Question

what are Millar indices ? Explain their importance. How these are determines
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Answer 1

Explanation:

If each atom in the crystal is represented by a point and these points are connected by lines, the resulting lattice may be divided into a number of identical blocks or unit cells; the intersecting edges of one of the unit cells defines a set of crystallographic axes.  

Miller indices are used to specify directions and planes. These directions and planes could be in lattices or in crystals. The number of indices will match with the dimension of the lattice or the crystal.

Miller indices are determined by the intersection of the plane with these axes.