A more detailed knowledge of the structures of metals, and binary and ternary phases of metals and non metals shows that:
*generally at low concentrations of the small atom, the phase can be described as a solution, and this approximates to the historical description of an interstitial compound above.
*at higher concentrations of the small atom, phases with different lattice structures may be present, and these may have a range of stoichiometries.
One example is the solubility of carbon in iron. The form of pure iron stable between 910 °C and 1390 °C, γ-iron, forms a solid solution with carbon termed austenite which is also known as steel.