3D Transition Metal Ordering and Rietveld Stacking Fault Quantification in the New Oxychalcogenides La2O2Cu2–4xCd2xSe2

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• 作者：Chris M. Ainsworth ; James W. Lewis ; Chun-Hai Wang ; Alan A. Coelho ; Hannah E. Johnston ; Helen E. A. Brand ; John S. O. Evans
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：May 10, 2016
• 年：2016
• 卷：28
• 期：9
• 页码：3184-3195
• 全文大小：765K
• 年卷期：0
• ISSN：1520-5002

文摘

A number of LnOCuCh (Ln = La–Nd, Bi; Ch = S, Se, Te) compounds have been reported in the literature built from alternating layers of fluorite-like [Ln₂O₂]p>2+p> sheets and antifluorite-like [M₂Se₂]p>2–p> sheets, where M is in the +1 oxidation state leading to full occupancy of available MSe_4/2 tetrahedral sites. There is also a family of related LnOM_0.5Se (Ln = La & Ce, M = Fe, Zn, Mn & Cd) compounds built from alternating layers of [Ln₂O₂]p>2+p> sheets and [MSe₂]p>2–p> sheets, where M is in the +2 oxidation state with half occupancy of available tetrahedral sites and complex ordering schemes in two dimensions. This paper reports a new family of compounds containing both +1 and +2 metal ions in the La₂O₂Cu_2–4xCd_2xSe₂ family. We show how Cup>1+p> and Cdp>2+p> ions segregate into distinct fully occupied and half occupied checkerboard-like layers respectively, leading to complex long-range superstructures in the third (stacking) dimension. To understand the structure and microstructure of these new materials we have developed and implemented a new methodology for studying low and high probability stacking faults using a Rietveld-compatible supercell approach capable of analyzing systems with thousands of layers. We believe this method will be widely applicable.