H. G. Haubruge  X. A. Gallez  B. Nysten  A. M. Jonas 《Journal of Applied Crystallography》2003,36(4):1019-1025

Image analysis of semi‐crystalline polymer systems in reciprocal space allows quantitative measurement of characteristic periodicities of the material. This paper proposes numerical techniques for the computation of power spectral densities (PSD) and correlation functions, appropriate to this objective, along with a theoretical justification. These methods are applied to transmission electron micrographs of isotactic polypropylene (iPP) and poly(ethylene terephthalate) (PET). Measured characteristic periodicities arise from electronic contrast between crystalline and stained amorphous phases. They correlate well with results obtained by small‐angle X‐ray scattering (SAXS) on non‐stained samples.  相似文献   

    

Axel Steuwer  Javier Roberto Santisteban  Philip J. Withers  Lyndon Edwards  Mike E. Fitzpatrick 《Journal of Applied Crystallography》2003,36(5):1159-1168

The pulsed neutron transmission diffraction technique exploits the sharp steps in intensity (Bragg edges) appearing in the transmitted spectra of thermal neutrons through polycrystalline materials. In this paper the positions of these edges acquired by the time‐of‐flight (TOF) technique are used to measure accurately the interplanar lattice distances to a resolution of Δd/d≃ 10⁻⁴ of specimens subjected to in situ uniaxial tensile loading. The sensitivity of the method is assessed for elastically isotropic (b.c.c. ferritic) and anisotropic (f.c.c. austenitic) polycrystalline specimens of negligible and moderately textured steels. For the more anisotropic austenitic steel, the elastic anisotropy is studied with regard to a Pawley refinement, and compared with previous results from conventional neutron diffraction experiments on the same material. It is shown that the method can be used to determine anisotropic strains, diffraction elastic constants, the residual and applied stress state as well as the unstrained lattice parameter by recording transmission spectra at different specimen inclinations, by complete analogy with the sin²ψ technique frequently used in X‐ray diffraction. The technique is shown to deliver reliable measures of strain even in the case of moderate texture and elastic anisotropy.  相似文献   

    

D. Schwabe  A. Polity 《Crystal Research and Technology》2003,38(10):868-873

We report the construction, operation and performance of a transmission spectrometer for the visible to the IR (up to 3.5 μm wavelength) to measure crystals up to a temperature of 1400 °C. The spectral resolution is almost comparable to that of a commercial spectrometer. The performance of the spectrometer and some problems are demonstrated by spectra of YAG : Nd at different temperatures. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

K. Watanabe  Y. Kikuchi  T. Yamazaki  E. Asano  N. Nakanishi  Y. Kotaka  E. Okunishi  I. Hashimoto 《Acta Crystallographica. Section A, Foundations and Advances》2004,60(6):591-597

Atomic resolution low‐angle bright‐field (LABF) scanning transmission electron‐microscope (STEM) images and high‐angle bright‐field (HABF) STEM images of [011]‐orientated Si have been experimentally obtained together with high‐angle annular dark‐field (HAADF) STEM images. The contrast formation mechanisms of the LABF STEM and HABF STEM images are examined in comparison with HAADF STEM images. The HABF STEM images independent of defocus and thickness have spatial resolution comparable with HAADF STEM images, and are shown to be given as a simple convolution under the non‐dispersion approximation of localized Bloch waves.  相似文献   

    

M. Boin  A. Hilger  N. Kardjilov  S. Y. Zhang  E. C. Oliver  J. A. James  C. Randau  R. C. Wimpory 《Journal of Applied Crystallography》2011,44(5):1040-1046

The ability to resolve the wavelength in neutron transmission experiments has opened up a wide range of applications investigating crystallographic structures and properties. The investigations presented in this paper apply the Bragg edge transmission technique to the study of texture in a cylindrical aluminium specimen. The feasibility of this method is the main focus of this work; hence, conventional pole‐figure measurements have been conducted with neutron diffraction to provide reference data for the evaluation of the transmission results. Furthermore, a Monte Carlo simulation has been developed to emulate the experimental conditions and allow investigations of instrument effects. The results have been compared and are discussed with respect to quantitative texture analysis.  相似文献   

    

Gang Ji  Jean‐Paul Morniroli 《Journal of Applied Crystallography》2013,46(2):430-442

The space group of a new metastable orthorhombic Al₂Cu phase, located in the Al‐rich interfacial region of an Al–Cu friction stir weld, was unambiguously identified as Ic2m by a recently developed systematic method combining precession electron diffraction and convergent‐beam electron diffraction. This metastable phase has the same tetragonal lattice as its stable θ‐Al₂Cu counterpart (tetragonal, I4/mcm, No. 140). The tetragonal‐to‐orthorhombic symmetry lowering is due to slight modifications of the atomic positions in the unit cell. This metastable phase can be transformed into the stable θ‐Al₂Cu phase by in situ irradiation within the transmission electron microscope.  相似文献   

    

N. Kumar  V. Sharma  N. Padha  N. M. Shah  M. S. Desai  C. J. Panchal  I. Yu. Protsenko 《Crystal Research and Technology》2010,45(1):53-58

Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350‐550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (T_s) on the structural, morphological, optical, and electrical properties of the films were investigated using x‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall‐effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80‐330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all T_s. With the increase of T_s the intensity of the diffraction peaks increased and well‐resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38‐1.18 eV. Hall‐effect measurements revealed the resistivity of films in the range 112‐20 Ω cm for films deposited at different T_s. The activation energy for films deposited at different T_s was in the range of 0.14 eV‐0.28 eV as derived from the analysis of the data of low‐temperature resistivity measurements. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

K. Z. Baba‐Kishi  M. Pasciak 《Journal of Applied Crystallography》2010,43(1):140-150

Incommensurate satellite reflections modulating along the 〈110〉* directions have been observed in the electron diffraction patterns of single crystals of the relaxor ferroelectric Pb₂ScTaO₆ (PST) recorded via transmission electron microscopy. The satellites occur characteristically within a specific temperature range and display differing or variable modulation vectors relative to their primary reflections. The satellites represent a weak frustrated antiferroelectric state in PST, termed the incommensurate antiferroelectric (IAFE) state. The observed IAFE state coexists with the ferroelectric and paraelectric states within a specific temperature regime and is dynamic in nature, meaning that the dispositions of the satellites can be altered by varying the temperature applied to the crystal, in‐situ in the transmission electron microscope. The observed satellites are associated with thin, needle‐shaped, closely packed striated domains of about 5–15 nm in width. The satellites appear exclusively in crystals of PST with an advanced degree of 1:1 chemical long‐range order, exceeding 90%. The satellites and their domains are interpreted as originating from a displacive, antiferroelectric coupling of the ions, driven in particular by the Pb ions. The Monte Carlo (MC) method was used exhaustively to evaluate the structural regimes that lead to the occurrence of the IAFE state. In the MC simulations, the displacements were correlated with the ferroelectric and antiferroelectric couplings, resulting in the IAFE domains and their associated satellites of differing dispositions or modulation vectors. The results of the MC simulations agree well with the electron diffraction observations, supporting the model of an antiferroelectric displacement with an incommensurate modulation of the Pb ions in the 〈110〉* directions.  相似文献   

    

X. H. Sang  A. Kulovits  J. M. K. Wiezorek 《Acta Crystallographica. Section A, Foundations and Advances》2010,66(6):694-702

Accurate Debye–Waller (DW) factors and several low‐index structure factors of chemically ordered β‐NiAl at different temperatures have been measured using an off‐zone‐axis multi‐beam convergent‐beam electron diffraction method. The temperature dependences of DW factors of Ni and Al atoms are compared with previous experimental measurements and theoretical calculations. The temperature below which the DW factor of Ni becomes smaller than that of Al was found to be lower than previously reported. Structure factors are determined with an accuracy of 0.05% and compared with prior reports.  相似文献   

    

X. H. Sang  A. Kulovits  J. M. K. Wiezorek 《Acta Crystallographica. Section A, Foundations and Advances》2010,66(6):685-693

Debye–Waller (DW) factors and structure factors have been measured for Si using convergent‐beam electron diffraction (CBED) experiments with a transmission electron microscope equipped with a field‐emission gun and a post‐column energy‐filtering device. Si has been used here to evaluate the accuracy of multi‐beam near‐zone‐axis orientations for the simultaneous refinement of DW factors and multiple structure factors. Strong dynamic interactions among different beams are obtained by tilting the crystal to specific four‐ or six‐beam orientations near major zone axes, which provide sufficient sensitivity to determine accurate DW factors and structure factors. The DW factors of Si were measured using four‐beam conditions near the [001] zone axis for temperatures ranging from 96 to 300 K. A comparison of the multi‐beam near‐zone‐axis orientations with other CBED methods for DW and structure factor F_g refinement is presented.  相似文献