共查询到20条相似文献,搜索用时 15 毫秒
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Jianhui ShiDeming Liu Lizhu TongXuwei Yang Hua Yang 《Journal of Alloys and Compounds》2011,509(42):10211-10216
In this paper, we report on the bifunctional Fe3O4@SiO2@YP0.1V0.9O4:Dy3+ nanocomposites were prepared by the solvothermal method and sol-gel method. The structure, photoluminescence (PL) and magnetic properties of the nanocomposites were characterized by means of X-ray diffraction, scanning electron microscope, transmission electron microscope, PL excitation and emission spectra and vibration sample magnetometry. It is shown that Fe3O4@SiO2@YP0.1V0.9O4:Dy3+ nanocomposites with a core-shell structure present excellent fluorescent and magnetic properties. Additionally, the effects of the magnetic field on the luminescence properties of nanocomposites were discussed. 相似文献
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Kouta Iwasaki Tsuyoshi Ito Masahito Yoshino Tsuneo Matsui Takanori Nagasaki Yuji Arita 《Journal of Alloys and Compounds》2007,430(1-2):297-301
The electrical conductivity (σ), Seebeck coefficient (S), and power factor (σS2) of perovskite-type LaFeO3, La1−xSrxFeO3 [0.1 ≤ x ≤ 0.4] and LaFe1−yNiyO3 [0.1 ≤ y ≤ 0.6] were investigated in the temperature range of 300–1100 K to explore their possibility as thermoelectric materials. The electrical conductivity of LaFeO3 showed semiconducting behavior, and its Seebeck coefficient changed from positive to negative around 650 K with increasing temperature. The electrical conductivity of LaFeO3 increased with the substitutions of Sr and Ni atoms, while its Seebeck coefficient decreased. The Seebeck coefficient of La1−xSrxFeO3 was positive, whereas that of LaFe1−yNiyO3 changed from positive to negative with increasing Ni content. The substitutions of Sr and Ni were effective in increasing the power factor of LaFeO3; 0.0053 × 10−4 Wm−1 K−2 for LaFeO3 (1050 K), 1.1 × 10−4 Wm−1 K−2 for La1−xSrxFeO3 (x = 0.1 at 1100 K) and 0.63 × 10−4 Wm−1 K−2 for LaFe1−yNiyO3 (y = 0.1 at 1100 K). 相似文献
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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
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Ag-doped Ca3Co4O9 thin films with nominal composition of Ca3−xAgxCo4O9 (x = 0∼0.4) have been prepared on sapphire (0 0 0 1) substrates by pulsed laser deposition (PLD). Structural characterizations and surface chemical states analysis have shown that Ag substitution for Ca in the thin films can be achieved with doping amount of x ≤ 0.15; while x > 0.15, excessive Ag was found as isolated and metallic species, resulting in composite structure. Based on the perfect c-axis orientation of the thin films, Ag-doping has been found to facilitate a remarkable decrease in the in-plane electrical resistivity. However, if doped beyond the substitution limit, excessive Ag was observed to severely reduce the Seebeck coefficient. Through carrier concentration adjustment by Ag-substitution, power factor of the Ag-Ca3Co4O9 thin films could reach 0.73 mW m−1 K−2 at around 700 K, which was about 16% higher than that of the pure Ca3Co4O9 thin film. 相似文献
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Ganghua ZhangGuobao Li Fuqiang HuangFuhui Liao Kuo LiYinxia Wang Jianhua Lin 《Journal of Alloys and Compounds》2011,509(41):9804-9808
Superconductors Ba1−xKxBiO3 and body-centered double perovskites Ba1−xKxBi1−yNayO3 have been selectively synthesized by a facile hydrothermal route. The appropriate ratio and adding sequence of initial reagents, alkalinity, reaction temperature and time are the critical factors that influence the crystal growth of the compounds. The purity and homogeneity of the crystals were detected by the ICP, SEM, EDX and TEM studies. Magnetic measurements show that the superconducting transition temperatures TC of Ba1−xKxBiO3 decrease from 22 K (for x = 0.35) to 8 K (for x = 0.55) with increasing the K doping level. 相似文献
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The microstructure and electrical properties of BaYxBi1−xO3 thick film negative temperature coefficient thermistors, fabricated by screen printing, were investigated. The sintered thick films were the single-phase solid solutions of the BaYxBi1−xO3 compounds with a monoclinic structure. The added Y2O3 led to a significant decrease in the grain size of the thermistors. The resistivity and coefficient of temperature sensitivity for the BaYxBi1−xO3 (0 ≤ x ≤ 0.15) thick film NTC thermistors decreased first with increasing x in the range of x < 0.04 and then increased with further increase in x. 相似文献
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Sr2FexMo2−xO6 (x = 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5 wt.%) (SFMO) double perovskite oxides of different compositions have been prepared by sol-gel method. These materials were subjected to X-ray diffraction and found that crystal structure changes from tetragonal to cubic around x = 1.2 wt.%. Lattice parameters and unit cell volume have been calculated using X-ray diffraction data. Magnetization studies have been carried out using Vibrating Sample Magnetometer ranging from −15 kOe to +15 kOe and saturation magnetization (Ms) has been determined. Electrical resistivity and magnetoresistance studies have been carried out in the magnetic field range of −40 kOe to +40 kOe keeping the temperature constant at 5, 150 and 300 K using standard four-probe method. Resistivity studies have also been carried out in the temperature ranging from 5 to 300 K keeping the magnetic field constant at 0, 10, 20 and 40 kOe. Maximum degree of Fe/Mo ordering (ηmax) of SFMO has been calculated and compared with magnetic and transport properties. It has been found that there is a strong correlation between 3 parameters ηmax, Ms and MR (%), i.e. all of them show a maximum at x = 1.0 wt.% and decreases as x deviates from 1.0 in SFMO. It has been also found that there is a different resistivity behavior between x ≤ 1.2 wt.% and x > 1.2 wt.% samples of SFMO. Semiconductor metal transition temperature was found to be maximum at x = 1.0 wt.%. 相似文献
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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
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I. MatosS. Sério M.E. LopesM.R. Nunes M.E. Melo Jorge 《Journal of Alloys and Compounds》2011,509(40):9617-9626
Nanocrystalline Ca1−xSmxMnO3 (0 ≤ x ≤ 0.4) manganites were prepared by a soft chemical method (Pechini method) followed by auto-combustion and sintering in air at 1073 or 1473 K. Single-phase powders with general composition Ca1−xSmxMnO3 were obtained after 18 h annealing. The particle and grain sizes of the substituted Sm-manganites did not exhibit variation with samarium content, but increase with increasing the sintering temperature. All manganites show two active IR vibrational modes near 400 and 600 cm−1 characteristic of the BO6 octahedron vibrations.For the samples sintered at Ts = 1473 K, the partial substitution of calcium by samarium in the CaMnO3 phase induces a marked decrease in the electrical resistivity, in the temperature range of 300-900 K, and at the same time a metal-to-insulator transition occurs; for Ts = 1073 K all the samples present semiconductor behaviour. With the increase of the annealing temperature the grain size increases and a metal-semiconductor transition appears. The results can be ascribed to the Mn4+/Mn3+ ratio and particle grain size. The effects of particle size on the electrical properties can be attributed to the domain status, changes in the Mn-O-Mn bond angle and Mn-O bond length. 相似文献
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M.K. Dalai R. KunduP. Pal M. BhanjaB.R. Sekhar C. Martin 《Journal of Alloys and Compounds》2011,509(29):7674-7676
We have studied the Mn 2p, Ca 2p, and Pr 4d core levels of Pr1-xCaxMnO3 (x = 0.2, 0.33, 0.4 and 0.84) as a function of x using X-ray photoelectron spectroscopy both at room temperature as well as 77 K. Suppression of chemical potential shifts have been observed at 77 K compared to that of room temperature spectra. We have discussed this result by considering the concept of phase separation. 相似文献
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The low temperature thermoelectric properties of Zn4Sb3 samples prepared by the gradient freeze (GF) method and sintering have been characterized. With decreasing temperature a dramatic rise in the thermal expansion is observed associated with the structural transition from β- to α-phase; Δl/l=2.8×10−4 at TsGF=257.4 K for GF and Δl/l=1.6×10−4 at TsS=236.5 K for sintered samples. Enhancement is observed in electrical conductivity and p-type thermopower at TsGF and TsS, while a reduction is observed in the magnetic susceptibility. The GF sample exhibits higher thermoelectric performance than the sintered sample. The power factor of the α-phase in the GF sample is twice as large as that of the β-phase; it exceeds 20 μW/cm·K2 between 120 and 240 K, indicating that the α-phase Zn4Sb3 is one of the prime candidates for thermoelectric materials for cryogenic use. 相似文献
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N. LiW.L. Li L.D. WangS.Q. Zhang J.W. YeW.D. Fei 《Journal of Alloys and Compounds》2011,509(31):8028-8031
Lead-free K0.4Na0.6Nb1−xVxO3 thin films were prepared by chemical solution deposition method. The effects of V doping on the phase composition and electrical properties of the films were studied at room temperature. The results indicate that the films are composed of orthorhombic and tetragonal phases, and the phase composition is affected by V content. It is also found that the ferroelectric and dielectric properties are improved by V doping (2Prmax = 35.5 μC/cm, ?max = 1189). The enhanced electrical properties are attributed to the more T-phase content and better quality of K0.4Na0.6Nb1−xVxO3 (x = 0.015) film. 相似文献
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Ziqi WangYu Yang Yuanjing CuiZhiyu Wang Guodong Qian 《Journal of Alloys and Compounds》2012,510(1):L5
Ce3+, Eu3+ and Tb3+ complexes were synthesized through facile and mild approaches with terephthalic acid (H2BDC) as the ligand. Their chemical compositions were determined as (CexEuyTb1−x−y)2(BDC)3(H2O)4 by elemental analysis (EA), Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) measurements. Fluorescent properties of the as-synthesized complexes were investigated by changing the molar ratio of Ce3+, Tb3+ and Eu3+ ions, and the optimized ratio of 3.0:2.0:0.15 for Ce3+:Tb3+:Eu3+ in the complex was determined for white-light emission. Tuning on the emitting color was realized by adjusting the ratio among lanthanide ions, indicating the energy transfer process inside the complex. It was found that Tb3+ could sensitize the fluorescence of Eu3+ while its own fluorescence was quenched by the latter ion, and concentration quenching of Ce3+ was also observed. Fairly good thermal stability and oxidation resistance of the as-synthesized complexes were also demonstrated. 相似文献
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Low dielectric ceramics in the Al2W3−xMoxO12 (x = 0-3) system have been prepared through solid state ceramic route. The phase purity of the ceramic compositions has been studied using powder X-ray diffraction (XRD) studies. The microstructure of the sintered ceramics was evaluated by Scanning Electron Microscopy (SEM). The crystal structure of the ceramic compositions as a result of Mo substitution has been studied using Laser Raman spectroscopy. The microwave dielectric properties of the ceramics were studied by Hakki and Coleman post resonator and cavity perturbation techniques. Al2MoxW3−xO12 (x = 0-3) ceramics exhibited low dielectric constant and relatively high unloaded quality factor. The temperature coefficient of resonant frequency of the compositions is found to be in the range −41 to −72 ppm/°C. 相似文献
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The formation of impurity LixNi1−xO when synthesizing spinel LiNi0.5Mn1.5O4 using solid state reaction method, and its influence on the electrochemical properties of product LiNi0.5Mn1.5O4 were studied. The secondary phase LixNi1−xO emerges at high temperature due to oxygen deficiency for LiNi0.5Mn1.5O4 and partial reduction of Mn4+ to Mn3+ in LiNi0.5Mn1.5O4. Annealing process can diminish oxygen deficiency and inhibit impurity LixNi1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi0.5Mn1.5O4 that contains LixNi1−xO can deliver about 120 mAh g−1. 相似文献
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Yi-Jie Gu Yun-Bo ChenHong-Quan Liu Yan-Ming WangCui-Ling Wang Hui-Kang Wu 《Journal of Alloys and Compounds》2011,509(30):7915-7921
We report the synthesis of LiNi0.85−xCo0.15MnxO2 positive electrode materials from Ni0.85−xCo0.15Mnx(OH)2 and Li2CO3. XRD and XPS are used to study the effect of Mn-doping on the microstructures and oxidation states of the LiNi0.85−xCo0.15MnxO2 materials. The analysis shows that Mn-doping promotes the formation of a single phase. With increasing substitution of Mn ions for Ni ions, the lattice parameter a decreases, while the lattice parameters c and c/a increase. XPS revealed that the oxidation states of Ni, Co and Mn in LiNi0.85−xCo0.15MnxO2 compounds (where x = 0.1, 0.2 and 0.4) were +2/+3, +3 and +4. The substitution of Mn ions for Ni ions induces a decrease in the average oxidation state of Ni. Because the substitution of Mn for Ni ions is complex, the extent of the changes between the lattice parameter and LM-O differ. The occupation of Ni in Li sites is affected by the ordering of Mn4+ with Ni2+ and Mn4+ with Li+. 相似文献