Electron Microscopic Study of Domains in Relaxor Ferroelectrics

1991 ◽  
Vol 243 ◽  
Author(s):  
Marc de Graef ◽  
J.S. Speck ◽  
D.R. Clarke ◽  
D. Dimos
Keyword(s):  
Relaxor Ferroelectrics ◽  
High Symmetry ◽  
Electron Microscopic ◽  
Domain Structures ◽  
System A ◽  
Transmission Electron ◽  
Wide Range ◽  
Cell Dimensions ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions

AbstractThe ferroelectric and antiferroelectric displacements in perovskite-based ceramics give rise to a wide range of domain structures. This paper reports on transmission electron microscopy observations as a function of temperature of such structures in PLZT and PLSnZT. In the PLZT system superposition of the diffraction patterns from modulated domains of low symmetry give rise to patterns with an apparent high symmetry. The ½(hkl)-type reflections become more intense with decreasing temperature and split into diffuse rods at high temperature. In the PLSnZT system a hierarchy of domain structures is observed with length scales ranging from unit cell dimensions to the full grain size. A temperature dependent long-period modulation along the < 110 > directions is observed.

Optimal Calibration Curves for Guinier-Type Focusing Cameras

1977 ◽  
Vol 21 ◽  
pp. 289-303
Author(s):  
Allan Brown
Keyword(s):  
Unit Cell ◽  
Routine Measurement ◽  
Calibration Curves ◽  
Cell Dimensions ◽  
Diffraction Patterns ◽  
To Come ◽  
Unit Cell Dimensions ◽  
Optimal Calibration

The inclusion of an internal calibrant in specimens prepared for Guinier-type focusing cameras is a well-established practice. The true reasons for performing calibration are, however, not always clearly understood. Accordingly, procedures adopted on the basis of this calibration for converting distances measured on the film into reliable values of θ vary in detail from one laboratory to another. The possibility that calibration curves can exhibit different degrees of reliability, depending upon camera alignment, is even less generally appreciated. The following account records efforts made over the years to come to terms with these problems in order to obtain unit cell dimensions at the 0.01 % level of precision from the routine measurement of Guinier diffraction patterns.

scholarly journals Structures of pseudo-decagonal approximants in Al−Co−Ni

2012 ◽  
Vol 370 (1969) ◽  
pp. 2949-2959 ◽  
Author(s):  
Sven Hovmöller ◽  
Linus Hovmöller Zou ◽  
Xiaodong Zou ◽  
Benjamin Grushko
Keyword(s):  
High Resolution Electron Microscopy ◽  
Limited Information ◽  
X Ray ◽  
X Ray Crystallography ◽  
Resolution Electron ◽  
Cell Dimensions ◽  
Diffraction Patterns ◽  
Quasi Crystals ◽  
Unit Cell Dimensions ◽  
Microscopy Images

Quasi-crystals shocked the crystallographic world when they were reported in 1984. We now know that they are not a rare exception, and can be found in many alloy systems. One of the richer systems for quasi-crystals and their approximants is Al−Co−Ni. A large series of pseudo-decagonal (PD) approximants have been found. Only two of them, PD4 and PD8, have been solved by X-ray crystallography. We report here the structures of PD1, PD2, PD3 and PD5, solved from the limited information that is provided by electron diffraction patterns, unit cell dimensions and high-resolution electron microscopy images.

NNN-ISING MODEL SIMULATION OF NANODOMAIN TEXTURES IN RELAXOR-TYPE LEAD SCANDIUM TANTALATE

1993 ◽  
Vol 07 (26) ◽  
pp. 4353-4369 ◽  
Author(s):  
H. QIAN ◽  
J.L. PENG ◽  
L.A. BURSILL
Keyword(s):  
Statistical Physics ◽  
Nearest Neighbor ◽  
Model Simulation ◽  
Dark Field ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Wide Range ◽  
Transmission Electron Microscopic ◽  
Long Range Ordering ◽  
Perovskite Type

Chemical domain textures for lead scandium tantalate (PST) are modelled using Monte Carlo (MCS) and next-nearest-neighbor Ising (NNNI) models. A wide range of degrees of short- and long-range ordering of the (Ta, Sc) atoms occur in ceramic specimens, depending on processing routes. The simulations help us understand and quantify the chemical domain textures, chemical domain wall configurations and other chemical defects which may occur in certain relaxor-type perovskite-type oxides. The results are compared to dark-field transmission electron microscopic observations. Some new types of small defects were discovered. These are described and classified. The results provide a first step towards the development of a microscopic statistical physics framework for analytical theories of the dielectric response of relaxor-type ceramics, where the frequency and temperature variation of the permittivity are due essentially to dipolar-type fluctuations on nanometer scales.

scholarly journals The crystal structures of two polyamides (‘nylons’)

1947 ◽  
Vol 189 (1016) ◽  
pp. 39-68 ◽  
Keyword(s):  
Crystal Structures ◽  
Unit Cell ◽  
Chain Molecule ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Dimensions ◽  
C Fibre ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions ◽  
Crystalline Forms

Detailed interpretations of the X -ray diffraction patterns of fibres and sheets of 66 and 6.10 polyamides (polyhexam ethylene adipamide and sebacamide respectively) are proposed. The crystal structures of the two substances are completely analogous. Fibres of these two polyam ides usually contain two different crystalline forms, α and β, which are different packings of geometrically similar molecules; most fibres consist chiefly of the α form. In the case of the 66 polymer, fibres have been obtained in which there is no detectable proportion of the β form. Unit cell dimensions and the indices of reflexions for the α form were determined by trial, using normal fibre photographs, and were checked by using doubly oriented sheets set at different angles to the X -ray beam. The unit cell of the a form is triclinic, with a — 4·9 A, b = 5·4 A, c (fibre axis) = 17·2A, α = 48 1/2º, β = 77º, γ = 63 1/2º for the 66 polymer; a = 4·95A, b = 5·4A, c (fibre axes) = 22·4A, α = 49º, β = 76 1/2º, γ = 63 1/2º for the 6.10 polymer. One chain molecule passes through the cell in both cases. Atomic coordinates in occrystals were determined by interpretation of the relative intensities of the reflexions. The chains are planar or very nearly so; the oxygen atoms appear to lie a little off the plane of the chain. The molecules are linked by hydrogen bonds between C = 0 and NH groups, to form sheets. A simple packing of these sheets of molecules gives the α arrangement.

scholarly journals Systemic Iridovirus Infection in the Banggai Cardinalfish (Pterapogon Kauderni Koumans 1933)

2009 ◽  
Vol 21 (3) ◽  
pp. 306-320 ◽  
Author(s):  
E. Scott Weber ◽  
Thomas B. Waltzek ◽  
Devon A. Young ◽  
Erica L. Twitchell ◽  
Amy E. Gates ◽  
...  
Keyword(s):  
Genomic Sequence ◽  
Sequence Data ◽  
Molecular Diagnostic ◽  
Molecular Testing ◽  
Electron Microscopic ◽  
Cytoplasmic Inclusions ◽  
Marine Habitats ◽  
Transmission Electron ◽  
Atpase Gene ◽  
Wide Range

Iridoviruses infect food and ornamental fish species from a wide range of freshwater to marine habitats across the globe. The objective of the current study was to characterize an iridovirus causing systemic infection of wild-caught Pterapogon kauderni Koumans 1933 (Banggai cardinalfish). Freshly frozen and fixed specimens were processed for histopathologic evaluation, transmission electron microscopic examination, virus culture, molecular virologic testing, microbiology, and in situ hybridization (ISH) using riboprobes. Basophilic granular cytoplasmic inclusions were identified in cytomegalic cells often found beneath endothelium, and hexagonal virus particles typical of iridovirus were identified in the cytoplasm of enlarged cells by transmission electron microscopy. Attempts at virus isolation in cell culture were unsuccessful; however, polymerase chain reaction (PCR)-based molecular testing resulted in amplification and sequencing of regions of the DNA polymerase and major capsid protein genes, along with the full-length ATPase gene of the putative iridovirus. Virus gene sequences were then used to infer phylogenetic relationships of the P. kauderni agent to other known systemic iridoviruses from fishes. Riboprobes, which were transcribed from a cloned PCR amplification product from the viral genome generated hybridization signals from inclusions within cytomegalic cells in histologic sections tested in ISH experiments. To the authors' knowledge, this is the first report of a systemic iridovirus from P. kauderni. The pathologic changes induced and the genomic sequence data confirm placement of the Banggai cardinalfish iridovirus in the genus Megalocytivirus family Iridoviridae. The ISH provides an additional molecular diagnostic technique for confirmation of presumptive infections detected in histologic sections from infected fish.

Electron Microscopy of Alcohol Oxidase Crystals from Pichia Pastoris

1990 ◽  
Vol 48 (1) ◽  
pp. 108-109
Author(s):  
Janet Vonck ◽  
Ernst F.J. van Bruggen
Keyword(s):  
Pichia Pastoris ◽  
Hansenula Polymorpha ◽  
Alcohol Oxidase ◽  
Unit Cell ◽  
Electron Microscopic ◽  
X Ray ◽  
X Ray Crystallography ◽  
Cell Dimensions ◽  
Microscopic Studies ◽  
Unit Cell Dimensions

Several yeast species are able to grow on methanol. When they are grown in a methanol-restricted culture, their peroxisomes contain large crystalline inclusions, consisting of alcohol oxidase (AOX). A monomer of AOX has a molecular weight of ca. 74,000. Inside the peroxisome, AOX occurs as octamers.Electron microscopic studies of AOX from Hansenula polymorpha have revealed that the eight subunits are slightly elongated and form two layers of four, which are twisted relative to each other. The molecule measures ca. 12 nm in all directions.Recently, crystals suitable for x-ray diffraction have been formed of AOX from Pichia pastoris . The space group is P21, with unit cell dimensions a=157.3Å, b=171.45Å, c=231.6Å, β=94°. These dimensions indicate that the unit cell contains four octamers, too much to solve by x-ray crystallography alone. Therefore, we have started an EM study of the crystals, to get information about the organization of the molecules in the crystal lattice.

Unit cell dimensions of the hydrated aluminium phosphate–sulphate minerals sanjuanite, kribergite, and hotsonite

1989 ◽  
Vol 53 (371) ◽  
pp. 385-386 ◽  
Author(s):  
H. De Bruiyn ◽  
G. J. Beukes ◽  
W. A. Van Der Westhuizen ◽  
E. A. W. Tordiffe
Keyword(s):  
Unit Cell ◽  
X Ray Diffraction ◽  
Aluminium Phosphate ◽  
Powder Diffraction File ◽  
Cell Parameters ◽  
Cell Dimensions ◽  
Unit Cells ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions ◽  
Hydrated Aluminium

AT the time when the hydrated aluminium phosphate-sulphate hotsonite (Beukes et al., 1984a) and its equally rare relative zaherite (Beukes et al., 1984b; De Bruiyn et al., 1985) were discovered near Pofadder, South Africa, very little was known about the unit cells of the other two hydrated aluminium phosphate-sulphate minerals sanjuanite and kribergite, originally described by De Abeledo et al. (1968) from Argentina and Sweden, respectively. Although the Powder Diffraction file (PDF) contains the X-ray diffraction patterns for sanjuanite and kribergite (PDF 20-47 and 20-48 respectively), they had not been indexed nor have their unit cell parameters been calculated thus far.

Replica Extraction Method on Nanostructured Gold Coatings and Orientation Determination Combining SEM and TEM Techniques

2014 ◽  
Vol 20 (6) ◽  
pp. 1654-1661 ◽  
Author(s):  
Christian Bocker ◽  
Michael Kracker ◽  
Christian Rüssel
Keyword(s):  
Electron Microscopy ◽  
Extraction Method ◽  
Electron Backscatter Diffraction ◽  
Substrate Surface ◽  
Complete Removal ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Nanostructured Gold ◽  
Diffraction Patterns ◽  
Convergent Beam

AbstractIn the field of electron microscopy the replica technique is known as an indirect method and also as an extraction method that is usually applied on metallurgical samples. This contribution describes a fast and simple transmission electron microscopic (TEM) sample preparation by complete removal of nanoparticles from a substrate surface that allows the study of growth mechanisms of nanostructured coatings. The comparison and combination of advanced diffraction techniques in the TEM and scanning electron microscopy (SEM) provide possibilities for operators with access to both facilities. The analysis of TEM-derived diffraction patterns (convergent beam electron diffraction) in the SEM/electron backscatter diffraction software simplifies the application, especially when the patterns are not aligned along a distinct zone axis. The study of the TEM sample directly by SEM and transmission Kikuchi diffraction allows cross-correlation with the TEM results.

MgSiO3 perovskite: a HRTEM study

1996 ◽  
Vol 60 (402) ◽  
pp. 799-804
Author(s):  
Ishmael Hassan ◽  
Yasuhiro Kudoh ◽  
Peter R. Buseck ◽  
Eui Ito
Keyword(s):  
X Ray Diffraction ◽  
Phase Boundaries ◽  
Orthorhombic Unit Cell ◽  
X Ray ◽  
Mgsio3 Perovskite ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Cell Dimensions ◽  
Crystal Fragment ◽  
Diffraction Patterns

AbstractSelected-area electron diffraction patterns for the [110] zone of MgSiO3 perovskite are consistent with the orthorhombic unit cell obtained by X-ray diffraction (a = 4.775, b = 4.929, c = 6.897 Å). Various areas of a crystal fragment show diffuse streaking along c*, and well-developed satellite reflections that give a 3-fold repeat along [10]*. Another fragment shows doubled cell dimensions when viewed down [30]. The variable occurrence of the satellite reflectioncs and diffuse streaking indicate subtle variations in ordering, chemistry, or both. Images obtained by high-resolution transmission electron microscopy contain perfectly ordered regions, out-of-phase boundaries, and intergrowths of the two orthorhombic forms of perovskite.

Octahedral tilt twinning and compositional modulation in NaLaMgWO6

2009 ◽  
Vol 65 (6) ◽  
pp. 676-683 ◽  
Author(s):  
Graham King ◽  
Susana Garcia-Martin ◽  
Patrick M. Woodward
Keyword(s):  
Unit Cell ◽  
Repeat Distance ◽  
One Dimensional ◽  
Compositional Modulation ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Cell Dimensions ◽  
Octahedral Tilting ◽  
Unit Cell Dimensions ◽  
Perovskite Unit Cell

A combination of selected-area electron diffraction (SAED), neutron powder diffraction (NPD) and high-resolution transmission electron microscopy (HRTEM) reveals a complex superstructure in the ordered perovskite NaLaMgWO6. Through indexing of SAED patterns the unit-cell dimensions are found to be 46.8 × 7.8 × 7.9 Å, which corresponds to a 12a p × 2a p × 2a p superstructure of the simple Pm\overline 3 m perovskite unit cell. HRTEM images reveal the formation of an unmistakable stripe contrast that repeats with the same periodicity. Doubling of the b and c axes is brought about by a combination of layered ordering of Na and La, rock-salt ordering of Mg and W, and octahedral tilting. The a axis repeat distance results from a one-dimensional twinning of the octahedral tilts in combination with a compositional modulation. Modeling of the NPD pattern shows that the underlying tilt system is a − a − c 0 with tilt angles of ∼ 8° about the a and b axes. The octahedral tilt-twin boundaries run perpendicular to the a axis and are separated by 6a p. Simulated HRTEM images show that octahedral tilt twinning alone cannot explain the stripes seen in the HRTEM images, rather a compositional modulation involving the A-site cations is necessary to explain the experimental images.

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