Dear Ling Yang, I don't think you really have texture. What your pattern suffers from is graininess which will, of course be modelled by some "crazy" preferred orientation if you allow to refine it. To avoid graininess, 1- make a proper sample preparation 2- open in plane divergence, especially at higher angles 3- rotate sample if possible. You can look at the discussion of grainy patterns in HP Klug, LE Alexander: X-ray diffraction procedures for polycrystalline and amorphous materials, Wiley (1974) 966p (costs even more, but you might find water digging in your library!)
Best mg On 26 Mar 2004 at 14:26, ling yang wrote: > > That's "far water for near fire", and the book is so expensive! I > just want to know if anyone ever encounter such kind of problems, > and how they magnage to do refinement for martensitic > transformation, especially when the fraction is low. thx:) > ----- Original Message ----- > From: Peter Zavalij > To: [EMAIL PROTECTED] > Sent: Friday, March 26, 2004 12:57 PM > Subject: RE: > > This is quite comprehensive question(s) and even not so > comprehensive answer could not be placed in one e-mail message. > However, all these issues and more are covered in book "Fundamentals > of Powder Diffraction and Structural Characterization of Materials" > by V.K.Pecharsky & P.Y.Zavalij. Kluwer Academic Publishers, Spring > 2003. (www.amazon.com, www.wkap.nl) > > Peter Zavalij > -----Original Message----- > From: ling yang [mailto:[EMAIL PROTECTED] > Sent: Friday, March 26, 2004 11:58 AM > To: [EMAIL PROTECTED] > Subject: > > Dear all, > > I have some questions concerning the refinement of the gppd data and > would appreciate your advice: 1) The patterns show some kind of > texture(up and down on the error curve), but the sample is > powder(although maybe the granules are large) and should be > isotropic. All banks show this characteristic texture behavior. 2) > For different banks, the sign of error for the same (hkl) gradually > reverse, and it's hard to refine. 3) If UISO factors are let free, > the refinement will go bad, even if they are constrained. 4) For one > series of sample, the peaks are really sharp, the error sign is > always like -/+/-, the positive error is very big and sharp. 5) > There are some small peaks, which may be due to martensitic > transformation. But they are really small, i don't know to what > degree i should trust these data. Somebody said maybe that's due to > contamination. If it is martensitic trans., how can i set a proper > model to refine the data? > > > Sincerely, > > Ling Yang > PhD student in Dr. Wang's group > 701 Scarboro Rd > Oak Ridge, TN 37830 > Tel: 865 574 0337 > Fax: 865 241 5177 ------- End of forwarded message --------- Miguel Gregorkiewitz Dip Scienze della Terra, Universit� via Laterino 8, I-53100 Siena, Europe fon +39'0577'233810 fax 233938 email [EMAIL PROTECTED]
