Powder Diffraction - Spallation Neutron Source

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$Single Crystal Diffraction - Spallation Neutron Source$

Limitations of Rietveld Rietveld can only discern parameters that have effects on the powder diffraction pattern – Cannot separate some effects ever • Absolute configuration • Magnetic moment directions unless they break symmetry If two parameters have approximately the same effect on the powder diffraction pattern, they correlate and they cannot be differentiated (e.g. occupancies & displacement parameters) 50
The physics that determine peak profiles Common factors Instrumental Resolution Axial Divergence (Low Angle Asymmetry) Sample placement/transparency Crystallite Broadening* Strain Broadening* * Note that these effects can vary for different classes of reflections (anisotropic peak broadening) Stacking faults* Less common factors Modulated Structures* Coherence differing by atom type* Compositional inhomogeneity! * Hard to model ! Sometimes impossible to model Results of these factors are convoluted to produce the observed peak shape. 51
Page 1 and 2: A Very Abbreviated Introduction to
Page 3 and 4: Where to go for more… There are m
Page 5 and 6: Basic Crystallography 5
Page 7 and 8: Lattice planes General Indices: la
Page 9 and 10: Diffraction from single crystals D
Page 11 and 12: Powder Diffraction 11
Page 13 and 14: Bragg cones in powder diffraction S
Page 15 and 16: Coherent Atomic Scattering Power (d
Page 18 and 19: Resonant Conditions X-rays X-ray fo
Page 20 and 21: Measuring powder diffraction Angul
Page 22 and 23: Highest resolution requires high co
Page 24 and 25: Powder Instruments: Constant Wavele
Page 26 and 27: Time of Flight Diffraction Time of
Page 28 and 29: Neutron Powder Diffraction with Spa
Page 30 and 31: Materials effects on Powder Diffrac
Page 32 and 33: Crystallite Size Broadening d*=cons
Page 34 and 35: Microstrain Broadening See GSAS Man
Page 36 and 37: Anisotropic strain broadening terms
Page 38 and 39: Fitting of Powder Diffraction Data
Page 40 and 41: Fitting crystallographic data -- wh
Page 42 and 43: Hugo Rietveld’s technique Hugo R
Page 44 and 45: Hugo Rietveld in the Petten Reactor
Page 46 and 47: Hugo Rietveld’s other breakthroug
Page 48 and 49: What sort of data are needed for Ri
Page 52 and 53: Approaches to Profile Models Three
Page 54 and 55: Voigt vs. Pseudo-Voigt A Gaussian c
Page 56 and 57: Axial Divergence (Low Angle Asymmet
Page 58 and 59: Sample Displacement & Transparency
Page 60 and 61: The Unit Cell The unit cell descri
Page 62 and 63: Lattice Types Centering causes latt
Page 64 and 65: Space Groups Not all combinations
Page 66: Reciprocal Lattice To simplify mat

Powder Diffraction - Spallation Neutron Source

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