Mechanism for LiNb3O8 phase formation during thermal annealing of crystalline and amorphous LiNbO3 thin films

The kinetics of second phase formation during the thermal annealing of crystalline and amorphous LiNbO3(LN) thin films was investigated. When c-axis-oriented LN texture film was annealed at temperatures higher than 700 °C, Li2O desorbed from the surface and grain boundaries, which induced epitaxial precipitation of the LiNb3O8phase on the LN (0001) plane. While the LiNb3O8volume exhibited saturation behavior against annealing time, oxygen atoms continued to diffuse out from the inner part of the film. Arrhenius plots of the rate of LiNb3O8formation and oxygen loss were scaled with common activation energy of 30.5 kcal/mol. In terms of phase formation from amorphous LN, annealing at 700 °C in a vacuum induced rapid crystallization into mixtures of LN and LiNb3O8, the volume ratio of which can be explained by the phase separation model. Annealing in an O2atmosphere, however, produced an incubation time before crystallization and a larger volume fraction of LiNb3O8after crystallization. Oxygen molecules that penetrated into the film will hinder the migration of atoms and decelerate crystallization. Vacancies produced as a result of Li2O loss will facilitate the nucleation of LN and LiNb3O8pairs while maintaining the epitaxial relation.