金纳米微粒晶格畸变和结合能的尺寸形状效应

利用紧束缚分子动力学的方法,模拟了球形和立方体金纳米微粒的最近邻原子间距以及结合能.研究表明,原子数为108,256的立方体纳米微粒的稳定结构是非晶态,而其他尺寸的球形和立方体形微粒则是面心立方结构.对于晶态结构,在一定的形状下,金纳米微粒的最近邻原子间距以及结合能随着微粒尺寸的减小而降低;而在微粒原子数一定时,球形金纳米微粒的最近邻原子间距以及结合能的变化量分别要小于立方体形微粒的相应变化量.由于晶体-非晶转变对于最近邻原子间距的影响非常明显,因此最近邻原子间距可以作为晶态和非晶态纳米微粒的一个判据.通过线性拟合模拟数据,定量地给出了形状对于最邻近原子间距变化量的贡献为总变化量的2%,而对于结合能的贡献为总变化量的15%.本文模拟的最近邻原子间距的数值与文献上报道的实验结果符合得很好.     

溅射超薄Ag膜中的晶格畸变

用直流溅射法制备了厚度从11．9到189．0nm的超薄Ag膜。X射线衍射（XRD）分析表明：样品中的Ag均为面心立方多晶结构，粒径从6.3到14.5nm。通过晶格常数的计算发现：晶格畸变为收缩，且随着粒径的减小收缩率增加，最大值为1．1％。结合不同方法制备纳米Ag材料的研究结果，讨论了影响晶格畸变的主要因素。     

氢致奥氏体不锈钢晶格畸变

对304L和316L奥氏体不锈钢试样在充氢后和充氢同时进行X射线衍射分析,观察到在充氢过程中存在奥氏体晶格膨胀-收缩-膨胀的现象;在充氢后时效一段时间的情况下,存在奥氏体晶格收缩-膨胀-收缩的现象,并初步讨论了可能的原因。     

纳米二氧化钛热处理过程研究

以四氯化钛为原料,采用碱中和法制备水合二氧化钛,然后在不同温度下热处理分别制备锐钛型纳米二氧化钛和金红石型纳米二氧化钛。采用拉曼光谱、XRD和紫外可见光谱等手段分析了热处理过程对样品的晶体结构、比表面积、微孔体积、紫外吸收光谱等性能的影响。试验结果表明,未经热处理的样品存在氧空位缺陷,具有较大的晶格畸变,随着热处理温度的提高,样品晶粒尺寸从6 nm逐渐长大至70 nm,比表面积从186 m~2·g~(-1)减少至5.6 m~2·g~(-1),总孔体积从0.085 cm~3·g~(-1)减小至0.001 3 cm~3·g~(-1),晶型由无定型向锐钛型和金红石相逐步转化,晶格畸变逐渐减小。在600℃以下热处理样品为锐钛型,在600～650℃的温度下处理形成金红石与锐钛的混晶,680～750℃有六钛酸钠生成,800℃以后全部转化为金红石结构。     

纳米稀土铁氧体磁性颗粒的制备研究

采用湿化学方法研究制备纳米稀土铁氧体磁性颗粒，研究纳米稀土铁氧体颗粒制备过程中主要影响因素，如pH和RE^3＋等对纳米稀土铁氧体颗粒粒径及磁性能的影响；同时对纳米Dy铁氧体颗粒的形貌、粒度分布、晶型结构及磁性能进行了分析和研究。研究发现轻稀土对Fe3O4颗粒的磁性有削弱作用，不宜掺杂；重稀土元素掺杂是提高铁氧体磁性颗粒磁性能的有效途径，改善磁性能的强弱顺序为Dy^3＋〉Gd^3＋〉Er^3＋。制备的Dy铁氧体颗粒的平均粒径为9．6nm，比饱和磁化强度98．27A·m^2·kg^-1，具有超顺磁特性。同时讨论了Dy^3＋在Fe3O4的晶体结构中取代Fe离子增强磁性能的可能形式。     

CoO纳米颗粒的制备及磁性研究

用聚乙烯醇溶胶-凝胶法制备出氧化钴(CoO)纳米颗粒。分析了胶体浓度、热处理温度和时间对制备CoO纳米颗粒工艺的影响。用X射线衍射仪和透射电子显微镜对样品的形貌、结构和物相进行了测试，用振动样品磁强计初步探讨了CoO纳米颗粒在室温下的磁性。结果发现胶体浓度为2：1时有利于形成CoO纳米颗粒，在氢气环境下对干胶进行煅烧时生成CoO纳米颗粒的温度范围在225～350℃之间。CoO纳米颗粒的结构为NaCl结构。在较低温度下烧结干胶时发现颗粒尺寸随着热处理时间的增加变化不大。用此方法制备的CoO纳米颗粒直径最小约为12nm。在室温下表现为类似于超顺磁性的特征。     

纳米级金属铁颗粒的制取

探讨了热解羰基铁法制备了纳米级金属铁颗粒的工艺过程与影响因素，并以羰基铁为原料通过热解成功地制取了纳米级金属铁颗粒。     

光还原法制备Cu/ZnO纳米复合粉末

使用四针状ZnO纳米晶须作为催化剂，通过光还原法制备Cu／ZnO复合纳米粒子。采用XRD，TEM对样品进行表征。当少量Cu沉积在ZnO晶须表面上时，复合纳米粒子仍为四针状，且由ZnO和Cu2O组成。当大量的Cu沉积在ZnO上时，复合纳米粒子呈颗粒状，且由ZnO，Cu5Zn8和Cu2O三相组成。     

电爆炸法制备金属Cu纳米粉末

本文研究了利用超细金属粉制备系统,采用电爆炸法制备金属Cu纳米粉,并对产物进行了X射线衍射分析(XRD)及透射电镜分析(TEM).实验结果表明:粒度分布均匀,颗粒尺寸小,超细金属粉体纯度高.Cu纳米粉的粒度分布40～100 nm,平均粒径为60 nm.     

Effect of Nd~(3+) doping on structure,microstructure, lattice distortion and electronic properties of TiO_2 nanoparticles

Doped and undoped TiCh nanoparticles were prepared by Stober method and thermally treated at 600 ℃.The effect of Nd~(3+) ion on the structure and micro structure of anatase-phase TiCh nanocrystals was studied by Rietveld refinement method using X-ray powder diffraction data.Bond lengths,bond angles,and edges distances were analyzed.The phase formation was confirmed by high-resolution transmission electron microscopy.The adjustment of Ti-0 bond length induced by the addition of Nd~(3+) ions,reduced the octahedral distortion and altered the octahedral array in the anatase-phase TiCh nanocrystal.The changes of structure and microstructure were mainly observed for TiCh nanoparticles doped with 0.1 at.%of Nd~(3+) ions and attributed to the cationic substitution of Ti~(4+) ions which promoted changes in the density of states and gap band of TiCh.The dopant insertion resulted in a better structural stability of the nanocrystals that enhanced their charge transference and photocatalytic efficiency.     

Computer simulation of local lattice distortion in Cu-Au solid solution

The local lattice-distortion effects in Cu-25 at Pct Au solid solution were investigated using a computer simulation in which the nearest-neighbor Lennard-Jones interactions with thermal vibration effects were assumed. The investigation revealed that the average displacements of Cu-Cu and Au-Au pairs in the nearest neighbor were negative and positive directions, respectively, with respect to the rigid lattice before the relaxation, and that the diffuse scattering intensity due to local lattice distortion and local atomic configuration can be calculated by taking the short-range configuration up to the 12th nearest-neighbor pairs into account. The results reproduced the overall tendency of the experimental observations. Formerly Graduate Student, Department of Metallurgical Engineering, Hokkaido University.     

Calculation of the lattice distortion due to carbon inα-iron

A method for calculating the static displacements of lattice atoms near a defect atom is presented and applied to carbon occupying the octahedral site in α-iron. The interaction between lattice atoms and the defect is assumed to extend to second neighbors, but a defect-lattice atom interatomic potential is neither assumed nor constructed. Instead the displacements of the first and second neighbors of the defect atom are treated as adjustable parameters, which can be determined experimentally, and the displacement field is calculated as a function of these parameters. A central, two-body Morse potential is used to describe the interaction of lattice atoms, and the lattice atom displacements are calculated for both harmonic and anharmonic (quartic) approximations of the potential. The latter calculation requires an iterative procedure that obtains self-consistent anharmonic displacements without sacrificing the convenience of the matrix inversion technique that is used to solve the harmonic problem. Formerly with Argonne National Laboratory, Idaho Falls, ID     

Thermodynamic consideration of the tetragonal lattice distortion of the L10 ordered phase

In an attempt to understand the thermodynamic consequences of the tetragonal distortion accompanying the L1₀ ordering, we have conducted a theoretical investigation by treating the problem of a rigid lattice free energy model. The problem is treated as an elasticity problem and a generalized formulation is proposed in a form which can be directly utilized to study incoherent two phase equilibria. By use of the Static Concentration Wave (SCW) mean field model as a rigid lattice free energy model, the formulation is applied to the case of our interest. We show that the thermodynamic stability of the L1₀ phase may be significantly influenced by the tetragonal lattice distortion, depending on the magnitude of the associated strain energy relative to the competing positive entropic contribution in the free energy of the stress free L1₀ phase. In association with this, we suggest that the neglect of tetragonal distortion (i.e. the use of a rigid lattice free energy model) could be a source of serious errors particularly for alloys with lower L1₀ ordering transition temperatures (e.g. CuAu and InMg). A prototype phase diagram of the 〈001〉_f.c.c.¹ special point structures, calculated with the tetragonal distortion taken into account, has indeed displayed topological features which are fundamentally different from those of a rigid lattice phase diagram and, furthermore, has reproduced the main topological features of the AuCuAu₃Cu and the InMgIn₃Mg sides of their respective phase diagrams.     

Production of copper nanoparticles by electrochemical process

There are numerous methods for preparing copper nanoparticles of which electrodeposition is one of the most suitable and simplest. The electrolyte used in the present investigation is an acidified aqueous solution of copper sulphate with suitable additives. By varying the input dc voltage with a constant current, a spongy layer of copper particles is deposited on the cathode surface. Particles are collected and characterized by XRD and UV-Vis, the surface morphological characterization is done by SEM and TEM.