Transcript of "972 B3102005 Diffraction Direction"
Diffraction: directions of diffraction <ul><li>For a set of plane (hkl), an incident x-ray </li></ul><ul><li>beam with wavelength will be diffracted when </li></ul><ul><li>incident, diffracted and plane normal are coplanar </li></ul><ul><li>incident and diffracted beams both make a Bragg angle B with the (hkl) plane, where =2d sin B </li></ul><ul><li>Provided the structure factor for (hkl) plane F(hkl) is not zero </li></ul>
Summation over all atoms in a unit cell with positions [x n , y n , z n ] and atomic scattering factor f n (to be defined later).
Difference between powder and single crystal diffraction <ul><li>For a single crystal sample, the whole sample is a large, continuous crystal </li></ul><ul><li>A powder sample is an assembly of randomly or partial randomly oriented tiny crystals called grains, it may be in a form of true powder or a piece of solid bulk. </li></ul><ul><li>For single crystal diffraction, both background and characteristic radiations from an x-ray tube are diffracted. </li></ul><ul><li>In powder diffraction, only characteristic radiations are considered because diffraction of weak background radiations by small grains is usually negligibly weak. </li></ul>