Synthesis and phase control of fullerene based superstructured materials

富勒烯基超结构材料的合成与相控制

基本信息

批准号：
15340106
负责人：
TAGUCHI Yasujiro
金额：
$ 9.22万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

In this fiscal year, we have tried to reveal universality and unique points in fullerene based compounds, dealing with layered nitride superconductors that also exhibit band insulator to superconductor transition similarly to the case of alkali metal intercalated fullerides. We have succeeded in preparing a series of samples with continuously changed Li-content (x<0.12), and have confirmed that these are of single phase by using synchrotron X-ray diffraction technique at BL2B-02, SPring 8. This fact makes striking contrast with the case of fullerides where only line phases exist and the intermediate phases can not be obtained, clearly indicating the anomalous solid state chemistry of fullerene compounds. Also, we have performed the specific heat measurements of layered nitride superconductors in magnetic fields, and have found that the normal-state Sommerfeld constant γ is very small (=1.0 mJ/mol K^2). We can obtain very small electron-phonon coupling constant λ(=0.22) by using this value and the density of states at the Fermi level predicted by several band calculations. This fact is in accord with the relatively narrow phonon lines observed in Raman scattering spectra. This fact also makes striking contrast with the fullerides where superconductivity is mediated by high frequency phonon with intermediate electron-phonon coupling strength, indicating the importance of Jahn-Teller interaction where the fullerene molecules show deformation. It is theoretically pointed out that Jahn-Teller interaction that couples with the degenerate LUMO orbitals is important in fullerides, and our result is consistent with this.

在本财年，我们试图揭示富勒烯基化合物的普遍性和独特性，处理层状氮化物超导体，该超导体也表现出与碱金属插层富勒烯类似的带绝缘体到超导体的转变，我们已经成功制备了一系列富勒烯化合物。锂含量连续变化的样品（x<0.12），并通过BL2B-02的同步加速器X射线衍射技术证实这些样品是单相的， SPring 8。这一事实与仅存在线相且无法获得中间相的富勒烯的情况形成鲜明对比，清楚地表明富勒烯化合物的反常固态化学。此外，我们还进行了层状氮化物的比热测量。磁场中的超导体，发现正常态索默菲常数γ非常小（=1.0 mJ/mol K^2），我们可以得到非常小的电子声子耦合常数。 λ(=0.22) 通过使用该值和通过几次能带计算预测的费米能级的态密度，这一事实与拉曼散射光谱中观察到的相对较窄的声子线一致，这一事实也与富勒烯形成了鲜明的对比。其中超导性是由具有中等电子声子耦合强度的高频声子介导的，这表明富勒烯分子变形时Jahn-Teller相互作用的重要性。与简并 LUMO 轨道耦合的 Jahn-Teller 相互作用在富勒烯中很重要，我们的结果与此一致。