Directional atomic bonds in MoSi2 and other transition-metal disilicides with the C11b, C40 and C54 structures

The elastic constants of MoSi2 as well as other transition-metal (TM) disilicides with the C11b, C40 and C54 structures are analysed by adopting an approach similar to the valence-force-field approach in order to elucidate the directional nature of atomic bonding. In the present approach, all interatomic forces are resolved into bond-stretching and bond-bending forces and the elastic properties are described with force constants corresponding to these two forces. The values of force constants are compared with each other. The directionality in atomic bonding in C11b disilicides is found to be stronger than any other disilicides with the C40 and C54 structures. Of the two C11b disilicides, the directionality in atomic bonding is stronger for WSi2 than for MoSi2.