| Co-Investigator(Kenkyū-buntansha) |
KOIKE Yoji Tohoku University, Graduate School of Engineering, Professor, 大学院・工学研究科, 教授 (70134038)
ADACHI Tadashi Tohoku University, Graduate School of Engineering, Research Associate, 大学院・工学研究科, 助手 (40333843)
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| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2004: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
We have investigated the search for new superconductors by the electrochemical Li-intercalation into layered perovskites, Sr_2CuO_2X_2 (X=Cl, Br, I) with the K_2NiF_4 structure and AB_2M_3O_<10> (M=Nb, Ta) of the Dion-Jacobson phase. As for Sr_2CuO_2X_2 which is essentially isostructural to the well-known high-T_c superconductor (La, Sr)_2CuO_4, Li^+ ions are intercalated between the electronegative X^- double layers which are weakly bound through the van der Waals force. The value of T_c in Li_xSr_2CuO_2X_2 is 8.0K and 4.5K for X=Br and I, respectively. However, no superconductivity appears for X=Cl. These compounds with the large a-axis length of 3.98-4.03Å are suitable for the electron-doping as opposed to the hole-doped (La, Sr)_2CuO_4 with the small a-axis length of 〜3.78Å. As for AB_2M_3O_<10> with the triple-layered MO_6 octahedrons, Li^+ ions are intercalated into the cation-defect AO_2 layers. Takano et al. and Fukuoka et al. have reported at first that Li_xKCa_2Nb_3O_<10>, which is prepared by the chemical Li-intercalation technique, shows the superconductivity below about 5K. On the other hand, we have succeeded in preparing superconducting Li_xASr_2Nb_3O_<10> (A=Rb, Cs) with T_c〜6K using the electrochemical Li-intercalation technique. For the layered tantalates of Li_xAB_2Ta_3O_<10>, however, superconductivity has not been observed.
In both Sr_2CuO_2X_2 and AB_2Nb_3O_<10>, electron carriers cannot be doped enough for the appearance of superconductivity through the partial substitution of cation. Thus, the Li-intercalation is a useful technique for the search for new superconductors.
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