A face-centered cubic (FCC) structure is a type of crystal lattice where atoms are located at each corner and the centers of all the cube's faces. This arrangement allows for a high packing efficiency, meaning that the atoms occupy a significant volume of space. Common metals like copper, aluminum, and gold exhibit this structure, which contributes to their strength and ductility. In an FCC lattice, each unit cell contains four atoms, as each corner atom is shared among eight adjacent cells, and each face-centered atom is shared between two cells. This geometric arrangement leads to a coordination number of 12, indicating that each atom is in contact with 12 others, enhancing the material's stability and properties.