What is the Difference Between Bragg and Laue Diffraction

Bragg diffraction and Laue diffraction are two techniques used in crystallography. These methods exploit the interaction between X-rays and the periodic lattice structure of crystals to generate diffraction patterns.

What is the difference between Bragg and Laue diffraction? Bragg diffraction focuses on specific crystal planes, while Laue diffraction focuses on all crystal planes simultaneously.

Key Areas Covered

1. What is Bragg Diffraction
      – Definition, Features, Structure
2. What is Laue Diffraction
      – Definition, Features, Structure
3. Similarities Between Bragg and Laue Diffraction
      – Outline of Common Features
4. Difference Between Bragg and Laue Diffraction
      – Comparison of Key Differences
5. FAQ: Bragg and Laue Diffraction
      – Answers to Frequently Asked Questions

Key Terms

Bragg Diffraction, Laue Diffraction

What is Bragg Diffraction

Bragg diffraction is a powerful technique used in crystallography to determine the atomic arrangement within crystalline materials. Consider a crystal as a stack of parallel planes, each containing atoms or ions arranged in a regular pattern. When X-rays hit these planes, they scatter in all directions.

But at specific angles, the constructive interference of scattered waves is seen. This produces a strong reflected beam. This is called Bragg diffraction.

Bragg’s law is as follows:

nλ = 2d sin θ 

Where:
n is an integer (order of diffraction)
λ is the wavelength of the incident wave 
d is the distance between the planes in the crystal lattice 
θ is the angle of incidence

The wavelength of the incident wave, the spacing between atomic planes, and the angle at which the wave is diffracted are related by Bragg’s law. Structure of the crystal can be determined by measuring the angles at which these diffraction peaks occur.

Bragg’s law has its applications across various industries. In material science, it is seen used in crystal structure determination, phase identification, and in stress and strain analysis. Moreover, in chemistry, it is used in the molecular structure determination and in polymorphism studies.

What is Laue Diffraction

Laue diffraction is used to determine the orientation and structure of a crystal lattice. Laue diffraction uses a continuous spectrum of X-rays. This technique is commonly seen used in crystallography.

When a polychromatic X-ray beam is incident on a crystal, a complex diffraction pattern emerges. This pattern is formed as different wavelengths within the beam satisfy Bragg’s law for various sets of crystal planes. Furthermore, the intersection of these diffracted beams is represented by the resulting spots on a photographic film or detector.

Furthermore, Laue diffraction has applications in many industries. In material science, it is used to study residual stress, determine the orientation of grains in polycrystalline materials, and analyze defects in crystals. It is also used in metallurgy and protein crystallography.

Similarities Between Bragg and Laue Diffraction

1. Both methods rely on the principle of constructive interference to produce diffraction patterns.
2. These techniques exploit the regular arrangement of atoms in a crystal lattice to produce diffraction patterns.
3. Moreover, both methods help to determine the crystal structure. This includes lattice parameters, atomic positions, and symmetry.

Difference Between Bragg and Laue Diffraction

Definition

• Bragg Diffraction is a technique for analyzing crystal structures by measuring how X-rays are reflected at certain angles, while Laue diffraction is a technique for analyzing crystal structures by observing the pattern of X-rays that pass through and scatter within a crystal.

X-Ray Source

• Bragg diffraction uses a monochromatic X-ray source, while Laue diffraction uses a polychromatic X-ray source.

Focus on Crystal Plane

• Bragg diffraction focuses on specific crystal planes, while Laue diffraction focuses on all crystal planes simultaneously.

Crystal Orientation

• Bragg diffraction requires precise crystal orientation, while Laue diffraction does not require precise crystal orientation.

Diffraction Pattern

• Bragg diffraction produces a simpler diffraction pattern, while Laue diffraction produces a complex diffraction pattern.

Set up

• Bragg diffraction requires more complex equipment with precise control of X-ray wavelength and crystal orientation while Laue diffraction requires a simpler experimental setup as it does not require precise control of the X-ray source or crystal orientation.

Conclusion

In brief, Bragg and Laue diffraction exploit the interaction between X-rays and the periodic lattice structure of crystals to generate diffraction patterns. However, the main difference between Bragg and Laue diffraction is that Bragg diffraction focuses on specific crystal planes while Laue diffraction focuses on all crystal planes simultaneously.

FAQ: Bragg and Laue Diffraction

1. What is the principle of Laue diffraction?

Laue diffraction uses a polychromatic X-ray beam to illuminate a crystal. When X-rays interact with the crystal lattice, they diffract at specific angles. The resulting diffraction pattern reveals information about the crystal’s structure and orientation.

2. What is the significance of the Laue equation?

Laue equation mathematically describe the conditions for constructive interference of X-rays scattered by a crystal lattice. Therefore, it’s an important technique in crystallography.

3. What is the significance of the Bragg’s law?

Bragg’s law relates the angle of incidence of X-rays to the spacing between atoms in a crystal. Thus, this helps scientists to determine the structure of materials at the atomic level.

4. What are the disadvantages of the Laue method?

The Laue method requires large, perfect crystals and cannot determine precise wavelengths due to using white radiation. It’s difficult to obtain low-resolution data from Laue photographs.

Reference:

1. “Bragg Law.” Encyclopedia Britannica.
2. “Laue Diffraction.” Encyclopedia Britannica.

Image Courtesy: 

1. “Laue Diffraction” By ARMICRON – Own work (Public Domain) via Commons Wikimedia
2. “Diffusion rayleigh et diffraction” By The.ever.kidGregors (talk) – Diffusion_rayleigh_et_diffraction.png with slight modification (CC BY-SA 3.0) via Commons Wikimedia