Deformation faults

All in all, the WPPM approach can provide a simultaneous structure and microstructure refinement, based on physical models of the phases under study, without using any arbitrary profile function. Considering the terms of Equation (26), refinement parameters to be optimized in a least-squares analysis are relatively few, namely, mean (p) and variance (cr) of a suitable distribution of coherent domain sizes, dislocation density (p), effective outer cut-off radius (R ) and character (/e, effective fraction of edge dislocations), twin fault (P), deformation fault (a) and APB (y) probabilities. 

PDs formation observed in as-grown GaN/PSC samples is related to deformation faulting within GaN films. Important is that deformation-related faulting in solids is known to contribute significantly to the XRD RC broadening [62-64]. This easily explains the above-mentioned illusory contradiction between the XRD and TEM data. 

M.S. Paterson, X-ray diffraction by face-centered cubic crystals with deformation faults,/. Appl. Pbys., 23, 805-811 (1952). 

Fig. 6.56 HREM structural images of the typical stacking faults found in pSiC ceramics sintered at 2000 °C a twin fault and b deformation fault Structural models based on the stacking sequence are shown [12], With kind permission of John Wiley and Sons...

Very variable high-energy deposition (mounding, cut-and-fill channeling), or major post-depositional deformation (faulting, movement of overpressured shale). 

Instrumentation for studies of this nature are usually variations of the normal powder X-ray diffractometer. Except for faulting and strain in single crystals, which are better treated as defects, the very nature of the material limits studies to powders or aggregates. X-ray powder patterns of simple metals can be analyzed to yield information on particle size, deformation fault probability, mean-square strain, and twinning. The theory and techniques used to study diffraction line broadening, peak shifts, and line profile asymmetry have been derived and applied by Warren, " and Warren and Averbach. To assess faulting probability, certain drastic assumptions are necessary, reducing the detectability limit to approximately one faulted layer in 200. 

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