1. Solid solutions occur when atoms of a solute dissolve into the crystal lattice of a solvent in the solid state. There are two main types of solid solutions: substitutional and interstitial.
2. In a substitutional solid solution, atoms of the solute substitute for atoms of the solvent in the lattice. This can be ordered, with solute and solvent atoms arranged in specific sites, or disordered.
3. In an interstitial solid solution, atoms of the solute occupy the spaces between atoms of the solvent in the lattice. This only occurs when the solute atom is much smaller than the solvent.