What is the void space of a FCC unit cell?

The void space of a face-centered cubic (FCC) unit cell refers to the empty spaces or interstices between the atoms within the cell. In an FCC lattice, each corner of the unit cell is occupied by an atom, while each face of the unit cell has an additional atom at its center. As a result, the void space in an FCC unit cell is primarily found between the atoms.

There are two main types of void spaces in an FCC lattice:

Tetrahedral Voids: These voids are located in the center of each of the unit cell's faces. They are so named because they form tetrahedra when connected to the surrounding atoms. Each tetrahedral void is surrounded by four atoms located at the corners of the adjacent unit cells.

Octahedral Voids: These voids are located at the center of the unit cell. They are called octahedral voids because they are surrounded by six atoms, one from each of the adjacent unit cells, arranged in an octahedral geometry.

Both tetrahedral and octahedral voids contribute to the overall void space within an FCC unit cell. These void spaces play a significant role in determining the packing efficiency and other physical properties of materials with an FCC crystal structure.