Incommensurate versus commensurate description of the A{sub x}BX{sub 3} hexagonal perovskite-type structure. Sr{sub 1.2872}NiO{sub 3} incommensurate composite compound example
- Univ. de Nantes (France). Lab. de Chimie des Solides
- Academy of Sciences of the Czech Republic, Praha (Czech Republic)
The authors report a new structure determination of the Sr{sub 1.2872}NiO{sub 3} incommensurate composite hexagonal perovskite compound. Three different refinement strategies are presented: (1) a 3D supercell approximation with a nonharmonic development of the atomic displacement factor, (2) an original (3+1)D incommensurate composite description with the use of crenel functions, and (3) a (3+1)D commensurate composite model. The three strategies are discussed and compared to previous refinements carried out for the hexagonal perovskites in a classical way or with the superspace group formalism. Out of the three methods, the incommensurate composite approach gives slightly better results with a final global R value of 2.89% for 635 independent reflections and only 60 parameters (R{bar 3}m(00{gamma})Os) superspace group. The use of crenel functions notably improves previously reported results. New structural features are evidenced for Sr{sub 1.2872}NiO{sub 3}: (1) an incommensurate character, (2) a splitting of the trigonal prismatic nickel atoms over 5 positions, (3) a definite stoichiometry which induces a perfect charge balance, and (4) a nonharmonic behavior of some Sr atoms. Those characteristics seem general to most hexagonal perovskite compounds and essential for correctly interpreting their interesting magnetic properties. Finally, a new generic formulation is proposed, which explains the various stoichiometries observed and suggests a new compound possibility.
- OSTI ID:
- 675627
- Journal Information:
- Chemistry of Materials, Vol. 10, Issue 10; Other Information: PBD: Oct 1998
- Country of Publication:
- United States
- Language:
- English
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