The OH vibrational spectrum in Bi2TeO5 single crystals

FTIR spectroscopy and linear dichroism measurements (in the range 9-300 K) are applied to the photorefractive Bi2TeO5 single crystals to identify the OH-vibrational absorption, the location and orientation of the OH-defect in the lattice, and its phonon coupling. At 9 K a complex absorption, compose d by a main peak at 3471 cm(-1) and a shoulder at 3494 cm(-1) characterised by a strong dichroism, is attributed to the stretching mode of OH, replaci ng for an O(4) in the orthorhombic Bi2TeO5 lattice, and mainly aligned alon g the [100] direction. The anharmonicity (x(e) similar to 0.028), put in ev idence by the isotopic replica induced by a deuterisation process, is discu ssed in the framework of the Morse model for an anharmonic oscillator.