Coupled Cation and Charge Ordering in the CaMn3O6 Tunnel Structure

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• 作者：Joke Hadermann ; Artem M. Abakumov ; Lisa J. Gillie ; Christine Martin ; Maryvonne Hervieu
• 刊名：Chemistry of Materials
• 出版年：2006
• 出版时间：November 14, 2006
• 年：2006
• 卷：18
• 期：23
• 页码：5530 - 5536
• 全文大小：467K
• 年卷期：v.18,no.23(November 14, 2006)
• ISSN：1520-5002

文摘

The synthesis and crystal structure of a mixed valent manganite CaMn₃O₆, equivalent to Ca_2/3Mn₂O₄,are reported, along with the magnetic properties. The structure was determined using electron diffractionand high-resolution transmission electron microscopy and refined from X-ray and neutron powderdiffraction data (a = 10.6940(3) Å, b = 11.3258(3) Å, c = 8.4881(2) Å, mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle"> = 122.358(2)mages/entities/deg.gif">, space groupP2₁/a, R_I = 0.037, R_P = 0.118). The structure is based on a framework of double chains of edge-sharingMnO₆ octahedra. The corner-sharing chains form a framework with six-sided tunnels, identical to that ofthe CaFe₂O₄ structure. The Ca²⁺ cations are located in the tunnels. Compared to CaFe₂O₄, one-third ofthe Ca positions in the tunnels remain vacant, with an ordered distribution of vacant and occupied sites.The empty sites in neighboring Ca chains are shifted relative to each other along the c-axis by oneperiod of the CaFe₂O₄ subcell, which results in a symmetry decrease from orthorhombic to monoclinic.Based on the interatomic Mn-O distances, the charge ordering in CaMn₃O₆ is discussed. The compoundexhibits a strong anti-ferromagnetic character, and differences between the zfc and fc magnetizationcurves at low temperature suggest ferro- or ferrimagnetic interactions.