Dear Luca: Thanks for the reply and your good comment.
Best regards, Angel > Because you are collecting just in Bragg-Brentano condition, or if > not for every collection you just see only one direction in the > sample, not all together. And if you homogenize all together you will > only observe a broadening of the peaks. > > Best regards, > > Luca Lutterotti > > On Jan 20, 2007, at 8:02 PM, [EMAIL PROTECTED] wrote: > >> Dear all: >> >> Let me make you the following question. >> >> Suppose a polycrystalline coating deposited onto a substrate in >> such a way >> that the coating is subjected to in-plane compressive residual >> stresses >> after the deposition process. The coating has a cubic fcc crystal >> structure before the deposition process, and also appears to be >> cubic fcc >> with increased out-of-plane lattice parameter after the deposition. I >> understand the increased out-of-plane lattice parameter because the >> stresses are compressive in nature and the XRD experiment collects >> information on the diffracting planes that are parallel to the sample >> surface. However, I have the following question: >> >> Since the residual stresses are compressive in nature, the fcc crystal >> structure will become distorted after the deposition process, and >> strictly >> will be no longer cubic. The change in the shape of the unit cell >> is most >> likely a function of the orientation of the unit cell with respect >> to the >> direction of the residual stresses. Thus, the cube can change to >> tetrahedron, rhombohedral, etc. If the stresses are large enough in >> magnitude (bout 1000 MPa), why the XRD pattern still shows a cubic >> crystal >> structure (there are no additional peaks, peak splitting, etc). >> >> Thanks in advance >> >> Angel >> >> >> >
