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Title: From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation

Abstract

The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu 4.39Al 1.61 to its cubic 2/1 crystalline approximant (CA) Ca 13Au 56.31(3)Al 21.69 (CaAu 4.33(1)Al1.67, Pa$$\bar{3}$$ (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ~570 °C and complete by ~650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au 59.86(2)Al 17.143.00] and an icosahedral shell of only Al [Al 10.51.5]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au–Al nearest neighbor contacts over homoatomic Al–Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. Finally, according to electronic structure calculations, a cubic 1/1 CA, “Ca 24Au 88Al 64” (CaAu 3.67Al 2.67) is proposed.

Authors:
ORCiD logo [1]; ORCiD logo [2];  [2];  [2];  [3];  [2];  [3]; ORCiD logo [4]
  1. Iowa State Univ., Ames, IA (United States). Dept. of Chemistry
  2. Ames Lab., Ames, IA (United States)
  3. Iowa State Univ., Ames, IA (United States). Dept. of Physics and Astronomy; Ames Lab., Ames, IA (United States)
  4. Iowa State Univ., Ames, IA (United States). Dept. of Chemistry; Ames Lab., Ames, IA (United States)
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division
OSTI Identifier:
1425483
Report Number(s):
IS-J-9592
Journal ID: ISSN 0002-7863; TRN: US1802115
Grant/Contract Number:  
AC02-07CH11358; AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 140; Journal Issue: 4; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Pham, Joyce, Meng, Fanqiang, Lynn, Matthew J., Ma, Tao, Kreyssig, Andreas, Kramer, Matthew J., Goldman, Alan I., and Miller, Gordon J. From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation. United States: N. p., 2017. Web. doi:10.1021/jacs.7b10358.
Pham, Joyce, Meng, Fanqiang, Lynn, Matthew J., Ma, Tao, Kreyssig, Andreas, Kramer, Matthew J., Goldman, Alan I., & Miller, Gordon J. From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation. United States. doi:10.1021/jacs.7b10358.
Pham, Joyce, Meng, Fanqiang, Lynn, Matthew J., Ma, Tao, Kreyssig, Andreas, Kramer, Matthew J., Goldman, Alan I., and Miller, Gordon J. Fri . "From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation". United States. doi:10.1021/jacs.7b10358.
@article{osti_1425483,
title = {From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca–Au–Al: In Situ Variable-Temperature Transformation},
author = {Pham, Joyce and Meng, Fanqiang and Lynn, Matthew J. and Ma, Tao and Kreyssig, Andreas and Kramer, Matthew J. and Goldman, Alan I. and Miller, Gordon J.},
abstractNote = {The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31(3)Al21.69 (CaAu4.33(1)Al1.67, Pa$\bar{3}$ (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at ~570 °C and complete by ~650 °C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14⟂3.00] and an icosahedral shell of only Al [Al10.5⟂1.5]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au–Al nearest neighbor contacts over homoatomic Al–Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. Finally, according to electronic structure calculations, a cubic 1/1 CA, “Ca24Au88Al64” (CaAu3.67Al2.67) is proposed.},
doi = {10.1021/jacs.7b10358},
journal = {Journal of the American Chemical Society},
number = 4,
volume = 140,
place = {United States},
year = {Fri Dec 29 00:00:00 EST 2017},
month = {Fri Dec 29 00:00:00 EST 2017}
}

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