kp = 13.4% and kt = 36.5%, ?r = 2123, loss tangent tan δ = 0.038, remanent polarization Pr = 4.76 μC/cm2, coercive field Ec = 12.68 kV/cm, and Curie temperature Tc = 260 °C. 相似文献
15.
(Ba0.68−xSr0.308Bi0.006Na0.006Mgx)(Ti0.99Sn0.01)O3 ceramics were synthesized by solid-state reaction process. The samples (X ≤ 0.010) are a mixture of cubic (major) and rhombohedral (minor) phases. The rhombohedral phase causes a large dielectric loss in low temperature regions and plays an important role in diffuse phase transition of ceramics. While X > 0.010, the rhombohedral phase decreases and gradually disappears. The dielectric loss of ceramics in the low temperature regions decreases, and the samples change from the diffuse phase transition to the phase transition of second order, and then to of first order. In the temperature range of 270-370 °C, intrinsic conduction dominates conductivity of ceramics. 相似文献
16.
M.R. BhandareH.V. Jamadar A.T. PathanB.K. Chougule A.M. Shaikh 《Journal of Alloys and Compounds》2011,509(6):L113
Dielectric properties of Cu substituted Ni-Zn-Mg ferrite samples having the general formula Ni0.5−xCuxZn0.3Mg0.2Fe2O4 (where x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) synthesized by Pramanik method are reported. The single phase formation of the ferrites was confirmed by XRD technique. The lattice parameter is found to increase with increase in Cu content. Average grain size, obtained from SEM micrographs, is found to increase with increase in Cu content. Dielectric parameters were measured as a function of frequency at room temperature as well as at higher temperatures. The variation in dielectric constant (?′) with temperature at four different fixed frequencies viz. 1 kHz, 10 kHz, 100 kHz, and 1 MHz was also studied. The room temperature dielectric constant (?′) and dielectric loss (tan δ) are found to decrease with increase in frequency. The ac conductivity (σac) is found to increase with increase in the frequency. 相似文献
17.
Ming He Shuren ZhangXiaohua Zhou Bo LiJing Wan 《Journal of Alloys and Compounds》2011,509(11):4260-4263
The behavior of dielectric and microwave properties against sintering temperature has been carried out on CaO-SiO2-B2O3 ceramic matrix composites with ZrO2 addition. The results indicated that ZrO2 addition was advantageous to improve the dielectric and microwave properties. X-ray diffraction (XRD) patterns show that the major crystalline β-CaSiO3 and a little SiO2 phase existed at the temperature ranging from 950 °C to 1050 °C. At 0.5 wt% ZrO2, CaO-SiO2-B2O3 ceramic matrix composites sintered at 1000 °C possess good dielectric properties: ?r = 5.85, tan δ = 1.59 × 10−4 (1 MHz) and excellent microwave properties: ?r = 5.52, Q · f = 28,487 GHz (11.11 GHz). The permittivity of Zr-doped CaO-SiO2-B2O3 ceramic matrix composites exhibited very little temperature dependence, which was less than ±2% over the temperature range of −50 to 150 °C. Moreover, the ZrO2-doped CaO-SiO2-B2O3 ceramic matrix composites have low permittivity below 5.5 over a wide frequency range from 20 Hz to 1 MHz. 相似文献
18.
The anisotropy compensation and magnetostrictive properties of Tb1−xHox(Fe0.8Co0.2)2 (0.60 ≤ x ≤ 1.0) alloys have been investigated. The easy magnetization direction (EMD) at room temperature rotates from the 〈1 1 1〉 axis (x ≤ 0.75) to the 〈1 0 0〉 axis (x ≥ 0.90) through an intermediate state 〈1 1 0〉, subjected to the anisotropy compensation between Tb3+ and Ho3+ ions. Composition anisotropy compensation is realized near x = 0.75. The Tb0.25Ho0.75(Fe0.8Co0.2)2 alloy has a minimum anisotropy and a large spontaneous magnetostriction coefficient λ111 (≈740 ppm) at room temperature. The strong 〈1 1 1〉-oriented 1-3 epoxy-bonded composite has been fabricated by curing under a moderate magnetic field. A high low-field magnetostriction of about 400 ppm at 3 kOe is obtained for the 1-3 epoxy/Tb0.25Ho0.75(Fe0.8Co0.2)2 composite with 40-vol% alloy particles, which can be attributed to the low magnetic anisotropy, EMD lying along 〈1 1 1〉 direction, the strong 〈1 1 1〉-textured orientation and the chain structure. 相似文献
19.
Ba(Zn1/3Ta2/3)O3 (BZT) dielectric resonators were prepared by solid-state reaction. The starting materials were BaCO3, ZnO, and Ta2O5 powders with high purity. The double calcined BZT pellets were sintered in air at temperatures of 1575, 1600, 1625, and 1650 °C for 4 h. The X-ray diffraction data allowed the study of the unit cell distortion degree and the presence of the secondary phases. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was observed with the increase of the sintering temperature. The dielectric constant of BZT resonators measured around 6 GHz was between 26 and 28. High values of Q × f product (120 THz) were obtained for BZT resonators sintered at 1650 °C/4 h. The temperature coefficient of the resonance frequency exhibits positive values less than 6 ppm/°C. The achieved dielectric parameters recommend BZT dielectric resonators for microwave and millimeter wave applications. 相似文献
20.
Cheng-Liang Huang Yu-Hua ChienChen-Yi Tai Chi-Yuen Huang 《Journal of Alloys and Compounds》2011,509(9):L150
The microwave dielectric properties and the microstructures of (Mg1−xZnx)Al2O4 (x = 0-0.1) ceramic system prepared by the conventional solid-state route were investigated. The forming of spinel-structured (Mg1−xZnx)Al2O4 (x = 0-0.1) solid solutions was confirmed by the XRD patterns and the measured lattice parameters, which linearly varied from a = b = c = 8.0815 Å for MgAl2O4 to a = b = c= 8.0828 Å for (Mg0.9Zn0.1)Al2O4. By increasing x, the Q × f of (Mg1−xZnx)Al2O4 can be tremendously boosted from 82,000 GHz at x = 0 to a maximum of 156,000 GHz at x = 0.05. The Zn substitution was effective in reducing the dielectric loss without detrimental effects on the ?r and τf values of the ceramics. 相似文献