Characterization of TiO2, LiNb3O8, and (Ti0.65Nb0.35)O2 compound growth observed during Ti:LiNbO3 optical waveguide fabrication

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Abstract
TiO2, LiNb3O8, and (Ti0.65Nb0.35)O2 compounds have been observed and characterized during the fabrication of optical waveguides by Ti indiffusion in LiNbO3, performed in a flowing dry O2 atmosphere. Ti oxidizes by reacting with both O atoms of the surrounding atmosphere and of the LiNbO3 substrate. TiO2 formation is followed by LiNb3O8 and (Ti0.65Nb0.35)O2 phase growth. With further increasing in the annealing temperature the TiO2 and LiNb3O8 compounds are consumed and vanish. After 30 min at 950 °C both Y‐ and Z‐cut substrates appear covered only by a uniform and epitaxial (Ti0.65Nb0.35)O2 layer which behaves as the real source for Ti diffusion. The LiNb3O8 formation and dissolution were also observed in samples uncoated with Ti. Similar results were observed in LiNbO3 samples annealed in dry N, Ar, and static air.