Indexing of diffraction patterns and indentification of fault vector in decagonal Al65Cu20Co15 phase

Characterisations of defect structures such as pencil disorder, faulting in quasiperiodic layers and dislocation in decagonal quasicrystals has assumed importance currently. The first step towards a complete understanding of these defects requires easy and unambiguous method of indexing the diffraction patterns. The present study is devoted to this task. New rules have been framed for an unambiguous indexing of the diffraction patterns following the model of Mandal and Lele. The scheme is applied to the indexing of important electron diffraction patterns from a decagonal Al₆₅ Cu₂₀ Co₁₅ alloy and the indices for the direction of streaking in some of the diffraction patterns have been found and are of the type .     

Numerical separation of background in X-ray diffraction studies

A method for the separation of X-ray background is suggested. The method is based on the integral digital filtration of experimental diffraction patterns and their “smoothening” and the subsequent combination of the smoothened and initial diffraction patterns. The combined diffraction pattern thus obtained is smoothened again, and the whole procedure is repeated anew. The criterion for concluding the iteration procedure (background criterion) is suggested to be the attainment of the situation where a certain percent of the points of the initial diffraction pattern would be below the background line determined. It is shown that, in some instances, the method yields more appropriate results than the traditional methods. The application of the new method is not limited by X-ray diffraction alone.     

Electron diffraction study of the structural features of kaolinites

The structural variations of kaolinites have been investigated based on oblique-texture electron diffraction patterns. The features of manifestation of the 2D lattice of kaolinite layers in the geometry of the 20l and 13l reflections have been revealed. The manifestation of violations in the regular alternation of layers in kaolinites in the diffraction patterns has been analyzed using a numerical simulation of the diffraction profiles along the first (02l, 11l) and second (20l, 13l) ellipses of oblique-texture electron diffraction patterns. The simulation was performed for finite sequences of ten layers using the statistical Markov model in the quasihomogeneous approximation. It is shown that oblique-texture electron diffraction patterns can be used to reveal the coexistence of two phases with different structural perfections and particle morphologies in kaolinite samples.     

The theory of the local structure of solid solutions of oxides with Perovskite structure: Example of Pb<Subscript>2</Subscript>(FeNb)O<Subscript>6</Subscript>

A method for constructing local-structure models for complex oxides with averaged perovskite-type structures has been developed. The constructed models take into account the probabilities of distributing different cations over sites belonging to the corresponding sublattices. The accepted approach to interpreting diffraction patterns is based on the same hypotheses as the commonly used one. As an example, a local-structure model is constructed for disordered PbFe_1/2Nb_1/2O₃ and, on the basis of this model, the diffraction patterns of this single crystal, disordered with respect to Fe and Nb sites at T = 433 K, have been interpreted.     

Enhancement of several Kikuchi lines in the vicinity of spot reflections

Kikuchi electron diffraction patterns of silicon have been obtained which demonstrate the simultaneous enhancement of several excess Kikuchi lines near different point reflections. This enhancement is explained within the elementary mechanism of the formation of Kikuchi patterns while taking into account the Kikuchi electron double diffraction.     

Nonidentified Kikuchi lines with reverse contrast

Electron diffraction patterns of silicon in transmission with contrast reversal from bright to dark for an unidentified Kikuchi line along its length have been obtained. The contrast reversal of an unidentified line is explained within the elementary mechanism of Kikuchi pattern formation taking into account the Kikuchi electron double diffraction.     

X-ray trajectories in crystals with x-depending deformation gradients

Based on the Eikonal theory analytical solutions of the trajectory-equation were calculated for some special x-depending deformation gradients, where x shows in the direction of the diffraction vector. For the discussion deformation gradients are chosen which are similar to those in crystals with varying concentrations of impurity atoms. The calculated trajectories allow to obtain properties of section- and traverse-topographs.     

Channeling‐enhanced EDX for polarity resolved crystal orientation determination

Using channeling‐enhanced energy‐dispersive X‐ray spectroscopy (EDX), we demonstrate polarity sensitive orientation determination of a non‐centrosymmetric crystal in the scanning electron microscope. The authors observe a characteristic asymmetry in the channeling‐enhanced, angle‐dependent EDX data of a GaAs sample, which is in good agreement to simulations using the dynamical theory of diffraction for the incident electron beam. This allows us to assign the orientation of the GaAs crystal according to the non‐centrosymmetric point group. The method shown here overcomes the limitation of a reduced point‐group sensitivity of electron backscatter diffraction patterns and electron channeling patterns for crystalline phases that contain atoms of approximately equal electron scattering cross sections.     

X-ray diffraction from ideal mosaic crystals in external fields of certain types, part III: Changes in space symmetry and symmetry of diffraction pattern

The change in the space symmetry and the symmetry of the corresponding diffraction pattern occurring under the effect of uniform electric and magnetic fields applied to a crystal have been analyzed. The tables of point symmetry groups for various directions of applied magnetic fields are constructed. It is shown that in the absence of an external field, the diffraction patterns are described by nine possible point groups; in an electric field, they are described by eleven point groups; and in a magnetic field, by only five point groups. The theoretically calculated diffraction parameters are compared with the corresponding experimental values.     

Twinning of quasicrystals and related crystals

Electron microscopy and electron diffraction have been employed to bring out the intimate relationship between icosahedral quasicrystal and various types of crystalline phases with emphasis on aluminium transition metal alloys. The relationship between quasicrystal and twinned rational approximant structures will be treated in the context of irrational twinning. The twinned aggregates show an icosahedral like symmetry in electron diffraction patterns. The crystallography of irrational twins has been discussed in terms of various ways of representing a twin relationship in a cubic lattice.     

Electron diffraction patterns with thermal diffuse scattering maxima around Kikuchi lines

Transmission electron diffraction patterns of silicon with thermal diffuse maxima around Kikuchi lines, which are analogs of the maxima of thermal diffuse electron scattering around point reflections, have been recorded. Diffuse maxima are observed only around Kikuchi lines with indices that are forbidden for the silicon structure. The diffraction conditions for forming these maxima are discussed.     

电场辅助电化学法沉积ZnO纳米线

采用电场辅助电化学沉积的方法成功的在阳极氧化铝模板中沉积出ZnO纳米线阵列.透射电子显微镜(TEM)、X射线衍射(XRD)测试结果表明,制备的纳米线是单晶ZnO纳米线,形貌均匀,直径大约为60nm,并且择优于(101)晶面.我们对生长过程中所加辅助电场的作用给出了初步的解释.     

Electron differaction patterns with curved Kikuchi lines

Curved Kikuchi lines have been observed in electron diffraction patterns obtained for silicon by transmission electron microscopy. It is found that the curvature of Kikuchi lines is related to the shift of point reflections from their normal positions. The formation of curved Kikuchi lines stems from the local structural defects in the crystals under study.     

Microstructure evolution and grain size distribution in nanocrystalline FeNbBCu from synchrotron XRD and TEM analysis

The microstructure evolution during nanocrystallization of an Fe₇₇Nb₇B₁₅Cu₁ amorphous alloy is investigated using in situ synchrotron X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure of the nanocrystallized alloy consists in dispersion of bcc-Fe nanocrystals of 4–6 nm of diameter embedded in a stabilized amorphous remaining matrix. The grain size distribution of the nanocrystalline Fe₇₇Nb₇B₁₅Cu₁ alloy was obtained using three different methodologies: statistical analysis of TEM images, the Warren–Averbach and Langford methods to analyse the XRD patterns and modelling of the diffraction pattern from the Debye equation. A lognormal distribution function has been assumed in all three methods in order to obtain comparable results. A good agreement is found in the calculated average radius and dispersion although some deviations are found with the Langford approach. The microstructure evolution during crystallization was obtained from the XRD patterns during heating (5.0 · 10^?3 K s^?1) at temperatures between 700 and 900 K. A decrease and prompt saturation of the growth rate is obtained, indicative of the diffusion barrier caused to the overlap between the concentration gradients at the interface of growing grains (soft impingement). A simple model assuming nucleation and initial fast growth of the crystalline grains followed by reduced growth capable of predicting microstructural evolution is presented. The modelling results agree with the experimental observations.     

New schemes for recording electron diffraction patterns of hexagonal and monoclinic crystals

Some new schemes for recording electron diffraction patterns of hexagonal crystals rotating around the axes lying in the (hk0) plane of the reciprocal lattice and monoclinic crystals rotating around the a and b axes of the direct lattice and the a* axis of the reciprocal lattice have been developed. Formulas for interpreting electron diffraction patterns are reported. The electron diffraction patterns obtained based on these schemes were used to solve the 2H and 3R polytypes of CdInGaS₄ crystals and the 3R polytype of Zn_1.5In₃Se₆ crystal with the parameters a = 4.046 and c = 59.292 Å, sp. gr. R3m.     

Aspects of the thermal and transport properties of crystalline salt in designing radioactive waste storages in halogen formations

Some of the properties of natural rock salt are described. This rock is of great practical interest, because, along with its conventional applications in the chemical and food industries, it is promising for use in engineering underground radioactive waste storages and natural gas reservoirs. The results of structural and texture studies of rock salt by neutron diffraction are discussed. The nature of the salt permeability under temperature and stress gradients is theoretically estimated.     

Development of the DIFFRACALC program for analyzing the phase composition of alloys

Crystallography Reports - The DiffraCalc software package is developed for automatic indexing of electron diffraction patterns. The program can operate with the existing base of X-ray diffraction...     

Peculiarities of X-ray diffraction in quartz monocrystals

The scattering of X-rays in quartz monocrystals has been investigated. It has been shown, that, even in thick quartz monocrystals, kinematic scattering takes place and pendular bands appear. It has been demonstrated experimentally that only a diffraction pattern of clearance is obtained in bicrystal quartz interferometers, whereas in tricrystal interferometers moiré patterns are not produced. The beam reflected from one part of the crystal is no longer reflected from the other parts of the same crystal.