Structure Analysis of Quasicrystal Approximants by Rotation Electron Diffraction (RED)

Complete 3D electron diffraction can be collected by rotation electron diffraction (RED) for single-crystal powder-sized samples, i.e., <0.1 μm, in all dimensions. Data collection takes about 1 h and data processing takes another hour. The crystal structures are solved by standard crystallographic techniques. X-ray crystallography requires crystals several micrometers big. For nanometer-sized crystals, electron diffraction and electron microscopy (EM) are the only possibilities. Two methods have been developed for collecting complete (except for a missing cone) three-dimensional (3D) electron diffraction data: the rotation electron diffraction and automated electron diffraction tomography (ADT). By collecting 1000–2000 electron diffraction patterns, a complete 3D data set is obtained. The geometry in RED is analogous to the rotation method in X-ray crystallography; the sample is rotated continuously along one rotation axis. In recent years, large number of crystal structures has been solved by RED. These include the most complex zeolites ever solved and quasicrystal approximants, such as the pseudo-decagonal approximants PD2 and PD1 in Al-Co-Ni. In this chapter, the results of our recent studies on the structure analysis of complex pseudo-decagonal (PD) quasicrystal approximants PD2 (a = 23.2, b = 32.3, c = 4.1 Å) and PD1 (a = 37.3, b = 38.8, c = 4.1 Å) by RED have been discussed. These are known to be the most complicated approximant structures ever solved to atomic resolution by electron crystallography. PD2 and PD1 are built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with other approximants in the PD series as well as with the results from high-resolution electron microscopy images

Evidence of Mechanical Alloying in Ball Milled ZrO2-Y2 O3 System Based on HRTEM Image Processing Analysis

We investigated, using high resolution electron microscopy and imageprocessing, the early stages of the mechanical alloying processof a mixture of zirconia and yttrium oxide powders. Molar fractionof yttrium oxide was 0.10. We focused our investigation on thegrain boundary region and the region of overlapping layers of zirconiaand yttria. Fourier filtering revealed, at the atomic level, onepossible sequence of alloying, which occurred in the grain boundaryand in the overlapping layers

Evidence of Mechanical Alloying in Bali Milled ZrO2-Y2O3 System Based on HRTEM Image Processing Analysis

We investigated, using high resolution electron microscopy and image processing, the early stages of the mechanical alloying process of a mixture of zirconia and yttrium oxide powders. Molar fraction of yttrium oxide was 0.10. We focused our investigation on the grain boundary region and the region of overlapping layers of zirconia and yttria. Fourier filtering revealed, at the atomic level, one possible sequence of alloying, which occurred in the grain boundary and in the overlapping layers

International visitor attitudes to Sagarmatha (Mt. Everest) National Park, Nepal : a thesis presented to Lincoln University in fulfilment of the thesis required for the degree of Master of Parks and Recreation Management

This study was done in Sagannatha (Mt. Everest) National Park (SNP), Nepal over a period of two months - December, 1991 and January, 1992. Sagarmatha National Park is a prime destination for many of the tourists who visit Nepal. It is a World Heritage Site and thus has great importance for conservation as well as for tourism. The success of the tourism industry depends on visitor satisfactions with their visits to these destinations. The success of SNP as a conservation area is equally dependent on visitor appreciation and sensitivity in terms of their activities while in the Park. This study explores visitor reasons for visiting SNP, visitor satisfaction with their visit to the Park and the local beliefs about the visitors. Data for this research were collected from the SNP visitors and local residents through questionnaire surveys and in-depth interviews. Due to field constraints, true random sampling was not possible. Trekking, viewing scenery, Mt. Everest and Sherpa culture were the main visitor reasons (motivations) for visiting SNP. Visitors reported "highly achieved" for each of these and thus were highly satisfied with their visit to SNP. It does not negate the fact that tourism brings with it many problems. In SNP rubbish and firewood were seen to be the major problems. Among the locals, lack of knowledge and awareness were seen as being the major drawbacks in trying to solve these problems. Visitors indicated a number of other issues which they felt needed improvement such as rubbish disposal, hygiene, sanitation and the quality of drinking water. These issues were not perceived as lessening visitor satisfactions as visitors indicated that they expected these conditions. This information points out that anticipated expectations of a destination were the determinant of the actual satisfaction. Visitors rated most of the SNP hotel/lodge facilities as "reasonable" or higher but in their comments and in-depth interviews they commented about needed improvements. Visitors evaluated these facilities in terms of what they anticipated not what they thought the facilities should be

Structure determination of the zeolite IM-5 using electron crystallography

The structure of the complex zeolite IM-5 (Cmcm, a = 14.33(4) Å, b = 56.9(2) Å, c = 20.32(7) Å) was determined by combining selected area electron diffraction (SAED), 3D reconstruction of high resolution transmission electron microscopy (HRTEM) images from different zone axes and distance least squares (DLS) refinement. The unit cell parameters were determined from SAED. The space group was determined from extinctions in the SAED patterns and projection symmetries of HRTEM images. Using the structure factor amplitudes and phases of 144 independent reflections obtained from HRTEM images along the [100], [010] and [001] directions, a 3D electrostatic potential map was calculated by inverse Fourier transformation. From this 3D potential map, all 24 unique Si positions could be determined. Oxygen atoms were added between each Si-Si pair and further refined together with the Si positions by distance-least-squares. The final structure model deviates on average 0.16 Å for Si and 0.31 Å for O from the structure refined using X-ray powder diffraction data. This method is general and offers a new possibility for determining the structures of zeolites and other materials with complex structure

A complicated quasicrystal approximant ∊16 predicted by the strong-reflections approach

The structure of the quasicrystal approximant ∊16 was predicted by the strong-reflections approach based on the known approximant ∊6

Structure analysis by crystallographic image processing Hommage à Jean Baptiste Joseph Fourier (1768-1830)

It is possible to determine the crystal structure of inorganic compounds to atomic resolution, by combining high resolution electron microscopy (HREM) with crystallographic image proceesing (CIP). An electron micrograph is a magnified, but distorted, image of the object. By quantitative analysis of the image it is possible to determine the distortions and correct for most of them. It is also possible to determine the symmetry of a crystal and even to find the atomic positions with an accuracy of at lcast 0.1 Ångström. The image processing is based on Fourier analysis of the experimental data in the form of a micrograph. The crystallographic symmetry is determined and made maximal use of in restoring a nearly distortion-free image.Il est possible de déterminer la structure cristalline d'un solide inorganique à l'échelle atomique en associant la microscopie électronique haute résolution avec un traitement cristallographique de l'image. La micrographie électronique constitue une image agrandie mais distordue de l'objet. Par l'analyse quantitative de cette image, il est possible de déterminer les distortions et de les corriger pour la plupart. Il est aussi possible de déterminer la symétrie du cristal et, avec une précision d'au moins 0,1 A, la position des atomes. Le traitement d'image est basé sur l'analyse de Fourier des données expérimentales contenues dans la micrographie. La symétrie cristallographique est déterminée et est utilisée largement pour retrouver une image pratiquement non distordue