Non-stoichiometric compound

While " classic " under stoichiometric compounds molecules are understood non-stoichiometric compounds can not be considered as molecules in the true sense. Such compounds are often crystalline phases of varying composition as isomorphous compounds ( isomorphism ), interstitial solid crystals with interstitials, substitutional solid crystals (exchange of atoms in the crystal lattice ), semiconductors.

In chemical notation the lack of stoichiometry is expressed by variables: for example CuxNi1 -x

Nonstoichiometry is with metal or Nebenvalenzbindung ( chemical bond ) widely used especially in substances and especially in chalcogenides, in metal hydrides, borides, carbides, silicides and phosphides, inclusion compounds, solid solutions of gases in metals, the occurrence of crystal defects, mixed crystals and alloys as well as compounds that absorb additional variable amounts of another metal (such as tungsten bronzes MxWO3, with M = alkali metal, Cu, Ag, Ti or Pb) often encountered.