Complex metallic alloy explained

Complex metallic alloys (CMAs) or complex intermetallics (CIMs) are intermetallic compounds characterized by the following structural features:^[1]

1. large unit cells, comprising some tens up to thousands of atoms,
2. the presence of well-defined atom clusters, frequently of icosahedral point group symmetry,
3. the occurrence of inherent disorder in the ideal structure.

Overview

Complex metallic alloys is an umbrella term for intermetallic compounds with a relatively large unit cell. There is no precise definition of how large the unit cell of a complex metallic alloy has to be, but the broadest definition includes Zintl phases, skutterudites, and Heusler compounds on the most simple end, and quasicrystals on the more complex end.^[2]

Research

Following the invention of X-ray crystallography techniques in the 1910s, the atomic structure of many compounds was investigated. Most metals have relatively simple structures. However, in 1923 Linus Pauling reported on the structure of the intermetallic NaCd₂, which had such a complicated structure he was unable to fully explain it.^[3] Thirty years later, he concluded that NaCd₂ contains 384 sodium and 768 cadmium atoms in each unit cell.^[4]

Most physical properties of CMAs show distinct differences with respect to the behavior of normal metallic alloys and therefore these materials possess a high potential for technological application.

The European Commission funded the Network of Excellence CMA^[5] from 2005 to 2010, uniting 19 core groups in 12 countries. From this emerged the European Integrated Center for the Development of New Metallic Alloys and Compounds (previously C-MAC, now ECMetAC), which connects researchers at 21 universities.^[6]

Examples

Example phases are:

• β-Mg₂Al₃: 1168 atoms per unit cell, face-centred cubic, atoms arranged in Friauf polyhedra.^[7]
• ξ'–Al₇₄Pd₂₂Mn₄: 318 atoms per unit cell, face-centred orthorhombic, atoms arranged in Mackay-type clusters.^[8]
• (Bergman phase): 163 atoms per unit cell, body centred cubic, atoms arranged in Bergman clusters.^[9]
• (Taylor phase): 204 atoms per unit cell, face-centred orthorhombic, atoms arranged in Mackay-type clusters.^{[10] [11]}

See also

• High-entropy alloys, alloys of multiple elements which ideally form no intermetallics
• Holmium–magnesium–zinc quasicrystal
• Frank–Kasper phases
• Laves phase
• Hume-Rothery rules

Further reading

• Urban. Knut. Feuerbacher, Michael. Structurally complex alloy phases. Journal of Non-Crystalline Solids. 2004. 334–335. 143–150. Elsevier B.V.. 10.1016/j.jnoncrysol.2003.11.029. 2004JNCS..334..143U.
• Book: Steurer . Walter . Dshemuchadse . Julia . 2016 . Intermetallics: Structures, Properties, and Statistics . . 978-0-19-871455-2 . 10.1093/acprof:oso/9780198714552.001.0001 . 8. Complex intermetallics (CIMs) . 439–465.
• Ovchinnikov. Alexander. Smetana. Volodymyr. Mudring. Anja-Verena. March 19, 2020. Metallic alloys at the edge of complexity: structural aspects, chemical bonding and physical properties. Journal of Physics: Condensed Matter. 32. 24. 243002. 10.1088/1361-648X/ab6b87. 210827213. free. 2020JPCM...32x3002O.

Notes and References

1. Urban. Knut. Feuerbacher, Michael. Structurally complex alloy phases. Journal of Non-Crystalline Solids. 2004. 334–335. 143–150. Elsevier B.V.. 10.1016/j.jnoncrysol.2003.11.029. 2004JNCS..334..143U.
2. Book: Dubois. Jean-Marie. Belin-Ferré, Esther. Complex Metallic Alloys: Fundamentals and Applications. 2011. Wiley-VCH. 978-3-527-32523-8. 10.1002/9783527632718.
3. Pauling . Linus . Linus Pauling . The Crystal Structure of Magnesium Stannide . Journal of the American Chemical Society . American Chemical Society (ACS) . 45 . 12 . 1923 . 0002-7863 . 10.1021/ja01665a001 . 2777–2780.
4. Linus . Pauling . Linus Pauling . The Stochastic Method and the Structure of Proteins . American Scientist . 43 . 2 . 285–297 . 27826614 . 1955.
5. Web site: Complex Metallic Alloys. Community Research and Development Information Service (CORDIS). 2023-08-26.
6. Web site: European Integrated Centre for the Development of New Metallic Alloys and Compounds. 2023-08-26.
7. Samson . S. . The crsytal structure of the phase β Mg₂Al₃ . Acta Crystallographica . International Union of Crystallography (IUCr) . 19 . 3 . 1965-09-01 . 0365-110X . 10.1107/s0365110x65005133 . 401–413.
8. Boudard . M. . Klein . H. . Boissieu . M. De . Audier . M. . Vincent . H. . Structure of quasicrystalline approximant phase in the Al-Pd-Mn system . Philosophical Magazine A . Informa UK Limited . 74 . 4 . 1996 . 0141-8610 . 10.1080/01418619608242169 . 939–956 . 1996PMagA..74..939B.
9. Smontara . A. . Smiljanić . I. . Bilušić . A. . Jagličić . Z. . Klanjšek . M. . Roitsch . S. . Dolinšek . J. . Feuerbacher . M. . Electrical, magnetic, thermal and thermoelectric properties of the "Bergman phase" Mg₃₂(Al,Zn)₄₉ complex metallic alloy . Journal of Alloys and Compounds . Elsevier BV . 430 . 1–2 . 2007 . 0925-8388 . 10.1016/j.jallcom.2006.05.026 . 29–38.
10. Taylor . M. A. . The space group of MnAl₃ . Acta Crystallographica . International Union of Crystallography (IUCr) . 14 . 1 . 1961-01-10 . 0365-110X . 10.1107/s0365110x61000346 . 84 . free. 1961AcCry..14...84T .
11. Hiraga . K. . Kaneko . M. . Matsuo . Y. . Hashimoto . S. . The structure of Al₃Mn: Close relationship to decagonal quasicrystais . Philosophical Magazine B . Informa UK Limited . 67 . 2 . 1993 . 1364-2812 . 10.1080/13642819308207867 . 193–205 . 1993PMagB..67..193H.