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1.
Zr substituted BiFeO 3 (BiFe 1?xZr xO 3 with x = 0.03, 0.07, 0.10 and 0.15) nanoparticles were synthesized by sol–gel method. Powder X-ray diffraction studies showed rhombohedral crystal structure for x = 0.03–0.10 samples. The substitution induced structural transformation from rhombohedral to triclinic phase has been observed for x = 0.15. Raman analysis confirmed this structural transformation as also the distortion induced spin phonon coupling. Enhanced magnetic behaviour with saturation magnetization of 7.62 emu/g has been observed in x = 0.07 sample. The dielectric measurements indicated the strong magneto-electric coupling in the range of Neel temperature. The impedance study over a wider frequency and temperature range suggests decrease in conductivity in the samples with increasing Zr concentration. UV–Vis diffuse reflectance spectra shows the strong absorption of visible light suggesting the band gap values from 2.22 to 2.15 eV corresponding to x = 0.03–0.15 compositions. 相似文献
2.
Polycrystalline BiFeO 3 (BFO), Bi 0.90Gd 0.10FeO 3 (BGF), Bi 0.90Gd 0.10Fe 1?xTi xO 3 (x = 0.03–0.10; BGFT x) ceramics were prepared via solid state reaction method. X-ray diffraction studies reveal R3c symmetry for BFO and BGF samples and coexistence of R3c + Pn2 1 a symmetries for BGFT x samples. The change in line width of Raman modes indicates the structural distortion and substitution of dopants ions in the BFO lattice. Magnetic studies show weak ferromagnetism in BGF and BGFT x samples as a result of Gd 3+–Fe 3+, Gd 3+–Gd 3+ interactions and imbalance created between two antiparallel Fe 3+ spin sublattices by Ti substitution. The maximum remnant magnetization of 0.141 emu/g is observed for BGFT x=0.10 sample. Further, electron spin resonance study confirms the weak ferromagnetism of BGFT x samples, associated with small grains and increase in anisotropy of particles distribution as found during SEM studies. UV–Visible absorption spectra in the spectral range from 1.6 to 3.5 eV showed one d–d crystal field transition and two charge-transfer transitions with optical band gap variation in visible region. Improved dielectric properties with very low values of dielectric loss have been observed for BGF and BGFT x samples. 相似文献
3.
Nb 3+-substituted garnet nanoparticles Y 3−xNd xFe 5O 12 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties
were investigated by using X-ray diffraction (XRD), thermal analysis (DTA/TG), and vibrating sample magnetometer (VSM). The
XRD patterns of Y 3−xNd xFe 5O 12 have only peaks of the garnet structure and the sizes of particles range from 34 to 70 nm. From the results of VSM, it is
shown that when the Nd concentration x ( 1.0, the saturation magnetization of Y 3−xNd xFe 5O 12 increases as the Nd concentration (x) is increased, and gets its maximum at x = 1.0, but when x ( 1.0, the saturation magnetization
decreases with increasing the Nd concentration (x), this may be due to the distortion of the microstructure of Y 3−xNd xFe 5O 12, which leads to the decrease of the effective moment formed by Fe 3+. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the
particle size is increased. 相似文献
4.
Spinel Co 1?xMn xFe 2 O 4 (x = 0, 0.25, 0.5, 0.75 and 1.0) nanoparticles were synthesized by a solvothermal method using polyethylene glycol (PEG) as a surfactant. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray absorption near edge structure ( XANES) spectroscopy and vibrating sample magnetometer (VSM) techniques were used to characterize phase, morphology, valence states, and magnetic properties of the samples. XRD analysis showed single phase of spinel structure, and the decrease of lattice constant on the effective Mn substitution was investigated. The effect of the PEG on the spherical aggregates of Co 1?xMn xFe 2 O 4 nanoparticles was observed. The result of XANES spectra showed Mn 2+/Mn 3+, Fe 3+, and Co 2+ exist in the samples. The samples showed ferromagnetism at room temperature with a maximum saturated magnetization of 72 emu/g and the smallest coercivity of 45 Oe for x = 1.0. The origin of ferromagnetic behavior is believed to be due to the occupation of Mn 2+/Mn 3+ ions. 相似文献
5.
High performance dielectric materials are highly required for practical application for energy storage technologies. In this work, high-k pristine and modified calcium copper titanate having nominal formula Ca 0.95Nd 0.05Cu 3Ti 4?xZr xO 12 (x?=?0.01, 0.03 & 0.10) were synthesized and characterized for structural and dielectric properties. Single phase formation of the synthesized compositions was confirmed by X-ray diffraction patterns and further analysed using Rietveld refinement technique. Phase purity of the synthesized ceramics was further confirmed by Energy-dispersive X-ray Spectroscopy (EDX) analysis. SEM images demonstrated that grain size of the modified CCTO ceramics was controlled by Zr 4+ ions due to solute drag effect. Impedance spectroscopy was employed to understand the grain, grain boundaries and electrode contribution to the dielectric response. Nyquist plots were fitted with a 2R-CPE model which confirms the non-ideality of the system. Substitution of specific concentration of Nd and Zr improved the dielectric properties of high dielectric permittivity (ε′ ~?16,902) and minimal tanδ (≤?0.10) over a wide frequency range. The giant ε′ of the investigated system was attributed to internal barrier layer capacitance (IBLC) effect and reduced tanδ accredited to enhanced grain boundaries resistance due to substitution of Zr 4+ ions at Ti 4+ site. 相似文献
6.
Zinc ferrite nanomaterials have been received significant attention in recent years on account of their potential applications in the fields of electronics, optoelectronics and magnetics. To enhance the magnetic properties of zinc ferrites, Nd-doped zinc ferrites (ZnFe 2?xNd xO 4, x?=?0, 0.01, 0.02, 0.03) nanoparticles (NPs) have been prepared by the sol–gel method. The effects of Nd doping concentration on the structural and magnetic properties of zinc ferrites were studied. The results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicated that the Nd ions were incorporated into the crystal lattice of ZnFe 2O 4 and substituted for the Fe 3+ sites. Unlike pure zinc ferrites with paramagnetism, Nd doped ZnFe 2O 4 NPs were superparamagnetic at room temperature. Vibrating sample magnetometry results showed, with the increase of Nd content, the saturation magnetization of Nd doped ZnFe 2O 4 NPs increased. 相似文献
7.
Sr 1?x Ho x (ZnZr) 0.5Fe 11O 19 ( x = 0.03, 0.06 and 0.09) hexaferrite nanocrystallites of average sizes in the range of 46–60 nm are synthesized by the citrate sol–gel method. Crystalline structure, morphology, magnetic properties, and microwave absorption properties of powders were studied via X-ray diffraction, field emission scanning electron microscope vibrating sample magnetometer, and vector network analyzer, respectively. The magnetic properties such as saturation magnetization ( M s ) and coercivity ( H c ) were calculated from hysteresis loops. The XRD patterns show that the main phase is M-type strontium hexaferrite without other impurity phases. Microwave absorption properties of hexaferrite (70 wt%)–acrylic resin (30 wt%) composites were measured by the standing-wave-ratio (SWR) method in the range from 12 to 20 GHz. Results showed that substitution of Ho 3+ ions for Sr 2+ ions in Sr(ZnZr) 0.5Fe 11O 19 resonance frequency moves to higher frequency. For samples with x = 0.03, a minimum reflection loss of ?42 dB was obtained at 16.6 GHz for a layer of 1.7 mm in thickness. It was concluded that the prepared composites could be good candidates for electromagnetic compatibility and other practical applications at high frequency. 相似文献
8.
A series of intense red emitting phosphors, Ca 0.8?x Zr x Mo 1?x Si x O 4:0.2Eu 3+ ( x = 0.025, 0.05, 0.075, 0.1) that could be effectively excited in the UV region was prepared by conventional high temperature solid state reaction route. Structural, morphological and photoluminescence properties of the prepared samples were studied in detail. The incorporation of Zr 4+ and Si 4+ ions in CaMoO 4 lattice maintained the powellite crystal structure. Luminescence properties were optimized for 7.5 mol% of Zr 4+ and Si 4+ concentration. Emission intensities improved more than twice in comparison with CaMoO 4:Eu 3+. Life times of the prepared samples improved and the quantum efficiency enhanced to ~39 %. The improvement in emission intensity and quantum efficiency is explained in terms of the local distortion around the Eu 3+ ions resulting in improved absorption in the UV region. The CIE color co-ordinates of the red emission were in agreement with the values of the standard red phosphors providing potentiality to be used in phosphor converted (pc) white LEDs. 相似文献
9.
Cr-doped ZnO, i.e. Zn 1−xCr xO ( x = 0.00, 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by sol–gel route. The structural and morphological properties of these nanoparticles were investigated by high resolution transmission electron microscope (HRTEM). The average particle size of Zn 1−xCr xO nanoparticles decreases from 75 to 40 nm with the increase in x from 0.00 to 0.20. The rings observed in selected area diffraction pattern revealed that up to x = 0.10 these nanoparticles have single phase ZnO. However, a secondary spinel phase of ZnCr 2O 4 was observed for higher Cr doping ( x ≥ 0.15). The optical band gap calculated using UV–visible absorption was decreased from 3.27 to 2.27 eV with the increase in Cr-doping from 0.00 to 0.20 in ZnO nanoparticles. The undoped ZnO (Zn 1−xCr xO; x = 0.00) nanoparticles did not show any hysteresis loop at room temperature, however, clear loops were obtained for x = 0.05–0.20. Additionally, magnetization ( M) vs. applied magnetic field ( H) loops for lower Cr-concentration ( x = 0.05) saturate at 5 kOe, and while those with higher Cr concentration ( x > 0.05) do not show saturation even at 10 kOe. This may be attributed to increase in the defects at higher Cr-doping into ZnO. The value of saturation magnetization was found to decrease from 4.24 emu g −1 to 1.96 emu g −1 with the increase in Cr doping from x = 0.05 to 0.20 in ZnO and may be due to the secondary ZnCr 2O 4 phase. 相似文献
10.
This paper reports the synthesis of Sn 1?x Mn x O 2 (for x=0, 0.01, 0.05 and 0.10) nanoparticles using the co-precipitation method. X-ray diffraction (XRD) results show that all samples are single phase with tetragonal crystalline structure. Rietveld refinements from XRD patterns show that the samples present particle average sizes of 4–30 nm confirmed by scanning electron microscopy. Magnetization results for SnO 2 nanoparticles at 5% and 10% of Mn synthesized at 800?°C exhibit a ferromagnetic behavior at room temperature and an increasing of the magnetization for increasing doping concentration. On the other hand, samples synthesized at 300?°C are paramagnetic. 相似文献
11.
The emulsion method was used to prepare nanocrystalline Ni 0.7Mn 0.3Gd x Fe 2-x O 4 ferrites. The growth of particles, the structure and the magnetic properties were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Furthermore, the influence of Gd 2O 3 on magnetic properties of Ni-Mn ferrite powders has been investigated in detail. When the crystallite sizes are about 30–40 nm, all the samples have the similar Ms values. The variational rules of saturation magnetization (Ms) and coercivity (Hc) along with doped-Gd contents at different sintering temperatures show that the maximum Gd ions content doped into ferrite lattices is x = 0.06. When Gd-doped content x is larger than 0.06, the doped Gd ions can’t enter into the ferrite lattice totally but reside at grain boundary, as the ionic radii of the Gd 3+ ions are larger than that of Fe 3+ ions. The ferrimagnetism have not disappeared completely, even if the crystallite size is 7.8 nm. 相似文献
12.
Ba(LaZn) x Fe 12?2x O 19 (0≤ x≤0.5) powders with Bi 2O 3 as an additive was synthesized by a sintered route at 900 °C or 950 °C. The structure and magnetic properties of La–Zn substituted M-type barium ferrites were also investigated. When 0≤ x≤0.5, only one crystal phase existed in the sample, and the morphology of the grains were shown to be gradually irregular. The little amount of La 3+ ions and Zn 2+ ions changed the equilibrium of Fe 2+ and Fe 3+ at the 2a site, which increased the Fe 3+–O–Fe 2+ superexchange interaction strength, and the saturation magnetization ( Ms) of the samples was also improved. Meanwhile, the substitution of La 3+ and Zn 2+ ions and the grains’ size bought great effects on the magnetocrystalline anisotropy field. As a result, with sintering at 950 °C for 6 h, the max Ms value of the samples with x=0.1 was 67.26 emu/g, and the minimum coercivity ( H c ) value was 1718.89 Oe with x=0.3, respectively. 相似文献
13.
BiFe 0.95?xMn 0.05Zr xO 3 thin films were prepared on ITO/glass substrates using a sol–gel method. The P–E hysteresis loops before and after the high electric field treatment were measured to investigate the deaging effect of Zr 4+ ions on BiFe 0.95Mn 0.05O 3 thin films. It was found that the BiFe 0.95Mn 0.05O 3 thin film shows typical double P–E hysteresis loops before the cycling of high electric field, indicating that the film was aged. The double-loop feature fades away gradually with the increase of zirconium doping content from 1 to 3 mol%, demonstrating that Zr 4+ ions indeed have deaging effect on the aged BiFe 0.95Mn 0.05O 3 film. Such deaging effect of Zr 4+ ions can be further proved by comparing the asymmetry of the coercive field before and after the cycling of high electric field as well as the charge retaining capability. 相似文献
14.
The structural and magnetic properties of the mixed spinel Co 1+x Si x Fe 2?2x O 4 system for 0·1≤ x≤0·6 have been studied by means of X-ray diffraction, magnetization, and Mössbauer spectroscopy measurements. X-ray intensity calculations indicate that Si 4+ ions occupy only tetrahedral (A) sites replacing Fe 3+ ions, and the added Co 2+ ions substitute for (B) site Fe 3+ ions. The Mössbauer spectra at 300 K have been fitted with two sextets in the ferrimagnetic state corresponding to Fe 3+ at the A and B sites, for x≤0·3. The Mössbauer intensity data shows that Si possesses a preference for the A site of the spinel. The variation of the saturation magnetic moment per formula unit measured at 300 K with the Si content, is explained on the basis of Neel’s collinear spin ordering model for x≤0·3 which is supported by Mössbauer, and X-ray data. The Curie temperature decreases nearly linearly with increase of the Si content, for x=0·1–0·6. 相似文献
15.
The magnetic properties of Ni-Zn ferrites have been upgraded by preparing hot-pressed Ni 0.4Zn 0.6–2xLi xFe 2+xO 4 ferrites wherein 2xZn 2+ ions have been substituted by xLi 1+ and xFe 3+ ions. This results in an increase of saturation magnetization, Curie temperature and dielectric constant, whereas resistivity and initial permeability are reduced. The values of saturation magnetization, Curie temperature and dielectric constant are improved due to hot pressing in which grain growth and densification are controlled simultaneously. The variations of saturation magnetization and Curie temperature can be explained by the preferential site occupancy of Li 1+ and Ni 2+ ions at the tetrahedral site, sublattice magnetization with canted spin structure, and magnetic exchange interactions. The inferences drawn from the bulk magnetic properties of these ferrites conform with the conclusions drawn from variations of internal magnetic field, obtained from Mössbauer studies of these samples. The decrease in d.c. resistivity due to substitution of Li 1+ ions is attributed to increased hopping due to formation of Fe 2+ and Ni 3+ ions. 相似文献
16.
The samples of the series Co1+ySnyFe2- 2y- xCrxO4 ferrites with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and y = 0.05, were prepared by the usual double sintering ceramic technique. The single- phase spinel structure of the samples was confirmed by using X- ray diffractometry technique. The lattice parameter ’a’ with an accuracy of ± 0.002 Å were determined using Bragg peaks of XRD pattern. The lattice parameter ’a’ decreases with concentration, x, which is due to the difference in the ionic radii of Cr3+ and Fe3+ ions. The X- ray intensity calculations were carried out in order to determine the possible cation distribution amongst tetrahedral (A) and octahedral [B] sites. The X- ray intensity calculations show Cr3+ ions occupying B site. The saturation magnetization, σs, and magneton number, nB (the saturation magnetization per formula unit), measured at 300 K determined from high field hysteresis loop technique decrease with increase in concentration, x, suggesting a decrease in ferrimagnetic behaviour. Thermal variation of low field a.c. susceptibility measurements from room temperature to about 800 K exhibits almost normal ferrimagnetic behaviour and the Curie temperature, TC determined from a.c. susceptibility data decreases with increase in x. 相似文献
17.
The K 2Cu 1?xMn xF 4 phase has been studied by magnetic X-ray and neutron diffraction measurements. For 0 ? x ? 0.20 the material is ferromagnetic with a slight decrease of the Curie temperature with increasing x. The magnetization also decreases with rising x due to antiferromagnetic couplings between Mn 2+ and Cu 2+ ions. 相似文献
18.
Single-phase, co-doped (La 3+, Zr 4+) in polycrystalline Bi 0.95La 0.05Fe 1−xZr xO 3 (with x = 0, 0.02, 0.04 and 0.06) ceramics (particle size ∼650 nm; tolerance factor ∼0.883) were prepared by solid state reaction of oxides, followed by rapid quenching of samples. Enhanced magnetization was observed in co-doped (La 3+, Zr 4+) BiFeO 3 which may be ascribed to the collapse of the spiral spin structure. Step magnetization was observed in zero field cooled (ZFC) and field cooled (FC) curves. The coexistence of ferromagnetism and ferroelectricity has been confirmed in the co-doped (La 3+, Zr 4+) in BiFeO 3 ceramics by means of ( M–H) and ( P–E) loops measurements. Magnetodielectric properties have been observed at room temperature. 相似文献
19.
In the present report, influence of Dy-substitution and size on the structural, magnetic and dielectric properties of BiFeO 3 nanoparticles has been investigated. The synthesis of pure and Dy-doped BiFeO 3 nanoparticles has been done successfully using sol–gel method. Size of Dy-doped BiFeO 3 nanoparticles was tailored by varying the calcination temperature. Structural analysis reveal that substitution of Dy 3+ leads to a change in structure from rhombohedral ( x=0) to orthorhombic ( x=0.15). The average crystallite size varies from 6 to 15 nm. Magnetic study reveals the enhancement in magnetization with the doping of Dy 3+. Further, this value decreases as the particle size increases. Dielectric property improves with the Dy 3+ substitution. All the nanoparticles display Debye-type relaxation. The low dielectric loss values observed are attributed to the nanosized grains. Remarkably, enhanced saturation magnetization value (13.8 emu/g) and dielectric constant value (95.8) were observed for Dy-doped BiFeO 3 nanoparticles having the smallest particle size. Thereby, the study indicates strong correlation between size and multiferroism. 相似文献
20.
M-type hexagonal ferrite powders, SrFe 12?2x La x (Mn 0.5Zr 0.5) x O 19 ( x=0.0, 0.2, 0.4, 0.6, 0.8), have been synthesized by the coprecipitation method. The X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer and vector network analyzer all were used to characterize the structure of the samples, their magnetic and microwave properties. The value of the saturation magnetization increased up to x=0.2 and then slowly decreased with increasing doping. A decreasing trend was observed in the value of coercivity with increasing substitution degree, and its value reached a minimum of 2420 Oe for x=0.6 and then increased with further increasing x. The relative complex permittivity and permeability of the composite powders were investigated in the X-band frequency range (8.2–12.4 GHz). 相似文献
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