xrd_peakpositions

xrd_peakpositions - X-ray Powder Diffraction II Peak...

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1 X-ray Powder Diffraction II ray Powder Diffraction II Peak Positions & Indexing Peak Positions & Indexing Chemistry 754 Solid State Chemistry Lecture #10 Outline Outline • Single crystal & powder diffraction • Information contained in a diffraction pattern • Geometrical considerations • Peak positions • Indexing cubic powder patterns • Auto indexing
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2 Single Crystal Diffraction Diffraction Incident Beam Diffracted Diffracted Beam Incident Beam Beam Diffracted Beam Powder Powder Diffraction Diffraction In powder diffraction only a small fraction of the crystals ( shown in blue ) are correctly oriented to diffract . Single Crystal Single Crystal Diffraction (3D) Diffraction (3D) Powder Diffraction (1D) Diffraction (1D) 0 200 400 600 800 1000 1200 1400 1600 1800 5 1 01 52 02 53 0 2-Theta (degrees) Intensity (Arb. Units)
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3 Single Crystal Single Crystal Diffractometer (4 circles) (4 circles) Powder Powder Diffractometer Diffractometer (2 circles) (2 circles) Powder Diffraction Methods Powder Diffraction Methods Qualitative Analysis Phase Identification Quantitative Analysis Lattice Parameter Determination Phase Fraction Analysis Structure Refinement Rietveld Methods Structure Solution Reciprocal Space Methods Real Space Methods Peak Shape Analysis Crystallite Size Distribution Microstrain Analysis Extended Defect Concentration
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4 Information in a Diffraction Pattern Information in a Diffraction Pattern Peak Positions The peak positions tell you about the translational symmetry. Namely what is the size and shape of the unit cell. Peak Intensities The peak intensities tell you about the electron density inside the unit cell. Namely where the atoms are located. Peak Shapes & Widths The peak widths and shapes can give information on deviations from a perfect crystal. You can learn about the crystallite size if it is less than roughly 100 – 200 nm. You can also learn about extended defects and microstrain. Debye Debye -Scherrer Scherrer Camera & Camera & Cones of Diffraction Cones of Diffraction λ = 2d hkl sin θ hkl
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5 Measuring Diffraction Rings Measuring Diffraction Rings Area Detector Film Strip Measuring Diffraction Rings Measuring Diffraction Rings U = 4 θ hkl R θ hkl = Bragg Angle R = Diffractometer Radius U
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6 Preferred Orientation/Texture Preferred Orientation/Texture Area Detector Film Strip Bragg Bragg -Brentano Brentano Parafocusing Parafocusing Diffractometer Diffractometer θ Horizontal Diffraction Circle Divergent X-ray Source Detector Divergence Slit Antiscatter Slit Receiving Slit Horizontal Soller Slits Sample (Vertical Flat Plate)
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7 Qualitative Analysis Qualitative Analysis Searching with the ICDD Once you have a powder pattern you can use it like a fingerprint to see if it matches the powder pattern of an already known compound. Nowadays this is usually done with the help of a computer.
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xrd_peakpositions - X-ray Powder Diffraction II Peak...

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