LESSON 11(X-ray Diffraction)

Diffraction

working principle

Bragg's Law

In phase

X-ray are produced by X-ray tube.

Completely out of phase

it relates to the wavelength of electromagnetic radiation to the diffraction angle and the lattice spacing in the crystalline sample

CRYSTALLINE STRUCTURE
In Phase : X-ray scattered in the same direction and result in constructive interference
Out of Phase : X-ray will scatter everywhere and cause destructive interference and result in low intensity diffracted beam

constructive interference

Destructive interference

Data Analysis and Interpretation: Peaks

Sample Preparation

How it is produce

peaks cannot be seen

Heated filament emits electrons by thermionic emission

nλ = 2d sin (theta)

peaks can be seen

Electrons are accelerated by high voltage

Copper rod for heat dissipation

X-rays produced when high speed electrons hit the metal target

Diffraction angle = 2 x theta

image

image

There are sharp intensity maxima at certain wavelengths superimposed on a continous X-ray spectrum

lattice parameter, a. Find distance between the two plane --> find theta --> diffraction angle

Arrangement of the atoms
Orderly with grain boundaries : several peaks shown as ths ordered structure have different lattice point


Randomly packed : will show a diffuse pattern as the atoms are not packed in an orderly manner

Intensity maxima - Characteristic of X-ray

X-ray diffraction technique require single wavelength X-ray radiation

X-ray diffraction based on the constructive interference of monochromatic X-rays and sample