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Revised Bismuth Chloroselenite System: Evidence of a Noncentrosymmmetric Structure with a Giant Unit Cell

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journal contribution
posted on 04.06.2014, 00:00 by Almaz Aliev, V. M. Kovrugin, Marie Colmont, Christine Terryn, Marielle Huvé, O. I. Siidra, S. V. Krivovichev, Olivier Mentré
The reactions between PbO, Bi2O3 (or BiOCl), and SeO2 by the chemical vapor transport method using HCl as a transporting agent afforded three novel bismuth/lead chloroselenites, namely, β-BiSeO3Cl (1), Bi6(SeO3)4Cl10 (2), and PbBi10(SeO3)12Cl8 (3). Compound 1 is noncentrosymmetric (space group Cc, SHG active) and has a giant unit cell (V = 19792(2) Å3). In the context of the complex BiSeO3Cl phase diagram reported by Oppermann et al., it was assigned to the undescribed β-form on the basis of its IR spectra and powder X-ray diffraction pattern. The comparison between the α-, β-, and γ-forms suggests their formation via the condensation of volatile Bi­(SeO3)Cl molecules. Analysis of the structures of the α-, β-, and γ-forms indicates that the α → β → γ phase transitions are associated with a dramatic fluctuation of structural complexity together with the transitional character of the β phase. Compounds 1 and 3 are layered compounds with identical ([M8Cl16]8+ and [M14(SeO3)24]6−) layers, where M stands for Bi in 1 and Pb/Bi in 3. There are additional [Bi12Cl32]4+ layered subunits in 1. The crystal structure of 2 consists of the [Bi6(SeO3)4Cl10] building blocks forming an open framework with six-membered-ring channels. These three compounds complete the poorly known bismuth selenium oxochloride panorama.