Structure Determination of Tl4V2O7 from Powder Diffraction Data using an Inel X-Ray PSD: Stereochemical Activity of Thallium(I) Lone Pair

Abstract

AbstractThe crystal structure of Tl4V2O7 is solved ab-initio from powder diffraction data collected in Debye-Scherrer geometry using an Inel X-ray Position Sensitive Detector. The structure has been determined from Rietveld analysis in space group ml, Z = 1, with a = 5.9388(2)Å and c = 7.7322(3)Å. The structure of Tl4V2O7 is built up from isolated V2O7 groups aligned along the trigonal c axis. Thallium atoms alternate along a 3-fold axis. The presence of stereochemically active lone pairs is demonstrated and their positions are calculated using a self-consistent electrostatic model. The influence of sample absorption is briefly discussed and the results are compared with those obtained in Bragg-Brentano geometry using flat-plate specimen.