Resolution of the Cationic Distribution in Synthetic Germanite Cu22Fe8Ge4S32 by an Experimental Combinatorial Approach Based on Synchrotron Resonant Powder Diffraction Data: A Case Study and Guidelines for Analogous Compounds
Résumé
The present work investigates the cationic distribution of a complex CuS compound belonging to a promising class of materials with significant prospects for thermoelectric generator and photovoltaic applications. We propose the use of powder resonant X-ray scattering in a combinatorial experimental approach with X-ray powder diffraction and single crystal, as a valid, general, and practical method to unravel the complex cation ordering encountered in the synthetic germanite Cu22Fe8Ge4S32. The generation and testing of all the possible structural models is rapid and rigorous as it is based on two modules written in python language: a module that takes care of model creation and ordering (permutation algorithm associated with some filtering and ordering algorithms) and a python parser for the refinement software (FullProf) input and output. Each possible cationic model is tested through combined Rietveld refinement of resonant X-ray data at selected edges and analyzed considering its global χ2 (Bragg contribution) agreement factor. This approach can easily integrate information coming from other techniques, as in our case EXAFS spectroscopy and single crystal X-ray diffraction. In spite of the complexity of the germanite, we were able to define the main characteristics of the cationic ordering (space group P4¯ 3n): (i) the "interstitial"site 2a is fully occupied by Fe, (ii) Ge is located only on the 6d site (or the symmetry equivalent one 6c), and (iii) the remaining Fe atoms are located preferentially on the 12f site and possibly on the 6d (or 6c) site along with Ge. Moreover, we single out a probable enrichment of Ge at the expense of Fe. The approach developed in this case study can be used as a guideline for the crystal structure resolution of analogous compounds. © 2022 American Chemical Society.
Mots clés
Diffraction data
Experimental approaches
Generator applications
Photovoltaic applications
Powder diffraction
Resonant X-ray scattering
Thermoelectric generators
Single crystals
Copper compounds
Crystal atomic structure
Extended X ray absorption fine structure spectroscopy
Germanium
Germanium compounds
High level languages
Indium compounds
Rietveld refinement
Thermoelectric equipment
X ray powder diffraction
Case-studies
Cationic distribution
Combinatorial approach
Domaines
MatériauxOrigine | Fichiers produits par l'(les) auteur(s) |
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