Compositional Dependence and Structure of Hydroxyl Ion Defects in Ferroelectric Potassium Lithium Niobate

The OH- stretch mode spectra have been measured in both ferroelectric (KLN-1) and non-ferroelectric (KLN-2) potassium lithium niobate crystals grown from different melt compositions. OH bond directions of about 15, 60, and 15 degrees with respect to the c-axis have been determined for the three main OH- bands in KLN-1 peaking at about 3440, 3500, and 3520 cm-1, respectively. Correlations have been found along the growth axis of the crystal between the decrease of the excess Nb content, the change of the hydroxyl band components at 3440 and 3520 cm-1, and the Raman modes at 540 cm-1 and 640 cm-1.