Two-dimensional Lattice Images Research Articles

Microstructure characteristics of illite from Chuanlingou Formation of Changcheng System in Jixian County, Tianjin City

The microstructure characteristics of illite from the Chuanlinggou Formation of Changcheng System (Chch) in Jixian County, Tianjin City has been studied by means of high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), X-ray energy dispersive spectrum (EDS) and X-ray powder diffraction (XRD). The Kubler index of “illite crystallinity” is 0.505° Δ2θ, which indicates that the host rock is in a middle diagenetic stage. The chemical analyses of EDS for illite studied indicate a heavily absent in interlayer cation and an average chemical formula of K0.57(Al1.80Mg0.42Fe2+0.12)Σ=2.34 (Si2.92Al1.08)Σ=4O10(OH)2. It is found, from one-dimensional lattice images, that the layers of illite not only stack in a flat way but also in a curving way. A “matting fabric” illite structure results from stacking faults. Combined with SAED analysis the illite studied can be affirmed as 1M illite. The two-dimensional lattice images are obtained from [100] and [110] incidences, whose lattice images have the same d-values but different intersecting angles. The two-dimensional lattice image with [100] incidence is orthogonal to each other, whilst that with [110] incidence is oblique. This paper provides some important structure information of authigenic clay minerals for the well-known mesoproterozoic section of Jixian County.

High-resolution electron microscopy on cellulose II and α-chitin single crystals

Single-crystalline cellulose II and α-chitin regenerated from low-molecular weight solutions using phosphoric acids as a solvent were investigated by electron diffraction together with high-resolution imaging. Cellulose II of two different degrees of polymerization (DP) were regenerated by precipitation either in water (DP = 15) or in ethanol (DP = 7), and the latter revealed better crystalline perfection. In both cases, the structures are in good accord with the previously published 2-chain monoclinic model. Although the lattice fringes of base planes of the crystal were identified by Fourier transform of negatives, the precise localization of cellulose molecules was not visualized due to local azimuthal fluctuation of the crystal. α-Chitin was regenerated by precipitation only in ethanol. The crystals are flat ribbons with a smooth surface and, in structure, fit well a previous antiparallel-chain model because their ab electron diffraction patterns agree well with the proposed P212121 symmetry. Two-dimensional lattice images were obtained with a resolution up to 0.38 nm. Molecular packing in the unit cell was demonstrated clearly with the help of image processing, and corroborated by kinematical calculation of high-resolution images of α-chitin. 0969--0239 © 1998 Blackie Academic & Professional

On the Effect of Substitutional Elements on the Out-Of-Step Distance in the Long Period Ordered Ag2Mg-Based Alloys

The long-period structure of Ag3Mg is studied by substituting some Mg-atoms with one of the elements Zn, Au, Cu, Al, and Sn. These elements are chosen to be able to vary the electron per atom ratio considerably. The out-of-step distances in each case are measured both, from the diffraction patterns and from the high-resolution two-dimensional lattice images. The concentrations of the samples are determined by means of X-ray microanalysis of the same areas where images and diffraction patterns are obtained.

High resolution electron microscopic study of the hexagonal bronze potassium niobium tungstate (PNT)

High-resolution electron microscopic studies are reported on the nature of the complex domain patterns which occur in the room temperature phase of the hexagonal bronze KWNb2O9. Two-dimensional lattice images reveal the domain wall configurations, with walls having virtually zero thickness, containing steps (kinks) of atomic dimensions. Wall rearrangements, following kink propagation under the influence of the electron beam, are also described. Symmetrical zone axis images, for extremely thin edges of the specimens, reveal directly the nature of the (W, Nb) atom displacements responsible for the hexagonal component of the superstructures occurring throughout five phases, which exhibit a series of structural phase transitions, including ferroelectric phases, in the temperature range 270-560°C.

Crystalline morphology of Valonia macrophysa cellulose III I revealed by direct lattice imaging

The crystalline ultrastructure of Valonia macrophysa Kütz cellulose III I has been investigated by means of high resolution electron microscopy. The optimum imaging conditions of about 0.4 nm resolution were determined based on the results of beam damage measurements by electron diffraction, and two-dimensional lattice images of (1 1 0), (110) or (200), and (002) lattice planes were clearly visualized. In a scrutinizing analysis of the micrographs, it was noticed that the cellulose III I has a similar crystalline nature as that observed with V. macrophysa cellulose I, having no definite long periodicities along the microfibrils and no considerable lattice distortion in a lateral direction. However, it was found that the transformation into cellulose III I from cellulose I was accompanied by subfibrillation of the original cellulose I crystallites, creating a longitudinal splitting between the adjacent (1 1 0) planes.

Electron Microscopic Investigations of Iron Oxyhydroxides and Accompanying Phases in Lateritic Iron-Crust Pisolites

AbstractPisolites from an iron crust in western Senegal were studied by conventional and high-resolution electron microscopy to determine their internal structure and the genetic processes that led to their formation. Each pisolite consisted of a concentric structure of hematite rimmed by goethite. Two types of goethite were distinguished: (1) large (≃ 0.6 μm long and 0.06 μm wide), euhedral laths arranged in fibrous aggregates of slightly misoriented grains devoid of internal defects as shown by their two-dimensional lattice images, and (2) a matrix of smaller (≃400 Å), anhedral grains surrounded by the larger laths. Based upon the crystal habit and the presence or absence of internal alveoles, the large goethite laths probably grew at the expense of the matrix goethite. Poorly crystalline kaolinite, presumably formed from well-crystalline precursor kaolinite, and clusters of partially dissolved quartz grains were also imaged. In addition, two uncommon phases were found—maghemite in topotactic relationship with hematite and a layered, Fe-rich, mica-like mineral with a 2M superstructure. Unlike kaolinite, this latter phase was likely in equilibrium with iron oxyhydroxides. Substituted Al probably was released during goethite recrystallization, and mass transfers probably took place through the heterogeneous porosity (i.e., large voids and cracks coupled with fine pores) revealed by transmission electron microscopy.

On the structure of {100} platelet defects in type la diamond

Abstract The elucidation of defect structure using two-dimensional lattice images is a difficult and time-consuming procedure owing to the number of variable experimental parameters in a high resolution experiment. In this paper the most important experimental parameters are determined prior to the attempt at structure determination, using a number of different techniques including image matching of perfect diamond images and matching the width and appearance of the central Fresnel fringe at the platelet. Having determined the experimental parameters, the image matching was then carried out using five different models for the platelet. It is found that the high resolution two-dimensional lattice images are sensitive to platelet structure and are consistent with a previously unknown platelet model, the double nitrogen layer zigzag model.

Correlation of x-ray and electron crystallography of biological structures

The development of electron crystallography of biological structures recapitulates in many ways the history of x-ray crystallography started by W.L. Bragg in 1913 and, more particularly, protein crystallography begun by Bernal and Crowfoot Hodgkin in 1934. By the early 1950s Perutz and Bragg were mapping the outline of the hemoglobin molecule by tracing the molecular transform through the use of a kind of negative staining for x-ray diffraction. The demonstration by Perutz and his colleagues that the isomorphous replacement method could be used to solve the phase problem in protein crystallography opened the way to determining the atomic structure of proteins starting with myoglobin.Electron crystallography was begun by Klug and his colleagues in the mid 1960s using optical diffraction to detect periodicities in the image and then applying optical filtering to separate superimposed two-dimensional lattice images and to average the image of the repeating unit. Following the underlying unity in the optics of image formation and diffraction of light, x-rays and electrons, DeRosier and Klug developed the theory and methodology of three-dimensional image reconstruction with the use of Fourier transforms of digitized images.

Measurement of lattice displacement of {100} platelets in diamond

Abstract Abstract Measurement of lattice fringe spacings to determine the expansion vector at {100}〈f00〉 platelet defects in type la diamonds is critically examined. Computer-simulated lattice images were measured and the apparent expansion parameter f′ was found to vary from 0·2 to 0·50 for one structural model of the platelets (f = 0·33); f′ was found to be strongly dependent on crystal thickness, specimen orientation and objective-lens defocus. Despite this it was possible to define electron-optical conditions for which f′=f, when reliable f values should be obtainable. Analyses of one- and two-dimensional lattice images were all consistent with f = 0·33 ± 0·05, after correction for electron-optical effects where necessary. The technique proved far less accurate than an alternative moire fringe measurement, which gave 0·350 ≤ f ≤ 0·362.

Two-dimensional lattice image of the Mg-base Friauf–Laves phase and a new type of defect

Two-dimensional lattice images have been obtained for the two-, four-, and nine-layer type structures of the Friauf-Laves phase, Mg(Cu0.535Al0.465)2. An intimate correlation is established between the lattice image and the crystal structure. With this relation, layer sequences of disordered stacking regions are determined. A new type of linear defect is found in the images and a structural model of the defect is proposed. The defect is always accompanied by a stacking fault, which is different from the usual stacking faults observed in close-packed structures.

Two-dimensional lattice images of stacking disorder in wollastonite

Two-dimensional lattice images of low-temperature triclinic wollastonite (α-CaSiO3) indicate that two types of stacking disorder occur: (1) simple stacking faults and (2) twinning which also involves displacement in the composition plane. Both types of defect produce very similar structures with monoclinic symmetry (parawollastonite). Dislocations are involved at the termination of lamellae of parawollastonite in a triclinic matrix and a model for the dislocation core is proposed.

Direct observation of lattice defects inH-Nb2O5by high resolution electron microscopy

Detailed two-dimensional lattice images, showing metal-atom positions in crystals of H-Nb2O5 quenched from the melt have been observed using a sophisticated electron microscope in both ordered and heavily disordered regions. The blocks in the structure were well ordered along the b axis, but heavily disordered in the ac plane; the sub-cell structure of ReO3 was still perfectly retained. Four kinds of planar defects, oriented parallel to low-index planes in the host structure, were revealed in the ordered region. Some of these planar defects produce non-stoichiometry. A new polymorph of Nb2O5, having the same structure as PNb9O25, was found in one of the defect structures, and several other new phases of Nb2O5 were observed in the heavily disordered region. Incoherently packed blocks and unusual-size blocks played an important role as one of possible origins of the defect planes.