摘要:

The contrast of dislocations in icosahedral Al62Cu25·5Fe12·5was investigated in the transmission electron microscope. It was found that the contrast vanishes under two basically different diffraction conditions. This is different from the behaviour in normal crystals and is due to the special structural features of dislocations in quasiperiodic lattices. Quantitative evaluation of the results indicates that the phason component of the dislocation strain field is substantially stronger than the phonon component.

ISSN:0950-0839    

DOI:10.1080/09500839208215141

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A chemical composition modulation, driven by diffusion, is suggested to occur during the transition from the icosahedral to the rhombohedra1 state of Al63·5Fe12·5Cu24, studied as a function of the temperature and time of annealing by electron diffraction, microscopy and X-ray energy-dispersive spectroscopy.

ISSN:0950-0839    

DOI:10.1080/09500839208215142

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A kinetic model based on the theory of strain-induced interactions is developed to describe the effect of elastic strain on structural transformation kinetics. An ordering transition resulting in a reduction in the crystal lattice point-group symmetry in a substitutional solid solution is considered. Our computer simulation of a two-dimensional model binary alloy revealed the detailed kinetics of formation of tweed morphologies and the tweed → twin coarsening process driven by the transformation-induced elastic strains.

ISSN:0950-0839    

DOI:10.1080/09500839208215143

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Structural changes after heat treatment of an icosahedral phase of melt-spun Al—Pd—Mn alloys have been studied by X-ray powder diffraction and transmission electron microscopy. Around the compositions Al70Pd20Mn10and Al70Pd23Mn7, no phase transition occurs on annealing, and the icosahedral phase is stable up to the melting point. However, for the Al70Pd26Mn4sample, the icosahedral phase transforms into a 2/1 cubic approximant crystalline phase at 750°C. A decagonal quasicrystal is formed for a melt-spun Al75Pd20Mn5alloy.

ISSN:0950-0839    

DOI:10.1080/09500839208215144

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

High-order Laue zone (HOLZ) line patterns of an Al70Co15Ni15quasicrystalline decagonal phase with a periodicity of 0·4 nm along the tenfold axis have been obtained experimentally with a large angular range by connecting a series of large-angle convergent-beam electron diffraction patterns. The computer-simulated HOLZ line patterns, which were calculated using the cut-and-projection method and a simple quasi-lattice model, show good agreement with the experimental observations.

ISSN:0950-0839    

DOI:10.1080/09500839208215145

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Amorphous silica structures which are a few nanometres in width and tens of nanometres in length are seen to become unstable under intense electron irradiation against plastic deformation, necking and failure. Similarly irradiated atomistically sharp tips, which are observed to be stable in crystalline materials, undergo rapid blunting in amorphous structures, caused by evaporation and enhanced viscous flow. The tip extremities separate into spherical bulbs by necking, and local clustering is seen during fluctuations in the microscopic structure. The observations provide information on the nature of microscopic diffusion and flow, during kinetic phenomena such as failure of amorphous structures.

ISSN:0950-0839    

DOI:10.1080/09500839208215146

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Quasiperiodicity related to four-dimensional space has been explored. A new method of generating quasiperiodic Penrose tilings and other quasiperiodic lattices is put forward. The method used here can easily be extended to other higher-dimensional spaces.

ISSN:0950-0839    

DOI:10.1080/09500839208215147

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

As-cast alloy ingots of nominal compositions Al65Co20Cu15, A160Co20Cu20, Al65Co15Cu20, and Al70Co15Cu15were studied with transmission electron microscopy and energy-dispersive X-ray spectroscopy. A compositional variation among the grains, in each alloy, allowed an examination of phase formation as a function of the ternary composition near the nominal compositions. Alloys of composition Al65Co20Cu15, often taken as a stable decagonal phase, instead form a large (about 100 Å) unit-cell crystal phase that approximates the decagonal phase. No decagonal phase forms near this composition. True decagonal phase formation is only observed in a narrow phase field centred near Al65Co15Cu20.

ISSN:0950-0839    

DOI:10.1080/09500839208215148

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The effect of light polarization on the photodoping of As2S3films is reported. Provided that the photodoping is performed with linearly polarized light, a large negative photodichroism is induced. If the sample is thermally doped prior to illumination with linearly polarized light, the photodichroism is positive and its value is much smaller. A microscopic model is proposed based on the assumption that linearly polarized light, being absorbed predominantly by glass fragments oriented parallel to the electric vector of the light, can either destroy these fragments or increase their number, which would result in different signs of the photo-induced dichroism.

ISSN:0950-0839    

DOI:10.1080/09500839208215149

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor