Infrared reflection, attenuated total reflection, prism coupling, and x-ray diffraction methods were used to characterize seven crystallographic HxLi1-xNbO3 phases in proton-exchanged Z-cut LiNbO3 waveguides. Drastic changes of the crystal lattice parameters and the lattice vibrational spectrum at the phase boundaries were observed. The LO–TO splitting, which is proportional to the width of the main band ranging from 580 to 900 cm-1, was demonstrated to vary significantly from phase to phase. Strong decrease of the LO–TO splitting for the polar mode attributed to NbO6 octahedra vibrations (800–900 cm-1) was detected. It was shown that the HxLi1-xNbO3 phases are organized as individual layers. © 1998 American Institute of Physics.