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，对双层晶矿过渡金属氧化物（以A'A“ B'B” O_ <6-Ω>表示）的性质进行了深入和广泛的研究以搜索“新功能”。我们专注于三种不同种类的铁 - 氧化双晶矿，以阐明铁/钴的价状态与各种物理特性之间的关系。在1999年4月3月的2003年3月，我们的研究的主要结果总结了：1。 A位置有序（缺氧）双层晶酮铁氧化物：Barefe_2O_ <5+δ>（1）用于合成BASMFE_2O_2O_ <5+δ>样品，这是一种新的技术，称为“带有氧气Getter的样品封装”方法。利用这种方法，成功制定了具有各种RES和氧含量的样品。（2）“ Verwey型过渡”（铁价状态下的相位跃迁）（basmfe_2O_2O_ <5+δ>（Δ<0.5））。通过Mossbauer光谱法，发现铁处于混合价值……更多的食物，fel^<ii/iii>上方t_v（= verwey-type过渡温度），被分为fe^<ii> plus fe^<ii> plus fe^<iii>以下t_v。压力）技术，i，e。 sr-for-for-for-for-for-for-for-for-for-for-for-for isOralent取代以及ca-for-sm Aliovalent取代。从样品的同步器X射线衍射分析的结果中，可以澄清的是，T_V值主要受晶体中RE平面的Fe-FE距离的影响。（4）对于RE = DY，Y样品，SupersPots，SuperSpots，由于T_V（低于T_V）的superspots（在T_V下）被Synchrotron X-Ray X-Ray difacraction and Electron and Electron所引起的电荷顺序（低于T_V）。 b站点有序的双重植物：sr_2femoo_6（sfmo）（1）“带有氧气getter getter”方法的“样品封装”已成功调节以合成高质量的SFMO样品。据表明，fe^<ii/iii>状态与化合物的“半金属性”密切相关。（3）建立了B-cation（FE/MO）位点的合成温度与SFMO的秩序程度之间的关系。（4）通过BA/CA/CA-FOR-SR和TA/W-For-MO替换成功地对SFMO的磁性和MR特性进行了控制。对于TA取代的样品（在5 K和7 t）的较大MR效应（最高为200％）。3。 A位点有序（缺氧）双植岩钴氧化物：Bareco_2O_ <5 +δ>带有RE = ND，EU，HO和Y的样品在正常状态下合成，并通过TCOD方法控制样品的氧气含量，5 +δ，样品的5 +δ。氧非化化计量对晶体结构，磁性和MR特征的影响进行了系统的研究以增强MR效应。 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已经阐明了过渡金属和各种物理特性（例如Verwey型过渡，电荷顺序，一半金属性等），并且已经建立了控制材料功能的有用基础。较少的