You might try using the ISODISPLACE/ISOTROPY programs from BYU to see what transitions are allowed by symmetry to see the best structures to try. See http://stokes.byu.edu/isodisplace.html
Tom Worlton, Tel. 630-252-8755 Argonne National Laboratory http://www.pns.anl.gov/computing/ -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Tuesday, May 22, 2007 10:31 AM To: [email protected] Subject: peaks splitting Dear all I need your kind help I am investigating a trigonal system. I collected neutron diffraction patterns at T=300K and T=4K. The data at T=300K can be nicely fitted with the spg R-3c. At T=4K again I can described the data with the spg R-3c, but I noticed that now the peaks with a larger c-axis component (see the (006) peak picture in attachment) are splitted in two: it is like as at low temperature there are two phases with different c-axis (10.5838 and 10.566 Amstrong) and same a-axis. I don't think that the sample is chemically phase separated because at room temperature the (006) reflection is clearly a single peak. The splitting appears only at low temperature. Could anyone suggest me any possible explanation of this splitting (lattice distortion, modulation, etc)? Could be possible a triclinic distortion? I don't know how to fit the data at T=4K. Should I change the space group because now I have two peaks while the R-3c gives me only one peak? Then by which criteria should I choose the new space group? thank you very very very much for your advices best regards Stefano Agrestini Physics Department The University of Warwick, UK ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.
