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EXPERIMENTAL DIFFRACTION TECHNIQUE (Diffractometer (Typical Diffraction…
EXPERIMENTAL DIFFRACTION TECHNIQUE
Laue Technique
Sample is a single crystal
Types of Laue technique
Transmission technique: Film use for recording the diffraction pattern is placed behind the sample and records the forward diffracted ray
Dots Pattern: Ellipse and hyperbolic shape
Reflected ray technique: Film use for recording the diffraction pattern is placed between source and sample
Dots Pattern: Hyperbolic shape
Ewald Construction : All reciprocal lattice points that touce the surface of the Ewald sphere between the two limiting spheres will satisfy Laue requirement
Crystal Rotation Technique
Definition:
Diffraction pattern is formed on the cylindrical shaped photographic film
Black spots are the peaks of maximum intensity
When the crystal rotates the reciprocal lattice also rotates
Some reciprocal lattice points pass through the surface of the Ewalds sphere
Ewald Construction
Reciprocal lattice points in the plane of the screen is rotated around an axis perpendicular to this plane and at the end point of the incident wave vector,q
Each intersection of these circles with the Ewald sphere produces a wave vector for the Bragg's reflected ray
Powder Technique
Sample powder is put into a container at placed in the line of monochromatic X-ray
If the crystal is rotated around an axis same as the incident beam, diffracted rays form a cone with its peak on the crystal and its cone angle is twice the diffraction angle
Single or polycrystals are ground into powder form
Diffractometer
Arrangement of diffractometer: Can observe periodic structure in a crystal
Used by Bragg to obtain diffraction from single crystal
Used to measure diffractions from powder samples or in X-ray florescence spectrocopy
Typical Diffraction Pattern
Solid crystals: Maximum peaks occur at twice Bragg's angle
Liquid or amorphous solids: No periodical peaks, which shows tendency of atoms to group together
