Spectroscopy ofhighervibrationalstates andlibrationalsidebands ofOHinLiNbO3

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Abstract
The fundamental transition Δi 01 and the higher transitions ΔG 02 and ΔG 03 are investigated in their polarization and temperature dependence. The spectral position of the transitions follows closely a Morse potential with D e = 4.75 eV and the mechanical anharmonicity w e x e = 88.5 cm−1 leaving no room for speculations about possible hydrogen bonding. The intensity ratio of higher vibrational transitions indicates a strong temperature dependence of the electrical anharmonicity. An absorption side band at 4436 cm−1 which follows in intensity the absorption of the ΔG 01 transition (and therefore the OH concentration), is identified as a vibrational + librational combination side bands. Its polarization displays a 3-dimensional behaviour with an intensity ratio I|I≅ 2 with respect to the z-direction. The librational frequency is an important input parameter for the discussion of the protonic conductivity.