X-ray diffraction

introduction to xray, bragg's law, miller indices,,,powder diffraction, instrumentation, application

1. X-Ray Diffraction Bindu Kshtriya

2. DISCOVERY OF X-RAY Wilhelm Conrad Roentgen discovered x-radiation in 1895 In 1912, Friedrich, Knipping, and von Laue demonstrated diffraction of x-radiation passing through a crystal The wavelength of x-radiation ranges from 10 -6 to 10 -1 nm

3. W C a t h o d e C u A n o d e ( - ) ( + ) X - r a y s electrons X-RAY GENERATION

4. ENERGY LEVELS

5. XRD 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.

6. SCHEMATIC DIAGRAM OF X-RAY DIFFRACTION

7. Constructive and Destructive Interference of Waves Constructive Interference In Phase Destructive Interference Out of Phase

8. smallest building block c a b a g Unit cell (Å) Cs Cl b d 1 Lattice d 2 A crystal consists of a periodic arrangement of the unit cell into a lattice. The unit cell can contain a single atom or atoms in a fixed arrangement. Crystals consist of planes of atoms that are spaced a distance d apart, but can be resolved into many atomic planes, each with a different d spacing. A , b and c (length) and a α , β and γ angles between a , b and c are lattice constants or parameters which can be determined by XRD.

9. SEVEN CRYSTAL SYSTEM

10. MILLER INDICES Miller indices-the reciprocals of the fractional intercepts which the plane makes with crystallographic axes Axial length 4Å 8Å 3Å Intercept lengths 1Å 4Å 3Å Fractional intercepts ¼ ½ 1 Miller indices 4 2 1 h k l

11. Several Atomic Planes and Their d-spacings in a Simple Cubic a b c 1 0 0 1 0 0 a b c 1 1 1 1 1 1 a b c 1 1 0 1 1 0 a b c 0 1 ½ 0 1 2 Cubic a=b=c=a0

12. WHY XRD • Measure the average spacings between layers or rows of atoms • Determine the orientation of a single crystal or grain • Find the crystal structure of an unknown material • Measure the size, shape and internal stress of small crystalline regions

13. X-RAY POWDER DIFFRACTION X-ray powder diffraction (XRD) is a rapid analytical technique primarily used for phase identification of a crystalline material and can provide information on unit cell dimensions. The analyzed material is finely ground, homogenized, and average bulk composition is determined

14. X-RAY POWDER DIFFRACTOMETER 1.) The X-ray tube 2.) The flat specimen 3.) The goniometer circle 5.) A slit 6.) A filter 7.) The detector 4.) Monochromator

15. Basic Features of Typical XRD Experiment

16. Steps involved :- 1.) Sample preparation 2.) Generate Analytical X-rays 3.)Direct the X-rays at a Powdered Specimen 4.) Measure X-Rays “Diffracted” by the specimen and obtain a diffraction pattern 5.) Determine the Crystalline Phases Present in the specimen

17. DETECTORS PHOTOGRAPHIC METHODS GEIGER MULLER TUBE METHOD PROPORTIONAL COUNTER SCINTILLATION DETECTOR COUNTER METHODS

18. DIFFRACTION SPECTRA

19. INTERPRETATION OF DATA International Centre Diffraction Data (ICDD) or formerly known as (JCPDS) Joint Committee on Powder Diffraction Standards is the organization that maintains the data base of inorganic and organic spectra. The data base is available from the Diffraction equipment manufacturers or from ICDD direct. Currently the data base is supplied either on magnetic or optical media. Two data base versions are available the PDF I and the PDF II.

20. The PDF I data base contains information on d-spacing, chemical formula, relative intensity, RIR quality information and routing digit. The information is stored in an ASCII format in a file called PDF1.dat. For search/match purposes most diffraction manufactures are reformatting the file in a more efficient binary format. The PDF II data base contains full information on a particular phase including cell parameters. Scintag’s newest search/match and look-up software package is using the PDF II format. Optimized data base formats, index files and high performance PC-computers make PDF II search times extremely efficient.

21. Significance of Peaks in XRD 1. Peak position 2. Peak width 3. Peak intensity 4. Peak area 5. Peak shape

22. “Anatomy” of the XRD pattern Information content of an idealized diffraction pattern. 28

23. Uses of X-Ray Powder Diffraction • Identification of single-phase materials – minerals, chemical compounds, ceramics or other engineered materials. • Identification of multiple phases in microcrystalline mixtures (i.e., rocks) • Determination of the crystal structure of identified materials • Identification and structural analysis of clay minerals • Recognition of amorphous materials in partially crystalline mixtures

24. Applications of XRD • XRD is a non destructive technique • To identify crystalline phases and orientation • To determine structural properties: Lattice parameters (10-4Å), strain, grain size, expitaxy, phase composition, preferred orientation (Laue) order-disorder transformation, thermal expansion • To measure thickness of thin films and multi-layers* • To determine atomic arrangement • Detection limits: ~3% in a two phase mixture; can be ~0.1% with synchrotron radiation Spatial resolution: normally none

25. Thank you Bindu Kshtriya