Re: Space group of Si standard in XRD

[Julius Schneider]

Hi Stephen, make sure that you use the second (centrosymmetric) setting in space group F d -3 m (no.227), i.e. Si at Wyckoff position 8a and coordinates:   1/8  1/8  1/8   in the Rietveld refinement. If you use the first setting and the 8a coordinates: 0 0 0 as coordinates the program will run alright but it will calculate wrong intensities !!  Our students often fall into this trap ! The exact lattice parameter depends on whether you have SRM 640, SRM 640b or SRM640c as silicon Standard Reference Material. Cheers, Julius [EMAIL PROTECTED] wrote: if I remember well, Fd-3m and 5.43Å. BTW, don't trust the flat plate sample distributed with your Philips goniometer, it is terribly grainy (you can see it with the naked eye) and you will never get a reasonable Rietveld fit with it! miguel On 2 Feb 2005 at 15:40, [EMAIL PROTECTED] wrote: Dear colleagues can anyone remind me the space group and lattice constants of the Si standard (flat plate) used in the Philips APD B-B diffractometer? Since I will like to do some comparison studies using GSAS. Many thanks, regards stephen