DIRECT OH AND OD LIBRATIONAL ABSORPTION-BANDS IN LINBO3

The presence of hydrogen (deuterium) defects in ABO(3) crystals is rev ealed by a characteristic OH (OD) stretching vibration near 3500 cm(-1 ) (2600 cm(-1)). Recently we reported about combination bands of the l ibration with the vibration of the OH (OD) oscillator observed for the first time in several ABO(3) crystals. Direct librational modes have not been reported so far for these crystals. In proton exchanged (PE) surface layers of LiNbO3 with a very high OH concentration the direct OH librational mode at 960 cm(-1) is observed by Raman scattering. The direct OD librational mode in deuteron exchanged LiNbO3:DE cm surface layers is hidden by phonon lines of the host lattice, but can be dete cted at 698 cm(-1) in IR reflection measurements. The observed OH and OD librational wavenumbers are in agreement with a description of the libration by a simple harmonic oscillator model.