Xrd

XRD & Different methods of diffraction

1. A seminar talk on X-Ray Diffraction(XRD) Presented by GITA KRUSHNA SATAPATHY Regd. no-160705120038

2. Plan of Talk What is XRD? Why XRD? Diffraction Methods. Applications of XRD. Advantages & Disadvantages.

3. Definition The atomic planes of a crystal cause an incident beam of X-rays to interfere with one another as they leave the crystal. The phenomenon is called X-ray diffraction. What is X-ray Diffraction ?

4. Why XRD? Measure the interplanar spacing between layers of atoms. Determine the orientation of a single crystal or grain . Determine crystal structure of an unknown material. Measure the size, shape and internal stress of small crystalline regions.

5. Diffraction Methods Method Wavelength Angle Specimen Bragg’s Laue Variable Variable Variable Fixed Single Crystal Single Crystal Rotating Crystal Fixed Variable (in part) Single Crystal Powder Fixed Variable Powder

6. Bragg’s Method n = 2dsin  n: Order of refl ection d: Plane spacing = : Bragg Angle λ < 2d Path difference must be integral multiples of the wavelength &  in = out in out 2 

7. Laue Method The diffraction spots generally lying on an ellipse Back-reflection method The diffraction spots generally lying on an hyperbola. Zone axis crystal Incident beam Film Reflection Zone axis crystal Incident beam Film U sed to assess crystal perfection from the size and shape . It is the only method for the study of large and thick specimens . Crystal orientation is determined from the position of the spots . Transmission Laue method

8. Rotating Crystal Method Determine the  shape & size of unit cell  as well as the  arrangement of atoms inside the cell.   The Lattice constant  of the crystal. film Determine the crystal structure of un known material.

9. Powder Method Useful for determining the complex structures of metals and alloys. D etermine the unit cell dimensions. M easure the sample purity. Incident Beam Sample Film

10. Determination of Structure Factor Bravais Lattice Reflections possibly present Reflections necessarily absent Simple All None Body Centered (h+k+l): Even (h+k+l): Odd Face Centered h, k, and l unmixed i.e. all odd or all even h, k, and l: mixed h,k,l : miller indices u,v,w : co-ordinates of the atoms in the lattice N : number of atoms f n : scattering factor Applications of XRD

11. BCC FCC

12. Significance of Peak Shape in XRD Peak position Peak width Peak intensity Important for Particle or grain size Residual strain Plane spacing

13. Bragg’s Law n  = 2d sin For 1 st order reflection n=1 So  = 2d sin For cubic crystals INTERPLANAR SPACING & LATTICE CONSTANT DETERMINATION

14. Crystallite size can be calculated using Scherer Formula T= T = crystallite thickness λ ( X-ray wavelength, Å) K ( Scherer’s constant ) ~ 0.9 B=Full width with half maximum =Diffraction angle at peak position   PARTICLE SIZE DETERMINATION

15. STRAIN EFFECTS

16. Also applicable for Phase analysis Lattice parameter determination Strain determination Texture and orientation analysis Order-disorder transformation & Thin film characterization

17. Advantages & Disadvantages of X RD Compared to Other Methods Advantages Least expensive , the most convenient . W idely used method to determine crystal structures . The best method for phase analysis . X- R ay s are not absorbed very much by air , so the sample need not be in an evacuated chamber. Disadvantage s X- R ay s do not interact very strongly with lighter elements . The intensity is times less than that of electron diffraction.