Positron-Annihilation Study of Icosahedral AlPdMn Alloys

Kanazawa, I.; Hamada, E.; Saeki, Takao; Sato, K.; Nakata, Masao; Takeuchi, Shin; Wollgarten, Markus

doi:10.1103/physrevlett.79.2269

Cited by 39 publications

(15 citation statements)

References 21 publications

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“…We sug- gest another mechanism responsible for the roughening procedure. It is well known that quasicrystals contain many vacancies the total concentration of which can exceed 10% as has been studied by positron lifetime investigations, for instance [8,14]. It is reasonable to assume that upon heating the vacancies assemble to form voids that requires heterogeneous nucleation, e.g.…”

Section: Discussionmentioning

confidence: 99%

Hillock Growth Phenomena during Post-Indentation Annealing of Quasicrystalline AlPdMn

Wolf

Baunack²,

Paufler

1999

phys. stat. sol. (a)

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Single‐quasicrystalline icosahedral AlPdMn was subject to Vickers microindentations at room temperature, annealed up to 750 °C in vacuum, and then inspected using optical microscopy, atomic force microscopy (AFM), wavelength dispersive microanalysis (WDX) and Auger spectroscopy (AES). At temperatures above 600 °C the whole sample surface became increasingly rough, exhibiting holes and small elevations, whereas the vicinity of the impressions remained free of surface alterations. The growth of large hillocks out of the impressions was observed at temperatures above 700 °C in the presence of oxygen. No growth of high elevations was noted for an oxygen partial pressure below 3 × 10—6 Pa. AES and WDX revealed an enrichment of manganese and the depletion of aluminium in the hillocks. The results are discussed in the frame of indentation induced defects and their impact on diffusion and surface migration.

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Section: Discussionmentioning

confidence: 99%

Hillock Growth Phenomena during Post-Indentation Annealing of Quasicrystalline AlPdMn

Wolf

Baunack²,

Paufler

1999

phys. stat. sol. (a)

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“…Furthermore, it seems reasonable to consider that the structures in some icosahedral and decagonal phases can also be regarded as modulated structures due to CDWs; the formation and stability of these phases are related to the valence electron concentration (Tsai et al, 1990(Tsai et al, , 1994. Positron annihilation measurements showed that a high density of atomic vacancies exists in icosahedral phases (Kanazawa et al, 1997). Moreover, it should be noted that the structure of/tAI4Mn (Shoemaker et al, 1989), which is closely related to the icosahedral and decagonal phases, is composed of layers with ordered atomic vacancies.…”

Section: Journal Of Applied Crystallographymentioning

confidence: 99%

Modulated-Crystal Model for the Twelvefold Quasicrystal Ta62Te38

Uchida¹,

Horiuchi²

1998

J Appl Cryst

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A transmission electron microscopy study reveals that the so-called twelvefold quasicrystal Ta62Te3s is a crystal subjected to structure modulation. It is composed of two incommensurate layers rotated by 30 ° to each other about their normal. High-resolution electron microscope images show the formation of commensurate domains and their discommensuration. The observed electron diffraction patterns may be explained by a kinematical calculation for the commensurate cell, designated as a 7 × 7 cell. The modulation is considered to be due to the rearrangement of atomic vacancies in response to the occurrence of charge-density waves.

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“…[1][2][3][4][5][6][7] Most investigations of defects in quasicrystals focused on line or planar defects, 8,9 which give rise to clear contrasts in transmissionelectron microscope images, or on phason strain fields, whose signatures can be observed by neutron-and x-ray scattering experiments. 10 Point defects, such as vacancies, turned out to be much more difficult to identify and characterize, because positron annihilation measurements [11][12][13] could not distinguish between missing atoms, i.e., real vacancies, and the densely distributed vacancylike sites arising from open spaces in, e.g., the perfect Al-Pd-Mn quasicrystal structure. 11,12 The high concentration of open spaces in the perfect icosahedral structure makes all positrons annihilate in such open spaces, which have long positron lifetimes and thus appear as vacancylike sites.…”

Section: Introductionmentioning

confidence: 99%

“…10 Point defects, such as vacancies, turned out to be much more difficult to identify and characterize, because positron annihilation measurements [11][12][13] could not distinguish between missing atoms, i.e., real vacancies, and the densely distributed vacancylike sites arising from open spaces in, e.g., the perfect Al-Pd-Mn quasicrystal structure. 11,12 The high concentration of open spaces in the perfect icosahedral structure makes all positrons annihilate in such open spaces, which have long positron lifetimes and thus appear as vacancylike sites. As a consequence the positron annihilation signals are saturated and no decomposition of the lifetime spectra is possible.…”

Section: Introductionmentioning

confidence: 99%

Surface structure of Al-Pd-Mn quasicrystals: Existence of supersaturated bulk vacancy concentrations

et al. 2003

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We identified the presence and chemical nature of bulk vacancies in Al-Pd-Mn quasicrystals by measuring the structure and composition of two-and fivefold cleavage surfaces of different preannealed quasicrystals subjected to postcleavage heat treatments using scanning electron microscopy and Auger electron spectroscopy. A strong dependence of the surface structure from the preannealing is observed and explained by varying concentrations of bulk vacancies. The analysis of the data shows that as-grown Al-Pd-Mn quasicrystals contain Al, Pd, and Mn vacancies in supersaturated but near stoichiometric concentrations, while long-term preannealed samples contain a much lower vacancy concentration, with a tendency to have excess Al vacancies. We found that Al and Mn vacancies are more mobile at lower temperatures than Pd vacancies, and that the diffusion of Mn vacancies is directly coupled to the mobility of Al vacancies. The results demonstrate that the evolution of the surface structure is primarily affected by bulk vacancies migrating toward the surface during heat treatments and provide a new methodology to characterize the vacancies in intermetallic alloys. We identified the presence and chemical nature of bulk vacancies in Al-Pd-Mn quasicrystals by measuring the structure and composition of two-and fivefold cleavage surfaces of different preannealed quasicrystals subjected to postcleavage heat treatments using scanning electron microscopy and Auger electron spectroscopy. A strong dependence of the surface structure from the preannealing is observed and explained by varying concentrations of bulk vacancies. The analysis of the data shows that as-grown Al-Pd-Mn quasicrystals contain Al, Pd, and Mn vacancies in supersaturated but near stoichiometric concentrations, while long-term preannealed samples contain a much lower vacancy concentration, with a tendency to have excess Al vacancies. We found that Al and Mn vacancies are more mobile at lower temperatures than Pd vacancies, and that the diffusion of Mn vacancies is directly coupled to the mobility of Al vacancies. The results demonstrate that the evolution of the surface structure is primarily affected by bulk vacancies migrating toward the surface during heat treatments and provide a new methodology to characterize the vacancies in intermetallic alloys. Keywords Ames Laboratory Disciplines Physical Chemistry Comments This article is from

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Positron-Annihilation Study of Icosahedral AlPdMn Alloys

Cited by 39 publications

References 21 publications

Hillock Growth Phenomena during Post-Indentation Annealing of Quasicrystalline AlPdMn

Hillock Growth Phenomena during Post-Indentation Annealing of Quasicrystalline AlPdMn

Modulated-Crystal Model for the Twelvefold Quasicrystal Ta62Te38

Surface structure of Al-Pd-Mn quasicrystals: Existence of supersaturated bulk vacancy concentrations

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