碳化硼及掺硅系列的量子化学计算研究

Quantum Chemistry Study on Boron Carbides and Si Doped Ones

应用离散变分Xα 量子化学分子轨道计算方法 ,根据 5类共 2 8个不同的结构模型 ,研究了碳化硼及掺硅系列组成 ,结构 ,化学键及热电性能之间的关系。不掺硅时碳化硼的典型结构是〔C -B -B(C)〕δ - 〔B1 1 C〕δ + 。C -B -B链连接B1 1 C二十面体的模型趋于更稳定地存在 ,它们的二十面体上的电荷最低 ,更有利于极化子的形成 ;符合碳含量为 13 .3 %时 ,碳化硼的电导率有极大值的实验结果。碳化硼掺硅后的典型结构是〔C -B -Si〕ε + 〔B1 1 C〕ε - 。由于掺硅后多种结构形式的形成 ,极化反应所需的能量降低 ,为极化子的跃迁提供更多的途径 ,导致电导率增大。同时 ,碳化硼掺硅后共价键减弱 ,热导率减小。因此 ,碳化硼掺硅后 。

The correlation among composition, structure, chemical bond and thermoelectric property of boron carbide and Si doped ones was studied using DV X α method, with 5 classes of 28 models. The representative structural unit of boron carbide is 〔C-B-B(C)〕 δ- 〔B 11 C〕 δ+ . The models with C-B-B chains and B 11 C icosahedra are the stablest, and the charges of their icosahedra are the lowest, so the bipolaron forms easily, which is consistent with the experimental result that the conductivity has the largest value when the carbon content is 13.3%. The representative structural unit of doping Si is 〔C-B-Si〕 ε+ 〔B 11 C〕 ε. As there are more types of structural units after the addtion Si, the energy required by the disproportionation reaction decreases, and there are more paths for the bipolaron to hopping. At the same time, the covalent bond becomes weaker, and the thermal conductivity decreases. Therefore, the thermoelectric property of Si doped boron carbides is improved.\;