低温固相反应法制备的NiFe2O4纳米颗粒的结构与磁性

采用低温固相反应法制备了晶粒尺寸在8-47 nm之间的NiFe2O4纳米颗粒系列样品,用X射线衍射仪(XRD)、高分辨中子粉末衍射谱仪、振动样品磁强计和超导量子干涉仪等对样品的晶体结构、宏观磁性和纳米颗粒的表面各向异性进行了分析研究.XRD和中子衍射测量结果显示纳米颗粒的晶格常数略高于块体材料,样品的氧参量表明纳米颗粒的晶格畸变程度没有块体材料严重.相对块体材料,纳米颗粒具有较小的磁化强度、较大的矫顽力和各向异性能密度.纳米颗粒从多畴转变为单畴的临界尺寸约为40 nm,超顺磁性临界尺寸约为16 nm.     

低温固相反应法制备的NiFe2O4纳米颗粒的结构与磁性

采用低温固相反应法制备了晶粒尺寸在8—47nm之间的NiFe₂O₄纳米颗粒系列样品，用X射线衍射仪(XRD)、高分辨中子粉末衍射谱仪、振动样品磁强计和超导量子干涉仪等对样品的晶体结构、宏观磁性和纳米颗粒的表面各向异性进行了分析研究.XRD和中子衍射测量结果显示纳米颗粒的晶格常数略高于块体材料，样品的氧参量表明纳米颗粒的晶格畸变程度没有块体材料严重.相对块体材料，纳米颗粒具有较小的磁化强度、较大的矫顽力和各向异性能密度.纳米颗粒从多畴转变为单畴的临界尺寸约为40nm，超顺磁性临界尺寸约为16nm.     

应用XRD方法研究AlN粉体的冲击波改性

 利用X射线衍射分析技术及Warren-Averbch分析方法，详细地研究了氮化铝陶瓷粉体在“名义压力”为9.8 GPa的冲击波压力作用下的晶格缺陷，得到了晶格畸变与晶胞柱尺寸的关系数值，分析结果表明，其相干散射区域尺寸远小于颗粒的真实尺寸，说明冲击波作用在氮化铝陶瓷粉体中产生了严重的晶格缺陷。     

Grain Growth Kinetics of BaTiO3 Nanocrystals During Calcining Process

以醋酸钡和钛酸四丁酯为原料,采用溶胶-凝胶法合成了纳米BaTiO3粉体;运用差示/热重、X射线衍射及透射电镜对前驱体凝胶和产物进行了表征,并根据XRD结果,研究了纳米BaTiO3的晶格常数、晶格畸变度和晶粒尺寸随焙烧温度及时间的变化。结果表明,焙烧温度与时间对纳米BaTiO3晶格常数的影响不明显;随焙烧温度或时间的延长,纳米BaTiO3的晶格畸变度减小,晶粒尺寸增大,但晶格畸变度和晶粒尺寸更敏感于焙烧温度. 基于扩散控制机理的传统模型探讨了焙烧过程纳米BaTiO3晶粒生长动力学,得出其晶粒生长指数为7,晶粒生长活化能为75.49 kJ/mol. 将基于扩散与反应共同控制机理的新型等温模型应用于本研究中,结果表明,新型等温模型更能真实地反映纳米BaTiO3焙烧过程中的晶粒生长行为,说明纳米BaTiO3晶粒生长过程同时受溶质扩散和表面反应控制,其藕合晶粒生长活化能为27.23 kJ/mol.     

纳米板钛矿基二氧化钛中的晶格畸变

借助精确的Ｘ射线衍射测量,结合独立衍射峰对不同晶粒度纳米板钛矿基二氧化钛样品中板钛矿和金红石相的微结构参量进行了较细致的研究,给出了标明物相、晶面指数（ｈｋｌ）和晶面间距ｄｈｋｌ值详细分析结果的系列ＸＲＤ谱,并得到了晶面间距、晶格常数、轴比、晶胞体积等参数数值及其相对常规粗晶的变化情况,从而初步揭示出其晶粒微结构的尺寸效应。首次发现,纳米板钛矿基二氧化钛样品中板钛矿和金红石相晶粒均存在着非单调的各     

高压处理的α－Fe_2O_3超微粒的X射线衍射研究

采用沉淀法制备了α－Ｆｅ２Ｏ３超微粒，将超微粒粉末在不同温度下进行了高压处理，利用Ｘ射线衍射，ＴＥＭ和穆斯堡尔谱学对高压处理前后的样品进行了研究。结果表明，室温下压力对微晶的晶粒尺寸没有产生明显的影响，热压使晶粒尺寸有较大增长。压力主要对微晶的晶格畸变程度及取向产生了影响     

CoSb3纳米热电材料的制备及热传输特性

以Sb，Co为起始原料，采用固相反应法合成了CoSb3.通过高能球磨制得CoSb3纳米粉末，用放电等离子烧结(SPS)方法制备出最小平均晶粒尺寸为150nm的块体材料.研究了晶粒尺寸与热传输性能之间的关系：CoSb3化合物结构纳米化对其晶格热导率κL有显著影响，当晶粒尺寸由微米尺度减小到纳米尺度，晶格热导率κL显著降低，但对载流子热导率κc的影响不甚显著.CoSb3化合物的热导率κ随晶粒尺寸的减小而降 低主要是由于晶格热导率κL随晶粒尺寸的减小而降低所致. 关键词： 纳米 Skutterudite 制备 热传输特性     

纳米晶体结构与性能的模拟研究

通过分子动力学方法模拟纳米晶体（1—3nm）的结构．利用模拟的结果，进行了X射线衍射点阵常数、晶粒尺寸及点阵畸变的模拟计算，还计算了结合能及弹性模量等．结果表明纳米晶体无论是晶界和晶粒都与传统的粗晶粒晶体材料没有本质的区别，只是由于晶粒尺寸变小，以及晶界的体积分数等的作用，导致一系列的性能差异 关键词：     

模拟纳米晶体原子分布及X射线散射理论图案

通过分子动力学方法模拟纳米晶体（1—3nm）的结构．利用模拟的结果，进行了X射线衍射及径向分布函数的模拟计算．结果表明：纳米晶体晶界呈短程有序，界面原子间距分布很宽；随着晶粒尺寸的减小，晶粒的畸变越大，原子体积常数也明显增大 关键词：     

高质量镍基超晶格薄膜的制备及表征

自发现镍基超导薄膜之后, 镍基材料体系已成为当前人们的研究热点. 而在相关报道中, 普遍认为高质量的镍基超导前驱体薄膜的制备对其拓扑还原后超导电性的实现具有重要影响. 前期研究表明高质量的前驱体薄膜只生长在SrTiO3 衬底附近, 这与我们的实验结果一致. 为了可控制备高质量的镍基超导前驱体薄膜, 本文利用脉冲激光沉积(PLD) 技术在SrTiO3 (001) 衬底上生长不同厚度的可层选择性还原的[SrTiO3 ]m/[ Nd0 .8Sr0 .2 NiO3 ]n[(STO)m/(NSNO)n ]超晶格薄膜. 采用反射高能电子衍射仪(RHEED) 及透射电子显微镜(STEM) 和 X 射线衍射(XRD) 技术对超晶格薄膜的结构进行原位检测及结构表征, 然后利用综合物性测量系统(PPMS) 测试薄膜的电磁输运性质. 结果表明, 超晶格薄膜的结构质量良好, 超晶格薄膜和高质量单层前驱体薄膜表现出类似的电阻和磁阻现象. 该研究为后续镍基超导薄膜的可重复制备提供了重要的参考.     

旋转磁场对凝固组织形成的影响

研究了旋转磁场作用下Pb-45%Sn亚共晶合金的凝固组织.实验发现,旋转磁场的频率恒定时,凝固组织的晶粒尺寸随着磁场强度的增强而线性减小,同时,初生相的生长形态从枝晶转变为椭球状.X射线测试结果表明,初生相Pb发生了点阵膨胀,并且晶格常数随着磁场强度的增强先变大后减小,磁场强度在此存在一个临界值.能谱分析显示,随着磁场强度的增强,初生相Pb内Sn的含量逐渐降低.根据电磁场理论和扩散定律,对上述现象进行了理论分析,揭示出旋转磁场引起了液相强烈流动,加快了溶质原子的扩散以及对熔体的加热效应,导致了形核率的提高和长大速度的降低. 关键词： 旋转磁场 液相流动 晶格常数 溶质分配     

纳米粉体CeO_2∶Eu~(3+)的溶胶-凝胶绿色合成及其发光性质

采用溶胶-凝胶法,以硝酸铈为原料,加入适量淀粉为分散剂,并通过氨水来调节溶液p H值,合成稀土Eu~(3+)掺杂的CeO_2红色纳米粉体。通过X射线衍射仪、场发射扫描电子显微镜、荧光分光光度计等手段研究不同煅烧温度对粉体结构、形貌、发光及显色性能的影响。结果表明,所得样品为立方晶系的萤石结构,空间群为Fm3m,颗粒呈近似球形,粒径范围在10~60 nm之间。随着煅烧温度的升高,CeO2晶粒尺寸逐渐增大,荧光粉的红色发光也逐渐增强。经800℃烧结后,近紫外(370 nm)和蓝光区(468 nm)的光都能对粉体有效地激发,这有利于其在固态照明中的应用。在溶胶-凝胶制备过程中,采用淀粉作分散剂,具有工艺简单、绿色环保的优点,有利于纳米氧化铈粉体的大规模制备。     

Structural characterisation of Ni clusters in AlN via X-ray absorption, X-ray diffraction and transmission electron microscopy

Ni ions were implanted in bulk AlN with the goal to form embedded metallic clusters. Combining several characterisation techniques such as X-ray absorption spectroscopy, X-ray diffraction and high resolution transmission electron microscopy, we determined the lattice parameter of the Ni clusters that display a fcc crystalline structure. The average size increases when the ion fluence is increased or after a thermal treatment. Thanks to moiré fringes observed by high resolution transmission electron microscopy and to satellite peaks seen on the diffraction patterns, we concluded that the annealed Ni clusters orientate their (002) planes on the (101) of AlN. Moreover, the satellite positions allowed us to calculate Ni cluster average diameters, that are in agreement with average sizes deduced by X-ray absorption spectroscopy. Received 25 August 1999 and Received in final form 8 February 2000     

Influence of Mn doping on structural and optical properties of ZnO nano thin films synthesized by sol–gel technique

Undoped and Mn-doped ZnO samples with different percentages of Mn content (1, 5 and 10?at%) were synthesized by a dip-coating sol?Cgel method. We have studied the structural, chemical and optical properties of the samples by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible spectroscopy. The XRD spectra show that all the samples are hexagonal wurtzite structures. We note that doping favors c-axis orientation along (002) planes. Up to 5?at% of Mn doping level, the c-axis lattice parameter shifts towards higher values with the increase of manganese content in the films. The expansion of the lattice constant of ZnO?CMn indicates that Mn is really doped into the ZnO. The SEM investigations of all samples revealed that the crystallites are of nanometer size. The surface quality of the ZnO?CMn film increases with Mn doping but no significant change of the grain size is observed from SEM images. The transmittance spectra show that the transparency of all the samples is greater than 85?%. We note, also, that a small doping (1?%) lowered the refractive index while the thickness of the layers and the gap increase. However, on raising the proportion of Mn beyond 5?%, practically the same values of index and gap as pure ZnO are found.     

Spectral Investigations on Cu<Superscript>2+</Superscript>-Doped ZnO Nanopowders

Cu²⁺-doped ZnO nanopowders, synthesized at room temperature by mild and simple solution method, are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), optical, electron paramagnetic resonance (EPR) and Fourier-transform infrared (FT-IR) techniques. From XRD and SEM, the crystal structure is identified as hexagonal, and the average crystallite size is around 53 nm. Lattice cell parameters are evaluated. The optical and EPR spectral investigations suggest that the Cu²⁺ ion enters the host lattice in two tetragonally distorted octahedral sites. Crystal field, tetragonal field, spin Hamiltonian and bonding parameters are estimated.     

Electric explosion nickel nanopowders

The structure and the morphology of the nickel nanopowders synthesized by an electric explosion of a metallic wire are comprehensively studied. The results of scanning and transmission electron microscopies show that the nickel nanoclusters have a spherical shape with an average diameter of 50 nm. An analysis of X-ray diffraction patterns demonstrates that the lattice parameter of the electric explosion nanopowder particles is larger than the standard parameter. The results of computer experiments agree well with the conclusions drawn from X-ray diffraction data. However, the causes of the lattice distortion in the nickel nanoclusters are still debatable.     

Synthesis and characterization of Ni-Zn ferrite nanoparticles

Nickel zinc ferrite nanoparticles Ni_xZn_1−xFe₂O₄ (x=0.1, 0.3, 0.5) have been synthesized by a chemical co-precipitation method. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, electron paramagnetic resonance, dc magnetization and ac susceptibility measurements. The X-ray diffraction patterns confirm the synthesis of single crystalline Ni_xZn_1−xFe₂O₄ nanoparticles. The lattice parameter decreases with increase in Ni content resulting in a reduction in lattice strain. Similarly crystallite size increases with the concentration of Ni. The magnetic measurements show the superparamagnetic nature of the samples for x=0.1 and 0.3 whereas for x=0.5 the material is ferromagnetic. The saturation magnetization is 23.95 emu/g and increases with increase in Ni content. The superparamagnetic nature of the samples is supported by the EPR and ac susceptibility measurement studies. The blocking temperature increases with Ni concentration. The increase in blocking temperature is explained by the redistribution of the cations on tetrahedral (A) and octahedral (B) sites.     

Effect of iron doping on the structural and magnetic properties of ZnO nanoparticles prepared by pulsed electron beam evaporation

Nanocrystalline ZnO, ZnO-Zn, and ZnO-Zn-Fe powders with a specific surface area up to 45 m²/g and a low Fe concentration (no more than 0.619 wt %) have been prepared using pulsed electron beam evaporation. The crystal structure, morphology, and size of the nanoparticles have been determined using X-ray powder diffraction, transmission electron microscopy, and scanning electron microscopy. It has been found that the magnetization of the ZnO-Zn and ZnO-Zn-Fe nanopowders increases after annealing in an oxidizing atmosphere. An elemental mapping with energy-dispersive X-ray analysis has revealed the absence of Fe clusters in the ZnO-Zn-Fe sample. A thermal analysis has demonstrated that dopants of Fe in ZnO increase the temperature of complete oxidation of Zn nanoparticles to 600°C, which creates favorable conditions for an increase in the density of structural defects upon oxidation of Zn to ZnO. The absence of clusters and secondary magnetic Fe phases in pure and doped ZnO-based nanopowders indicates the intrinsic nature of ferromagnetism at room temperature in nanopowders prepared by pulsed electron beam evaporation.     

低温缓冲层对氧化锌薄膜质量的影响

利用金属有机化学气相沉积(MOCVD)法,在Si衬底上外延生长ZnO薄膜。为了改善氧化锌薄膜的质量,首先在Si衬底上生长低温ZnO缓冲层,然后再生长高质量的ZnO薄膜。通过XRD、SEM、光致发光(PL)光谱的实验研究,发现低温ZnO缓冲层可有效降低ZnO薄膜和Si衬底之间的晶格失配以及因热膨胀系数不同引起的晶格畸变。利用低温缓冲层生长的ZnO薄膜的(002)面衍射峰的强度要比直接在Si上生长的ZnO薄膜样品的高,并且衍射峰的半高宽也由0.21°减小到0.18°,同时有低温缓冲层的样品室温下的光致发光峰也有了明显的增高。这说明利用低温缓冲层生长的ZnO薄膜的结晶质量和光学性质都得到了明显改善。