Solid solution

A solid solution is a single crystalline phase in which atoms or ions of one substance occupy sites within another substance’s crystal structure. Its composition can vary without forming a separate phase.

Substitutional solid solution: A solid solution in which solute atoms replace host atoms at regular lattice sites. It is one principal way atoms enter a host crystal without creating a second phase.
Crystal structure: The ordered, repeating arrangement of atoms, ions, or molecules in a crystalline material. A solid solution preserves one underlying crystalline arrangement while its site occupants vary.
Alloy: A metallic material containing two or more elements, at least one of which is a metal. Many alloys derive their composition-dependent properties from one or more solid-solution phases.
Mechanical mixture: A physical combination of distinct material particles or phases that retain separate identities. Unlike a solid solution, its components remain distinct rather than sharing one crystal phase.
Interstitial solid solution: A solid solution in which small solute atoms occupy spaces between host atoms in a crystal lattice. Small atoms can dissolve between host lattice sites rather than replace host atoms.
Lattice site: A position in a crystal lattice associated with an atom, ion, or molecular unit. Solid-solution definitions hinge on whether solute occupies host sites or spaces between them.
Brass: A copper-zinc alloy whose phases and properties depend on composition and temperature. Copper and zinc form a well-known substitutional solid solution over part of their composition range.
Intermetallic compound: A metallic compound with an ordered crystal structure and a characteristic range of compositions. Its ordered stoichiometry contrasts with the variable occupancy typical of a solid solution.
Hume-Rothery rules: Empirical criteria that help predict extensive substitutional solubility between metallic elements. Atomic size, crystal structure, and valence help explain why some substitutions are more soluble than others.
Chemical composition: The identities and relative amounts of the elements or compounds in a material. A solid solution can change composition while remaining a single phase.

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