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Ferroelectrics of charge ordering type and its non-linear response in triangular mixed valence iron oxide

三角形混合价氧化铁中电荷有序型铁电体及其非线性响应

基本信息

批准号：
18340094
负责人：
IKEDA Naoshi
金额：
$ 10.05万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18340094/
关键词：
RFe2O4 Electronic Ferroelectricity Triangular lattice Chrage Ordering Charge Frustration 電子誘電性 RFe2O4

项目摘要

We made a research for triangular mixed valence material RFe2O4 which exhibits a polar charge ordering from the frustrated charge interaction. In this two years we had built up an air tight furnace having sample weight measurement system. From the detailed information of the sample weight change during the various heat treatment, we developed couple of method in obtaining fine sample of RFe2O4. During the course of the research we found the various electronic phases and properties for YbFe2O4, RFeCoO4, RFeCuO4 and RGaCuO4 (R.= Yb, Lu)Recently the ferroelectricity arise from the polar ordering of electrons have got much attention, however the usability for the actual application on the ferroelectric material have still been an open question. For example high electronic conductivity that possibly exist in the correlated electron system may prevent the usual application for the ferroelectrics like as insulator, charge condenser and so on. This report is one of the possibility search for s … More uch quests. For example in some sample treatment condition can possibly realize a high resistivity states of electronic ferroelectrics. It is also interesting that the sample having less oxygen vacancy shows high activation energy than non-stoichiometric material. It has been explained that the origin of the dielectric dispersion for Rfe_2O_4 is the boundary motion for polar domains. The higher Q value for higher stoichiometric sample indicates that the less oxygen vacant sample has larger charge ordering coherence length. Which realizes lamer scale of the collective electron motion.We emphasize that such ferroelectricity, defined by the electron distribution, is crucially different from previously known ferroelectrics. The difference in the origin of ferroelectricity may enable the development of a new class of device application in the near future. For example an anomaly report exists in electron microscope observation, which revealed an extremely small ferroelectric domain having a coherent size of 10 nm scale. This is a consistent estimate from the X-ray diffraction experiments. The superlattice profile is wider than the fundamental Bragg spot. Using the Schemer's formula the coherence length was estimated as about 10 nm from the full width of the half maximum of the peak profile in the a-b plane. In this ferroelectric the Coulomb interactions between Fe^<3+> and Fe^<2+> dominate the total energy for the presence of the domain sizes, that is decoupled from the lattice distortion. This indicates a typical property of the ferroelectricity by ordered electrons, free of lattice distortion. Future study may reveal such an extremely small ferroelectric element in high density electric devices in such extremely small domains.The applicability of electronic ferroelectric material for conventional ferroelectrics is still an open question. We should continue to find out better method to realize high stoichiometric RFe_2O_4, or also we should find out more characteristic application that may suit for such material having electric polarization and good conductivity. Less

我们对三角形混合价材料RFe2O4进行了研究，该材料由于受阻电荷相互作用而呈现出极性电荷有序。在这两年里，我们建立了气密炉，具有样品重量测量系统。根据样品在不同热处理过程中重量变化的详细信息，我们提出了几种获得RFe2O4细小样品的方法。在研究过程中，我们发现了YbFe2O4，RFeCoO4，RFeCuO4和RGaCuO4(R=Yb，Lu)的各种电子相和性质。近年来，由于电子的极性有序而产生的铁电性引起了人们的关注，但在铁电材料上的实际应用仍然是一个悬而未决的问题。例如，相关电子系统中可能存在的高电子导电性可能会阻碍铁电材料作为绝缘体、电荷电容器等的正常应用。这篇报道是对S…的可能性搜索之一更多这样的任务。例如，在某些样品处理条件下，可以实现铁电材料的高电阻态。同样有趣的是，氧空位较少的样品表现出比非化学计量比材料更高的活化能。解释了RFE_2O_4介电色散的起因是极磁区的边界运动。高化学计量比样品的Q值越高，表明氧空位越少的样品具有更大的电荷有序相干长度。这实现了集体电子运动的更小尺度。我们强调，这种由电子分布定义的铁电性与先前已知的铁电性有很大的不同。铁电性起源的不同可能在不久的将来开发出一类新的器件应用。例如，在电子显微镜观察中存在异常报告，它揭示了一个极小的铁电畴，其相干尺寸为10 nm尺度。这是从X射线衍射实验中得出的一致估计。超晶格的轮廓比基本的布拉格光斑宽。利用图解公式，从a-b面上峰值轮廓的半最大值的全宽度估算出相干长度约为10 nm。在这种铁电体中，Fe^-lt；3+-gt；和Fe^-lt；2+-gt；之间的库仑相互作用主导着存在磁畴尺寸的总能量，这与晶格扭曲是解耦的。这表明有序电子的铁电性是典型的，没有晶格扭曲。未来的研究可能会在如此小的领域内揭示出高密度电子器件中的极小铁电元件。电子铁电材料对传统铁电材料的适用性仍然是一个悬而未决的问题。我们应该继续寻找更好的方法来实现高化学计量比的RFE_2O_4，或者也应该找到更多适合于具有电极化和良好导电性的材料的特性应用。较少