A practical approach to Rietveld analysis. Comparison of some programs running on personal computers

Three computer programs for Rietveld analysis DBWS-9411, HILL-93.06, and FU LLPROF-3.1 have been tested and compared using data for two samples of diff erent complexity, spinel, and anglesite. The investigation shows that resul ts are ''program dependent.'' The obtained R indices for spinel are in the ranges 10.60%-13.26%(R-wp) and 3.15%-5.25%(R-B). Similarly, the ranges for anglesite are 9.76%-14.06%(R-wp) and 2.15%-5.06%(R-B). Some atom and displa cement parameters are significantly different, too. In attempt to define th e standard procedure for Rietveld analysis, three parameters, n, BKPOS, and RLIM were examined. It was found that the most appropriate values for them are: n = 8-10, BKPOS = 90 degrees, and RLIM = 40 degrees 2 theta. Using Fo urier filtering for background modeling, significantly lower R indices were obtained in comparison to polynomial and interpolated background. At the s ame time the great numbers of atom and cell parameters agree within +/-3 si gma(max) and e.s.d.'s were identical or lower than those achieved for polyn omial and interpolated background. It was found that the function given by Berar and Baldinozzi (1993) (J. Appl. Crystallogr. 26, 128-129) much better described asymmetric peak profiles at low 2 theta angles. This function an d Fourier filtering were implemented only in FULLPROF, which has more possi bilities and some advantages over the other two programs. In addition, the peak shift parameters (sample displacement and transparency) were tested. I t was shown that under present circumstances these parameters do not have m uch effect on atom parameters and R indices. However, differences in unit c ell parameters were considerable greater, most probably because of the larg e correlation between zero-point, lattice, and peak shift parameters. (C) 1 999 International Centre for Diffraction Data. [S0885-7156(99)00101-3].