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

β-菱面体硼(β-B^&lt；105&gt；)是二十面体团簇固体中的一种，金属元素掺杂后存在高温超导电性的可能性。我们尝试在β-B^&lt；105&gt；中掺入镁，并讨论了金属和超导转变的可能性。我们在β-B105&gt；中实现了较高的镁掺杂浓度，高达11.5&gt；(8.6 mg/cell)，即电子掺杂足以使费米能(E_F)超过本征受主能级(IAL)。然而，既没有观察到金属转变，也没有观察到超导转变。结合X射线粉末衍射、Rietveld方法、电导率和磁化率测量，讨论了其结构和电学性质的变化。我们估算了E_F处的态密度，并讨论了β-B^&lt；105&gt；的电子态。结果表明，在晶界上方存在局域态，可能起源于具有结构缺陷的B28团簇。我们测量了具有α-四方晶体结构的单晶B纳米带的电导。用气相扩散法进行了镁的掺杂实验。纯的硼纳米带是p型半导体，室温下的电导率估计为10^&lt；-3&gt；(Ωcm)^&lt；-1&gt；。室温下测得纯B纳米带的载流子迁移率约为10^&lt；-3&gt；(cm^2/vs)，激活能约为0.19 eV。镁掺杂的硼纳米带具有与原始纳米带相同的α-四方晶体结构。镁蒸气扩散后，纳米带仍为半导体，电导提高了100~500倍。没有观察到掺杂向金属或超导体的转变。

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.