A holmium–magnesium–zinc (Ho–Mg–Zn) quasicrystal is a quasicrystal made of an alloy of the three metals holmium, magnesium and zinc that has the shape of a regular dodecahedron, a Platonic solid with 12 five-sided faces. Unlike the similar pyritohedron shape of some cubic-system crystals such as pyrite, this quasicrystal has faces that are true regular pentagons. The crystal is part of the R–Mg–Zn family of crystals, where R=Y, Gd, Tb, Dy, Ho or Er. They were first discovered in 1994. These form quasicrystals in the stoichiometry around R9Mg34Zn57. Magnetically, they form a spin glass at cryogenic temperatures. While the experimental discovery of quasicrystals dates back to the 1980s, the relatively large, single grain nature of some Ho–Mg–Zn quasicrystals has made them a popular way to illustrate the concept.
See also Complex metallic alloys
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