Partial structure
From Online Dictionary of Crystallography
Structure partielle (Fr).
The crystal structure formed by a subset of elements and their symmetry equivalents.
In describing or analyzing a crystal structure it is sometimes convenient to consider only the structure formed by the selected atoms.
Example
The structure of [math]BaTiO_3[/math] is tetragonal with a primitive unit cell and lattice constants [math]a[/math] and [math]c[/math]. The partial structure of Ba has the same lattice constants whereas the partial structure of O has also a primitive cell but with the lattice constant [math]a_O = a/ \sqrt{2}[/math], [math]c[/math] being equal
See synonymous Substructure