Computer simulation of ferroelastic phase transition in LaNbO4

1997 ◽  
Vol 12 (9) ◽  
pp. 2428-2437 ◽  
Author(s):  
K. Parlinski ◽  
Y. Hashi ◽  
S. Tsunekawa ◽  
Y. Kawazoe
Keyword(s):  
Phase Transition ◽  
Domain Walls ◽  
Unit Cell ◽  
Model Parameters ◽  
Domain Pattern ◽  
Degree Of Deformation ◽  
Ferroelastic Phase Transition ◽  
Tetragonal Unit Cell ◽  
Transmission Electron ◽  
Potential Parameters

A model of lanthanum orthoniobate which possesses a ferroelastic tetragonalmonoclinic phase transition is proposed. It contains only one particle per unit cell, but it is constructed consistently with symmetry changes at the phase transition. The model parameters are chosen to reproduce the bare soft mode, degree of deformation of the tetragonal unit cell to a monoclinic one, and the phase transition temperature. The ferroelastic system with free boundary conditions was simulated by the molecular dynamics technique, and the second order phase transition was reproduced. The studied annealing process shows formation of the stripe lenticular domain pattern, which has been interrupted by the appearance of a temporary band of perpendicularly oriented lenticular domains. The maps contain W′-type domain walls whose orientations are fixed only by interplay of potential parameters and not by symmetry elements. The simulated domain pattern has the same features as those observed by transmission electron microscopy.

INTERNAL FRICTION ASSOCIATED WITH DOMAIN WALLS AND FERROELASTIC PHASE TRANSITION IN LNPP

1985 ◽  
Vol 46 (C10) ◽  
pp. C10-609-C10-612 ◽  
Author(s):  
SUN WENYUAN ◽  
SHEN HUIMIN ◽  
WANG YENING ◽  
LU BAOSHENG
Keyword(s):  
Phase Transition ◽  
Internal Friction ◽  
Domain Walls ◽  
Ferroelastic Phase Transition

Ferroelastic orientation states and domain walls in lead phosphate type crystals

2000 ◽  
Vol 64 (2) ◽  
pp. 233-239 ◽  
Author(s):  
U. Bismayer ◽  
D. Mathes ◽  
D. Bosbach ◽  
A. Putnis ◽  
G. van Tendeloo ◽  
...  
Keyword(s):  
Domain Walls ◽  
X Ray Diffraction ◽  
Lead Phosphate ◽  
Pure Lead ◽  
X Ray ◽  
Force Microscopy ◽  
Lead Arsenate ◽  
Atomic Force ◽  
Ferroelastic Phase Transition ◽  
Transmission Electron

AbstractThe monoclinic structural distortion in lead phosphate and lead arsenate is correlated with the ferroelastic phase transition R3̄m → C2/c and R3̄m → P21/c respectively. The resulting domain patterns in the mixed compounds depend on their chemical composition. The intersection of ferroelastic W domain walls with the (100) surface of lead phosphate-arsenate mixed crystals has been imaged using tapping mode atomic force microscopy. Dilution of the strain leads to characteristic surface deformations which deviate from those in pure lead phosphate. In high twinned lead phosphate-arsenate, X-ray diffraction (XRD) was used to show renormalization effects and scattering phenomena stemming from the twin walls. The wall trajectory was found to be independent of chemical variations using transmission electron microscopy.

Microstructural evolution of mullites produced from single-phase gels

2007 ◽  
Vol 40 (2) ◽  
pp. 260-276 ◽  
Author(s):  
Marek Andrzej Kojdecki ◽  
Esther Ruiz de Sola ◽  
Francisco Javier Serrano ◽  
Estefanía Delgado-Pinar ◽  
María Mercedes Reventós ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Unit Cell ◽  
Molar Ratio ◽  
Model Parameters ◽  
X Ray Diffraction ◽  
Unit Cell Parameters ◽  
X Ray ◽  
Cell Parameters ◽  
Transmission Electron ◽  
Diffraction Patterns

The crystalline microstructure of mullites obtained by heating monophasic gels has been investigated. Gels with alumina to silica molar ratio of 3:2 (as in secondary mullite) and 2:1 (as in primary mullite) were prepared by gelling mixtures of aluminium nitrate and tetraethylorthosilicate. Phase transformations were induced by heating the gel precursors, with different final treatment temperatures between 1173 and 1873 K. The mullites formed as a result of thermal treatment were studied by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The crystalline structure (unit-cell parameters) and microstructure were determined from X-ray diffraction patterns. The formation of mullites of homogeneous chemical composition and with unit-cell parameters depending almost linearly on the treatment temperature was found. Their compositions, expressed as alumina to silica molar ratio, were determined from the unit-cell parameters and were in the range of those characterizing primary and secondary mullites. Mullites processed at lower temperatures were accompanied by small amounts of vitreous phase. The crystalline microstructure of the obtained mullites was interpreted by means of a mathematical model of polycrystalline material, involving prevalent crystallite shape, volume-weighted crystallite size distribution and second-order crystalline lattice strain distribution as model parameters. The model parameters were determined for each sample by modelling its X-ray diffraction pattern and fitting it to a measured pattern. Bimodality of the size distribution was observed and explained as a consequence of two crystallite nucleation and growth processes, which started from small alumina-rich and alumina-poor domains, spontaneously formed in a precursor gel at early stages of heating. Images produced by scanning and transmission electron microscopy agreed well with the characteristics obtained from the analysis of the X-ray diffraction patterns.

HREM study of ferroelectric domain wall in barium titanate

1994 ◽  
Vol 52 ◽  
pp. 566-567
Author(s):  
Laurent. Normand ◽  
Alain. Thorel ◽  
Yvan. Montardi
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Barium Titanate ◽  
Domain Walls ◽  
Ferroelectric Phase ◽  
Ferroelectric Domain ◽  
Transmission Electron ◽  
The One

This study focuses on High Resolution Transmission Electron Microscopy of barium titanate in its tetragonal ferroelectric phase, and especially on the structure of domain walls. This phase is stable between about 0 °C and 130 °C. During cooling, at 130 °C barium titanate changes from a cubic parraelectric phase to a tetragonal ferroelectric phase. In this phase the spontaneous polarisation is along one of the six [001] pseudo-cubic directions. Two types of domains can be formed during the phase transition :90° and 180° domains. In 90° domains the polarisation is at 90° from the polarisation of the next domain (exactly 2* ArcTan(a/c) if a and c are the lattice parameters). For these domains the domain walls are <110< type planes ; In 180° domains the polarisation is at 180° from the one in the next domain. 180° domain walls are <100< type plane and are assumed to be purely ferroelectric.

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