Model Experiment on Thermodynamic Stability of Retained Intergranular Amorphous Films

To test the stability of intergranular amorphous films against crystallization, a model experiment was conducted wherein a thin SiO2 film was deposited on a single-crystal TiO₂ substrate, annealed to form a eutectic liquid in equilibrium with the substrate, then quenched and crystallized below the eutectic temperature. This geometry is free of residual stresses and capillary effects proposed by others as kinetic limitations to complete crystallization. Furthermore, using a binary system removes solute rejection barriers to complete crystallization. A remnant amorphous film ∼1.5 nm thick retained at the hetero-interface shows unequivocally that the amorphous film is thermodynamically preferred to a crystal/crystal interface in this system.