Neutron diffraction study of phi-Bi(8)Pb(5)O(17): structure refinement and analysis of cationic ordering.
The triclinic crystal structure of the varphi phase in the structure of the Bi(2)O(3)-PbO phase diagram has been recently solved by the synergetic use of electron and X-ray diffraction on a polycrystalline Bi(8)Pb(5)O(17) sample. In the present work the problem is re-examined on the basis of powder neutron diffraction data: the structure has been confirmed and refined by the Rietveld method. The increased accuracy of the O-atom positions allowed the study of the cationic ordering in this structure by means of bond-valence calculations and charge distribution analysis. The results, confirmed by the refinement of the site occupancies, indicate that the structure is ordered to a large extent, with Bi and Pb atoms occupying preferentially different lattice sites. In this frame, the varphi phase being the most ordered one in the considered region of the Bi(2)O(3)-PbO phase diagram, it should represent the thermodynamically stable low-temperature polymorph.
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Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica and CNR-CSSD, Università di Parma, Viale delle Scienze, 43100 Parma, Italy. borchi06@nemo.cce.unipr.it
Calestani
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Gemmi
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Migliori
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Bettinelli
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