Combination transitions due to stretching and librations of OH⁻ ions in LiNbO₃.

A new absorption band has been detected at 4009 cm⁻¹ in stoichiometric LiNbO₃ single crystals. Based on present and earlier experiments and recent calculations, this band has been assigned as a combination transition involving the OH stretching and an OH librational mode. The librational mode participating in this combination is of lower fundamental frequency than that contributing to the combination band at 4415 cm¹ observed by Gröne and Kapphan [J. Phys. Condens. Matter 7, 3051 (1995)].