2001 Fiscal Year Final Research Report Summary
Charge Ordering, Superconductivity and Dimensionality in Perovskite-type Bismuth Oxides
| Project/Area Number |
12640332
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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 |
固体物性Ⅱ(磁性・金属・低温)
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| Research Institution | Tohoku University |
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Principal Investigator |
KOIKE Yoji Tohoku University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (70134038)
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| Project Period (FY) |
2000 – 2001
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| Keywords | Bismuth Oxide / Superconductivity / Charge Ordering Dimensionality / Crystal Structure / Substitution Carrier / 置換 / キャリア |
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| Research Abstract |
Perovskite-type BaBiO_3 has a monoclinic structure with a tilt of the BiO_6octahedra. It is a CDW insulator with an ordered network of Bi^<3+>and Bi^<5+>. The relation between Tc and the structure at low temperatures has been investigated for Ba_<1-x>Rb_xBiO_3. It has been found that the appearance of superconductivity prefers a cubic symmetry and small lattice parameters. The localized electrons in Bi 6s orbit are expected to itinerate due to the gain of transfer energy, which leads to the suppression of CDW and the transition to metal.
Under high pressures, the lattice parameters of BaBiO_3 are expected to become small. If the crystal structure of BaBiO_3 will transform to cubic under high pressures, the appearance of superconductivity with higher Tc is expected. The electrical resistivity under high pressures up to 8 GPa has been measured for semiconductive Ba_<1-x>K_xBiO_3. However, it still remains semiconductive. This is because the tilt angle of BiO_6 octahedra may become large under high pressures.
Electron-doped Ba^<2+>_<0.6>Bi^<3+>_<0.4>BiO_3 has been prepared. However, this sample is an insulator. One of the reasons of non-superconductivity may be the existence of oxygen vacancies. Another may be the existence of the CDW in a short range.
Li-intercalated Nb oxides with the layered structure, which does not show the CDW, have been prepared as referential material. New superconductors with Tc〜5K of Li_xRbSr_2Nb_3O_<10> and Li_xCsSr_2Nb_3O_<10> have been found. The reason why the value of Tc in the present Nb oxides is lower than that in Bi oxides is not clear yet.
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Research Products
(6 results)
