Complex Metallic Alloys
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Complex metallic
alloys An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
(CMAs) or complex intermetallics (CIMs) are
intermetallic An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elem ...
compounds characterized by the following structural features: #large
unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessari ...
s, comprising some tens up to thousands of atoms, #the presence of well-defined atom clusters, frequently of icosahedral
point group In geometry, a point group is a mathematical group of symmetry operations ( isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every ...
symmetry, #the occurrence of inherent disorder in the ideal structure.


Overview

''Complex metallic alloys'' is an umbrella term for
intermetallic An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elem ...
compounds with a relatively large
unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessari ...
. 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 compound Heusler compounds are magnetic intermetallics with face-centered cubic crystal structure and a composition of XYZ (half-Heuslers) or X2YZ (full-Heuslers), where X and Y are transition metals and Z is in the p-block. The term derives from the name ...
s on the most simple end, and
quasicrystal A quasiperiodic crystal, or quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical ...
s on the more complex end.


Research

Following the invention of
X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angle ...
techniques in the 1910s, the atomic structure of many compounds was investigated. Most
metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typi ...
s have relatively simple structures. However, in 1923
Linus Pauling Linus Carl Pauling (; February 28, 1901August 19, 1994) was an American chemist, biochemist, chemical engineer, peace activist, author, and educator. He published more than 1,200 papers and books, of which about 850 dealt with scientific top ...
reported on the structure of the
intermetallic An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elem ...
NaCd2, which had such a complicated structure he was unable to fully explain it. Thirty years later, he concluded that NaCd2 contains 384 sodium and 768 cadmium atoms in each
unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessari ...
. 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 The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body ...
funded the Network of Excellence CM

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 C-MA

which connects researchers at 21 universities.


Examples

Example phase (matter), phases are: *β- Mg2Al3: 1168 atoms per unit cell, face-centred
cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system, a crystal system w ...
, atoms arranged in Friauf polyhedra. *ξ'–Al74Pd22Mn4: 318 atoms per unit cell, face-centred
orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with ...
, atoms arranged in Mackay-type clusters. * Mg32(Al,Zn)49 (Bergman phase): 163 atoms per unit cell, body centred cubic, atoms arranged in Bergman clusters. *Al3Mn (Taylor phase): 204 atoms per unit cell, face-centred orthorhombic, atoms arranged in Mackay-type clusters.


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


References


Further reading

* * *{{cite journal , last1= Ovchinnikov , first1= Alexander , last2= Smetana , first2= Volodymyr , last3= Mudring , first3= Anja-Verena , date= March 19, 2020 , title= Metallic alloys at the edge of complexity: structural aspects, chemical bonding and physical properties , journal= Journal of Physics: Condensed Matter , volume= 32 , issue= 24 , pages= 243002 , doi= 10.1088/1361-648X/ab6b87 , s2cid= 210827213 , url= https://iopscience.iop.org/article/10.1088/1361-648X/ab6b87 , access-date=2022-01-16 Intermetallics Crystal structure types