Science
Answer questions on XRD
Use the book attached in the following link and any other relevant source to answer the following questions. https://drive.google.com/file/d/1-kN9QMjGsyeQXoBXHLt8kP9IwC1oswz-/view?usp=sharing
Make your answers short and cite the source (and page number or link) of each of your answer. Kindly, I should be able to reproduce you answer from the page you cite.
- Examine figure 2.57 in Brandon & Kaplan which shows a TEM diffraction pattern from a single grain of α-Fe (BCC Fe). Examine the apparent symmetry of the pattern (note spot diam is used to indicate the intensity of the diffracted beams) – what is the zone axis for this pattern? (hint:the diffraction pattern MUST reflect AT LEAST the symmetry of the real crystal along that direction but could appear to be higher symmetry. Index the pattern, remembering the following rules:
- The zone axis (vector that the e-beam is travelling along) points straight out of the page and is centered in the center of the pattern
- The in-plane vectors to the diffraction spots are the momentum transfer vectors and reciprocal lattice vectors ∆k=G. Since the zone axis is normal to the page and all the G vectors are in plane, the dot products of G*zone axis vector must be zero.
- The radius from pattern center to each spot is the magnitude of the G vector times a scale factor. So you can take ratios of these radii and invert them to get the ratios of d-spacings in real space.
- The d-spacing as function of hkl for a cubic crystal is equation 2.38 in B&K book.
- Briefly explain the origins of Kikuchi lines (see chapter 2 near end for discussion in context of a TEM diffraction pattern. Also read sections 5.6.4-5.6.6. What changes in the discussion for the OIM / EBSD context as opposed to TEM context?
