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首页> 外文期刊>Physical review >Structural properties in RFe_2O_4 compounds (R = Tm, Yb, and Lu)
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Structural properties in RFe_2O_4 compounds (R = Tm, Yb, and Lu)

机译：RFe_2O_4化合物的结构性质（R = Tm，Yb和Lu）

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摘要

We report a complete characterization of the crystal structure between 400 and 80 K for REe_2O_4 (R = Rm, Yb, and Lu) compounds using high resolution x-ray synchrotron powder diffraction. The three samples have a hexagonal structure (space group R3m) characterized by a sequence of double layers of mixed valence iron and oxygen atoms forming two-dimensional triangular layers separated by a single R-O layer along the c axis. This structure is stable down to 80 K for TmFe_2O_4 and YbFe_2O_4 though a sudden expansion in the c axis is observed at around 300 K coupled to a variation in the electrical properties. However, LuFe_2O_4 exhibits two structural transitions upon cooling. The splitting of some reflections and the occurrence of superstructure peaks below 320 K reveal a structural phase transition. The unit cell is monoclinic (space group C2/m), and there are four nonequivalent Fe sites with a maximum charge disproportionation of 0.5 e. The hexagonal to monoclinic transition is characterized by a sudden expansion of the c axis on cooling, and it seems to be driven by the condensation of Y_2 modes. At lower temperatures (～ 170 K) additional splitting of several peaks indicate that the unit cell is no longer monoclinic but triclinic (space group P1). This transition is characterized by a contraction of the monoclinic ab plane, while the c axis remains almost unchanged. There are six nonequivalent Fe sites in the triclinic cell, and the charge disproportionation magnitude is little affected.
机译：我们报告了高分辨率X射线同步加速器粉末衍射的REe_2O_4（R = Rm，Yb和Lu）化合物在400至80 K之间的晶体结构的完整表征。这三个样品具有六边形结构（空间群R3m），其特征在于一系列混合的化合价铁和氧原子双层，形成沿c轴由单个R-O层隔开的二维三角层。对于TmFe_2O_4和YbFe_2O_4，该结构在低至80 K时都稳定，尽管在300 K附近观察到c轴突然膨胀，这与电性能的变化有关。然而，LuFe_2O_4在冷却时表现出两个结构转变。一些反射的分裂和低于320 K的超结构峰的出现揭示了结构相变。晶胞是单斜晶（空间群C2 / m），并且有四个非等价的Fe位，最大电荷歧化度为0.5 e。六角形到单斜变的特征是冷却时c轴突然膨胀，似乎是由Y_2模式的凝结驱动的。在较低温度（〜170 K）下，几个峰的额外分裂表明晶胞不再是单斜晶而是三斜晶（空间群P1）。这种转变的特征是单斜ab平面的收缩，而c轴几乎保持不变。在三斜晶系细胞中有六个非等价的Fe位，并且电荷歧化幅度几乎不受影响。

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  • 来源
    《Physical review》 |2014年第9期|094119.1-094119.11|共11页
  • 作者

    J. Blasco; S. Lafuerza; J. Garcia; G. Subias;

  • 作者单位

    Instituto de Ciencia de Materiales de Aragon and Departamento de Fisica de la Materia Condensada, Consejo Superior de Investigaciones Cientificas y Universidad de Zaragoza, 50009 Zaragoza, Spain;

    The European Synchrotron Radiation Facility (ESRF), 71, Avenue des Martyrs, 38042 Grenoble Cedex, France;

    Instituto de Ciencia de Materiales de Aragon and Departamento de Fisica de la Materia Condensada, Consejo Superior de Investigaciones Cientificas y Universidad de Zaragoza, 50009 Zaragoza, Spain;

    Instituto de Ciencia de Materiales de Aragon and Departamento de Fisica de la Materia Condensada, Consejo Superior de Investigaciones Cientificas y Universidad de Zaragoza, 50009 Zaragoza, Spain;

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  • 正文语种 eng
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  • 关键词

    inorganic compounds; general studies of phase transitions; manganites;

    机译：无机化合物相变的一般研究;锰矿;

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