2006 Fiscal Year Final Research Report Summary
Searching for new 4d, 5d transition metal oxides by high-pressure synthesis and investigation of their physical properties
| Project/Area Number |
16340111
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | National Institute for Materials Science |
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Principal Investigator |
MUROMACHI Eiji National Institute for Materials Science, Advanced Nano Materials Laboratory, Director general, ナノ物質ラボ, ラボ長 (30343833)
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| Co-Investigator(Kenkyū-buntansha) |
SAKURAI Hiroya National Institute for Materials Science, Advanced Nano Materials Laboratory, Researcher, ナノ物質ラボ, 研究員 (60421400)
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| Project Period (FY) |
2004 – 2006
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| Keywords | High-pressure synthesis / Transition Metal / Oxide / Physical property / Magnetism / Low-spin configuration / Superconductivity / Material searching |
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| Research Abstract |
The target of this research project is mainly on discovering new 4d, 5d transition metal oxides and on elucidation of their physical properties caused by low-spin states. In addition, it is also aimed to study related materials in order to deepen understanding of the physics of low-spin system.
NaRh_2O_4 and CaRhO_3 were found by high-pressure synthesis. The former was proved to be an n-type metal with strongly correlated electrons. The metallic behavior is gradually changed into insulating one by substitution of Ca for Na. No magnetic transition was observed in the solid-solution system. On the other hand, physical properties of CaRhO_3 are hard to change by substitution of Sr for Ca, which is in sharp contrast to CaRuO_3.
Many compounds, such as Sr_2CoO_4 and high-pressure phase LiMn_2O_4, were discovered by high-pressure synthesis. Sr_2CoO_4 has the highest Curie temperature of 255 K among two-dimensional metals, and was found to have intermediate spin state. LiMn_2O_4, which is isostructural with NaRh_2O_4, has spin-glass transition around 10 K. In addition, superconducting eta-Mo_3C_2, gamma-Mo_2N and NbN were made under high pressures, to determine some superconducting parameters.
Superconducting mechanism of low-spin system Nax(H_3O)zCoO_2 yH_2O was investigated. Co valence and Na content were independently controlled to establish the superconducting phase diagram, by which active bands were suggested. Furthermore, magnetically ordered phase was found next to the superconducting phase. Nuclear quadrupole resonance measurements strongly suggest that the superconductivity is induced magnetic fluctuations caused by quantum criticality related to the magnetic phase.
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