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Structure of a metastable Al3Ni decagonal quasicrystal: comparison with a highly perfect Al72Ni20Co8
Journal of Alloys and Compounds 342 (2002) 96–100
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Structure of a metastable Al 3 Ni decagonal quasicrystal: comparison with a highly perfect Al 72 Ni 20 Co 8 E. Abe*, A.P. Tsai Aperiodic Solids Research Team, National Institute for Materials Science, 1 -2 -1 Sengen, Tsukuba 305 -0047, Japan
Abstract We study the structure of a decagonal quasicrystalline phase formed in a rapidly-solidified Al 3 Ni alloy, by using electron diffraction and atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM). Electron diffraction patterns of the metastable Al 3 Ni phase reveal features quite similar to those of the stable Al 72 Ni 20 Co 8 phase; a large number of reflections in the tenfold symmetry plane and no significant diffuse streaks in the twofold patterns, indicating a good quasiperiodic order of the phase. Z-contrast STEM imaging shows that the structure of the Al 3 Ni phase can be interpreted based on a decagonal atomic cluster column with broken tenfold symmetry, being basically isostructural with that of the Al 72 Ni 20 Co 8 phase. Structural disorders are found to be significant at the core of the decagonal atomic clusters in the metastable Al 3 Ni decagonal phase. 2002 Elsevier Science B.V. All rights reserved. Keywords: Al–Ni system; Decagonal quasicrystal; Metastable phase; Electron diffraction; Atomic-resolution Z-contrast
1. Introduction The Al–Ni–Co system is one of the well-studied quasicrystal-forming alloys, in which various structural types of thermodynamically stable decagonal (d-) quasicrystal occur depending on alloy composition. In particular, the decagonal structure is sensitive to the Ni / Co ratios for the compositions around Al |70 Ni |302x Co x . Among these, a highly-perfect d-phase with significantly less structural disorders can be obtained for a very narrow composition range at Ni-rich side [1,2], e.g. Al 72 Ni 20 Co 8 , while other d-Al–Ni–Co phases exhibit significant diffuse streaks. This nearly-ideal quasicrystalline phase, referred to as a Ni-rich d-Al–Ni–Co with basic structure, is thus an excellent sample for structural analysis and has been studied extensively [3–10]. One of the interesting findings is a broken tenfold-symmetry of decagonal clusters with a diameter of |2 nm [3] (denoted as 2-nm cluster hereafter), which is a structural unit of the d-Al–Ni–Co phase and had been believed to be tenfold-symmetry. This symmetry breaking feature is found to be due not to random disorders [4,5] but to an intrinsic configuration of the structure [6,7], leading to a structural model based on the cluster with *Corresponding author. Tel.: 181-298-592-349; fax:181-298-592301. E-mail address: [email protected] (E. Abe).
broken tenfold symmetry, alternative to previous highsymmetric cluster models. Some crystalline phases of compositions similar to corresponding quasicrystalline phases may provide significant information on building unit clusters such as those likely to exist in the quasicrystals, a typical example of which is known as approximant crystals. For the d-Al–Ni– Co quasicrystals, Al 13 TM 4 (TM5Fe or Co), t-inflated Al 13 Co 4 [11] and W–Al 72.5 Ni 7.5 Co 20 [12] compounds are expected to possess key structural features, and in fact the latter two compounds are found to be composed of a 2-nm cluster with fivefold-symmetry [12,13]. One may claim that this fivefold-symmetry cluster should be a basic structural unit for the d-Al–Ni–Co quasicrystals [4,5]; this is actually confirmed to be true for the d-Al–Ni–Co phases which essentially reveal superlattice reflections and strong diffuse streaks [14]. However, this fivefold symmetry cluster description is evidently not appropriate for the Al 72 Ni 20 Co 8 phase with basic structure, for which the symmetry of the 2-nm clusters is not ten- or fivefold but mirror or lower one. Therefore, it may be quite controversial to treat the above crystalline compounds as being closely related structurally to the basic Al 72 Ni 20 Co 8 phase. It should be noted that these compounds occur in a binary Al–Co or Co-rich side in Al |70 Ni |302x Co x alloys, and hence are likely to correspond to the Co-rich d-Al–Ni–Co phases.
0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )00150-0
E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
In the present work, we show that, based on electron diffraction and atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) observations, a metastable d-phase formed in a rapidly solidified Al 3 Ni alloy [15] has a well-ordered quasiperiodic structure exhibiting characteristics quite similar to those of the basic d-Al 72 Ni 20 Co 8 quasicrystal. Interestingly, the corresponding stable crystalline phase, a stoichiometric Al 3 Ni compound, has rather a simple structure (orthorhombic, Pnma, a56.61, b57.37, c54.81 ˚ which is neither a well-defined approximant crystal nor A), is composed of decagonal atomic clusters. Nevertheless, Al 3 Ni is a potential crystalline phase that forms a quasicrystalline phase of high structural quality, as will be clearly demonstrated in the present work.
97
2. Experimental An Al 3 Ni alloy was rapidly solidified using a meltspinning apparatus with a single Cu roller (diameter of 20 cm) rotating at 4000 rpm. It is confirmed by powder X-ray diffraction that the product alloy-flakes are composed of almost single d-Al 3 Ni phase, and hence the present dphase is regarded as a metastable product of the orthorhombic Al 3 Ni crystalline phase. For electron microscope observations, alloy-flakes were crushed into powder and then dispersed on perforated carbon films. An atomicresolution Z-contrast image was obtained by a 200-kV field-emission transmission electron microscope (Jeol ˚ JEM-2010F) which provides a minimum probe of |1.5 A with a convergence angle of |10 mrad. The annular
Fig. 1. Electron diffraction patterns of the Al 3 Ni decagonal phase, taken with the incident beam parallel to the (a) tenfold and (b), (c) twofold symmetry axes. Twofold patterns of (b) and (c) are taken with the incidence along A- and B-directions in (a), respectively. Note that there are no significant diffuse streaks at the positions indicated by arrows.
E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
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detector was set to collect the electrons scattered at angles between 60 and 120 mrad, which are high enough to achieve the incoherent imaging condition and hence expected to reveal significant atomic-number dependent, Zcontrast.
3. Results and discussion Fig. 1(a)–(c) shows electron diffraction (ED) patterns
obtained from the metastable d-Al 3 Ni phase. In the tenfold symmetry pattern of (a), a large number of sharp reflections appear, and most reflections are located at correct tenfold symmetry positions, indicating a good long-range quasiperiodic order of the phase. Examination of the twofold patterns of (b) and (c) shows a periodic length ˚ and an extinction that causes the along c-axis of 4 A quasiperiodic reflection arrays in (b) to disappear in (c); see the position indicated by an arrow in (c). This indicates the existence of a 10 5 screw axis and / or a c-glide plane,
Fig. 2. (a) Atomic-resolution Z-contrast STEM image of the Al 3 Ni decagonal phase. (b) Overlap decagon (Gummelt) tiling and hexagon-boat-star (HBS) tiling superimposed onto the image, confirming that the Ni atom positions are quasiperodically well-correlated across the entire region. Note that some deviations of the spot positions from the tilings are due to image shift (sample-drift) during recording of a scanning image.
E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
leading to a plausible space group of P10 5 /mmc. All these diffraction features are quite similar to those of the basic d-Al 72 Ni 20 Co 8 of high structural perfection. It should be noted that, for the stable d-Al–Ni–Co phases except for the basic d-Al 72 Ni 20 Co 8 , this extinction is not completed, and some diffuse streaks remain in the pattern (c). Further, it is also pointed out that extra diffuse streaks frequently appear at the position indicated by arrows in (b) for the Co-rich d-Al–Ni–Co phases including those with superlat˚ tice structures, resulting in periodic c-length of 8 A. Evidently, there are no such diffuse streaks in (b) of the d-Al 3 Ni phase. Here, it is noteworthy that the Al 13 TM 4 (TM5Fe or Co), t-inflated Al 13 Co 4 and W–Al 72.5 ˚ along Ni 7.5 Co 20 compounds all have a unit length of |8 A that corresponding to the c-axis of the d-Al–Ni–Co phases, indicating that these compounds are structurally related to the Co-rich d-Al–Ni–Co phases. Fig. 2(a) shows an atomic-resolution Z-contrast image of the metastable d-Al 3 Ni phase. In the image, there is a quasiperiodic arrangement of bright dots representing Ni (or Ni-rich) atomic columns. Clearly, the 2-nm cluster can also be defined for the d-Al 3 Ni structure as a structuralunit, and the cluster commonly reveals a contrast of tenfold-symmetry breaking feature in the same manner as observed for the basic d-Al 72 Ni 20 Co 8 structure; see the 2-nm cluster indicated in Fig. 2(a). The symmetry breaking directions are found to be well-correlated across the entire region in the figure, as shown by superimposing the overlap decagon (Gummelt) tiling and the hexagon-boatstar (HBS) tiling, demonstrating that the d-Al 3 Ni has a well-ordered quasiperiodic atomic structure (note that for these two types of tiling correlated with the scale length in
99
Fig. 2(b), the overlap decagon tiling represents a local symmetry strictly more than HBS tiling, e.g. local symmetries of each star-tile in the HBS tiling could be different according to the background drawings of overlap tiling). On the basis of electron diffraction and Z-contrast STEM observations described above, we conclude that the dAl 3 Ni is basically isostructural with the highly-perfect d-Al 72 Ni 20 Co 8 phase. Although the phase is basically well-ordered, we also point out that significant structural disorders occur at the core of the 2-nm clusters in the metastable d-Al 3 Ni; a typical example is shown in Fig. 3, to compare with the stable d-Al 72 Ni 20 Co 8 . It is evident that the contrasts become relatively weak and diffuse around the core of the cluster for the d-Al 3 Ni phase, as compared with contrast appearances of the d-Al 72 Ni 20 Co 8 , indicating that structural disordering due to mainly chemical disorder is significant at atomic sites around the cluster center for the d-Al 3 Ni phase (note that the cluster still reveals tenfold symmetry breaking feature even with significant chemical disordering). Such disorder-related diffuse contrasts are frequently found for some of the 2-nm cluster centers in the d-Al 3 Ni phase, as marked by circles in Fig. 2(a). Here, it is noteworthy that, even for the stable dAl 72 Ni 20 Co 8 phase, a certain amount of chemical disordering is found to exist at the core of the 2-nm cluster [4,5], although the degree of disordering is not as high as that of the metastable d-Al 3 Ni phase. Therefore, it can be said that both the d-Al 3 Ni and d-Al 72 Ni 20 Co 8 phases tend to have structural disorders at the same atomic sites around the core of the 2-nm cluster, and a degree of disordering might have been enhanced for the metastable d-Al 3 Ni phase
Fig. 3. Contrast appearances of the decagonal cluster with a diameter of 2 nm for both the thermodynamically stable Al 72 Ni 20 Co 8 (left) and metastable Al 3 Ni (right) decagonal quasicrystals. Note that the brightest spots at the core of the left cluster are significantly weakened and diffused for the right one.
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E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
prepared by rapid-solidification, during which structural disordering is highly likely to take place and is quenchedin. This aspect of disordering tendency also supports the view that d-Al 3 Ni and d-Al 72 Ni 20 Co 8 phases are basically isostructural. Further studies on structural details and origin of the disorders in terms of phasons are now in progress and will be published elsewhere.
References
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
[1] S. Ritch et al., Phil. Mag. Lett. 74 (1996) 99. [2] A.P. Tsai, A. Fujiwara, A. Inoue, T. Masumoto, Phil. Mag. Lett. 74 (1996) 233. [3] K. Saitoh et al., Jpn. J. Appl. Phys. 36 (1997) L1400.
[14] [15]
Y. Yan, S.J. Pennycook, Nature 403 (1999) 266. Y. Yan, S.J. Pennycook, Phys. Rev. B 61 (2000) 14291. P.J. Steinhardt et al., Nature 396 (1998) 55. E. Abe et al., Phys. Rev. Lett. 84 (2000) 4609. H. Abe et al., Jpn. J. Appl. Phys. 39 (2000) L1111. H. Takakura, A. Yamamoto, A.P. Tsai, Acta Cyrstallogr. A57 (2001) 576. ˇ M. Widom, J. Alloys Comp. 342 C.L. Henley, M. Mihalkovic, (2002) 221. X.L. Ma, K.H. Kuo, Metall. Mater. Trans. 25A (1994) 47. K. Sugiyama, S. Nishimura, K. Hiraga, J. Alloys Comp. 342 (2002) 65. K. Saitoh, T. Yokosawa, M. Tanaka, A.P. Tsai, J. Electron Microsc. 48 (1999) 105. K. Hiraga, T. Ohsuna, W. Sun, K. Sugiyama, J. Alloys Comp. 342 (2002) 110. X.Z. Li, K.H. Kuo, Phil. Mag. Lett. 58 (1988) 167.
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Structure of a metastable Al 3 Ni decagonal quasicrystal: comparison with a highly perfect Al 72 Ni 20 Co 8 E. Abe*, A.P. Tsai Aperiodic Solids Research Team, National Institute for Materials Science, 1 -2 -1 Sengen, Tsukuba 305 -0047, Japan
Abstract We study the structure of a decagonal quasicrystalline phase formed in a rapidly-solidified Al 3 Ni alloy, by using electron diffraction and atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM). Electron diffraction patterns of the metastable Al 3 Ni phase reveal features quite similar to those of the stable Al 72 Ni 20 Co 8 phase; a large number of reflections in the tenfold symmetry plane and no significant diffuse streaks in the twofold patterns, indicating a good quasiperiodic order of the phase. Z-contrast STEM imaging shows that the structure of the Al 3 Ni phase can be interpreted based on a decagonal atomic cluster column with broken tenfold symmetry, being basically isostructural with that of the Al 72 Ni 20 Co 8 phase. Structural disorders are found to be significant at the core of the decagonal atomic clusters in the metastable Al 3 Ni decagonal phase. 2002 Elsevier Science B.V. All rights reserved. Keywords: Al–Ni system; Decagonal quasicrystal; Metastable phase; Electron diffraction; Atomic-resolution Z-contrast
1. Introduction The Al–Ni–Co system is one of the well-studied quasicrystal-forming alloys, in which various structural types of thermodynamically stable decagonal (d-) quasicrystal occur depending on alloy composition. In particular, the decagonal structure is sensitive to the Ni / Co ratios for the compositions around Al |70 Ni |302x Co x . Among these, a highly-perfect d-phase with significantly less structural disorders can be obtained for a very narrow composition range at Ni-rich side [1,2], e.g. Al 72 Ni 20 Co 8 , while other d-Al–Ni–Co phases exhibit significant diffuse streaks. This nearly-ideal quasicrystalline phase, referred to as a Ni-rich d-Al–Ni–Co with basic structure, is thus an excellent sample for structural analysis and has been studied extensively [3–10]. One of the interesting findings is a broken tenfold-symmetry of decagonal clusters with a diameter of |2 nm [3] (denoted as 2-nm cluster hereafter), which is a structural unit of the d-Al–Ni–Co phase and had been believed to be tenfold-symmetry. This symmetry breaking feature is found to be due not to random disorders [4,5] but to an intrinsic configuration of the structure [6,7], leading to a structural model based on the cluster with *Corresponding author. Tel.: 181-298-592-349; fax:181-298-592301. E-mail address: [email protected] (E. Abe).
broken tenfold symmetry, alternative to previous highsymmetric cluster models. Some crystalline phases of compositions similar to corresponding quasicrystalline phases may provide significant information on building unit clusters such as those likely to exist in the quasicrystals, a typical example of which is known as approximant crystals. For the d-Al–Ni– Co quasicrystals, Al 13 TM 4 (TM5Fe or Co), t-inflated Al 13 Co 4 [11] and W–Al 72.5 Ni 7.5 Co 20 [12] compounds are expected to possess key structural features, and in fact the latter two compounds are found to be composed of a 2-nm cluster with fivefold-symmetry [12,13]. One may claim that this fivefold-symmetry cluster should be a basic structural unit for the d-Al–Ni–Co quasicrystals [4,5]; this is actually confirmed to be true for the d-Al–Ni–Co phases which essentially reveal superlattice reflections and strong diffuse streaks [14]. However, this fivefold symmetry cluster description is evidently not appropriate for the Al 72 Ni 20 Co 8 phase with basic structure, for which the symmetry of the 2-nm clusters is not ten- or fivefold but mirror or lower one. Therefore, it may be quite controversial to treat the above crystalline compounds as being closely related structurally to the basic Al 72 Ni 20 Co 8 phase. It should be noted that these compounds occur in a binary Al–Co or Co-rich side in Al |70 Ni |302x Co x alloys, and hence are likely to correspond to the Co-rich d-Al–Ni–Co phases.
0925-8388 / 02 / $ – see front matter 2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 02 )00150-0
E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
In the present work, we show that, based on electron diffraction and atomic-resolution Z (atomic number)-contrast scanning transmission electron microscopy (STEM) observations, a metastable d-phase formed in a rapidly solidified Al 3 Ni alloy [15] has a well-ordered quasiperiodic structure exhibiting characteristics quite similar to those of the basic d-Al 72 Ni 20 Co 8 quasicrystal. Interestingly, the corresponding stable crystalline phase, a stoichiometric Al 3 Ni compound, has rather a simple structure (orthorhombic, Pnma, a56.61, b57.37, c54.81 ˚ which is neither a well-defined approximant crystal nor A), is composed of decagonal atomic clusters. Nevertheless, Al 3 Ni is a potential crystalline phase that forms a quasicrystalline phase of high structural quality, as will be clearly demonstrated in the present work.
97
2. Experimental An Al 3 Ni alloy was rapidly solidified using a meltspinning apparatus with a single Cu roller (diameter of 20 cm) rotating at 4000 rpm. It is confirmed by powder X-ray diffraction that the product alloy-flakes are composed of almost single d-Al 3 Ni phase, and hence the present dphase is regarded as a metastable product of the orthorhombic Al 3 Ni crystalline phase. For electron microscope observations, alloy-flakes were crushed into powder and then dispersed on perforated carbon films. An atomicresolution Z-contrast image was obtained by a 200-kV field-emission transmission electron microscope (Jeol ˚ JEM-2010F) which provides a minimum probe of |1.5 A with a convergence angle of |10 mrad. The annular
Fig. 1. Electron diffraction patterns of the Al 3 Ni decagonal phase, taken with the incident beam parallel to the (a) tenfold and (b), (c) twofold symmetry axes. Twofold patterns of (b) and (c) are taken with the incidence along A- and B-directions in (a), respectively. Note that there are no significant diffuse streaks at the positions indicated by arrows.
E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
98
detector was set to collect the electrons scattered at angles between 60 and 120 mrad, which are high enough to achieve the incoherent imaging condition and hence expected to reveal significant atomic-number dependent, Zcontrast.
3. Results and discussion Fig. 1(a)–(c) shows electron diffraction (ED) patterns
obtained from the metastable d-Al 3 Ni phase. In the tenfold symmetry pattern of (a), a large number of sharp reflections appear, and most reflections are located at correct tenfold symmetry positions, indicating a good long-range quasiperiodic order of the phase. Examination of the twofold patterns of (b) and (c) shows a periodic length ˚ and an extinction that causes the along c-axis of 4 A quasiperiodic reflection arrays in (b) to disappear in (c); see the position indicated by an arrow in (c). This indicates the existence of a 10 5 screw axis and / or a c-glide plane,
Fig. 2. (a) Atomic-resolution Z-contrast STEM image of the Al 3 Ni decagonal phase. (b) Overlap decagon (Gummelt) tiling and hexagon-boat-star (HBS) tiling superimposed onto the image, confirming that the Ni atom positions are quasiperodically well-correlated across the entire region. Note that some deviations of the spot positions from the tilings are due to image shift (sample-drift) during recording of a scanning image.
E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
leading to a plausible space group of P10 5 /mmc. All these diffraction features are quite similar to those of the basic d-Al 72 Ni 20 Co 8 of high structural perfection. It should be noted that, for the stable d-Al–Ni–Co phases except for the basic d-Al 72 Ni 20 Co 8 , this extinction is not completed, and some diffuse streaks remain in the pattern (c). Further, it is also pointed out that extra diffuse streaks frequently appear at the position indicated by arrows in (b) for the Co-rich d-Al–Ni–Co phases including those with superlat˚ tice structures, resulting in periodic c-length of 8 A. Evidently, there are no such diffuse streaks in (b) of the d-Al 3 Ni phase. Here, it is noteworthy that the Al 13 TM 4 (TM5Fe or Co), t-inflated Al 13 Co 4 and W–Al 72.5 ˚ along Ni 7.5 Co 20 compounds all have a unit length of |8 A that corresponding to the c-axis of the d-Al–Ni–Co phases, indicating that these compounds are structurally related to the Co-rich d-Al–Ni–Co phases. Fig. 2(a) shows an atomic-resolution Z-contrast image of the metastable d-Al 3 Ni phase. In the image, there is a quasiperiodic arrangement of bright dots representing Ni (or Ni-rich) atomic columns. Clearly, the 2-nm cluster can also be defined for the d-Al 3 Ni structure as a structuralunit, and the cluster commonly reveals a contrast of tenfold-symmetry breaking feature in the same manner as observed for the basic d-Al 72 Ni 20 Co 8 structure; see the 2-nm cluster indicated in Fig. 2(a). The symmetry breaking directions are found to be well-correlated across the entire region in the figure, as shown by superimposing the overlap decagon (Gummelt) tiling and the hexagon-boatstar (HBS) tiling, demonstrating that the d-Al 3 Ni has a well-ordered quasiperiodic atomic structure (note that for these two types of tiling correlated with the scale length in
99
Fig. 2(b), the overlap decagon tiling represents a local symmetry strictly more than HBS tiling, e.g. local symmetries of each star-tile in the HBS tiling could be different according to the background drawings of overlap tiling). On the basis of electron diffraction and Z-contrast STEM observations described above, we conclude that the dAl 3 Ni is basically isostructural with the highly-perfect d-Al 72 Ni 20 Co 8 phase. Although the phase is basically well-ordered, we also point out that significant structural disorders occur at the core of the 2-nm clusters in the metastable d-Al 3 Ni; a typical example is shown in Fig. 3, to compare with the stable d-Al 72 Ni 20 Co 8 . It is evident that the contrasts become relatively weak and diffuse around the core of the cluster for the d-Al 3 Ni phase, as compared with contrast appearances of the d-Al 72 Ni 20 Co 8 , indicating that structural disordering due to mainly chemical disorder is significant at atomic sites around the cluster center for the d-Al 3 Ni phase (note that the cluster still reveals tenfold symmetry breaking feature even with significant chemical disordering). Such disorder-related diffuse contrasts are frequently found for some of the 2-nm cluster centers in the d-Al 3 Ni phase, as marked by circles in Fig. 2(a). Here, it is noteworthy that, even for the stable dAl 72 Ni 20 Co 8 phase, a certain amount of chemical disordering is found to exist at the core of the 2-nm cluster [4,5], although the degree of disordering is not as high as that of the metastable d-Al 3 Ni phase. Therefore, it can be said that both the d-Al 3 Ni and d-Al 72 Ni 20 Co 8 phases tend to have structural disorders at the same atomic sites around the core of the 2-nm cluster, and a degree of disordering might have been enhanced for the metastable d-Al 3 Ni phase
Fig. 3. Contrast appearances of the decagonal cluster with a diameter of 2 nm for both the thermodynamically stable Al 72 Ni 20 Co 8 (left) and metastable Al 3 Ni (right) decagonal quasicrystals. Note that the brightest spots at the core of the left cluster are significantly weakened and diffused for the right one.
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E. Abe, A.P. Tsai / Journal of Alloys and Compounds 342 (2002) 96 – 100
prepared by rapid-solidification, during which structural disordering is highly likely to take place and is quenchedin. This aspect of disordering tendency also supports the view that d-Al 3 Ni and d-Al 72 Ni 20 Co 8 phases are basically isostructural. Further studies on structural details and origin of the disorders in terms of phasons are now in progress and will be published elsewhere.
References
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
[1] S. Ritch et al., Phil. Mag. Lett. 74 (1996) 99. [2] A.P. Tsai, A. Fujiwara, A. Inoue, T. Masumoto, Phil. Mag. Lett. 74 (1996) 233. [3] K. Saitoh et al., Jpn. J. Appl. Phys. 36 (1997) L1400.
[14] [15]
Y. Yan, S.J. Pennycook, Nature 403 (1999) 266. Y. Yan, S.J. Pennycook, Phys. Rev. B 61 (2000) 14291. P.J. Steinhardt et al., Nature 396 (1998) 55. E. Abe et al., Phys. Rev. Lett. 84 (2000) 4609. H. Abe et al., Jpn. J. Appl. Phys. 39 (2000) L1111. H. Takakura, A. Yamamoto, A.P. Tsai, Acta Cyrstallogr. A57 (2001) 576. ˇ M. Widom, J. Alloys Comp. 342 C.L. Henley, M. Mihalkovic, (2002) 221. X.L. Ma, K.H. Kuo, Metall. Mater. Trans. 25A (1994) 47. K. Sugiyama, S. Nishimura, K. Hiraga, J. Alloys Comp. 342 (2002) 65. K. Saitoh, T. Yokosawa, M. Tanaka, A.P. Tsai, J. Electron Microsc. 48 (1999) 105. K. Hiraga, T. Ohsuna, W. Sun, K. Sugiyama, J. Alloys Comp. 342 (2002) 110. X.Z. Li, K.H. Kuo, Phil. Mag. Lett. 58 (1988) 167.