Each ion or atom that forms an fcc unit cell is surrounded by

In fcc unit cell, a corner atom can support 8 unit cells. In each cube, at a distance of 3a/4from corner atom, there is tetrahedral void; it implies each atom is surrounded by eight tetrahedral voids.At the center of edge, there is an octahedral void. Each corner can support six edges and hence it is surrounded by six octahedral voids.