1998 Fiscal Year Final Research Report Summary
High-Pressure Stabilization of New Transition Metal Oxides with the Perovskite Structure and Their Physical Properties
| Project/Area Number |
09640680
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
機能・物性・材料
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
SYONO Yasuhiko IMR.TOHOKU UNIVERSITY,Prof., 金属材料研究所, 教授 (80013481)
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| Co-Investigator(Kenkyū-buntansha) |
ATOU Toshiyuki IMR.TOHOKU UNIVERSITY,Res.Assoc., 金属材料研究所, 助手 (40241567)
KUSABA Keiji IMR.TOHOKU UNIVERSITY,Res.Assoc., 金属材料研究所, 助手 (60186385)
KIKUCHI Masae IMR.TOHOKU UNIVERSITY,Assoc.Prof., 金属材料研究所, 助教授 (00005951)
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| Project Period (FY) |
1997 – 1998
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| Keywords | High-pressure synthesis / BiMnO_3 / Ferromagnetism / Crystal structure analysis / Neutron diffraction / Tl-based cuprates / Superconductivity / 超伝導 |
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| Research Abstract |
High pressure synthesis has been utilized to stabilize new transition metal oxides with the perovskite structure, thereby achieving interesting physical properties like ferromagnetism and superconductivity. A ferro-magnet BiMnO_3 with T_cof 105K was synthesized at 4 GPa and 600ﾟC.Sr substitution for Bi reduces electrical resistivity considerably, but no metallic states were realized, unlike metallic, ferromagnet (La, Sr)MnO_3. Magnetic moment rather decreased with increasing Sr concentration and ferromagnetism completely disappeared around 40% Sr concentration.
Crystal structure of monoclinically distorted perovskite was determined by neutron diffraction. Structure refinement using Rietveld analysis of powder pattern revealed that the Bi atom deviated remarkably from regular 12-coordinated sites owing to polarized 6s2 lone pair of Bi^<3+> ions. Every Mn^<3+> ions showed Jahn-Teller distortion. Superexchange interaction between adjacent Mn^<3+> ions were expected to be parallel for 2/3 and anti-parallel for 1/3, hence ferromagnetic interactions were considered to be dominated. Unlike LaMnO_3, rather homogeneous distribution of vacant dx_<2-y2> orbitals would explain the ferromagnetism of BiMnO_3.
High pressure synthesis of TI-based cuprates was carried out for 1 .5-2.5GPa and around 1000ﾟC.New high Tc oxides of TlSr_2Ca_2Cu_3O_y and TlSr_2Ca_3Cu4O_<yp> wiht T_c of 97K and 90K were obtained. High pressure condition was considered to be favorable for preventing TI evaporation in long time annealing which was necessary for establishing ordered arrangement of Ca and Sr.
Shock synthesis of high Tc cuprates was also tried. Tetragonal EuBa_2Cu_2O_<6.5> with cla= 3.0 was successfully synthesized by shock loading of the component mixture, but no superconductivity was realized by oxygen treatment. Superconductivity appeared only after annealing the as-shock-synthesized product above 900ﾟC, which established perfect order among Eu and Ba.
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