The length of a unit cell (a) in the Ni crystal is 0.352 nm. The diffraction of X-rays of 0.154 nm wavelength (λ) from a Ni crystal occurs at 22.2°,25.9°, and 38.2°. By using Bragg's law, (nλ = 2d sin θ), and assuming that the diffractions are first order (n = 1),the distances are calculated to be 0.204 nm, 0.176nm and 0.124 nm. The various structures for the Ni crystal are represented as:If the distance (d) is 0.204 nm represent which structure?The distance (d) of 0.176 nm represent which structure?The distance (d) of 0.124 nm represent which structure?

The distance 0.204 nm comes out to be "a/3 "  which corresponds to the perpendicular distance between a corner of unit cell and the plane of the three adjacent corners.The distance 0.176 nm is half the unit cell length (a/2) which corresponding to the perpendicular distance between the layers of atoms in one face of the unit cell and the center (Fig. I)The distance 0.124nm corresponds to 2/4 times the unit cell dimension, i.e., one-fourth of the distance from one edge of the cell to the opposite edge (Fig. II). The plane intersects the face-centered atoms of the two sides. The plane including the edge atoms is equivalent to the plane across the center of the unit cell.