CaFeO2: a new type of layered structure with iron in a distorted square planar coordination.
CaFeO2: a new type of layered structure with iron in a distorted square planar coordination.
复制标题
DOI：
10.1021/ja8072269
复制
发表时间：
2009-01
影响因子：
15
通讯作者：
C. Tassel;J. M. Pruneda;N. Hayashi;Takashi Watanabe;A. Kitada;Y. Tsujimoto;H. Kageyama;K. Yoshimura;M. Takano;M. Nishi;K. Ohoyama;M. Mizumaki;N. Kawamura;J. Íñiguez;E. Canadell
中科院分区：
文献类型：
--
作者：
C. Tassel;J. M. Pruneda;N. Hayashi;Takashi Watanabe;A. Kitada;Y. Tsujimoto;H. Kageyama;K. Yoshimura;M. Takano;M. Nishi;K. Ohoyama;M. Mizumaki;N. Kawamura;J. Íñiguez;E. Canadell
据报道，CaFeO(2) 是一种表现出前所未有的层状结构的材料，其中包含高自旋扭曲方形平面配位的 3d(6) 铁。通过使用氢化钙的低温还原过程获得的新相已通过粉末中子衍射、同步加速器 X 射线衍射、穆斯堡尔光谱、XAS 实验以及第一原理 DFT 计算进行了表征。整个固溶体 (Sr(1-x)Ca(x))FeO(2) 的 Fe-K 边缘附近的 XAS 光谱支持铁在 0 </= x </= 0.8 时处于方形平面配位，但清楚地表明 x = 1 时配位发生变化。新结构包含无限的 FeO(2) 层，其中 FeO(4) 单元前所未有地从方形平面向四面体扭曲并沿 c 轴旋转，与经过充分研究和接受的概念是，钙钛矿氧化物中发生八面体旋转，但八面体形状几乎保持规则。新相表现出与 SrFeO(2) 一样的高自旋构型和 G 型反铁磁有序性。然而，FeO(2) 层的变形仅导致尼尔温度相对于 SrFeO(2) 略有降低。第一原理 DFT 计算为 CaFeO(2) 的结构和物理观察提供了清晰的合理化，并强调了阳离子的性质如何影响 AFeO(2) 族化合物（A = Ca、Sr、Ba）的结构细节。在这些计算的基础上，讨论了CaFeO(2) 中FeO(2) 层变形的驱动力。
CaFeO(2), a material exhibiting an unprecedented layered structure containing 3d(6) iron in a high-spin distorted square-planar coordination, is reported. The new phase, obtained through a low-temperature reduction procedure using calcium hydride, has been characterized through powder neutron diffraction, synchrotron X-ray diffraction, Mossbauer spectroscopy, XAS experiments as well as first-principles DFT calculations. The XAS spectra near the Fe-K edge for the whole solid solution (Sr(1-x)Ca(x))FeO(2) supports that iron is in a square-planar coordination for 0 </= x </= 0.8 but clearly suggests a change of coordination for x = 1. The new structure contains infinite FeO(2) layers in which the FeO(4) units unprecedentedly distort from square-planar toward tetrahedra and rotate along the c-axis, in marked contrast to the well-studied and accepted concept that octahedral rotation in perovskite oxides occurs but the octahedral shape is kept almost regular. The new phase exhibits high-spin configuration and G-type antiferromagnetic ordering as in SrFeO(2). However, the distortion of the FeO(2) layers leads to only a slight decrease of the Neel temperature with respect to SrFeO(2). First-principles DFT calculations provide a clear rationalization of the structural and physical observations for CaFeO(2) and highlight how the nature of the cation influences the structural details of the AFeO(2) family of compounds (A = Ca, Sr, Ba). On the basis of these calculations the driving force for the distortion of the FeO(2) layers in CaFeO(2) is discussed.