Molecular Dynamics Simulations of the Locations of La Ions in La-Si-O-N Intergranular Films in Silicon Nitride

摘要

Molecular dynamics computer simulations were used to determine the locations and energies of La ions in silicate intergranular films (IGFs) between basal and prism-oriented silicon nitride crystals as a function of composition. La segregation to the interfaces occurs at each surface with no nitrogen present in the IGF, but segregates preferentially to the prism surface with nitrogen in the IGF. La adsorption onto the prism surface occurs in the simulations at the two sites observed previously in studies using high-angle annular dark field scanning transmission electron microscopy. The binding energies of La at the two sites differ with no nitrogen in the IGF, and both are more strongly bonded than for La in the interior of the IGF. However, with nitrogen in the IGF, the binding energies are less different between the two prism surface sites and the interior of the IGF, indicating a decreased driving force for segregation. The simulations provide evidence justifying the preferential segregation of La ions to the prism surface and also indicate that a variation in the local composition would cause some IGFs to show segregation of all La to the interface, leaving little La within the glassy IGF, while other IGFs may show more La remaining in the glassy IGF.