X-ray Diffraction: A Technique to Determine the Atomic Structure of Materials

August 31, 2024 4 min read Science Technology Physics X-Ray Diffraction Crystallography Atomic Structure Analytical Techniques Material Science

X-ray Diffraction (XRD) is a powerful analytical technique used to determine the atomic and molecular structure of a crystal by observing the patterns formed by X-rays scattered off a crystal.

On this page

X-ray Diffraction (XRD) is a powerful analytical technique used in chemistry, physics, geology, and material science to determine the atomic and molecular structure of a crystal. When a crystal is exposed to X-rays, the atoms within the crystal scatter the X-ray beams, resulting in a diffraction pattern. This pattern provides valuable information about the arrangement of atoms in the crystal.

Historical Context

X-ray diffraction was discovered in 1912 by Max von Laue, a German physicist, who was awarded the Nobel Prize in Physics in 1914 for this discovery. The method was later developed by William Henry Bragg and William Lawrence Bragg, father and son, who also received the Nobel Prize in Physics in 1915 for their services in the analysis of crystal structures by means of X-rays.

Types of X-ray Diffraction

Single Crystal X-ray Diffraction (SCXRD)

This method is used to determine the crystal structure of a single crystal. It provides highly accurate data on the arrangement of atoms within the crystal.

Powder X-ray Diffraction (PXRD)

Used for the analysis of polycrystalline or powdered samples. It is commonly used in material science for phase identification and characterization of materials.

Key Events

1912: Discovery of X-ray diffraction by Max von Laue.
1913: Development of the Bragg’s Law by William Lawrence Bragg.
1914: Max von Laue receives Nobel Prize for the discovery.
1915: William Henry Bragg and William Lawrence Bragg receive Nobel Prize for their work in crystallography.

Detailed Explanation

Bragg’s Law

Bragg’s Law is the fundamental principle governing X-ray diffraction and is given by:

n\lambda = 2d \sin \theta

where:

\( n \) is the order of reflection (an integer),
\( \lambda \) is the wavelength of the incident X-ray beam,
\( d \) is the distance between the crystal planes,
\( \theta \) is the angle of incidence.

The equation describes the condition for constructive interference of the X-rays scattered by the crystal planes.

X-ray Diffraction Pattern

When X-rays interact with a crystal, they are diffracted in many directions. By measuring the angles and intensities of these diffracted beams, a three-dimensional picture of the electron density within the crystal can be generated. This electron density map is used to determine the positions of the atoms in the crystal.

    graph LR
	    A(X-ray Source) -->|X-ray beam| B(Crystal Sample)
	    B -->|Scattered X-rays| C(Detector)
	    C --> D(Diffraction Pattern)

Importance and Applicability

Material Science: Identification and characterization of materials.
Chemistry: Determination of molecular structures.
Geology: Analysis of mineral compositions.
Pharmaceuticals: Drug development through crystallography.

Examples

Determining the structure of DNA: X-ray diffraction was crucial in elucidating the double helix structure of DNA.
Characterizing new materials: Understanding the atomic arrangement in novel materials.

Considerations

Sample purity is critical for accurate results.
Requires highly sophisticated equipment.
Interpretation of results often requires expertise.

Crystallography: The study of crystal structures and properties.
Electron Diffraction: A technique similar to X-ray diffraction but uses electrons instead of X-rays.
Neutron Diffraction: Uses neutrons for diffraction to analyze materials.

Comparisons

X-ray Diffraction vs. Electron Diffraction: Electron diffraction uses electrons, which have shorter wavelengths than X-rays and can provide higher resolution.
X-ray Diffraction vs. Neutron Diffraction: Neutron diffraction is more sensitive to lighter elements like hydrogen and can provide different contrast than XRD.

Interesting Facts

The determination of DNA’s structure was awarded the Nobel Prize in 1962 to James Watson, Francis Crick, and Maurice Wilkins.
X-ray diffraction has been used to determine the structures of numerous proteins and biomolecules.

Famous Quotes

“Seeing is not believing – it’s only seeing.” – Rosalind Franklin, who played a key role in discovering the DNA structure.

FAQs

What is the principle behind X-ray diffraction?

X-ray diffraction is based on the constructive interference of X-rays scattered by the periodic array of atoms in a crystal, as described by Bragg’s Law.

What are some applications of X-ray diffraction?

XRD is used in material science for phase identification, in chemistry for molecular structure determination, in geology for analyzing minerals, and in pharmaceuticals for drug development.

What kind of samples can be analyzed using X-ray diffraction?

Both single crystals and powdered samples can be analyzed using different methods of XRD, such as SCXRD and PXRD.

References

Max von Laue’s Nobel Lecture.
Bragg, W.H., & Bragg, W.L. (1913). The reflection of X-rays by crystals.
“Introduction to X-ray Crystallography” by M.J. Glazer.

Summary

X-ray Diffraction (XRD) is a pivotal analytical technique for determining the atomic structure of crystalline materials. Since its discovery over a century ago, XRD has become an indispensable tool in various fields, including material science, chemistry, geology, and pharmaceuticals. By analyzing the patterns of X-rays diffracted through a crystal, scientists can deduce the positions of atoms within the material, offering profound insights into its properties and behavior. Through its various methods such as SCXRD and PXRD, XRD continues to play a crucial role in scientific and industrial advancements.