Indexing of powder diffraction patterns for low-symmetry lattices by the successive dichotomy method

Abstract

The dichotomy method for indexing powder diffraction patterns for low-symmetry lattices is studied in terms of an optimization of bound relations used in the comparison of observed data with the calculated patterns generated at each level of the analysis. A rigorous mathematical treatment is presented for monoclinic and triclinic cases. A new program, DICVOL91, has been written, working from the cubic end of the symmetry sequence to triclinic lattices. The search of unit cells is exhaustive within input parameter limits, although a few restrictions for the hkl indices of the first two diffraction lines have been introduced in the study of triclinic symmetry. The efficiency of the method has been checked by means of a large number of accurate powder data, with a very high success rate. Calculation times appeared to be quite reasonable for the majority of examples, down to monoclinic symmetry, but were less predictable for triclinic cases. Applications to all symmetries, including cases with a dominant zone, are discussed.

Tuning the magneto-structural properties of non-porous coordination polymers by HCl chemisorption

“…The resulting 12 patterns were summed to give the final pattern for structural analysis. The diffraction pattern was indexed using DICVOL91 44 to a monoclinic cell [F(18) = 71.0, M(18) = 19.8] and space group P2 1 /n was assigned from volume considerations and a statistical consideration of the systematic absences. The data set was background subtracted and truncated to d = 2.795 Å (2θ = 17.00°), for Pawley refinement 45 and the structure was solved ab initio using the simulated annealing (SA) global optimization procedure implemented in the DASH computer program 46,47 .…”

High-pressure structural behavior of large-void CoSn-type intermetallics: Experiments and first-principles calculations

“…18 Unit cell parameters were obtained by indexing and leastsquare refinement with the program DICVOL91. 19 Equations of state were described by the Birch-Murnaghan equation using the software EOSFIT. 20 For multianvil experiments, powdered samples of FeSn, CoSn, and NiIn were pressed into pellets, which were placed in boron nitride ͑BN͒ capsules.…”

Structural exploration on powder diffraction a nice tool for rexamination of phase diagram

“…x High temperature From the analysis of the X-ray powder diffraction data collected on the MPD-PRO at 1000°C, we were able to obtain good solutions from two different autoindexing programs Treor [7] and Dicvol [8] implemented in X'Pert High Score Plus [9]. The solutions determined by both programs are very similar: a= 12.688Å; b= 9.198Å, c= 5.985Å, V= 698.43Å 3 , with a figure of merit M 20 =25.0 [10] and M 20 =85.0 respectively for Treor and Dicvol.…”