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Successive Transition of Polaron Phases in Triangular Charge Competing System YFe_2O_4

三角电荷竞争体系YFe_2O_4中极化子相的连续跃迁

基本信息

批准号：
15540324
负责人：
IKEDA Naoshi
金额：
$ 2.3万
依托单位：
Japan Synchrotron Radiation Research Institute
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

In a series of oxides RFe_2O_4 (R=rare earth between Dy and Lu, or Y), equal numbers of Fe^<2+> and Fe^<3+> are located on a layer composed of two triangular nets stacked together. These oxides have several phase transitions where the arrangement of Fe^<2+> and Fe^<3+> ions transforms from one type to another. Unique dielectric properties of these oxides have been explained in connection with the charge ordering.We made a research of low oxygen deficient YFe_2O_4 in which the charge frustration effect is considered to be dominant. We gave a discussion that the possible origin of the successive transition of the superstructure arose from the competition between the nearest neighbor and next nearest neighbor interaction of charges in triangular plane. We had synthesized the low oxygen deficient YFe_2O_4 with a furnace which equipped an electric circuit system which control an oxygen partial pressure. A synchrotron radiation X-ray diffraction, transmission electron microscope experiment r … More evealed that, stoichiometric YFe_2O_4, the superstructure of the Fe^<2+> and Fe^<3+> order transformed into a triple, double, quadruple and septenary charge structure in the temperature range from room temperature to 130 K. A slow relaxation of the superstructure was found at 130 K. Time dependence of the magnetic moment was observed at about 240 K to suggest a similar relaxation.By a transmission electron microscopy observation for YFe_2O_4, a characteristic diffuse scattering elongated along the [001] direction through the (1/3 1/3 0)-type reciprocal positions was found at RT, which is related to the micro domains due to the CO with a size of 10-20nm. In addition, it was also found that the superlattice structures characterized by (1/3-・1/3-・0)-type modulation vector, which should be due to the vacancy ordering, coexist with the microdomains due to the CO. On the other hand, in stoichimetric YFe_2O_4, we found temperature variations of the superlattice structures on warming from 100 K, which should be strongly related to the dielectric anomalies in YFe_2O_4.A resonant X-ray diffraction revealed that the charge superstructure is originated from the long range ordering of Fe^<2+> and Fe^<3+> in triangular plane.In addition to the above researches we made a structure analysis of topological crystal. And we made some researches in which a coupling between charge and spin of transition metal d-electron plays a central role to drives a lattice distortion or phase transition. Less

在一系列氧化物RFe_2O_4（R= Dy和Lu之间的稀土，或Y）中，等量的Fe^<2+>和Fe^<3+>位于由两个三角形网堆叠在一起组成的层上。这些氧化物有几个相变，其中Fe^<2+>和Fe^<3+>离子的排列从一种类型转变为另一种类型。本文还对以电荷阻挫效应为主的低氧YFe_2O_4进行了研究。讨论了超结构连续跃迁的可能起因是三角形平面内最近邻电荷与次最近邻电荷相互作用的竞争。我们用装有控制氧分压的电路系统的炉子合成了低氧缺YFe_2O_4。同步辐射X射线衍射、透射电镜实验 ...更多信息结果表明，在室温至130 K的温度范围内，YFe_2O_4由Fe^<2+>和Fe^<3+>有序超结构转变为三重、双重、四重和七重电荷结构。在130 K时，超结构出现缓慢弛豫.在240 K左右观察到磁矩随时间的变化，表明YFe_2O_4也有类似的弛豫现象.透射电镜观察到YFe_2O_4在室温下有一个沿[001]方向沿着延伸的漫散射特征，它与CO的微畴（10- 20 nm）有关.此外，还发现，（1/3-·1/3-·0）型调制矢量与CO引起的微畴共存，这可能是由于空位有序化引起的。另一方面，在化学计量比的YFe_2O_4中，我们发现超晶格结构在100 K升温时的温度变化，共振X射线衍射分析表明，这种电荷超结构是由Fe^<2+>和Fe^<3+>的长程有序引起的除了上述研究外，我们还对拓扑晶体进行了结构分析。我们还研究了过渡金属d电子的电荷和自旋之间的耦合对晶格畸变或相变的驱动作用。少