退火温度对Ti0.95Fe0.05O2纳米颗粒结构和磁性的影响

采用溶胶-凝胶工艺制备了磁性Fe掺杂TiO2基稀磁半导体的纳米颗粒,在空气氛围中以不同温度对样品进行退火处理.通过差热/热重综合热分析仪(TG-DTA)、X射线衍射仪(XRD)、拉曼光谱(Raman)分析了纳米颗粒的结构和相变温度.研究发现:退火温度450℃和500℃时样品为锐钛矿结构,在600℃时既有锐钛矿相,又有金...     

Co掺杂量对Ti1-xCoxO2纳米颗粒结构及磁性的影响

以钛酸丁酯、六水硝酸钴等为原料,采用溶胶凝胶法合成Ti1-xCoxO2干凝胶前驱体,将前驱体在500℃空气氛围下进行退火处理,得到一系列Ti1-xCoxO2纳米颗粒样品.采用差热/热重综合热分析仪(TG-DTA)、X射线衍射仪(XRD)、拉曼光谱(Raman)和振动样品磁场计(VSM)对样品的结构和磁性进行研究.结果表...     

锂铁氧体纳米晶磁性的研究

研究了颗粒平均直径由9.1—860nm范围的锂铁氧体纳米晶的磁性.它们的比饱和磁化强度σ_s随其颗粒尺寸减小而线性减小.测量了样品A(颗粒直径为D=860nm),样品B(D=11.8nm)和样品C(D=9.1nm)的比饱和磁化强度随温度的变化曲线σ(T)和穆斯堡尔谱.发现样品B和C的居里温度比样品A的低50℃.从样品C的σ(T)曲线看,样品C好像由二种磁相所构成.利用超顺磁和表面磁性讨论了样品C的特异磁性. 关键词：     

用SAXS和XRD方法研究Ti02纳米颗粒微观结构

用溶胶一凝胶方法制备了TiO2纳米样品.并对该样品在300℃到800℃温度区域进行了退火处理.应用同步辐射x射线粉未衍射(XRD)方法研究了经不同热处理温度的TiO2纳米颗粒的结构相变.应用同步辐射小角x射线散射(SAXS)方法研究了TiO2纳米颗粒的表面分形与界面特性.得到纳米颗粒粒度与退火温度的变化规律,讨论r表面界面特征与相变的关系.     

锰锌铁氧体纳米粒子制备与热磁性研究

采用化学共沉淀法制备锰锌铁氧体磁性颗粒并进行了表征,用X射线荧光光谱仪（XRF）、X射线衍射（XRD）测试分析了颗粒组成、结构、平均粒径,表明制备的样品为锰锌铁氧体纳米粒子,平均粒径约为17nm.用振动样品磁强计（VSM）测量了颗粒的磁滞回线和热磁特性.     

温和的苯热溶剂条件下GaP纳米棒的形成机理研究

采用金属Na，白磷和GaCl₃为原料，在温和的苯热溶剂条件下制备了直径为20—40nm，长度为200—500nm的GaP纳米棒和直径为20—40nm的球形颗粒.利用X射线衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)研究了反应条件对产物结晶性和形貌的影响.实验结果表明，当反应温度低于250℃时，产物基本上为GaP纳米棒，并随着反应温度升高，产物逐渐转化为球形纳米颗粒；当反应温度超过280℃时，产物完全为规则的球形.同时，GaP纳米棒的生长遵循SLS生长机理. 关键词： 纳米GaP 苯热 SLS生长机理     

用SAXS和XRD方法研究TiO2纳米颗粒微观结构

用溶胶-凝胶方法制备了TiO₂纳米样品,并对该样品在300℃到800℃温度区域进行了退火处理.应用同步辐射X射线粉末衍射(XRD)方法研究了经不同热处理温度的TiO₂纳米颗粒的结构相变.应用同步辐射小角X射线散射(SAXS)方法研究了TiO₂纳米颗粒的表面分形与界面特性.得到纳米颗粒粒度与退火温度的变化规律,讨论了表面界面特征与相变的关系. 关键词： X射线小角散射 X射线衍射 2纳米颗粒')" href="#">TiO₂纳米颗粒     

H2O2氧化法制备Fe3O4纳米颗粒及与共沉淀法制备该样品的比较

在近中性条件下,利用H2O2氧化Fe(OH)2胶体成功制备了Fe3O4纳米颗粒.分别利用透射电镜(TEM),x射线衍射仪(XRD),振动样品磁强计(VSM)和超导量子干涉仪(SQUID)对样品的形貌,结构,宏观磁性进行了表征和测量.TEM图像表明样品为球形颗粒,直径大小约18nm,且分布较均匀.XRD结果表明样品为立方尖晶石结构.穆斯堡尔谱测量表明样品室温下对应两套六线谱,样品的晶体结构存在缺陷,内磁场略小于块体Fe3O4的值.宏观磁测量表明样品的饱和磁化强度可达67×10-3A·m2/g,在20 K出现了Verwey转变.选择该法制备的Fe3O4纳米颗粒与共沉淀法得到的样品作了磁性比较.宏观磁测量表明共沉淀法制备的样品在外磁场为1T时仍未饱和,磁化强度仅为46×10-3A·m2/g,在178K出现了超顺磁转变温度,且在测量温度范围内没有发现Verwey转变.     

纳米镁粉对制备MgB2超导样品的作用

我们对用纳米镁粉(平均颗粒度≤40nm)在常压下制备MgB2超导样品(以下简称纳米MgB2超导样品)进行了研究.得到了一组与用普通颗粒镁粉分别在真空条件下和流动氩气下制备MgB2超导样品时得到的原位ρ-T曲线不同的曲线.实验结果表明纳米MgB2超导样品的成相温区是430℃到490℃之间,低于用普通颗粒镁粉分别在真空条件下和流动氩气下制备MgB2超导样品时的成相温度:640℃～700℃和530℃～630℃.所得到的纳米MgB2超导样品的密度是1.46g/cm3.它高于用其他各种镁粉原料在常压下制备通过一次烧结制得的MgB2超导样品.     

竹节状α-Fe2O3纳米棒的制备、表征和性能研究

以硝酸铁为铁源,氨水为沉淀剂,聚乙二醇(PEG)为分散剂,采用共沉淀法制备氢氧化铁前驱体,然后将获得的前驱体在450℃、氮气保护下热处理2 h,最后利用透射电镜、X射线衍射、拉曼光谱和近边X射线精细结构光谱(NEXAFs)表征样品的形貌和结构,并使用HH-50型振动样品磁强计测量样品在室温下的磁学行为.透射电镜结果显示,获得的样品由氧化铁纳米颗粒和竹节状氧化铁纳米棒组成,纳米颗粒的粒径范围为50～100 nin,纳米棒的直径大约为10 nin.XRD表征显示样品中氧化铁纳米棒和纳米颗粒为赤铁矿型α-Fe2O3;光谱实验结果证实了样品中氧化铁纳米颗粒和纳米棒的结构是α-Fe2O3;磁学性能测试表明获得的样品表现为典型铁磁性材料的磁滞回线,其饱和磁感应强度约为64.65 emu·g-1,矫顽力的大小约为15.13 Oe.     

形貌可控的Fe3O4纳米粒子的水热合成及磁性能研究

Fe3O4是一种重要的磁性材料.由于其独特的光、电、磁、热等性能而备受关注.在本文中,我们采用水热溶剂热法合成了Fe3O4磁性纳米粒子.利用X-射线衍射仪（XRD）、场发射扫描电子显微镜（FESEM）和振动样品磁强计（VSM）对产物的结构、形貌及磁性能进行了研究.结果表明,通过前驱物的适当选择,可以实现Fe3O4纳米粒...     

TiO2及其掺Fe材料的制备和EPR谱的研究

以钛酸四丁酯、无水乙醇、冰醋酸为原料,在室温下用溶胶-凝胶法制备得到二氧化钛及其掺Fe样品的湿凝胶,室温放置2天后,100 ℃干燥得到干凝胶,在500 ℃下焙烧得到二氧化钛及其掺Fe的粉末状样品. 利用X射线衍射、电子顺磁共振等测试手段对样品进行分析,结果显示所得样品均为锐钛矿,Fe被引入了二氧化钛晶格中,Ti³⁺氧化中心信号强度随Fe掺杂量的增加而增强,峰值向磁场减小方向小幅偏移. 在不同测试温度下, 含Fe量为0.1%的Fe-TiO₂样品中Ti³⁺氧化中心信号强度随温度升高而增强,峰值也向磁场减小方向小幅偏移. 根据电子顺磁共振理论以及二氧化钛在空气中与O₂的反应解释了这些现象.     

Non-equilibrium cation distribution and enhanced spin disorder in hollow CoFe2O4 nanoparticles

We present magnetic properties of hollow and solid CoFe(2)O(4) nanoparticles that were obtained by annealing of Co(33)Fe(67)/CoFe(2)O(4) (core/shell) nanoparticles. Hollow nanoparticles were polycrystalline whereas the solid nanoparticles were mostly single crystal. Electronic structure studies were performed by photoemission which revealed that particles with hollow morphology have a higher degree of inversion compared to solid nanoparticles and the bulk counterpart. Electronic structure and the magnetic measurements show that particles have uncompensated spins. Quantitative comparison of saturation magnetization (M(S )), assuming bulk Néel type spin structure with cationic distribution, calculated from quantitative XPS analysis, is presented. The thickness of uncompensated spins is calculated to be significantly large for particles with hollow morphology compared to solid nanoparticles. Both morphologies show a lack of saturation up to 7 T. Moreover magnetic irreversibility exists up to 7 T of cooling fields for the entire temperature range (10-300 K). These effects are due to the large bulk anisotropy constant of CoFe(2)O(4) which is the highest among the cubic spinel ferrites. The effect of the uncompensated spins for hollow nanoparticles was investigated by cooling the sample in large fields of up to 9 T. The magnitude of horizontal shift resulting from the unidirectional anisotropy was more than three times larger than that of solid nanoparticles. As an indication signature of uncompensated spin structure, 11% vertical shift for hollow nanoparticles is observed, whereas solid nanoparticles do not show a similar shift. Deconvolution of the hysteresis response recorded at 300 K reveals the presence of a significant paramagnetic component for particles with hollow morphology which further confirms enhanced spin disorder.     

Effect of a SiO2 coating on the magnetic properties of Fe3O4 nanoparticles

In this work the effect of a SiO2 coating on the magnetic properties of Fe3O4 nanoparticles obtained by the sol-gel method is analyzed. Two sets of samples were prepared: Fe3O4 nanoparticles and Fe3O4@SiO2 core-shell composites. The samples display the characteristic spinel structure associated with the magnetite Fe3O4 phase, with the majority of grain sizes around 5-10 nm. At room temperature the nanoparticles show the characteristic superparamagnetic behavior with mean blocking temperatures around 160 and 120 K for Fe3O4 and Fe3O4@SiO2, respectively. The main effect of the SiO2 coating is reflected in the temperature dependence of the high field magnetization (μ(0)H = 6 T), i.e. deviations from the Bloch law at low temperatures (T < 20 K). Such deviations, enhanced by the introduction of the SiO2 coating, are associated with the occurrence of surface spin disordered effects. The induction heating effects (magnetic hyperthermia) are analyzed under the application of an AC magnetic field. Maximum specific absorption rate (SAR) values around 1.5 W g(-1) were achieved for the Fe3O4 nanoparticles. A significant decrease (around 26%) is found in the SAR values of the SiO2 coated nanocomposite. The different heating response is analyzed in terms of the decrease of the effective nanoparticle magnetization in the Fe3O4@SiO2 core-shell composites at room temperature.     

Phosphine-free synthesis of FeTe_2 nanoparticles and self-assembly into tree-like nanoarchitectures

Manipulating the self-assembly of transition metal telluride nanocrystals(NCs) creates opportunities for exploring new properties and device applications. Iron ditelluride(FeTe_2) has recently emerged as a new class of magnetic semiconductor with three-dimensional(3D) magnetic ordering and narrow band gap structure, yet the self-assembly of FeTe_2 NCs has not been achieved. Herein, the tree-like FeTe_2 nanoarchitectures with orthorhombic crystal structure have been successfully synthesized by hot-injection solvent thermal approach using phosphine-free Te precursor. The morphology, size, and crystal structure have been investigated using transmission electron microscopy(TEM), high-resolution TEM(HRTEM),and powder x-ray diffraction(XRD). We study the formation process of tree-like FeTe_2 NCs according to trace the change of the sample morphology with the reaction time. It was found that the FeTe_2 nanoparticles show oriented aggregation and self-assembly behavior with the increase of reaction time, which is attributed to size-dependent magnetism properties of the samples. The magnetic interaction is thought to be the driving force of nanoparticle self-organization.     

新型螯合磁性纳米Fe_3O_4的制备及其性能研究

采用共沉淀法制备了磁性四氧化三铁(Fe3O4)纳米粒子,并通过硅烷偶联剂对其表面进行改性,进一步在其表面偶联修饰氨基硫脲,制备了螯合磁性纳米Fe3O4粒子。利用广角X射线衍射仪(WAXD)、红外光谱仪(FTIR)、分光光度计等对磁性纳米粒子的结构和性能进行了表征。结果表明,纳米Fe3O4为反尖晶石结构,通过偶联修饰可以实现氨基硫脲在纳米粒子表面的化学改性。螯合磁性纳米粒子具有良好的分散性和磁响应性,且对多种金属离子(Pb2+、Hg2+、Zn2+、Cd2+)具有良好的螯合效果。     

NiFe_2O_4纳米粉末的制备及磁性研究

以硝酸铁、硝酸镍以及柠檬酸为原料,采用凝胶-热分解法制备了N iFe2O4纳米粉末。利用X射线衍射确定了粉体的相结构、比表面积和晶格常数,扫描电子显微镜(SEM)观察了颗粒的形貌,振动样品磁强计(VSM)测量样品的磁性能。结果表明:所制备的样品均为尖晶石结构,颗粒粒径为36nm~68nm,且颗粒的粒径随着热处理温度的升高而增大,样品的比饱和磁化强度最大可达54.63 emu/g。同时,文章也对反应的动力学原理进行了研究,得出N iFe2O4纳米颗粒形成的活化能为15.8kJ/mol。     

Gas-phase preparation and size control of Fe nanoparticles

The magnetic, electrical and optical properties of nanoparticle systems often depend on the size and size distribution of nanoparticles. In order to optimize those properties of nanoparticle-assembled materials, only varying the mean size of nanoparticles was not enough, and narrowing the size distribution was also of immense importance. In this study, uniform-sized Fe nanoparticles with different diameters were prepared using a magnetron sputtering combined with inert gas condensation technique. The size and morphology of nanoparticles were observed by transmission electron microscopy (TEM). The statistic results revealed that the size of Fe nanoparticles increased with increasing the flow rate of Ar gas, but a reverse trend was observed when increasing the flow rate of He gas. By adjusting the flow rate of Ar and He gases, uniform-sized Fe nanoparticles with diameter ranging from 6 to 13?nm were obtained. Moreover, the size effects on the electrical and magnetic properties of Fe nanoparticle-assembled films with thickness of about 500?nm were also investigated. The magnetic properties showed that the coercivity increased with increasing the nanoparticle size. The in-situ resistance measurement results of Fe nanoparticle assembled-films also showed a size-dependent behavior.