An electron diffraction and Monte Carlo simulation study of diffuse scattering in Pb(Zr,Ti)O3

2008 ◽  
Vol 41 (5) ◽  
pp. 930-938 ◽  
Author(s):  
K. Z. Baba-Kishi ◽  
T. R. Welberry ◽  
R. L. Withers
Keyword(s):  
Monte Carlo ◽  
Composition Range ◽  
Rhombohedral Phase ◽  
Boundary Region ◽  
Three Dimensions ◽  
Computer Simulation Model ◽  
Strongly Correlated ◽  
Monte Carlo Simulation Study ◽  
Transmission Electron ◽  
Diffraction Patterns

Transverse polarized diffuse streaks have been recordedviatransmission electron microscopy for a range of Pb(Zr1−xTix)O3ceramics spanning the entire phase diagram from the rhombohedral phase (x= 0.3), through the monoclinic morphotropic phase boundary region (MPB;x= 0.48) to the tetragonal phase (x = 0.7). Although the same type of streaks are observed over the whole composition range, they are strongest and most distinct in the rhombohedral phase and diminish in clarity as the MPB is approached. The streaks have been shown to correspond to diffuse planes of scattering in three dimensions and are oriented normal to the (cubic) 〈111〉cdirections. A Monte Carlo computer simulation model has been developed that convincingly reproduces the observed diffraction patterns in the rhombohedral phase. In this model the displacements of Pb ions in chains running along each of the 〈111〉cdirections are directed along the chain and are strongly correlated from cell to cell. There is no evidence of lateral correlation, indicating that neighbouring chains are essentially independent.

An electron diffraction and Monte Carlo simulation study of an incommensurate antiferroelectric state in the relaxor ferroelectric Pb2ScTaO6

2009 ◽  
Vol 43 (1) ◽  
pp. 140-150 ◽  
Author(s):  
K. Z. Baba-Kishi ◽  
M. Pasciak
Keyword(s):  
Monte Carlo ◽  
Electron Diffraction ◽  
Relaxor Ferroelectric ◽  
Advanced Degree ◽  
Monte Carlo Simulation Study ◽  
Transmission Electron ◽  
Incommensurate Modulation ◽  
Pb Ions ◽  
Specific Temperature ◽  
Diffraction Patterns

Incommensurate satellite reflections modulating along the 〈110〉* directions have been observed in the electron diffraction patterns of single crystals of the relaxor ferroelectric Pb2ScTaO6(PST) recordedviatransmission electron microscopy. The satellites occur characteristically within a specific temperature range and display differing or variable modulation vectors relative to their primary reflections. The satellites represent a weak frustrated antiferroelectric state in PST, termed the incommensurate antiferroelectric (IAFE) state. The observed IAFE state coexists with the ferroelectric and paraelectric states within a specific temperature regime and is dynamic in nature, meaning that the dispositions of the satellites can be altered by varying the temperature applied to the crystal,in-situin the transmission electron microscope. The observed satellites are associated with thin, needle-shaped, closely packed striated domains of about 5–15 nm in width. The satellites appear exclusively in crystals of PST with an advanced degree of 1:1 chemical long-range order, exceeding 90%. The satellites and their domains are interpreted as originating from a displacive, antiferroelectric coupling of the ions, driven in particular by the Pb ions. The Monte Carlo (MC) method was used exhaustively to evaluate the structural regimes that lead to the occurrence of the IAFE state. In the MC simulations, the displacements were correlated with the ferroelectric and antiferroelectric couplings, resulting in the IAFE domains and their associated satellites of differing dispositions or modulation vectors. The results of the MC simulations agree well with the electron diffraction observations, supporting the model of an antiferroelectric displacement with an incommensurate modulation of the Pb ions in the 〈110〉* directions.

Diffuse scattering and Monte Carlo simulations of cyclohexane–perhydrotriphenylene (PHTP) inclusion compounds, C6H12/C18H30

1999 ◽  
Vol 32 (3) ◽  
pp. 464-471 ◽  
Author(s):  
S. C. Mayo ◽  
Th. Proffen ◽  
M. Bown ◽  
T. R. Welberry
Keyword(s):  
Monte Carlo ◽  
Scattering Data ◽  
Mutual Orientation ◽  
Computer Simulation Model ◽  
Guest Molecules ◽  
X Ray Scattering ◽  
Reversible Phase Transition ◽  
Crude Model ◽  
Diffraction Patterns ◽  
System Inclusion

A recently developed method for fitting a Monte Carlo computer simulation model to observed single-crystal diffuse X-ray scattering has been applied to (hk0) scattering data obtained for the guest–host system (inclusion compound) cyclohexane–perhydrotriphenylene (cyclohexane–PHTP), C6H12/C18H30, at 295 K. A simple two-dimensional model representing the projection of the structure downcwas used, which allowed refinement of short-range order parameters describing the mutual orientation of guest molecules within neighbouring channels, together with a parameter describing the coupling of these orientations to distortions of the host framework. Since the guest site still appears very disordered in projection, only a crude model for the shape of the guest molecule was used. The resulting calculated diffraction patterns showed good qualitative agreement with the observed pattern, but quantitatively the achieved agreement factor (R≃ 38%) was considerably higher than that achieved in comparable studies of a different system. Calculations of the contribution to the diffraction pattern of the guest alone and the host alone clearly indicate that the host framework distortion is modelled well, but the guest is not so well described. The lattice distortion revealed by the study indicates a tendency for the hexagonal network to distort towards local monoclinicity. This is consistent with the observation that at ~273 K, the compound undergoes a reversible phase transition to a micro-twinned monoclinic phase.

scholarly journals Comparative study of two lead-free piezoceramics using diffraction techniques

2010 ◽  
Vol 43 (4) ◽  
pp. 805-810 ◽  
Author(s):  
Ljubomira Ana Schmitt ◽  
Manuel Hinterstein ◽  
Hans-Joachim Kleebe ◽  
Hartmut Fuess
Keyword(s):  
Comparative Study ◽  
Rhombohedral Phase ◽  
Local Scale ◽  
Lead Free ◽  
Structural Investigations ◽  
X Ray ◽  
Space Groups ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
Two Phases

A comparative study of two distinct lead-free piezoceramics, (Bi0.5Na0.5TiO3)0.92–(BaTiO3)0.06–(K0.5Na0.5NbO3)0.02and (Bi0.5Na0.5TiO3)0.94–(BaTiO3)0.05–(K0.5Na0.5NbO3)0.01, termed 92-06-02 and 94-05-01, respectively, is presented. The samples were investigated by complementary diffraction techniques, namely X-ray, neutron and electron diffraction. Transmission electron microscopy (TEM) and powder diffraction experiments clearly revealed the presence of both rhombohedral and tetragonal phases in space groupsR3candP4bm, respectively. Superlattice reflections observed in the diffraction patterns were used to identify the two phases. It was found that sample 92-06-02, with a high proportion of the nonpolar tetragonal phase, shows a grainy contrast, whereas specimen 94-05-01 features domain-like contrast, related to a higher rhombohedral phase fraction. The combination of local scale analysesviaTEM with X-ray and neutron diffraction provides the experimental basis for further structural investigations.

Diffuse X-ray scattering from 4,4′-dimethoxybenzil, C16H14O4: analysis via automatic refinement of a Monte Carlo model

2003 ◽  
Vol 59 (6) ◽  
pp. 760-769 ◽  
Author(s):  
T. R. Welberry ◽  
A. P. Heerdegen
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Model ◽  
Force Constants ◽  
Computer Simulation Model ◽  
X Ray ◽  
X Ray Scattering ◽  
Degree Of Certainty ◽  
Data Points ◽  
Diffraction Patterns ◽  
Ray Scattering

A recently developed method for fitting a Monte Carlo computer-simulation model to observed single-crystal diffuse X-ray scattering has been used to study the diffuse scattering in 4,4′-dimethoxybenzil, C16H14O4. A model involving only nine parameters, consisting of seven intermolecular force constants and two intramolecular torsional force constants, was refined to give an agreement factor, \omega R = \left[ \textstyle\sum \omega \, (\Delta I \,)^2 / \sum \omega \, I_{\rm obs}^2 \right] ^{1/2}, of 18.1% for 118 918 data points in two sections of data. The model was purely thermal in nature. The analysis has shown that the most prominent features of the diffraction patterns, viz. diffuse streaks that occur normal to the {\rm [1 0 }\overline {\rm 1}] direction, are due to longitudinal displacement correlations along chains of molecules extending in this direction. These displacements are transmitted from molecule to molecule via contacts involving pairs of hydrogen bonds between adjacent methoxy groups. In contrast to an earlier study of benzil itself, it was not found to be possible to determine, with any degree of certainty, the torsional force constants for rotations about the single bonds in the molecule. It is supposed that this result may be due to the limited data available in the present study.

Electronic Cone Illumination with the Conventional Transmission Electron Microscope

1977 ◽  
Vol 35 ◽  
pp. 72-73
Author(s):  
William Krakow
Keyword(s):  
Electronic Device ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Hollow Cone ◽  
Transmission Electron ◽  
Lissajous Figures ◽  
High Resolution Images ◽  
Imaging Mode ◽  
Diffraction Patterns ◽  
Transmission Microscope

An electronic device has been constructed which manipulates the primary beam in the conventional transmission microscope to illuminate a specimen under a variety of virtual condenser aperture conditions. The device uses the existing tilt coils of the microscope, and modulates the D.C. signals to both x and y tilt directions simultaneously with various waveforms to produce Lissajous figures in the back-focal plane of the objective lens. Electron diffraction patterns can be recorded which reflect the manner in which the direct beam is tilted during exposure of a micrograph. The device has been utilized mainly for the hollow cone imaging mode where the device provides a microscope transfer function without zeros in all spatial directions and has produced high resolution images which are also free from the effect of chromatic aberration. A standard second condenser aperture is employed and the width of the cone annulus is readily controlled by defocusing the second condenser lens.

Deviations from Ideal Decagonal Symmetry in Electron Diffraction Patterns of the “Decagonal” Phase in the Al-Co-Cu Alloy System

1991 ◽  
Vol 49 ◽  
pp. 914-915
Author(s):  
Atul S. Ramani ◽  
Earle R. Ryba ◽  
Paul R. Howell
Keyword(s):  
Electron Microscope ◽  
Alloy System ◽  
Nominal Composition ◽  
Dimensional Lattice ◽  
3 Dimensional ◽  
Decagonal Phase ◽  
Cu Alloy ◽  
Transmission Electron ◽  
Lattice Periodicity ◽  
Diffraction Patterns

The “decagonal” phase in the Al-Co-Cu system of nominal composition Al65CO15Cu20 first discovered by He et al. is especially suitable as a topic of investigation since it has been claimed that it is thermodynamically stable and is reported to be periodic in the dimension perpendicular to the plane of quasiperiodic 10-fold symmetry. It can thus be expected that it is an important link between fully periodic and fully quasiperiodic phases. In the present paper, we report important findings of our transmission electron microscope (TEM) study that concern deviations from ideal decagonal symmetry of selected area diffraction patterns (SADPs) obtained from several “decagonal” phase crystals and also observation of a lattice of main reflections on the 10-fold and 2-fold SADPs that implies complete 3-dimensional lattice periodicity and the fundamentally incommensurate nature of the “decagonal” phase. We also present diffraction evidence for a new transition phase that can be classified as being one-dimensionally quasiperiodic if the lattice of main reflections is ignored.

An Interactive Minicomputer Program for the Indexing and Simulation of Electron Diffraction Patterns

1976 ◽  
Vol 34 ◽  
pp. 542-543
Author(s):  
R.P. Goehner ◽  
W.T. Hatfield ◽  
Prakash Rao
Keyword(s):  
Electron Diffraction ◽  
Real Time ◽  
Pattern Analysis ◽  
Flow Diagram ◽  
Hard Copy ◽  
Time Analysis ◽  
Real Time Analysis ◽  
Transmission Electron ◽  
One Step ◽  
Diffraction Patterns

Computer programs are now available in various laboratories for the indexing and simulation of transmission electron diffraction patterns. Although these programs address themselves to the solution of various aspects of the indexing and simulation process, the ultimate goal is to perform real time diffraction pattern analysis directly off of the imaging screen of the transmission electron microscope. The program to be described in this paper represents one step prior to real time analysis. It involves the combination of two programs, described in an earlier paper(l), into a single program for use on an interactive basis with a minicomputer. In our case, the minicomputer is an INTERDATA 70 equipped with a Tektronix 4010-1 graphical display terminal and hard copy unit.A simplified flow diagram of the combined program, written in Fortran IV, is shown in Figure 1. It consists of two programs INDEX and TEDP which index and simulate electron diffraction patterns respectively. The user has the option of choosing either the indexing or simulating aspects of the combined program.

Effects of High-Energy Ions on Synthetic Quartz

1972 ◽  
Vol 30 ◽  
pp. 544-545
Author(s):  
Joseph J. Comer ◽  
Charles Bergeron ◽  
Lester F. Lowe
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Beam ◽  
High Energy ◽  
Transmission Electron ◽  
Kikuchi Lines ◽  
High Energy Ions ◽  
Diffraction Patterns ◽  
Dauphiné Twinning ◽  
Beam Damage

Using a Van De Graaff Accelerator thinned specimens were subjected to bombardment by 3 MeV N+ ions to fluences ranging from 4x1013 to 2x1016 ions/cm2. They were then examined by transmission electron microscopy and reflection electron diffraction using a 100 KV electron beam.At the lowest fluence of 4x1013 ions/cm2 diffraction patterns of the specimens contained Kikuchi lines which appeared somewhat broader and more diffuse than those obtained on unirradiated material. No damage could be detected by transmission electron microscopy in unannealed specimens. However, Dauphiné twinning was particularly pronounced after heating to 665°C for one hour and cooling to room temperature. The twins, seen in Fig. 1, were often less than .25 μm in size, smaller than those formed in unirradiated material and present in greater number. The results are in agreement with earlier observations on the effect of electron beam damage on Dauphiné twinning.

A Novel TEM Technique for Characterizing As-Grown CVD Diamond Films

1991 ◽  
Vol 49 ◽  
pp. 956-957 ◽  
Author(s):  
Z.L. Wang ◽  
J. Bentley ◽  
R.E. Clausing ◽  
L. Heatherly ◽  
L.L. Horton
Keyword(s):  
Diamond Films ◽  
Chemical Vapor ◽  
Growth Direction ◽  
Dark Field ◽  
Growth Surface ◽  
Specimen Preparation ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
First Time ◽  
Microstructural Studies

Microstructural studies by transmission electron microscopy (TEM) of diamond films grown by chemical vapor deposition (CVD) usually involve tedious specimen preparation. This process has been avoided with a technique that is described in this paper. For the first time, thick as-grown diamond films have been examined directly in a conventional TEM without thinning. With this technique, the important microstructures near the growth surface have been characterized. An as-grown diamond film was fractured on a plane containing the growth direction. It took about 5 min to prepare a sample. For TEM examination, the film was tilted about 30-45° (see Fig. 1). Microstructures of the diamond grains on the top edge of the growth face can be characterized directly by transmitted electron bright-field (BF) and dark-field (DF) images and diffraction patterns.

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