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New Materials Designing With Unique Approaches
2018-07-12 08:47:39 | 【 【打印】【关闭】

  SEMINAR
The State Key Lab of
High Performance Ceramics and Superfine Microstructure
Shanghai Institute of Ceramics, Chinese Academy of Sciences

  中 国 科 学 院 上 海 硅 酸 盐 研 究 所 高 性 能 陶 瓷 和 超 微 结 构 国 家 重 点 实 验 室 

  New Materials Designing With Unique Approaches

  Speaker

  Mitsuru Itoh

  (伊藤 满)

  Materials and Structures Laboratory, Tokyo Institute of Technology

  时间:2015年11月16日(星期一)上午 10: 30

  地点: 四号楼十四楼第一会议室

  欢迎广大科研人员和研究生参与讨论!

  联系人:余建定(2507) 李勤(1708)

  报告人简介:

  伊藤满(Itoh Mitsuru)教授, 东京工业大学应用陶瓷研究所前任所长,世界著名钙钛矿结构无机功能材料专家,荣获今年日本科学技术奖。伊藤教授长期以来利用独特的新颖方法研制出300多种锂离子体、铁电体、导体、磁铁和荧光发光体等无机功能新材料,并和世界多国研究机构及研究人员共同合作对新材料的结构和功能机理等进行了深入透彻的研究,开创了氧化物新型功能材料研制的新体系,发表了400多篇相关论文。伊藤教授的学生遍天下,人才辈出,培育出几十位在世界著名大学和研究机关工作的教授和研究员。伊藤教授在任所长期间,受聘于中科院的外籍特聘专家,签订了中科院上海硅酸盐研究所和日本东京工业大学的学术合作交流协议。每年邀请数名上海硅酸盐研究所及国内大学和研究机关的研究人员到日本东京工业大学担任客座教授,为中日科学合作及学术交流做了大量工作和重要贡献。

  报告摘要:

  Freezing of the optical soft modes, i.e., the Slater and Last modes, in the phase transition of displacive-type perovskite oxides ABO3 such as BaTiO3 and PbTiO3 is a straightforward way to imagine the mechanism of ferroelectricity, as well as the collective order?disorder-type transition in a permanent dipole system such as NaNO2. In ABO3 perovskites, A-O bond disproportionality also plays an important role in the manifestation of ferroelectricity.

  Here we report the discovery of a new mechanism for the evolution of ferroelectricity in ABO3 (A,B = Al, Ga, Fe) with a non-perovskite κ-alumina-type structure, which can be a compromise between two close-packed oxygen systems, corundum and spinel. Shearing of the close-packed oxygen layers in this structure triggers polarization switching, leading to a recombination of cations from 6(4) to 4(6) coordination. The compounds with a κ-Al2O3-type structure were known to have a non-centrosymmetric space group of Pna21 and consequently was classified as a pyroelectric, the polarization direction of which cannot be switched by the external electric field, however small polarization was reported for this materials group. Corundum and spinel structures have close-packed oxygen layers in the sequence of ABAB… and ABCABC…, respectively, where A, B, and C are oxygen close-packed layers, while κ-Al2O3 has a sequence of ABACABAC……. . Cations of κ-Al2O3-type structure in the interlayer octahedral and tetrahedral sites between the oxygen close-packed layers of C and A and between B and A change their coordination under an electric field from 6(4) to 4(6), respectively. We report a ferroelectricity of κ-Al2O3-type metastable oxides of κ-Al2O3, e-Ga2O3, and e-Fe2O3 using first principles calculation and confirm the polarization experimentally in the solid solution system of GaxFe2-xO3 . The newly discovered mechanism for the evolution of ferroelectricity opens the door for the development of new ferroelectric oxides composed of abundant elements and moreover, a new concept of material design based on bond recombination caused by the shearing of the close-packed oxygen layers under an electric field, a concept distinct from that of the perovskite system

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