The X-ray diffractometer (XRD) is based on the Bragg diffraction principle, which measures the diffraction signal of X-rays in crystals to reveal the crystal structure, phase composition, and stress state of substances. Its core working principle can be broken down into the following steps:

1、 X-ray Generation: Energy Conversion of High Speed Electron Impact on Target Materials

XRD uses an X-ray tube as a light source, and its cathode emits a high-speed electron flow that collides with an anode target material (such as a Cu target) under the acceleration of a high-voltage electric field of tens of thousands of volts. Electrons interact with the inner layer electrons of the target material atoms, exciting the inner layer electrons and releasing X-rays of a specific wavelength when the outer layer electrons transition to fill vacancies. For example, the wavelength of K α rays generated by Cu targets is 0.154nm, which is suitable for most crystal structure analyses.

2、 Crystal diffraction: interference effect of atomic periodic arrangement

When monochromatic X-rays are irradiated onto a crystal, the regularly arranged atoms in the crystal become scattering sources. The X-ray wavelength scattered by each atom is the same as the incident wave, but the phase varies due to differences in atomic position. Due to the periodicity of the crystal structure, scattered waves undergo constructive interference in a specific direction (satisfying the Bragg equation), forming diffraction peaks. The Bragg equation 2dsin θ=n λ is the core theoretical basis, where d is the interplanar spacing, θ is the incident angle, n is the diffraction order, and λ is the X-ray wavelength.

3、 Signal detection and processing: from diffraction peaks to structural information

Diffraction X-rays are precisely adjusted in angle by a goniometer (core component), received by a detector, and converted into electrical signals. The system records diffraction angle (2 θ) and intensity data to generate diffraction patterns. By analyzing the position, intensity, and shape of diffraction peaks in the spectrum, the crystal structure (such as crystal system and cell parameters), phase composition (compared with standard PDF cards), and residual stress (peak shift analysis) can be determined. For example, the crystallinity of materials can be evaluated by the intensity ratio of peaks to background noise.