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1.
M IIM IV(PO 4) 2 (M II = Ca, Sr, Ba, Pb; M IV = Ti, Zr, Hf, Ge, Sn) ceramics were prepared by solid state reaction method and consolidated by spark plasma sintering in order to study their electrical properties. The dielectric study performed at room temperature was aimed to determine the basic electrical properties of these compounds. Maxwell-Wagner polarization contributions, which are active at low frequencies cause a strong extrinsic increase of both real and imaginary part of permittivity as well of the dc-conductivity for BaZr(PO 4) 2, BaTi(PO 4) 2, BaHf(PO 4) 2, and SrGe(PO 4) 2 double orthophosphates. Moderate real ( ε′r=20-150) and imaginary low-frequency permittivity ( ε′r=7-300) and typical Debye relaxation with relaxation time in the range of ms is typical for: PbHf(PO 4) 2, PbZn(PO 4) 2, and CaGe(PO 4) 2. At high-frequency ( f = 10 9 Hz), the ceramics have permittivities of 2.29÷8.02 and tangent loss of 0.003÷0.153. The compounds SrGe(PO 4) 2, BaGe(PO 4) 2, BaZr(PO 4) 2 and BaSn(PO 4) 2 have excellent high-frequency dielectric characteristics, with losses of 3÷6% and permittivity slightly above 2 and are possible candidate as microwave ceramics. 相似文献
2.
Bulk polycrystalline Sn 0.95Fe 0.05O 2−σ and Sn 0.93Fe 0.05M 0.02O 2−σ (M = Sb/Mg) samples were fabricated. Detailed X-ray diffraction and transmission electron microscopy analyses revealed that the dopants most probably replaced the Sn in SnO 2 structure, instead of forming impurity phase or nanocluster. By varying the dopant M (Sb/Mg), the electron- (Sb) and hole- (Mg) doping effect on the magnetic properties of Sn 0.93Fe 0.05M 0.02O 2−σ was investigated. Compared with Sn 0.95Fe 0.05O 2−σ, the saturation magnetization decreased after doping with Sb and increased after doping with Mg. The changes of Fe oxidation state and carrier type, discovered from X-ray photoelectron spectroscopy, are believed to be responsible for the co-doping tuned ferromagnetism in Sn 0.93Fe 0.05M 0.02O 2−σ. 相似文献
3.
The crystallization process of bismuth substituted yttrium iron garnet (Bi xY 3−xFe 5O 12; x = 0, 1, 2) powder prepared by the metal-organic decomposition method has been studied with various sintering temperatures. The pure garnet phase was observed for the x = 1 powder at 900 °C sintering temperature, whereas the x = 0, 2 powder showed secondary phases. The x = 0 powder showed a similar crystallization process to that of the solid state reaction method. For the x =1, 2 powders, it is proposed that the lowering of the crystallization temperature is due to the lowered stability of the intermediate phase. The infrared spectroscopy and magnetic properties were also investigated. The pure garnet phase showed three absorption bands located at 563, 598, 655 cm −1 that shifted to 555, 588, 639 cm −1 along with an increase of bismuth concentration. The maximum values of saturation and remanence magnetization and the minimum value of coercivity were observed for the x = 1 powder sintered at 900 °C, which were 20.8 emu/g, 2.67 emu/g, and 31.9 Oe, respectively. 相似文献
4.
The experimental study of the optical properties of CeNi 5, CeNi 4Cu and CeNi 4Al compounds was carried out in the 0.083-5.64 eV energy range using the ellipsometry method. The optical constants, dielectric functions and electronic parameters (plasma and relaxation frequencies) were determined. The energy dependencies of the optical interband conductivities are discussed by using the available information on the electronic band structure of these compounds. In the ternary alloys the optical spectra show the presence of peculiarities related to effect of Cu or Al substitution at Ni sites. 相似文献
5.
In order to investigate the electrical transport in LaNi 3/4Mo 1/4O 3 and LaNi 3/4W 1/4O 3, the dc conductivity and dielectric properties in these polycrystalline materials are investigated in the temperature range from 163 K to 383 K and frequency range from 50 Hz to 1 MHz. The X-ray diffraction patterns of the samples show monoclinic phase at room temperature. The homogeneity of the samples is determined by energy dispersive analysis of X-ray (EDAX) attached with a scanning electron microscope. The temperature dependence of dc conductivity shows the semiconducting nature of the materials. The complex impedance plane plots show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The frequency-dependent electrical data are also analyzed in the framework of ac conductivity formalism. The ac conductivity spectra follow the universal power law. The activation energies required for bulk conduction is 0.143 and 0.165 eV for LNM and LNW respectively. The scaling behaviour of loss tangent suggests that the relaxation describes the same mechanism at various temperatures. 相似文献
6.
Cobalt ferrite CoFe 2O 4 films were fabricated on SiO 2/Si(1 0 0) by the sol-gel method. Films crystallized at/above 600 °C are stoichiometric as expected. With increase of the annealing temperature from 600 °C to 750 °C, the columnar grain size of CoFe 2O 4 film increases from 13 nm to 50 nm, resulting in surface roughness increasing from 0.46 nm to 2.55 nm. Magnetic hysteresis loops in both in-plane and out-of-plane directions, at different annealing temperatures, indicate that the films annealed at 750 °C exhibit obvious perpendicular magnetic anisotropy. Simultaneously, with the annealing temperature increasing from 600 °C to 750 °C, the out of plane coercivity increases from 1 kOe to 2.4 kOe and the corresponding saturation magnetization increases from 200 emu/cm 3 to 283 emu/cm 3. In addition, all crystallized films exhibit cluster-like structured magnetic domains. 相似文献
7.
In this work, we report the fabrication of core-shell Fe 3O 4@SiO 2@MS (M = Pb, Zn, and Hg) microspheres through a wet-chemical approach. The Fe 3O 4@SiO 2@MS microspheres have both ferromagnetic and photocatalytic properties. The sulfide nanoparticles on the surfaces of microspheres can degrade organic dyes under the illumination of UV light. Furthermore, the microspheres are easily separated from the solution after the photocatalytic process due to the ferromagnetic Fe 3O 4 core. The photocatalysts can be recycled for further use with slightly lower photocatalytic efficiency. 相似文献
8.
Here we demonstrated a simple and reliable method to prepare single or multiple core/shell structured capsules and then demonstrate how to produce single or multiple-layer hollow spheres. Those capsules or hollow spheres could be made of organic and/or inorganic functional materials depending on the experimental design. Core–shell composite capsules consisting of TiO 2–polyaniline (PANI) shell and polystyrene (PS) core were prepared by using core–shell structured sulfonated-PS spheres as templates. Aniline was polymerized in the shell of sulfonated-PS spheres. Since the PANI was in situ doped by sulfonic acid, the as-synthesized composite capsules had good conductivity. After PS cores were dissolved in solvent, hollow TiO 2–PANI spheres formed, which could be further calcined to produce mesoporous hollow TiO 2 spheres. The cavity size of the hollow spheres was uniform, at approximately 170 nm in diameter and with a shell thickness of 30 nm. The cavity size and the shell thickness can be synchronously controlled by adjusting the sulfonation reaction time of PS spheres. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray powder scattering were employed to characterize these as-prepared spheres. 相似文献
9.
The hydrophilic phenol formaldehyde resin coated Fe 3O 4 nanocrystals are prepared via a novel one-step solvothermal approach at 160 °C for 6-9 h without inert gas protection. Water-glycol mixture is used as solvent in common air surrounding. FeSO 4·7H 2O, hexamethylenetetramine and phenol are used as resource materials without any others additives or surfactants. The transmission electronic microscope images show the samples are composed of sphere-like particles with sizes about 10-20 nm. The X-ray diffraction data indicate cube-phase Fe 3O 4 nanocrystals are obtained at given conditions. Fourier transform infrared spectra further reveal the samples are consisted of Fe 3O 4 and PFR. Without modified pH and added surfactants, the solubility of the obtained sample is over 1% in water, which is far more than its solubility in toluene. Room-temperature hysteresis loop indicate that the as-obtained nano-crystals possess soft magnetic properties with high saturated mass magnetization (50.6 emu/g) and negligible coercivity. 相似文献
10.
The effect of substitution of Co and Fe for Ni in TbNi 5 on the structural, magnetic and magneto-thermal properties has been investigated. Considerable enhancement of Curie temperature is observed with Fe substitution, whereas the increase is nominal in the case of Co. Neutron diffraction measurements reveal the redistribution of moments and site preference of substitutional ions in Ni 2 c and 3 g sites. In TbNi 4Fe, both Ni and Fe as well as Tb are found to carry moment while in the case of TbNi 4Co, mainly Tb carries the moment. Magnetocaloric behavior has been investigated from the magnetization and the heat capacity measurements. The magnetic and magnetocaloric properties are found to be strongly correlated in these compounds. 相似文献
11.
Titanium dioxide (TiO 2) of the anatase phase has recently attracted much attention as a novel transparent conducting oxide (TCO) due to its rich availability, high refractive index with low absorption in the solar spectrum. While it has been found that Nb is a dopant to obtain low resistivity (~ 10 − 4 Ωcm), other metals such as Ta, W etc., are also considered as potential effective dopants. In this paper, we carried out a parallel study on Nb- and Ta-doped TiO 2 anatase films both theoretically by first principles calculation and experimentally by sputtering deposition and optical/electrical characterizations. The Nb-TiO 2 films deposited on glass by co-sputtering at room temperature were amorphous, and the films crystallized into an anatase structure after vacuum-annealing, with the measured resistivity values comparative to the reported. The Ta-TiO 2 films were deposited similarly, and the structure and properties were compared with the Nb-doped ones. Results showed that better performance was found in Nb-TiO 2 films than that in Ta-TiO 2 films. Theoretical calculations indicate that the larger lattice distortion by substitution of Ta for Ti is the dominating factor to suppress crystal growth and weaken the ability of electron mobility. 相似文献
12.
La 1.90Eu 0.10TeO 6:RE 3+ (RE = Gd, Sm) and Y 2TeO 6:Eu 3+nanophosphors were prepared by the Pechini sol-gel process, using lanthanide sesquioxides and telluric acid as precursors. X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectra (PL) and fluorescence lifetime were used to characterize the resulting phosphors. The results of XRD indicate that all samples crystallized completely at 1073 K and are isostructural with orthorhombic Ln 2TeO 6. The SEM study reveals that the samples have a strong tendency to form agglomerates with an average size ranging from 40 to 65 nm. The luminescence decay curves suggest for all samples a monoexponential behavior. The photoluminescence intensity and chromaticity were improved for excitation at 395 nm when the co-doping concentration reaches the 1% mol. The optimized phosphorsLa 1.88Eu 0.10Gd 0.02TeO 6and La 1.88Eu 0.10Sm 0.02TeO 6, could be considered an efficient red-emitting phosphor for solid-state lighting devices based on InGaN LEDs. 相似文献
13.
A spinel CuIr 2S 4 exhibits a temperature-induced metal-insulator (M-I) transition at around 226 K. Non-magnetic substitution effect on the M-I transition, TM-I, in Cu(Ir 1−xM x) 2S 4 (M = Sn, Hf) has been studied on the focus of the rather low composition region of x. Magnetic property of Cu(Ir 1−xM x) 2S 4 (M = Sn, Hf) has been examined experimentally. The TM-I decreases with increasing x and the temperature hysteresis becomes unclear within the experimental errors. The step anomaly in the magnetic susceptibility smears out and the TM-I becomes ill defined around x = 0.20 in Cu(Ir 1−xSn x) 2S 4, and x = 0.10 in Cu(Ir 1−xHf x) 2S 4, respectively. These substitutions play an important role in decoupling the spin-dimerization of Ir 4+-Ir 4+ in CuIr 2S 4, and lead the destruction of the metal-insulator transition. 相似文献
14.
A series of Ce 3+ doped novel borate phosphors MSr 4(BO 3) 3 (M = Li or Na) were successfully synthesized by traditional solid-state reaction. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. The optimal concentrations of dopant Ce 3+ ions in compound MSr 4(BO 3) 3 (M = Li or Na) were determined through the measurements of photoluminescence spectra of phosphors. Ce 3+ doped phosphors MSr 4(BO 3) 3 (M = Li or Na) show strong broad band absorption in UV spectral region and bright blue emission under the excitation of 345 nm light. In addition, the temperature dependences of emission spectra of M 1+xSr 4−2xCe x(BO 3) 3 (M = Li or Na) phosphors with optimal composition x = 0.05 for Li and x = 0.09 for Na excited under 355 nm pulse laser were also investigated. The experimental results indicate that the M 1+xSr 4−2xCe x(BO 3) 3 (M = Li or Na) phosphors are promising blue emitting phosphors pumped by UV light. 相似文献
15.
A series of core-shell bifunctional magnetic-optical YVO 4:Ln 3+@Fe 3O 4 (Ln 3+ = Eu 3+ or Dy 3+) nanocomposites have been successfully synthesized via two-step method. The nanocomposites have the advantage of high magnetic responsive and unique luminescence properties. The structure, luminescent and magnetic properties of the nanocomposites were investigated by XRD, TEM, PL and VSM. The maximum emission peaks of the nanocomposites are at 618 nm (doping Eu 3+), 574 nm (doping Dy 3+). The special saturation magnetization of the nanocomposites is 54 emu/g. The diameter of the nanocomposites is 400-900 nm. 相似文献
16.
Samples of pure and rare earth (RE)-doped nanocrystalline Zn 2TiO 4 (RE = Eu, Er, Tm) have successfully been prepared by the single batch sol-gel method in a form of powders. The powders were annealed up to 1200 °C and analyzed by DTA and XRD methods. Sizes of formed nanocrystals were calculated from the Scherer equation and verified by the SEM analysis. Activation energies of crystallization were calculated using the Kissinger, Ozawa and Augis-Bennett approximations and reaction mechanisms were proposed evaluating the Avrami exponents from the Johnson-Mehl-Avrami equation. It has been found that RE elements particularly substitute zinc ions in the crystal lattice and are fully soluble up to 0.5 at.% related to the some of cations. Furthermore, the results have shown that the presence of RE elements blocks the crystallite growth and supports the nucleation process leading to the formation of smaller and more uniform nanocrystals compared to the undoped Zn 2TiO 4. 相似文献
17.
Nanopowders of MgFe 2O 4 have been synthesized by the novel and facile reverse microemulsion route. The effects of changing the continuous phase on the particle size and the magnetic property have been studied. The average particle size, morphology and saturation magnetization are shown to be dependent on the continuous phase. The average diameters of the particle prepared with heptane are 20.9 ± 4.3 nm. On the contrary, the product with toluene and cyclohexane is highly aggregated. The values of saturation magnetization for our samples prepared with heptane, toluene and cyclohexane are 14.5, 30 and 37 emu/g. 相似文献
18.
New bis(ethylenedithio)tetraselenafulvalene (BETS) based radical cation salts with tetrahedral dianions [CdBr 4] 2− and [HgBr 4] 2− of the (BETS) 4MBr 4(PhBr) composition were prepared by electrochemical crystallization. Room-temperature crystal structure of (BETS) 4CdBr 4(PhBr) determined by single crystal X-ray diffraction involves BETS radical cation layers of the θ-type packing and insulating layers consisting of [CdBr 4] 2− anions and PhBr molecules. In the neighboring conducting layers, the stacks are arranged perpendicular to each other. A metal-to-metal transition within 225–230 K range was found in both (BETS) 4CdBr 4(PhBr) and (BETS) 4HgBr 4(PhBr). The behavior of electrical resistivity of these salts differs substantially along and across conducting layers. The study of magnetoresistance of (BETS) 4HgBr 4(PhBr) revealed weak Shubnikov-de Haas oscillations in fields higher than 6 T. 相似文献
19.
In the present work, the spectroscopic and magnetic properties of heteronuclear Cu:Pr squarate are reported. Single crystals of [Pr 2Cu(C 4O 4) 4(H 2O) 16]·2H 2O were obtained by reaction of squaric acid, praseodymium chloride and copper chloride in water solution according to the procedure described earlier. The crystals of title compound are isomorphic with [La 2Cu(C 4O 4) 4(H 2O) 16]·2H 2O crystal, where squarate anions participate as bridging ligands between metal ions. The UV region of absorption spectra of the title compound is dominated by C–T band of Cu(II), f–d transition of Pr(III) and internal π–π*(A1g→Eu) and π–π*(A1g→Eg) ligand transitions. In visible and IR regions, t2g–eg of copper Cu(II) as well as 3H4→3PJ, 1D2, 1G4, 3FJ, 3H6 Pr(III) transitions at 293 and 4 K were recorded. At low temperature splitting given by Jahn–Teller effect can be observed. Significant anisotropy of d–d transitions intensities confirms well the Jahn–Teller effect, too. Unexpectedly high intensity of 3H4→1G4 transition is probably due to the intensity borrowing from the Cu (II) d–d transition. The 3P0 and 1D2 emission of Pr(III) in the [Pr2Cu(C4O4)4(H2O)16]·2H2O crystals is quenched even at 77 K. Whereas emission of appropriate polynuclear europium squarate was detected. The pathways of excited state quenching by eg levels of Cu(II), multhiphonon relaxation and concentration quenching can be considered in the system under studies. Magnetic susceptibility measurements were carried out in 300–1.7 K temperature range and are discussed in relation to the structure. Effect of the polymeric structure on spectroscopic behaviour is presented. Selectivity of polymeric europium squarate in vitro test for different tumor cells is shown. 相似文献
20.
The magnetic and magnetocaloric properties of GdTX (T = Mn, Fe, Ni, Pd, X = Al, In) and GdFe 6Al 6 ternary compounds for possible applications in magnetic refrigeration have been investigated. Magnetization measurements have been performed in the temperature range of 2-400 K and magnetic field range of 0-7 T. The magnetic entropy changes Δ Sm have been calculated indirectly from the magnetization measurements. The calculated values of entropy change Δ Sm for examined compounds amount −13.63 J/K kg, −13.05 J/K kg, −6.13 J/K kg, −3.72 J/K kg, −1.38 J/K kg and −0.94 J/K kg, respectively, for GdNiAl, GdPdAl, GdPdIn, GdFeAl, GdFe 6Al 6 and GdMnAl at 7 T. 相似文献
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