Question

What is the fundamental principle of XRD?

Answer 1

The fundamental principle of X-ray Diffraction (XRD) is based on the interaction between X-rays and the atomic structure of a material. Here's how it works:

1. X-ray Interaction with Crystals: When a beam of X-rays hits a crystalline material, it is scattered by the atoms in the crystal. The crystal has a regular arrangement of atoms in layers, known as planes.
   

1. Diffraction Condition: For constructive interference (which results in a measurable signal), the X-rays must scatter in such a way that the path difference between the rays scattered from different planes of atoms is an integer multiple of the X-ray wavelength. This condition is described by Bragg's Law:
   

   
   \[
   n\lambda = 2d \sin(\theta)
   \]

   where:
   - \(n\) is the order of reflection (usually 1),
   - \(\lambda\) is the wavelength of the X-ray,
   - \(d\) is the distance between the planes of atoms in the crystal (called the d-spacing),
   - \(\theta\) is the angle of incidence (and reflection) of the X-ray beam.

1. Constructive Interference: When the X-rays meet this condition, they interfere constructively, meaning the waves reinforce each other, creating a diffraction pattern. This pattern can be detected and used to analyze the crystal structure.
   

1. Analysis of the Diffraction Pattern: The angles and intensities of the diffraction peaks provide information about the spacing between the atomic planes, the arrangement of atoms, and the symmetry of the crystal structure.
   

In short, XRD works by measuring how X-rays are diffracted by the atoms in a crystalline material, and by applying Bragg's law, scientists can determine the material's crystal structure.