The coherent scattering amplitude associated with a specified spatial arrangement, obtained by summing the site amplitudes with their relative wave phases. Distinguish the crystal lattice structure factor, which sums over lattice sites, from the crystal basis structure factor, which sums the chemical atoms inside a unit cell. In a periodic crystal the two factors multiply. A basis factor can vanish even at an allowed reciprocal lattice vector, causing an extinct reflection.
The structure factor is a crucial concept in the fields of crystallography and solid-state physics. It describes how the scattering of X-rays, neutrons, or electrons by a crystal lattice depends on the arrangement of atoms within the unit cell of the crystal.
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