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1.
A new compound, CaMg2Fe16O27, is synthesized for the first time, in polycrystalline form, using stoichiometric mixture of oxides with standard ceramic technique and characterized by X-ray diffraction. It is found to have a hexagonal W-type structure with lattice parametersa = 5.850 Å andc = 33.156 Å. Electrical studies show that the compound is a semiconductor with energy of activation, ΔE = 0.56 eV. Electrical conductivity results show a transition in the conductivity vs temperature plot near the Curie temperature. The activation energy value obtained for the paramagnetic phase is found to be higher than that of the ferrimagnetic phase. The molar magnetic susceptibility was measured in the temperature range 300–850 K and the results show that the compound is ferrimagnetic at room temperature. The compound also shows hysteresis at 300 K. Paramagnetic nature of the sample above Curie temperature is also studied. The Curie molar constantC M bdcalculated from the plot of 1/χM vsT(K) bdis found to be nearly in agreement with the expected value. 相似文献
2.
A new compound MgCoMnO4 has been synthesised by the oxide method. It crystallizes in a tetragonal spinel structure witha=8.30 A andc=8.46 A. The observed crystal symmetry is associated with the existence of Mn+3 on theB sites. The compound isn type semi-conductor with activation energy ΔE=0.33 eV. The electrical properties show that it can be regarded as a properly substituted MgMn2O4 by Co+3 ions. It is paramagnetic withC
M=5.75 and ϑ
a
=−160°K. All these results show the ionic configuration of the compound as Mg+2 [Co+3 Mn+3] O4. 相似文献
3.
A spinel CoMnAlO4 has been synthesised by the oxide method. It has a tetragonal structure withA=8.10 A andC=8.22 A. A break is found in the plot of logρ against 1/T at 573°K when activation energy changes from 0.62 eV to 0·52 eV. The electrical properties show that it can be regarded as
a properly substituted CoMn2O4 by Al+3 ions. It is paramagnetic withC
M = 4.72 and ϑ
a
= −298°K. These results show the ionic configuration of the compound as Co+2 [Mn+3 Al+3]O4. 相似文献
4.
A R James G S Kumar T Bhimasankaram S V Suryanarayana 《Bulletin of Materials Science》1994,17(6):951-958
The ferroelectric Bi4SrTi4O15 has been synthesized and a study of the electrical (AC) conductivity was made on both poled and unpoled samples in the frequency
range from 100 Hz to 1 MHz and from room temperature to 550°C. In the case of unpoled samples the activation energy was found
to be 0·54 eV and subsequent to poling it was lowered to 0·39 eV indicating an increased conductivity after poling. Further
the conductivity increased with increasing frequency and temperature. DC conductivity measurements were also carried out.
Dielectric measurements indicate a peak in the dielectric constant at 530°C. 相似文献
5.
The ceramic samples of lithium-samarium modified lead molybdate, Pb(Li1/4 Sm1/4 Mo1/2)O3 (PLSM)—a member of ABO3 family were prepared by solid state reaction technique at ≈ 600–700°C. Preliminary X-ray analysis suggests the formation
of single phase orthorhombic compound of PLSM. Studies of surface morphology, uniform particle/grain distribution, and presence
of elements in the compound were completed using scanning electron microscope (SEM). Measurements of dielectric constant (ɛ), loss (tanδ) and conductivity (σ) at different frequencies and temperatures provided that the compound has a strong dielectric anomaly at 107°C. 相似文献
6.
The DC electrical resistivity results of La4 −x
Sr1 +x
Cu5 −x
Fe
x
O12 + δ (0 ≤x ≤ 1·0) showed that for S1 (x = 0) and S2 (x = 0·25) the temperature coefficient of resistivity (TCR), dρ/dT, is positive and slightly increases with increasing temperature in the range 20–270 K. This shows the metallic nature of
S1 and S2. For the samples S3(x = 0·5) and S4 (x = 0·75), TCR slightly increases in the range 20–270 K, with change in sign from negative to positive at ∼ 80 K and ∼ 130
K, respectively. These results show the metal-insulator type transition in S3 and S4. For the sample S5 (x = 1·0), the TCR is negative and gradually increases in the range 20–270 K, which shows its semiconductor-like behaviour.
The activation energy for S5 is found to be 0·21 × 10−2 eV. Furthermore, the DC resistivity results of S1–S5 in the range 350–660 K are in conformity with the low temperature results.
The very weak temperature dependence of magnetic susceptibility results of S1–S3 show Pauli-paramagnetic behaviour in the
range 77K–400 K, while S4 and S5 exhibit Pauli-paramagnetic behaviour in the range 77–850 K. Long-range antiferromagnetic
interaction is observed in S5 (x = 1·0) belowT
c ∼ 100 K. The room temperature EPR lineshapes gradually improve from metallic S1 (x = 0) to semiconductor-like S5(x = 1·0). Negativeg-shift is observed in the samples S2–S5 with increasing trend ing
iso-values of 1·880 in S2 to 1·961 in S5. However, theg
iso-value for S1 could not be observed due to very poor lineshape. 相似文献
7.
《Materials Research Bulletin》2006,41(3):525-529
Ferromagnetic Fe3O4 nanoparticles with diameter of ∼27 nm were prepared by a hydrothermal route in the presence of a surfactant, sodium bis(2-ethylhexyl)sulfosuccinate (AOT). The as-synthesized product was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The hysteresis loops of the iron oxide nanoparticles were measured using a physical property measuring system (PPMS), and the results showed a superparamagnetic behavior at room temperature. 相似文献
8.
Suneetha T. Rao G. Narayana Ramesh T. 《Journal of Materials Science: Materials in Electronics》2021,32(11):14420-14436
Journal of Materials Science: Materials in Electronics - Nanoparticles of quaternary Mn0.5?xCuxZn0.5Fe2O4 ferrite (x?=?0.05, 0.15, 0.25, and 0.35) have been investigated to... 相似文献
9.
We report the nanoparticle Co0.2Zn0.8Fe2O4 spinel oxide, synthesized by room temperature mechanical milling. The system is stabilized mainly in spinel oxide phase after 78 hrs milling time and no other phases have been observed from the XRD spectra of the 100 hrs milled sample. We have studied the particle size effects on structural as well as on magnetic properties by annealing the 100 hrs as milled sample at different temperatures for 12 hours. The XRD and TEM data show that the particle size decreases with increasing milling time upto 60 hrs and then show an increasing trend with milling time. The particle size also increases with annealing the 100 hrs as milled sample with better crystalline structure. It is observed that the magnetic properties of the annealed samples can be correlated with the structural change without breaking the crystal symmetry of the cubic spinel phase of Co0.2Zn0.8Fe2O4 spinel oxide. The change in the crystal structural as revealed by the XRD spectra can be associated with the non-equilibrium to equilibrium cationic distribution between tetrahedral (A) and octahedral (B) sites of the spinel structure. 相似文献
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11.
采用酸碱共滴定法,以超顺磁性的纳米Fe3 O4为形核剂,成功制备 HAP/Fe3 O4、CS-HAP/Fe3 O4磁性纳米载体。利用透射电镜(TEM)、X 射线衍射仪(XRD)、傅里叶红外光谱分析仪(FT-IR)、振动样品磁强计(VSM)和 MTT 法对样品的显微结构、物相、磁性能和生物学性能进行了表征和分析。结果表明,所制备载体表现为超顺磁性,尺寸约为100 nm,均为20 nm左右的羟基磷灰石颗粒包裹20 nm 左右的Fe3 O4颗粒而成。其中双相载体中的 HAP 颗粒呈球形,三相载体中的 H AP颗粒呈短棒状。双相载体为1级细胞毒性反应,三相载体为0级毒性反应,具有促细胞增殖作用。 相似文献
12.
以FeCl3和FeCl2混合液为浸渍溶液,以普通云南杉木为基体,在常温条件下,采用原位化学合成法制备出Fe3O4/木材复合材料。用X射线衍射仪、红外光谱仪及扫描电镜对复合材料的结构进行了表征,用振动样品磁强计研究了材料的磁性能。结果表明,木材中生成Fe3O4晶粒的平均粒径为14nm,但有一定团聚,木材空隙中的部分铁氧体增大到0.5~2.5μm;合成的Fe3O4与木材间有较强的相互作用,影响了复合材料的磁性能;浸渍溶液浓度对材料的磁性能具有一定影响,当浸渍溶液中Fe离子总浓度为1.2mol/L时材料磁性最强,浸渍溶液浓度过高或过低都会引起材料磁性能的降低;木材的纤维结构对材料磁性能也有一定影响,当外加磁场方向平行于材料纤维方向时,材料的剩余磁化强度要大于磁场方向垂直纤维方向时材料的剩余磁化强度。 相似文献
13.
采用射频磁控溅射在基片Si(100)和Fe3O4(20nm)/Si(100)上制备了钴铁氧体(CoFe2O4)薄膜,制备的薄膜在空气气氛中进行300~1000℃的退火处理,采用XRD、VSM分析了薄膜的微结构以及磁性能。结果表明,制备的钴铁氧体薄膜均具有尖晶石结构,Fe3O4缓冲层薄膜促进了钴铁氧体薄膜的结晶,但降低了钴铁氧体薄膜的垂直各向异性和垂直于膜面方向的矫顽力,而钴铁氧体薄膜的磁化强度和矩形度得到了一定的提高。 相似文献
14.
CaAl2−yO4:yMn4+ (y = 0–1.6 mol%) phosphors are synthesized by a solid-state reaction method in air, and their crystal structure and luminescence property are investigated. To compare luminescence property, CaAl3.99O7:1%Mn4+ and SrAl1.99O4:1%Mn4+ phosphors are also synthesized at the same condition. Broad band excitation spectra are observed within the range 220–550 nm, and emission spectra cover from 600 to 720 nm with the strongest emission peak at ∼658 nm owing to the 2E → 4A2 transition of Mn4+ ion. The influence of crystal field to luminous intensity is discussed, and the possible luminous mechanism of Mn4+ ion is explained by using energy level diagram of Mn4+ ion. CaAl1.99O4:1%Mn4+, CaAl3.99O7:1%Mn4+, and SrAl1.99O4:1%Mn4+ phosphors under excitation 325 nm light emit red light, and their CIE chromaticity coordinates are (0.7181, 0.2813), (0.7182, 0.2818), and (0.7198, 0.2801), respectively. These contents in the paper are helpful to develop novel and high-efficient Mn4+-doped phosphor for white LEDs. 相似文献
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16.
《Journal of Experimental Nanoscience》2013,8(6):652-664
The electrical and thermal properties of thin films of polyimide/silica nanocomposites prepared via sol–gel process were studied as a function of nanosilica particles content, temperature and applied field frequency. It was found that the dielectric constant and dielectric loss of the nanocomposites decrease with both the frequency and the nanosilica content, while increase with temperature. The AC-conductivity measured in frequency range 200?kHz–1.5?MHz decreases with the filler concentration and increases with increasing temperature. For the (25?wt%) nanocomposite, it was found that the AC-conductivity increases with temperature, and the Cole–Cole plots showed that the calculated activation energy and relaxation time decrease with temperature. The observed thermal conductivity increases gently with temperature. The empirical universal law was used to fit the observed electrical data under the measuring conditions. 相似文献
17.
In this study, size and surface effects on temperature and frequency dependent magnetic properties of superparamagnetic Fe3O4 nanoparticles in a size range of 1.1-11 nm are investigated by SPR technique. We used a theoretical formalism based on a distribution of diameters or volumes of the nanoparticles following lognormal proposed by Berger et al. The nanoparticles are considered as single magnetic domains with random orientations of magnetic moments and thermal fluctuations of anisotropic axes. The individual line shape function is derived from the damped precession equation of Landau-Lifshitz. Magnetic properties of the samples were strongly temperature and size dependent. The increase in SPR line width, the decrease in the resonance field and also increase in anisotropy filed by decreasing the temperature core-shell type structure of the nanoparticles and disordered magnetic structure (spin-glass like phase) of the particle surface. A linear microwave frequency dependence of the resonance field and the increase in the blocking temperature of the particles by the particle size were also observed. 相似文献
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E. D. Solov’eva E. V. Pashkova A. E. Perekos B. S. Khomenko A. G. Belous 《Inorganic Materials》2013,49(6):621-625
We have studied the effect of “double” substitution in Ba0.7Sr0.3Fe12 ? 2x Co x Ti x O19 on the structural and magnetic properties of M-type barium hexaferrite. The basic composition of Ba1 ? x Sr x Fe12O19 obtained by heat-treating carbonate-hydroxide precipitates has been optimized (x = 0.3). 2Fe3+ → Co2+ + Ti4+ substitutions considerably reduce the coercive force (H c) and increase the magnetization (M s) relative to Ba0.7Sr0.3Fe12 O19. 相似文献