New Material Development by Metal Doping and Electronic Properties for Boron-rich Solids having Icosahedron and Soccer-ball Clusters

1)通过分子轨道计算的结合能计算，我们发现在富硼体系中理论上可以存在α-菱面体B型准晶，并通过计算结果和结晶学数据预测了B-C系准晶结构的成分范围小于9at.%C。在成分范围内，我们发现了非晶相退火后的二十面体准晶的一种新的近似相。这一发现表明，在富硼固体中实现半导体准晶是非常有希望的，这是实现这一目标的有价值的第一步。2)利用石英和钽组成的双封接管，成功地在β-三方体硼(β-B)中掺入Li。用同样的方法，我们尝试制备了掺Li的α-菱面体B，通过能带结构计算预测它是一种超导体。3)指出了…的结构相似性贝塔-硼和f.c.c.C&lt；60&gt；之间的差异更大，因为贝塔-硼也由位于菱面体单胞每个顶点的足球团簇组成。高达几个at.%的Li或Cu掺杂仍表现出半导体的电导率特征，磁化率仍为抗磁性。这些行为与C_&lt；60&gt；的情况不同。根据电导率表现为变程跳跃型电导和磁化率随掺杂几乎保持不变的结果，我们认为掺杂的β-B原子的电子结构如下：当掺杂的电子占据来源于B&lt；12&gt；团簇的本征受主能级并且在局域能级之间跳跃时，由于电子-声子相互作用，有效的电子-电子相互作用为负。4)测量了β-B的光学吸收边光谱的温度依赖性，证实了从本征受主能级到导带的电子跃迁是被禁止的。这与偶极矩的计算是一致的。我们首次成功地测量了光致发光光谱。从峰值能量和强度对温度的依赖关系，我们得出结论，发光对应于本征受主能级中的空穴和最高陷阱能级中的电子之间的复合。较少

1) From cohesive energy calculations using molecular orbital calculation, we found that alpha-rhombohedral boron type quasicrystal can be exist theoretically in boron-rich systems, and predict that the composition range for the quasicrystalline structure in boron-carbon system is less than 9at.% carbon by accounting the results and crystallographic data. In the composition range, we discovered a new type of approximant phase of an icosahedral quasicrystal after annealing amorphous phase. This discovery suggests that realization of semiconducting quasicrystal in boron-rich solids is strongly expected and this is a valuable first step for the realization. 2) We succeeded in Li doping into beta-rhombohedral boron (beta-boron) using double-sealed tube constituted by quartz and tantalum. By the same method, we have tried to prepare Li-doped alpha-rhombohedral boron which is predicted to be a superconductor by energy band structure calculation. 3) We pointed out the structural similarity bet … More ween beta-boron and f.c.c.C_<60> because beta-boron also consists of soccer ball clusters located at each vertex of a rhombohedral unit cell. Up to several at.% of Li or Cu doping electrical conductivity still exhibited characteristic feature of that of semiconductor and magnetic susceptibility was still diamagnetic. These behaviors are different from those in the case of C_<60>. On the basis of the results that electrical conductivity reveals variable range hopping type conduction and magnetic susceptibility remain almost constant against the doping, we consider the electronic structure of the doped beta-boron as follows ; whereas the doped electrons occupy the intrinsic acceptor levels originated from B_<12> cluster and they jump between the localized levels, effective electron-electron interaction is negative due to electron-phonon interaction. 4) We measured the temperature dependence of optical absorption edge spectrum for beta-boron, and confirmed that the electronic transition from the intrinsic acceptor level to the conduction band is forbidden. This is consistent with the dipole moment calculation. We succeeded in measuring photoluminescence spectrum for the first time. From the peak energy and the temperature dependence of the intensity, we concluded that the luminescence corresponds to recombination between a hole in the intrinsic acceptor level and an electron in the highest trapping level. Less