Journal of Non-Crystalline Solids
Complete solid-state amorphization has been realized in elemental selenium by means of mechanical milling of crystalline Se powder. Extended X-ray-absorption fine-structure measurements (EXAFS) indicated that the amorphization process of crystalline Se was accompanied with a decrease of the nearest neighboring coordination number and the bond length, and the increase of the Debye-Waller factor. Combined with the previous study, we conclude that the mechanical milling results in the strengthening of intra-chain and weakening of inter-chain interactions of Se during amorphization. Compared to the structure of the as-quenched amorphous Se, the first nearest neighbor coordination number of the as-milled amorphous Se becomes smaller, while the Debye-Waller factor is larger, which is caused by the milling process. (C) 2004 Published by Elsevier B.V.
关键词:
absorption fine-structure;different grain sizes;amorphous selenium;silicon;attrition;crystal;alloys;zr
Nanostructured Materials
Lattice parameters for nanocrystalline (nc) materials were found to be alerted with respect to the corresponding coarse-grained polycrystalline counterparts in several systems. In this work, experimental evidences of the lattice structure distortion in various nc materials processed by means of different approaches will be summarized and discussed. Strong evidences showed the lattice structure distortion in nc samples which is manifested by an evident change in the lattice parameters, Debye-Waller parameter, and the thermal properties of the nanocrystalline lattice. These results imply that the property changes of nc materials should be attributed not only to the numerous non-equilibrium grain boundaries, but to the distorted nanocrystallites as well. (C) 1999 Acta Metallurgica Inc.
关键词:
x-ray-diffraction;thermal-properties;selenium;metals
刘文
,
黄胜涛
,
唐承欢
,
李苏桥
,
汪根时
,
曹明中
材料研究学报
本文用扩展X 射线吸收谱(EXAFS)研究了晶态、非晶态TiCu 合金及其氢化物的结构。从CuK 吸收限的EXAFS 数据计算了这些样品中Cu 原子最近邻原子壳层的径向距离R,配位数N 和Debye—Waller 因子σ~2,并讨论了氢原子进入点阵间隙后对R、N、σ~2的影响、金属原子间的成键特征及其产生原因。此外还对这种合金的高吸氢量性质作了理论解释。
关键词:
Nanostructured Materials
The precise X-ray diffraction structural study of a nanocrystalline Cu sample processed by severe plastic deformation was carried out. The obtained results were compared with the data fi om an initial reference Cu sample. By analysis of the centroid position, broadening, shape of Bragg reflections and background integrated intensities from these two samples, such structural features as a lattice parameter, crystallite size, r.m.s. microstrain, dislocation density Debye-Waller parameter and atomic displacements were determined. A conclusion concerning the specific defect structure in the nanocrystallite Cu sample was drawn. (C) 1997 Acta Metallurgica Inc.
关键词:
crystalline
Physical Review B
Porosity-free nanocrystalline (nc) element Se samples with mean grain sizes ranging from 13 to 70 nm were synthesized by crystallizing a melt-quenched amorphous Se solid. Microstructures of the nc-Se (with a hcp structure) samples were characterized by means of quantitative x-ray-diffraction measurements. The Bragg reflection-and the background intensities, as well as the reflection shape of the x-ray-diffraction patterns for the ne Se were analyzed according to data fitting of Me measurement results. The grain-size dependencies of the microstrain, lattice parameters, unit-cell volume, and the mean Debye-Waller parameter were determined. With a reduction of grain size, the microstrain increases significantly along [100] direction but decreases along [104] direction, and exhibits an increasing anisotropic microstrain behavior. The lattice parameter a was found to increase evidently while c decreased slightly with a decreasing gain size, resulting in a significant lattice distortion vith a dilated unit-cell volume. it agrees with the observation that the mean Debye-Waller parameter increases with a reduction of grain size, suggesting larger displacements of atoms from their ideal lattice sites in the nc-Se samples with smaller grains. The similarity of the grain-size dependencies of these structural parameters as that of the grain-boundary volume fraction implies that the intrinsic microstructure feature of ne materials is closely related to the crystallite dimension and the amount of grain boundaries.
关键词:
x-ray-diffraction;particles;alloys;pd;cu
Acta Materialia
The microstructural evolution and thermal properties of nanocrystalline (nc) Fe during mechanical attrition were investigated by using quantitative X-ray diffraction and thermal analysis techniques. Upon milling of the Fe powders with coarse grains, grain refinement takes place gradually and a steady-state grain size in the nanometer regime is reached after a certain period of milling. With the further milling of the nc Fe within the stage of the steady-state grain size, we observed a grain boundary relaxation process that was manifested by evident decreases in the thermal expansion coefficient and the stored enthalpy, as well as slight decreases in the lattice strain and the Debye-Waller parameter. The grain boundary enthalpy of the nc Fe was estimated, showing a decreasing tendency with the milling time. The present work indicated with clear experimental evidence that the nc materials with the same grain size may exhibit very different properties that depend upon the microstructure of the numerous metastable grain boundaries. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
关键词:
attrition;X-ray diffraction (XRD);iron;microstructure;thermal;properties;x-ray-diffraction;grain-size dependence;thermodynamic properties;metals;iron;particles;selenium;temperature;boundaries;expansion
常龙存
,
陆坤权
,
赵雅琴
,
韩福森
,
赵忠贤
金属学报
用RU-1000转靶X射线源及其测角仪系统,采集了金属玻璃Cu_(70)Ti_(30)室温(T=300K)和低温(T=80K)Cu的K吸收EXAFS谱。用本实验室编的“EXAFS数据处理程序库”对数据进行处理,以理论计算背散射振幅及相移值作数据拟合的方法,得到Cu原子与近邻原子的间距、配位数及Debye-waller因子等。讨论了Cu_(70)Ti_(30)金属玻璃中化学短程有序及Cu原子近邻结构的特征。
关键词:
Journal of Applied Physics
X-ray diffraction investigations in a temperature range from 85 to 295 K were performed on an ultrafine-grained (UFG) Ni sample processed by severe plastic deformation. A significantly enhanced thermal expansion coefficient of 3.75x10(-5) K-1 was observed in the UFG Ni sample, which is three times higher than in the conventional coarse-grained Ni polycrystal. The Debye-Waller parameter and its temperature-dependent and temperature-independent components are revealed to be larger in the UFG Ni sample. The obtained Debye temperature in the UFG Ni sample is decreased by 22%. The altered thermal properties in the UFG Ni sample are attributed to the nonequilibrium dislocations that disturb grain boundaries leading to large atomic displacements near interfaces. (C) 1998 American Institute of Physics. [S0021-8979(98)08416-3]
关键词:
x-ray-diffraction;submicrocrystalline structure;copper
