Superlattice is an ordered array of atoms that occur during their rearrangement from random site locations in the disordered solution to specific lattice sites in the ordered structure during phase transformation. This article provides a description of antiphase boundaries, their dislocations and degrees of ordering (long and short order). It focuses on the common superlattice structures and ordered phases observed in copper-gold and iron-aluminum alloy systems. These superlattice types can be referred to by Strukturbericht symbols and the prototype phase.

In some phase diagrams, the appearance of several reactions is the result of the presence of intermediate phases. These are phases whose chemical compositions are intermediate between two pure metals, and whose crystalline structures are different from those of the pure metals. This article describes the order-disorder transformation that typically occurs on cooling from a disordered solid solution to an ordered phase. It provides a table that lists selected superlattice structures and alloy phases that order according to each superlattice. The article informs that spinodal decomposition has been particularly useful in the production of permanent magnet materials, because the morphologies favor high magnetic coercivities. It also describes the theory of spinodal decomposition with a simple binary phase diagram.

Crystal structure is the arrangement of atoms or molecules in the solid state that involves consideration of defects, or abnormalities, in idealized atomic/molecular arrangements. The three-dimensional aggregation of unit cells in the crystal forms a space lattice or Bravais lattice. This article provides a brief review of the terms and basic concepts associated with crystal structures. It also discusses some of the significant defects obstructing plastic flow in real crystals, namely point defects, line defects, stacking faults, twins, and cold work. Several tables in the article provide information on the crystal structures and lattice parameters of allotropes of metallic elements.

This article is a compilation of abbreviations and symbols related to metallography and microstructures.