Evidence of different beta-phases in highly protonated z-cut H : LiNbO3 waveguides by raman scattering

In this paper, evidence of different B-phases in highly protonated z-cut H: LiNbO3 waveguides is demonstrated by the Raman scattering technique. Multim ode waveguides have been produced by using pyrophosphoric, benzoic, and dil uted benzoic acids as a proton source. The proton-exchanged (PE) layers are subjected to annealing (APE samples) with different rates of cooling: slow (s) and quick (q). The effect of Li-H replacing is considered in the frequ ency range below 800 cm(-1) and about 3500 cm(-1) (OH modes). The analysis of the spectral data leads to some important conclusions about the changes in the H:LiNbO3 lattice. We demonstrate that applying (s) <----> (q) proced ures on HxLi1-xNbO3 waveguides with x > 0.56 leads to phase transitions bet ween different states. The high-temperature phase modifications (metastable at room temperature) are characterized by strongly broadened q-Raman bands which imply a high degree of disorder. Although the Raman measurements sup port the presence of different phases in H:LiNbO3 waveguides, some conclusi ons, different from those reported elsewhere, have been made.