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

1)以无定形硼（a-B）和六方氮化硼（h-BN）的混合粉末为原料，研究了锂蒸气热退火法制备BN纳米管的条件。用h-AlN代替h-BN作为起始材料可以制备BN纳米管和BN扭曲层的周围结构。而a-B在N_2气氛中氮化和h-BN在Li蒸汽中热退火则不能形成。因此，它们被认为是在Li蒸气下通过a-B的氮化形成的。当以β-菱面体硼（β-B）代替α-B作为起始原料时，发现了两种新的结构。它们是从h-BN颗粒边缘沿颗粒方向之沿着生长的单层纳米管<10-10>和一堆顶角约为20°的单层BN锥体。2）在Li掺杂的α-菱面体硼（α-B）中研究了金属相变和超导电性。对掺Li的α-B进行了Reitpyruvate分析，晶格常数的变化小于0.1%，整个样品中没有Li的掺杂。部分样品具有金属光泽，Li掺杂后费米棱的出现和化学位移表明样品发生了金属相变。用SQUID磁强计测量样品的磁化率时，认为铁磁分量上叠加了一个铁磁分量。3）在a-B中发生了约1at.%的金属转变钒（V）掺杂，虽然二十面体团簇（B_<12>）为基础的局部结构保持，直到几个原子%。由于V在α-B中占据的位置类似于β-B中的A_1-位置，因此认为周围四个B_的成键性质<12>由共价键转变为金属键。这与金属键转化然后金属转变发生超过10at.%形成对比。在a-Si中进行金属掺杂，破坏四面体结构，形成类金属化合物结构。

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.