A perovskite containing quadrivalent iron as a charge-disproportionated ferrimagnet.
A perovskite containing quadrivalent iron as a charge-disproportionated ferrimagnet.
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DOI：
10.1002/anie.200801482
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发表时间：
2008-09
影响因子：
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通讯作者：
I. Yamada;Kazuhide Takata;N. Hayashi;S. Shinohara;M. Azuma;S. Mori;S. Muranaka;Y. Shimakawa
中科院分区：
文献类型：
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作者：
I. Yamada;Kazuhide Takata;N. Hayashi;S. Shinohara;M. Azuma;S. Mori;S. Muranaka;Y. Shimakawa
已知大量含有 FeII 和/或 FeIII 的氧化物，而只有少数，如 (Sr, Ca) FeIVO3[1–3] 和 K2FeVIO4，含有较高氧化态的铁。 [4]在探索通式AA’3B4O12的A位有序钙钛矿的过程中，我们成功获得了CaCuII 3FeIV 4O12（CCFO），这是近三十年来首次发现的FeIV氧化物。人们发现，CCFO 在 210 K 时会发生有趣的相变，转变为电荷歧化亚铁磁态。这种电荷歧化 (CD) 属于 CaFeO3 (CFO) 类型 (2FeIV! FeIII+ FeV)[5]，并伴随着结构转变，使这些异价物质以岩盐方式有序排列。[6, 7] 然而，这两种物质的磁性行为却截然不同：CCFO 具有较大的自发磁性磁化强度，而 CFO 是一种反铁磁体，其 NØel 温度相对较低，为 116 K。[3] CCFO 在高于 9 GPa 的压力和约 1300 K 的温度下在固态反应中形成。然而，我们在表征过程中注意到 FeIII 倾向于在 A’位取代，并且随着施加压力的增加，FeIII 的量会减少。杂质量也以同样的方式减少。这里讨论的样品是在 15 GPa 的最高可用压力下制备的。室温同步加速器 X 射线粉末衍射 (SXRD) 和 Rietveld 精修证实了 2a0 2a0 2a0 立方钙钛矿晶胞中所需的 Ca/Cu 有序性（a0：简单钙钛矿立方体；图 1a 和表 1）。
A large number of oxides containing FeII and/or FeIII are known, whereas only a few, like (Sr, Ca) FeIVO3[1–3] and K2FeVIO4, contain iron in higher oxidation states.[4] During the course of our exploration of A-site-ordered perovskites with the general formula AA’3B4O12, we successfully obtained CaCuII 3FeIV 4O12 (CCFO), which is the first FeIV oxide to be discovered in almost three decades. CCFO has been found to undergo an interesting phase transition to a charge-disproportionated ferrimagnetic state at 210 K. This charge disproportionation (CD) is of the CaFeO3 (CFO) type (2FeIV! FeIII+ FeV)[5] and is accompanied by a structural transition that leaves these aliovalent species ordered in the rock-salt manner.[6, 7] The magnetic behavior of these two species is strikingly different however: CCFO features a large spontaneous magnetization whereas CFO is an antiferromagnet with a relatively low NØel temperature of 116 K.[3] CCFO forms in a solid-state reaction at pressures above 9 GPa and a temperature of around 1300 K. However, we noticed during the characterization process that FeIII tends to substitute at the A’site and that the amount decreases as the applied pressure increases. The amount of impurities also decreased in the same manner. The sample to be discussed here was prepared at the highest available pressure of 15 GPa. Synchrotron X-ray powder diffraction (SXRD) at room temperature followed by a Rietveld refinement confirmed the desired Ca/Cu-ordering in a cubic perovskite cell of 2a0 2a0 2a0 (a0: simple perovskite cube; Figure 1a and Table 1).