NOVEL FUNCTIONAL DOUBLE-PEROVSKITE OXIDES

新型功能性双钙钛矿氧化物

基本信息

批准号：
11305002
负责人：
YAMAUCHI Hisao
金额：
$ 23.53万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2002
项目状态：
已结题

项目摘要

In our present research, the properties of double-perovskite transition-metal oxides (expressed as A'A"B'B"O_<6-ω>) were intensively and extensively investigated to search for "novel functions". We focused on three different kinds of iron- and cobalt-oxide double-perovskites to elucidate the relationships between the valence state of iron/cobalt and various physical properties. Major results of our research during the period of April 1999-March 2003 are summarized in the following :1. A-site ordered (oxygen-deficient) double-perovskite iron oxides : BaREFe_2O_<5+δ>(1) For synthesizing BaSmFe_2O_<5+δ> samples, a novel technique named "sample encapsulation with an oxygen getter" method was developed. Utilizing this method, samples with various Res and oxygen contents were successfully prepared.(2) A "Verwey-type transition" (a phase transition in the iron valence state) was discovered for BaSmFe_2O_<5+δ> (δ< 0.5). By Mossbauer spectroscopy, it was found that iron is in a mixed-valence st … More ate, Fel^<II/III> above T_v( = the Verwey-type transition temperature) and gets split into Fe^<II> plus Fe^<III> below T_v.(3) A wide-range control on T_v was attained for BaREFe_2O_<5+δ> through different kinds of substitution (i.e. chemical pressure) techniques, i,e. Sr-for-Ba and RE'-for-RE isovalent substitutions, and Ca-for-Sm aliovalent substitution. From the results of synchrotron x-ray diffraction analysis for the samples, it was clarified that the T_v value is influenced mainly by the Fe-Fe distance across the RE plane in the crystals.(4) For RE = Dy, Y samples, superspots due to a charge ordering (below T_v) were for the first time observed by synchrotron x-ray diffraction and electron diffraction.2. B-site ordered double-perovskites : Sr_2FeMoO_6 (SFMO)(1) The "sample encapsulation with an oxygen getter" method was successfully tuned to synthesize high-quality SFMO samples.(2) From the results of Mossbauer spectroscopy, iron in SFMO was found to be in a mixed-valence state, i.e. Fe^<II/III>. It was revealed that the Fe^<II/III> state is strongly correlated with the "halfmetallicity" of the compound.(3) The relationship between the synthesis temperature and the degree of order at the B-cation (Fe/Mo) site was established for SFMO. The influence of the degree of order on the various physical properties was clarified.(4) The control on the magnetic properties and the MR characteristics of SFMO was successfully made through the Ba/Ca-for-Sr and Ta/W-for-Mo substitutions. Large MR effect of up to 200 % was attained for a Ta-substituted sample (at 5 K and 7 T).3. A-site ordered (oxygen-deficient) double-perovskite cobalt oxides : BaRECo_2O_<5+δ>Samples with RE=Nd, Eu, Ho and Y were synthesized under normal condition and the oxygen content, 5 +δ, of the sample was controlled by the TCOD method. The effects of oxygen nonstoichiometry on the crystal structure, magnetism, and MR characteristics were systematically studied to enhance the MR effect. For a sample with RE = Nd and δ= 0.46, tunneling-type MR (TMR) effect was detected above 200 K, suggesting the appearance of half metallic state in this cobalt oxide.In summary, the key contributions we have achieved through the present research work on double-perovskite oxides are : (i) novel phenomena including a Verwey-type transition were discovered, (ii) the relationships between the valence state of the transition metal and various physical properties (such as Verwey-type transition, charge ordering, half metallicity, etc.) have been clarified, and (iii) useful bases for controlling the material functions have been established. Less

在我们目前的研究中，对双钙钛矿过渡金属氧化物（表示为 A'A"B'B"O_<6-ω>）的性质进行了深入而广泛的研究，以寻找“新功能”，我们重点关注三个方面。不同种类的氧化铁和氧化钴双钙钛矿，以阐明铁/钴的价态与各种物理性质之间的关系。我们四月份研究的主要结果。 1999-2003年3月总结如下： 1. A位有序（缺氧）双钙钛矿铁氧化物：BaREFe_2O_<5+δ>（1）用于合成BaSmFe_2O_<5+δ>样品，一种名为BaSmFe_2O_<5+δ>的新技术。开发了“吸氧剂封装样品”方法，成功制备了不同Res和氧含量的样品。(2)通过穆斯堡尔谱发现BaSmFe_2O_<5+δ>（δ<0.5）存在“Verwey型转变”（铁价态的相变）。 ate，Fel^<II/III> 高于 T_v（= Verwey 型转变温度）并分裂为 Fe^<II> 加上 Fe^<III> 低于 T_v。(3) A通过不同类型的取代（即化学压力）技术，即 Sr-for-Ba 和 RE'-for-RE 等价取代以及 Ca-for-BaREFe_2O_<5+δ> 实现了对 T_v 的大范围控制。 -Sm异价取代从样品的同步加速器X射线衍射分析结果可知，T_v值主要受RE平面上的Fe-Fe距离的影响。 (4)对于RE=Dy、Y样品，首次通过同步加速器X射线衍射和电子衍射观察到由于电荷排序(低于T_v)而产生的超级斑点。2． Sr_2FeMoO_6 (SFMO)(1)“吸氧剂封装样品”方法成功合成了高质量的SFMO样品。(2)从结果来看穆斯堡尔谱分析发现，SFMO 中的铁处于强混合价态，即 Fe^<II/III> 态，表明 Fe^<II/III> 态与化合物的“半金属性”相关。 (3)建立了SFMO的合成温度与B-阳离子(Fe/Mo)位点有序度之间的关系,阐明了有序度对各种物理性能的影响。(4)控制通过 Ba/Ca 替代 Sr 和 Ta/W 替代 Mo 成功地获得了 SFMO 的磁性能和 MR 特性，Ta 替代样品获得了高达 200% 的大 MR 效应（在 5 时）。 K 和 7 T).3. A 位有序（缺氧）双钙钛矿钴氧化物：BaRECo_2O_<5+δ>RE=Nd 的样品，在正常条件下合成Eu、Ho和Y，并通过TCOD方法控制样品的氧含量5 +δ，系统研究了氧非化学计量对晶体结构、磁性和磁流变特性的影响，以增强样品的氧含量。对于 RE = Nd 且 δ= 0.46 的样品，在 200 K 以上检测到隧道型 MR (TMR) 效应，表明该钴中出现半金属态。总之，我们通过目前对双钙钛矿氧化物的研究工作取得的关键贡献是：（i）发现了包括Verwey型过渡在内的新现象，（ii）过渡金属价态之间的关系各种物理性质（如Verwey型转变、电荷有序性、半金属丰度等）已得到阐明，并且（iii）已建立了控制材料功能的有用基础。

项目成果

期刊论文数量（237）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

T.Motohashi, R.Ueda, E.Naujalis, T.Tojo, I.Terasaki, T.Atake, M.Karppinen, H.Yamauchi: "Unconventional Magnetic Transition and Transport Behavior in Na_<0.75>CoO_2"Physical Review B. 67. 064406-1-064406-5 (2003)

T.Motohashi、R.Ueda、E.Naujalis、T.Tojo、I.Terasaki、T.Atake、M.Karppinen、H.Yamauchi：“Na_<0.75>CoO_2 中的非常规磁转变和输运行为”物理评论 B.

DOI：
发表时间：
期刊：
影响因子：
0
作者：
通讯作者：

C.A.Cardoso, F.M.Araujo-Moreira, V.P.S.Awana, E.Takayama-Muromachi, O.F.de Lima, H.Yamauchi, M.Karppinen: "Spin glass behavior in RuSr_2Gd_<1.5>Ce_<0.5>Cu_2O_<10-δ>"Physical Review B. 67. R20407-R20410 (2003)

C.A.Cardoso、F.M.Araujo-Moreira、V.P.S.Awana、E.Takayama-Muromachi、O.F.de Lima、H.Yamauchi、M.Karppinen：“RuSr_2Gd_<1.5>Ce_<0.5>Cu_2O_<10-δ>中的自旋玻璃行为”物理审查 B.67.R20407-R20410 (2003)