Miller indices are a notation system in crystallography for planes and directions in crystal lattices.In particular, a family of lattice planes is determined by three integers , , and , the Miller indices. They are written and denote planes orthogonal to a direction in the basis of the reciprocal lattice vectors. By convention, negative integers are written with a bar, as in for . The integers are usually written in lowest terms, i.e. their greatest common divisor should be 1.
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