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日本京都大学的Shimakawa教授应邀来我组进行学术交流

  日本京都大学的Shimakawa教授于2010年10月21日应邀访问我组并做了题为“Charge disproportionation and charge transfer in A-site ordered perovskites”的中关村论坛学术报告。

 

个人简介 :

Prof. Yuichi Shimakawa
Laboratory in the Department of Chemistry, Kyoto University

  He obtained his Ph.D. from Kyoto University in 1991, from 1987 to 2003 he served as the principal researcher in Fundamental Research Laboratories of NEC Corporation, then became a professor of Kyoto University from 2003. His research interest is solid state chemistry and physics on functional oxide materials, and high-pressure synthesis and epitaxial thin film growth.

 

报告内容摘要:

  A very unusual ordered arrangement of the A-site ions produces AA'3B4O12 complex perovskites. The A site accommodates alkaline metals, alkaline-earth metals, and lanthanides like those in simple perovskites. At the originally 12-fold coordinated A' site, transition-metal ions such as Cu2+ and Mn3+ form square coordinated units that align perpendicular to each other. The presence of the transition-metal ions at the A' site produces A'-A' and and/or A'-B interactions in addition to B-B interaction usually seen in simple perovskite materials. Competitive and/or cooperative interplay of these interactions gives rise to diverse and intriguing physical properties. Two new A-site ordered perovskite structure oxides, CaCu3Fe4O12 and LaCu3Fe4O12, are highlighted.They were synthesized under high-pressure and high-temperature conditions. The compounds contain unusually high valence states of iron: Fe4+ in CaCu3Fe4O12 and Fe3.75+ in LaCu3Fe4O12. Instabilities of the high oxidation states at low temperatures are resolved in CaCu3Fe4O12 by charge disproportionation from Fe4+ to Fe3+ and Fe5+ and in LaCu3Fe4O12 by charge transfer between A-site Cu and B-site Fe ions. The charge disproportionation and the charge transfer are accompanied by significant changes in structural, transport, and magnetic properties.