Compositional and Structural AtomisticStudy of Amorphous Si-B-N Networks of Interest for High-Performance Coatings

We explore by computational modeling the effects of boron nitrogen (BN) composition on the thermal and mechanical properties of amorphous silicon boron nitride (Si-B-N), a synthetic ceramic material with superior thermal protection, mechanical attributes, and oxidation resistance at high temperatures. Network-derived Si-B-N models optimized with ab initio molecular dynamics serve as input structures for classical molecular dynamics simulations. Atomistic Green Kubo simulations on relaxed supercells and structural relaxations on strained cells are used to screen the thermal and mechanical properties of a collection of network structures with low enthalpies of formation. We find that when the material is composed of well-mixed parts rather homogeneously spread within the material, the thermal conductivity and elastic constants are isotropic and exhibit a weak dependence on composition and network structure. In contrast, when separation into BN-rich layers occurs, the material exhibits anisotropic behavior, with an increase in thermal conductivity along the layer direction and decrease in elastic constant in the cross-layer direction. The insights provided into the composition structure property relationships can be useful for the rational design of amorphous Si-B-N materials targeting high-performance coating applications.