Structural Chemistry and Electronic Properties of the n = 3 Ruddlesden-Popper Phases Ca4Mn2FeO9.75 and Sr4Mn2FeO9.80

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• 作者：P. D. Battle ; W. R. Branford ; A. Mihut ; M. J. Rosseinsky ; J. Singleton ; J. Sloan ; L. E. Spring ; and J. F. Vente
• 刊名：Chemistry of Materials
• 出版年：1999
• 出版时间：March 1999
• 年：1999
• 卷：11
• 期：3
• 页码：674 - 683
• 全文大小：300K
• 年卷期：v.11,no.3(March 1999)
• ISSN：1520-5002

文摘

The room-temperature crystal structures of the n = 3 Ruddlesden-Popper phases Ca₄Mn₂FeO_9.75 and Sr₄Mn₂FeO_9.80 have been refined from neutron and X-ray powder diffractiondata. Both adopt space group I4/mmm with (a,c) = (Ca, 3.73683(1), 27.0860(1) Å), (Sr,3.83393(1), 27.8148(1) Å). In both compounds the cation site at the center of the perovskiteblocks is preferentially occupied by Fe (Ca, Mn:Fe = 0.424:0.576(4)), and the anion vacanciesare found around this site. The occupied anion sites show static disorder in Ca₄Mn₂FeO_9.75but not in Sr₄Mn₂FeO_9.80. Both compounds are electrical insulators which order antiferromagnetically at T_N = 75 K (Ca) or 90 K (Sr). Susceptibility and M(H) data suggest that notall the Mn and Fe cations take part in the long-range magnetic ordering, and there is evidenceof a spin glass transition in both compounds at ~11 K. The magnetic structure of Ca₄Mn₂FeO_9.75 at 5 K has been determined by neutron diffraction. No ordered moment was detectedon the Mn/Fe site at the center of the perovskite blocks; 0.74(1) _B per transition metalcation was measured at the sites on the block edges. Possible causes of magnetic frustrationin this crystal structure are considered. Ca₄Mn₂FeO_9.75 has a magnetotresistance of -4% at137 K in a 14 T field.