Structural Phase Transitions Of Decagonal Quasicrystals

MRS Proceedings ◽

10.1557/proc-553-159 ◽

1998 ◽

Vol 553 ◽

Cited By ~ 4

Author(s):

W. Steurer

Keyword(s):

Phase Transitions ◽

Structural Phase ◽

Atomic Scale ◽

Atomic Diffusion ◽

Modulated Structure ◽

Positional Disorder ◽

Atomic Displacements ◽

Decagonal Quasicrystals ◽

Step Model ◽

Quasiperiodic Structures

AbstractA two step model for the transformation of decagonal quasicrystals (DQC) to their crystalline approximants is presented. First, a partially disordered approximant domain structure results rapidly from small atomic displacements. Subsequently, atomic diffusion leads very slowly to an ordered approximant crystal (AC) structure. The model is discussed on atomic scale. Its basic idea is to describe the structure of a quasicrystal (QC) as incommensurately modulated structure (IMS). In that description, the average structure (AS) of a QC is at the same time the AS of all its irrational and rational approximants. In this approach, the positional quasicrystal- to-approximant-crystal (QC-AC) transformation can be performed by atomic displacements smaller than any interatomic distance. This mechanism, however, leads inherently to to a certain amount of chemical disorder. In most cases also some positional disorder will result. The tools developed for the description of phase transitions of IMS can analogously be used for QC. Examples for one- and two-dimensional quasiperiodic structures are discussed.

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The quasicrystal-to-crystal transformation. I. Geometrical principles

Zeitschrift für Kristallographie - Crystalline Materials ◽

10.1524/zkri.2000.215.6.323 ◽

2000 ◽

Vol 215 (6) ◽

Cited By ~ 12

Author(s):

Walter Steurer

Keyword(s):

Three Dimensional ◽

Geometrical Model ◽

Atomic Scale ◽

Atomic Diffusion ◽

Positional Disorder ◽

Average Structure ◽

Crystal Transformation ◽

Atomic Displacements ◽

Modulated Phases ◽

Quasiperiodic Structures

A geometrical model of the quasicrystal-to-crystal transformation is discussed on atomic scale. The central idea is to describe a quasiperiodic structure as a special type of incommensurately modulated structure. As a consequence thereof, the periodic average structure of a quasicrystal is also the average structure of all its rational and irrational approximants. Then, quasicrystals can formally be transformed to approximants by atomic displacements smaller than any interatomic distance. This transformation, however, leads to chemically partially disordered resultants, and in the case of two- and three-dimensional quasiperiodic structures also to a certain amount of positional disorder. Fully ordered approximant structures can only be obtained by atomic diffusion. One of the advantages of the present approach is that tools can be used that were developed for the description of phase transitions of incommensurately modulated phases. Examples for one- and three-dimensional quasiperiodic structures are discussed in detail.

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AMPLIMODES: symmetry-mode analysis on the Bilbao Crystallographic Server

Journal of Applied Crystallography ◽

10.1107/s0021889809028064 ◽

2009 ◽

Vol 42 (5) ◽

pp. 820-833 ◽

Cited By ~ 263

Author(s):

Danel Orobengoa ◽

Cesar Capillas ◽

Mois I. Aroyo ◽

J. Manuel Perez-Mato

Keyword(s):

Phase Transitions ◽

Structural Phase ◽

Mode Analysis ◽

Higher Symmetry ◽

Atomic Displacements ◽

Driving Mechanisms ◽

Distorted Structure ◽

Symmetry Structure ◽

Symmetry Mode ◽

Low Symmetry

AMPLIMODESis a computer program available on the Bilbao Crystallographic Server that can perform a symmetry-mode analysis of any distorted structure of displacive type. The analysis consists in decomposing the symmetry-breaking distortion present in the distorted structure into contributions from different symmetry-adapted modes. Given the high- and the low-symmetry structures,AMPLIMODESdetermines the atomic displacements that relate them, defines a basis of symmetry-adapted modes, and calculates the amplitudes and polarization vectors of the distortion modes of different symmetry frozen in the structure. The program uses a mode parameterization that is as close as possible to the crystallographic conventions, expressing all quantities for the asymmetric unit of the low-symmetry structure. Distorted structures are often related to their higher-symmetry counterparts by temperature- and/or pressure-driven phase transitions, ferroic phase transitions being a particular example. The automatic symmetry-mode analysis performed byAMPLIMODEScan be very useful for establishing the driving mechanisms of such structural phase transitions or the fundamental instabilities at the origin of the distorted phases.

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Methods for pseudosymmetry evaluation: a comparison between the atomic displacements and electron density approaches

Zeitschrift für Kristallographie - Crystalline Materials ◽

10.1524/zkri.220.8.691.67076 ◽

2005 ◽

Vol 220 (8) ◽

Cited By ~ 3

Author(s):

Cesar Capillas ◽

Mois I. Aroyo ◽

Juan Manuel Perez-Mato

Keyword(s):

Phase Transitions ◽

Electron Density ◽

High Temperatures ◽

Structural Phase ◽

Fundamental Property ◽

Computer Programs ◽

Structural Phase Transitions ◽

Atomic Displacements ◽

Web Tools ◽

Form Part

AbstractStructural pseudosymmetry is a fundamental property to be considered when trying to predict structural phase transitions at high temperatures. In the present work, two methods for detecting and characterizing pseudosymmetry, the here-calledAlgorithmic procedures based on the two approaches have been implemented in two computer programs. They form part of the Bilbao Crystallographic Server as free web tools.

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