XRAY DIFFRACTION (XRD)

2. X-Ray Diffraction Spectroscopy

3. CONTENTS • INTRODUCTION • BRAGG’S LAW • X-RAY DIFFRACTION • METHODS • APPLICATIONS OF XRD • ADVANTAGES AND DISADVANTAGES

4. INTRODUCTION: • It is the novel and destructive method of chemical analysis and a variety of x-ray techniques are available in practice. These area as follows: • X-Ray Absorption, • X-Ray Diffraction • X-Ray Fluorescence. X-Ray Diffraction: "Every crystal substance gives a pattern;and in a mixture of substances each produces its pattern independently of others." The X-Ray Diffraction pattern of a pure substance is therefore like a fingerprint of the substance. It is based on the scattering of x-rays by crystals. Definition: The atomic planes of a crystal cause an incident beam of x-rays, to interfere with one another as they leave the crystal. This phenomenon is known as x-ray diffraction

6. BRAGG’S LAW • After few months, In 1913,English Physicists Sir William Henry Bragg and his son Sir William Lawrence Bragg developed a relationship to explain why the cleavage faces of crystals appear to reflect X-Ray beams at certain angles of incidence (θ). • The variable d is the distance between atomic layers in a crystal,and the variable λ is the wavelength of the incident X-ray beam; where ‘n’ is an integer.

7. Although Bragg’s law was used to explain the interference pattern of X-rats scattered by crystals, diffraction has been developed to study the structure of all states of matter with any beam. • Bragg’s carried out a series of experiments,the results of which he published the Bragg’s Equation: nλ=2dsinθ Where assume n = 1 for the first order reflection. λ = wavelength θ = X-ray incidence angle d = distance between atomic layers.

8. X-Ray Diffraction METHODS: • Generally, there are three methods which is used for diffraction of X-ray: • Laue Method • Rotating Crystal Method • Powder Method Laue Rotating crystal Powder Orientation Single Crystal Polychromatic Beam Fixed Angle Lattice constant Single Crystal Monochromatic Beam Variable Angle Lattice Parameters Polycrystal(powdered) Monochromatic Beam Fixed Angle

9. Powder Method If a powdered specimen is used,instead of a single crystal, then there is the specimen, because there will always be some crystals at an orientation for which diffraction is permitted. Here a monochromatic X-ray beam is incident on a powdered or polycrystalline sample. This method is used for samples that are difficult to obtaining single crystal form.

10. For every set of crystal planes, by chance, one or more crystals will be in the correct orientation to give correct Bragg’s angle to satisfy Bragg’s equation. Every crystal plane is thus capable of diffraction. Each diffraction line is made up of a large number of small spots, each from a spectral crystal. Each spot is so small as to give the appearance of a continue line.

11. POWDER DIFFRACTION PATTERN

12. ADVANTAGES AND DISADVANTAGES OF X-RAYs ADVANTAGES: • X-ray is the most cheapest, the most convenient and widely used method. • X-rays are not absorbed very much air, so the specimen need not be in an evacuated chamber. DISADVANTAGES: • They do not interact very strongly with lighter elements.