Fe掺杂BaTiO3的第一性原理研究

基于密度泛函理论的全势缀加平面波十局域轨道方法,对Fe掺杂BaTiO3的电子结构进行了计算,研究了Fe掺杂BaTiO3的铁磁性.在BaTiO3陶瓷材料中掺杂适量铁元素,不仅可以改善材料的介电性质,又能赋予材料复合性质,可使材料产生新的功能特性—铁磁性.为研究其微观机制,计算了纯BaTiO3的电子结构,超胞体系BaTi0.5Fe0.5O3的电子结构,计算结果表明由于Fe的掺杂使材料具有了磁性,从Fe和O的态密度图比较能够看出Fe的3d电子和O的2p电子存在轨道杂化现象,表明共价键、离子键共存.     

铟掺杂PZT铁电陶瓷性能研究

采用传统固相烧结法制备In2O3掺杂的锆钛酸铅(PZT)铁电陶瓷,研究了In2O3掺杂量对PZT铁电陶瓷材料的相组成、微观结构、介电性能、压电性能及铁电性能的影响。研究结果表明,随着In2O3掺杂量的增加,PZT材料在准同型相界处三方相增加四方相减少,适量掺入In2O3有利于晶粒均匀生长。在不同的铟掺杂剂量下,PZT陶瓷材料分别具有最佳的铁电及压电性能。当铟掺杂量为0.1%(质量分数)时,PZT材料具有最佳的铁电性能,其剩余极化强度为23.43μC/cm2,矫顽场为9.783kV/cm。当铟掺杂量为0.3%(质量分数)时,PZT材料具有最好的压电性能,其tanδ=0.023,d33=540pC/N,εr=1513,Kp=0.764,Qm=1819。     

纳米材料

<正>乌克兰科学家研发纳米级超薄硒化铟纳米级超薄硒化铟是一种具有独特性能的类石墨烯新半导体材料,其厚度从一层(约0.83nm)到几十层不等。这种新半导体材料的电学和光学性能研究是在2010年物理学诺贝尔奖得主—英国曼彻斯特大学教授安德烈·海姆的实验室进行的。近日乌克兰和英国科学家在《Nature Nanotechnology》杂志上发表联合文章,认为硒化铟的实际应用有可能导致纳米电子学的革命。     

铁磁电材料BiFeO3及研究进展

BiFeO3是一种典型的铁磁电材料,因为室温下共存的铁电性与磁性以及在新型存储器件,自旋电子器件方面都有着广泛的应用前景使其受到了广泛的关注.综述了BiFeO3陶瓷和薄膜的结构、性能以及制备方法,并提出了研究中需要解决的一些问题.     

多铁材料中的耦合效应和单相BiFeO3的研究状况

多铁材料同时自发地具有铁电性、铁磁性或铁弹性,这些性质在一定条件下相互耦合,极大地改变了多铁材料的性能.人们又发现BiFeO3的居里温度Tc=820K和奈尔温度TN=643K远在室温之上,在同一相中同时具有铁电有序和反铁磁有序,这样可以用外加电场控制反铁磁畴提高磁性或者用外加磁场控制铁电畴,提高极化强度,所以该材料已成为一个研究热点.主要介绍了单相BiFeO3薄膜的结构和物理性质,同时介绍了多种提高单相BiFeO3薄膜磁化强度、铁电性和压电性的方法.     

微波辅助制备掺铁纳米TiO2溶胶及其性能研究

为了进一步提高纳米二氧化钛溶胶的光催化活性,采用微波辅助胶溶的方法制备了不同铁掺杂量的纳米二氧化钛(Fe-TiO2)溶胶,并以偶氮染料活性艳红X-3B为目标物,分别考察不同铁掺杂量对纳米Fe-TiO2溶胶光催化活性的影响,研究表明原子数分数为0.05%的Fe3+掺杂量最佳;对Fe-TiO2溶胶、TiO2溶胶及P25(Degussa纳米TiO2)悬浮液的光催化活性进行对比,结果表明:TiO2溶胶与P25悬浮液光催化活性相当,而Fe-TiO2溶胶较前两者具有更高的光催化活性.采用XRD、DLS、AFM和DRS的分析方法对溶胶进行表征,结果表明:微量铁掺杂对纳米TiO2的晶型及粒径分布无显著影响;但铁掺杂可以使纳米TiO2对紫外光的吸收有较大程度的增强,同时吸收边带发生了较明显的红移.铁掺杂对于提高纳米TiO2溶胶的光催化活性和拓展其光吸收范围均具有显著的积极的作用.     

非化学计量溶液区熔法生长大尺寸InSe晶体及表征（英文）

硒化铟(InSe)是一种具有奇异物理性能的Ⅲ-Ⅵ族半导体材料,在光伏、光学、热电等领域有着广泛的应用潜力。由于InSe的非一致熔融特性及InSe、In₆Se₇和In₄Se₃之间复杂的包晶反应,制备大尺寸In Se晶体十分困难。本研究采用区熔法制备了InSe晶体,该方法具有成本低、固液界面优化等优点。基于In-Se体系的包晶反应,发现In与Se的初始物质的量比对InSe晶体生长非常重要,本工作使用精确非化学计量的In0.52Se0.48溶液生长晶体,使In Se晶体的获得率达到83%左右。实验最终获得了?27 mm×130 mm的晶棒,并成功剥离出尺寸?27 mm×50 mm的片状In Se单晶, XRD图谱中检测到(00l)衍射峰,说明晶体的质量良好。In Se晶体呈现六方结构,各元素在基体中均匀分布,在1800 nm波长下的透射率为～55.1%,带隙能量为～1.22 e V。在800 K下, In Se晶体沿(001)方向的最大电导率σ约为1.55×10² S·m^–...     

纳米铁和氮化铁超顺磁体复合吸收剂的研制

为了以纳米氮化铁作为吸波材料的吸收剂,利用气相化学反应方法,以氨基有机络合物为活化剂,液态五羰基铁为原料,获得了纳米量级亚单畴磁性氮化铁颗粒．利用TEM和S参数测量仪分析产物的结构和电磁参数．研究表明：制备的材料颗粒尺寸大都在10～100nm之间,材料主要由Fe和Fe3N的混合物组成;材料在微波段（8～13GHz）具有一定的介电损耗和磁损耗,可用作吸波材料的吸收剂．计算表明,在该波段,1mm厚度的吸波材料对电磁波能量最高衰减可达到10dB以上,具有较好的性能,可作为雷达吸波材料．     

掺杂对BiFeO3薄膜电、磁特性影响综述

随着科技的高速发展,多铁性材料已经成为传感器、微波器件、数据存储、自旋电子学及太阳能电池等领域的研究热点,在智能材料与器件方向显示出可观的应用潜力。BiFeO_3及其衍生的一系列材料Bi_(1-x)AxFeO_3(A=La,Nd,Sm)、BiFe_x B_(1-x)O_3(B=Ni,Mn,Co)的发现使得多铁性材料获得了更迅猛的发展。这类材料属于单相钙钛矿氧化物型多铁材料,在室温以上同时具有铁电、压电、介电、电光、铁磁、光伏、磁电耦合、光催化等效应。BiFeO_3作为一种单相多铁性材料,与同类的多铁性材料相比,其具有较高的居里温度、尼尔温度以及较小的光学禁带宽度和较好的化学稳定性等特点。然而,在制备BiFeO_3的过程中,部分Fe~(3+)向Fe~(2+)转变,并且铋元素熔点较低容易挥发,产生大量的氧空位,造成漏电流较大,很难得到具有较高剩余极化强度的样品;并且BFO薄膜室温下弱的磁性等性质使其实际应用受到极大的限制。多年来国内外学者致力于改善制备条件和参数,使用更先进的制备方法,改用更合适的衬底材料及进行离子掺杂等,以制备多层复合薄膜。其中,离子掺杂对减小漏电流,提高铁电性及室温磁性方面的效果最为理想。各国研究者已经制备出比纯BiFeO_3材料性能更好的掺杂和复合BiFeO_3材料。在不同的位置掺杂多种元素较掺杂单一元素能更好地改善材料的性能。最新报道的采用溶胶-凝胶法制备的多个混合掺杂离子Bi_(0.88)Sr_(0.03)Gd_(0.09)Fe_(0.94)Mn_(0.04)Co_(0.02)O_3薄膜的剩余极化强度增加到108μC/cm~2,显著高于La、Mn、Zn等元素单掺杂得到的极化强度(69.47μC/cm2)。同时,掺杂BiFeO_3薄膜的磁化强度比纯BiFeO_3薄膜提高了3～4倍。这可能是源于:掺杂离子抑制Bi3+的挥发和Fe3+的还原,减小氧空位和缺陷浓度,从而减小漏电流,进一步改善BiFeO_3薄膜的铁电性能;掺杂离子也会导致结构的畸变而打破其螺旋磁结构,从而产生较强的室温磁性。本文首先简单介绍了BiFeO_3材料的结构及其掺杂元素的种类,然后讨论了A位、B位和AB位共掺杂离子对提高BiFeO_3薄膜弱的室温磁性以及减小漏电流、提高铁电性产生的影响,并进一步分析了产生影响的原因,最后提出了未来研究工作的方向。     

Fex（In2O3）1—x磁性颗粒膜的结构及光学性质

用射频溅射法制备了金属／半导体Fex(In2O3)1-x颗粒膜。实验结果表明：纳米尺度的Fe颗粒比较均匀地分布在非晶态母体In2O3中。退火可使In2O3晶化。该样品在室温下表现出超顺磁驰豫,符合Langevin方程。光学测量表明：嵌Fe的磁性颗粒膜,其电子的带间跃迁由In2O3的直接跃迁变为间接跃迁,基本吸收边红移;随磁性增强,局域态尾变宽,带隙变窄。     

Electronic ferroelectricity from charge ordering in RFe(2)O(4)

We report our recent discovery of novel ferroelectricity arising from the polar ordering of Fe(3)+ and Fe(2)+ in a mixed valence triangular lattice oxide LuFe(2)O(4), where the electric polarization is not a result of ionic displacement. The polar ordering of Fe(3)+ and Fe(2)+ was confirmed with a resonant x-ray scattering study in SPring-8. The origin of such ordering is the competitive interaction between Fe(3)+ and Fe(2)+ in the triangular lattice, i.e., the charge frustration. The polar superlattice of Fe(3)+ and Fe(2)+ develops below 350 K, where the electric polarization appears. The ferroelectricity arising from the polar charge ordering or the polar electron distribution may have great potential for the future application of ferroelectrics.     

A Simple Fabrication of FeSe Superconductors with High Upper Critical Field

A simple and reproducible fabrication process for the synthesis of FeSe superconductors has been developed. The properties were characterized by X-ray diffraction, scanning electron microscope, superconductivity quantum interference device, and physical property measurement system. It showed a zero resistance superconducting critical temperature of ??7.9?K and an onset critical temperature of ??13.9?K. The upper critical magnetic field at zero temperature was estimated to be 31?T. The growth mechanism of FeSe flakes was also discussed.     

Electronic structure studies of nanoferrite Cu(x)Co(1-x)Fe2O4 by X-ray absorption spectroscopy

Pure and mixed cobalt copper ferrites are of great interest due to their widespread application in electronics and medicine. We report on the electronic structure of a nanoferrite Cu(x)Co(1-x)Fe2O4 (0.0 < or = x < or = 1.0) system studied by X-ray absorption spectroscopy. These magnetic nanoferrites (average crystallite size approximately 31-43 nm) were synthesized by an auto combustion method and are characterized by high resolution X-ray diffraction and near edge X-ray absorption fine structure measurements at the O K and Co, Cu, and Fe L-edges. The O K-edge spectra suggest that there is a strong hybridization between O 2p and 3d electrons of Co, Cu and Fe cations and Fe L3,2-edge spectra indicate that Fe ions coexist in mixed valence states (Fe3+ and Fe2+) at tetrahedral and octahedral sites of the spinel structure. Copper and cobalt ions are distributed in the divalent state in octahedral sites of the spinel structure. The origin of high saturation magnetization and coercivity in cobalt-copper ferrites are explained in light of these results.     

Ni doped Fe3O4 magnetic nanoparticles

In this work, the effect of nickel doping on the structural and magnetic properties of Fe3O4 nanoparticles is analysed. Ni(x)Fe(3-x)O4 nanoparticles (x = 0, 0.04, 0.06 and 0.11) were obtained by chemical co-precipitation method, starting from a mixture of FeCl2 x 4H2O and Ni(AcO)2 x 4H2O salts. The analysis of the structure and composition of the synthesized nanoparticles confirms their nanometer size (main sizes around 10 nm) and the inclusion of the Ni atoms in the characteristic spinel structure of the magnetite Fe3O4 phase. In order to characterize in detail the structure of the samples, X-ray absorption (XANES) measurements were performed on the Ni and Fe K-edges. The results indicate the oxidation of the Ni atoms to the 2+ state and the location of the Ni2+ cations in the Fe2+ octahedral sites. With respect to the magnetic properties, the samples display the characteristic superparamagnetic behaviour, with anhysteretic magnetic response at room temperature. The estimated magnetic moment confirms the partial substitution of the Fe2+ cations by Ni2+ atoms in the octahedral sites of the spinel structure.     

Magnetic moments and curie temperatures of (Fe, Ni)80(P, B)20amorphous alloys

The magnetic moment per transition metal atom at 0°K and the Curie temperature were obtained for a series of (Fe, Ni)80(P, B)20amorphous quenched alloy ribbons. Fe/Ni and P/B compositions were varied separately. The moment data can be fitted well by assigning 2.1 Bohr magnetons per Fe atom and 0.6 per Ni atom, with the moment being lowered by 0.3 per B atom and 1.0 per P atom. Alternatively, moments varying with composition, as shown by neutron diffraction in crystalline alloys, combined with a lowering of 1.2 per B atom and 2.1 per P atom, also fit well. For a given P/B composition, Tcshows a broad maximum at Fe:Ni of about 3:1. For a given transition metal composition, Tcincreases with increasing B content.     

EuFe2As2: Magnetic Structure and Local Charge Distribution Anisotropies as Seen by Resonant X-ray Scattering

Non-resonant and element specific magnetic X-ray scattering has been used to determine the orientation of Eu and Fe magnetic moments in EuFe₂As₂ iron pnictide. Experiments have been carried out on single crystal samples at the ESRF. Resonant measurements on magnetic reflections at the Eu L₃ absorption edge indicate that the orientation of the Eu moments in the antiferromagnetic phase (T<T _N=19 K) lie parallel to the crystallographic a-axis. In addition, non-resonant magnetic X-ray measurements indicate that the Fe moments are aligned along the same direction in the spin density-wave ordered phase (T<T _S=190 K). The temperature dependence of the integrated intensities suggests that the Fe magnetic sublattice is barely affected by the onset of Eu ordering at T _N. The observation of non-zero resonant intensity on nuclear-forbidden reflections with wavevector corresponding to the Fe magnetic propagation vector at both the Eu L₃ and As K absorption edges may be interpreted as the result of the polarization of the Eu 5d and As 4p electronic bands via hybridization with the Fe 3d states.     

DyFe10Si2Nx化合物的结构与磁性

利用中子粉末衍射技术确定了77K温度下化合物中Si原子占位和原子磁矩，研究了DyFe10Si2化合物低温下的结构与磁性．结果表明，在77K化合物的易磁化方向与ab平面之间有较小的夹角．采用全势能线性缀加平面波（（L）APW）＋局域轨道（10）方法计算了DyFe10Si2及其氮化物的磁性和间隙原子效应，分析了化合物中间隙N原子在Si原子不同占位时的作用．结果表明，N原子的杂化作用能提高化合物的饱和磁矩（不显著），使其居里温度有显著的提高（15％-20％）.     

Cupric oxide as an induced-multiferroic with high-TC

Materials that combine coupled electric and magnetic dipole order are termed 'magnetoelectric multiferroics'. In the past few years, a new class of such materials, 'induced-multiferroics', has been discovered, wherein non-collinear spiral magnetic order breaks inversion symmetry, thus inducing ferroelectricity. Spiral magnetic order often arises from the existence of competing magnetic interactions that reduce the ordering temperature of a more conventional collinear phase. Hence, spiral-phase-induced ferroelectricity tends to exist only at temperatures lower than approximately 40 K. Here, we propose that copper(II) oxides (containing Cu2+ ions) having large magnetic superexchange interactions can be good candidates for induced-multiferroics with high Curie temperature (T(C)). In fact, we demonstrate ferroelectricity with T(C)=230 K in cupric oxide, CuO (tenorite), which is known as a starting material for the synthesis of high-T(c) (critical temperature) superconductors. Our result provides an important contribution to the search for high-temperature magnetoelectric multiferroics.     

Sr、Co共掺多铁性材料BiFeO3的性能

利用溶胶-凝胶法制备了BiFeO_3、Bi_(0.95)Sr_(0.05)FeO_3、BiFe_(0.95)Co_(0.05)O_3和Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3样品,并对样品的结构、形态、元素含量、铁电性和铁磁性进行了研究。结果表明,共掺杂样品Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3的晶体结构发生了变化,铁电性明显增强,但漏电流变大;Bi_(0.95)Sr_(0.05)FeO_3、BiFe_(0.95)Co_(0.05)O_3样品的磁性都有所增强,但Bi_(0.95)Sr_(0.05)Fe_(0.95)Co_(0.05)O_3样品的磁性并没有随着Sr和Co的共同掺杂而进一步提高,从氧空位浓度、Fe-O共价键结构的变化和晶体尺寸三个方面对产生这种现象的原因进行了分析。     

Tb2Fe17-xCrx化合物的结构与磁性

通过X射线衍射及磁测量手段研究了Tb2Fe17-xCrx（x=0、0．5、1．0、1．5、2．0、3．0)化合物的结构与磁性。研究结果表明Tb2Fe17-xCrx化合物具有Th2Ni17型结构，随着Cr替代量x的增加，Tb2Fe17-xCrx化合物的单胞体积呈现非线性的减小，而晶胞参数a、c呈现复杂的变化。分析表明Tb2Fe17-xCrx化合物中存在着较强的磁一弹耦合效应。对磁性质的研究结果表明随着Cr替代量x的增加，Tb2Fe17-xCrx化合物的居里温度升高，在x=1．0时达到最大值，为539K，当Cr替代量x继续增加时，Tb2Fe17-xCrx化合物的居里温度下降。随着Cr替代量x的增加，Tb2Fe17-xCrx化合物的自发磁化强度急剧下降，分析表明在Tb2Fe17-xCrx化合物中，Cr的磁矩反平行于Fe的磁矩。