The effect of Si alloying on the thermal stability of Al2O3 films deposited by filtered cathodic arc

The effect of Si alloying on the phase transformation sequence and phase formation temperatures of Al2O3 thin films deposited by filtered cathodic arc was investigated by annealing experiments in air. By addition of Si the transformation of γ- to δ- and θ-Al2O3 is restrained by 100 °C. The thermal stability range of the δ- and θ-phase is also increased by ≥ 200 °C with respect to the unalloyed Al2O3 thin film and the formation of α-Al2O3 is restrained by 200 °C upon addition of Si. Based on the observed Si addition induced changes in phase formation, crystallite size and bonding it appears reasonable that the presence of SiO2 at the grain boundaries impeding mass transport governs the Si induced stability enhancement of the metastable γ-/δ- and θ-Al2O3 phases and the restrained α-Al2O3 formation. The competing proposal assuming a random substitution of Al by Si on the lattice sites is not consistent with the XPS data.