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1.
Fe/Fe3C-functionalized carbon nanotubes (CNTs) have been prepared by the floating catalyst chemical vapor-deposition method. It
is demonstrated that the Fe and Fe3C nanostructures are both encapsulated in the CNTs or decorated on the surface of CNTs. The Fe/Fe3C content in the composites can easily be adjusted by changing the ferrocene concentration in the preparation. The electromagnetic
properties of the CNTs have been evaluated in the frequency range of 2–18 GHz, and the nanocomposites exhibit excellent microwave
absorbing performance. The CNT composites with higher Fe/Fe3C content show enhanced microwave reflection losses. The significant influence of the Fe/Fe3C nanostructures on the microwave absorption is realized by tuning the characteristic impedance of the nanocomposites. With
increasing thickness, the maximum reflection loss peak shifts to lower frequency. The microwave absorbing performance of the
composites is mainly caused by dielectric loss, resulting from the continuous CNT networks with excellent electrical conductivity. 相似文献
2.
R.N.P. Choudhary K. Perez P. Bhattacharya R.S. Katiyar 《Applied Physics A: Materials Science & Processing》2007,86(1):131-138
The polycrystalline (Bi1-xPbx)(Fe1-xZr0.6xTi0.4x)O3 (x=0.15, 0.25, 0.40, 0.50) (BPFZT) nanoceramic composites were synthesized using mechanical activation and solid-state reaction techniques. The formation of single-phase compounds with 100% solubility of BiFeO3 and Pb(Zr0.6Ti0.4)O3 was confirmed by an X-ray diffraction (XRD) technique. Detailed structural analysis of the fabricated BPFZT composites suggests the formation of tetragonal structure (i.e., distorted perovskite) for all composition. The dielectric constant and loss-tangent of the BPFZT composites decrease on increasing frequency and temperature. It has also been observed that the leakage current and loss-tangent are reduced by increasing the contents of PZT in the BPFZT composites, and hence they may be considered useful for some applications. The values of activation energies and the nature of variation of conductivity with temperature and frequencies suggest that the space charge and oxygen ion vacancies play a significant role in the conduction process. PACS 61.10.Nz; 77.22.Ch; 77.84.Lf; 81.20.Ev 相似文献
3.
The polycrystalline samples of (Bi1?x K x ) (Fe1?x Nb x ) O3 (BKFN) for x = 0.0, 0.1, 0.2 and 0.3 were synthesized by a solid-state reaction method. The X-ray diffraction patterns of BKFN exhibit that the addition of KNbO3 in BiFeO3 gradually changes its structure from rhombohedral to pseudocubic. The analysis of scanning electron micrograph clearly showed that the sintered samples have well-defined and uniformly distributed grains. Addition of KNbO3 to BiFeO3 enhances the dielectric, ferroelectric and ferromagnetic properties of BiFeO3. Detailed studies of impedance and related parameters of BKFN using the complex impedance spectroscopic technique exhibit the significant contributions of grain and grain boundaries in the resistive and transport properties of the materials. Some oxygen vacancies created in the ceramic samples during high-temperature processing play an important role in the conduction mechanism. The leakage current or tangent loss of BiFeO3 is greatly reduced on addition of KNbO3 to the parent compound BiFeO3. Preliminary studies of ferroelectric and magnetic characteristics of the samples reveal the existence of ferroelectric, and weak ferromagnetic ordered ceramics. 相似文献
4.
LiFePO4/graphene composites have been prepared by using tailoring graphene oxide (GO) nanosheets as precursors. The structure and electrochemical properties of the composites were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman microscopy, and a variety of electrochemical testing techniques. The decrease in graphene size reduces the contact resistance between activated materials, and enhances the lithium-ion transport in LiFePO4/graphene composites. With low weight fractions of small-size graphene sheets, the composites show better electrochemical performance than those with large size graphene sheets. 相似文献
5.
The density of liquid and undercooled BiFeO3 and high-temperature solid, liquid, and undercooled BaTiO3 was measured with an electrostatic levitation furnace. The density was obtained with an ultraviolet-based imaging technique that allowed excellent sample contrast throughout all phases of processing, including at elevated temperatures. Over the 1250- to 1490-K temperature range, the density of liquid BiFeO3 can be expressed as L(T)=6.70×103–1.31(T-Tm)(kgm-3) (±2 per cent) with Tm=1423 K, yielding a volume coefficient of thermal expansion L(T)=1.9×10-4 K-1. For BaTiO3, the density of the solid can be expressed as S(T)=5.04×103–0.21(T-Tm) (Tm=1893 K) over the 1220- to 1893-K range, yielding a volume coefficient of thermal expansion S(T)=4.2×10-5 K-1, whereas that of the liquid can be expressed as L(T)=4.04×103-0.34(T-Tm) over the 1300- to 2025-K range with L(T)=8.4×10-5 K-1. PACS 77.84.-s; 81.05.Je; 81.20.n 相似文献
6.
S. A. Sadykov D. K. Palchaev Zh. Kh. Murlieva M. Kh. Rabadanov N. M.-R. Alikhanov V. V. Samsonova S. N. Kallaev Z. M. Omarov R. M. Emirov A. Kh. D. Khashafa 《Physics of the Solid State》2016,58(5):959-966
This paper presents the results of an investigation of changes in the structure, magnetic, electrical, and thermal properties of a nanostructured bismuth ferrite powder prepared by the combustion of nitrateorganic precursors before and after heat treatment at temperatures of 500, 600, 700, and 800°C. It has been shown that there is a dependence of the magnetic properties on the dispersion of the particles. The specific features of the temperature and frequency dependences of the dielectric properties over wide ranges of frequencies and temperatures, as well as near the Néel temperature, have been considered. 相似文献
7.
I. O. Troyanchuk M. V. Bushinsky A. N. Chobot O. S. Mantytskaya N. V. Tereshko 《JETP Letters》2009,89(4):180-184
The magnetic properties of the Bi1 ? x Ln x FeO3 (Ln is a rare-earth ion), Bi1 ? x A x FeO3 ? x/2 (A is an alkali earth ion), and BiFe1 ? x Ti x O3 + δ solid solutions in magnetic fields up to 14 T have been studied. The concentration ranges of the existence of the ferroelectric phase described by the space group R3c have been determined. It is shown that the substitution of the rare-earth ions for the Bi3+ ions leads to a sharp decrease in the critical fields inducing the metamagnetic transition from a modulated antiferromagnetic state to a weakly ferromagnetic one; however, the modulated structure in the concentration range of the R3c phase is mainly retained. The substitution of the alkali earth ions (x ~ 0.1) for the bismuth ions leads to the total destruction of the modulated structure and to the implementation of the weakly ferromagnetic state within the R3c phase. A homogeneous weakly ferromagnetic state has been revealed when the Ti4+ ions (x = 0.1) are substituted for the Fe3+ ions in the ferroelectric R3c phase. 相似文献
8.
A. V. Nazarenko A. G. Razumnaya M. F. Kupriyanov Yu. V. Kabirov A. G. Rudskaya P. Yu. Teslenko N. B. Kofanova 《Physics of the Solid State》2011,53(8):1599-1602
The (1 − x)BiFeO3−x
YMnO3 solid solutions have been found to undergo the following sequence of phase transformations with increasing x: R3c → Pbnm → C2 → Pnma → P63
cm. It has been established that the Pbnm and Pnma phases have different orientations of atomic displacements and can exhibit antiferroelectric properties. 相似文献
9.
K. P. Andryushin A. A. Pavelko I. A. Verbenko O. N. Razumovskaya L. A. Shilkina V. A. Aleshin L. A. Reznichenko 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1082-1084
Ceramic samples of bismuth ferrite and solid solutions of Bi1 − x
A
x
FeO3 type (where A = Lu, Yb, Tm, Er, Ho, Dy, Tb, Gb, Eu, Sm, Nd, Pr, La; 0.05 ≤ x ≤ 0.20; Δx = 0.05) were prepared. Spectra of the real part of electrical conductivity were studied within the range 10−4–10−6 Hz. The dependence of the samples’ thermal stability and electrical conductivity on the size of the substituting ions was
established. 相似文献
10.
A. A. Amirov A. B. Batdalov S. N. Kallaev Z. M. Omarov I. A. Verbenko O. N. Razumovskaya L. A. Reznichenko L. A. Shilkina 《Physics of the Solid State》2009,51(6):1189-1192
Thermophysical, magnetic, and dielectric properties of multiferroic BiFeO3 and Bi0.95La0.05FeO3 ceramic compounds were comprehensively studied. Anomalies of the permittivity near an antiferromagnetic phase transition related to the structural variations were detected. The temperature T N was determined from the temperature dependences of the thermal expansion coefficient, heat capacity, and differential susceptibility. It is shown that the transition point is shifted to higher temperatures as the rare-earth La ion substitutes for Bi. It is established that an insignificant substitution of lanthanum for bismuth enhances the magnetic properties of bismuth ferrite and the magnetodielectric effect. 相似文献
11.
Yu Feng Can Wang ShiLu Tian Yong Zhou Chen Ge HaiZhong Guo Meng He KuiJuan Jin GuoZhen Yang 《中国科学:物理学 力学 天文学(英文版)》2017,60(6):067711
BiFeO3 (BFO) thin films with BaTiO3 (BTO) or SrTiO3 (STO) as buffer layer were epitaxially grown on SrRuO3-covered SrTiO3 substrates. X-ray diffraction measurements show that the BTO buffer causes tensile strain in the BFO films, whereas the STO buffer causes compressive strain. Different ferroelectric domain structures caused by these two strain statuses are revealed by piezoelectric force microscopy. Electrical and magnetical measurements show that the tensile-strained BFO/BTO samples have reduced leakage current and large ferroelectric polarization and magnetization, compared with compressively strained BFO/STO. These results demonstrate that the electrical and magnetical properties of BFO thin films can be artificially modified by using a buffer layer. 相似文献
12.
The crystal structure and magnetic properties of the Bi1 ? x Ca x Fe1 ? x/2Nb x/2O3 system were studied. It is shown that, at x ≤ 0.15, the unit-cell symmetry of solid solutions is rhombohedral (space group R3c). Solid solutions with x ≥ 0.3 have an orthorhombic unit cell (space group Pbnm). The rhombohedral compositions are antiferromagnetic, while the orthorhombic compositions exhibit a small spontaneous magnetization due to Dzyaloshinski?-Moriya interaction. In CaFe0.5Nb0.5O3, the Fe3+ and Nb5+ ions are partially ordered and the unit cell is monoclinic (space group P21/n). In the concentration range 0.15 < x < 0.30, a two-phase state (R3c + Pbnm) is revealed. 相似文献
13.
The vibrational frequencies of the BiFeO3 crystal lattice in the cubic phase (Pm3m) and the rhombohedral paraelectric phase (R3c) are calculated in terms of the ab initio model of an ionic crystal with the inclusion of the dipole and quadrupole polarizabilities. In the ferroelectric phase with the symmetry R3c, the calculated spontaneous polarization of 136 μC cm?2 agrees well with the experimental data. The dependences of the unit cell volume, the elastic modulus, and the vibrational frequencies on the pressure are calculated. It is found that the frequency of an unstable ferroelectric mode in both the cubic (Pm3m) and rhombohedral (R3c) phases are almost independent of the applied pressure, in contrast to classical ferroelectrics with a perovskite structure, where the ferroelectric instability is very sensitive to a variation in the pressure. 相似文献
14.
P. Yu. Teslenko Yu. V. Kabirov O. N. Razumovskaya L. A. Reznichenko 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1133-1135
Concentration and temperature regions of the existence of different phases (R3c, Pbnm, P4mm, Amm2, Pbcm, and Pm3m) in solid solutions of BiFeO3-BiMnO3, BiFeO3-KNbO3, and BiFeO3-NaNbO3 are determined. 相似文献
15.
The effects of the 57Fe isotope content and high-frequency magnetic field amplitude h
1 on the shape of the NMR spectrum of multiferroic BiFeO3 at T = 4.2 K are studied by pulsed nuclear magnetic resonance. The NMR spectrum shape and transverse relaxation time T
2 are found to depend strongly on the 57Fe isotope content and h
1 in multiferroic BiFeO3 in the presence of a spatial spin-modulated structure of a cycloid type. In a sample with a high 57Fe isotope content, the Suhl-Nakamura interaction contributes substantially to T
2. When these dynamic effects are taken into account for analysis of the NMR spectrum shape, an undisturbed (without an anharmonicity
effect) spatial spin-modulated structure of a cycloid type is shown to exist in BiFeO3. 相似文献
16.
J. Lu A. Günther F. Schrettle F. Mayr S. Krohns P. Lunkenheimer A. Pimenov V. D. Travkin A. A. Mukhin A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(4):451-460
Magnetic dc susceptibility between 1.5 and 800 K, ac
susceptibility and magnetization, thermodynamic properties, temperature
dependence of radio and audio-wave dielectric constants and conductivity,
contact-free dielectric constants at mm-wavelengths, as well as
ferroelectric polarization are reported for single crystalline BiFeO3.
A well developed anomaly in the magnetic susceptibility signals the onset of
antiferromagnetic order close to 635 K. Beside this anomaly no further
indications of phase or glass transitions are indicated in the magnetic dc
and ac susceptibilities down to the lowest temperatures. The heat capacity
has been measured from 2 K up to room temperature and significant
contributions from magnon excitations have been detected. From the
low-temperature heat capacity an anisotropy gap of the magnon modes of the
order of 6 meV has been determined. The dielectric constants measured in
standard two-point configuration are dominated by Maxwell-Wagner like
effects for temperatures T > 300 K and frequencies below 1 MHz. At lower
temperatures the temperature dependence of the dielectric constant and loss
reveals no anomalies outside the experimental errors, indicating neither
phase transitions nor strong spin phonon coupling. The temperature
dependence of the dielectric constant was measured contact free at microwave
frequencies. At room temperature the dielectric constant has an intrinsic
value of 53. The loss is substantial and strongly frequency dependent
indicating the predominance of hopping conductivity. Finally, in small thin
samples we were able to measure the ferroelectric polarization between 10
and 200 K. The saturation polarization is of the order of 40 μC/cm2, comparable to reports in literature. 相似文献
17.
Y.W. Li J.Q. Xue J.L. Sun X.J. Meng Z.M. Huang J.H. Chu L.H. Ding W.F. Zhang 《Applied Physics A: Materials Science & Processing》2007,87(1):125-128
We report the electrical and optical properties of P-doped epitaxial ZnO thin films grown heteroepitaxially on sapphire substrates
or homoepitaxially on ZnO wafers grown by the hydrothermal method, respectively. As-grown heteroepitaxial thin films exhibit
semi-insulating to strongly n-conducting behavior depending on the P-content and the oxygen partial pressure applied during
deposition. New features are observed in the recombination spectra compared to nominally undoped ZnO thin films. The spectral
position of these new features also depends on the growth conditions making a clear correlation between P-incorporation and
particular spectral features feasible. For the homoepitaxially grown thin films lateral scanning capacitance microscopy measurements
revealed areas of both n- and p-type majority carriers. 相似文献
18.
The pure phase P2-Na2/3Ni1/3Mn2/3O2 was synthesized by a solid reaction process. The optimum calcination temperature was 850 °C. The as-prepared product delivered a capacity of 158 mAh g?1 in the voltage range of 2–4.5 V, and there was a phase transition from P2 to O2 at about 4.2 V in the charge process. The P2 phase exhibited excellent intercalation behavior of Na ions. The reversible capacity is about 88.5 mAh g?1 at 0.1 C in the voltage range of 2–4 V at room temperature. At an elevated temperature of 55 °C, it could remain as an excellent capacity retention at low current rates. The P2-Na2/3Ni1/3Mn2/3O2 is a potential cathode material for sodium-ion batteries. 相似文献
19.
C. Ederer 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(3):349-354
In this paper we present an analysis of the magnetic toroidal moment
and its relation to the various structural modes in R3c-distorted
perovskites with magnetic cations on either the perovskite A or B
site. We evaluate the toroidal moment in the limit of localized
magnetic moments and show that the full magnetic symmetry can be taken
into account by considering small induced magnetic moments on the
oxygen sites. Our results give a transparent picture of the possible
coupling between magnetization, electric polarization, and toroidal
moment, thereby highlighting the different roles played by the various
structural distortions in multiferroic BiFeO3 and in the recently
discussed isostructural material FeTiO3, which has been predicted
to exhibit electric field-induced magnetization switching. 相似文献
20.
S. A. Gridnev A. A. Kamynin A. S. Shportenko P. V. Kulakov M. V. Hahlenkov D. P. Kozlenko B. N. Savenko S. E. Kichanov E. V. Lukin 《Bulletin of the Russian Academy of Sciences: Physics》2016,80(9):1092-1096
Dielectric properties of 0.85BiFeO3–0.15MgFe2O4 composite fabricated with conventional ceramic technology are studied in the temperature interval of 20–250°C at frequencies of 25 Hz to 1 MHz. Dielectric relaxation is observed, the nature of which is discussed in the context of a mechanism of interaction between ferroelectric domain boundaries and point defects. 相似文献