Direct observation of structural phase changes in proton-exchanged LiNbO3 waveguides using transmission electron microscopy

Abstract
Transmission electron microscopy of proton‐exchanged LiNbO3 waveguide channels reveals regions of diffuse intensity within the single‐crystal electron diffraction patterns of LiNbO3. The diffuse intensity was not observed from areas of LiNbO3 which had been masked with Cr before exchange. Heating the waveguides in air at 550 °C for 2 h sharpened some of the diffuse intensity into diffraction spots, some of whose lattice spacings matched Nb2O5 or LiNb3O8. Other reflections also appeared which matched these phases. Small (∼20 nm diam) cavities were also observed in the exchanged channels after heating and suggest the occurrence of a dehydration reaction.