Polymorphism (materials science)

Polymorphism is according to EA Mitscherlich in materials science and mineralogy the property that a substance in various manifestations can occur ( modifications ). They have the same chemical composition (stoichiometry ), but differ in the spatial arrangement of the atoms and have different properties. Different structures can be due to influences such as pressure and / or temperature form ( solvothermal ).

A special form of polymorphism is the polytypism, which occurs at crystallizing in layer lattices compounds, such as silicon carbide or silicon nitride.

Also, some organic molecules such as drugs, pigments, fats or explosives may be polymorphic in the crystalline state.

Examples

  • Graphite, diamond, fullerenes and graphene are modifications of carbon. ( Diamond is an insulator, while graphite is an anisotropic conductor. )
  • Modifications of a natural silica and a α - quartz, β - quartz, tridymite and cristobalite, are present in nature.
  • α - sulfur, sulfur - β and γ - sulfur modification of sulfur.
  • White phosphorus, red phosphorus, violet phosphorus and black phosphorus are modifications of phosphorus.
  • Selenium occurs in five modifications.
  • Three modifications of calcium carbonate are orthorhombic aragonite, vaterite hexagonal and trigonal calcite.
  • Pyrite and marcasite are minerals different modification of FeS2.
  • Three modifications of the aluminum silicate Al2SiO5 are andalusite, kyanite and sillimanite.
  • Tin comes as α - tin, β - tin and tin - γ before ( tin pest ).
  • Ammonium nitrate ( NH4NO3 ) occurs in five modifications.

Terms

With two modifications is called dimorphism, with three modifications of Trimorphie. If there is a mirror-image modification, so it is called enantiomorphism.

If various modifications can be mutually converted into each other, there is enantiotropy; if the direct conversion in only one direction is possible monotropy.

In presence of one and the same element in different forms is referred to as state allotropy, for example carbon as graphite as well as diamond.

Eilhard Mitscherlich Solvothermal synthesis Active ingredient
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