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Chemistry · Glossary

What is Ewald sphere?

Definition 9.8 University Chemistry — Year 3 · Chapter 9 — Crystallography and X-ray Diffraction

The Ewald sphere has radius 1/λ1/\lambda and passes through the origin of the reciprocal lattice, its centre at −k-\mathbf k from the origin; a reflection occurs whenever a reciprocal-lattice node lies on it.

The Ewald construction in two dimensions (the circle passes through the origin O of the reciprocal lattice). A node G lying on the circle gives a diffracted beam k' = k + G. Here the circle, of radius chosen for the drawing, passes through the node (-1, 2).
The Ewald construction in two dimensions (the circle passes through the origin OO of the reciprocal lattice). A node G\mathbf G lying on the circle gives a diffracted beam k′=k+G\mathbf k' = \mathbf k + \mathbf G. Here the circle, of radius chosen for the drawing, passes through the node (−1,2)(-1, 2).
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