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How to interpret (tally) the XRD data

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  2. 2. Introduction • It is a novel & non destructive method of chemical analysis and a variety of x –ray techniques are available in practice. • These are : X – Ray Absorption : X-ray diffraction X-ray Fluorescence • “ Every crystalline substance gives a pattern; the same substance 2 • “ Every crystalline substance gives a pattern; the same substance always gives the same pattern; and in a mixture of substances each produces its pattern independently of the others”. • The X-ray diffraction pattern of a pure substance is, therefore, like a “fingerprint of the substance”.
  3. 3. Electro-magnetic Spectrum 3
  4. 4. Wilhelm Conrad Röntgen 4 Wilhelm Conrad Röntgen discovered 1895 the X-rays. In 1901 he was honoured by the Noble prize for physics.
  5. 5. C. Gordon Darwin 5 C. Gordon Darwin, developed 1912 dynamic theory of scattering of X-rays at crystal lattice
  6. 6. What is X-ray Diffraction ? 6
  7. 7. Why to select XRD? • Measure the average spacing's between layers of atoms. • Determine the orientation of a single crystal. 7 • Find the crystal structure of an unknown material. • Measure the size, shape and internal stress of small crystalline regions.
  8. 8. What is Crystallography??? • The atoms are arranged in a regular pattern, and there is as smallest volume element that by repetition in three dimensions describes the crystal. This 8 dimensions describes the crystal. This smallest volume element is called a unit cell. • The dimensions of the unit cell is described by three axes : a, b, c and the angles between them α, β , and γ are lattice constants which can be determined by XRD.Lattice
  9. 9. Diffraction Conditions Fraunhofer diffraction Bragg diffraction }d  }d  9 For constructive interference, d sin = n  For constructive interference, 2(d sin) =n    d } }  d d sin } }d  d sin d sin
  10. 10. How X-rays are Produced??? 10 X-rays are produced whenever high-speed electrons collide with a metal target. A source of electrons – hot W filament, a high accelerating voltage between the cathode (W) and the anode and a metal target, Cu, Al, Mo, Mg.
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  12. 12. X-rays Bragg’s Law Bragg’s law = n ƛ =2d sin θ set of lattice planes d   X-rays d sin 
  13. 13. D8 ADVANCE Bragg-Brentano Diffractometer • A scintillation counter may be used as detector instead of film to yield exact intensity data. • Using automated goniometers step by step scattered intensity 13 step by step scattered intensity may be measured and stored digitally. • The digitised intensity may be very detailed discussed by programs. • More powerful methods may be used to determine lots of information about the specimen.
  15. 15. Powder Diffraction Pattern 15
  16. 16. Experimental XRD data are compared to reference patterns to determine what phases are present 16  The reference patterns are represented by sticks the position and intensity of the reference sticks should match the data.  A small amount of mismatch in peak position and intensity is acceptable experimental error.
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  18. 18. Most diffraction data contain K-alpha1 and K-alpha2 peak doublets rather than just single peaks 18
  19. 19. The experimental data should contain all major peaks listed in the reference pattern 19
  20. 20. Diffraction peak broadening may contain information about the sample microstructure 20
  21. 21. All calculations are more accurate if you use more peaks over a longer angular range 21  If you use one or two peaks, you must assume: – That there is no specimen displacement error when calculating lattice parameters – That there is no microstrain broadening when calculating crystallite size.
  22. 22. If you use many peaks over a long angular range (for example, 7+ peaks over a 60° 2theta range), you can: Calculate and correct for specimen displacement when solving lattice parameters. 22 solving lattice parameters.  Calculate and account for microstrain broadening when calculating crystallite size.  Improve precision by one or two orders of magnitude.
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  24. 24. Applications of XRD  XRD is a non destructive technique to identify crystalline phases.  The powder xrd pattern may be thought of as 24  The powder xrd pattern may be thought of as finger print of the single crystal structure, and it may be used conduct qualitative and quantitative analysis.  XRD is a technique used to determine the orientation of the given crystal compound.
  25. 25.  Obtain XRD pattern are used to measure d-spacings of the given compound.  Determination of Cis-Trans isomerism. 25  Determination of Cis-Trans isomerism.  To measure thickness of thin films and multi-layers.  To determine atomic arrangement.
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