A diffuse interface model of interfaces: Grain boundaries in silicon nitride

A diffuse-interface model for interfaces in multi-component systems with energetic contributions from chemistry, defects, structure, orientation, electrostatics and gradients is proposed. The energy minimizing profiles of planar grain boundaries in the pseudo-binary SiO2-SiN4/3 system are calculated in the SiN4/3-rich single-phase field. Intergranular films are found to be stable below the eutectic temperature. Evidence of first-order grain boundary order-disorder transitions is found in misorientation and chemical potential space. Interface transitions predicted with the model can be plotted on equilibrium phase diagrams to produce "interfacial phase diagrams." These could be a tool for designing processing routes to optimize bulk, polycrystalline material properties through control of grain boundary characteristics.