In the space lattice considered above, it was assumed that there are points only at the corners of the unit cell. The detailed study of the internal structure by Bravais (1848) has shown that the points (particles) may be present not only at the corners of unit cells but at the centre of the faces or within the body of the unit cells. The gives rise to different types of lattices corresponding to the seven crystallographic systems already described. These 14 types f lattice are called Bravais lattices. The terms simple, face-centered, end-centered and body-centre imply as under:

(i)    Simple. When the points are present only at the corners of the unit cell.

(ii)    Face-centered. When in addition to the points at the corners, there are points present at the centre of each face of the unit cell.

(iii)    End-centered. When in addition to the points at the corners, there is one point present within the body of each unit cell.

(iv) Body-centred. When in addition to the points at the corners, there is one point present within the body of each unit cell..

The simple unit cell i.e., when the points are present are present only at the corners of the unit cell, is called primitive unit cell. The other types of unit cells are called non-primitive unit cells.

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