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1.
Ball milled nanocrystalline iron with minor zirconium additions was examined using 57Fe Mössbauer spectroscopy and X-ray diffraction. Powder samples were synthesized using 0, 5, and 10 wt.% zirconium additions and milled at room temperature for periods up to 24 h. Progressive decrease in grain size as determined by X-ray diffraction was observed as a function of milling time. Mössbauer spectroscopy indicates increased iron-zirconium coordination with increased milling time. After milling, the powder samples were then heat treated in an inert atmosphere of argon at up to 925 K for various times up to 25 min. Analysis of X-ray peak line width (FWHM) was used to characterize grain size and grain growth kinetics as a function of heat treatment, milling time, and alloy content and reveal an increasingly finer post-heated structure in the alloy samples containing more zirconium. Mössbauer measurements were made and suggest Zr is steadily distributed into the Fe lattice with milling and rapidly diffuses to the grain boundaries with heat treatment. The impurity-rich grain boundaries appear to considerably stabilize the refined structure. 相似文献
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T. Ostapchuk J. Petzelt M. Savinov V. Buscaglia L. Mitoseriu 《Phase Transitions》2013,86(6-7):361-373
The article offers comparative study of two nanocrystalline (50 and 100?nm averaged grain size) and two coarse-grain (1.2 and 10?µm averaged grain size) ceramics by means of Fourier transform infrared spectroscopy in a broad temperature range (10–570?K). Far infrared reflectivity spectra were fitted with the factorized model of the dielectric function and the evaluated dielectric function was compared with the results of low-frequency dielectric measurements. It appears that the stiffening and weakening of the overdamped soft mode is the only reason for the reduced dielectric permittivity of nanocrystalline ceramics in the paraelectric phase, but a strong grain-size dependence of the dielectric constant in the ferroelectric phase is not connected with the changes in lattice dynamics. All single-crystal symmetry changes were detected in all of the samples, but no phase-transition discontinuities was seen in nanocrystalline ceramics. A coexistence of more than one phase is suggested. Strong dependence of the Curie-Weiss temperature on the grain size, earlier revealed by others, is confirmed. 相似文献
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CeNiSn是一种很有趣的重费米子化合物,其基态为Kondo绝缘体.采用化学元素替代的方法研 究Cu掺杂对CeNiSn多晶样品低温比热的影响.在流动高纯氩气的保护下,用电弧炉制备了一 系列的多晶样品CeNi1-xCuxSn(x=0,002,006,008).X射 线粉末衍射分析表明,制备出来的样品均为单相多晶.随着Cu掺杂量的增加,样品的晶格参 数增大.采用绝热热脉冲法测量样品的比热,结果表明随着Cu掺入量的增加,相应样品的低温比热也随之增大,能隙逐渐减小
关键词:
重费米子
Kondo绝缘体
CeNiSn
比热
反铁磁有序 相似文献
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Shen Wu Aizhi Sun Wenhuan Xu Qian Zhang Fuqiang Zhai Philip Logan Alex A. Volinsky 《Journal of magnetism and magnetic materials》2012
This paper focuses on iron-based soft magnetic composites which were synthesized by utilizing Mn–Zn ferrite nanoparticles to coat iron powder. The nanocrystalline iron powders, with an average particle diameter of 20 nm, were obtained via the sol–gel method. Scanning electron microscopy, energy dispersive X-ray spectroscopy and distribution maps show that the iron particle surface is covered with a thin layer of Mn–Zn ferrites. Mn–Zn ferrite uniformly coated the surface of the powder particles, resulting in a reduced imaginary permeability, increased electrical resistivity and a higher operating frequency of the synthesized magnets. Mn–Zn ferrite coated samples have higher permeability and lower magnetic loss when compared with the non-magnetic epoxy resin coated compacts. The real part of permeability increases by 33.5% when compared with the epoxy resin coated samples at 10 kHz. The effects of heat treatment temperature on crystalline phase formation and on the magnetic properties of the Mn–Zn ferrite were investigated via X-ray diffraction and a vibrating sample magnetometer. Ferrites decomposed to FeO and MnO after annealing above 400 °C in nitrogen; thus it is the optimum annealing temperature to attain the desired permeability. 相似文献
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采用退火后处理的方法,使SiOx∶H(0<x<2)形成纳米硅与二氧化硅的镶嵌结构.利用红外透射谱、Raman谱和光致发光谱,系统地研究了不同退火温度对薄膜微结构及室温光致发光谱的影响.发现发光谱均由两个Gauss线组成,其中主峰随着退火温度的升高而红移,而位于835nm的伴峰不变.指出退火前在720—610nm的波长范围内强的主峰可能来源于膜中的非晶硅原子团,随退火温度的升高主峰的红移是由于非晶硅原子团的长大.而伴峰可能来自硅过剩或氧欠缺引入的某种发光缺陷.1170℃退火后在850n
关键词: 相似文献
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A. K. Murtazaev K. Sh. Khizriev V. M. Uzdin 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(2):152-155
A model of iron/vanadium superlattice has been proposed to study the phase transition in multilayers. The temperature dependences of the magnetization, susceptibility, and specific heat have been obtained. Two specific heat peaks are revealed at small ratios between the interlayer and intralayer exchanges. 相似文献
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O. V. Klyavin V. I. Nikolaev B. I. Smirnov L. V. Khabarin Yu. M. Chernov V. V. Shpeĭzman 《Physics of the Solid State》2007,49(9):1666-1671
A relation between the characteristics of plastic deformation and the specific features of mechanodynamic penetration of helium into nanocrystalline iron compressively strained at 4.2 K is investigated. Iron samples with a grain size of about 200 nm are prepared by the multiple equal-channel angular pressing technique. The samples deformed in giant (6–7%) sample-averaged serrations, which amounts to several thousand percent strain in a shear band. The amount of helium in samples strained to various degrees is measured, and curves of helium extraction from these samples are obtained in the temperature range 300–1400 K. At a strain of ~50%, the amount of helium built up in a sample is found to be substantially higher (more than hundredfold) than that in samples subjected to lower strains. It is found that an increase in the strain rate gives rise to a strain within a serration (the strain localization is enhanced) and that the amount of accumulated helium decreases, most probably, because of the shorter deformation time. The helium extraction curves obtained with increasing temperature exhibit several peaks. The temperature positions of some of them are about the same for samples strained to different extents, while the other peaks are characteristic of samples subjected to a specific strain only. The results obtained suggest the existence of helium traps of different types, which depend on the original structure and the magnitude of the strain and differ both in the amount of helium they contain and in the temperatures at which helium is released from these traps. 相似文献
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测量了石墨和纳米碳在不同温度下的正电子寿命谱,研究了石墨和纳米碳中缺陷和电子密度随温度的变化.结果表明,纳米碳中缺陷的开空间和缺陷浓度分别大于和高于石墨晶体;纳米碳的平均自由电子密度低于石墨晶体.当温度从25K升至295K时,石墨和纳米碳中的平均自由电子密度随温度的升高而下降:石墨晶体中的自由电子密度随温度的升高变化较小;纳米碳的自由电子密度随温度的升高变化较大.随着温度的升高,石墨和纳米碳中的热空位数量增多,而且这些空位可迁移至微孔洞的内表面使微孔洞的开空间增大. 相似文献
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The magnetic susceptibility χ of coarse-grained and nanocrystalline tungsten carbides was studied in the temperature range 300–1250 K. The temperature dependence of the susceptibility χ(T) of coarse-grained carbide WC is typical of weak Pauli paramagnets and has no specific features. The χ(T) dependence of nanocrystalline carbide (n-WC) in the range 550–920 K exhibits features associated with annealing of microstrains, which leads to a decrease in the contribution of orbital paramagnetism to the magnetic susceptibility of n-WC and initiates precipitation of minor impurities of iron and cobalt as superparamagnetic particles. A nanocrystalline n-WC powder retains a stable particle size of ~55 nm after long annealing at temperatures of 300 to 1200 K, whereas microstrains relax at 550–920 K. 相似文献
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This paper reports the results of a complex investigation into the properties of nanocrystalline iron prepared through mechanical dispersion in a hydrogen atmosphere. Magnetic measurements reveal changes in the magnetic characteristics of iron samples obtained for different times of milling (i.e., samples with different grain sizes). The structural transformations responsible for these changes are studied by x-ray diffraction, Mössbauer spectroscopy, and thermogravimetry. It is found that incorporation of hydrogen into the boundary region between single-domain particles of consolidated nanocrystalline iron leads to an increase in the coercive force. Magnetic anisotropy induced by strains is observed. It is established that the strain-induced magnetic anisotropy affects the field dependence of the saturation magnetization of nanocrystalline iron. 相似文献
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T. M. Ul’yanova N. P. Krut’ko L. V. Titova Yu. G. Zonov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(4):603-608
The correlation between temperature treatment conditions and the ratio of components in nanostructured fibrous powders with
a composition of ZrO2-Y2O3-Al2O3 and their porous crystal structure and physicochemical properties is studied. The dependences of the ratio between zirconia
tetragonal and monoclynic phases on the treatment temperature and the alumina content are found to have a nonmonotonic character.
The growth of zirconia crystallite size is suppressed by introduced nanocrystalline alumina in a temperature range of 600–1200°C,
which is caused by the processes of ternary solid solution formation. The bulk and picnometric density values of materials
are proportional to the temperature of heat treatment. The temperature dependence of the specific surface and the size of
oxide grain particles has an inversely proportional character. With increasing alumina content in the powders, the specific
surface increases, while the picnometric and bulk densities decrease. 相似文献
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纳米晶ZnO可见发射机制的研究 总被引:18,自引:7,他引:11
利用化学沉淀法制备了纳米ZnO粉体,室温下测量了样品的光致发光谱(PL)、X射线衍射谱(XRD),给出了样品的透射电子显微照片(TEM).X射线衍射(XRD)的结果表明:纳米晶ZnO具有六角纤锌矿晶体结构,颗粒呈球形或椭球形.观察到二个荧光发射带,中心波长分别位于398 nm的紫带和510 nm的绿光带.发现随退火温度升高,粒径增大,紫带的峰值减弱、绿带的峰值增强.证实了纳米晶ZnO绿光可见发射带来自氧空位形成的施主和锌空位形成的受主之间的复合. 相似文献
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采用自悬浮定向流法制备纳米Ni粉体,利用放电等离子烧结技术制备出了直径10 mm、厚2 mm,致密度为96.8 %,显微硬度为4.17 GPa的纳米块体材料。用X射线衍射仪、扫描电子显微镜和显微硬度计分析了烧结块体样品的相组成、晶粒尺寸、微观形貌和显微硬度。研究表明:随烧结温度的升高,块体样品的致密度和晶粒尺寸增大,当烧结温度为650 ℃时,致密度最高,晶粒尺寸为44.8 nm;显微硬度随烧结温度的增高先增大后减小,当烧结温度为550 ℃时,显微硬度最大为4.33 GPa;较高烧结温度下,断口微观形貌的纳米级韧窝出现,显示了韧性断裂的特征。 相似文献
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S. Vilminot R. Kuentzler Y. Dossmann A. Derory M. Drillon 《Physica C: Superconductivity and its Applications》1989,160(5-6)
Magnetic and low temperature specific heat measurements have been performed on iron doped YBa2(Cu1−xFex)3O7−δ samples with different oxygen contents (δ0 and δ1). Iron doping induces an orthorhombic to tetragonal transition and a decrease of both Tc and diamagnetic signal. Low temperature specific heat measurements reveal a Schottky type anomaly for δ0 samples with x=0.01 (1.8 K) and x=0.02 (3 K). This anomaly is attributed to magnetic interactions within iron limited chains. A numerical analysis of this effect is proposed. 相似文献
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Hardness and Young's modulus were measured by nanoindentation on a series of electrodeposited nanocrystalline nickel and nickel–iron alloys. Hardness values showed a transition from regular to inverse Hall–Petch behaviour, consistent with previous studies. There was no significant influence of grain size on the Young's modulus of nanocrystalline nickel and nickel–iron alloys with grain sizes greater than 20?nm. The Young's modulus values for nanocrystalline nickel and nickel–iron alloys for grain sizes less than 20?nm were slightly reduced when compared to their conventional (randomly oriented) polycrystalline counterparts. The observed trend with decreasing grain size was found to be consistent with composite model predictions that consider the influence of intercrystalline defects. However, there was some notable variability of the measured values when compared to the model predictions. Three theoretical relationships were used to characterise the anisotropic elastic behaviour of these materials. As a result, texture was also considered to have an influence on the measured Young's modulus and used to explain some of the observed variability for the entire grain size range (9.8–81?nm). 相似文献