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

1)研究了无定形B(a-B)和六方氮化硼(h-BN)混合粉末在Li蒸气中热退火制备BN纳米管的条件。以h-AlN代替h-BN为原料，可以制备出BN纳米管和扭曲的BN层周围结构。然而，它们不是a-B在N_2中氮化和h-BN在Li蒸气中热退火形成的。因此，它们被认为是由a-B在Li蒸气下氮化形成的。当用β-菱面体硼(β-B)代替a-B作为原料时，发现了两种新的结构。它们是从h-BN颗粒边缘沿-lt；10-10&gt；方向生长的锯齿形纳米管，颗粒和堆积的单层BN锥体的顶角约为20°。2)在Li掺杂的α-菱面体硼(α-B)中寻找到金属转变和超导电性。Reitvelt分析结果表明，掺Li的α-B的晶格常数变化均小于0.1%，且Li不是在整个样品中掺杂。部分样品具有金属光泽，掺杂Li后出现费米边缘和化学位移，表明样品发生了金属相变。在用SQUID磁强计测量样品的磁化率时，认为超导成分叠加在铁磁性成分上。然而，超导相的体积分数约为0.02%。3)钒(V)掺杂约1 at.%时，a-B中发生了金属相变，但二十面体团簇(B_&lt；12&>t；)的局域结构直到几at.%时才保持不变。通过与β-B中的A_1位相似的A-B位的V占据，认为周围四个B_(12)&gt；的成键性质由共价转变为金属。与此形成对比的是，a-Si中金属掺杂超过10at.%，破坏了四面体构型，形成了类金属化合物结构，发生了金属成键转化和金属相变。

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.