Inner displacement and directional bonding in transition metal disilicides

在本项目的第一步，我们测量了具有C11_b，C40和C54结构的过渡金属二硅化物的单晶弹性常数。弹性常数已被分析的价力场的方法，其中原子间的相互作用被分为两项：键拉伸和键弯曲。这两项的系数的相对值为每个过渡金属二硅化物指示原子间键合的方向性。C11_b结构的材料中原子间相互作用的方向性最强，C40结构的材料中原子间相互作用的方向性可分为两类。TiSi_2的强度位于两组C40结构的中间位置。分析表明，材料中硅原子的位置与数据手册中的位置略有偏移。这种位移与Si-Si和Si-TM原子间的各向异性相互作用有关，这一点从用最大熵方法测得的衍射强度构造的电子分布图中得到了清楚的证明。

For the first step of this project, we have measured single crystal elastic constants of transition metal disilicides with the C11_b, C40 and C54 structures. The elastic constants have been analyzed by the valence force field approach where the inter-atomic interaction is classified into two terms ; bond-stretching and bond-bending. Relative values of the coefficients of these two terms for each transition metal disilicide indicate the directionality of the inter-atomic bonding. The directionality of inter-atomic interaction in the materials with the C11_b structure is the strongest one, and that in the materials with the C40 structure are classified into two groups. The strength of TiSi_2 is located at the middle position between the two groups of the C40 structure.For the next step, we have performed the X-ray analysis to refine the crystallographic parameters of these compounds. The analysis indicates that the position of silicon atoms in the materials are slightly displaced from the position compiled in the data book. The displacement is associated with the anisotropic inter-atomic interactions of Si-Si and Si-TM.This is clearly demonstrated from the electron distribution maps which are constructed from the measured intensities of the diffraction by the maximum entropy method.