Why are crystals useful for diffracting X-rays?

Crystals are essential for diffracting X-rays because their internal atomic structure acts as a natural, three-dimensional diffraction grating.12

This utility arises from two primary factors:

• Atomic Spacing: The atoms within a crystal are arranged in regular, uniform patterns with spacing typically around 1 angstrom (${10}^{-10}$ metre). This distance is ideal because it is comparable to the short wavelengths of X-rays, a requirement for producing observable diffraction effects.123
• Constructive Interference: When an X-ray beam strikes the crystal, it reflects off the parallel atomic planes. According to the Bragg law, defined as $n\lambda =2d\sin \theta$, these reflections interfere constructively when the path length difference between waves is an integer multiple of the wavelength. This reinforcement creates a strong, measurable signal that allows scientists to deduce the internal arrangement of atoms within the crystal.1453

By observing these interference patterns, researchers can identify unknown X-ray wavelengths or determine the complex structures of materials, such as protein molecules.35