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

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waveguides is demonstrated by the Raman scattering technique. Multimode waveguides have been produced by using pyrophosphoric, benzoic, and diluted 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 frequency 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) procedures on H_xLi_1-xNbO₃ waveguides with x>0.56 leads to phase transitions between 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 support the presence of different phases in H:LiNbO₃ waveguides, some conclusions, different from those reported elsewhere, have been made.