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Convergent-beam Electron Diffraction (convergent-beam + electron_diffraction)
Selected AbstractsChemInform Abstract: Determination of the Space Group of LaCrO3 by Convergent-Beam Electron Diffraction.CHEMINFORM, Issue 10 2001Takuya Hashimoto Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Zinc Vanadates in Vanadium Oxide-Doped Zinc Oxide VaristorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2001Huey-Hoon Hng Convergent-beam electron diffraction has been used to determine the space groups of ,- and ,-Zn3(VO4)2 particles in vanadium oxide-doped zinc oxide varistors. The crystal structure of ,-Zn3(VO4)2 has been determined to be monoclinic with space group P21 and lattice parameters of a= 9.80 Å, b= 8.34 Å, c= 10.27 Å, and ,= 115.8°, whereas that of ,-Zn3(VO4)2 is monoclinic with space group Cm and a= 10.40 Å, b= 8.59 Å, c= 9.44 Å, and ,= 98.8°. Energy-dispersive X-ray microanalysis of these two phases shows significant deviations from their expected stoichiometry. It is apparent that the ,-phase is, in fact, the metastable Zn4V2O9 phase, whereas the ,-phase either is a new oxide that consists of zinc, vanadium, and manganese or, more likely, is a zinc vanadate phase with a Zn:V atomic ratio of 1:1 that has the ability to go into solid solution with manganese. [source] Structure of the quaternary alloy Zn0.6Mn0.4In2S4 from synchrotron powder diffraction and electron transmission microscopyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2006Asiloé J. Mora The aim of the present work was to determine the structure of the quaternary alloy Zn0.6Mn0.4In2S4 and to locate the Mn2+. This was accomplished by means of powder synchrotron X-ray diffraction, high-resolution microscopy and convergent-beam electron diffraction (CBED). The powder X-ray diffraction pattern was indexed in a rhombohedral cell, with cell constants a = 3.875,(2), c = 37.208,(4),Å, and possible space groups Rm or R3m. Rietveld refinements using different cationic arrangements in these space groups were performed. A model in space group R3m, in which the tetrahedral and octahedral sites were occupied by different proportions of Zn, Mn and In atoms, gave the best result. The Rietveld refinement of this model led to figures of merit Rwp = 9.8%, Rp = 9.1% and ,2 = 11.1. Selected-area electron diffraction patterns and high-resolution transmission electron micrographs along [001] reveal the rhombohedral configuration. CBED patterns perpendicular to [001], showing the distinctive 3m symmetry, confirmed space group R3m and the breaking of the centrosymmetry of the parent compound, ZnIn2S4. [source] New developments in the characterization of dislocation loops from LACBED patternsJOURNAL OF MICROSCOPY, Issue 3 2006J. P. MORNIROLI Summary The characterization of the Burgers vector of dislocations from large-angle convergent-beam electron diffraction (LACBED) patterns is now a well-established method. The method has already been applied to relatively large and isolated dislocation loops in semiconductors. Nevertheless, some severe experimental difficulties are encountered with small dislocation loops. By using a 2 µm selected-area aperture and a carbon contamination point to mark the loop of interest, we were able to characterize both the plane and the Burgers vector of dislocation loops of a few tens of nanometres in size present in Al-Cu-Mg alloys. [source] Structure of the (110) antiphase boundary in gallium phosphideJOURNAL OF MICROSCOPY, Issue 2 2002D. Cohen Summary The morphology of antiphase boundaries in GaP films grown by molecular beam epitaxy on Si (001) has been studied by transmission electron microscopy. The inversion of the crystal polarity between antiphase domains was confirmed by convergent-beam electron diffraction. The APBs were often found to facet parallel to {110} planes. Strong-beam ,-fringe contrast observed along the (110) facets indicates that adjacent antiphase domains are related by an additional rigid-body lattice translation. Diffraction-contrast analysis shows that this R corresponds to a shear parallel to the [001] direction and a small expansion. The magnitude of the translation was inferred, quantitatively, through a comparison between energy-filtered zero-loss images of the ,-fringe contrast with numerical calculations. The components of the rigid-body lattice translation were determined to be 0.023 ± 0.0033 nm in the [001] direction and 0.005 ± 0.002 nm in the 0 direction. Based upon a geometric model of the {110} antiphase boundary, the lengths of the Ga and P antisite bonds were calculated to be 254 ± 2 pm and 227 ± 4 pm, respectively. [source] Analysis of phase transition and expansion behaviour of Al2(WO4)3 by temperature-regulated X-ray diffractionPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2008Takuya Hashimoto Abstract X-ray diffraction measurements of Al2(WO4)3 were carried out under various temperatures from 123 K to 373 K. Diffraction patterns above 273 K and below 253 K could be successfully explained as orthorhombic Pbcn (No. 60) and monoclinic P21/n (No. 14) with superstructure, respectively, which were in agreement with the results of convergent-beam electron diffraction. Thermal expansion of low-temperature monoclinic phase and slight shrinkage of high-temperature orthorhombic phase were observed from the temperature dependence of lattice constants and molar volume, showing agreement with the result of dilatometry. It is revealed that abrupt expansion of Al2(WO4)3 at the structural phase transition is attributed to an abrupt increase of the c -axis, which is parallel to the 21 screw axis and perpendicular to the n-glide plane. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Refinement of crystal structural parameters and charge density using convergent-beam electron diffraction , the rhombohedral phase of LaCrO3ACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2002Kenji Tsuda Atom positions and anisotropic Debye,Waller factors of the rhombohedral phase of LaCrO3 have been refined simultaneously with the low-order structure factors, using a structure-analysis method of convergent-beam electron diffraction (CBED) proposed by Tsuda & Tanaka [Acta Cryst. (1999), A55, 939,954]. The method is based on the least-squares fitting between full dynamical calculations and energy-filtered intensities of two-dimensional higher-order Laue-zone (HOLZ) and zeroth-order Laue-zone (ZOLZ) CBED patterns. The positions of the oxygen atoms have been determined with a high precision. Clear anisotropy of the thermal vibrations of the oxygen atoms has been successfully determined by the CBED method for the first time. The charge transfer from the La and Cr atoms to the O atoms has been found from the deformation charge-density map. [source] Distinction between space groups having principal rotation and screw axes, which are combined with twofold rotation axes, using the coherent convergent-beam electron diffraction methodACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2001Koh Saitoh 23 sets of space groups remain indistinguishable by the convergent-beam electron diffraction (CBED) method. Recently, Tsuda, Saitoh, Terauchi, Tanaka & Goodman [Acta Cryst. (2000), A56, 359,369] demonstrated that the coherent CBED method can distinguish two space-group pairs (I23, I213) and (I222, I212121) by observing the relative arrangements of 2-fold-rotation and 21 -screw axes. The other ten space-group sets, which are composed of principal rotation and screw axes and other 2-fold-rotation axes such as P321 and P3121 (P3221), are shown to be distinguishable using the coherent CBED method. [source] Electron diffraction of ABX3 perovskites with both layered ordering of A cations and tilting of BX6 octahedraACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009Kyosuke Kishida It is shown that 21 ABX3 perovskites with tilted BX6 octahedra and layered ordering of A cations can be generated on the basis of group,subgroup relations. These structures (with 16 different space groups) are classified into ten diffraction types in terms of the conditions for superstructure reflections caused by the ordering of A cations, tilting of BX6 octahedra and structural absences. SAED (selected-area electron diffraction) allows the distinction of seven of the 21 different perovskites, while additional symmetry analysis by CBED (convergent-beam electron diffraction) is needed for the remaining 14 structures. The space groups of lithium lanthanum titanate pseudomorphs (with discrete chemical compositions) are successfully deduced by electron diffraction experiments. [source] Chiral determination: direct interpretation of convergent-beam electron diffraction patterns using the series expansion of Cowley and MoodieACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2007Andrew W. S. Johnson Given a small number of structure factors of a known chiral structure of unknown hand, it is shown that the hand can be determined from the sign of the contrast difference of two reflections in a suitably oriented convergent-beam electron diffraction (CBED) pattern. A simple formula for this difference, which takes into account all the significant second-order scattering, is derived using the series expansion of Cowley and Moodie for n -beam diffraction. The reason for the success of a three-beam interpretation is investigated. The method is applied to patterns from thin crystals in which a mirror projection symmetry can be found and its validity is demonstrated by agreement with experiment using samples of known hand. The advantages of recording patterns near major zone axes are discussed as well as some other experimental aspects of chiral determination using CBED. [source] Space group and atomic structure determination of a nano-sized ordered phase derived from a f.c.c. structure in maraging steel 12Cr,9Ni,4Mo,2Cu using transmission electron microscopyACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2003Ping Liu The unique properties of maraging steel Sandvik 1RK91 were attributed to unique precipitation: a nano-sized L phase in addition to the quasi-crystalline R, phase, which differs from any precipitation system in conventional maraging steels. The L phase was observed after ageing at either 748 or 823,K. It has flake morphology with dimensions ,100 × 500 × 500,Å. In the present study the structure of the L phase was examined using convergent-beam electron diffraction (CBED), energy-dispersive X-ray analysis (EDX) and high-resolution electron microscopy (HREM). The L phase could be described as Ti19Fe9Mo9Al8Cr5Ni50 or simply M50Ni50 (M = Ti, Fe, Mo, Al and Cr). The L phase is isostructural to FeNi. Its crystal structure was determined to have the ordered structure of the uAu-I type (L10, P4/mmm, a = 3.52, c = 3.63,Å and Z = 2) with two Ni atoms at ½ 0 ½ and 0 ½½, and two M atoms at 0 0 0 and ½½ 0. The crystal structure of the L phase can also be described using a primitive tetragonal cell and lattice parameters: a = 2.49 and c = 3.63,Å, Z = 1. The volume of the primitive tetragonal unit cell is 22.5,Å3 and the density is ,6.98,g,cm,3. The present study has demonstrated the possibility of determining the structure of an extremely small crystal by utilizing the information from CBED, EDX analysis and HREM. [source] | ||||||||||