Although the term "intermetallic compounds", as it applies to solid phases, has been in use for many years, its introduction was regretted, for example by Hume-Rothery in 1955.
Schulze in 1967, defined intermetallic compounds as solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents. Under this definition, the following are included
The definition of a metal is taken to include:
Homogeneous and heterogeneous solid solutions of metals, and interstitial compounds (such as the carbides and nitrides), are excluded under this definition. However, interstitial intermetallic compounds are included, as are alloys of intermetallic compounds with a metal.
In common use, the research definition, including post-transition metals and metalloids, is extended to include compounds such as cementite, Fe3C. These compounds, sometimes termed interstitial compounds, can be stoichiometric, and share similar properties to the intermetallic compounds defined above.