Search for High Critical Temperature Superconductivity in Li- or Mg-doped Boron Icosahedral Cluster Solids

寻找锂或镁掺杂硼二十面体团簇固体的高临界温度超导性

基本信息

批准号：
15360332
负责人：
KIMURA Kaoru
金额：
$ 9.79万
依托单位：
The University of Tokyo
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 2005
项目状态：
已结题

项目摘要

There is a possibility of high-Tc superconductivity upon metallic-element doping into β-rhombohedral boron (β-B^<105>), which is one of the boron icosahedral cluster solids. We attempted magnesium (Mg) doping into β-B^<105> and discussed the possibility of metal and superconductive transitions. We achieved a higher concentration of Mg doping into β-B^<105>, up to MgB_<11.5> (8.6 Mg/cell), i.e., electron doping sufficient for the Fermi energy (E_F) to reach over the intrinsic accepter level (IAL). However, neither metal nor superconductive transition was observed. The change in the structure and electronic properties are discussed on the basis of the X-ray powder diffraction (XRD), using the Rietveld method, and electrical conductivity and magnetic susceptibility measurements, respectively. We estimated the density of states (DOS) at the E_F and discussed the electronic states of β-B^<105>. As a result, it is suggested that a localized state exists above the IAL probably originating from B28 cluster with structural defects.We measured electrical conductance of single crystalline boron nanobelts having α-tetragonal crystalline structure. The doping experiment of Mg was carried out by vapor diffusion method. The pure boron nanobelt is a p-type semiconductor and its electrical conductivity was estimated to be on the order of 10^<-3> (Ωcm)^<-1> at room temperature. The carrier mobility of pure boron nanobelt was measured to be on the order of 10^<-3> (cm^2/Vs) at room temperature and has an activation energy of 〜0.19 eV. The Mg-doped boron nanobelts have the same α-tetragonal crystalline structure as the pristine nanobelts. After Mg vapor diffusion, the nanobelts were still semiconductor, while the electrical conductance increased by a factor of 100〜500. Transition to metal or superconductor by doping was not observed.

将金属元素掺杂到β-菱面体硼（β-B^<105>）中可能会出现高温超导，β-菱形硼是硼二十面体簇固体之一。我们尝试将镁（Mg）掺杂到β-B中。 ^<105> 并讨论了金属和超导转变的可能性，我们实现了更高浓度的 Mg 掺杂到 β-B^<105> 中，最高可达MgB_<11.5>（8.6 Mg/电池），即电子掺杂足以使费米能级（E_F）达到本征受主能级（IAL），但是，没有观察到金属和超导转变。基于 X 射线粉末衍射 (XRD)、使用 Rietveld 方法以及电导率和磁化率测量，分别讨论了结构电子特性，我们分别估计了态密度。 (DOS) 并讨论了 β-B^<105> 的电子态。结果表明，IAL 上方存在局域态，可能源自具有结构缺陷的 B28 团簇。我们测量了单个团簇的电导率。具有α-四方晶体结构的晶体硼纳米带通过气相扩散法进行了Mg的掺杂实验，纯硼纳米带是p型半导体，其电导率被认为是良好的。室温下为10 ^ -3 (Ωcm) ^ -1 量级纯硼纳米带的载流子迁移率在室温下测量为10 ^ -3 (cm ^ 2/Vs)量级。 Mg掺杂硼纳米带在室温下具有~0.19 eV的活化能，在Mg蒸气扩散后具有与原始纳米带相同的α-四方晶体结构。纳米带仍然是半导体，但电导率增加了100~500倍，没有观察到通过掺杂向金属或超导体的转变。