Production of Nanotubes by Thermal Annealing and Development of Boron-Network Solids

1)研究了非晶态硼（a- b）和六方氮化硼（h-BN）混合粉末在Li蒸气下热退火制备BN纳米管的条件。以h-A1N代替h-BN作为起始材料，可以制备BN纳米管及其周围的扭曲BN层结构。而a-B在氮气中氮化和h-BN在Li蒸气下热退火均不能形成。因此，它们被认为是由a-B在Li蒸气下氮化形成的。当以β-菱形体硼（β-B）代替a-B作为起始材料时，发现了两个新的结构。它们是从h-BN颗粒边缘沿颗粒<10-10>方向生长的锯齿形纳米管，以及顶端角约为20°的单层BN锥堆。2)研究了li掺杂α-菱形体硼（α-B）的金属跃迁和超导性。通过对Li掺杂α-B的Reitvelt分析，晶格常数的变化小于0.1%，样品中没有掺杂Li。部分样品具有金属光泽，掺杂后的费米边缘和化学位移表明样品有金属跃迁。在SQUID磁强计测量样品磁化率时，认为超导元件叠加在铁磁性元件上。而超导相的体积分数约为0.02%。3) a-B中发生了约1 at的金属转变。钒(V)掺杂后，虽然以二十面体簇（B_<12>）为基础的局部结构一直保持到几个百分点。通过V占据a-B中类似于β-B中a_1位点的位置，可以认为周围4个B_<12>的成键性质是由共价键转变为金属键。这与金属键转换和金属跃迁发生的时间相差10个以上。在a-Si中掺杂金属，破坏四面体结构，构建金属类化合物结构。

1) Formation conditions of BN nanotubes by thermal annealing under Li vapor starting from a mixed powder of amorphous boron (a-B) and hexagonal boron nitride (h-BN) were investigated. BN nanotubes and the surrounding structures of twisted BN layers could be produced using h-A1N instead of h-BN as the starting material. However, they were not formed by nitridation of a-B in N_2 gas and by thermal annealing of h-BN under Li vapor. Therefore they are considered to form by nitridation of a-B under Li vapor. When β-rhombohedral boron (β-B) was used as the starting material instead of a-B, two new structures were discovered. They were zigzag-type nanotubes growing from edge of h-BN particles along one of <10-10> directions of the particles and piles of monolayer BN cones with apex angle of about 20°.2) Metal transition and superconductivity were searched in Li-doped α-rhombohedral boron (α-B). As a result of Reitvelt analysis for the Li-doped α-B, the changes of lattice constants were below 0.1 % and Li was doped not in the whole of specimen. Parts of the sample had metallic luster and metal transition was suggested by the appearance of Fermi edge and chemical shift after Li doping. In magnetic susceptibility of the sample measured by SQUID magnetometer, a superconductive component was considered to superpose on a ferromagnetic one. However, volume fraction of the superconductive phase was about 0.02 %.3) Metal transition occurred in a-B by about 1 at.% Vanadium (V) doping, though the icosahedral cluster(B_<12>)-based local structure was maintained until several at.%. By V occupation of the site in a-B similar to the A_1-site in β-B, the bonding nature of surrounding four B_<12> was considered to convert from covalent to metallic. This contrast that metallic bonding conversion and then metallic transition occur by more than 10 at.% metal doping in a-Si with destruction of the tetrahedral configuration and construction of metallic compound-like structure.